Setting the white balance of a video frame

1. A method on a personal communications device for setting a white balance in a frame of a video, the video comprising a previous frame, the method comprising:

receiving, by the personal communications device, the video and an ambiguous color reference list;

logically dividing, by the personal communications device, the frame into a plurality of sub-regions;

for each sub-region, comparing, by the personal communications device, an averaged color of pixels in the sub-region with a set of neutral reference color values predefined under a plurality of lighting conditions and determining that the sub-region is possibly dominantly monochromatic if a difference between the averaged color of the sub-region pixels and each color value in the neutral reference color set is greater than a first threshold;

for each sub-region not determined to be possibly dominantly monochromatic, for each color value in the neutral reference color set whose difference from the averaged color of the sub-region pixels is less than or equal to the first threshold, determining, by the personal communications device, that the sub-region is possibly dominantly monochromatic if the neutral reference color value and an illuminant type of a previous frame matches, within a second threshold, an element of the ambiguous color reference list; and

white balancing the frame based on sub-regions determined not to be possibly dominantly monochromatic.

2. The method of claim 1 further comprising:

white balancing the frame only if a total area of sub-regions determined to be possibly dominantly monochromatic is less than a third threshold, wherein the third threshold is a percentage of a total area of the frame.

3. The method of claim 1 wherein white balancing comprises adjusting color gains based, at least in part, on averaged colors of the sub-regions determined not to be possibly dominantly monochromatic.

4. The method of claim 1 wherein white balancing is based, at least in part, on a gray-world assumption for sub-regions not determined to be possibly dominantly monochromatic.

5. The method of claim 1 further comprising:

for each sub-region determined not to be possibly dominantly monochromatic, incrementing a counter for the sub-region's illuminant type; and

after proceeding through all sub-regions of the frame determined not to be possibly dominantly monochromatic, assigning an illuminant type of the frame to be an illuminant type with a highest counter.

6. The method of claim 1 further comprising:

repeating the method for a next frame of the video.

7. The method of claim 1 further comprising:

creating the ambiguous color reference list, the creating comprising:

comparing a neutral reference color with a plurality of reference colors under a plurality of illuminants; and

based, at least in part, on the comparing, creating the list of ambiguous color points, wherein each element of the list indicates a reference color under a first illuminant that has a color value whose difference from a color value of the neutral reference color under a second illuminant is less than a fourth threshold.

8. The method of claim 7 wherein the reference colors comprise Macbeth colors.

9. The method of claim 7 wherein illuminants comprise lightings with different color temperatures selected from the group consisting of: day lighting, cloudy lighting, fluorescent lighting, and tungsten lighting.

10. A personal communication device comprising:

a memory configured for storing a frame of a video, a previous frame of the video, and an ambiguous color reference list;

a processor operatively coupled to the memory and configured for logically dividing the frame into a plurality of sub-regions, for each sub-region, for comparing an averaged color of pixels in the sub-region with a set of neutral reference color values predefined under a plurality of lighting conditions and for determining that the sub-region is possibly dominantly monochromatic if a difference between the averaged color of the sub-region pixels and each color value in the neutral reference color set is greater than a first threshold, for each sub-region not determined to be possibly dominantly monochromatic, for each color value in the neutral reference color set whose difference from the averaged color of the sub-region pixels is less than or equal to the first threshold, determining that the sub-region is possibly dominantly monochromatic if the neutral reference color value and an illuminant type of a previous frame matches, within a second threshold, an element of an ambiguous color reference list, and for white balancing the frame based on sub-regions determined not to be possibly dominantly monochromatic; and

a transceiver operatively coupled to the memory and to the processor and configured for receiving the video and the ambiguous color reference list.

11. The personal communication device of claim 10 wherein white balancing comprises adjusting color gains based, at least in part, on averaged colors of the sub-regions determined not to be possibly dominantly monochromatic.

12. The personal communication device of claim 10 wherein the processor is further configured for:

for each sub-region determined not to be possibly dominantly monochromatic, incrementing a counter for the sub-region's illuminant type; and

after proceeding through all sub-regions of the frame determined not to be possibly dominantly monochromatic, assigning an illuminant type of the frame to be an illuminant type with a highest counter.

13. The personal communication device of claim 10 wherein the processor is further configured for:

creating the ambiguous color reference list, the creating comprising:

comparing a neutral reference color with a plurality of reference colors under a plurality of illuminants; and

based, at least in part, on the comparing, creating the list of ambiguous color points, wherein each element of the list indicates a reference color under a first illuminant that has a color value whose difference from a color value of the neutral reference color under a second illuminant is less than a third threshold.