Method for statistical analysis of images for automatic white balance of color channel gains for image sensors

• US 20070008417A1
• Filed: 06/23/2006
• Published: 01/11/2007
• Est. Priority Date: 06/04/2002
• Status: Active Grant

• Current Assignee: Igor Subbotin, Michael Kaplinsky
• Original Assignee: Igor Subbotin, Michael Kaplinsky
• Inventors: Subbotin, Igor, Kaplinsky, Michael
• Granted Patent: US 8,300,930 B2
• Time in Patent Office: Days
• US Class Current: 348/223.100
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control

Abstract

A process for performing white balancing of an image is performed by subdividing an image into a plurality of subframes, and then analyzing each subframe to determine if that subframe is predominantly monochromatic other than gray. If so, that subframe is excluded from the computation of the gain adjustments in the white balancing operation. As a result, the white balance process is performed using only the multicolored and/or gray subframes, thus allowing the overall white-balance of the image to be shifted only when a change in the color average is due to a change in the spectra of illumination, and not a presence of large monochromatic areas in the image.

Claims

1-27. -27. (canceled)

28. A method of performing a white balance operation comprising:

supplying image data to a processor by;

obtaining an image;

dividing the image into a plurality of subframes;

determining whether each subframe is substantially monochromatic or not; and

performing a white balance operation on the image only using the subframes which are determined to be not substantially monochromatic.

29. The method of claim 28, wherein the determining step comprises:

obtaining a hue value for each pixel in the subframe;

calculating a mean hue for the subframe;

calculating a standard deviation of hue variances for the subframe using sums of the squares of the differences between the hue for each pixel in the subframe and the mean hue; and

comparing the standard deviation with a threshold value.

30. The method of claim 29, wherein the hue value obtained for each pixel is expressed as a value within a range from 0 to 360.

31. The method of claim 29, wherein the hue value obtained for each pixel is expressed as a value within a range from 0 to 96.

32. The method of claim 28, wherein the determining step comprises:

obtaining a hue value for each pixel in the subframe;

calculating a mean hue for the subframe;

calculating a standard deviation of the hue variances for the subframe using sums of the absolute values of the differences between the hue for each pixel in the subframe and the mean hue; and

comparing the standard deviation with a threshold value.

33. The method of claim 32, wherein the hue value obtained for each pixel is expressed as a value within a range from 0 to 360.

34. The method of claim 32, wherein the hue value obtained for each pixel is expressed as a value within a range from 0 to 96.

35. The method of claim 28, wherein the determining step comprises:

obtaining a hue value for each pixel in the subframe;

calculating a mean hue for the subframe based on the obtained hue values for a subset of the lines in the subframe;

calculating a standard deviation of the hue variances for the subframe using sums of the squares of the differences between the hue for each pixel in the lines of the subframe not used to calculate the mean hue and the mean hue; and

comparing the standard deviation with a threshold value.

36. The method of claim 35, wherein the hue value obtained for each pixel is expressed as a value within a range from 0 to 360.

37. The method of claim 35, wherein the hue value obtained for each pixel is expressed as a value within a range from 0 to 96.

38. The method of claim 28, wherein the determining step comprises:

obtaining a hue value for each pixel in the subframe;

calculating a mean hue for the subframe based on the obtained hue values for a subset of the lines in the subframe;

calculating a standard deviation of the hue variances for the subframe using sums of the absolute values of the differences between the hue for each pixel in the lines of the subframe not used to calculate the mean hue and the mean hue; and

comparing the standard deviation with a threshold value.

39. The method of claim 38, wherein the hue value obtained for each pixel is expressed as a value within a range from 0 to 360.

40. The method of claim 38, wherein the hue value obtained for each pixel is expressed as a value within a range from 0 to 96.

41. The method of claim 28, further comprising subdividing each subframe into a plurality of macropixels, wherein the determining step comprises:

obtaining a hue value for each macropixel in the subframe;

calculating a mean hue for the subframe based on the obtained macropixel hue values;

calculating a standard deviation of the hue variances for the subframe using sums of the squares of the differences between the hue for each macropixel in the subframe and the mean hue; and

comparing the standard deviation with a threshold value.

42. The method of claim 28, further comprising subdividing each subframe into a plurality of macropixels, wherein the determining step comprises:

obtaining a hue value for each macropixel in the subframe;

calculating a mean hue for the subframe based on the obtained macropixel hue values;

calculating a standard deviation of the hue variances for the subframe using sums of the absolute values of the differences between the hue for each macropixel in the subframe and the mean hue; and

comparing the standard deviation with a threshold value.

43. The method of claim 28, wherein performing the white balance operation comprises:

calculating a respective sum of all hue values for each color component in the remaining subframes;

determining a weight for each respective sum so that the three components are equal; and

adjusting the hue values for each pixel in the image according to the determined weight for each color component.

44. A method comprising:

obtaining an image;

outputting an image signal that includes pixel image data for each line of the image; and

processing the image signal by;

dividing the image into a plurality of subframes and determining whether or not each subframe is substantially monochromatic; and

performing a white balance operation on the image only using subframes which are determined to be not substantially monochromatic.

45. A method for performing a white balance operation comprising:

receiving image data; and

supplying the image data to a processor by;

obtaining an image and outputting an image signal,

processing the image signal,

selecting divided portions of an image determined to be substantially grey and divided portions of the image determined to be substantially multicolored and calculating a white balance of the image based only on the selected portions.