Automatic white balancing for photography

• US 8,698,918 B2
• Filed: 12/30/2009
• Issued: 04/15/2014
• Est. Priority Date: 10/27/2009
• Status: Active Grant

• Current Assignee: NVIDIA Corporation
• Original Assignee: NVIDIA Corporation
• Inventors: Silverstein, Amnon, Cabral, Brian
• Primary Examiner(s): GILES, NICHOLAS G
• Application Number:
  US12/650,202
• Publication Number:
  US 20110096190A1
• Time in Patent Office: 1,567 Days
• Field of Search: 348/222.1, 348/223.1, 348/224.1, 348/225.1, 348/234, 348/235
• US Class Current: 348/223.1
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control

Abstract

Embodiments of the claimed subject matter are directed to methods for automatic white balancing in an image-capture device. In one embodiment, given an estimated illuminant color (e.g., derived from the Gray World method), a more optimal illuminant color can be found by projecting this point to a plot of common illuminants to determine the closest point on the plot of common illuminants. Once the closest point of the plot of common illuminants is derived, the actual image (e.g., pixel) data of the scene is adjusted by the value of the closest point on the plot of common illuminants so that the light is normalized for the scene.

Claims

1. A method for automatic white balancing in an imaging device, the method comprising:

accessing image data corresponding to a captured scene, said image data comprising a plurality of pixels, said plurality of pixels comprising a plurality of color values corresponding to a plurality of color channels;

plotting said plurality of pixels in a color space comprising a plurality axes corresponding to said plurality of color channels;

calculating an average color value for said plurality of pixels;

projecting, in said color space, said average color value to a plot of common illuminants;

deriving, on said plot of common illuminants, a set of balanced color values comprising a plurality of color values corresponding to a closest approximation on said plot of common illuminants to said average color value; and

adjusting said plurality of color values of said plurality of pixels by said set of balanced color values to arrive at a plurality of adjusted pixels,

wherein said plot of common illuminants comprises a plot of common illuminants specifically corresponding to an attribute of said captured scene.

2. The method according to claim 1, wherein said calculating said average color value comprises:

determining a selection of said plurality of pixels to aggregate into a centroid;

aggregating said selection into a centroid; and

averaging, for each of said plurality of color channels, a plurality of color values comprised by said plurality of pixels comprising said selection.

3. The method according to claim 2, wherein said determining a selection comprises establishing, in said color space, a bounded area encompassing said plot of common illuminants, wherein pixels of said plurality of pixels which are disposed outside of said boundary are excluded from said aggregating of said centroid.

4. The method according to claim 1, wherein said plot of common illuminants comprises a line.

5. The method according to claim 1, wherein said plot of common illuminants comprises a curved line.

6. The method according to claim 1, wherein said plot of common illuminants comprises a multi-dimensional figure.

7. The method according to claim 1, wherein said deriving said set of color values comprises determining a single point on said plot of common illuminants most proximate to said average color value.

8. The method according to claim 1, wherein said adjusting comprises:

for each color channel of said plurality of color channels, adjusting a color value corresponding to a color channel of a pixel of said plurality of pixels by multiplying the color value corresponding to a color channel by a reciprocal of a color value of the set of color values corresponding to the same color channel.

9. The method according to claim 1, further comprising:

determining a first light intensity corresponding to said scene, said first light intensity comprised within a range of light intensities, wherein said plot of common illuminants is specific to said first light intensity.

10. The method according to claim 1, wherein said color space comprises a horizontal axis and a vertical axis, and wherein further a pixel of said plurality of pixels comprises a plurality of values corresponding to a horizontal coordinate and a vertical coordinate in said color space.

11. The method according to claim 10, further

instituting, on said plot of common illuminants, a first limit, said first limit comprising a first vertical coordinate corresponding to said vertical axis of said color space and a second limit, said second limit comprising a first horizontal coordinate corresponding to said horizontal axis of said color space;

determining whether a pixel of said plurality of pixels comprises a second vertical coordinate greater than said first vertical coordinate and whether a pixel of said plurality of pixels comprises a second horizontal coordinate greater than said first horizontal coordinate;

in response to said determining, clamping said second vertical coordinate of said pixel to said first vertical coordinate when said second vertical coordinate of said pixel is greater than said first vertical coordinate and clamping said second horizontal coordinate of said pixel to said first horizontal coordinate when said second horizontal coordinate of said pixel is greater than said first horizontal coordinate, wherein said instituting and said determining are performed prior to said clamping.

12. The method according to claim 1, wherein said plot of common illuminants comprises a multidimensional probability field, wherein said plot of common illuminants comprises at least one axis corresponding to a likelihood of an illuminant in a scene.

13. The method according to claim 1, wherein said color space is a red, green blue (RGB) color space.

14. The method according to claim 1, wherein said color space is a luminance chrominance color space.

15. A system for automatic white balancing for photography, said system comprising:

an image capture device comprising a lens, said image capture device configured to perform a method automatic light balancing, the method of automatic light balancing comprising;

accessing image data corresponding to an imaged scene, said image data comprising a plurality of pixels, said plurality of pixels comprising a plurality of color values corresponding to a plurality of color channels;

plotting said plurality of pixels in a color space comprising a plurality axes corresponding to said plurality of color channels;

aggregating, in said color space, a centroid from said plurality of pixels;

projecting, in said color space, said centroid to a plot of common illuminants;

deriving, on said plot of common illuminants, a set of balanced color values, said set of balanced color values comprising a plurality of color values corresponding to a closest approximation on said plot of common illuminants to said plurality of color values comprised by said centroid; and

adjusting said plurality of color values of said plurality of pixels by said set of balanced color values to arrive at a plurality of adjusted pixels,

wherein said plot of common illuminants comprises a plot of common illuminants specifically corresponding to an attribute of said captured scene.

16. The system according to claim 15, wherein said image data comprises a photograph.

17. The system according to claim 15, wherein said image data comprises an image from a video.

18. The system according to claim 15, wherein said plot of common illuminants comprises a plot of a plurality of common illuminants specific to a derived light intensity.

19. The system according to claim 15, wherein a pixel comprised in said plurality of pixels beyond pre-determined constraints is excluded from said aggregating.

20. A method for automatic white balancing for photography in an image capture device, the method comprising:

capturing a scene in an image capture device;

obtaining pixel data corresponding to said scene, said pixel data comprising a plurality of color values corresponding to a plurality of color channels and a light intensity;

determining said light intensity of said scene from said pixel data;

selecting a plot of common illuminants from a plurality of plots of common illuminants, said plot of common illuminants being selected to corresponding to said light intensity of said scene;

plotting said pixel data in a color space comprising a plurality of axes corresponding to said plurality of color channels;

aggregating a plurality of discrete data points comprised in said pixel data into a centroid;

projecting said centroid to said plot of common illuminants, wherein said projecting is performed by deriving a perpendicular line to a point on said plot of common illuminants;

deriving a balanced set of color values, said balanced set of color values comprising a plurality of color values corresponding to said point on said plot of common illuminants; and

adjusting said pixel data by said balanced set of color values to arrive at a plurality of digital pixels,

wherein said plot of common illuminants comprises a plot of common illuminants specifically corresponding to an attribute of said captured scene.