Method for automatic white balance of digital images
View Patent ↗A method of adjusting the color characteristics of a digital image includes receiving a digital image including a plurality of pixels, receiving non-pixel data relating to camera capture parameters including an aperture value, an exposure time value, and a speed value specific to the received digital image; using the aperture value, time value, and speed value to calculate a scene brightness value; and using the calculated scene brightness value to adjust the color of the digital image.
1. A method of adjusting the color characteristics of a previously captured digital image comprising:
(a) receiving the previously captured digital image that has a plurality of pixels,
(b) receiving non-pixel data relating to camera capture parameters including an aperture value, an exposure time value, and a shutter speed value specific to the received digital image;
(c) using the aperture value, time value, and speed value to calculate a scene brightness value without using any measured scene brightness; and
(d) using the calculated scene brightness value to adjust the color of the previously captured digital image.
2. The method of claim 1 wherein step (d) further includes:
(e) using the calculated scene brightness value to determine a scene illuminant type; and
(f) using the scene illumination type to adjust the color of the digital image.
3. The method of claim 2 further including using one or more color coordinate values to determine the scene illuminant type.
4. The method of claim 3 further including the steps of:
determining a white balance parameter value responsive to the scene illuminant type, the calculated scene brightness value, and the color coordinate values;
providing at least one white balance correction curve;
determining the white balance correction from the white balance parameter value and at least one white balance correction curve for the determined scene illuminant type; and
using the white balance correction to adjust the color of the digital image.
5. The method of claim 2 wherein the scene illuminant types include daylight, flash, tungsten, and fluorescent.
6. The method of claim 3 wherein the color coordinate value relates to a chrominance axis pertaining to a hue line that approximates a blackbody radiation source.
7. The method of claim 3 wherein the color coordinate value is defined by
ILL
=
B
-
R
2
where ILL is the color coordinate value, R is red and B is blue.
8. The method of claim 4 where the white balance correction curve is defined by
c=B 1 ×B V +B 2 ×aveill+B 3
where aveill is a color coordinate value, B 1 , B 2 , and B 3 are coefficients responsive to the scene illuminant type.
9. The method of claim 2 further including providing at least one white balance correction curve for each scene illuminant type.
10. The method of claim 9 where the scene illuminant types includes daylight, flash, tungsten, and fluorescent.
11. The method of claim 9 where the color coordinate value is defined by
ILL
=
B
-
R
2
where ILL is the color coordinate value, R is red and B is blue.
12. The method of claim 9 where the white balance parameter value is defined by
s=A 1 ×B V +A 2 ×aveill+A 3
where B V is the scene brightness value, aveill is a color coordinate value, and A 1 , A 2 , and
A 3 are coefficient responsive to the scene illuminant type.
13. The method of claim 9 where the white balance correction curve is defined by
c=B 1 ×B V +B 2 ×aveill+B 3
where aveill is a color coordinate value, B 1 , B 2 , and B 3 are coefficients responsive to the scene illuminant type.
14. A computer storage product having at least one computer storage medium having instructions stored therein causing one or more computers to perform the method of claim 1 .
15. The method of claim 1 wherein the digital image is derived from a digital camera.