U.S. patent application number 16/050301 was filed with the patent office on 2018-11-22 for display device including signal processor that superimposes visible light communication signals on backlight control signals generated based on an image signal.
The applicant listed for this patent is Panasonic Corporation. Invention is credited to Koji AOTO, Hideki AOYAMA, Toshiyuki MAEDA, Koji NAKANISHI, Mitsuaki OSHIMA, Akira SHIOKAWA, Takashi SUZUKI, Akihiro UEKI.
Application Number | 20180336848 16/050301 |
Document ID | / |
Family ID | 52992476 |
Filed Date | 2018-11-22 |
United States Patent
Application |
20180336848 |
Kind Code |
A1 |
SUZUKI; Takashi ; et
al. |
November 22, 2018 |
DISPLAY DEVICE INCLUDING SIGNAL PROCESSOR THAT SUPERIMPOSES VISIBLE
LIGHT COMMUNICATION SIGNALS ON BACKLIGHT CONTROL SIGNALS GENERATED
BASED ON AN IMAGE SIGNAL
Abstract
A display device includes: a display panel including a display
screen; a backlight having a light emission surface that
illuminates the display screen of the display panel from behind; a
second processor that superimposes the visible light communication
signals on backlight control signals generated based on the image
signal; and a second controller that divides the light emission
surface of the backlight into regions and establishes a period
during which control of light emission in each of the regions and
control for turning off the backlight in each of the regions a
different time are performed based on the backlight control signals
outputted by the second processor. When superimposing the visible
light communication signals on the backlight control signals, the
second processor does not superimpose a visible light communication
signal in a period indicating an OFF state of the backlight in the
backlight control signals.
Inventors: |
SUZUKI; Takashi; (Osaka,
JP) ; MAEDA; Toshiyuki; (Kanagawa, JP) ; UEKI;
Akihiro; (Kanagawa, JP) ; SHIOKAWA; Akira;
(Osaka, JP) ; AOTO; Koji; (Kanagawa, JP) ;
NAKANISHI; Koji; (Kanagawa, JP) ; AOYAMA; Hideki;
(Osaka, JP) ; OSHIMA; Mitsuaki; (Kyoto,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Corporation |
Osaka |
|
JP |
|
|
Family ID: |
52992476 |
Appl. No.: |
16/050301 |
Filed: |
July 31, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15054573 |
Feb 26, 2016 |
10068532 |
|
|
16050301 |
|
|
|
|
PCT/JP2014/003999 |
Jul 30, 2014 |
|
|
|
15054573 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G09G 2320/062 20130101;
G09G 3/3406 20130101; G09G 3/342 20130101; G09G 2320/08 20130101;
G09G 2310/08 20130101; G09G 2360/16 20130101; G09G 2320/064
20130101; H04B 10/116 20130101; G09G 2310/024 20130101 |
International
Class: |
G09G 3/34 20060101
G09G003/34; H04B 10/116 20130101 H04B010/116 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2013 |
JP |
2013-221934 |
Claims
1-5. (canceled)
6. A display device that outputs visible light communication
signals, the display device comprising: a display panel including a
display screen on which an image is displayed; a display controller
that causes the display panel to display an image on the display
screen of the display panel based on an image signal; a backlight
having a light emission surface that illuminates the display screen
of the display panel from behind; a signal processor that
superimposes the visible light communication signals on backlight
control signals generated based on the image signal; and a
backlight controller that divides the light emission surface of the
backlight into regions and establishes a period during which
control of light emission in each of the regions and control for
turning off the backlight in each of the regions a different time
are performed based on the backlight control signals outputted by
the signal processor, wherein when superimposing the visible light
communication signals on the backlight control signals, the signal
processor does not superimpose a visible light communication signal
in a period indicating an OFF state of the backlight in the
backlight control signals, the signal processor superimposes the
visible light communication signals on the backlight control
signals corresponding to groups of neighboring regions among the
regions, the visible light communication signals superimposed on
the backlight control signals in the same group are in phase with
one another, and for each group, corresponding visible light
communication signals are superimposed in entirety in a period
during which control of light emission of the backlight based on
the backlight control signals corresponding to the groups is
performed.
7. The display device according to claim 6, wherein based on the
backlight control signal corresponding to a predetermined region
among the groups, the signal processor matches phases of the
visible light communication signals superimposed on the backlight
control signals corresponding to the groups.
8. The display device according to claim 6, wherein the
predetermined region is a brightest region among the regions.
9. The display device according to claim 6, wherein among the
visible light communication signals superimposed on the backlight
control signal phases corresponding to the groups, a visible light
communication signal superimposed on a backlight control signal
corresponding to a first group among the groups and a visible light
communication signal superimposed on a backlight control signal
corresponding to a second group among the groups are out of
phase.
10-20. (canceled)
Description
FIELD
[0001] The present disclosure relates to a display device that
outputs visible light communication signals and a method of
controlling such a display device.
BACKGROUND
[0002] Patent Literature (PTL) 1 and 2 disclose techniques related
to visual light communication. PTL 1 and 2 disclose communication
techniques of superimposing communication information via visible
light during normal video display in a video display device
including a display or projector, for example.
CITATION LIST
Patent Literature
[0003] [PTL 1] Japanese Unexamined Patent Application Publication
No. 2007-43706
[0004] [PTL 2] Japanese Unexamined Patent Application Publication
No. 2009-212768
SUMMARY
Technical Problem
[0005] The present disclosure provides a display device capable of
outputting visible light communication signals without
significantly deteriorating the quality of the display image, and
capable of reducing receiving error of output visible light
communication signals, and a method for controlling such a display
device.
Solution to Problem
[0006] The display device according to the present disclosure
outputs visible light communication signals, and includes: a
display panel including a display screen on which an image is
displayed; a display controller that causes the display panel to
display an image on the display screen of the display panel based
on an image signal; a backlight having a light emission surface
that illuminates the display screen of the display panel from
behind; a signal processor that superimposes the visible light
communication signals on backlight control signals generated based
on the image signal; and a backlight controller that divides the
light emission surface of the backlight into regions and
establishes a period during which control of light emission in each
of the regions and control for turning off the backlight in each of
the regions a different time are performed based on the backlight
control signals outputted by the signal processor. When
superimposing the visible light communication signals on the
backlight control signals, the signal processor does not
superimpose a visible light communication signal in a period
indicating an OFF state of the backlight in the backlight control
signals.
Advantageous Effects
[0007] The display device according to the present disclosure is
capable of outputting visible light communication signals without
significantly deteriorating the quality of the display image, and
capable of reducing receiving error of output visible light
communication signals.
BRIEF DESCRIPTION OF DRAWINGS
[0008] These and other objects, advantages and features of the
invention will become apparent from the following description
thereof taken in conjunction with the accompanying drawings that
illustrate a specific embodiment of the present invention.
[0009] FIG. 1 is a schematic view of one example of a visible light
communication system according to Embodiment 1.
[0010] FIG. 2 is a block diagram of one example of a display device
according to Embodiment 1.
[0011] FIG. 3A illustrates one example of a state before visible
light communication signals are superimposed on BL control signals
according to Example 1 of Embodiment 1.
[0012] FIG. 3B illustrates one example of a state after the visible
light communication signals have been superimposed on the BL
control signals according to Example 1 of Embodiment 1.
[0013] FIG. 4 is a timing chart illustrating a first method
according to Example 2 of Embodiment 1.
[0014] FIG. 5 is a timing chart illustrating the first method
according to Example 2 of Embodiment 1.
[0015] FIG. 6A is a timing chart illustrating a second method
according to Example 2 of Embodiment 1.
[0016] FIG. 6B is a timing chart illustrating the second method
according to Example 2 of Embodiment 1.
[0017] FIG. 6C is a timing chart illustrating the second method
according to Example 2 of Embodiment 1.
[0018] FIG. 6D is a timing chart illustrating the second method
according to Example 2 of Embodiment 1.
[0019] FIG. 7A is a timing chart illustrating the second method
according to Example 2 of Embodiment 1.
[0020] FIG. 7B is a timing chart illustrating the second method
according to Example 2 of Embodiment 1.
[0021] FIG. 7C is a timing chart illustrating the second method
according to Example 2 of Embodiment 1.
[0022] FIG. 7D is a timing chart illustrating the second method
according to Example 2 of Embodiment 1.
[0023] FIG. 8 is a timing chart illustrating a method according to
Example 3 of Embodiment 1 of superimposing visible light
communication signals on BL control signals.
[0024] FIG. 9 is a flow chart illustrating operations performed by
the second processor according to Embodiment 2.
[0025] FIG. 10A illustrates a specific method for superimposing
encoded signals on BL control signals according to Embodiment
2.
[0026] FIG. 10B illustrates a specific method for superimposing
encoded signals on BL control signals according to Embodiment
2.
[0027] FIG. 10C illustrates a specific method for superimposing
encoded signals on BL control signals according to Embodiment
2.
[0028] FIG. 10D illustrates a specific method for superimposing
encoded signals on BL control signals according to Embodiment
2.
[0029] FIG. 11 illustrates a different specific method for
superimposing encoded signals on BL control signals according to
Embodiment 2.
[0030] FIG. 12 is a flow chart illustrating operations performed by
the second processor according to Embodiment 3.
[0031] FIG. 13 is a timing chart of an example of the division of
the regions into groups according to Embodiment 3.
[0032] FIG. 14 is a timing chart of another example of the division
of the regions into groups according to Embodiment 3.
[0033] FIG. 15 is a timing chart of another example of the division
of the regions into groups according to Embodiment 3.
[0034] FIG. 16 is a flow chart illustrating operations performed by
the second processor according to Embodiment 4.
[0035] FIG. 17A illustrates the relationship between the phases of
the BL control signal and the visible light communication signal
according to Embodiment 4.
[0036] FIG. 17B illustrates the relationship between the phases of
the BL control signal and the visible light communication signal
according to Embodiment 4.
[0037] FIG. 18A is a timing chart illustrating operations performed
by the second processor according to Embodiment 4.
[0038] FIG. 18B is a timing chart illustrating operations performed
by the second processor according to Embodiment 4.
[0039] FIG. 18C is a timing chart illustrating operations performed
by the second processor according to Embodiment 4.
[0040] FIG. 19A is a timing chart illustrating operations performed
by the second processor according to Embodiment 5.
[0041] FIG. 19B is a timing chart illustrating operations performed
by the second processor according to Embodiment 5.
[0042] FIG. 20 is a timing chart illustrating backlight control
when local dimming is used according to Embodiment 6.
[0043] FIG. 21 is a flow chart illustrating an example of
operations performed by the second processor according to
Embodiment 6.
[0044] FIG. 22 is a timing chart illustrating an example of
operations performed by the second processor according to
Embodiment 6.
[0045] FIG. 23 is a flow chart illustrating an example of
operations performed by the second processor according to
Embodiment 6.
[0046] FIG. 24 is a timing chart illustrating an example of
operations performed by the second processor according to
Embodiment 6.
[0047] FIG. 25 is a timing chart illustrating an example of
operations performed by the second processor according to
Embodiment 6.
DESCRIPTION OF EMBODIMENTS
Embodiment 1
(Underlying Knowledge Forming Basis of the Present Disclosure)
[0048] In recent years, in fields related to display devices, and
in particular liquid crystal displays and projectors that use
liquid crystals, a technique known as backlight scanning has been
employed in an effort to improve image quality. Backlight scanning
is a backlight control method which improves the slow reaction
speed of the liquid crystals and improves motion blur that can be
seen in sample-and-hold displays. In this method, the display
screen is divided into regions (backlight regions), and light
emission of the backlight is controlled such that the regions
sequentially emit light at fixed periods. More specifically,
backlight scanning is a control method that establishes backlight
OFF periods, and the timing for these cyclic OFF periods (blanking
periods) for each of the backlight regions are set to be different
from one another. Generally, control is often performed to
synchronize the timing of the blanking period with the timing of
the scanning.
[0049] However, as disclosed in PTL 1, in visible light
communication, visible light communication signals are superimposed
by strobing the backlight. As such, transmission of visible light
communication signals is not possible during the backlight OFF
period. Moreover, this OFF period can cause signal transmission
failure. As such, the only choice is to stop the scanning of the
backlight and transmit the visible light communication signals,
which sacrifices image quality.
[0050] In light of this, the present disclosure provides a display
device capable of outputting visible light communication signals
without significantly deteriorating the quality of the display
image, and capable of reducing receiving error of output visible
light communication signals.
[0051] Hereinafter, non-limiting embodiments will be described in
detail with reference to the accompanying drawings. However,
unnecessarily detailed descriptions may be omitted. For example,
detailed descriptions of well-known matters or descriptions of
components that are substantially the same as components described
previous thereto may be omitted. This is to avoid unnecessary
redundancy and provide easily read descriptions for those skilled
in the art.
[0052] The following description and drawings are provided to
assist those skilled in the art in understanding the present
disclosure, and are not intended to limit the scope of the
claims.
Embodiment 1
[0053] Hereinafter, Embodiment 1 will be described with reference
to FIG. 1 through FIG. 8.
(1. Configuration)
[0054] FIG. 1 is a schematic view of one example of a visible light
communication system according to Embodiment 1.
(1.1 Visible Light Communication System Configuration)
[0055] The visible light communication system 10 illustrated in
FIG. 1 includes a display device 100 and a smartphone 200.
[0056] The display device 100 is, for example, a television, and
can display an image on a display screen 110. The display device
100 can also superimpose visible light communication signals onto
the display screen 110.
[0057] The smartphone 200 is one example of an electronic device
that receives visible light communication signals, and can receive
the visible light communication signals transmitted from the
display device 100. With this, the user of the smartphone 200 can
obtain, for example, information on the image being displayed on
the display device 100.
[0058] Note that in Embodiment 1, the display device 100 is merely
exemplified as a monitor that displays an image, such as a
television or display; the display device 100 is not limited to
this example. The display device 100 may be a device that projects
an image such as a projector. Similarly, the smartphone 200 is
merely given as an example of an electronic device that receives
visible light communication signals output from the display device
100; any device that can receive visible light communication
signals is acceptable and is not limited to a smartphone. For
example, the electronic device may be a receiver that conforms to
the JEITA CP-1222 standard. Moreover, the electronic device is not
limited to a smartphone and may be a general handheld device.
Moreover, the electronic device may obtain information by receiving
visible light communication signal and decoding the received
visible light communication signals.
[0059] The information transmission method used to transmit the
visible light communication signals may be a method that conforms
to the JEITA CP-1223 standard currently being developed as an
international standard, or the IEEE P802.15 standard already
instituted. Stated differently, the electronic device may use a
receiver that conforms to one or more of these standards.
(1.2. Configuration of Display Device)
[0060] FIG. 2 is a block diagram of one example of the display
device according to Embodiment 1.
[0061] The display device 100 illustrated in FIG. 2 is a display
device that outputs visible light communication signals, and
includes a first input unit 120, a first processor 130, a first
controller 140, a display panel 150, a second input unit 160, a
second processor 170, a second controller 180, and a backlight
190.
[0062] The first input unit 120 receives an input of an image
signal related to an image displayed on the display panel 150. The
image signal is input into the first input unit 120 via, for
example, an antenna cable, image signal line, composite cable, HDMI
(R) cable, PJLink cable, or LAN cable, from, for example, a
broadcast wave, a video recording and playback device, or PC. Here,
the image signal may be stored on various kinds of recording
mediums using a video recording device or playback device, for
example.
[0063] The first processor 130 receives an input of the image
signal from the first input unit 120. The first processor 130
performs general image processing, such as image enhancement, on
the image signal. The first processor 130 transmits the
image-processed image signal to the first controller 140. The first
processor 130 also transmits information indicating the size,
display timing, brightness, etc., of the subframes and image signal
to the first controller 140 and the second processor 170.
[0064] Note that the first processor 130 may output a duty ratio
calculated based on the image signal and the backlight control
signal (hereinafter also referred to as BL control signal) for each
region to the second processing unit.
[0065] The display panel 150 is, for example, a liquid crystal
display panel, and includes the display screen 110 that displays an
image.
[0066] The first controller 140 is one example of the display
controller. The first controller 140 causes the display panel 150
to display an image on the display screen 110 of the display panel
150 based on an image signal. In Embodiment 1, the first controller
140 causes the display panel 150 to display an image based on an
image signal transmitted from the first processor 130. More
specifically, the first controller 140 controls the aperture of the
liquid crystals of the display panel 150 based on an image signal
transmitted from the first processor 130.
[0067] The second input unit 160 receives an input of a signal used
in visible light communication (hereinafter also referred to as a
visible light communication signal), and transmits the input
visible light communication signal to the second processor 170. In
Embodiment 1, a visible light communication signal generated on,
for example, a PC is input into the second input unit 160 via a
proprietary cable or a LAN cable, for example.
[0068] Note that the visible light communication signal may be
superimposed on part of a radio wave and input into the second
input unit 160 via an antenna cable. The visible light
communication signal may also be recorded on a variety of different
types of recordable mediums via a video recording device or
playback device and input into the second input unit 160. For
example, a visible light communication signal recorded by a video
recording device may be placed on a portion of a line of a HDMI (R)
cable or a PJLink cable, for example, and input into the second
input unit 160. Moreover, a visible light communication signal
generated on a separate PC may be superimposed on an image signal,
and the image signal may be input into the second input unit 160
from a video recording device or playback device.
[0069] Note that other than receiving inputs from external devices,
the second input unit 160 may obtain the visible light
communication signal by reading server information via the internet
using information internally stored in the display device, such as
the ID of the display device.
[0070] The second processor 170 generates an encoded signal by
encoding the visible light communication signal input via the
second input unit 160, and calculates a duty based on at least one
of the image signal and the visible light communication signal. The
second processor 170 superimposes the encoded signal onto the BL
control signal input from the first processor 130.
[0071] In Embodiment 1, the encoded signal is described as a signal
having a given proportion of ON periods and OFF periods. Moreover,
the encoded signal is described as a signal encoded using an
inverted-4 PPM method. Note that the encoded signal may be encoded
using Manchester encoding, for example. Moreover, the modulated
signal is described as having a 100% ON/OFF modulation percentage,
but the modulated signal is not limited to this example. For
example, when high/low modulation is used rather than 100%
modulation percentage, ON/OFF in the following description may be
read as high/low and implemented. Regarding the duty of the visible
light communication signal as well, in addition to the ON period
being a value determined by a standard for the whole period during
which the signal is transmitted, it may be read in concert with
(high level.times.high period+low level.times.low period)/(signal
transmission period.times.high level).
[0072] More specifically, the second processor 170 is one example
of the signal processor, and superimposes the visible light
communication signals on the backlight control signals generated
based on the image signals. However, when the second processor 170
superimposes the visible light communication signals on the
backlight control signals, the second processor 170 does not
superimpose the visible light communication signals in periods
indicating an OFF state of the backlight in the backlight control
signals. Note that the encoded visible light communication signal
(encoded signal) may also be referred to simply as the visible
light communication signal.
[0073] The second controller 180 is one example of the backlight
controller. The second controller 180 divides the light emission
surface of the backlight 190 into regions and, based on the
backlight control signal (BL control signal) outputted by the
second processor 170, establishes a period during which control of
light emission in each of the regions and control for turning off
each of the regions a different time are performed. In Embodiment
1, the second controller 180 controls the brightness of and timing
for the backlight 190 based on the backlight control signal (BL
control signal) transmitted from the second processor 170.
[0074] The backlight 190 emits light from behind the display panel
150. More specifically, the backlight 190 has a light emission
surface that emits light from behind the display screen 110 of the
display panel 150. This allows the viewer to view an image
displayed on the display panel 150.
[0075] In Embodiment 1, the light emission surface of the backlight
190 is divided into a plurality of regions, and the light emission
of each region is sequentially controlled to scan the backlight.
Note that the regions of the light emission surface of the
backlight 190 correspond to regions of the display screen 110.
(2. Display Device Operations)
[0076] Next, operations performed by the display device 100 having
the above configuration will be described.
[0077] The display device 100 sequentially scans the backlight
across the entire screen of the display panel 150 by sequentially
turning off the backlight in conjunction with writing of the image
signal.
[0078] Typically, with liquid crystal display panels, the phase
change of the liquid crystals is slow, and even if image signals
are switched to indicate different gradations, switching between
the signals takes time. Thus, by temporarily turning off the
backlight of the display panel to scan the backlight, video
characteristics can be improved, such as bleeding resulting from
video being displayed while switching the signals. However,
scanning speed for switching continues to improve year by year;
typical scanning speed of 60 frames per second has improved to
where double or four times that scanning speed is possible. When
scanning at high speeds, more fluid video characteristics can be
achieved by interpolating frames between normal frames to change
the images in more gradual steps.
[0079] For this reason, backlight scanning in which the backlight
is turned off while scanning the backlight is significantly
important to improving video characteristics, and not superimposing
the visible light communication signal during the OFF periods
associated with backlight scanning is better in terms of video
characteristics.
[0080] For the above reasons, in the display device 100, visible
light communication signals are not output during the OFF periods
(hereinafter also referred to as blanking periods) associated with
backlight scanning.
[0081] Hereinafter a method for (operations for) receiving visible
light communication signals at a high success rate with a receiver
such as the smartphone 200 even when the display device 100 does
not output visible light communication signals during the blanking
periods of the backlight control signals (BL control signals) will
be described.
Example 1 of Embodiment 1
(2.1.1 One Example of Operations Performed by Second Processor)
[0082] FIG. 3A illustrates one example of a state before the
visible light communication signals are superimposed on the BL
control signals according to Example 1 of Embodiment 1, and FIG. 3B
illustrates one example of a state after the visible light
communication signals have been superimposed on the BL control
signals according to Example 1 of Embodiment 1.
[0083] FIG. 3A and FIG. 3B illustrate an example in which BL
control signals A through H, which correspond to the eight regions
A through H resulting from dividing the display region of the
display screen 110, are input to control the backlight 190. The
hatched portions indicate regions where encoded signal (visible
light communication signal) is present.
[0084] The encoded signal illustrated in FIG. 3A is superimposed on
the BL control signals A through H at different phases, and when
out of phase encoded signals are mixed within the reception range
of the receiver, an error (visible light communication signal
receiving error) occurs when the receiver decodes the encoded
signals.
[0085] Therefore, in Example 1 of Embodiment 1, in a given region
of the display region, the encoded signals (visible light
communication signals) are superimposed in phase, as illustrated in
FIG. 3B.
[0086] Here, "in phase" is exemplified as meaning the
synchronization of the rise timing, but "in phase" is not limited
to this example. Any point from a state before the start of the
rise to a state at which the rise ends may determined as the rise
time.
[0087] Moreover, since there is a delay time along the control
signal voltage, for example, in synchronization does not mean that
the timings simply match; "in phase" also includes instances where
a given delay time or a delay time within a given period exist. The
same applies hereinafter.
[0088] Here, since the backlight sequentially turns off with each
region in the case of sequential scanning, it is difficult to
superimpose the encoded signals without including the OFF periods
(blanking periods) at all. Thus, in Example 1 of Embodiment 1, in a
specific region among regions into which the display region is
divided (hereinafter the specific region is also referred to as the
reference region), the timing at which the encoded signal is
superimposed is synchronized with the end of the OFF period (the
blanking period). Note that in regions other than the specific
region (the reference region), encoded signals are superimposed in
phase with the encoded signal of the reference region as well, but
the encoded signals are not superimposed during the OFF periods
(the blanking periods), which are the periods during which the
backlight is turned off.
[0089] In the example illustrated in FIG. 3B, the second processor
170 sets region C into which BL control signal C is inputted as the
reference region, and the encoded signals are superimposed on the
BL control signals A through H in phase after adjusting the
superimposition timing of the encoded signals to synchronize the
head (rise timing) P2 of the encoded signal with the rise timing P1
of BL control signal C in FIG. 3A. Then, upon superimposing the
encoded signals on the BL control signals A through H, the second
processor 170 superimposes the encoded signals during the ON
periods of the BL control signal but does not superimpose the
encoded signals during the OFF periods.
[0090] Note that the reference region is not limited to region C.
Hereinafter, examples will be given of regions that can be set as
the reference region in Example 1 of Embodiment 1. For example, the
reference region may be the brightest region among regions into
which the display region is divided (in other words, the region
whose blanking period is the shortest or the region where the light
transmissivity of the display panel is the greatest).
[0091] Note that even when the brightest region is set as the
reference region, when the position of the reference region is
changed every frame, further provision is required. This is because
the position of the encoded signal superimposed every frame
changes, and the balance of the video drastically changes every
frame, leading to flickering. Moreover, when provisions such as
cutting off one of overlapping encoded signals midway when periods
of encoded signals to be superimposed overlap between regions or
not superimposing during a first predetermined period are not
implemented, receiving errors at the receiver may arise. Thus, when
changing the position of the reference region every frame, at least
for one frame period, a period where the encoded signal is not
superimposed may be established.
[0092] Moreover, when a bright region is set as the reference
region, the bright region may be determined with reference to
transition of the center of the brightness of the image based on
the image signal by the first processor 130, rather than the bright
region bring determined with reference to the brightness of the
display region in every frame.
[0093] Moreover, when there is no change in brightness of the
entire display region above a certain level, such as when the scene
does not switch for a given period of time, a region including the
brightest location in the display region based on the average of
the image signal during the given period of time may be set as the
reference region. Note that the reference region may be determined
in advance.
(2.1.2 Advantageous Effects, etc.)
[0094] As described above, the display device (100) according
Example 1 of Embodiment 1 outputs visible light communication
signals, and includes: a display panel (150) including a display
screen on which an image is displayed; a display controller (the
first controller 140) that causes the display panel to display an
image on the display screen of the display panel based on an image
signal; a backlight (190) having a light emission surface that
illuminates the display screen of the display panel (150) from
behind; a signal processor (the second processor 170) that
superimposes the visible light communication signals on backlight
control signals generated based on the image signal; and a
backlight controller (the second controller 180) that divides the
light emission surface of the backlight (190) into regions and
establishes a period during which control of light emission in each
of the regions and control for turning off the backlight in each of
the regions a different time are performed based on the backlight
control signals outputted by the signal processor (the second
processor 170). When superimposing the visible light communication
signals on the backlight control signals, the signal processor (the
second processor 170) does not superimpose a visible light
communication signal in periods indicating an OFF state of the
backlight (190) in the backlight control signals.
[0095] This configuration provides a display device capable of
outputting visible light communication signals without
significantly deteriorating the quality of the display image, and
capable of reducing receiving error of output visible light
communication signals.
[0096] Moreover, the signal processor (the second processor 170)
may superimpose the visible light communication signals on the
backlight control signals corresponding to the regions in a
one-to-one manner, and the visible light communication signals
superimposed on the backlight control signals corresponding to the
regions may be in phase with one another.
[0097] With this, receiving error of the visible light
communication signals can be inhibited.
[0098] Here, for example, based on the backlight control signal
corresponding to a predetermined region among the regions, the
signal processor may match phases of the visible light
communication signals superimposed on the backlight control signals
corresponding to the regions.
[0099] With this, periods of visible light communication signals
not superimposed during blanking periods can be minimized.
[0100] Moreover, the predetermined region may be the brightest
region among the regions, and may be a region corresponding to an
edge portion of the display screen among the regions.
[0101] With this, the effect of the decrease in brightness due to
the turning off of the backlight due to the visible light
communication signal can be inhibited.
Example 2 of Embodiment 1
[0102] Hereinafter an example will be given where the length of the
blanking period is the same for each region in the display
region.
[0103] The total time the backlight 190 is turned off (the total
OFF period) is calculated by adding the blanking period, which is
the OFF period of the BL control signal, and the OFF period of the
encoded signal.
[0104] As such, even if the encoded signal is superimposed right
after the end of the blanking period in the reference region and
the encoded signal is completely included from that blanking period
to the next blanking period, the period during which the backlight
190 is turned off is extended by the length of the OFF period of
the encoded signal superimposed on the BL control signal. In other
words, when the encoded signal is superimposed, the reference
region is darker than before the encoded signal is
superimposed.
[0105] However, in a region other than the reference region, for
example, since the encoded signal is not superimposed during the
blanking period, this overlaps with the blanking period, and the
length of time the backlight 190 is turned off is shorter than the
reference region by the length of the OFF period among the encoded
signal periods during which the encoded signals are not
superimposed. In other words, in a region other than the reference
region, for example, if the encoded signal is superimposed, there
are instances where that region will become brighter than the
reference region.
[0106] In order to improve this, two methods for establishing an
adjustment period during which the backlight 190 is either turned
on or turned off are conceivable. The first method is matching the
total OFF periods of the other regions to the total OFF period of
the reference region in order to make the total OFF period of the
reference region the longest. The second method is matching the
total OFF periods for all regions to a total OFF period determined
based on the original image signal.
(2.2.1 One Example of Operations Performed by Second Processor in
Accordance with First Method)
[0107] First, operations performed by the second processor 170 in
accordance with the first method will be described with reference
to FIG. 4 and FIG. 5.
[0108] FIG. 4 and FIG. 5 are timing charts illustrating the first
method according to Example 2 of Embodiment 1. (a) in FIG. 4
illustrates the BL control signal corresponding to the reference
region before superimposition of the encoded signal, and (b) in
FIG. 4 illustrates the BL control signal corresponding to the
reference region after superimposition of the encoded signal. (a)
in FIG. 5 illustrates the BL control signal corresponding to a
different region before superimposition of the encoded signal, and
(b) in FIG. 5 illustrates the BL control signal corresponding to a
different region after superimposition of the encoded signal.
[0109] More specifically, FIG. 4 illustrates an example of when the
second processor 170 superimposes the encoded signal on the BL
control signal after adjusting the head (rise timing) of the
encoded signal to the rise timing of the BL control signal of the
reference region (time t12). FIG. 5 illustrates an example of when
the second processor 170 superimposes, on the BL control signal
corresponding to a different region, an encoded signal in phase
with the encoded signal superimposed on the BL control signal
corresponding to the reference region.
[0110] In other words, FIG. 4 and FIG. 5 illustrate an example of
when the second processor 170 superimposes, on the BL control
signals corresponding to the regions, encoded signals in phase with
the other regions at the same time as the blanking period of the
reference region ends. Note that not superimposing the encoded
signal during the blanking period is a priority for the blanking
periods for each of the regions, similar to Example 1 of Embodiment
1.
[0111] As illustrated in (b) in FIG. 4, in the reference region,
other than the blanking period B1 from, for example, time t11 to
time t12, encoded signal OFF period T1, which is the total OFF
period of the encoded signal during the encoded signal period C1
from, for example, time t12 to time t14, is also present.
[0112] Thus, in the reference region illustrated in (b) in FIG. 4,
when the duty of the encoded signal is used, the total OFF period
of the encoded signal in one frame from, for example, time t11 to
time t13 (the encoded signal OFF period) can be represented as
encoded signal OFF period T1=encoded signal period
C1.times.(1-Duty).
[0113] As illustrated in (b) in FIG. 4, in the reference region,
since there is generally no period in which the encoded signal
period C1 and the blanking period B1 overlap, total OFF period T2
for one frame=blanking period B1+encoded signal OFF period T1. In
other words, the total OFF period in the reference region is longer
than the other regions.
[0114] However, in a region other than the reference region, there
is a chance that the encoded signal period and the blanking period
will overlap. As described above, with respect to the blanking
period, the BL control signal takes priority over the encoded
signal, so the encoded signal is not superimposed.
[0115] As such, as is illustrated in (b) in FIG. 5, in a region
other than the reference region, in the encoded signal period C1
between, for example, time t21 and time t24, the total OFF period
is shorter than that of the reference region by the length of the
encoded signal OFF period in the encoded signal period C1 that
overlaps with the blanking period B2 between time t22 and time
t23.
[0116] Here, when the period of the encoded signal that overlaps
with the blanking period is B2, the total encoded signal OFF period
in the encoded signal period C1 (the encoded signal OFF period) can
be represented as (encoded signal OFF period)=(encoded signal
period C1-blanking period B2).times.(1-Duty).
[0117] As described above, when the total OFF period for each
region of the screen (display region) is different, the brightness
of the regions is uneven, which reduces image quality.
[0118] Therefore, by operating according to the first method where
an adjustment period during which the backlight 190 is either
turned on or turned off is established, the second processor 170
can match the total OFF periods for the regions in the screen.
[0119] More specifically, the second processor 170 matches the
total OFF period for the regions other than the reference region
with the total OFF period of the reference region in accordance
with the first method, and establishes an adjustment period for
adjusting the difference in the regions other than the reference
region with the total OFF period per frame in the reference region.
Note that as described above, in Example 2 of Embodiment 1, it is
presumed that the length of the blanking period for each region is
the same.
[0120] Here, in (b) in FIG. 5, the adjustment period from time t24
to time t26 is represented as blanking period B2.times.(1-Duty). In
other words, the adjustment period in each region other than the
reference region can be calculated from the blanking period,
encoded signal period, and encoded signal phase of each region
including the reference region. In (b) in FIG. 5, the adjustment
period is exemplified as being located in one frame between one
frame from time t21 to time t25.
[0121] In this way, the display device 100 according to Example 2
of Embodiment 1 causes the second processor 170 to establish an
adjustment period according to the first method. With this, the
display device 100 can output encoded signals without greatly
altering image quality, although the brightness of the screen
(display region) as a whole decreases by a certain amount due to
the superimposition of the encoded signals on the BL control
signals.
[0122] Note that the second processor 170 establishing the
adjustment period directly after the encoded signal period is
preferred because the adjustment period can be stably located as
close as possible to the blanking period, during which change in
phase of the liquid crystals of the display panel 150 is great, but
this is merely an example to which the placement of the adjustment
period should not be limited. The second processor 170 may
establish the adjustment period up to the time when the next
encoded signal is to be superimposed.
(2.2.2 One Example of Operations Performed by Second Processor in
Accordance with Second Method)
[0123] Next, operations performed by the second processor 170 in
accordance with the second method will be described.
[0124] The adjustment period during which the backlight 190 is
either turned on or off to adjust the total OFF period generally
can be defined as follows. When the original OFF period of the
backlight 190 based on the image signal (the blanking period and
the black video period) is T4, the total OFF period of the encoded
signal in an encoded signal period not overlapping with the
blanking period among encoded signal periods is T5, and the
blanking period after superimposition of the visible light
communication signal is T6, the adjustment period can be
represented as T4-T5-T6. Note that, as previously described, the
adjustment period is preferably located as close as possible to the
blanking period.
[0125] For example, in the reference region, T5 can be calculated
by first summing the totals of encoded signal OFF periods in the
encoded signal period and then subtracting the totals of OFF
periods in the portion of the encoded signal overlapping the
blanking period.
[0126] Hereinafter, operations performed by the second processor
170 in accordance with the second method will be described in
detail with reference to FIG. 6A through FIG. 7D.
[0127] FIG. 6A through FIG. 7D are timing charts illustrating the
second method according to Example 2 of Embodiment 1.
[0128] First, with reference to FIG. 6A through FIG. 6D, operations
performed by the second processor 170 with respect to establishing
an adjustment period according to the second method when the
encoded signal period and the blanking period do not overlap will
be described.
[0129] In FIG. 6A through FIG. 6D, the top half, as indicated by
(a), illustrates the BL control signal before superimposition of
the encoded signal, and the bottom half, as indicated by (b)
through (e), indicates the (i) BL control signal after
superimposition of the encoded signal and (ii) the BL control
signal adjusted in accordance with the second method. In these
figures, the blanking period is indicated as B1 and the encoded
signal period is indicated as C1.
[0130] The method of adjusting the BL control signal superimposed
with the encoded signal in accordance with the second method is
separated into four different cases illustrated in FIG. 6A through
FIG. 6D based on the relationship between (i) a sum (temporal sum)
of the adjustment period, the encoded signal period, and the
blanking period and (ii) whether the adjustment period is positive
or negative. Hereinafter, each case will be described.
(Adjustment Method for when Encoded Signal Period and Blanking
Period do not Overlap (Case 1))
[0131] FIG. 6A illustrates an example where the adjustment period
is 0 or greater and (adjustment period+encoded signal
period+blanking period) is shorter than or equal to the length of
one frame.
[0132] As illustrated in the top half of (b) in FIG. 6A, part of
the adjustment period starts at the end time P2 of blanking period
B1 and ends at the start time P3 of the encoded signal period C1,
and the remaining part of the adjustment period is located after
the encoded signal period, preferably directly after the encoded
signal period (at time P5).
[0133] As a result of the second processor 170 establishing the
adjustment period indicated in the top half of (b) in FIG. 6A, the
BL control signal superimposed with the encoded signal is adjusted,
as indicated in the bottom half of (b) in FIG. 6A.
[0134] In this way, the second controller 180 turns off the
backlight 190 even after the blanking period B1 until before the
start of the encoded signal period C1 in accordance with the
adjusted BL control signal, and further turns off the backlight 190
until a period from the adjustment period minus the period from P2
to P3, during the encoded signal period C1 and after the end of the
encoded signal period C1.
[0135] Note that when the adjustment period is shorter than the
period from P2 to P3, the adjustment period may be established
between P2 and P3 only. Moreover, when P2=P3, the entire adjustment
period may be established after the end of the encoded signal
period C.
(Adjustment Method for When Encoded Signal Period and Blanking
Period Do Not Overlap (Case 2))
[0136] FIG. 6B illustrates an example where the adjustment period
is 0 or greater and (adjustment period+encoded signal
period+blanking period) is longer than the length of one frame.
[0137] As illustrated in the top half of (c) in FIG. 6B, part of
the adjustment period starts at the end time P2 of blanking period
B1 and ends at the start time P3 of the encoded signal period C1,
and the remaining part of the adjustment period goes back from the
end time P4 of one frame.
[0138] As a result of the second processor 170 establishing the
adjustment period indicated in the top half of (c) in FIG. 6B, the
BL control signal superimposed with the encoded signal is adjusted,
as indicated in the bottom half of (c) in FIG. 6B.
[0139] In this way, the second controller 180 turns off the
backlight 190 after the blanking period B1 until the start time P3
of the encoded signal period C1 in accordance with the adjusted BL
control signal, and turns off the backlight 190 from time P5 before
the end of the encoded signal period C1 until time P4. In other
words, during the period from time P5, which overlaps with the
remaining adjustment period and the encoded signal period C1, to
the end time P10 of encoded signal period C1, the encoded signal is
not superimposed on the adjusted BL control signal (or the signal
is set to OFF) so as not to transmit the encoded signal.
[0140] Note that when P2=P3 (i.e., they are the same point in
time), the entire adjustment period may be established after the
encoded signal period.
(Adjustment Method for when Encoded Signal Period and Blanking
Period do not Overlap (Case 3))
[0141] FIG. 6C illustrates an example where the adjustment period
is less than 0 and (adjustment period+encoded signal
period+blanking period) is shorter than or equal to the length of
one frame. Here, an adjustment period less than 0 means an
adjustment period during which the backlight 190 is turned on.
[0142] As illustrated in the top half of (d) in FIG. 6C, the
adjustment period is located from the end time P2 of the blanking
period B1 counting back by an amount of time corresponding to the
absolute value of the adjustment period (i.e., the adjustment
period is between time P6 and time P2).
[0143] As a result of the second processor 170 establishing the
adjustment period indicated in the top half of (d) in FIG. 6C, the
BL control signal superimposed with the encoded signal is adjusted,
as indicated in the bottom half of (d) in FIG. 6C.
[0144] In this way, the second controller 180 turns on the
backlight 190 during the period from time P6 during the blanking
period B1 until time P2, based on the adjusted BL control
signal.
[0145] Moreover, when P2=P3, the entire adjustment period may be
established after the encoded signal period C1. Moreover, when the
adjustment period is longer than the blanking period, taking into
consideration the duty cycle of the encoded signal, the OFF period
may be set counting back from the end time of the encoded signal
period C1 until an amount of on-time required to supply the
deficiency can be secured, without superimposing the encoded
signal.
(Adjustment Method for When Encoded Signal Period and Blanking
Period Do Not Overlap (Case 4))
[0146] FIG. 6D illustrates an example where the adjustment period
is less than 0 and (adjustment period+encoded signal
period+blanking period) is longer than the length of one frame.
[0147] As illustrated in the top half of (e) in FIG. 6D, the
adjustment period is located from the end time P2 of the blanking
period B1 counting back by an amount of time corresponding to the
absolute value of the adjustment period (i.e., the adjustment
period is between time P7 and time P2). With this, the backlight
190 is turned on during the period from time P7 to time P2 in the
blanking period B1.
[0148] Note that regardless of the fact that the blanking period
and the encoded signal period do not overlap and that the
adjustment period is negative, there are instance where the
absolute value of the adjustment period may be longer than the
blanking period. In this case, when the entire adjustment period is
located based on time P2 at the end of the blanking period B1, time
P7 is equal to or ahead of time P1, whereby the blanking period is
no longer present. When not all are to be turned on during the
blanking period and still some regions require the backlight 190 to
be turned on (some regions are required to be brightened), the
backlight may be turned on during the OFF period of the encoded
signal of the encoded signal period as the period remaining after
excluding the blanking period portion of the adjustment period. In
other words, the remaining adjustment period may be located from
time P9 counting back (until time P8), and superimposition of the
encoded signal may be skipped and turning-on of the backlight may
be continued.
[0149] Here, time P8 needs to be determined because blanking period
B1 is equal to the total OFF period during a period obtained by
subtracting the period between time P8 and time P9 from the encoded
signal period C1. More specifically, time P8 can be calculated
based on the relationship: blanking period B1=(encoded signal
period C1-(time P9-time P8)).times.(1-Duty).
[0150] With this, the second processor 170 can adjust the BL
control signal such that the second controller 180 causes the
backlight 190 to continue being on from time P8 to the start of the
next blanking period in addition to during the blanking period
B1.
[0151] Note that when P2=P3, the entire adjustment period may be
located after the encoded signal period C1.
[0152] Next, with reference to FIG. 7A through FIG. 7D, operations
performed by the second processor 170 with respect to establishing
an adjustment period according to the second method when the
encoded signal period and the blanking period overlap will be
described.
[0153] In FIG. 7A through FIG. 7D, the top half, as indicated by
(a), illustrates the BL control signal before superimposition of
the encoded signal, and the bottom half, as indicated by (b)
through (e), indicates the (i) BL control signal after
superimposition of the encoded signal and (ii) the BL control
signal adjusted in accordance with the second method. In these
figures, the blanking period is indicated as B1, the encoded signal
period is indicated as C1, and the period from time Q1 to time Q6
is one frame.
[0154] The method of adjusting the BL control signal superimposed
with the encoded signal in accordance with the second method is
separated into four different cases illustrated in FIG. 7A through
FIG. 7D based on the relationship between (i) a sum of the
adjustment period, the encoded signal period, and the blanking
period and (ii) whether the adjustment period is positive or
negative. Hereinafter, each case will be described.
(Adjustment Method for When Encoded Signal Period and Blanking
Period Overlap (Case 1))
[0155] FIG. 7A illustrates an example where the adjustment period
is 0 or greater and (adjustment period+encoded signal
period+blanking period) is shorter than or equal to the length of
one frame.
[0156] As indicated by the top half of (b) in FIG. 7A, the
adjustment period is located based on the end time Q4 of the
encoded signal period C1.
[0157] As a result of the second processor 170 establishing the
adjustment period indicated in the top half of (b) in FIG. 6A, the
BL control signal is adjusted so as to not be superimposed with the
encoded signal during the period from time Q4 to time Q5, which is
the adjustment period, and the period from time Q2 to time Q3,
which overlaps with the blanking period B1, as indicated in the
bottom half of (b) in FIG. 7A.
[0158] In this way, the second controller 180 turns off the
backlight 190 during the period from time Q2 to time Q3, which
overlaps with the blanking period B1, and during the period from
time Q4 to time Q5 in accordance with the adjusted BL control
signal. Note that during the period from time Q4 to time Q5, the
backlight 190 is turned off and encoded signals are not
transmitted.
(Adjustment Method for When Encoded Signal Period and Blanking
Period Overlap (Case 2))
[0159] FIG. 7B illustrates an example where the adjustment period
is 0 or greater and (adjustment period+encoded signal
period+blanking period) is longer than or equal to the length of
one frame.
[0160] As indicated in the top half of (c) in FIG. 7B, based on the
start time Q6 of the encoded signal for the next frame and counting
backwards, the adjustment period is located between time Q8 and
time Q6, which is the adjustment period.
[0161] As a result of the second processor 170 establishing the
adjustment period indicated in the top half of (c) in FIG. 7B, the
BL control signal is adjusted so as to not be superimposed with the
encoded signal during the period from time Q8 to time Q6, which is
the adjustment period, and the period from time Q2 to time Q3,
which overlaps with the blanking period B1, as indicated in the
bottom half of (c) in FIG. 7B.
[0162] In this way, the second controller 180 turns off the
backlight 190 during the period from time Q2 to time Q3, which
overlaps with the blanking period B1, and during the period from
time Q8 to time Q6 in accordance with the adjusted BL control
signal. Note that during the period from time Q8 to time Q6, the
backlight 190 is turned off and encoded signals are not
transmitted.
(Adjustment Method for when Encoded Signal Period and Blanking
Period Overlap (Case 3))
[0163] FIG. 7C illustrates an example where the adjustment period
is less than 0 and (adjustment period+encoded signal
period+blanking period) is longer than or equal to the length of
one frame.
[0164] As illustrated in the top half of (d) in FIG. 7C, the
adjustment period is located from the end time Q3 of the blanking
period B1 counting back by an amount of time corresponding to the
absolute value of the adjustment period.
[0165] As a result of the second processor 170 establishing the
adjustment period indicated in the top half of (d) in FIG. 7C, the
BL control signal is adjusted such that the backlight 190 turns on
during the period from time Q9 to time Q3, which is the adjustment
period, and adjusted so as to not be superimposed with the encoded
signal during the blanking period B1, as indicated in the bottom
half of (d) in FIG. 7C.
[0166] In this way, the second controller 180 turns on the
backlight 190 during the period from time Q9 until time Q3, in
accordance with the adjusted BL control signal.
[0167] Note that the encoded signal may be superimposed during the
adjustment period. In this case, the adjustment period may be
elongated by the total encoded signal OFF period. Furthermore, when
the adjustment period is longer than the blanking period, based on
the duty cycle of the encoded signal, the deficient on-time during
the adjustment period can be supplemented by turning on the
backlight 190 without superimposing the encoded signal during a
predetermined period counting back from the end time of the encoded
signal period C1.
(Adjustment Method for when Encoded Signal Period and Blanking
Period Overlap (Case 4))
[0168] FIG. 7D illustrates an example where the adjustment period
is less than 0 and (adjustment period+encoded signal
period+blanking period) is longer than the length of one frame.
[0169] As illustrated in the top half of (e) in FIG. 7D, the
adjustment period is located from the end time Q3 of the blanking
period B1 counting back by an amount of time corresponding to the
absolute value of the adjustment period until time Q10.
[0170] With this, the backlight 190 is turned on during the period
from time Q10 to time Q3 overlapping with the blanking period
B1.
[0171] Note that the adjustment period may be elongated by the
encoded signal total OFF period, and the encoded signal may be
superimposed during the adjustment period.
[0172] Moreover, similar to (e) in FIG. 6D, when the adjustment
period is substantially long and the absolute value thereof is
greater than that of the blanking period B1, the backlight may be
turned on during the OFF period of the encoded signal of the
encoded signal period as the period remaining after excluding the
blanking period B1 portion of the adjustment period.
[0173] Here, time Q11 needs to be determined because the original
blanking period B1 is equal to the total OFF period during a period
obtained by subtracting the period between time Q11 and time Q12
from the encoded signal period C1. More specifically, time Q11 can
be calculated based on the relationship: blanking period
B1=(encoded signal period C1-(time Q12-time
Q11)).times.(1-Duty).
[0174] With this, the second processor 170 can adjust the BL
control signal such that the second controller 180 causes the
backlight 190 to continue being on from time Q11 to the start time
Q7 of the next blanking period in addition to during the blanking
period B1.
(2.2.3 Advantageous Effects, etc.)
[0175] As described above, with Example 2 of Embodiment 1,
backlight control methods for improving video characteristics such
as backlight scanning and transmission of visible light
communication signals using the backlight can both be achieved by
performing adjustment that equalizes the OFF periods by the visual
light communication encoded signals or reverts the OFF period to
that of the original image signal.
[0176] Here, for example, in the display device according to
Example 2 of Embodiment 1, when superimposing the visible light
communication signals on the backlight control signals, if the
regions include a region whose backlight control signal indicates
an OFF state of the backlight in a period that overlaps a period of
the visible light communication signal being superimposed, the
signal processor (the second processor 170) may establish a ON
adjustment period for the region with overlapping periods and
adjust ON/OFF of the backlight control signal during the ON
adjustment period, the ON adjustment period being for adjusting
brightness of the region with overlapping periods.
[0177] With this, by establishing the adjustment period in a region
in which the visible light communication signal period and the
backlight OFF period overlap, when the visible light communication
signals (encoded signals) are superimposed on the BL control
signals, differences in brightness across the display region are
less perceivable.
[0178] Note that in Example 2 of Embodiment 1, the reference region
is described as a "bright" region, but this may be interpreted as a
region in which the aperture of the display panel 150 is set to a
large value.
Example 3 of Embodiment 1
[0179] (2.3.1 One Example of Operations Performed by Second
Processor in Accordance with Second Method)
[0180] In Example 2 of Embodiment 1, the brightness of the display
screen 110 (display region) of the display panel 150 is equalized
by establishing an adjustment period during which the backlight 190
is either turned on or off, but this is merely one example.
[0181] In Example 3 of Embodiment 1, a method with which an
adjustment period is not established will be described with
reference to FIG. 8.
[0182] FIG. 8 is a timing chart illustrating a method according to
Example 3 of Embodiment 1 of superimposing visible light
communication signals on BL control signals. Here, in (a) in FIG.
8, the BL control signal for a predetermined region is shown. Note
that in Example 3 of Embodiment 1, signal detection is performed
only with rising waveform signals.
[0183] As illustrated in FIG. 8, without establishing an adjustment
period, the duty cycle of the visible light communication signal
for only the portion corresponding to the adjustment period--i.e.,
the high period of the signal--may be varied to adjust the
brightness of the region.
[0184] More specifically, for example, when the adjustment period
in Example 2 of Embodiment 1 is positive--i.e., when the adjustment
turns off the backlight 190--the high period of the BL control
signal may be shortened as illustrated in (b) in FIG. 8.
[0185] More specifically, for example, when the adjustment period
in Example 2 of Embodiment 1 is negative--i.e., when the adjustment
turns on the backlight 190--the high period of the BL control
signal may be lengthened as illustrated in (c) in FIG. 8.
[0186] Note that varying the duty cycle of the BL control signal
for each region in the display region is also conceivable. In this
case, in order to drive the BL control signals at a constant duty
cycle in the screen, a mixture of the adjustment period in Example
2 of Embodiment 1 recalculated to include the duty cycle variation
and the method of varying the high period of the visible light
communication signals according to Example 3 of Embodiment 1 may be
used.
[0187] Furthermore, in the above description, a uniform brightness
across the screen and prevention of a decrease in image quality are
achieved by performing brightness control utilizing control (PWM
(pulse width modification) control) of the high period of the
backlight 190, but this is merely an example. The second controller
180 that controls the backlight may approximate the brightness of
the visible light communication regions to the brightness of the
other regions by controlling the current supplied to the backlight
190 of each region. Furthermore, the brightness of the visible
light communication regions may be approximated to the brightness
of the other regions with a combination of the PWM control of the
backlight 190 and the electrical current control.
(2.3.2 Advantageous Effects, etc.)
[0188] As described above, with Example 3 of Embodiment 1,
backlight control methods for improving video characteristics
relating to backlight scanning and transmission of visible light
communication signals using the backlight can both be achieved by
performing adjustment that equalizes the OFF periods by the visual
light communication encoded signals or reverts the OFF period to
that of the original image signal.
[0189] Note that in Example 3 of Embodiment 1, it is described that
signal detection is performed only with rising signals, but this is
merely an example. When the BL control signal maintains the
position of the fall of the waveform and changes the position of
the rise of the waveform, signal detection may be performed with a
falling signal. In Example 3 of Embodiment 1, the encoded signals
are superimposed using the rise of the BL control signals as a
reference, but the timing at which the encoded signals are
superimposed may be based on other characteristics of the BL
control signals such as the fall of the BL control signals, and may
be based on a synchronization signal of the image signal itself.
Moreover, a signal of the synchronization signal of the image
delayed by a certain amount of time may be generated, and that
signal may be used as a reference.
(3. Advantageous Effects)
[0190] Embodiment 1 provides a display device capable of outputting
visible light communication signals without significantly
deteriorating the quality of the display image, and capable of
reducing receiving error of output visible light communication
signals.
Embodiment 2
[0191] In Embodiment 1, operations performed by the display device
100 when the encoded signal period is shorter than the BL control
signal ON period are described. In Embodiment 2, operations
performed by the display device 100 when the encoded signal period
is longer than the BL control signal ON period will be
described.
(1. Display Device Operations)
[0192] The following description will focus on operations performed
by the second processor 170.
[0193] FIG. 9 is a flow chart illustrating operations performed by
the second processor according to Embodiment 2.
[0194] First, in step S801, the second processor 170 re-encodes the
visible light communication signal. More specifically, after the
second processor 170 encodes the visible light communication
signal, the second processor 170 generates (re-encodes) the encoded
signal added with a header, for example. Moreover, the second
processor 170 calculates the transmission time for the encoded
signal based on the carrier frequency of the encoded signal.
[0195] Next, in step S802, the second processor 170 determines
whether the length of the encoded signal is greater than the BL
control signal ON period (the time during which the backlight is
turned on, i.e., the ON duration).
[0196] More specifically, the second processor 170 compares the
time during which the backlight 190 is turned on (the ON duration)
based on the BL control signal duty cycle calculated by the first
processor 130 against the transmission time for the encoded signal
(encoded signal length). When the second processor 170 determines
that the transmission time for the encoded signal is shorter (No in
S802), the process proceeds to step S806, and when the second
processor 170 determines that the transmission time for the encoded
signal is longer (Yes in S802), the process proceeds to step
S803.
[0197] Next, in step S803, the second processor 170 determines
whether to perform visible light communication. When the second
processor 170 determines to perform visible light communication
(Yes in S803), the process proceeds to step S804, and when the
second processor 170 determines to not perform visible light
communication (No in S803), the process proceeds to step S809.
[0198] Next, in step S804, the second processor 170 re-encodes the
visible light communication signal. More specifically, the second
processor 170 generates the signal (re-encodes the visible light
communication signal) such that the signal duty cycle of the header
is for the most part OFF when the signal is encoded with a signal
array such that it is inconceivable that the data in the header is
the payload. Next, the second processor 170 advances the encoded
signal transmission start time such that the timing of the rise of
the BL control signal matches the final signal in the header (the
signal indicating an ON state at the final edge of the header).
Note that further detailed description is omitted.
[0199] Next, in step S805, the second processor 170 determines
whether the length of the encoded signal is greater than the BL
control signal ON period (the ON duration).
[0200] More specifically, the second processor 170 compares the ON
duration of the backlight 190 based on the BL control signal duty
cycle against the encoded signal transmission time. Then, when the
second processor 170 determines that the encoded signal
transmission time is shorter (No in S805), the process proceeds to
step S806, and when the second processor 170 determines that the
encoded signal transmission time is longer (Yes in S805), the
process proceeds to step S807.
[0201] Here, in step S806, the second processor 170 superimposes
the encoded signal on the part of the BL control signal other than
the blanking period part (in other words, the ON period of the BL
control signal, outputs it to second controller 180, and ends the
process.
[0202] On the other hand, in step S807, the second processor 170
determines whether to divide the encoded signal. More specifically,
the second processor 170 compares the transmission time of the
re-encoded encoded signal against the ON duration of the backlight
190. Then, when the encoded signal transmission time is longer, the
second processor 170 determines to divide the encoded signal (Yes
in S807) and proceeds to step S808, and when the encoded signal
transmission time is shorter, the second processor 170 determines
to not divide the encoded signal (No in S807) and proceeds to step
S809.
[0203] Next, in step S808, the second processor 170 divides the
encoded signal to achieve a data length that fits in the ON
duration of the backlight. The second processor 170 then adjusts
the encoded signal such that the encoded signal is superimposed on
a part of the backlight control signal other than the blanking
period (i.e., the BL control signal ON period), and ends the
process.
[0204] Note that in step S809, the second processor 170 does not
transmit the encoded signal to the second controller 180. In other
words, transmission of the visible light communication signal is
cancelled.
(2. Operation Details)
[0205] Hereinafter, details regarding (i.e., a specific example of)
operations performed by the display device 100 according to
Embodiment 2 will be described with reference to FIG. 10A
through
[0206] FIG. 10D and FIG. 11.
2.1. Specific Example 1
[0207] FIG. 10A through FIG. 10D illustrate a specific method for
superimposing encoded signals on BL control signals according to
Embodiment 2.
[0208] In Embodiment 2, the second processor 170 encodes visible
light communication signal using an encoding method such as 4 PPM
or inverted-4 PPM. Significant variations in brightness due to the
signal can be relatively mitigated by encoding using 4 PPM or
inverted-4 PPM, making it possible to avoid instability in
brightness. Note that the visible light communication signals may
be encoded using, for example, Manchester encoding.
[0209] For example, as illustrated in FIG. 10A, the encoded signal
includes a header 90 and a payload 91 in which code, for example,
is stored. The header 90 is assumed to include a signal array
inconceivable for data signals. Here, when encoding using inverse-4
PPM, in principle, the high period accounts for 75% of the signal
period. Moreover, ON states are generally input into the header in
three continuous slots or more (three slots being the smallest unit
of the encoded signal). The header also generally ends in an OFF
state at the separation point of the header.
[0210] FIG. 10B illustrates a case where the encoded signal period
is shorter than the BL control signal ON period. In other words, as
illustrated in FIG. 10B, when the entire encoded signal including
the header is shorter than the period excluding the blanking period
in one frame of the BL control signal (i.e., the BL control signal
ON period), the encoded signal can be superimposed in the BL
control signal ON period with no problem.
[0211] However, when the encoded signal period is longer than the
BL control signal ON period, the entire encoded signal including
the header cannot be included in the BL control signal ON period,
so the encoded signal is divided and included in the BL control
signal ON period, as described above with regard to step S807.
[0212] FIG. 10C illustrates an example of when the encoded signal
is divided and superimposed in the BL control signal ON period due
to the entire encoded signal including the header exceeding the
length of one frame of the BL control signal. More specifically,
the payload 91 of the encoded signal is divided into a payload 91-1
and a payload 91-2, included with a header 90 and a header 92, and
superimposed in the BL control signal ON period. The header 92
includes a discriminant signal indicating that the payload 91-2 is
divided from payload 91 and the payload 91-2 follows the payload
91-1.
[0213] Note that when the encoded signal period is longer than the
BL control signal ON period, only the header 90 may be superimposed
in the BL control signal blanking period and the payload 91 may be
superimposed in the BL control signal ON period, as illustrated in
FIG. 10D.
2.2. Specific Example 2
[0214] Next, an aspect different from that shown in FIG. 10D will
be described. More specifically, a specific example where only the
header of the encoded signal is superimposed in the BL control
signal blanking period if the encoded signal period is longer than
the BL control signal ON period will be described.
[0215] FIG. 11 illustrates a specific method for superimposing
encoded signals on BL control signals according to Embodiment
2.
[0216] (a) in FIG. 11 illustrates an encoded signal encoded using
inverse-4PRM.
[0217] As illustrated in (b) in FIG. 11, the header from (a) in
FIG. 11 may be re-encoded using 4 PPM instead of inverse-4 PPM. In
this case, as illustrated in (b) in FIG. 11, the header has been
changed from an ON state leading into an OFF state to an OFF state
leading into an ON state.
[0218] Then, as illustrated in (c) in FIG. 11, the encoded signal
illustrated in (b) in FIG. 11 is superimposed on the BL control
signal. In the example illustrated in (c) in FIG. 11, an encoded
signal including the header 200, which is a signal of an OFF state,
the header 101, which is a signal of an ON state, and the payload
102 is superimposed on the BL control signal.
[0219] More specifically, the second processor 170 encodes the
visible light communication signals to generate encoded signals and
superimposes the encoded signals, as the visible light
communication signals, on the backlight control signals, and when
superimposing the encoded signals on the backlight control signals,
if the regions include a region whose backlight control signal
indicates an OFF state of the backlight in a period that overlaps a
period of the encoded signal being superimposed, a header portion
of the encoded signal is superimposed on the backlight control
signal during the period indicating an OFF state of the backlight
190, and a portion of the encoded signal other than the header
portion is superimposed on the backlight control signal during a
period other than the period indicating an OFF state of the
backlight.
[0220] With this, even when the encoded signal period is longer
than the BL control signal ON period, the payload of the encoded
signal can be superimposed in the BL control signal ON period.
[0221] In other words, for example, as illustrated in (c) in FIG.
11, by superimposing the header 200, which is a signal of an OFF
state, during the BL control signal blanking period, the encoding
time can be reduced.
[0222] Note that when the adjustment period described in Embodiment
1 is established, a period during which the header 90 of the
encoded signal illustrated in, for example, FIG. 10D is
superimposed in the BL control signal blanking period and the
backlight is turned on during the blanking period needs to be
subtracted from the adjustment period.
[0223] However, as illustrated in (c) in FIG. 11, for example, when
the end time of the header 200 of the encoded signal (the point in
time of the final ON state) is synchronized with the end time of
the blanking period and the phase is determined, the backlight is
not turned on during the blanking period, so there is no need to
subtract from the adjustment period.
(3. Advantageous Effects, etc.)
[0224] Embodiment 2 provides a display device capable of outputting
visible light communication signals without significantly
deteriorating the quality of the display image, and capable of
reducing receiving error of output visible light communication
signals.
[0225] Note that in Embodiment 2, an example of using the header of
the encoded signal encoded using a typical 4 PPM encoding method is
given, but this is merely an example. For example, when the average
duty cycle of the header of the encoded signal is high, a header in
which the ON signals and OFF signals have been reversed may be
superimposed in the blanking period. In this case, as previously
described, adjustment in which the decrease in the OFF period of
the blanking period is inserted into the adjustment period is
preferable.
[0226] Moreover, when the entire encoded signal including the
header can be superimposed in the BL control signal ON period
(i.e., in the ON duration of the backlight 190), encoding may be
performed such that the duty cycle of the header increases.
[0227] Moreover, even when the header is superimposed in the
blanking period, there are cases when the header will not fit in
the blanking period due to the length of the blanking period. In
this case, different types of headers may be prepared and used in
accordance with the length of the blanking period.
Embodiment 3
[0228] In Embodiment 3, a method of dividing the plurality of
regions of the display region into groups and superimposing the
encoded signal so that it is possible to superimpose the entire
encoded signal period of the encoded signal in the BL control
signal ON period will be described.
(1. Second Processor Operations)
[0229] Hereinafter, an example will be given of a method of
determining a time at which to superimpose the encoded signal about
the brightest region, based on region brightness.
[0230] FIG. 12 is a flow chart illustrating operations performed by
the second processor according to Embodiment 3.
[0231] First, in step S1101, the second processor 170 encodes the
visible light communication signal. More specifically, after the
second processor 170 encodes the visible light communication
signal, the second processor 170 generates the encoded signal added
with a header, for example. Moreover, the second processor 170
calculates the transmission time for the encoded signal based on
the carrier frequency of the encoded signal.
[0232] Next, in step S1102, the second processor 170 divides the
display region into a plurality of regions.
[0233] Next, in step S1103, the second processor 170 detects a
bright region with respect to display. More specifically, the
second processor 170 detects the brightness of each of the regions,
and based on the result, selects the brightest region with respect
to display. Here, brightness with respect to display means the
brightest place with respect to signal level indicating light
emission energy of the image, and not a place where the BL control
signal duty cycle is large. Detection of the bright location will
be described in detail later.
[0234] Next, in step S1104, the second processor 170 matches the
phase of the encoded signal to that of the bright region with
respect to display. More specifically, the second processor 170
superimposes an in-phase encoded signal on a BL control signal
corresponding to all regions in time with the BL control signal of
the brightest region, or corresponding to a portion of selected
regions (a plurality of selected regions).
[0235] However, similar to other embodiments, the encoded signal is
not superimposed in the blanking period of the BL control signal.
This is equivalent to operations of AND calculations for each BL
control signal and the encoded signal. Note that steps S801 through
S809 in FIG. 9 may be performed as necessary.
[0236] Next, in step S1105, the second processor 170 determines
whether the encoded signal and the blanking period overlap. More
specifically, the second processor 170 determines whether part of
the encoded signal period and the blanking period of the BL control
signal overlap on a per region basis, and when the encoded signal
period and the blanking period of the BL control signal do not
overlap (Yes in S1105), the process proceeds to step S1106, where
the second processor 170 superimposes the encoded signal on the BL
control signal and ends the processing. When there is an
overlapping portion (No in S1105), the process proceeds to
S1107.
[0237] In step S1107, the second processor 170 determines whether
to perform visible light communication. When the second processor
170 determines to not perform visible light communication (No in
S1107), the process proceeds to step S1108. When the second
processor 170 determines to perform visible light communication
(Yes in S1107), the process proceeds to step S1110, where the
second processor 170 adjusts the duty cycle such that the encoded
signal is not transmitted, and ends the processing.
[0238] Next, in step S1108, the second processor 170 changes the
phase of the encoded signal, and superimposes the encoded signal
with the changed phase on the BL control signal.
[0239] Next, in step S1109, the second processor 170 determines
whether the blanking period overlaps a bright region or not. When
the second processor 170 determines that the blanking period does
not overlap a bright region (No in S1109), the process proceeds to
step S1110. When the second processor 170 determines that the
blanking period does overlap a bright region (Yes in S1109), the
process proceeds to step S1111.
[0240] Next, in step S111, the second processor 170 determines
whether processing has been performed for all regions. When the
second processor 170 determines that processing has not been
performed for all regions (No in S1111), the process returns to
step S1105. When the second processor 170 determines that
processing has been performed for all regions (Yes in S1111), the
process proceeds to step S1112.
[0241] Next, in step S112, the second processor 170 determines
whether there is a region for which no encoded signal has been
superimposed. When the second processor 170 determines that there
is no region for which no encoded signal has been superimposed (No
in S1112), the process returns to step S1103. When the second
processor 170 determines that there is a region for which no
encoded signal has been superimposed (Yes in S1112), the process
ends.
(2. Operation Details)
[0242] Next, details regarding (i.e., a specific example of) the
display device 100 according to Embodiment 3 will be described with
reference to FIG. 13 and FIG. 14.
[0243] FIG. 13 is a timing chart of one example of the division of
the regions into groups according to Embodiment 3, and FIG. 14 is a
timing chart of another example of the division of the regions into
groups according to Embodiment 3. In FIG. 13 and FIG. 14, the
shaded (hatched) portions indicate the periods in which the encoded
signals are interposed (i.e., the encoded signal periods).
[0244] For example, as illustrated in FIG. 13, the regions of the
display region are divided into three groups. More specifically,
region A, region B, and region C are divided into group G1; region
F, region G, and region H are divided into group G2; and region D
and region E are divided into group G3. Then, as illustrated in
FIG. 13, the encoded signals are superimposed in each group, at the
same time in the same period. For example, in group G1,
superimposition is performed using the brightest region--region
C--as a reference, and in group G2, superimposition is performed
using the brightest region--region E--as a reference.
[0245] Note that, as illustrated in FIG. 14, the regions of the
display region may be divided into two groups. In other words,
region A, region B, region C, and region D may be divided into
group G1, and region E, region F, region G, and region H may be
divided into group G2. Then, the encoded signals are superimposed
in each group, at the same time in the same period.
(3. Advantageous Effects, etc.)
[0246] In this way, with the display device according to Embodiment
3, the signal processor (the second processor 170) superimposes the
visible light communication signals on the backlight control
signals corresponding to groups of neighboring regions among the
regions, the visible light communication signals superimposed on
the backlight control signals in the same group are in phase with
one another, and for each group, corresponding visible light
communication signals are superimposed in entirety in a period
during which control of light emission of the backlight (190) based
on the backlight control signals corresponding to the groups is
performed.
[0247] With this, since the display device can superimpose the
entirety of the encoded signals for the encoded signal periods
during the BL control signal ON periods, receiving error of output
visible light communication signals can be reduced. Stated
differently, since the visible light communication signals can be
superimposed without loss of data in the BL control signal ON
periods, receiving error of output visible light communication
signals can be reduced.
[0248] Moreover, based on the backlight control signal
corresponding to a predetermined region among the groups, the
signal processor (the second processor 170) may match phases of the
visible light communication signals superimposed on the backlight
control signals corresponding to the groups.
[0249] With this, for each of the selected groups, the display
device can output the visible light communication signal with less
loss of data.
[0250] Here, the predetermined region is the brightest region among
the regions.
[0251] With this, the display device 100 can make the difference in
brightness across the display region less perceivable.
[0252] Moreover, among the visible light communication signals
superimposed on the backlight control signal phases corresponding
to the groups, a visible light communication signal superimposed on
a backlight control signal corresponding to a first group among the
groups and a visible light communication signal superimposed on a
backlight control signal corresponding to a second group among the
groups are out of phase.
[0253] With this, for each of the selected groups, the display
device 100 can output the visible light communication signal with
less loss of data.
[0254] Note that there are instances where the regions cannot be
divided into groups, as described above. In other words, there are
instances where there are regions in which in-phase encoded signals
cannot fit even when the regions are divided into groups.
Operations performed in this case are described hereinafter.
[0255] FIG. 15 is a timing chart of another example of the division
of the regions into groups according to Embodiment 3. In FIG. 15,
the shaded (hatched) portions indicate the periods in which the
encoded signals are interposed (i.e., the encoded signal
periods).
[0256] For example, the example illustrated in FIG. 15 is a special
example of FIG. 13 and FIG. 14. As illustrated in FIG. 15, after
the regions have been divided into groups, when there is an
in-phase encoded signal that cannot fit, transmission of the
encoded signal may be cancelled.
[0257] More specifically, region A, region B, region C, and region
D are divided into one group, and all other regions are divided
into another group, and encoded signals in phase with one another
are superimposed in region A, region B, region C, and region D.
Here, in region D, the encoded signal is not superimposed in the
overlapping period of the encoded signal and the blanking period.
Furthermore, in the example illustrated in FIG. 15, encoded signals
are not superimposed in the regions after region D (i.e., regions E
through H).
[0258] Note that when there are regions in which in-phase encoded
signals cannot fit even when the regions are divided into groups, a
reference region may be designated, and the encoded signals may be
superimposed only in regions surrounding the reference region
(i.e., regions neighboring the reference region). In this case, the
range of the superimposition of the encoded signals may be
determined based on previously described flow charts, and may be
limited to a predetermined range.
[0259] Moreover, the above-described adjustment period may be
established to prevent brightness difference between regions in
which the encoded signals are superimposed and regions in which the
encoded signals are not superimposed, as well as within the region
in which the encoded signals are superimposed.
[0260] Note that in Embodiment 3, the encoded signals are
superimposed using the rise of the BL control signals as a
reference, but the timing at which the encoded signals are
superimposed may be based on other characteristics of the BL
control signals such as the fall of the BL control signals, and may
be based on a synchronization signal of the image signal itself.
Moreover, a signal of the synchronization signal of the image
delayed by a certain amount of time may be generated, and that
signal may be used as a reference.
[0261] In all regions of the display region, searching for periods
which are not blanking periods is very difficult, and even if there
is such a period, it is significantly short. In the present
disclosure, even when the encoded signals are superimposed on the
BL control signal, by giving the blanking period as much priority
as possible, loss of image quality is avoided by controlling the
turning on of the backlight during the blanking period.
[0262] However, even if the blanking period and the encoded signal
period do not overlap in a given region, most of the time there are
other regions in which the blanking period and the encoded signal
period do overlap.
[0263] As such, in Embodiment 3, a method is disclosed for avoiding
overlapping of the blanking period and the encoded signal period in
as many regions as possible among the regions of the display
region. In other words, in Embodiment 3, the regions are divided
into groups, and in each group, the encoded signals are
superimposed at a given phase. With this, overlapping of the
blanking period and the encoded signal in the groups can be
reduced.
[0264] Note that in Embodiment 3, examples are given in which the
groups are divided into two or three groups, but these are merely
examples.
[0265] Moreover, regarding the method of dividing the regions into
groups, the regions into a predetermined number of groups, and how
the phase will be shifted, for example, may be set in advance.
[0266] Moreover, in Embodiment 3, the regions are divided into
groups in such a manner that the length of the encoded signal
(i.e., the entirety of the encoded signal period) can be
superimposed based on the bright region, but this is merely an
example. Since dividing the regions into groups based on this may
yield a large number of groups, the number of groups may be
limited. Regarding the division of the regions into groups, it is
not necessarily required for the entirety of the encoded signal
period to be superimposable.
[0267] Moreover, the encoded signals superimposed in the regions in
each group may be the same or may be different. Note that when the
encoded signal obtained on the receiver side is composed of two or
more signals mixed together, the chance of a false recognition or
error increases. Here, "two or more signals" means when different
encoded signals are received by the same receiver at the same time,
two or more of the same encoded signals that are out of phase are
received by the same receiver at the same time, or a combination
thereof. With this, the chance of a false recognition or error can
be reduced.
[0268] Moreover, division of groups based on some reference is not
limited to the example described above; the second processor 170
may divide the groups based on a signal processing result based on
the relationship between the image signal and the encoded
signal.
[0269] Moreover, with a backlight that uses, for example, LEDs,
since the light sources are substantially small (nearly spots of
light), in order to light up the screen like in a LCD, a light
guide plate or a diffuser panel is used to spread the region. As
such, when controlling the LEDs in each region, adjacent regions
are designed to overlap one another, and leak light of a certain
amount of more is present.
[0270] Thus, with a backlight that uses LEDs, for example, even
when dividing the regions into groups, since a different signal
bleeds in as noise from leak light from at least adjacent regions,
there is a need to avoid encoded signals of regions including
adjacent blocks temporally overlapping. As such, for example,
encoded signals are not transmitted in that frame at that location,
or temporally consecutive or overlapping encoded signals in a
different region may be transmitted.
[0271] When encoded signals are not transmitted in that frame at
that location, a region from which to output the encoded signal may
be determined on a per frame basis. Alternatively, an encoded
signal from a specified location (linked to the image signal) may
be preferentially transmitted.
[0272] Moreover, when transmission periods of out of phase encoded
signals from different regions overlap one another, this is
acceptable so long as the regions are not continuous or a given
period is between them. When limiting the region and receiving the
signals, this is acceptable because the signals are receivable.
Note that the period between out of phase regions must be
determined based on the range of the light of the backlight
leaking, and thus is a numerical value that changes depending on
the characteristics of the display device used.
[0273] Moreover, each of the regions may be divided into blocks,
and the above method may be applied to the blocks.
Embodiment 4
[0274] When using a light intensity sensor with a substantially
fast response time, such as a photodiode, to receive the encoded
signals, the phase difference between the image and the encoded
signal is not very problematic.
[0275] However, when the encoded signal is imaged and obtained
using an image sensor such as a smartphone or cellular phone camera
or a digital still camera, due to a slight phase difference, the
exposure timing and the ON-OFF edge of the signal or the timing of
the start and/or the end of sequential encoded signal periods are
off by a slight difference in time or occur at the same time, which
can cause a useful signal to be unobtainable. In other words, since
a typical imaging cycle for an image sensor is 30 FPS, when a 60
FPS image signal is synchronized with an encoded signal, for
example, if the timing of the encoded signal cycle is not
synchronized with the timing of the imaging by the image sensor,
the timing of the imaging cycle and the encoded signal cycle will
never match.
[0276] Thus, in Embodiment 4, in order to avoid the above, a method
of shifting the phases of the encoded signals will be
described.
(1. Display Device Operations)
[0277] The following description will focus on operations performed
by the second processor 170.
[0278] FIG. 16 is a flow chart illustrating operations performed by
the second processor according to Embodiment 4.
[0279] First, in step S1501, the second processor 170 shifts the
synchronization of the signal. More specifically, the second
processor 170 shifts the synchronization of the encoded signal when
the synchronization of the display panel 150 and the backlight 190
is not fixed. This is effective in increasing the probability of
successful imaging by the smartphone 200.
[0280] Next, in step S1502, the second processor 170 calculates the
AND of the BL control signal and the encoded signal from the duty
cycle based on the image signal output by the first processor
130.
[0281] Next, in step S1503, the second processor 170 adjusts the
duty cycle based on at least one of the image signal and the
visible light communication signal.
[0282] More specifically, the second processor 170 finds out
whether the encoded signal period and the blanking period overlap
one another and establishes an adjustment period accordingly, as
described in Embodiment 1. When the duty cycle of the BL control
signal for a frame is different from the duty cycle of the BL
control signal based on the original image signal by an amount
equivalent to the adjustment period, the second processor 170
adjusts the duty cycle using, for example, a period in which
transmission of the encoded signal is stopped. Here, for example,
the second processor 170 adjusts the duty cycle by setting the
period during which the backlight 190 is turned off (the OFF period
of the BL control signal) to a period other than the blanking
period. Then, the second processor 170 outputs to the second
controller 180 the BL control signal superimposed with the encoded
signal adjusted by establishment of the adjustment period.
[0283] Note that when the phase relationship of the encoded signal
and the image signal return to the original relationship after a
certain period, the signals may be corrected to a predetermined
phase difference.
[0284] Furthermore, so long as the phase of the encoded signal and
the phase of the image signal change temporally at a frequency
other than the frequency of the image signal--that is to say, one
is not equal to approximately the integer multiple of the
other--there is no particular need to perform phase matching
control. This is because, even if the two phases are not matched in
particular, after a certain amount of time passes, the relationship
between both phases will return to the original state, whereby at
some point in time there will be a time period in which signal
reception is difficult and a time period in which signal reception
can be done without complication.
[0285] FIG. 17A and FIG. 17B illustrate the relationship between
the phases of the BL control signal and the visible light
communication signal according to Embodiment 4.
[0286] For example, in FIG. 17A, using BL control signal X as a
reference, it can be seen that the encoded signal based on the
visible light communication signal and the BL control signal X
become in-phase at a certain period. Note in FIG. 17A and FIG. 17B,
the diagonal line portions indicate periods in which the encoded
signal is actually transmitted, and as one example, the encoded
signal is output at a longer cycle than the BL control signal and
in shorter periods than the BL control signal, but the relationship
between signal lengths is such that one is longer than the other,
as previously described. Moreover, it is not required that one of
the actual transmission period of the encoded signal and the length
of the BL control signal is not long, but the encoded signal
transmission period is preferably shorter than the BL control
signal. Here, the encoded signal repeats 7 times in the period
during which the BL control signal X repeats 12 times, and when the
BL control signal is 60 fps, for example, both are in-phase at
periods of 0.2 seconds. However, as illustrated in FIG. 17B, there
is no particular correlation between the BL control signal X and
the encoded signal, but the phase relationship between the start of
the transmission period of the encoded signal and the start of a BL
control signal per frame changes. For example f1 is located in the
first half of a BL control signal, f2 is located at the second half
of a BL control signal, and f3 is located roughly in the middle of
a BL control signal. However, although the two have a least common
multiple and the phase relationship will not return to the original
state, since the phases gradually shift, error due to imaging
timing can be avoided at somewhere along the line. Moreover,
although the encoded signal is cut-off midway in region X at points
f2, at which the encoded signal is transmitted in the period
falling on the segue of the BL control signal, and f5, this is not
a problem since the encoded signal can be transmitted in a
different region without fail. The correlation between the video
and the communication information is saved in a buffer, for
example, and the previously written data is read, encoded as a
communication signal and used. Moreover, when the time it takes for
the phase relationship of both to return to the original
relationship is substantially long (for example, a few seconds or
longer), the phase relationship may be forcefully reset to the
original relationship. For example, time is provided between the
end of the encoded signal at f8 and f9 in FIG. 17B. The phases of
the BL control signal and the encoded signal may or may not be
resynchronized during this time. Moreover, the cycle for
synchronizing them can be every one second, for example, or can be
skipped.
(2. Operation Details)
[0287] Next, details regarding (i.e., a specific example of)
operations performed by the display device 100 according to
Embodiment 4 will be described with reference to FIG. 18A, FIG. 18B
and FIG. 18C.
[0288] FIG. 18A, FIG. 18B, and FIG. 18C are timing charts
illustrating operations performed by the second processor according
to Embodiment 4. The shaded (hatched) portions indicate regions
where encoded signals are present. FIG. 18A illustrates a timing
change for the BL control signals before superimposition of the
encoded signals, and FIG. 18B illustrates a timing chart for the BL
control signals after superimposition of the encoded signals. FIG.
18C illustrates an example of when the relationship between the
phases of the backlight control signal and the visible light
communication signal is temporally changed by setting a delay time
from the point in time of the rise or fall of the backlight control
signal, which is used as a reference for the encoded signal.
[0289] For example, as illustrated in FIG. 18A, the synchronization
of the encoded signal and the BL control signal is shifted. With
this, on the reception side, such as at the smartphone 200, timing
at which reception of the encoded signal is possible can be
achieved with certainty. Here, the above-described adjustment
period may be calculated per phase difference in each frame and
established.
[0290] Note that, for example, using region A as a reference, the
time difference .beta.1 between the rise of the backlight control
signal and the start V2 of the visible light communication signal
may be set as the delay time in advance and superimposition may be
performed, as illustrated in FIG. 18C. Moreover, with regard to the
time difference .beta.2 between the rise U2 and the start V3 of the
visible light communication signal in the next frame, the same
operations may be performed as with .beta.1 or different operations
may be performed. Moreover, in the example illustrated in FIG. 18C,
.beta. represents a positive numerical value of delay (time), but
may represent a negative value (time) as well.
[0291] Moreover, a frame where .beta.=0 maybe mixed in. The region
to be used as a reference may be any region, and may be selected
based on the above described criteria. The reference time is
described as being the rise of the backlight control signal, but
the reference time may be the fall or any other waveform
characteristic. Moreover, other than a characteristic portion of a
backlight control signal in a predetermined region, a
synchronization signal of the image signal itself may be used as a
reference and, alternatively, a signal of the synchronization
signal of the image delayed by a certain amount of time may be
generated, and that signal may be used as a reference.
[0292] Moreover, in Embodiment 4, since the image signal and the
encoded signal do not correspond on a one-to-one basis, various
encoding data and imaging data may be buffered in advance in memory
(not shown in the drawings) in the display device 100 before
performing the above processing.
[0293] Note that the cycle (one frame length) of the image signal
and the cycle on which the encoded signal is superimposed
preferably have a least common multiple within one second, and
further preferably within 0.5 seconds. Moreover, when these two
cycles synchronize, tracking may be performed from the time of
synchronization on a cycle equivalent to a least common multiple or
an integer multiple, and the minute temporal offset (phase
difference) resulting from the margin of error may be
corrected.
[0294] Moreover, as described above, when the cycle and/or
frequency of the image signal and the cycle and/or frequency of the
encoded signal have a relationship that changes the temporal phase
relationship thereof, even if each cycle does not include a least
common multiple within one second, if the rate of change is
fast--for example, when the above change that repeats the same
phase relationship can be achieved within one second--there is no
particular need to control the relationship between the two phases.
Regarding the rate of change, a relationship such as the one
described hereinafter is preferable, but is merely an example.
(3. Advantageous Effects, etc.)
[0295] As described above, in the display device according to
Embodiment 4, the signal processor (the second processor 170)
temporally changes a delay time of encoding the visible light
communication signals (encoded signals) on the backlight control
signals corresponding to the regions, based on one backlight
control signal corresponding to a given region among the
regions.
[0296] With this, on the reception side, such as at the smartphone
200, timing at which reception of the encoded signal is possible
can be achieved with certainty.
[0297] Note that the signal processor (the second processor 170)
may superimpose the visible light communication signals (encoded
signals) on the backlight control signals on a different cycle than
a cycle of the backlight control signals, and in each of the
regions a relationship between a phase of the backlight control
signal and a phase of the visible light communication signal may
change with a change in frames.
[0298] Here, the cycle of the backlight control signals and the
different cycle on which the visible light communication signals
are superimposed may change temporally.
[0299] Moreover, the visible light communication signals to be
superimposed on the backlight control signals may be in phase with
one another across all regions in which the visible light
communication signals are superimposed.
[0300] Moreover, a phase-shift cycle of the visible light
communication signals superimposed on the backlight control signals
corresponding to the regions and a cycle of one frame of the
backlight control signals may have a least common multiple within
one second, inclusive.
[0301] With this, on the reception side, such as at the smartphone
200, timing at which reception of the encoded signal is possible
can be achieved with certainty in a relatively short period of
time.
[0302] Moreover, the signal processor (the second processor 170)
may correct a start of a phase-shift cycle of the visible light
communication signals (encoded signals) superimposed on the
backlight control signals corresponding to the regions to a cycle
of one frame of the backlight control signals on a cycle equivalent
to a least common multiple or an integer multiple of the
phase-shift cycle of the visible light communication signals
(encoded signals) superimposed on the backlight control signals
corresponding to the regions and the cycle of one frame of the
backlight control signals.
[0303] With this, by correcting the phase shift, on the reception
side, such as at the smartphone 200, timing at which reception of
the encoded signal is possible can be kept from happening over a
long period of time.
[0304] Here, assuming that the positional relationship and
environment allows for reception of communication signals, so long
as the time indicating the least common multiple of the above
described two types of cycles is a value (time) sufficient for
reception to be performed, the time must be no longer than a person
trying to receive the data with the receiver is willing to hold the
receiver and wait to receive the data. With typical NFC, for
example, the amount of time a person is willing to hold the
receiver and wait can be one second, and thus one second or less is
preferable. Furthermore, as an amount of time that strain the
psyche, 0.5 seconds can be used as a further preferable amount of
time within which the least common multiple is included.
Embodiment 5
[0305] In Embodiments 1 through 4, cases in which each area is
sequentially controlled at a normal scanning speed when displaying
an image signal, but each area may be sequentially controlled at a
sped-up speed scanning speed faster than the normal scanning speed
when displaying an image signal.
[0306] In Embodiment 5, a case in which each area is sequentially
controlled when a 2.times. speed video signal is scanned at
4.times. scanning speed will be given as an example. Hereinafter,
the example will be based on the assumption that the blanking
period is 2.times. speed.
(1. Display Device Operations)
[0307] The following description will focus on operations performed
by the second processor 170.
[0308] FIG. 19A and FIG. 19B are timing charts illustrating
operations performed by the second processor according to
Embodiment 5. The shaded (hatched) portions indicate regions where
encoded signals are present. FIG. 19A illustrates a timing chart
for the BL control signals before superimposition of the encoded
signals, and FIG. 19B illustrates a timing chart for the BL control
signals after superimposition of the encoded signals.
[0309] For example, as illustrated in FIG. 19A, there are no
periods across BL control signal A through BL control signal H in
which the backlight is turned on at the same time. In other words,
this indicates that the encoded signals cannot be superimposed for
all regions of the display region at the same time.
[0310] Thus, in Embodiment 5, for example, the scanning period for
the blanking periods between regions may be set to half the normal
amount, as illustrated in FIG. 19B. Then, the region whose BL
control signal blanking period has the latest start time among a
plurality of regions (among all regions is also acceptable)--region
H--is selected.
[0311] The second processor 170 superimposes the encoded signal on
the selected region H in synchronization with the timing of the end
of the blanking period for region H and the start of the turning on
of the backlight 190 (i.e., the point in time at which the BL
control signal H turns "ON").
[0312] In the example illustrated in FIG. 19B, the second processor
170 superimposes the encoded signals on all regions in the display
region in synchronization with the timing of the end of the
blanking period for the BL control signal H and the time at which
the BL control signal H turns "ON".
[0313] As a result, the second processor 170 can set the period for
superimposing the encoded signal for any region in the display
region to a period that is at most one half of a frame.
(2. Advantageous Effects, etc.)
[0314] As described above, in the display device according to
Embodiment 5, the display controller (first controller 140) causes
the display panel (150) to display an image on the display screen
of the display panel in accordance with a sped-up scanning speed
faster than a scanning speed indicated by the image signal.
[0315] With this, the display device can lengthen the period in
which the encoded signals can be output.
[0316] Note that when the encoded signal length (encoded signal
period), is long, the encoded signal cannot be superimposed only in
the BL control signal ON period (period other than the blanking
period), and there is a region that overlaps the blanking period,
the encoded signal is not superimposed during the blanking period
in that region.
[0317] Moreover, an adjustment period for turning on the backlight
190 in the blanking period that is equivalent in length to the ON
time from the encoded signal superimposed during the BL control
signal ON period may be established. In this case, the adjustment
period may be generated using a method described in the above
embodiments or the header of the encoded signal may be superimposed
in the blanking period. Moreover, the regions of the display region
may be divided into groups and the encoded signals may be
superimposed.
[0318] Moreover, the same processes may be performed in a region
above the above-described region (in another region), and no signal
may be outputted at all. In this case, using methods described in
the above embodiments, an OFF adjustment period may be established
to equalize, across the entire screen, duty cycles based on at
least one of the visible light communication signals and the image
signals. Moreover, similar to Embodiment 3, the brightest region
may be selected and encoded signals may be superimposed at timings
determined based on that region. Note that in Embodiment 5, the
encoded signals are superimposed using the rise of the BL control
signals as a reference, but the timing at which the encoded signals
are superimposed may be based on other characteristics of the BL
control signals such as the fall of the BL control signals, and may
be based on a synchronization signal of the image signal itself.
Moreover, a signal of the synchronization signal of the image
delayed by a certain amount of time may be generated, and that
signal may be used as a reference.
[0319] Note that in Embodiment 5, an example is given in which the
scanning speed is sped from 2.times. scanning speed to 4.times.
scanning speed, but this is merely an example. The number of frames
may be kept the same and only the scanning speed may be
increased.
[0320] Moreover, in Embodiment 5, this sort of embodiment is
achieved in advance and signals are transmitted, but the second
processor may use a method in which signals according to Embodiment
5 are transmitted based on the relationship between the image
signal and the encoded signal. In this case, in order for the
signals to be transmitted from the second processor 170 to the
first processor 130 in FIG. 2, the arrow that connects these two
blocks may be a two-headed arrow.
Embodiment 6
[0321] In Embodiment 1 through 5, the control method in which a
period for controlling the turning off of a backlight at a
different timing for each of a plurality of regions is exemplified
as being applied to backlight scanning, but this is merely an
example. This method may be applied to local dimming.
[0322] In Embodiment 6, operations performed when the method is
applied to local dimming will be described.
[0323] Here, local dimming is a backlight control method for
reducing power by dividing the display region (screen) into a
plurality of regions, increasing the transmittivity of the liquid
crystals in the region beyond the normal amount, and decreasing the
brightness of the backlight by the corresponding amount (i.e.,
decreasing the duty cycle). When the transmittivity of the
brightest pixel in the region can be increased (when the brightness
of the brightest pixel is a relatively low value), it is possible
to reduce power consumption with the above method. Moreover, by
receding the duty cycle of the backlight, the period during which
the backlight is on can be reduced, leading to an increase in
contrast.
(1. Backlight Control by Local Dimming)
[0324] Next, BL control signals controlled by local dimming will be
described.
[0325] FIG. 20 is a timing chart illustrating backlight control
when local dimming is used according to Embodiment 6.
[0326] When local dimming is used to control the backlight, for
example, in adjacent regions, although the period T between the
start of each blanking period is the same throughout, the lengths
of the blanking periods are different, as illustrated in FIG.
20.
[0327] For this reason, in each of the regions of the display
region, the display device 100 according to Embodiment 6 may store
the BL control signal blanking period determined based on an image
signal previously displayed in memory and perform processing
(operations) as follows.
(2. Display Device Operations)
[0328] The following description will focus on operations performed
by the second processor 170. Note that Embodiment 6 relates to
signal control when OFF periods per frame for each region in the
display region are aligned.
(2.1. One Example of Operations Performed by Second Processor)
[0329] FIG. 21 is a flow chart illustrating operations performed by
the second processor according to Embodiment 6.
[0330] First, in step S1901, the second processor 170 calculates
the adjustment period. More specifically, when the OFF time in the
encoded signal is N1 and the OFF time in the BL control signal
input by the first processor is N2, adjustment period N=N2-N1. With
this, the second processor 170 can calculate the adjustment
period.
[0331] Next, in step S1902, the second processor 170 determines
whether the sum of adjustment period N and encoded signal period C
(i.e., N+C) is less than or equal to one frame period.
[0332] When the second processor 170 determines that (N+C) is less
than or equal to one frame period (Yes in S1902), the process
proceeds to step S1903. When the second processor 170 determines
that (N+C) is greater than one frame period (No in S1902), the
process proceeds to step S1906, where no encoded signal is output,
and processing ends.
[0333] Next, in step S1903, the second processor 170 determines
whether the adjustment period N is greater than or equal to 0.
[0334] When the second processor 170 determines that N is greater
than or equal to 0 (Yes in S1903), the process proceeds to S1904,
where a OFF period is established from the start of the next
encoded signal counting back by a length of time equivalent to the
adjustment period. Moreover, the encoded signal is not output in
this period, and processing is ended.
[0335] When the second processor 170 determines that N is smaller
than 0 (No in S1903), the process proceeds to S1905, where an ON
period equivalent to the length of the adjustment period is
established in the blanking period of the BL control signal,
counting back from the end time of the blanking period of the BL
control signal. Moreover, the encoded signal is not output in this
adjustment period.
[0336] FIG. 22 is a timing chart illustrating one example of
operations performed by the second processor according to
Embodiment 6. Here, the bold lines indicate the ON periods and the
OFF periods of the BL control signals, and in the following
description, region A will be the reference region. Note that the
region controlled by BL control signal X (where X is one of A
through H) in each figure is also referred to as region X.
[0337] For example, as illustrated in FIG. 22, the second processor
170 superimposes in-phase encoded signals on all of the regions at
a timing determined based on the start of the frame region A, which
is the reference region, and establishes an adjustment period. Note
that the adjustment period may be established in accordance with
the second method described in Embodiment 1, but since the second
method has already been described above, duplication here will be
omitted.
[0338] In Embodiment 6, in principle, encoded signals are not
superimposed during the BL control signal OFF periods (blanking
periods), and are superimposed during the BL control signal ON
periods, similar to embodiments 1 through 5. Note that the
adjustment period may be changed based on the duty cycle of the
encoded signal, and in that case, if the adjustment period is a
period in which the encoded signal is output, the encoded signal
may be superimposed and output.
(2.2. One Example of Operations Performed by Second Processor)
[0339] In local dimming as well, provision of a sequential blanking
period may be given priority similar to when normal backlight
scanning control is performed. Operations performed in this case
are described hereinafter.
[0340] FIG. 23 is a flow chart illustrating an example of
operations performed by the second processor according to
Embodiment 6.
[0341] First, in step S2101, the second processor 170 calculates
the adjustment period. More specifically, when the blanking period
in a predetermined region is N1, the OFF time in the encoded signal
is N2, and the blanking period for that period is N3, adjustment
period N=N1-N2-N3. With this, the second processor 170 can
calculate the adjustment period.
[0342] Next, in step S2102, the second processor 170 determines
whether the sum of adjustment period N, encoded signal period C,
and the blanking period N2 of that region (i.e., N+C+N3) is less
than or equal to one frame period, and stores the determination
result.
[0343] Next, in step S2103, the second processor 170 determines
whether the adjustment period N is greater than or equal to 0, and
stores the determination result.
[0344] After completing the above steps, the second processor 170,
for example, establishes an adjustment period and displays the
visible light communication signal through video, based on the N1
through N3 stored per region and the determination results from
steps S2102 and S2103.
[0345] Note that the adjustment period may be established based on
a combination of the second method described in Embodiment 1 and
the methods described in Embodiments 2 through 5, for example.
[0346] FIG. 24 is a timing chart illustrating one example of
operations performed by the second processor according to
Embodiment 6. In FIG. 24, the adjustment period is established
based on the second method described in Embodiment 1. Here, the
bold lines indicate the ON periods and the OFF periods of the BL
control signals, and in the following description, region A will be
the reference region.
[0347] For example, as illustrated in FIG. 24, the second processor
170 superimposes in-phase encoded signals on all of the regions in
a period from time P to time Q starting after a predetermined
amount of time has elapsed from the start of the frame region A,
which is the reference region, and establishes an adjustment
period. Note that the adjustment period may be established in
accordance with the second method described in Embodiment 1, but
since the second method has already been described above,
duplication here will be omitted.
[0348] In Embodiment 6, in principle, encoded signals are not
superimposed during the BL control signal OFF periods (blanking
periods), and are superimposed during the BL control signal ON
periods, similar to embodiments 1 through 5. As such, for example,
in region A, since a given period starting at time P is a blanking
period where the BL control signal A is OFF, the encoded signal is
not superimposed. The adjustment period is established after the
encoded signal period C.
[0349] Note that the adjustment period may be changed based on the
duty cycle of the encoded signal, and in that case, if the
adjustment period is a period in which the encoded signal is
output, the encoded signal may be superimposed and output.
(2.3. One Example of Operations Performed by Second Processor)
[0350] FIG. 25 is a timing chart illustrating one example of
operations performed by the second processor according to
Embodiment 6.
[0351] When the backlight is controlled with a local dimming
method, the blanking period of the BL control signal is typically
different for each frame and each region. As such, to expedite
calculations, a temporary blanking period (hereinafter also
referred to as a provisional blanking period) is established. The
adjustment period can then be calculated in accordance with the
second method described in Embodiment 2 based on the provisional
blanking period, the encoded signal period, the phase difference
between the two, and the original blanking period. Hereinafter, an
example when this is the case is described with reference to FIG.
25. The bold line in FIG. 25 indicates the waveform of the original
blanking period.
[0352] The provisional blanking period is established based on the
average length of the blanking periods on the screen, or the
shortest period. Here, the provisional blanking period is
exemplified as an OFF period during which the encoded signal is not
superimposed. The encoded signal period is a period during which
the encoded signal is superimposed.
[0353] Moreover, the adjustment period may be established using the
second method described in Embodiment 1. If the adjustment period
is positive, the BL control signal may be adjusted such that the
backlight 190 is turned off during this period, and if the
adjustment period is negative, the BL control signal may be
adjusted such that the backlight 190 is turned on during this
period. When the adjustment period is established counting back
from the blanking period, the BL control signal may be adjusted
such that the backlight 190 is also turned on during the blanking
period. Note that when the adjustment period is negative, if the
encoded signal is superimposed on the BL control signal in the
adjustment period, the adjustment period may be corrected based on
the duty cycle.
(3. Advantageous Effects, etc.)
[0354] As described above, in the display device according to
Embodiment 6, the backlight controller (the second controller 180)
establishes a period during which control of light emission in each
of the regions and control for turning off each of the regions a
different time in accordance with a light emission amount of the
backlight based on each of image signals, each of which is the
image signal, are performed based on the backlight control signals
outputted by the signal processor (the second processor 170), and
changes a duty of the backlight, the duty being based on the image
signals and the visible light communication signals.
[0355] Note that in Embodiment 3, the encoded signals are
superimposed using the rise of the BL control signals as a
reference, but the timing at which the encoded signals are
superimposed may be based on other characteristics of the BL
control signals such as the fall of the BL control signals, and may
be based on a synchronization signal of the image signal itself.
Moreover, a signal of the synchronization signal of the image
delayed by a certain amount of time may be generated, and that
signal may be used as a reference.
[0356] Although the above embodiment describes a case where local
dimming is applied, since local dimming also includes a case in
which the regions are two-dimensionally divided and the image
signals are scanned and written concurrently in a given direction,
there are combinations are regions whose blanking periods are
different but in-phase, but the techniques described in Embodiment
6 can be applied in this case as well.
[0357] As described above, the non-limiting embodiment has been
described by way of example of techniques of the present
disclosure. To this extent, the accompanying drawings and detailed
description are provided.
[0358] Thus, the components set forth in the accompanying drawings
and detailed description include not only components essential to
solve the problems but also components unnecessary to solve the
problems for the purpose of illustrating the above non-limiting
embodiments. Thus, those unnecessary components should not be
deemed essential due to the mere fact that they are described in
the accompanying drawings and the detailed description.
[0359] The above non-limiting embodiment illustrates techniques of
the present disclosure, and thus various modifications,
permutations, additions and omissions are possible in the scope of
the appended claims and the equivalents thereof.
[0360] For example, in the above embodiments, the encoded signals
are described as being superimposed using the rise of the BL
control signals as a reference, but this is merely an example. For
example, the timing at which the encoded signals are superimposed
may be based on a characteristic timing of the BL control signal,
and may be based on a synchronization signal of the image signal
itself. Moreover, a signal of the synchronization signal of the
image delayed by a certain amount of time may be generated, and
that signal may be used as a reference.
[0361] Although only some exemplary embodiments of the present
invention have been described in detail above, those skilled in the
art will readily appreciate that many modifications are possible in
the exemplary embodiments without materially departing from the
novel teachings and advantages of the present invention.
Accordingly, all such modifications are intended to be included
within the scope of the present invention.
INDUSTRIAL APPLICABILITY
[0362] The present disclosure is applicable to a display device
capable of outputting visible light communication signals without
significantly deteriorating the quality of the display image, and
capable of reducing receiving error of output visible light
communication signals, and a method for controlling such a display
device. More specifically, the display device according to the
present disclosure is applicable to a wide variety of applications
relating to the forwarding and transmission of all sorts of
information accompanying images, such as outdoor signage,
information devices, information display devices since they can
actively and securely obtain necessary information as needed, in
addition to household devices such as televisions, personal
computers and tablets since they can actively and securely obtain
information other than images.
* * * * *