Color display based on spatial clustering
A color display has a monochrome modulator. An active area of the modulator is illuminated by an array of light sources. The light sources include light sources of three or more colors. The intensities of the light sources may be adjusted to project desired luminance patterns on an active area of the modulator. In a fast field sequential method different colors are projected sequentially. The modulator is set to modulate the projected luminance patterns to display a desired image. In a slow field sequential method, colors are projected simultaneously and the modulator is set to modulate most important colors in the image.
1. A method for controlling a display to display an image specified by image data, the image data comprising a plurality of color channels, the display comprising a modulator located to be illuminated by light from a plurality of groups of light sources, the light sources of each group emitting light of a corresponding one of the plurality of colors, a spatial distribution of light from each of the groups of light sources on an active area of the modulator controllable by applying light source control signals to the light sources of the group, the method comprising:
processing the image data to select one of the plurality of colors which exhibits a greatest degree of spatial clustering in at least a part of the image;
based at least in part on the color channel of the image data corresponding to the selected color determining first pixel driving values for pixels of the modulator corresponding to at least the part of the image;
determining light source control signals for the light sources of one or more colors other than the selected color based on the first pixel driving values and color channels of the image data corresponding to the one or more colors other than the selected color; and
applying the first pixel driving values to drive the pixels of the modulator to selectively allow light from the active area to pass to a viewing area and while applying the first pixel driving values to drive the pixels of the modulator:
operating the light sources of the selected color to illuminate the active area of the modulator with light of the selected color; and
applying the light source control signals for the light sources of the one or more colors other than the selected color to drive the light sources of the one or more colors other than the selected color;
wherein selecting one of the plurality of colors which exhibits a greatest degree of spatial clustering is based on a determination of a number of contiguous pixels in the part of the image that have similar pixel values for each of the plurality of colors.
2. A method according to claim 1 comprising, based on the color channel for the selected color determining selected color light source control signals for the light sources of the selected color, wherein operating the light sources of the selected color comprises applying the selected color light source control signals to drive the light sources of the selected color to emit light of the selected color with a spatial distribution at the modulator determined by the selected color light source control signals.
3. A method according to claim 2 comprising generating the first pixel driving values by steps that include:
estimating a first luminance pattern that would be produced on the modulator by driving the selected group of light sources with the selected color light source control signals; and,
computing the first modulator values based upon the channel of the image data corresponding to the first color and the first luminance pattern.
4. A method according to claim 1 comprising, for each of a plurality of areas of the image selecting a different selected color and, for each of the plurality of areas performing the method using the selected color corresponding to the area.
5. A method according to claim 1 wherein:
applying the first pixel driving values to drive the pixels of the modulator is performed in a first time interval; and
the method comprises, during a second time interval distinct from the first period, controlling the pixels of the modulator according to second pixel driving values based upon a color channel of the image data corresponding to a second one of the colors.
6. A method according to claim 5 comprising, while controlling the pixels of the modulator according to the second pixel driving values operating the groups of light sources corresponding to both of the selected and second colors.
7. A method according to claim 6 wherein:
applying the light source control signals for the light sources of the one or more colors other than the selected color comprises applying light source control signals for the group of light sources corresponding to the second color;
the method comprises, while controlling the pixels of the modulator according to the second pixel driving values driving the light sources of the group of light sources corresponding to the second color with new light-source control signals different from those used to drive the light sources of the group of light sources corresponding to the second color while controlling the pixels of the modulator according to the first pixel driving values.
8. A method according to claim 7 comprising generating the new light-source control signals from the color channel of the image data corresponding to the second color.
9. A method according to claim 7 comprising generating the second pixel driving values by steps that include:
determining a set of correction factors for the second color based upon a difference between the values specified in the image data for the second color and estimated light output values for the second color in the first time interval; and
generating the second modulator values based at least upon: the channel of the image data corresponding to the second color, the correction factors, and an estimated luminance pattern for the second color.
10. A method according to claim 9 wherein the set of correction factors include correction factors for each pixel in an area of the modulator.
11. A method according to claim 9 wherein generating the second modulator values comprises setting the second modulator values so that the second modulator values do not differ from the first modulator values by more than a threshold amount.
12. A method according to claim 5 comprising, during at least one of the first and second time intervals, operating a third one of the groups of light sources to create on the modulator a luminance pattern in a third color.
13. A method according to claim 5 wherein the first and second time intervals occur within a cycle that is repeated and wherein, during each cycle, none of the modulator values are based upon the values specified by the image data for a least-important one of the colors.
14. A method according to claim 5 wherein the first and second time intervals both occur in a cycle that repeats at a rate not exceeding 110 Hz.
15. A method according to claim 1 performed in a repeating cycle wherein the cycle comprises a plurality of time intervals, in one of the time intervals:
operating only the group of light sources corresponding to the selected color to provide a luminance pattern on the modulator; and,
controlling the pixels of the modulator to have modulator values based upon values specified in the image data for the selected color;
and in another of the time intervals:
operating two or more of the groups of light sources to provide a corresponding plurality of overlapping luminance patterns on the modulator; and
controlling the pixels of the modulator to have modulator values based upon values specified in the image data for colors corresponding to one of the two or more groups of light sources being operated.
16. A method according to claim 1 wherein the image data comprises video data comprising a plurality of frames and the method is repeated for each of the frames of the video data.
17. A method according to claim 16 wherein the modulator is a monochrome modulator.
18. A method according to claim 1 wherein point spread functions of different ones of the light sources in each of the groups overlap with one another at the modulator.
19. A method according to claim 1 wherein processing the image data to select one of the plurality of colors comprises computing for each of the plurality of colors a weighted combination of the degree of spatial clustering with one or more of: average brightness per pixel, highest average pixel value, maximum brightness for any pixel, maximum pixel value for any pixel and maximum variation in brightness or pixel value.
20. A method according to claim 1 comprising simultaneously driving the light sources of each group of light sources to emit light for each setting of the modulator.