|Title of Invention||
"A METHOD FOR RENDERING INPUT IMAGE DATA OF A FIRST COLOR SPACE ONTO A DISPLAY OF A SECOND COLOUR SPACE"
|Abstract||The present application discloses several methods, techniques and systems for rendering source image data onto high brightness subpixel arrangements- for example, RGBW display panels. Additionally, these techniques have application for rendering data onto 3-color displays as well. Figure 1 is the representative figure.|
|Full Text||TECHNICAL FIELD
[01 ] The present application relates to methods and systems for rendering image data
of a first color space onto a display system which may render image data into a second color
 In commonly owned United States Patent Applications: (1) United States Patent
Application Serial No. 09/916,232 ("the '232 application"), entitled "ARRANGEMENT OF
COLOR PIXELS FOR FULL COLOR IMAGING DEVICES WITH SIMPLIFIED
ADDRESSING," filed July 25, 2001; (2) United States Patent Application Serial No.
10/278,353 ("the '353 application"), entitled "IMPROVEMENTS TO COLOR FLAT PANEL
DISPLAY SUB-PDCEL ARRANGEMENTS AND LAYOUTS FOR SUB-PIXEL
RENDERING WITH INCREASED MODULATION TRANSFER FUNCTION RESPONSE,"
filed October 22,2002; (3) United States Patent Application Serial No. 10/278,352 ("the '352
application"), entitled 'IMPROVEMENTS TO COLOR FLAT PANEL DISPLAY SUBPDfBL
ARRANGEMENTS AND LAYOUTS FOR SUB-PDCEL RENDERING WITH SPLIT
BLUE SUB-PDCELS," filed Octoter 22,2002; (4) United States Patent Application Serial No.
10/243,094 ("the '094 application), entitled "IMPROVED FOUR COLOR ARRANGEMENTS
AND EMITTERS FOR SUB-PDCEL RENDERING," filed September 13, 2002; (5) United
States Patent Application Serial No. 10/278,328 C the '328 application"), entitled
"IMPROVEMENTS TO COLOR FLAT PANEL DISPLAY SUB-PIXEL ARRANGEMENTS
AND LAYOUTS WITH REDUCED BLUE LUMINANCE WELL VISIBILITY," filed
October 22, 2002; (6) United States Patent Application Serial No. 10/278,393 One '393
application"), entitled "COLOR DISPLAY HAVING HORIZONTAL SUB-PDCEL
ARRANGEMENTS AND LAYOUTS," filed October 22, 2002; (7) United States Patent
Application Serial No. 01/347,001 ("the '001 application") entitled "IMPROVED SUB-PDCEL
ARRANGEMENTS FOR STRIPED DISPLAYS AND METHODS AND SYSTEMS FOR
SUB-PDCEL RENDERING SAME," filed January 16, 2003, each of which is herein
incorporated by reference in its entirety, novel sub-pixel arrangements are disclosed for
improving the cost/performance curves for image display devices.
 For certain subpixel repeating groups having an even number of subpixels in a
horizontal direction, the following systems and techniques to affect improvements, e.g. proper
dot inversion schemes and other improvements, are disclosed and are herein incorporated by
reference in their entirety: (1) United States Patent Application Serial Number 10/456,839
entitled "IMAGE DEGRADATION CORRECTION IN NOVEL LIQUID CRYSTAL
DISPLAYS"; (2) United States Patent Application Serial No. 10/455,925 entitled "DISPLAY
PANEL HAVING CROSSOVER CONNECTIONS EFFECTING DOT INVERSION"; (3)
United States Patent Application Serial No. 10/455,931 entitled "SYSTEM AND METHOD
OF PERFORMING DOT INVERSION WITH STANDARD DRIVERS AND BACKPLANE
ON NOVEL DISPLAY PANEL LAYOUTS"; (4) United States Patent Application Serial No.
10/455,927 entitled "SYSTEM AND METHOD FOR COMPENSATING FOR VISUAL
EFFECTS UPON PANELS HAVING FIXED PATTERN NOISE WITH REDUCED
QUANTIZATION ERROR"; (5) United States Patent Application Serial No. 10/456,806
entitled "DOT INVERSION ON NOVEL DISPLAY PANEL LAYOUTS WITH EXTRA
DRIVERS"; (6) United States Patent Application Serial No. 10/456,838 entitled "LIQUID
CRYSTAL DISPLAY BACKPLANE LAYOUTS AND ADDRESSING FOR NONSTANDARD
SUBPIXEL ARRANGEMENTS"; (7) United States Patent Application Serial
No. 10/696,236 entitled "MAGE DEGRADATION CORRECTION IN NOVEL LIQUID
CRYSTAL DISPLAYS WITH SPLIT BLUE SUBPDCELS", filed October 28, 2003; and (8)
United States Patent Application Serial No. 10/807,604 entitled "IMPROVED TRANSISTOR
BACKPLANES FOR LIQUID CRYSTAL DISPLAYS COMPRISING DIFFERENT SIZED
SUBPIXELS", filed March 23,2004.
 These improvements are particularly pronounced when coupled with sub-pixel
rendering (SPR) systems and methods further disclosed in those applications and in commonly
owned United States Patent Applications: (1) United States Patent Application Serial No.
10/051,612 ("the '612 application"), entitled "CONVERSION OF RGB PIXEL FORMAT
DATA TO PENTILE MATRIX SUB-PIXEL DATA FORMAT," filed January 16, 2002; (2)
United States Patent Application Serial No. 10/150,355 ("the '355 application"), entitled
"METHODS AND SYSTEMS FOR SUB-PIXEL RENDERING WITH GAMMA
ADJUSTMENT," filed May 17, 2002; (3) United States Patent Application Serial No,
10/215,843 ("the '843 application"), entitled "METHODS AND SYSTEMS FOR SUB-PIXEL
RENDERING WITH ADAPTIVE FILTERING," filed August 8, 2002; (4) United States
Patent Application Serial No. 10/379,767 entitled "SYSTEMS AND METHODS FOR
TEMPORAL SUB-PDCEL RENDERING OF IMAGE DATA" filed March 4,2003; (5) United
States Patent Application Serial No. 10/379,765 entitled "SYSTEMS AND METHODS FOR
MOTION ADAPTIVE FILTERING," filed March 4, 2003; (6) United States Patent
Application Serial No. 10/379,766 entitled "SUB-PIXEL RENDERING SYSTEM AND
METHOD FOR IMPROVED DISPLAY VIEWING ANGLES" filed March 4, 2003; (7)
United States Patent Application Serial No. 10/409,413 entitled "IMAGE DATA SET WITH
EMBEDDED PRE-SUBPIXEL RENDERED IMAGE" filed April 7, 2003, which are hereby
incorporated herein by reference in their entirety.
 Improvements in gamut conversion and mapping are disclosed in commonly
owned and co-pending United States Patent Applications: (1) United States Patent Application
Serial No. 10/691,200 entitled "HUE ANGLE CALCULATION SYSTEM AND METHODS",
filed October 21, 2003; (2) United States Patent Application Serial No. 10/691,377 entitled
"METHOD AND APPARATUS FOR CONVERTING FROM SOURCE COLOR SPACE TO
RGBW TARGET COLOR SPACE", filed October 21, 2003; (3) United States Patent
Application Serial No. 10/691,396 entitled "METHOD AND APPARATUS FOR
CONVERTING FROM A SOURCE COLOR SPACE TO A TARGET COLOR SPACE", filed
October 21, 2003; and (4) United States Patent Application Serial No. 10/690,716 entitled
"GAMUT CONVERSION SYSTEM AND METHODS" filed October 21, 2003 which are all
hereby incorporated herein by reference in their entirety.
 Additional advantages have been described in (1) United States Patent Application
Serial No. 10/696,235 entitled "DISPLAY SYSTEM HAVING IMPROVED MULTIPLE
MODES FOR DISPLAYING IMAGE DATA FROM MULTIPLE INPUT SOURCE
FORMATS", filed October 28, 2003 and (2) United States Patent Application Serial No.
10/696,026 entitled ! "SYSTEM AND METHOD FOR PERFORMING IMAGE
RECONSTRUCTION'AM SUBPKEL RENDERING TO EFFECT SCALING FOR MULTIMODE
DISPLAY" filed October 28,2003.
 Additionally, these co-owned and co-pending applications are herein incorporated
by reference in their entirety: (1) United States Patent Application Serial No. [ATTORNEY
DOCKET NUMBER 08831.0064] entitled "SYSTEM AND METHOD FOR IMPROVING
SUB-PIXEL RENDERING OF IMAGE DATA IN NON-STRIPED DISPLAY SYSTEMS"; (2)
United States Patent Application Serial No. [ATTORNEY DOCKET NUMBER 08831.0065]
entitled "SYSTEMS AND METHODS FOR SELECTING A WHITE POINT FOR IMAGE
DISPLAYS"; (3) United States Patent Application Serial No. [ATTORNEY DOCKET
NUMBER 08831.0066] entitled "NOVEL SUBPDCEL LAYOUTS AND ARRANGEMENTS
FOR HIGH BRIGHTNESS DISPLAYS"; (4) United States Patent Application Serial No.
[ATTORNEY DOCKET NUMBER 08831.0067] entitled "SYSTEMS AND METHODS FOR
IMPROVED GAMUT MAPPING FROM ONE IMAGE DATA SET TO ANOTHER"; which
are all hereby incorporated by reference. All patent applications mentioned in this specification
are hereby incorporated by reference in their entirety.
DISCLOSURE OF THE INVENTION
 In one embodiment of the present application, a method and system for
rendering image data of a first color space onto said display of a second color space is given.
A suitable display may substantially comprise a subpixel repeating group, said group may
further comprise at least one white subpixel and a plurality of colored subpixels. The steps of
said method and system comprise inputting image data to be rendered on said display,
converting said image data from said first color space to image data of said second color
space and subpixel rendering each individual color plane.
BRIEF DESCRIPTION OP THE DRAWINGS
 The accompanying drawings, which are incorporated in, and constitute a part
of this specification illustrate exemplary implementations and embodiments of the invention
and, together with the description, serve to explain principles of the invention.
 FIGS. 1 through 3B are embodiments of high brightness layouts for displays
of all types as made in accordance with the principles of the present invention.
[Oil] FIG. 4 is one exemplary embodiment of a resampling of one of the color
planes for one of the above high brightness layouts.
 BIGS. 5A and SB are yet other embodiments of a high brightness layout for
displays as made in accordance with the principles of the present invention.
 FIG. 6 is one exemplary embodiment of a resampling of one of the color
planes for the layout as shown in FIG. 5.
 FIGS. 7 and 8 are yet other embodiments of high brightness layouts for
displays as made in accordance with the principles of the present invention.
 FIG. 9 is one exemplary embodiment of a resampling of one of the color
planes for the layout as shown in FIG. 8,
 FIG. 10 is one example of a reconstruction grid being superimposed onto a
target 3-color subpixel layout
 FIGS. 11 through 14C are examples of various resample areas depending on
the relative positioning of input image data grid to target subpixel layout.
 FIG. 15 is another embodiment of the relative position of a 3-color target
subpixel layout shifted with respect to an input image data grid.
 FIG. 16A through 18C are examples of various resample areas for the
example of FIG. 15.
 Reference will now be made in detail to implementations and embodiments,
examples of which are illustrated in the accompanying drawings. Wherever possible, the
same reference numbers will be used throughout the drawings to refer to the same or like
Subpixel Rendering for Five Color systems w/whtte
 Figure 1 shows one embodiment of a portion of a high-brightness,
multiprimary display 100 substantially comprising a subpixel repeating group 102 as shown.
Group 102 is an octal subpixel repeating group comprising white (or no color filter)
subpixels 104, red subpixels 106, green subpixel 108, blue subpixels 110 and cyan subpixels
112. The white subpixel is added to help achieve the high brightness performance of the
display. Additionally, as the white subpixels are good Candidates for being centers of
luminance for subpixel rendering (SPR) - the white, as the majority subpixel, gives high
MTF Limit performance. In this embodiment, there are equal numbers of red, green, cyan,
and blue subpixels - of course, other embodiments may deviate some from this color
partitioning. Given that the white subpixel is adding brightness to the system and that the
use of the cyan color is to give a wider color gamut, it may be advantageous to set the color
points of the minority subpixels to be deeply saturated to result in a wide color gamut. It
should be noted that these color points and energies are only "substantially" the colors
described as "red", "green", "blue", "cyan", and "white". The exact color points may be
adjusted to allow for a desired white point when all of the subpixels are at their brightest
 Figure 2 shows a portion of another embodiment of a high brightness, 5-color
display. Here, the subpixel repeating group is group 202 - which is larger than the one
shown in Figure 1 because the color subpixels are placed on a hexagonal grid. One possible
advantage of a hexagonal grid is that it tends to scatter the Fourier energies in more directions
and points. This may be especially useful for the dark luminance wells caused by the blue
subpixels. Another possible advantage is that each row contains all four colors as well as the
white subpixels, allowing for horizontal lines to be black and white, fully sharpened, without
 One possible embodiment of a display system using mis layout may process
image data and render it as follows:
(1) Convert conventional data (e.g. RGB, sRGB, YCbCr,or the like) to RGBCW+L
image data, if needed;
(2) Subpixel render each individual color plane;
(3) Use the "L" (or "Lumhiance") plane to sharpen each color plane.
 The subpixel rendering filter kernels may be constructed from area resampling
theory, as disclosed earlier in many incorporated applications noted above. Both layouts may
be subpixel rendered from data sets that have a one-to-one mapping. That is to say, one
incoming conventional pixel maps to one white subpixel. The white subpixels may then fully
reconstruct the bulk of the non-saturated luminance signal of the image. The surrounding
colored subpixels then operate to provide the color signal. The incoming image may be any
format of color signal, as long as color gamut mapping with or without gamut expansion, may
operate to convert said format to RGBCW expected by the subpixel rendering engine. It will
be appreciated that such area resampling filters may be replaced by other suitable subpixel
rendering techniques: resampling using bicubic filter, sine filters, windowed-sine filter and
any convolutions thereof. It will be further appreciated that the scope of the present invention
encompasses the use of these other techniques.
 As the white subpixels are mapped one to one, they may use a unity filter with
no further processing required. The color planes may be filtered using several possible
kernels. For example, assuming that the image is band-limited, one embodiment might shift
the phase of each of the color planes and the Luminance plane to the interstitial positions of
the color subpixels in the horizontal direction. This may be accomplished with a simple
cubic interpolation filter: -Vi$, 9/i6»9/i6, -Vie. It should be note that the white plane may
not need to be shifted. For non-band-limited images (e.g. text or sharp edges in images),
there may not need to be the cubic filtered phase shift as above.
 Then, the color planes may be filtered with an area resample filter. A
Difference of Gaussian (DOG) filter applied to luminance may optionally be added, examples
are given here:
2 4 2
I 2 1 (Divide by 16)
Area Resample Filter for hexagonal and square arrangement
0 (Divide by 16)
DOG Filter for hexagonal arrangement of FIG. 2.
 It should be noted that non-zero values coincide with the same color to keep
the color balanced. Using the luminance signal implements a simplified "crosscolor"
 la another embodiment, one could also perform actual cross-color sharpening,
distributing the values of the cross-color coefficients among the color filter kernels such that
the matrices add up to the desired numbers such as above. One method that may be useful is
to divide the values of the actual subpixcl luminances ~ red, green, blue, and cyan - by the
luminance value of the color that is being sharpened then multiply it by the matrix above
times a suitable normalization constant such that it adds up to the matrix above. Another way
might be to not perform the normalization, which would mean that some colors would
experience greater than unity gain sharpening. The colors that experienced the greatest gain
would be the colors with the lowest luminance. This last property may be useful to reduce
the "dottiness" of the high spatial frequency detail, increasing the quality of the signal. These
methods and techniques of using varying sharpening gain on the colors may also be driven by
the luminance signal as above.
 In one embodiment, multiplying the values of the sharpening matrix by a
constant allows adjustment of the gain of the system. For this embodiment, if the constant is
less than one, the filter is softer; if the constant is greater than one, the filter is sharper. Of
coarse, other embodiments are contemplated by the present invention with different matrices
 It should also be noted that the one possible method uses the simplest subpixel
rendering filter kernels with the math being performed substantially by bit shift division
and addition. Other methods and embodiments may give numbers that require more multi-bit
precision multipliers. Of course, performing the color gamut mapping may require such
multipliers as well.
 As well as cross-color sharpening, one embodiment of the system may be
implemented using self-sharpening by adding the two matrices together. For example, the
following may be useful for the arrangement of FIG. 2:
0 Divide by 16
 Since the mapping of the conventional pixel data, in what ever form it comes
in, to the multi-primary space is indeterminate, mis may introduce a degree of freedom that
could be advantageous. For example, choosing any given algorithm may always give the
right color over all; but may not give the best visual result. For example, the color subpixels,
not all having the same luminance, may introduce a spurious pattern for many non-optimal
mappings. The desired color mapping would give the most even texture for patches of a
given color, minimizing visible spatial frequencies of luminance modulation, over the
broadest range of colors; hue, saturation, and brightness. Such a mapping would allow the
fine details to be displayed using the algorithm disclosed above. In another embodiment, the
system might work with a plurality of transform matrices, if no single transform matrix
provides optimal result for all colors. It may be advantageous to create domains, or even
continuously variable transforms.
Rendering Novel RGBW Panels
 In many cases, novel RGBW panels (and 5-,6-, n- color panels, for mat matter)
will be called upon to render legacy RGB or other 3-color image data. In many applications
incorporated by reference above, there are described various embodiments for subpixel
rendering resampling a modified conventional image data set. The modification is that each
and every incoming conventional pixel has four (or more) — instead of three - color
component values; e.g. Red, Green, Blue, and "White". The "White" in quotes denotes that
this color point may or may not be at the white point of the display when all color subpixels
are set to their maximum values. It may be desirable that any Gamut Mapping Algorithm
(GMA) conversion from RGB to RGBW (or other multiprimary color space) occur before the
subpixel rendering to keep the image from being blurred. The filter set could be designed to
produce good results for both text and photographs. For example, in the '094 application
incorporated by reference, there is shown some novel RGBW and RGBC layouts. For these
layouts, one embodiment of the filters for the SPR for layouts that have a red/green
checkerboard such as shown in:
Red and Green use:
-.0625 0 -.0625 0 .125 0 -.0625 .125 -
0 .25 0 + .125 .5 .125 - .125 .75
..0625 0 -.0625 0 .125 0 -.0625 .125 -
DOG Wavelet + Area Resample = Cross-Color Sharpening
 The Red and Green color planes are area resampled to remove any spatial
frequencies that will cause chromatic aliasing. The DOG wavelet is used to sharpen the
image using the cross-color component. That is to say, the red color plane is used to sharpen
the green subpixel image and the green color plane is used to sharpen the red subpixel image.
This allows the cross-color luminance signal to be impressed onto the color subpixels, 'filling
in the holes' in color images. It should be noted that for monochromatic images, the results
of cross-color DOG wavelet sharpening is the same as self-color sharpening. It should also
be noted that the coefficients disclosed above are exemplary of one particular embodiment
and that the present invention contemplates many other matrices having suitable coefficients
 The Blue color plane may be resampled using one of a plurality of filters. For
example, blue could be resampled with a simple 2X2 box filter.
 Alternatively, the Blue color plane could be resampled using a box-tent filter
centered on the blue subpixel:
.125 .25 .125
.125 .25 .125
 Moreover, the white plane could also be filtered using one of a plurality of
filters. For example, the white or cyan color plane could be resampled using a non-axisseparable
4X4 box-cubic filter
-Va % %
-Va 10/32 %
- /32 • In
 Alternatively, to help abate that there is no phase error, nor aliasing, on the
white or cyan subpixel, an axis-separable 3X4 tent-cubic filter might be used:
'/ i/ i/ - /64 - /32 -
9i 9, 9, / m /
9/ 9, 9/
'64 '32 /
- /64 - /32 - /64
 The use of the box-cubic and tent-cubic filters may help to reduce the moir6
artifacts in photographs while maintaining sharpness in text by taking advantage of the midposition
of the white subpixels. Although not necessary, it is possible to use the same filters
for both blue and white color planes. One could use either the plain box or tent for both, or
the box-cubic or tent-cubic for both. Alternatively, the cubic filters should be chosen for
 Figures 3A and 3B show embodiments of a high brightness display having the
repeating subpixel groupings as shown. Although these layouts may have any aspect ratio
possible, Figures 3Aand 3B depicts this layout with all subpixels having a 1:3 aspect ratio.
That produces subpixels that are taller and thinner than a possible square outline or 2:3 aspect
ratio. This layout comprises a combination where the blue sub-pixels have the same size as
the red and green and the same number - which results in a substantially color-balanced
RGBW layout, since there is the same area coverage of the red, green, and blue emitters using
the same filters as would be found in conventional RGB display panels.
[041 ] The layouts of Figures 3 A and 3B have a potential advantage in that it may be
manufactured on a standard RGB stripe backplane with a suitable change in the color filter.
One embodiment of a panel having one of these layouts may use any suitable form of SPR
algorithm, as discussed herein or in applications incorporated by reference.
 In one embodiment, the image source data to the display might assume a
square aspect ratio - thus, with no scaling, each input pixel would map to three sub-pixels in
this layout. However, these RGBW 1:3 layouts are 4 sub-pixels wide per repeat cell. If
source pixels are mapped to groups of three such sub-pixels, then three of the layouts tiled
horizontally might suffice before all the possible combinations are found. For each different
combination of three output sub-pixels grouped like this, a different set of area resample
filters might suffice. This is similar to the process of finding a repeat cell and generating
different sets of filters for scaling, as disclosed in applications incorporated above.
 In fact, the same logic that does scaling might be used to select suitable filters.
In one embodiment, there could be a simplification that may be easier to implement than
scaling. As in scaling, there-may be symmetries that reduce the total number of filters, and in
this case, there are only three filters that are used over and over again in different
combinations of colors. Figure 4 depicts the resample areas and filters so generated for the
red subpixels. The filters for green, blue and white are identical, but appear in a different
order or orientation.
 As may be seen in Figure 4, the resample areas may be hexagons with three
different alignments: offset 1/3 to the left (as seen as areas 404), centered (as seen as areas
4060, or offset 1/3 to the right (as seen as area 402). The three resulting unique area
resampling filters are:
2 12 0
82 146 0
2 12 0
0 14 0
0 14 0
0 2 12
0 2 12
Area Resample Filters
[04S] The resulting images may have a slightly blurred appearance, and thus, it may
be possible to apply cross-luminosity sharpening filters to substantially correct this:
0 32 0
0 32 0
0 32 0
Cross Luminosity Filters
 It will be appreciated that these cross-luminosity filters are distinguishable
from cross-color sharpening filters. One possible advantage of cross-luminosity filtering is
that blue and white can be sharpened, as well as red and green (as before with cross-color)
with a single value, thus reducing the number of operations. In a low cost RGBW
implementation, these luminosity values may be calculated using any of the embodiments
disclosed in several applications incorporated herein. One example uses the formula:
 It should be noted that this luminosity value can be calculated by performing
only shifts and adds in hardware or software.
 hi one embodiment, the color values may be sampled using the area resample
filters above, the luminosity "plane" may be sampled using the cross-luminosity filters, and
the two results are added together. This can occasionally produce values below zero or above
tile maximum, so the results may be clamped to the allowed range,
 The area resampling filters above correct for the offset position of the subpixel
with in the source pixel with coefficients mat sample a little more of the color to one
side or the other. An alternative way to accomplish this may be to use a horizontal cubic
filter to change me phase of the input data. When an output sub-pixel lands in the center of
an input pixel, no phase adjustment is necessary and the centered area resample filter can be
used. When the output sub-pixel lands in an offset position in an input pixel, one of the
following two cubic filters may be used to generate a "psuedo-sample" that is aligned with
the center of the output sub-pixel;
Horizontal Cubic Filters
 Once the phase is aligned, die centered area resample filter and
sharpening filter may be used for all output sub-pixels. In one exemplary hardware
implementation, these cubic filters may be implemented using special purpose logic to do the
multiplies by fixed numbers. This calculation could be done on input values before passing
them to the sub-pixel rendering logic. The sub-pixel rendering logic may thus be simplified,
at the cost of the pre-conditioning of the data with the cubic filter. In one exemplary software
implementation, it might be advantageous to convolve the cubic filters with the centered area
resample filter. This results in two filter kernels shown below:
Cubic plus Area Resampling Filters
 These two filters can be substituted for the offset filters in the first area
resampling case to simulate the cubic case with no other changes to the software. When these
filters are used, the luminosity plane may also be phase aligned which might employ
convolving the centered sharpening filter with the two horizontal cubic filters:
Cubic plus Sharpening Filters
 As the layouts of Figures 3A and 3B are similar to the conventional RGB
stripe layout, one low cost system might proceed by copying or assigning the nearest RGB or
value into the output sub-pixel without performing area resampling. However, undesirable
color error might occur. The horizontal component of this error may be reduced by using the
horizontal cubic filters above. As this system would require no line buffers, low hardware
costs reduce the overall cost of the system. Additionally, as the cubic filters have a slight
sharpening effect, separate sharpening may not be not needed. The horizontal lines of fonts
may look reasonably good, however the vertical components of fonts may still exhibit color
error. Such a low cost system might be acceptable in an image-only application, such as a
 Figures 5A and SB are yet other, embodiments of a high brightness RGBW
layout - but have a 1:2 aspect ratio for their subpixels. This subpixel repeating group
comprising blue sub-pixels the same size as the red and green and adding two white subpixels
tends to result in a color-balanced RGBW layout. It will be appreciated that the layouts of
Figures 3A, 3B, 5A, and SB - while placing the red and green subpixels and the blue and
white subpixels, or red and blue subpixels and the green and white subpixels, on a
checkerboard pattern - may be viewed as having other patterns alternatively. For example,
any mirror image or rotation or other symmetries are contemplated. Additionally, the
subpixels need not be placed on a fully intertwined checkerboard for the purposes of the
present invention, an example of which is given in Figure 7.
 In one embodiment, each input pixel image data may be mapped to two subpixels.
In effecting this, there are still a number of different ways to align the input pixels
and generate the area resampling filters. The first considered was to simply align 4 input
pixels directly with the layouts shown in Figures 5A and SB. Figure 6 shows one example of
an area resampling of the red color plane as described. Input pixel image data is depicted on
grid 602 and the repeating group 604 of subpixels of Figure 5 A is superimposed upon the
grid. Red subpixels 606 and 610 and their associated "diamond" filters 608 and 612 are also
shown. Area resampling may then occur in the manner described herein and in many
applications incorporated herein, an example is given here:
-.0625 0 -.0625 0 .125 0 -.0625 .125 -
0 .25 0 + .125 .5 .125 = .125 .75
-.0625 0 -.0625 0 .125 0 -.0625 .125 -
DOG Wavelet + Area Resample = Luminance Sharpening
 For non-band-limited images, such as text, computer aided drafting (CAD),
line art, or other computer generated images, it may be advantageous to treat pairs of
subpixels as though they were substantially coincident, using the substantially exact same
filter kernel to resample the image. This will result in sharp verticals and horizontal lines
 Alternatively, these diamond filters may be offset by 1A of an input pixel. For a
panel with the arrangement of Figure 5A, the filter kernels, shown below, may be
substantially the same for red and green; while blue and white use filters may be offset in the
opposite direction horizontally.
4 28 0
4 28 0
0 28 4
0 28 4
 Another embodiment might offset the input pixels until their center points are
aligned with the centers of some of the repeating sub-pixels. One example of filters that may
suffice are as follows:
32 128 32
Rag/green (or blue/white) Blue/white (or red/green, respectively)
 One of these is the "diamond" filter while the other is split down the middle.
This split may results in a blurring of the to fonnation in two of the primaries. In one
embodiment, by assuming the input pixels are offset % pixel to the left, the red and green
sub-pixels become perfectly aligned while the white and blue sub-pixels use the split filter.
In another embodiment, it may be possible to align the pixels with the highest luminosity, so
if the input pixels are assumed to be offset Vi pixel to the right then the white and blue subpixels
are aligned while the rod and green sub-pixels are split across an input pixel. The
assignment of the above filters would be modified for a panel based on the arrangement of
Figure SB, as would be obvious from this teaching to one skilled in the art
 This split may be further processed by using a cubic filter to move the phase of
the input data for the split sub-pixels until they are also centered. This may be accomplished
by using the following cubic filter to do this H pixel offset:
-16 144 144 -16
Vi input pixel cubic offset filter
 This offset filter may be easy to implement as shifts and adds in hardware or
software. The input pixels are assumed to be shifted 1A pixel one direction for half of the
output sub-pixels and they may be tendered with the diamond filter. The other 4 sub pixels
may have their input shifted with the above cubic filter then they may also be rendered with
the diamond filter.
 In hardware, it is easy to implement the above cubic shift on the input data as
it flows through the SPR controller. In software, it is often more convenient to convolve the
cubic filter with the diamond filter and perform a single filtering operation on the input for
the non-aligned sub-pixels. In this case, the following combined filter kernel is used:
 For the cases when the sub-pixels are aligned or brought into alignment with
cubic filters, the standard cross-color or cross-luminosity sharpening filter may be used. If,
however, the input pixels remain centered around pairs of output sub-pixels, then it is
possible to use the following cross-luminosity filters for sharpening:
-4 0 -28
 Figure 7 is yet another embodiment of the novel high brightness layouts made
in accordance with the principles of the present invention. It may be seen that the red and
green - as well as the blue and white - subpixels are created on a checkerboard pattern. It
will be appreciated that the similar filters as described above may be used on this alternative,
although they may be used in a different order or slightly different filter kernels than the other
 Figure 8 is yet another embodiment of a high brightness color filter
arrangement as made in accordance with the principles of the present invention. In Figure 8,
the subpixels are shown (in grid 802) having its colored subpixels with a 2:3 aspect ratio but
white sub-pixels with an aspect ratio of 1:3. In this embodiment, arranging three rows of
three color pixels in a mosaic or diagonal stripe arrangement, the layout becomes color
balanced. It should be noted that, with a narrow white subpixel next to each color sub-pixel,
each logical pixel has a bright luminosity center, hi one embodiment, the input pixels may be
centered on these white sub-pixels, so the white value may be simply sampled at each input
location. All the color sub-pixels may be split in this alignment, but due to the diagonal
stripe layout, the area resampling filter may be a tilted hexagon as in Figure 9.
 Looking at Figure 9, input image data grid 900 is shown. Superimposed on
grid 900 is target subpixel grid 802. Centers of red subpixels and their associated resatnple
areas (centered around dots 902a, 902b, and 902c) are also shown. In one embodiment, the
hexagonal resample areas may be calculated by considering the surrounding red subpixel
centers and drawing even boundaries lines between the centers. For example, red center 902a
and its associated resample area has a boundary line 906 which substantially bisects the line
between center 902 and red center 904. Similarly, lines 908 and 910 substantially bisect the
lines between center 902a and 902b and 902c respectively. It will be appreciated that other
resample area shapes may be formed hi other manners for other embodiments. It suffices that
the resample areas are substantially correlated with input image data in a spatial manner. It
will also be appreciated mat the green color plane - or any other color plane - may be treated
 The resulting filter kernels may be identical for every sub-pixel of every color
and could be a 4x3 filter. However, when converted to Sbit integers, the small areas on the
right and left became very small and may be discarded, resulting in the following exemplary
 Alternatively, the !4 pixel cubic offset filter may be used to adjust Hie phase of
the input pixels until the psuedo-samples land on the centers of the output sub-pixels again.
In this case, the area resample filters may become a 3x3 filters, as given below. Once
centered like this, it is possible to use a cross-lummosity sharpening filter for this alignment,
as given below.
 As with the other layouts disclosed herein, the cubic interpolation
accomplishing the I/a pixel alignment may be done on a scan-line basis and may be done to
the input data as it arrives. However, in software implementations, it may be convenient to
convolve the cubic filter with the above two filters to do each sample in a single step. In this
case, the combined cubic and area resampling filter is given below on the left with the
combined cubic and sharpening filter on the right:
-1 7 29 19 -2 0
-2 14 64 64 14 -2
0 -2 19 29 7 -1
1 - 9 - 9 1 0 0
0 0 2-20 -20 2
0 -6 58 58 -6 0
2 -20-20 2 0 0
0 0 1 - 9 - 9 1
 In another embodiment, the layout of Figure 8 may use a cubic area
resampling filter above, but may use a non-cubic cross-luminosity filter. This filter may be
desirable for images with sharp edges such as text.
Sab-Pixel Rendering Filters and Offset Assumptions
 Apart from use on high brightness layouts, the techniques of performing image
data offsets to achieve advantageous filter kernels is also applicable to the full range of other
subpixel layouts (e.g. 3-color, 4-color, 5-color, etc.) disclosed herein and in the applications
incorporated by reference. The technique of area resampling may be thought, in one sense, in
a geometric model for calculating the filter kernels. A picture of a target layout may be
typically drawn on top of a grid of source RGB pixels. A center point, called a resample
point, may be chosen for each of the sub-pixels in the target layout. Shapes, called resample
areas, may be drawn which enclose substantially all of the area that lies closer to one
resample point than any other of the same color.
 Figure 10 depicts a three-color subpixel repeating pattern 1000 that
substantially comprises red 1002, green 1004 and blue 1006 subpixels of approximately the
same size. Grid lines 1008 depict an overlay of source input image data that should be
remapped to the target subpixel layout. As may be seen, the input image data grid seems to
split the blue subpixels in some ratio (e.g. one half), hi the case of the layout of Figure 10,
these blue resample areas are simple rectangles. The resample points for red and green were
chosen to make the resample areas turn out to be diamonds, or squares rotated 45 degrees as
shown in Figure 11. In both squares and diamonds, the shapes of the resample areas were
simple enough mat the intersection of the areas of the source pixels and the resample areas
could be calculated analytically or geometrically.
 These choices for red and green resample points are in some sense a
simplification, done to make the resample areas easier to calculate and the resulting filters
less expensive to implement in hardware. In these filter designs, the resample points of the
red and green sub pixels were not placed at the centers 1102 of the sub-pixels, but were
moved slightly left or right to make them align with the centers 1104 of the source pixels or
logical pixels, as seen in Figure 11. If these resample points are placed substantially at the
centers 1102 of each target sub-pixels, then the resample areas become more complicated
asymmetrical diamond-like shapes, as seen Figure 12. These shapes sometimes resemble
kites flying sideways — so the resulting filters are termed "kite filters". These new shapes
may be more difficult to calculate geometrically and they may change with every variation of
any given subpixel layout. In some cases, it may be advantageous to leave the resample
points substantially on the cento* of the subpixels. For example, this may reduce color error
in some images. In other cases, it may be advantageous to move the resample points
substantially to the center of the resample area. For example, this may simplify the filters and
make implementing them in hardware less expensive.
New Filter Generation:
 One embodiment of generating resample areas and their filter kernels will now
(1) A first step is to accept a list of resample points and create a picture or otiiet
representation in a bitmap file.
(2) Each pixel in this image is substantially compared against all the resample
points to find out which resample point is closest In doing this, it may be
desirable to consider all neighboring resample points above, below, left, right
as well as in all four diagonal direction.
(3) A second pass through the bitmap image may be taken and the count of the
number of pixels that are tagged as closest to one resample point may be an
approximation of the resample area for that resample point. The number of
tagged pixels inside each source pixel square may also be counted.
(4) The ratio of these two numbers may be an approximation of the coefficient for
the filter kernel for each source pixel. The bitmap image can be displayed or
printed out to see what the resulting shape looks like and to verify mat the
shapes make sense.
 It will be appreciated mat other methods and steps may be taken to generate
filter kernels for the mapping of input image data to a target subpixel layouts. It suffices for
the purposes of the present invention that the filter kernels extract out image data that is
substantially correlated to the target subpixels in a spatial manner.
Translating Edge Assumptions:
 Using a point near the exact center of the sub-pixel as the resample point, hi
some cases, may be simplified by changing the edge assumptions. A simplifying assumption
of placing a target layout (such as shown in the '353 application and other applications
incorporated herein) on top of 4 source pixels may result in diamonds and boxes that may be
out-of-phase with the input pixels. One example is seen in Figures 13A, 13B, and 13C -
depicting the red, green and blue resample areas respectively. Translating all the resample
points together is not a simplification since the choice of edge alignment could be arbitrary,
hi many of the layouts, a slight shift to the left of all the resample points resulted in much
simpler filters and sharper greens. For example, such suitable shifts result in the resampling
areas seen in Figures 14A, 14B, and 14C.
Adjusting Center Locations:
 When points close to the exact sub-pixel center are used as the resample points
for the layout shown in Figure 15 (e.g. two blue subpixels 110 staggered within a
substantially checkerboarded pattern of red and green subpixels), a large set of different
filters may result. For example, Figures 16A, 16B and 16C are one possible set of filters for
such a layout
 In another embodiment, both the red resample points can be moved slightly to
make the red filter areas diamonds, as may be seen in Figure 17A - with Figures 17B and
17C depicting the green and blue filters respectively. Yet another embodiment might be a
combination of translation and adjustments to make the two green areas the diamonds -
while the red and blue would remain "kites", as is shown in Figures ISA, 18B and 18C. This
may have the effect of keeping green sharper. Since green has most of the luminosity, this
may result hi a sharper total image. In addition, having all the green resample points centered
on input pixels would allow them to be sharpened with cross-color sharpening.
 Adjusting the relationship between source pixels and the subpixels in the
layout shown in Figure IS might also help with decimating RGB data into such a display. As
may be seen in Figure IS, there may be a red or a green sub-pixel completely inside each
source pixel. In a simple-to implement hardware decimation mode, the correct red or green
primary value from the underlying ROB pixel could be copied directly into the target sub
pixels. The blue sub-pixels may be split and may be averaged or even have one of the two
source blue values used arbitrarily without noticeable problems hi the image.
 If the edges of the source pixels are aligned with the target layout, one of the
green sub pixels may be split between two source pixels. Averaging the two source greens
may produce a faizy image; while picking one source value may result in some degradation
of image quality. Alternatively, the remapping grid 1502 could be shifted between the source
pixels so mat the green sub pixels are not split, as may be seen in Figure 15. This will result
in one of the red sub pixels being split between two source pixels, but since green contributes
more to the luminosity of the image, splitting one of the reds may not degrade the image as
 While the invention has been described with reference to an exemplary
embodiment, it will be understood by those skilled in the art mat various changes may be
made and equivalents may be substituted for elements thereof without departing from the
scope of the invention. In addition, many modifications may be made to adapt a particular
situation or material to the teachings without departing from the essential scope thereof.
Therefore, it is intended that me invention not be limited to the particular embodiment
disclosed as the best mode contemplated for carrying out this invention, but that the invention
will include all embodiments falling within the scope of the appended claims.
1. A method for rendering input image data of a first color space onto a
display 100 of a second colour space, said display 100 comprising a subpixel repeating group 102, wherein said subpixel repeating group 102 comprises at least one white subpixel and a plurality of colored subpixels and wherein colors of said subpixels define a second color space, the steps of said method comprising:
receiving input image data for rendering on said display 100; converting said input image data from said first color space to image data of said second color space;
subpixel rendering each individual color plane of said image data of said second color space to produce subpixel rendered image data; and sharpening the subpixel rendered image data with a luminance signal.
2. The method as claimed in Claim 1 wherein a format of said input image data is one of a group, said group comprising: RGB, sRGB, and YCbCr.
3. The method as claimed in Claim 2 wherein said second color space is one of a group, said group comprising: RGBW, RGBCW+L, and RGBMW+L.
4. The method as claimed in Claim 1 wherein the step of subpixel rendering comprises constructing filter kernels from area resampling.
5. The method as claimed in Claim 4 wherein said step of constructing filter kernels comprises mapping luminance image data onto said white subpixels 104.
6. The method as claimed in Claim 4 wherein the step of subpixel rendering comprises mapping the chrominance data onto said plurality of colored subpixels.
7. The method as claimed in Claim 6 wherein the step of mapping the chrominance data onto said plurality of colored subpixels comprises shifting the phase of at least one color plane to interstitial positions of said colored subpixels.
8. The method as claimed in Claim 1 wherein the step of sharpening said subpixel rendered image data comprises sharpening at least one color plane with luminance data.
9. The method as claimed in Claim 8 wherein the step of sharpening at least one color plane with luminance data comprises sharpening with a difference of gaussian filter.
10. The method as claimed in Claim 6 wherein the step of mapping the chrominance data onto said plurality of colored subpixels comprises cross-color sharpening said chrominance data.
11. The method as claimed in Claim 1 wherein the step of sharpening said subpixel rendered image data onto said plurality of colored subpixels comprises self-sharpening.
12. The method as claimed in Claim 5 wherein said step of mapping luminance image data onto said white subpixels 104 comprises using one of a group of filters, said group comprising: a tent filter, a box filter, a unity filter, a box-cubic filter, and a tent-cubic filter.
13. The method as claimed in Claim 4 wherein the step of constructing filter kernels from area resampling comprises finding a reduced set of filters according to reconstruction symmetries.
14. The method as claimed in Claim 13 wherein the step of finding a reduced set of filters comprises applying corrections for offset positions.
|Indian Patent Application Number||5175/DELNP/2006|
|PG Journal Number||43/2011|
|Date of Filing||08-Sep-2006|
|Name of Patentee||CLAIRVOYANTE, INC.|
|Applicant Address||874 GRAVENSTEIN HWY S,SUITE 14, SEBASTOPOL, CA 95472, USA.|
|PCT International Classification Number||G09G 5/00|
|PCT International Application Number||PCT/US2005/010022|
|PCT International Filing date||2005-03-23|