Automatic color constancy for image sensors
An electronic imaging system operates as closely as possible to the cone spectral response space to obtain a human eye-like long, medium, short (LMS) wavelength response. An input image, for example, red-green-blue (RGB), is transformed to an LMS color space similar to the human long-, middle-, and short-wavelength cone receptor responses. Adaptation levels for each LMS component are calculated. The adaptation levels are then used to adjust the sensitivity of each LMS sensor response to obtain an LMS component image. The LMS component image then is transformed back to an RGB component image for further processing or display.
1. An imager comprising:
means for transforming an input image to an image in a color space corresponding to that of a human eye, the color space image having a plurality of components;
means for calculating adaptation levels for each component;
means for adjusting the sensitivity of each component based on the adaptation levels; and
means for transforming the adjusted color space image to an output image.
2. The imager of claim 1 , wherein the means for transforming, calculating, and adjusting comprises one of hardware, software, or a combination of hardware and software.
3. An imaging device comprising:
an imager providing an input image;
a transforming unit for transforming an input image from the imager to an image in a color space corresponding to that of a human eye, the color space having a plurality of components;
a calculating unit for calculating adaptation levels for each component;
an adjusting unit for adjusting a sensitivity of each component based on the adaptation levels; and
a transforming unit for transforming the adjusted color space image to an output image.
4. The imaging device as-in of claim 3 , further comprising a display device having a screen, and circuitry for displaying the RGB component image on the screen.
5. An output image comprising:
an image produced by a method of:
transforming an input image to an image in a color space corresponding to that of a human eye, the color space having a plurality of components;
calculating adaptation levels for each of the plurality of components;
adjusting a sensitivity of each of the plurality of components based on the adaptation levels; and
transforming the adjusted color space image to the output image.
6. A computer-readable storage medium containing a program for use in maintaining color constancy under different illumination conditions in an imager sensor, the program comprising instructions for:
transforming an input image to an image in a color space corresponding to that of a human eye, the color space having a plurality of components;
calculating adaptation levels for each of the plurality of components;
adjusting a sensitivity of each of the plurality of components based on the adaptation levels; and
transforming the adjusted color space image to an output image.
7. A method for improving color constancy under different illumination conditions, comprising:
transforming an input image to an image in a color space corresponding to that of a human eye, the color space image having a plurality of components;
calculating adaptation levels for each of the plurality of components;
adjusting a sensitivity of each of the plurality of components based on the adaptation levels; and
transforming the color space image to an output image.
8. The method of claim 7 , wherein the input image originates from an image sensor.
9. The method of claim 7 , wherein the input image originates from a digital image sensor.
10. The method of claim 7 , wherein the input image originates from a CMOS image sensor.
11. The method of claim 7 , wherein the input image is an RGB image.
12. The method of claim 11 , wherein the color space corresponding to that of a human eye is an LMS color space.
13. The method of claim 11 , wherein the input image is an RGB image which is transformed to an LMS color space.
14. The method of claim 11 , wherein the input image is an RGB image which is transformed using a transformation matrix representing the concatenation of an RGB to CIE tri-stimulus XYZ space transform and a CIE ti-stimulus XYZ space to LMS transform.
15. The method of claim 11 , wherein the adaptation levels are calculated for each LMS component.
16. The method of claim 7 , wherein the adaptation levels are calculated as root means of individual pixel intensity values.
17. The method of claim 16 , wherein the root means are calculated by obtaining a geometric sum of the pixel intensity values to the Kth power, and finding the Kth root of the geometric sum, as follows:
gsum
=
∑
i
=
1
N
pow
(
Pi
,
K
)
adapt
-
level
=
pow
(
gsum
N
,
1.0
K
)
where Pi denotes a pixel intensity value for each of a plurality of pixels i, i ranging from 1 to N, with N being a total number of pixels, and K is a high degree power factor.
18. The method of claim 17 , wherein K is at least about 4.
19. An imager comprising:
an image processing system, the system configured to:
transform an input image to an image in a color space corresponding to that of a human eye, the color space image having a plurality of components;
calculate adaptation levels for each component;
adjust the sensitivity of each component based on the adaptation levels; and
transform the adjusted color space image to an output image.
20. A method for improving color constancy comprising:
receiving a captured image, the captured image having a plurality of first color values in a first color space;
converting the plurality of first color values to a plurality of second color values in a second color space corresponding to that of a human eye;
calculating adaptation levels for each of the second plurality of color values; and
adjusting a sensitivity of each of the second plurality of color values based on the adaptation levels.
21. The method of claim 20 , wherein receiving a captured image comprises receiving the captured image from an image sensor.
22. The method of claim 20 , wherein receiving a captured image comprises receiving the captured image from a digital image sensor.
23. The method of claim 20 , wherein receiving a captured image comprises receiving the captured image from a CMOS image sensor.
24. The method of claim 20 , wherein the first plurality of color values comprise red, green, and blue values.
25. The method of claim 20 , wherein calculating adaptation levels comprises calculating a root means of individual pixel intensity values.
26. A method for improving color constancy under different illumination conditions, comprising:
transforming an input red/green/blue (RGB) image, the RGB image having red, green, and blue color values, to a long-, middle-, and short-wavelength (LMS) image, the LMS image having long-, middle-, and short-wavelength color values;
calculating adaptation levels for each of the LMS color values;
adjusting a sensitivity of each of the LMS color values based on the adaptation levels; and
transforming the adjusted LMS image to an output RGB image.
27. An apparatus for improving color constancy under different illumination conditions, comprising:
an image processing system, the system configured to:
transform an input red/green/blue (RGB) image, the RGB image having red, green, and blue color values, to a long-, middle-, and short-wavelength (LMS) image, the LMS image having long-, middle-, and short-wavelength color values;
calculate adaptation levels for each of the LMS color values;
adjust a sensitivity of each of the LMS color values based on the adaptation levels; and
transform the adjusted LMS image to an output RGB image.