Detection from two chrominance directions

1. A detector apparatus comprising:

memory for storing data representing color image data comprising first color data and second color data, in which the first color data comprises signal encoding including a first polarity, and in which the second color data comprises the signal encoding including a second polarity that is inversely related to the first polarity, the first polarity and the second polarity offsetting luminance attributable to the signal encoding;

one or more processors programmed for:

selectively weighting the first color data and the second color data so that the signal encoding is emphasized while image content is de-emphasized when weighted first color data and weighted second color data are combined;

detecting the signal encoding from combined, weighted first color data and weighted second color data; and

outputting data corresponding to detected signal encoding.

2. The detector apparatus of claim 1 in which combining the weighted first color data and the weighted second color data subtracts the weighted second color data from the weighted first color data.

3. The detector apparatus of claim 1 in which the signal encoding comprises digital watermarking, and the weighting aligns digital watermark detection along an a−b direction, where a represents a first color axis, and b represent a second color axis.

4. A handheld device comprising the detector apparatus of claim 3 .

5. A cell phone comprising the handheld device of claim 4 .

6. The detector apparatus of claim 1 in which the weighted first color data comprises red color data and the weighted second color data comprises green color data, in which red color data and the green color data are combined according to 0.35*red color data−1.05*green color data.

7. The detector apparatus of claim 1 in which the image color data also comprises third color data, and said selectively weighting the first color data and the second color data also selectively weights the third color data so that the signal encoding is emphasized while image content is de-emphasized when weighted first color data, weighted second color data and weighted third color data are combined.

8. The detector apparatus of claim 7 in which the weighted first color data comprises red color data and the weighted second color data comprises green color data, and the weighted third color data comprises blue color data, and in which the red color data, the green color data and the blue color data are combined according to 0.35*red color data−1.05*green color data +0.70*blue color data, plus a constant.

9. A detector apparatus comprising:

memory for storing data representing color image data comprising first color data and second color data, in which the first color data comprises signal encoding including a first polarity, and in which the second color data comprises the signal encoding including a second polarity that is inversely related to the first polarity, and in which the first color data corresponds to a first multi-color axis, and the second color data corresponds to a second multi-color axis;

one or more processors programmed for:

combining the first color data and the second color data by subtracting the second color data and the first color data, the subtracting emphasizing the signal encoding while de-emphasizing image content;

detecting the signal encoding from the combined first color data and second color data; and

outputting data corresponding to detected signal encoding.

10. A handheld device comprising the detector apparatus of claim 9 .

11. A cell phone comprising the handheld device of claim 10 .

12. The detector apparatus of claim 9 in which the signal encoding comprises digital watermarking and said combining aligns digital watermark detection along an a−b color direction in an Lab color space.

13. A detector apparatus comprising:

memory for storing data representing color image data comprising first color data and second color data, in which the first color data comprises signal encoding including a first polarity, and the second color data comprises the signal encoding including a second polarity that is inversely related to the first polarity;

means for weighting the first color data and the second color data so that the signal encoding is emphasized while image content is de-emphasized when weighted first color data and weighted second color data are combined, in which said means for weighting aligns encoded signal detection along a multi-axis color direction;

means for detecting the signal encoding from combined, weighted first color data and weighted second color data; and

more or more processors configured for outputting data corresponding to detected signal encoding.

14. The detector apparatus of claim 13 comprising means for combining the weighted first color data and the weighted second color data by subtracting the weighted second color data from the weighted first color data.

15. The detector apparatus of claim 13 in which the signal encoding comprise digital watermarking, and said means for weighting aligns digital watermark detection along an a−b direction, in which the multi-axis color direction corresponds to an a−b color axis in an Lab color space.

16. The detector apparatus of claim 15 in which the image color data also comprises third color data, and said means for weighting the first color data and the second color data also weights the third color data so that the digital watermarking is emphasized while image content is de-emphasized when weighted first color data, weighted second color data and weighted third color data are combined.

17. The detector apparatus of claim 16 , in which the first color data comprises red color data, and the second color data comprises green color data, and the third color data comprises blue color data.

18. A handheld device comprising the detector apparatus of claim 13 .

19. A cell phone comprising the handheld device of claim 18 .

20. A non-transitory computer readable medium comprising instructions stored thereon, that, when executed by a processor, causes the processor to perform the following:

accessing data representing color image data comprising first color data and second color data, in which the first color data comprises signal encoding including a first polarity, and the second color data comprises the signal encoding including a second polarity that is inversely related to the first polarity;

weighting the first color data and the second color data so that the signal encoding is emphasized while image content is de-emphasized when weighted first color data and weighted second color data are combined, in which said weighting aligns encoded signal detection along a multi-axis color direction;

combining the weighted first color data and the weighted second color data by subtracting the weighted second color data from the weighted first color data, the combining yielding combined weighted first color data and weighted second color data;

decoding a plural-bit identifier from the signal encoding within the combined weighted first color data and weighted second color data; and

providing the plural-bit identifier as an output.

21. The non-transitory computer readable medium of claim 20 in which the image color data further comprises third color data, and in which the weighting the first color data and the second color data also weights the third color data so that the signal encoding is emphasized while image content is de-emphasized when weighted first color data, weighted second color data and weighted third color data are combined.

22. The non-transitory computer readable medium of claim 21 , in which the first color data comprises red color data, and the second color data comprises green color data, and the third color data comprises blue color data.

23. The non-transitory computer readable medium of claim 20 in which the signal encoding comprises digital watermarking.

24. The non-transitory computer readable medium of claim 23 in which the multi-axis color direction corresponds to an a−b color axis in an Lab color space.