U.S. patent application number 13/548762 was filed with the patent office on 2012-11-08 for multiple display channel system with high dynamic range.
Invention is credited to Robert Mark CLODFELTER.
Application Number | 20120281031 13/548762 |
Document ID | / |
Family ID | 39791460 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120281031 |
Kind Code |
A1 |
CLODFELTER; Robert Mark |
November 8, 2012 |
MULTIPLE DISPLAY CHANNEL SYSTEM WITH HIGH DYNAMIC RANGE
Abstract
A multi-channel display system comprises a plurality of display
devices, each display device having a non-pixel addressable light
output part, e.g. a backlight, and a pixel addressable light output
part, e.g. an LCD panel, in an optical path. The non-pixel
addressable light output part and the pixel addressable light
output part are arranged to both have a temporal modulation, so
that a perceivable optical output of the display device is a
combination of the outputs of the temporal modulation of the pixel
addressable light output part and the temporal modulation of the
non pixel addressable light output part. At least two of the
display devices are arranged for displaying adjacent image parts.
The display system furthermore comprises a linking means for
linking the driving of the non pixel addressable light output part
of at least the two display devices being arranged for displaying
adjacent image parts.
Inventors: |
CLODFELTER; Robert Mark;
(Dayton, OH) |
Family ID: |
39791460 |
Appl. No.: |
13/548762 |
Filed: |
July 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11889089 |
Aug 9, 2007 |
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13548762 |
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Current U.S.
Class: |
345/690 ;
345/1.1 |
Current CPC
Class: |
H04N 9/3147
20130101 |
Class at
Publication: |
345/690 ;
345/1.1 |
International
Class: |
G09G 5/10 20060101
G09G005/10; G09G 5/00 20060101 G09G005/00 |
Claims
1. A display system comprising: a plurality of display devices,
each display device having a non-pixel addressable light output
part and a pixel addressable light output part in an optical path,
the non-pixel addressable light output part and the pixel
addressable light output part being arranged to both have a
temporal modulation, so that a perceivable optical output of the
display device is a combination of the outputs of the temporal
modulation of the pixel addressable light output part and the
temporal modulation of the non pixel addressable light output part,
and at least two of the display devices being arranged for
displaying adjacent image parts, wherein the display system
furthermore comprises a linking means for linking the driving of
the non pixel addressable light output part of at least the two
display devices being arranged for displaying adjacent image parts
so that continuity is ensured between the image parts provided by
each of the at least two display devices.
2. A display system according to claim 1, wherein the linking means
comprises a controller adapted to set a global value for the
driving of the temporal modulation of the non pixel addressable
light output parts of at least the two display devices being
arranged for displaying adjacent image parts.
3. A display system according to claim 2, wherein the controller is
adapted to determine the global value for the driving of the
temporal modulation of the non pixel addressable light output parts
based on the maximum and minimum video levels to be displayed by at
least the two display devices being arranged for displaying
adjacent image parts.
4. A display system according to claim 1, wherein the linking means
comprises a controller adapted to provide a gradient in luminance
levels displayed by at least the two display devices arranged for
displaying adjacent image parts.
5. A display system according to claim 1, wherein the non-pixel
addressable light output part comprises a controllable light
source, and the pixel addressable light output part comprises a
transmissive or reflective part.
6. A method for driving a display system comprising a plurality of
display devices, each display device having a non-pixel addressable
light output part and a pixel addressable light output part in an
optical path, the method comprising: driving the non pixel
addressable light output parts of the display devices, the driving
including temporal modulation of the drive level depending on image
content to be displayed, and individually applying temporal
modulation to the pixel addressable light output parts of the
plurality of display devices for generating the image, the combined
output of the temporal modulation of the non pixel addressable
light output part and the temporal modulation of the pixel
addressable light output part of a display device generating a
perceivable optical output of the display device, wherein driving
the non pixel addressable light output parts of the display devices
comprises synchronising the dynamic range of at least two display
devices arranged for displaying adjacent image parts.
7. A method according to claim 6, wherein synchronising the dynamic
range includes determining an overlapping dynamic range common to
all display devices in the display system and using this
overlapping dynamic range for driving the display devices.
8. A computer device comprising loaded thereon a program product
for executing the methods as claimed in claim 6, the computing
device being associated with a multi-channel display system.
9. A non-transitory computer readable medium for storing the
computer program product of claim 8.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/889,089, filed on Aug. 9, 2007, which is
incorporated by reference herein in its entirety.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to multiple display channel
apparatus, and more particularly to multiple display channel
apparatus with high dynamic range as well as to methods of
manufacture and operation of the same as well as software for
carrying out the methods.
BACKGROUND OF THE INVENTION
[0003] Dynamic range or contrast ratio is the ratio of intensity of
the highest luminance parts of a scene and the lowest luminance
parts of a scene. For example, an image projected by a prior art
video projection system may typically have a maximum dynamic range
of 300:1. It is desired to have image display apparatus with higher
dynamic range.
[0004] Image display apparatus with enhanced dynamic range are
known. U.S. Pat. No. 5,978,142 describes a monochromatic image
display apparatus comprising projector means, a light source, a
first modulator, a second modulator and relay means, the first and
second modulators both being such as to modulate light received
from the light source, the first modulator modulating the light to
produce an image, the relay means optically relaying the image to
the second modulator, the second modulator being such as to further
modulate the image to perform optical image enhancement whereby
finite minimum brightness above true black is reduced, whereby
contrast range of the projected image is extended, and whereby the
optical image enhancement achieved is determined by a driving
signal to the second modulator.
[0005] U.S. Pat. No. 6,985,272 applies the above technique to
multi-colour image display apparatus and describes an image display
apparatus comprising projector means, optical means for splitting
incident light into red, green and blue light, a first modulator
for modulating red light, a second modulator for modulating green
light, a third modulator for modulating blue light, and optical
means for recombining the modulated red light, green light and blue
light. A fourth modulator is provided for modulating the combined
red light, green light and blue light, and control means in the
form of look-up tables for controlling the operation of the first,
second, third and fourth modulators such that the dynamic range of
the image display apparatus is enhanced.
[0006] It is known in the industry that the dynamic range of video
images produced by light modulators such as LCD and others can also
be extended by dynamically modulating the intensity of the
backlight illumination system in response to the desired intensity
of its video input. This intensity change may be essentially equal
across the backlight of the entire display.
[0007] WO 2006/045585 describes a display with a backlight having a
temporal modulation applied and a pixel addressable LCD in an
optical path, the pixel addressable LCD being arranged to output
each pixel of a frame as a temporal sequence of output values,
different values of the sequence coinciding with different output
levels of the modulated backlight. The apparent luminance or colour
of the pixels can be made to take intermediate values between the
gradations dictated by the stepsize corresponding to a least
significant bit of the pixel addressable LCD, to enable more
accurate reproduction of both colour and greyscale images. A
convertor generates a temporal modulation of the pixels for the LCD
according to a value of the pixels in an input signal, and
synchronised to the temporal modulation of the backlight.
[0008] Display results when applying the above backlight modulation
technique to multiple display channel applications are not
satisfactory as disturbing artefacts between adjacent images are
noticeable.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide good
apparatus or methods for displaying images with high dynamic range
in multiple display channel applications. With "high dynamic range"
in the context of the present description is meant a dynamic range
of at least 1,000:1 or more, preferably at least 10,000:1.
[0010] The above objective is accomplished by a method and device
according to the present invention.
[0011] In a first aspect, the present invention provides a display
system comprising a plurality of display devices, each display
device having a non-pixel addressable light output part, e.g. a
backlight or a controllable light source, and a pixel addressable
light output part, e.g. a light modulator, such as for example an
LCD panel, in an optical path. The non-pixel addressable light
output part and the pixel addressable light output part are
arranged to both have a temporal modulation, so that a perceivable
optical output of the display device is a combination of the
outputs of the temporal modulation of the pixel addressable light
output part and the temporal modulation of the non pixel
addressable light output part. In the display system according to
embodiments of the first aspect of the present invention, at least
two of the display devices are arranged for displaying adjacent
image parts. In accordance with embodiments of the present
invention, the display system furthermore comprises a linking means
for linking the driving of the non pixel addressable light output
part of at least the two display devices being arranged for
displaying adjacent image parts.
[0012] It is an advantage of embodiments of the present invention
that an enhanced dynamic range of the display system is obtained by
the modulation of the non pixel addressable part. It is a further
advantage that a limited number, a reduced number or even no
disturbing artefacts occur between adjacent image parts due to the
presence of the linking means which prevents adjacent image parts
from having completely different black and white image levels.
[0013] In a display system according to embodiments of the present
invention the linking means may comprise a controller adapted to
set a global value for the driving of the temporal modulation of
the non pixel addressable light output parts of at least the two
display devices being arranged for displaying adjacent image parts.
Such algorithm is advantageous in that it is simple and easy to
implement. The linking means may comprise a controller adapted to
set a global value for the driving of the temporal modulation of
the non pixel addressable light output parts of each of the
plurality of display devices.
[0014] The controller may be adapted to determine the global value
for the driving of the temporal modulation of the non pixel
addressable light output parts based on the maximum and minimum
video levels to be displayed by at least the two display devices
being arranged for displaying adjacent image parts.
[0015] The linking means may comprise a controller adapted to
provide a gradient in luminance levels displayed by at least the
two display devices arranged for displaying adjacent image parts.
This has the advantage that channels with bright imagery can be
operated with a high intensity backlight setting, while channels
with dark imagery can be operated with a low intensity backlight
setting. On top of that, still limited or reduced or even no
visible artefacts are present at seems between adjacent image
parts.
[0016] The non-pixel addressable light output part of the display
system may comprise a controllable light source, and the pixel
addressable light output part may comprise a transmissive or
reflective part.
[0017] In a second aspect, the present invention provides a method
for driving a display system comprising a plurality of display
devices, each display device having a non-pixel addressable light
output part and a pixel addressable light output part in an optical
path. The method comprises driving the non pixel addressable light
output parts of the display devices, the driving including temporal
modulation of the drive level depending on image content to be
displayed, and individually applying temporal modulation to the
pixel addressable light output parts of the plurality of display
devices for generating the image. The combined output of the
temporal modulation of the non pixel addressable light output part
and the temporal modulation of the pixel addressable light output
part of a display device generates a perceivable optical output of
the display device. In accordance with embodiments of the present
invention, driving the non pixel addressable light output parts of
the display devices comprises synchronising the dynamic range of at
least two display devices arranged for displaying adjacent image
parts.
[0018] In accordance with embodiments of the present invention,
synchronising the dynamic range of at least two display devices
arranged for displaying adjacent image parts may comprise
determining an overlapping dynamic range common to at least the two
display devices arranged for displaying adjacent image parts, and
using this overlapping dynamic range for driving the non pixel
addressable light output parts of at least the two display devices
arranged for displaying adjacent image parts. Synchronising the
dynamic range may include determining an overlapping dynamic range
common to all display devices in the display system and using this
overlapping dynamic range for driving the display devices.
[0019] In embodiments of the present invention, synchronising the
dynamic range of at least two display devices arranged for
displaying adjacent image parts may include determining the dynamic
range of at least the two display devices arranged for displaying
adjacent image parts, and adding a dynamic range gradient to the
driving of at least one of the display devices arranged for
displaying adjacent image parts.
[0020] In a further aspect, the present invention provides a
control unit for a multi-channel display system comprising a
plurality of display devices, each display device having a
non-pixel addressable light output part and a pixel addressable
light output part in an optical path. The control unit comprises
means for driving the non pixel addressable light output parts of
the display devices, the driving including temporal modulation of
the drive level depending on image content to be displayed, and
means for individually applying temporal modulation to the pixel
addressable light output parts of the plurality of display devices
for generating the image. The combined output of the temporal
modulation of the non pixel addressable light output part and the
temporal modulation of the pixel addressable light output part of a
display device generates a perceivable optical output of the
display device. The control unit furthermore comprises means for
synchronising the dynamic range of at least two display devices
arranged for displaying adjacent image parts.
[0021] In a further aspect, the present invention provides a
computer program product for executing any of the methods according
to embodiments of the present invention when executed on a
computing device associated with a multi-channel display system.
The computer program product provides the functionality of any of
the methods according to embodiments of the present invention when
executed on a computing device associated with a multi-channel
display system. The program may run under an operating system, and
may include a user interface that enables a user to interact with
the program, for example a choice between different algorithms may
be made by a user.
[0022] The computer program product may be part of a computer
software product (i.e. a carrier medium) that includes one or more
code segments that cause a processor such as a CPU of the
processing system to carry out the steps of the method. The
computer program product can be tangibly embodied in a carrier
medium carrying machine-readable code for execution by a
programmable processor. Hence, the present invention also provides
a machine readable data storage device for storing the computer
program product according to embodiments of the present invention.
The term "carrier medium" or "machine readable data storage device"
or "data carrier" refers to any medium that participates in
providing instructions to a processor for execution. Such a medium
may take many forms, including but not limited to, non-volatile
media, and transmission media. Non volatile media includes, for
example, optical or magnetic disks, such as a storage device which
is part of mass storage. Common forms of computer readable media
include, a CD-ROM, a DVD, a flexible disk or floppy disk, a
diskette, a memory key, a tape, a memory chip or cartridge or any
other medium which stores the computer program product in a machine
readable form and from which a computer can read. Various forms of
computer readable media may be involved in carrying one or more
sequences of one or more instructions to a processor for
execution.
[0023] Nowadays, such software is often offered on the Internet or
a company Intranet for download, hence the present invention
includes transmitting the computer program product according to
embodiments of the present invention via a carrier wave over a
local or wide area network, such as a LAN, a WAN or the Internet.
Transmission media include coaxial cables, copper wire and fibre
optics, including the wires that comprise a bus within a computer.
The computing device may include one of a microprocessor and an
FPGA.
[0024] Particular and preferred aspects of the invention are set
out in the accompanying independent and dependent claims. Features
from the dependent claims may be combined with features of the
independent claims and with features of other dependent claims as
appropriate and not merely as explicitly set out in the claims.
[0025] The above and other characteristics, features and advantages
of the present invention will become apparent from the following
detailed description, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of
the invention. This description is given for the sake of example
only, without limiting the scope of the invention. The reference
figures quoted below refer to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a schematic top view of a multi-channel display
system according to an embodiment of the present invention.
[0027] FIG. 2 is a diagrammatic illustration of a first embodiment
of the display system as illustrated in FIG. 1.
[0028] FIG. 3 is a diagrammatic illustration of a second embodiment
of the display system as illustrated in FIG. 1.
[0029] FIG. 4 is a schematic illustration of a processing element
which can be used in a display system in accordance with
embodiments of the present invention.
[0030] FIG. 5 illustrates how to determine overall minimum and
maximum video levels over a plurality of channels in a
multi-channel system, for use in accordance with an embodiment of
the present invention.
[0031] FIG. 6 illustrates different luminance values of three
adjacent projectors controlled with an algorithm according to a
first embodiment of the present invention.
[0032] FIG. 7 illustrates different luminance values of three
adjacent projectors controlled with an algorithm according to a
second embodiment of the present invention.
[0033] In the different figures, the same reference signs refer to
the same or analogous elements.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0034] The present invention will be described with respect to
particular embodiments and with reference to certain drawings but
the invention is not limited thereto but only by the claims. The
drawings described are only schematic and are non-limiting. In the
drawings, the size of some of the elements may be exaggerated and
not drawn on scale for illustrative purposes. The dimensions and
the relative dimensions do not correspond to actual reductions to
practice of the invention.
[0035] Furthermore, the terms first, second, third and the like in
the description and in the claims, are used for distinguishing
between similar elements and not necessarily for describing a
sequential or chronological order. It is to be understood that the
terms so used are interchangeable under appropriate circumstances
and that the embodiments of the invention described herein are
capable of operation in other sequences than described or
illustrated herein.
[0036] Moreover, the terms top, bottom, over, under and the like in
the description and the claims are used for descriptive purposes
and not necessarily for describing relative positions. It is to be
understood that the terms so used are interchangeable under
appropriate circumstances and that the embodiments of the invention
described herein are capable of operation in other orientations
than described or illustrated herein.
[0037] It is to be noticed that the term "comprising", used in the
claims, should not be interpreted as being restricted to the means
listed thereafter it does not exclude other elements or steps. It
is thus to be interpreted as specifying the presence of the stated
features, integers, steps or components as referred to, but does
not preclude the presence or addition of one or more other
features, integers, steps or components, or groups thereof. Thus,
the scope of the expression "a device comprising means A and B"
should not be limited to devices consisting only of components A
and B. It means that with respect to the present invention, the
only relevant components of the device are A and B.
[0038] Similarly, it is to be noticed that the term "coupled", also
used in the claims, should not be interpreted as being restricted
to direct connections only. Thus, the scope of the expression "a
device A coupled to a device B" should not be limited to devices or
systems wherein an output of device A is directly connected to an
input of device B. It means that there exists a path between an
output of A and an input of B which may be a path including other
devices or means.
[0039] The invention will now be described by a detailed
description of several embodiments of the invention. It is clear
that other embodiments of the invention can be configured according
to the knowledge of persons skilled in the art without departing
from the true spirit or technical teaching of the invention, the
invention being limited only by the terms of the appended
claims.
[0040] The embodiments described relate to a scheme that includes
at least a combined modulation in time of both pixel data and
backlight illumination (in luminance and/or colour point) of a
plurality of display devices of a multi-channel display system.
According to embodiments of the present invention, a linking
mechanism is provided between the plurality of display devices,
which linking mechanism can ensure continuity between multiple
abutted or blended image parts provided by each of the display
devices on a common display screen, the display screen including a
system of segmented screens with one or more projectors projecting
images on a screen segment. The segmented screens may be adjacent
to one another. Without such a linking mechanism, each display
device may determine its own local optimum settings, in particular
backlight settings, that will lead to disturbing artifacts between
adjacent images in the form of differing black and white image
levels. The present invention discloses the uses of such a link and
corresponding control algorithms to balance the video images within
and between multiple channels to produce a complete seamless image
of maximal dynamic range and fidelity.
[0041] In a typical set-up of a multi-channel display system, each
display device provides its part of a complete image to be shown on
a display screen, the display screen being a single display screen
or a segmented display screen, and these parts are put adjacent
each other on the display screen so as to form the image to be
displayed. In the embodiments of FIG. 1, FIG. 2, and FIG. 3, 3
display devices on a row are illustrated, each providing a part of
the complete image to be shown, the complete image being an image
formed by these three image parts. In other embodiments, however
not illustrated, more or fewer display devices may be provided, and
they do not need to be aligned. Any regular or irregular array of
adjacent or overlapping image parts may be shown, so as to form a
complete image.
[0042] FIG. 1 is a top view of a multi-channel display system 10 in
accordance with an embodiment of the present invention. The
multi-channel display system 10 comprises a plurality of display
devices 12, in the embodiment illustrated in FIG. 1 for example
three projection devices, each for projecting an image part 14 onto
a common display screen 16, the image parts 14 together forming a
complete image to be displayed. The common display screen 16 may be
a single display screen, or may be composed of a plurality of
segmented display screens. The image parts are shown in FIG. 1 as
partially overlapping. However, abutted operation is also possible
as part of embodiments of this invention. According to embodiments
of the present invention, a linking mechanism 18 is provided
between the plurality of display devices 12, which linking
mechanism 18 can ensure continuity between multiple abutted or
blended image parts 14 provided by each of the display devices 12
on a common display screen 16.
[0043] FIG. 2 is a schematic view of a first embodiment of a
multi-channel display system 10 as in FIG. 1.
[0044] The display devices 12 may be any suitable display devices,
such as for example full projectors, stand-alone projection boxes
or monitors. In the following description, projectors are
considered, but this is not intended to be limiting for the
invention. All kinds of electronic display devices are suitable
display devices in the light of the present invention, especially
fixed format display devices such as liquid crystal displays (LCD),
digital light processor (DLP) displays, MEMS based grating light
valve (GLV) or GEMS displays which may be used in projection or
direct view concepts. Monochrome and colour displays, and
transmissive, diffractive, reflective and trans-reflective display
technologies fulfilling the feature that each pixel or sub-pixel is
individually addressable, are included within the scope of the
present invention. Displays useful for the present invention may
display an arbitrary video or still image by at least using
selective addressing of pixels and or sub-pixel elements of the
display.
[0045] FIG. 2 shows in more detail a first embodiment of display
devices 12 for use in the present invention, in which each display
device 12 has a pixel addressable light output part 20 and a
non-pixel addressable light output part 22 in an optical path. In
the embodiment illustrated, the pixel addressable light output part
may be a pixel addressable light modulator, e.g. an LCD panel, and
the non pixel addressable light output part may be an optical
source, e.g. a backlight of which the light output can be
modulated.
[0046] In accordance with the present invention, the display system
10 comprises a linking mechanism 18 for linking the light output on
the optical path of the plurality of display devices 12, and more
particularly for linking their dynamic range, so that continuity in
dynamic range between multiple abutted or blended images is
obtained. In the embodiment illustrated in FIG. 2, the linking
mechanism 18 comprises a processing element 24 for providing drive
signals for driving these pixel addressable and non pixel
addressable light output parts 20 and 22 of the display devices 12.
The processing element 24 provides such drive signals to a display
device 12 based on an input signal corresponding to the image part
14 to be shown by that display device 12 and based on the image
part 14 to be shown by at least one neighbouring display device 12.
The image part 14 to be shown by that display device 12 is a part
of a larger image to be shown by the plurality of display devices
12 in the display system 10. A neighbouring display device 12 is a
display device providing an image part 14 abutting to or blending
with the image part 14 of the present display device 12. The
processing element 24 provides drive signals for providing temporal
modulations to the non pixel addressable light output part 22, e.g.
backlight, and provides drive signals for providing temporal
modulations to the pixel addressable light output part 20, so that
the apparent luminance or colour of a pixel of the display device
12 will correspond to a desired average output, and so that
continuity in dynamic range between multiple abutted or blended
images is obtained. By averaging of a sequence of different
combinations, the apparent luminance or colour of the pixels can be
made to take intermediate values between the gradations dictated by
the step size corresponding to a least significant bit of the
control provided by the pixel addressable light output part 20. In
other words, the amount of apparent quantization is increased in a
selected part of the range, which enables more accurate
reproduction of both colour and greyscale images. There is some
freedom to choose the values of the driving levels for the pixel
addressable light output parts 20, as long as the combination of
the temporal modulations to the pixel addressable light output
parts and of the temporal modulations to the corresponding non
pixel addressable light output part provides the desired output
value.
[0047] The input to the linking mechanism 18, in particular to the
processing element 24 thereof, is one or more image data signals
encoding image parts to be displayed, the one or more image data
signals emanating from at least one image source 26, such as e.g.
an image generator (IG) for generating images to be displayed. This
image data signal may be provided separately, i.e. by separate
image sources 26, for each of the display devices 12, such as
projectors, of the multi-channel display system 10, as illustrated
in FIG. 3. This means that a plurality of image sources 26 may be
provided, each providing an image part 14. Alternatively, the image
data signals encoding the image to be displayed may be provided by
a single image source 26, as illustrated in FIG. 2, and distributed
over the plurality of display devices 12. Other embodiments,
although not illustrated, are also covered by the present
invention, e.g. in which at least one image source 26 provides
image data signals encoding image parts 14 for at least two display
devices 12, and at least another image source 26 provides image
data signals encoding an image part 14 for at least another display
device 12. The at least another display device 12 may be a single
display device. The image source or image sources 26 may be any
kind of image source, such as one or a plurality of cameras, or an
IG, which is a computer or computing device adapted for generating
images. In case a plurality of image sources 26 are provided, they
may be of different types, for example a first image source
comprising a plurality of cameras providing image data signals for
a first display device 12, and a second image source comprising an
image generator for providing image data signals for a second
display device.
[0048] Other features, optionally taken from other embodiments, can
be added to the features of this embodiment without departing from
the present invention.
[0049] FIG. 3 illustrates a second embodiment of a multi-channel
display system 10 in accordance with the present invention, in
which a plurality of image sources 26 are provided for providing
the plurality of image data signals encoding the image parts 14
together forming the image to be displayed. As in the previous
embodiment, the plurality of image sources 26 can be of the same or
different type. There may be the same number of image sources 26 as
the number of display devices 12. In alternative embodiments, there
may be more or fewer image sources 26 than display devices 12. One
image source 26 can provide image data signals encoding image parts
14 to be displayed by one or more display devices 12.
Alternatively, in this embodiment as well, a single image source 26
could be provided. In the embodiment illustrated in FIG. 3, the
display devices 12 also comprise a pixel addressable light output
part 20 and a non-pixel addressable light output part 22. The pixel
addressable light output part 20 provides an image from light
impinging on it. In this embodiment, the non-pixel addressable
light output part 22 is separate from the backlight 30. In this
embodiment, the backlight 30 is driven with substantially constant
driving parameters, e.g. with a substantially constant drive
current, and produces a substantially constant light output. The
non-pixel addressable light output part 22 converts this constant
light output into a modulated light output, and may for example be
an LCD device or mechanical shutter or dimmer.
[0050] In accordance with embodiments of the present invention, the
display system 10 comprises a linking mechanism 18 for linking the
light output on the optical path of the plurality of display
devices 12, and more particularly for linking their dynamic range,
so that continuity in dynamic range between multiple abutted or
blended images is obtained. In the embodiment illustrated in FIG.
3, the linking mechanism 18 comprises a processing element 24 which
provides drive signals to drive the pixel addressable and non pixel
addressable light output parts 20 and 22 of each of the display
devices 12. The drive signals for the pixel addressable light
output part 20 and the non-pixel addressable light output part 22
of each display device 12 are generated by the processing element
24 based on an image data signal encoding the image part 14 to be
shown by that display device 12 and on the image data signal
encoding an image part 14 to be shown by at least one neighbouring
display device 12. The image part 14 to be shown by that display
device 12 is a part of a larger image to be shown by the plurality
of display devices 12 in the display system 10. A neighbouring
display device 12 is a display device providing an image part 14
abutting to or blending with the image part 14 of the present
display device 12. The processing element 24 provides temporal
modulations to the non pixel addressable light output part 22, and
provides temporal modulations to the pixel addressable light output
part 20, so that the apparent luminance or colour of a pixel of the
display device 12 corresponds to a desired average output, and so
that continuity in dynamic range between multiple abutted or
blended images is obtained.
[0051] Other features, possibly taken from other embodiments, can
be added to the features of this embodiment without departing from
the present invention.
[0052] According to embodiments of the present invention, the order
of the pixel addressable and non pixel addressable light output
parts 20, 22 in the optical path can be reversed, depending on
whether an optical source is in either of the parts, as in FIG. 2,
or before either of the parts, as in FIG. 3.
[0053] It is to be noted that in the above embodiments, the
modulation frequency of the non pixel addressable light output part
22 does not need to be exactly the output frame rate of the display
devices 12: a modulation period of a number of display frame
periods is also possible. It is also possible to modulate at a
higher frame rate than the output frame rate of the display system
(for instance 100 Hz while the display output frequency is 50
Hz).
[0054] An embodiment of a suitable processing element 24 of the
linking mechanism 18 is illustrated in FIG. 4. The processing
element 24 illustrated comprises means 40 for creating a temporal
modulation drive signal for driving the pixel addressable light
output part 20 and means 42 for creating a temporal modulation
drive signal for driving the non pixel addressable light output
part 22. Both means 40 and 42 are controlled by a controller
43.
[0055] The means 40 for creating a temporal modulation drive signal
for driving the pixel addressable light output part 20 may be
adapted so as to generate, from an input image data signal encoding
an image part to be displayed by a particular display device 12, a
time-series of image data drive signals for driving each pixel of
the pixel addressable light output part 20 of the display device
during a pre-determined time sequence. The means 42 for creating a
temporal modulation drive signal for driving the non pixel
addressable light output part 22 are adapted for, at the same time,
providing corresponding drive signals for driving the non pixel
addressable light output part 22, so that the combination of both
sequences generates an apparent luminance or colour of all pixels
of that display device 12 corresponding to the average output over
the length of the time-sequence. The temporal sequences for each
pixel of the pixel addressable light output part 20 may be created
in this example by a look-up table 44, which generates a series of
drive values for each pixel of the output signal. The series may be
spread across a number of frame buffers (frame 1-frame 3), and the
frame buffers may for example be read out one after another to
drive the pixel addressable light output part 20. The temporal
sequences for each pixel of the non pixel addressable light output
part 22 may also be created in this example by a look-up table 45,
which generates a series of drive values for the non pixel
addressable light output part 22. The series may be spread across a
number of frame buffers (frame 1-frame 3), and the frame buffers
may be read out one after another to drive the non pixel
addressable light output part 22.
[0056] A synchronisation circuit 46 may keep the drive signals for
the non pixel addressable light output part 22 synchronised to the
drive signals for the pixel addressable light output part 20,
typically by synchronising to the input image data signal.
[0057] The processing element 24 can be implemented in conventional
hardware or a mixture of hardware and software elements. The
controller 43 of the processing element 24 may include a computing
device, e.g. microprocessor, for instance it may be a
micro-controller. In particular, it may include a programmable
controller, for instance a programmable digital logic device such
as a Programmable Array Logic (PAL), a Programmable Logic Array, a
Programmable Gate Array, especially a Field Programmable Gate Array
(FPGA).
[0058] Hereinafter the invention is explained in more detail by
reference to a specific embodiments.
[0059] For a Simple Projector Model, notations can be as follows:
[0060] L.sub.Max:a projector's maximum possible luminance output
[0061] CR.sub.P:a projector's Contrast Ratio (defined as its Peak
light output divided by its minimum light output) [0062] Projector
Inputs: [0063] V.sub.P:Projector video input (0.0-1.0) [0064]
G.sub.P:Projector backlight gain (0.0-1.0)
[0065] The light output of the simple projector model is
therefore:
L.sub.OUTPUT=G.sub.PL.sub.Max[(CR.sub.P-1) V.sub.P+1]/CR.sub.P
[0066] The maximum L.sub.OUTPUT of a projector is therefore:
L.sub.OUTPUT.sub.--.sub.MAX=G.sub.PL.sub.Max when G.sub.P is
1.0
[0067] The minimum L.sub.OUTPUT of a projector is therefore:
L.sub.OUTPUT.sub.--.sub.MIN=G.sub.PL.sub.Max/CR.sub.P
[0068] In accordance with embodiments of the present invention the
contrast ratio of the system is expanded across multiple display
channels beyond the contrast ratio of the individual display
devices. The system contrast ratio is defined as:
[0069] CR.sub.S=System Maximum Luminance/System Minimum Luminance
or thus
CR.sub.S=L.sub.OUTPUT.sub.--.sub.MAX/L.sub.OUTPUT.sub.--.sub.MIN
Substituting with the formulae for L.sub.OUTPUT.sub.--.sub.MAX and
L.sub.OUTPUT.sub.--.sub.MIN given hereinabove this yields
CR.sub.S=L.sub.MAX/(G.sub.PL.sub.MAX/CR.sub.P)=CR.sub.P/G.sub.P
Solving for G.sub.P at the minimum light output gives:
G.sub.P.sub.--.sub.MIN=CR.sub.P/CR.sub.S
[0070] The Image Generator (IG) output V.sub.IG has a value between
0.0-1.0. [0071] V.sub.IG=1 to obtain a desired system brightness
output of L.sub.MAX [0072] V.sub.IG=0 to obtain a desired system
brightness output of L.sub.MAX/CR.sub.S
[0073] With these definitions in mind it is now possible to define
the algorithmic transformations necessary between the video
source(s) 26 and the control inputs to the display devices 12.
[0074] In a first embodiment, a global control is provided, with
equal settings to all display devices 12. The controller 43 of the
linking mechanism 18 may comprise an algorithm sharing the maximum
and minimum video levels required in each display device 12 or
video channel between all channels and setting a global value for
the non pixel addressable light output part, e.g. a global
backlight value, as well as a global video gain factor for
processing. From the image data signals emanating from the image
source(s) 26, the processing element 24 determines the overall
minimum luminance and maximum luminance levels. The overall minimum
luminance level is the minimum luminance level of that one of the
display devices 12 having the highest value for the minimum
luminance level. The overall maximum luminance level is the maximum
luminance level of that one of the display devices 12 having the
lowest value for the maximum luminance level. In the example
illustrated in FIG. 5, the minimum and maximum luminance levels of
a first channel are given by mini and maxi, respectively (left hand
side of FIG. 5), and the minimum and maximum luminance levels of a
second channel are given by min2 and max2, respectively (right hand
side of FIG. 5). In this case, the overall minimum and maximum
luminance levels for these two panels are given by min1 and max2,
respectively, as can be appreciated from FIG. 5.
[0075] These overall minimum and maximum luminance levels are used
by the linking mechanism 18 for determining the drive signals to be
used for each of the display systems 12. For any level of light
source attenuation provided by the non pixel addressable light
output part 22, e.g. backlight attenuation by modulating the
backlight itself, it will be necessary to have a corresponding and
reciprocal gain in the video level (assuming linear space).
Luminance=video level*video gain factor*backlight attenuation
factor*backlight intensity
[0076] For any scene at any one time, the instantaneous contrast of
the scene is not increased over the native contrast of the
projectors used to create the scene in the embodiment. However, as
the displayed scene changes from nominally bright scenes to dark
scenes and back, the display system will react and reduce or
increase its maximum light output according to the scene and
therefore extend the depth of its luminance range to maximize
detail in the scene and increasing the effective system
contrast.
[0077] The instantaneous maximum V.sub.IG across all displayed
video inputs is defined as V.sub.IG.sub.--.sub.MAX. From this
value, the desired system luminance at V.sub.IG.sub.--.sub.MAX is
determined from:
L.sub.SYSTEM.sub.--.sub.MAX=L.sub.Max[(CR.sub.S-1)
V.sub.IG.sub.--.sub.MAX+1]/CR.sub.S
[0078] As this is the maximum luminance required anywhere in the
multi-channel image, all projector backlight gains may be adjusted
such that the maximum output from each equals
L.sub.SYSTEM.sub.--.sub.MAX. This has the advantage of suppressing
the minimum black level in the image and maintaining the maximum
dynamic range in the system even when operating at reduced
luminance levels.
G.sub.P=L.sub.SYSTEM.sub.--.sub.MAX/L.sub.Max
G.sub.P=[(CR.sub.S-1) V.sub.IG.sub.--.sub.MAX+1]/CR.sub.S
[0079] For practical reasons, G.sub.P may be limited to a lower
bound such as G.sub.P.sub.--.sub.MIN.
[0080] For a given setting of G.sub.P, the video input to the
projector must be correspondingly modified as shown:
V.sub.P=V.sub.IG/G.sub.P
[0081] In this mapping, the maximum luminance point for any setting
of Gp will match the desired luminance point for the system as
defined over the entire system dynamic range. However, all other
luminance levels will diverge from the system ideal towards the
projector minimum for the given G.sub.P setting. This divergence
occurs because the projector contrast is less than the desired
system contrast and therefore the projector is unable to produce an
image as dark as desired.
[0082] An alternative mapping may be defined as:
V.sub.P=(V.sub.IG-D)/(G.sub.P-D)
where:
D=(CR.sub.SG.sub.P-CR.sub.P)/(CR.sub.PCR.sub.S-CR.sub.P)
[0083] This mapping has the advantage that the system matches any
desired luminance level that is possible for the given G.sub.P
setting. The disadvantage is that those darkest values that cannot
be produced by the projector due to its contrast ratio limitation
are clipped to the minimum luminance value possible for the G.sub.P
setting.
[0084] Other mappings are also possible that combine the properties
of these two mappings in order to reduce the deviations in desired
luminance while avoiding the clipping of out of range values to a
single minimum value.
[0085] The determination of the instantaneous maximum V.sub.IG
value for any given scene may require temporal processing to
account for inherent delays in the display system such as other
image processing operations and the responsiveness of the control
or modulation of the non pixel addressable light output part 22,
e.g. back light control/modulation system. This processing may also
be influenced by additional information from the image source(s) 26
such as Time Of Day (TOD) information typically available in the
simulator environment. The temporal processing may also include
elements related to the human visual system in order to avoid
perceptually distracting changes in the image.
[0086] In a system of display devices 12, e.g. projectors, it is
not normally the case that the maximum luminance and contrast
values exactly match between the different display devices 12.
However, it is known by those trained in the art how to match
individual display devices 12, e.g. projectors, in this way prior
to applying the above algorithms according to embodiments of the
present invention for controlling a set of these display devices
12, e.g. projectors, dynamically. For example, one control not
mentioned in this discussion is the common brightness control that
effectively offsets the minimum possible luminance output. This
control therefore sets the contrast ratio of the projector and can
be used to match CR.sub.p between display devices 12, e.g.
projectors.
[0087] It is also possible to modify the above algorithms to
account for differences in the display device, e.g. projector,
dynamic ranges and luminances directly in the algorithms
themselves. This can be performed by using display device specific
L.sub.MAX and CR.sub.P values for the display devices 12, e.g.
projectors. This relates to what is illustrated in FIG. 5.
[0088] In the graph given in FIG. 6, one sees that the L.sub.MAX
and L.sub.MIN values are constant for all the display devices 12,
in the example illustrated three projectors. The realized system
contrast is limited to 1,000:1, equal to CR.sub.P.
[0089] The first embodiment of the linked dynamic black system
produces a visually continuous image with no discontinuities in the
white, black or intermediate gray levels resulting from its
operation. However, the display system is limited at any one time
to the dynamic range of no more than that of an individual
projector. It is possible to further extend the system dynamic
ratio under certain operational conditions to that far beyond that
of a single projector.
[0090] Imagine a system with two projectors side by side. The image
to be displayed includes a full amplitude white square in the
center of the first projector and black everywhere else. In the
first embodiment, the backlight gain G.sub.P must be set to 1.0 as
the total image includes a full white square implying a V.sub.IG of
1.0 at the location of the square. Now image, the situation for the
second projector. Its V.sub.IG input is 0.0 everywhere. Ignoring
the conditions imposed by the linking, its backlight gain could
drop to the minimum value. In this case, the display would have a
displayed contrast equal to the desired system contrast because the
first projector would have a full white area and the second
projector would have a maximally black area. The problem with this
approach is that at the boarder or overlap between these two
projectors a discontinuity will be seen. It is the intention of the
second embodiment of this invention to eliminate this discontinuity
and thereby expand the instantaneous contrast possible in a
scene.
[0091] In a second embodiment, individual control is provided, with
unique settings to each display device 12. The controller 43 takes
into account knowledge of the spatial arrangement of the channels
or display devices 12, allowing for effective gradients to be
developed between and within channels to allow channels with bright
imagery to operate with a high intensity non pixel addressable
light output part setting, e.g. backlight setting, while other
channels with less bright imagery may be operated with lower
intensity non pixel addressable light output part setting, e.g.
with lower backlight intensity. This is illustrated in FIG. 7. The
gradients between channels are calculated and applied to the
channel via a spatially varying video gain factor and by matching
black levels via the use of a "beta plane" that also varies across
an individual image, thus allowing a much greater instantaneous
dynamic range throughout the entire display than possible with
conventional algorithms, while avoiding distracting luminance and
black level differences between adjacent channels.
[0092] When going back to the example given above with respect to
the first embodiment discontinuity is eliminated by the use of
interpolative surfaces providing spatially dependent offset and
gain variations to the V.sub.P signals to the projectors. In the
situation described above, an offset and corresponding gain change
is applied to the VP signals to the second projector. The offset
would equalize the luminance at the interface between the two
projected images. The offset would then reduce as the distance from
the interface is increased. The rate and profile of the reduction
may be linear, curved or any other shape that produces a pleasing
affect to the observer minimizing the discontinuity. Since this
spatially dependent offset effectively reduces CR.sub.P of the
projector in its region of influence, the video gain factor between
V.sub.IG and V.sub.P must also be modulated in this area.
[0093] The algorithm to be carried out may be as follows: [0094]
Using the equations outlined in embodiment 1, for each display
devide 12, e.g. projector, determine V.sub.IG.sub.--.sub.MAX,
L.sub.SYSTEM.sub.--.sub.MAX, and G.sub.P based upon only the
V.sub.IG input to the specific projector.
[0094]
L.sub.SYSTEM.sub.--.sub.MIN=L.sub.SYSTEM.sub.--.sub.MAX/CR.sub.P
[0095] Based upon the L.sub.SYSTEM.sub.--.sub.MIN values for each
display device 12, e.g. projector, and their spatial arrangement,
determine a luminance surface for each display device 12, e.g.
projector, that when added to the individual
L.sub.SYSTEM.sub.--.sub.MIN values, produces smooth surface across
all projectors. This surface is identified as SmoothSurface(x,y).
The notation (x,y) indicates that this surface is composed of
spatially dependent values.
[0096] The projector video input V.sub.P can be determined as
follows for each location in the image:
B.sub.OFFSET=SmoothSurface(x,y)/(L.sub.SYSTEM.sub.--.sub.MAX-L.sub.SYSTE-
M.sub.--.sub.MIN)
A.sub.GAIN=(L.sub.SYSTEM.sub.--.sub.MAX-SmoothSurface(x,y))/(L.sub.SYSTE-
M.sub.--.sub.MAX-L.sub.SYSTEM.sub.--.sub.MIN))
V.sub.P=A.sub.GAINV.sub.IG/G.sub.P+B.sub.OFFSET
[0097] An example illustrates the process:
[0098] The system illustrated in FIG. 7 assumes CR.sub.s of
10,000:1 and a projector CR.sub.P of 1,000:1. Three projectors are
assumed stacked three in a row left to right. In the graph of FIG.
7 the output of each projector is sampled at 20 points each.
Projector one's samples are labelled 0-19, two's are labelled
20-39, and the third as 40-59. Only one dimension is shown for
simplification purposes.
[0099] The input video follows a Gaussian curve with alternating
pixels set to zero to show the performance at the black level in
addition to the white. The desired luminance based upon the video
level and CR.sub.S of 10,000:1 is shown with diamonds and an
interconnecting line. The solid lines labelled L_MAX and L_MIN show
the three projectors' maximum luminance and minimum luminance based
upon their calculated backlight settings and contrast ratios. The
projector luminance is shown by the squares. It can be clearly seen
that the projector luminance overlays the desired luminance very
well for the bright portions of the image and the track well to the
minimum black levels possible for the CR.sub.P and backlight
values.
[0100] One should notice that the realized system contrast is
nearly 10,000:1 (actually 7662:1) despite the fact that the
individual projector contrast is only 1,000:1 (CR.sub.P). This is
the benefit of embodiment two over embodiment one. In embodiment
one, a contrast no better than the individual projectors' contrast
ratio CR.sub.P is possible. The amount that the system contrast can
be extended is highly dependent upon the images displayed. Very
uniform images will have little expansion while images that are
highly differentiated in a luminance sense between channels will
have the greatest increase.
[0101] Also notice the Beta Plane line 70. This line 70 is
representative of the smooth interpolation surface
(SmoothSurface(x,y)) discussed earlier. This surface forces the
normally disparate black levels illustrated by the L_MIN line with
its discontinuities to smoothly join at the intersections of the
projected images.
[0102] As will be appreciated by those skilled in the art,
embodiments of the present invention may be embodied as a method,
an apparatus such as a special purpose apparatus, or a carrier
medium, e.g. a computer program product carrier medium carrying one
or more computer readable code segments for controlling a
processing element to carry out a set of steps. Accordingly, the
present invention may take the form of an entirely hardware
embodiment, an entirely software embodiment, or an embodiment
combining software and hardware aspects. Furthermore, the present
invention may take the form of carrier medium (e.g., a computer
program product on a computer-readable storage medium) carrying
computer-readable program code segments embodied in the medium. Any
suitable computer readable medium may be used including a magnetic
storage device such as a diskette or a hard disk, or an optical
storage device such as a CD-ROM. For example, the computer program
product may be part of a mass storage device, the computer program
product having computer-readable program code segments.
[0103] It will be understood that the steps of methods discussed
are performed in one embodiment by an appropriate processor such as
the controller 43 of the processing element 24 shown in FIG. 4
executing instructions (code segments) stored in a storage (not
illustrated). It will also be understood that the invention is not
limited to any particular implementation or programming technique
and that the invention may be implemented using any appropriate
techniques for implementing the functionality described herein. The
invention is not limited to any particular programming language or
operating system.
[0104] The instructions (e.g. computer readable code segments in
the storage) may be read from storage into memory. Execution of
sequences of instructions contained in memory causes the controller
43 to perform the process steps described herein. In alternative
embodiments, hard-wired circuitry may be used in place of or in
combination with software instructions to implement the invention.
Thus, embodiments of the invention are not limited to any specific
combination of hardware circuitry and software.
* * * * *