U.S. patent application number 13/337058 was filed with the patent office on 2015-02-26 for techniques for dynamically regulating display images for ambient viewing conditions.
This patent application is currently assigned to Vimicro Corporation. The applicant listed for this patent is Xiaopeng LU. Invention is credited to Xiaopeng LU.
Application Number | 20150054858 13/337058 |
Document ID | / |
Family ID | 41514033 |
Filed Date | 2015-02-26 |
United States Patent
Application |
20150054858 |
Kind Code |
A9 |
LU; Xiaopeng |
February 26, 2015 |
TECHNIQUES FOR DYNAMICALLY REGULATING DISPLAY IMAGES FOR AMBIENT
VIEWING CONDITIONS
Abstract
Techniques pertaining to dynamically regulating brightness of
backlighting in display devices are disclosed. According to one
aspect of the present invention, the brightness dynamic range of a
display device is adjusted according to the current ambient viewing
conditions. In order words, the original brightness dynamic range
of the display image is mapped to the brightness dynamic range
suitable for human eyes under the current ambient viewing
conditions. The brightness of the display image is corrected
according to a histogram to enhance the contrast and details of the
display image, thereby a high quality displayed image can be
presented under the current ambient viewing conditions.
Inventors: |
LU; Xiaopeng; (Beijing,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LU; Xiaopeng |
Beijing |
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CN |
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Assignee: |
Vimicro Corporation
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20120092393 A1 |
April 19, 2012 |
|
|
Family ID: |
41514033 |
Appl. No.: |
13/337058 |
Filed: |
December 24, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/CN2010/074373 |
Jun 24, 2010 |
|
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13337058 |
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Current U.S.
Class: |
345/690 |
Current CPC
Class: |
H04N 21/4318 20130101;
H04N 5/58 20130101; H04N 21/42202 20130101; H04N 21/41407
20130101 |
Class at
Publication: |
345/690 |
International
Class: |
G09G 5/10 20060101
G09G005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2009 |
CN |
200910087669.8 |
Claims
1. A method for dynamically regulating a display image for human
eyes to view on a display device under current ambient viewing
conditions, the method comprising: determining an original dynamic
range of the display image; determining a dynamic range suitable
for human eyes under the current ambient viewing conditions
according to the original dynamic range; regulating an original
brightness value of each pixel of the display image to a regulated
brightness value suitable for the human eyes according to the
original dynamic range of the display image and the dynamic range
suitable for human eyes under the current ambient viewing
conditions; and correcting the regulated brightness value of each
pixel of the display image to a corrected brightness value
according to a histogram determined from the regulated brightness
value of each pixel of the display image.
2. The method according to claim 1, wherein the display image is
displayed on the display device according to the current ambient
viewing conditions, where the display image is dynamically adjusted
when the current ambient viewing conditions change to present a
displayed image with proper contrast and details.
3. The method according to claim 2, wherein said correcting the
regulated brightness value of each pixel of the display image to a
corrected brightness value comprises: determining one or more first
midpoints linearly dividing current 2.sup.n-1 brightness ranges of
the regulated brightness value of the display image into 2.sup.n
brightness ranges; determining one or more second midpoints
dividing the current 2.sup.n-1 brightness ranges of the histogram
into 2.sup.n brightness ranges symmetrically according to a number
of pixels in the display image; calculating one or more brightness
correction points according to the first midpoints and the second
midpoints; dividing the current 2.sup.n-1 brightness ranges of the
regulated brightness value of the display image into the 2.sup.n
brightness ranges according to endpoints of the current 2.sup.n-1
brightness ranges and brightness correction points; setting n=n+1
and repeating above operations until n is equal to a bit number of
the display image, wherein an initial value of n is 1; and setting
the corrected brightness value corresponding to the regulated
brightness value of the pixel of the display image within one
brightness range to be equal to a brightness value of one endpoint
of the one brightness range when n is equal to the bit number of
the display image.
4. The method according to claim 3, wherein said calculating one or
more brightness correction points according to the first midpoints
and the second midpoints is based on a formula:
le.sub.N/2=l.sub.N/2+.beta.(e.sub.N/2-l.sub.N/2), wherein l.sub.N/2
is one of the first midpoints, e.sub.N/2 is one of the second
midpoints, .beta. is a mapping curve correction parameter and
ranges from 0 to 1, and N is the number of the brightness ranges
after n times division.
5. The method according to claim 1, further comprising: calculating
output color components of each pixel according to the corrected
brightness value of each pixel of the display image.
6. The method according to claim 5, wherein each of the color
components includes an R component, a G component and a B
component, and wherein said calculating output color components of
each pixel comprises: calculating an input R component, an input G
component and an input B component of the original brightness value
of each pixel of the display image; looking up the regulated
brightness value suitable for the human eyes according to the
original brightness value; obtaining corresponding corrected
brightness value according to the regulated brightness value
suitable for the human eyes; and calculating the output R
component, the output G component and the output B component
respectively according to the corrected brightness value, the input
R component, the input G component and the input B component.
7. The method according to claim 1, wherein the regulated
brightness value suitable for the human eyes is calculated
according to: D ( I ) = ( D max - D m i n ) * log ( I + .tau. ) -
log ( I m i n + .tau. ) log ( I max + .tau. ) - log ( I m i n +
.tau. ) + D m i n . ##EQU00006## wherein I is the original
brightness value, D(I) is the corresponding regulated brightness
value, I.sub.max and I.sub.min are the maxima value and the minimal
value of the original brightness respectively, D.sub.max and
D.sub.min are the maximal value and the minimal value of the
brightness suitable for human eyes respectively, and .tau. is a
mapping regulation parameter and ranges from 0 to .infin..
8. A device for dynamically regulating brightness of a display
image for human eyes to view under current ambient viewing
conditions, the device comprising: a display; a sensor to sense the
current ambient viewing conditions; an adaptive brightness
regulation module provided for determining a brightness dynamic
range suitable for human eyes under the current ambient viewing
conditions according to an original dynamic range of the display
image, and regulating an original brightness value of each pixel of
the display image into a regulated value suitable for the human
eyes according to the original dynamic range of the display image
and the dynamic range suitable for the human eyes under the current
environment; and a histogram regulation module provided for
correcting the regulated brightness value of each pixel of the
display image into a corrected brightness value according to a
histogram of the regulated brightness value of the display
image.
9. The device according to claim 8, wherein the histogram
regulation module comprises: a first midpoint calculation
sub-module provided for determining one or more first midpoints
which linearly divide current 2.sup.n-1 brightness ranges of the
regulated brightness value of the display image into 2.sup.n
brightness ranges; a second midpoint calculation sub-module
provided for determining one or more second midpoints which divide
the current 2.sup.n-1 brightness ranges of the histogram of the
regulated brightness value of the display image into 2.sup.n
brightness ranges symmetrically according to the number of the
pixels; a brightness correction point calculation sub-module
provided for calculating one or more brightness correction points
according to the first midpoints and the second midpoints; a
brightness range dividing sub-module provided for dividing the
current 2.sup.n-1 brightness ranges of the regulated brightness
value of the display image into the 2.sup.n brightness ranges
according to endpoints of the current 2.sup.n-1 brightness ranges
and the brightness correction points; and a cycle control
sub-module provided for setting n=n+1 and repeating above
operations until n is equal to a bit number of the display image,
wherein an initial value of n is 1; and wherein the corrected
brightness value corresponding to the regulated brightness value of
the pixel of the display image within one brightness range is set
to be equal to a brightness value of one endpoint of the one
brightness range when n is equal to the bit number of the display
image.
10. The device according to claim 9, further comprising: a color
correction module provided for calculating output color components
of each pixel according to the corrected brightness value of each
pixel of the display image.
11. The device according to claim 10, wherein the color components
can include an R component, a G component and a B component, and
the color correction module further comprises: an original color
component calculation sub-module provided for calculating an input
R component, an input G component and an input B component of the
original brightness value of each pixel of the display image; a
corrected brightness searching sub-module provided for looking up
the regulated brightness value suitable for the human eyes
according to the original brightness value, and obtaining
corresponding corrected brightness value according to the regulated
brightness value suitable for the human eyes; an output color
component calculation sub-module provided for calculating the
output R component, the output G component and the output B
component respectively according to the corrected brightness value,
the input R component, the input G component and the input B
component.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is related to the area of image
display, particularly related to techniques for dynamically
regulating brightness of backlighting in display device (e.g., a
mobile device, a laptop and a television).
[0003] 2. Description of Related Art
[0004] More and more mobile devices (e.g., a mobile phone, a
personal digital assistant (PDA) and the like) can support
multimedia functions, such as displaying an electronic book,
playing a three dimensional game, viewing pictures or watching a
video. Hence, image quality for the display on the mobile devices
has become one of the selling factors to gain popularity among
consumers.
[0005] Brightness exhibited in the real environment has a very
broad dynamic range. A visual system in human eyes can only sense
the brightness of about five orders of magnitude in the brightness
dynamic range of the real environment. A mobile display device
generally has lower image contrast and usually cannot be adaptive
to the ambient light changes largely due to the limitation in
hardware. For example, an image displayed on a mobile phone may be
too dark to see the details in the relatively dark areas of the
image when in a bright environment such as outdoors with bright
sunshine. Furthermore, the liquid crystal material of the display
device in a mobile phone cannot block the backlighting completely
under the dark environment, so that a dark state light leakage
phenomenon may occur in the dark areas of the image to cause the
reduction of the image contrast.
[0006] A conventional method is to regulate the brightness of the
backlighting manually, typically by a user. For example, the
brightness of the backlighting in some mobile phones is divided
into several levels for the user to adjust. However, such a control
manner is troublesome to use. Furthermore, a superior display
quality cannot be achieved only by enhancing the brightness of the
backlighting in the bright environment. Moreover, the power for the
mobile device may not be efficiently used in a dark
environment.
[0007] Therefore, techniques for regulating the backlighting
brightness under all lighting conditions are desired. As such, a
mobile display device with a low dynamic range is able to display a
high dynamic range and a good visual effect. Further such a mobile
display device can save power, thereby prolonging the use of an
internal battery.
SUMMARY OF THE INVENTION
[0008] This section is for the purpose of summarizing some aspects
of the present invention and to briefly introduce some preferred
embodiments. Simplifications or omissions in this section as well
as in the abstract or the title of this description may be made to
avoid obscuring the purpose of this section, the abstract and the
title. Such simplifications or omissions are not intended to limit
the scope of the present invention.
[0009] In general, the present invention is related to dynamically
regulating brightness of backlighting in display devices. According
to one aspect of the present invention, the brightness dynamic
range of a display device is adjusted according to a current
ambient light. In order words, the original brightness dynamic
range of the display image is mapped to the brightness dynamic
range suitable for human eyes under the current ambient light
conditions, and then the brightness of the display image is
corrected according to a histogram to enhance the contrast and
details of the display image, thereby a high quality image can be
presented on a display under the current ambient light
conditions.
[0010] The present invention may be implemented in many forms as a
method, an apparatus, or a part of system. According to one
embodiment, the present invention is a method for dynamically
regulating brightness of backlighting in a display device. The
method comprises determining a brightness dynamic range suitable
for human eyes under a current environment according to a current
environmental brightness and an original brightness dynamic range
of a display image; regulating an original brightness value of each
pixel of the display image into a regulated brightness value
suitable for the human eyes according to the original brightness
dynamic range of the display image and the brightness dynamic range
suitable for the human eyes under the current environment; and
correcting the regulated brightness value of each pixel of the
display image into a corrected brightness value according to a
histogram of the regulated brightness value of the display
image.
[0011] According to another embodiment, the present invention is a
device for dynamically regulating brightness of backlighting, the
device comprises: an adaptive brightness regulation module provided
for determining a brightness dynamic range suitable for human eyes
under current environment according to a current environmental
brightness and an original brightness dynamic range of a display
image, and regulating an original brightness value of each pixel of
the display image into a regulated brightness value suitable for
the human eyes according to the original brightness dynamic range
of the display image and the brightness dynamic range suitable for
the human eyes under the current environment; and a histogram
regulation module provided for correcting the regulated brightness
value of each pixel of the display image into a corrected
brightness value according to a histogram of the regulated
brightness value of the display image.
[0012] One of the features, benefits and advantages in the present
invention is to provide techniques for dynamically regulating
brightness of backlighting in display devices to present a display
optimized for the current viewing conditions.
[0013] Other objects, features, and advantages of the present
invention will become apparent upon examining the following
detailed description of various embodiments thereof, taken in
conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] These and other features, aspects, and advantages of the
present invention will become better understood with regard to the
following description, appended claims, and accompanying drawings
where:
[0015] FIG. 1 is a schematic diagram showing three different
dynamic ranges;
[0016] FIG. 2 is a flow chart showing a method for dynamically
regulating brightness of backlighting according to one embodiment
of the present invention;
[0017] FIG. 3 is a schematic diagram of a mapping curve; and
[0018] FIG. 4 is a block diagram showing a device for dynamically
regulating the brightness of the backlighting according to one
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The detailed description of the present invention is
presented largely in terms of procedures, steps, logic blocks,
processing, or other symbolic representations that directly or
indirectly resemble the operations of devices or systems
contemplated in the present invention. These descriptions and
representations are typically used by those skilled in the art to
most effectively convey the substance of their work to others
skilled in the art.
[0020] Reference herein to "one embodiment" or "an embodiment"
means that a particular feature, structure, or characteristic
described in connection with the embodiment can be included in at
least one embodiment of the invention. The appearances of the
phrase "in one embodiment" in various places in the specification
are not necessarily all referring to the same embodiment, nor are
separate or alternative embodiments mutually exclusive of other
embodiments. Further, the order of blocks in process flowcharts or
diagrams or the use of sequence numbers representing one or more
embodiments of the invention do not inherently indicate any
particular order nor imply any limitations in the invention.
[0021] The present invention can be suitable for various display
devices, particularly for mobile display devices, such as a mobile
phone, a PDA (personal digital assistant), a digital camera and the
like. The present invention can adaptively regulate brightness of
backlighting in a display device. Thereby, a display device using
one embodiment of the present invention can display a high dynamic
range (HDR) and images/videos of high quality, and use power
effectively at the same time.
[0022] A dynamic range refers to a ratio of the highest value to
the lowest value of a signal. In simple terms, an HDR can be
summarized as follows: 1) bright parts can be very bright; 2) dark
areas can be very dark; 3) details of the bright parts and the dark
areas both are visually presented or clearly visible.
[0023] FIG. 1 is a schematic diagram showing three different
brightness dynamic ranges. The visual system in the human eyes can
sense the ambient brightness in about five orders of magnitude. In
addition to seeing pictures displayed on a display device, the
human eyes can also be exposed to the surroundings beyond the
display device. Under a bright outdoor environment, a sensible
brightness dynamic range for human eyes tends to move rightwards,
and the brightness dynamic range of the display device is
compressed to a dark side of the sensible brightness dynamic range
for human eyes. Thus the visual system of the human eyes fails to
fully restore the pictures displayed on the display device, thus
many details of the pictures displayed on the display devices
become dark and undistinguishable. Under a dark environment, the
sensible brightness dynamic range for human eyes tend to move
leftwards and the brightness dynamic range of the display device is
compressed to a right side of the sensible brightness dynamic range
for human eyes, thereby leading to power waste in the display
device.
[0024] To solve the problem mentioned above, one embodiment of the
present invention is to adjust the brightness dynamic range of a
display device according to the current ambient lighting
conditions. In order words, the original brightness dynamic range
of the display image is mapped to the brightness dynamic range
suitable for human eyes under the current ambient lighting
conditions. Then the brightness of the display image is corrected
according to a histogram to enhance the contrast and details of the
display image, thus a high quality image can be presented in the
current ambient lighting conditions
[0025] FIG. 2 is a flowchart or a process 200 of dynamically
regulating the brightness of backlighting in a display device
according to one embodiment of the present invention. The process
200 may be implemented in software, hardware or a combination of
both. In one embodiment, a software module is implemented according
to the process 200 and executed by a processor in a mobile device
with a display device illuminated by backlighting (e.g., LCD).
[0026] At 201, a brightness dynamic range suitable for the human
eyes under the current ambient lighting conditions is determined
according to an original brightness dynamic range of a display
image. Depending on implementation, the display device may employ a
photosensor such as a photoresistor or other light sensitive
devices to sense the ambient lighting conditions or current
environmental brightness.
[0027] At 202, an original brightness value of each pixel of the
display image is regulated to a regulated brightness value suitable
for the human eyes according to the original brightness dynamic
range of the display image and the brightness dynamic range
suitable for the human eyes under the current ambient lighting
conditions.
[0028] In one embodiment, a full mapping algorithm is used to
regulate the original brightness value of each pixel of the display
image into a regulated brightness value suitable for the human
eyes. The full mapping algorithm maps each pixel of the display
image to a displayed image via a point-to-point corresponding
function (curve). The mapping algorithm is characterized by
one-to-one, i.e., the pixels in the original image with the same
value are mapped into the same values of the displayed image. The
mapping algorithm has advantages of fast computation and
maintaining excellent overall bright/dark effects.
[0029] In one embodiment, the regulated brightness value can be
calculated based on the following formula:
D ( I ) = ( D max - D m i n ) * log ( I + .tau. ) - log ( I m i n +
.tau. ) log ( I max + .tau. ) - log ( I m i n + .tau. ) + D m i n ,
##EQU00001##
where, I is the original brightness value, D(I) is corresponding
regulated brightness value, I.sub.max and I.sub.min are the maxima
value and the minimal value of the original brightness
respectively, D.sub.max and D.sub.min are the maximal value and the
minimal value of the brightness suitable for human eyes
respectively, and .tau. is a mapping regulation parameter and
ranges from 0 to .infin..
[0030] For example, under the bright outdoor environment, when the
current environmental brightness sensed by the photosensor is
larger than a reference brightness, the brightness values of the
pixels in dark areas of the display image need to be raised. It is
assumed that the original brightness dynamic range of the display
image is [0, 255], the brightness dynamic range suitable for the
human eyes under the current environment is [120, 255], so
I.sub.max=255, I.sub.min=0, D.sub.max=255 and D.sub.min=120. Thus,
the regulated brightness value D(I) suitable for the human eyes
corresponding to the original brightness value I of each pixel can
be calculated based on the above formula. For example, the pixels
with the original brightness value being from 0 to 50 are mapped
into the regulated brightness value 120 suitable for the human
eyes, and the pixels with the original brightness value being 60
are mapped to the regulated brightness value 125 suitable for the
human eyes.
[0031] Under a dark environment, when the current environmental
brightness sensed by the photosensor is smaller than the reference
brightness, the brightness values of the pixels in bright areas of
the display image need to be lowered. It is assumed that the
brightness dynamic range suitable for the human eyes under the
current environment is [0, 200], so I.sub.max=255, I.sub.min=0,
D.sub.max=200 and D.sub.min=0. Thus, the regulated brightness value
D(I) suitable for the human eyes corresponding to the original
brightness value I of each pixel can be calculated based on the
above formula. For example, the pixels with the original brightness
value being from 200 to 255 are mapped into the regulated
brightness value 200 suitable for the human eyes, and the pixels
with the original brightness value being 100 are mapped to the
regulated brightness value 150 suitable for the human eyes. Such a
way of reducing the original brightness value of the display image
according to the environmental brightness is favorable for saving
power efficiently, thereby prolonging a use cycle of a battery
powering the mobile display device.
[0032] FIG. 3 is a schematic diagram of mapping curves. As shown in
FIG. 3, each .tau. corresponds to a mapping curve. It can be seen
that D(I)=I when .tau..fwdarw..infin.. A gradient of the mapping
curve is steeper at low gray level when .tau..fwdarw.0. Hence, the
details of the dark areas can be displayed more visibly. However,
the other gray levels after mapping are compressed, thereby causing
reduction of image contrast. Hence, the regulated brightness value
requires to be further corrected according to one embodiment of the
present invention.
[0033] Referring back to FIG. 2, at 203, the regulated brightness
value of each pixel of the display image is corrected to a
corrected brightness value according to a histogram of the
regulated brightness value of the display image.
[0034] Depending on implementation, the correction of the corrected
brightness values comprises the following operations: A1, one or
more first midpoints which linearly divide current 2.sup.n-1
brightness ranges of the regulated brightness value of the display
image into 2.sup.n brightness ranges are determined. A2, one or
more second midpoints which divide current 2.sup.n-1 brightness
ranges of the histogram of the regulated brightness value of the
display image into 2.sup.n brightness ranges symmetrically
according to the number of the pixels are determined. A3, one or
more brightness correction points are calculated according to the
first midpoints and the second midpoints. A4, the 2.sup.n-1
brightness ranges of the regulated brightness value of the display
image are divided into the 2.sup.n brightness ranges again
according to endpoints of the current 2.sup.n-1 brightness ranges
and the brightness correction points.
[0035] Then, n=n+1 is set and A1-A4 operations described above are
repeated until n is equal to a bit number of the display image,
wherein an initial value of n is 1. When n is equal to the bit
number of the display image, the corrected brightness value
corresponding to the regulated brightness value of the pixels of
the display image within one brightness range is set to be equal to
a brightness value of one endpoint of the one brightness range.
[0036] In one embodiment, a calculation formula of the brightness
correction points may be
le.sub.N/2=l.sub.N/2+.beta.(e.sub.N/2-l.sub.N/2), where l.sub.N/2
is one of the first midpoints, e.sub.N/2 is one of the second
midpoints, .beta. is a mapping curve correction parameter and
ranges from 0 to 1, and N=2.sup.n.
[0037] For example, provided that the display image is an 8-bit
image, i.e., the bit number of the display image is 8. Thus, the
corrected brightness values can be calculated by 8 iterations. The
first iteration is described hereafter.
[0038] S11, the first midpoint l.sub.N/2 which divides the
regulated brightness value D(I) of the current display image into 2
brightness ranges with the same length is determined. For example,
the first midpoint l.sub.N/2 may be 127 if D(I) ranges from 0 to
255.
[0039] S12, the second midpoint e.sub.N/2 which divides the
regulated brightness value D(I) into 2 brightness ranges with the
same pixel distribution probability is determined based on the
histogram constructed by the regulated brightness value D(I). E.g.
the second midpoint e.sub.N/2 may be 155.
[0040] S13, the brightness correction point le.sub.N/2 is
calculated according to
le.sub.N/2=l.sub.N/2+.beta.(e.sub.N/2-l.sub.N/2). Provided that the
brightness correction point le.sub.N/2 is 130 when the first
midpoint is 127 and the second midpoint is 155.
[0041] Thus, two brightness ranges [0, 130] and [130, 255] are
formed after the first times iteration. Then, the second iteration
is described hereafter.
[0042] S21, two first midpoints l.sub.N/2 which divide the two
brightness ranges of the regulated brightness value D(I) into four
brightness ranges with the same length respectively are determined.
For example, the first midpoint of the brightness range [0, 130] is
64 and the first midpoint of the brightness range [130, 255] is
192.
[0043] S22, two second midpoints e.sub.N/2 which divide the two
brightness ranges of the regulated brightness value into four
brightness ranges with the same pixel distribution probability are
determined based on the histogram constructed by the regulated
brightness value D(I). For example, the second midpoint of the
brightness range [0, 130] is 78 and the second midpoint of the
brightness range [130, 255] is 206.
[0044] S23: corresponding brightness correction points le.sub.N/2
are calculated. It is assumed that the result calculated according
to the first midpoint 64 and the second midpoint 78 is 72, and the
result calculated according to the first midpoint 192 and the
second midpoint 206 is 200.
[0045] Thus, four brightness ranges [0, 72], [72, 130], [130, 200]
and [200, 255] are formed after the second iteration.
[0046] After the 8 iterations as described above, a previous
distribution of the regulated brightness value of the pixels in the
range from 0 to 255 is corrected into a new distribution of the
corrected brightness values. For example, the pixels originally in
the brightness range [0, 1] are possibly corrected into the
brightness range [1, 2]. A brightness value of anyone endpoint of
the brightness range can be assigned to the pixels as the
brightness value thereof.
[0047] One of the features, benefits and advantages in the present
invention is that an optimization can be found between linear
mapping and histogram equalization. The dynamic range image with
better visual effect, abundant details and moderate contrast is
obtained by using adaptive linear histogram equalization technology
in one embodiment.
[0048] According to another embodiment, in order to further ensure
a display of color images without color dissertation, the method
for dynamically regulating the brightness of the backlighting may
further comprise the following operation: calculating output color
components of each pixel according to the corrected brightness
value of each pixel of the display image. It is well known that a
color component includes an R component, a G component and a B
component. Accordingly, the operation of calculating output color
components of each pixel comprises the following operations.
[0049] B1, an input R component, an input G component and an input
B component of the original brightness value of each pixel of the
display image are calculated.
[0050] B2, the mapped regulated brightness value suitable for the
human eyes is looked up according to the original brightness value,
and corresponding corrected brightness values are obtained
according to the regulated brightness value suitable for the human
eyes.
[0051] B3, an output R component, an output G component and an
output B component of each pixel of the display image are
calculated respectively according to the corrected brightness
value, the input R component, the input G component and the input B
component.
[0052] In one embodiment, the output R component, the output G
component and the output B component are calculated according to
following formulas:
R out = ( R i n L i n ) .gamma. L out , G out = ( G i n L i n )
.gamma. L out , B out = ( B i n L i n ) .gamma. L out ,
##EQU00002##
where R.sub.in, G.sub.in and B.sub.in are the input R component,
the input G component and the input B component of each pixel of
the display image respectively, R.sub.out, G.sub.out and B.sub.out
are the output R component, the output G component and the output B
component of each pixel of the display image respectively, L.sub.in
is the original brightness value of each pixel of the display
image, L.sub.out is the corrected brightness value, and .gamma.
typically ranges from 0.5 to 1.
[0053] When
( R i n L i n ) .gamma. > 1 ##EQU00003##
and L.sub.out=255, i.e., the pixels cross a boundary, R.sub.out can
be clamped in the range of [0, 255]. It should be noted that
generating and regulating the brightness mapping curve by the full
mapping algorithm mentioned above is used as an example only. Those
skilled in the art that other mappings such as a local mapping
technique may be applicable.
[0054] FIG. 4 is a block diagram showing a device for dynamically
regulating the brightness of the backlighting according to one
embodiment of the present invention. Referring to FIG. 4, the
device comprises the following modules.
[0055] An adaptive brightness regulation module 401 is provided for
determining a brightness dynamic range suitable for human eyes
under current environment according to a current environmental
brightness and an original brightness dynamic range of a display
image, and regulating an original brightness value of each pixel of
the display image into a regulated brightness value suitable for
the human eyes according to the original brightness dynamic range
of the display image and the brightness dynamic range suitable for
the human eyes under the current environment.
[0056] A histogram regulation module 402 is provided for correcting
the regulated brightness value of each pixel of the display image
into a corrected brightness value according to a histogram of the
regulated brightness value of the display image.
[0057] In one embodiment, the regulated brightness value suitable
for the human eyes can be calculated based on the following
formula:
D ( I ) = ( D max - D m i n ) * log ( I + .tau. ) - log ( I m i n +
.tau. ) log ( I max + .tau. ) - log ( I m i n + .tau. ) + D m i n ,
##EQU00004##
where I is the original brightness value, D(I) is corresponding
regulated brightness value, I.sub.max and I.sub.min are the maxima
value and the minimal value of the original brightness
respectively, D.sub.max and D.sub.min are the maximal value and the
minimal value of the brightness suitable for human eyes
respectively, and .tau. is a mapping regulation parameter and
ranges from 0 to .infin..
[0058] In one embodiment, the histogram regulation module 402
further comprises the following sub-modules.
[0059] A first midpoint calculation sub-module is provided for
determining one or more first midpoints which linearly divide
current 2.sup.n-1 brightness ranges of the regulated brightness
value of the display image into 2.sup.n brightness ranges.
[0060] A second midpoint calculation sub-module is provided for
determining one or more second midpoints which divide the current
2.sup.n-1 brightness ranges of the histogram of the regulated
brightness value of the display image into 2.sup.n brightness
ranges symmetrically according to the number of the pixels.
[0061] A brightness correction point calculation sub-module is
provided for calculating one or more brightness correction points
according to the first midpoints and the second midpoints.
[0062] A brightness range dividing sub-module is provided for
dividing the current 2.sup.n-1 brightness ranges of the regulated
brightness value of the display image into the 2.sup.n brightness
ranges according to endpoints of the current 2.sup.n-1 brightness
ranges and the brightness correction points.
[0063] A cycle control sub-module is provided for setting n=n+1 and
repeating above operations until n is equal to a bit number of the
display image, wherein an initial value of n is 1.
[0064] The corrected brightness value corresponding to the
regulated brightness value of the pixel of the display image within
one brightness range is set to be equal to a brightness value of
one endpoint of the one brightness range when n is equal to the bit
number of the display image.
[0065] Specifically, the brightness correction points can be
obtained according to the following formula:
le.sub.N/2=l.sub.N/2+.beta.(e.sub.N/2-l.sub.N/2), wherein l.sub.N/2
is one of the first midpoints, e.sub.N/2 is one of the second
midpoints, .beta. is a mapping curve correction parameter and
ranges from 0 to 1, and the number of the brightness ranges after n
times division.
[0066] In a preferred embodiment, the device shown in FIG. 4
further comprises a color correction module 403 provided for
calculating output color components of each pixel according to the
corrected brightness value of each pixel of the display image. The
color components can include an R component, a G component and a B
component. The color correction module 403 further comprises the
following sub-modules.
[0067] An original color component calculation sub-module is
provided for calculating an input R component, an input G component
and an input B component of the original brightness value of each
pixel of the display image.
[0068] A corrected brightness searching sub-module is provided for
looking up the regulated brightness value suitable for the human
eyes according to the original brightness value, and obtaining
corresponding corrected brightness value according to the regulated
brightness value suitable for the human eyes.
[0069] An output color component calculation sub-module is provided
for calculating the output R component, the output G component and
the output B component respectively according to the corrected
brightness value, the input R component, the input G component and
the input B component.
[0070] Specifically, the output color components can be obtained
according to the following formulas:
R out = ( R i n L i n ) .gamma. L out , G out = ( G i n L i n )
.gamma. L out , B out = ( B i n L i n ) .gamma. L out ,
##EQU00005##
where R.sub.in, G.sub.in and B.sub.in are the input R component,
the input G component and the input B component of each pixel of
the display image respectively, R.sub.out G.sub.out and B.sub.out
are the output R component, the output G component and the output B
component of each pixel of the display image respectively, L.sub.in
is the original brightness value of each pixel of the display
image, L.sub.out is the corrected brightness value, and typically
ranges from 0.5 to 1.
[0071] Thus, the low quality input image processed by the adaptive
brightness regulation module 401, the histogram regulation module
402 and the color correction module orderly becomes the high
quality output image.
[0072] Depending on implementation, the device and the method for
dynamically regulating the brightness of the backlighting can be
implemented on a mobile display device employed with a photosensor
such as an external photoresistance sensing the environmental
brightness in real-time.
[0073] The present invention has been described in sufficient
details with a certain degree of particularity. It is understood to
those skilled in the art that the present disclosure of embodiments
has been made by way of examples only and that numerous changes in
the arrangement and combination of parts may be resorted without
departing from the spirit and scope of the invention as claimed.
Accordingly, the scope of the present invention is defined by the
appended claims rather than the foregoing description of
embodiments.
* * * * *