Geometric enumerated watermark embedding for colors and inks
The present disclosure relates generally to digital watermarking and signal encoding. Various colors can be evaluated and modified to carry an encoded or auxiliary signal.
1. An apparatus comprising:
an input to receive data representing pixels associated with a digital image;
means for evaluating, for each of a set of pixels from the digital image, candidate pixel changes to carry an encoded signal, the pixel changes corresponding to +/−n increments of an ink percentage for a first color ink, wherein n is an integer, in which said means for evaluating considers a perceptual error per pixel associated with each pixel change;
means for determining which of the pixel changes fall within an allowable visibility threshold, said determining identifying a subset of pixel changes;
means for reducing the number of pixel changes within the subset of pixel changes according to minimum and maximum percent (%) dot press limits, said reducing yielding remaining pixel changes;
means for weighting the remaining pixel changes according to color weights to yield weighted pixel changes; and
means for comparing at least one of the weighted pixel changes relative to printing press constraints to identify a weighted pixel change associated with a pixel, the weighted pixel change used to alter the digital image to carry the encoded signal.
2. The apparatus of claim 1 in which the visibility threshold is defined by an allowable visibility error per pixel.
3. The apparatus of claim 2 in which the allowable visibility error is scaled by a luminance masking function.
4. The apparatus of claim 1 in which the color weights are aligned with an embedding color direction.
5. The apparatus of claim 1 further comprising means for ranking, prior to operating said means for comparing, the weighted pixel changes according to signal strength magnitude.
6. The apparatus of claim 5 in which the weighted pixel change with the largest signal magnitude is the at least one of the weighted pixel changes.
7. The apparatus of claim 6 further comprising means for adjusting the at least one of the weighted pixel changes when said means for comparing determines that the at least one of the weighted pixel changes exceeds the printing press constraints, the means for adjusting yielding an adjusted weighted pixel change.
8. The apparatus of claim 7 in which the adjusted weighted pixel change is used instead of the weighted pixel change to alter the digital image to carry the encoded signal.
9. The apparatus of claim 1 further comprising means for transforming the digital image with a plurality of weighted pixel changes to carry the encoded signal therein.
10. A non-transitory computer readable medium comprising instructions stored therein that, when executed by an electronic processor, cause the electronic processor to perform the following:
for each of a set of pixels from a digital image, access candidate pixel changes to help carry an encoded signal, the pixel changes corresponding to +/−n increments of an ink percentage for a first color ink, wherein n is an integer, the access candidate pixel changes considers a perceptual error per pixel associated with each pixel change;
determine which of the pixel changes fall within an allowable visibility threshold, the determine identifying a subset of pixel changes;
reduce the number of pixel changes within the subset of pixel changes according to minimum and maximum percent (%) dot press limits, said reducing yielding remaining pixel changes;
weight the remaining pixel changes according to color weights to yield weighted pixel changes; and
evaluate at least one of the weighted pixel changes relative to printing press constraints to identify a weighted pixel change associated with a pixel, the weighted pixel change used to alter the digital image to help carry the encoded signal.
11. The non-transitory computer readable medium of claim 10 in which the allowable visibility threshold is scaled by a luminance masking function.
12. The non-transitory computer readable medium of claim 10 in which the allowable visibility threshold is defined by an allowable visibility error per pixel.
13. The non-transitory computer readable medium of claim 10 in which the color weights are aligned with an embedding color direction.
14. The non-transitory computer readable medium of claim 10 , and prior to the evaluate, sorting the weighted pixel changes according to signal strength magnitude.
15. The non-transitory computer readable medium of claim 10 in which a weighted pixel change with a largest signal magnitude is the at least one of the weighted pixel changes.
16. The non-transitory computer readable medium of claim 15 further comprising instructions which clip the at least one of the weighted pixel changes when said evaluate determines that the at least one of the weighted pixel changes exceeds the printing press constraints, the clip yielding a clipped weighted pixel change.
17. The non-transitory computer readable medium of claim 16 in which the clipped weighted pixel change is used instead of the weighted pixel change to alter the digital image to carry the encoded signal.
18. The non-transitory computer readable medium of claim 16 further comprising instructions that alter the digital image with a plurality of weighted pixel changes to carry the encoded signal therein.