Color adaptive watermarking

1. A method to encode an image with a digital watermark, wherein the image comprises a plurality of color channels, said method comprising:

determining a color characteristic for a group of image samples;

based at least in part on the characteristic, determining for the group of image samples which of the plurality of color channels should receiving encoding;

transforming from the group of image samples at least one determined color channel that should receive encoding into a transform domain; and

altering transform domain coefficients of the at least one determined color channel to encode the digital watermark.

2. The method of claim 1 , further comprising transforming an altered color channel into a spatial domain.

3. The method of claim 1 , where the characteristic identifies which of the color channels will best hide the digital watermark in terms of visibility.

4. A method of encoding a color image with an auxiliary signal, wherein the auxiliary signal comprises encoding values, and wherein the color image comprises an array of color values, said method comprising:

providing a set of encoding values for an image sample;

determining a color characteristic for the image sample based on its color values; and

selectively scaling color values in the image sample based on the color characteristic to encode at least a portion of the auxiliary signal in the color image in accordance with at least the encoding values.

5. The method of claim 4 , wherein the scaling effects a change in luminance.

6. The method of claim 5 , wherein the scaling comprises a scale to black.

7. The method of claim 5 , wherein the scaling comprises a scale to white.

8. The method of claim 4 , wherein the color characteristic comprises yellow content.

9. A method to encode data representing imagery with a digital watermark, wherein the data represents a plurality of colors, said method comprising:

determining a color characteristic for a group of data samples;

based at least in part on the characteristic, determining for the group of data samples which of the plurality of colors should receiving encoding;

transforming from the group of data samples data representing at least one determined color that should receive encoding into a transform domain; and

altering transform domain coefficients of the data representing at least one determined color to encode the digital watermark.

10. The method of claim 9 further comprising transforming data representing an altered color into a spatial domain.

11. The method of claim 9 where the characteristic identifies which of the colors will best hide the digital watermark in terms of visibility.

12. The method of claim 9 wherein the imagery comprises a digital image or video.

13. A method of encoding data representing color imagery with an auxiliary signal, said method comprising:

providing a set of encoding values for a data sample;

determining a color characteristic associated the data sample based on associated color values; and

selectively scaling color values in the data sample based on the color characteristic to encode at least a portion of the auxiliary signal in the data representing color imagery.

14. The method of claim 13 wherein the selectively scaling effects a change in luminance.

15. The method of claim 14 wherein the selectively scaling comprises a scale to black.

16. The method of claim 14 wherein the selectively scaling comprises a scale to white.

17. The method of claim 13 , wherein the color characteristic are associated with yellow content.

18. The method of claim 13 wherein the color imagery comprises a digital color image or video.

19. The method of claim 18 wherein the auxiliary data is steganographically encoded in the data representing color imagery.