TECHNICAL FIELD

The present disclosure relates generally to advanced image signal processing, color science, signal encoding and digital watermarking, particularly for printed objects including, e.g., product packaging, labels and hangtags.

BACKGROUND AND SUMMARY

This document describes technology to encode information signals in host carriers, such as color artwork and images. One form of information encoding is “steganography.” Another form of information encoding includes digital watermarking. For purposes of this disclosure, the terms “digital watermark,” “watermark,” “data encoding” and “data hiding” are used interchangeably. We sometimes use the terms “encoding,” “encode,” “embedding,” “embed,” and “data hiding” to mean modulating or transforming data representing imagery or video to include information therein. For example, data encoding embeds an information signal (e.g., a plural bit payload or a modified version of such, e.g., a 2-D error corrected, spread spectrum signal) in a host signal. This can be accomplished, e.g., by modulating a host signal (e.g., image, video or audio) in some fashion to carry the information signal. One way to modulate a host signal is to overprint a first color with additional colors. Another way to modulate a host signal is to tweak (or adjust) an ink value relative to its original value.

Some of the present assignee's work in signal encoding, data hiding, and digital watermarking is reflected, e.g., in U.S. Pat. Nos. 6,947,571; 6,912,295; 6,891,959. 6,763,123; 6,718,046; 6,614,914; 6,590,996; 6,408,082; 6,122,403 and 5,862,260, and in published specifications WO 9953428 and WO 0007356 (corresponding to U.S. Pat. Nos. 6,449,377 and 6,345,104). Each of these patent documents is hereby incorporated by reference herein in its entirety. Of course, a great many other approaches are familiar to those skilled in the art. The artisan is presumed to be familiar with a full range of literature concerning signal encoding, steganography, data hiding and digital watermarking.

The described technology provides apparatus, systems, methods and non-transitory computer readable medium to encode color artwork with an information signal. In some embodiments, encoding prioritizes a low resulting luminance change after encoding. This can be achieved by offsetting the changed luminance while preserving a target robustness. Robustness can be modeled by a target reflectance value representing the color artwork combined with an information signal at or around 660 nm. A few particular combinations include the following. Others will be evident from the detailed description and drawings.

A first combination includes a method of estimating signal robustness of an encoded artwork element within a PDF file, said method comprising: obtaining the encoded artwork element, the encoded artwork element comprising a signal encoded therein comprising a synchronization component and a message component; generating an interference mask representing PDF file elements which overlay the encoded artwork element; applying the interference mask to encoded artwork element to yield a masked, encoded artwork element; computing local robustness scores from the masked, encoded artwork element, in which said local robustness scores represent a score associated with both the synchronization component and the message component; outputting computed local robustness scores.

Another combination includes a method to encode a PDF file with a signal, the PDF file comprising a plurality of elements including an artwork element, said method comprising: disassembling the PDF file to obtain the artwork element; first encoding the artwork element according to a first signal encoding, said first encoding yielding a first encoded artwork element; second encoding the artwork element according to a second signal encoding, said second encoding yielding a second encoded artwork element; third encoding the artwork element according to a third signal encoding, said third encoding yielding a third encoded artwork element; generating a signal robustness score for each of the first encoded artwork element, the second encoded artwork element and the third encoded artwork element; selecting the first encoded artwork element, the second encoded artwork element, or the third encoded artwork element based on generated signal robustness scores, said selecting yield a selected encoded artwork element; reassembling the PDF file so as to include the selected encoded artwork element instead of the artwork element.

Still another combination includes an image processing method comprising: obtaining a reflectance value representing an image pixel or group of image pixels at or around 660 nm, the image pixel representing artwork including cyan, magenta, yellow and black channels; altering the reflectance value according to an information carrying signal, said altering yielding a target reflectance value at or around 660 nm; changing in a first direction the cyan value of the image or group of image pixels pixel to achieve the target reflectance value, said changing yielding changed pixel colors; evaluating the luminance (L*) of the changed pixel colors relative to the luminance of the image pixel or group of image pixels; changing in a second direction opposite of the first direction the magenta value of the changed pixel color to minimize a change in luminance (*L) while maintaining the target reflectance value within 0.02-5%.

Another combination includes an image processing method comprising: obtaining a pixel corresponding to color values including cyan, magenta, yellow and black values, the cyan, magenta, yellow and black values corresponding to L*a*b* values; changing the cyan value to achieve a target reflectance value at or around 660 nm, the target reflectance value corresponding to a reflectance representing pixel reflectance and information signal reflectance at or around 660 nm, the changing the cyan value yielding a changed cyan value, in which the changed cyan value, magenta value, yellow value and black values correspond to first changed L*a*b* values; changing the magenta value in a direction opposite to the change in cyan value to reduce a luminance difference between the L*a*b* values and the first changed L*a*b* values, said changing the magenta value yields a changed magenta value, in which the changed cyan value, the changed magenta value, the yellow value and the black value correspond to second changed L*a*b* values.

In some embodiments the above image processing method also includes changing the yellow value and the changed magenta value to reduce a b* difference between the L*a*b* values and the second changed L*a*b* values, said changing the yellow value and the changed magenta value yielding a changed yellow value and a second changed magenta value.

Still another combination includes an image processing method comprising: obtaining target reflectance values representing reflectance of i) artwork and ii) an information signal at or around 660 nm, the artwork comprising at least first cyan values, magenta values and yellow values; obtaining second cyan values from a blend model using the target reflectance values, the magenta values and the yellow values, said obtaining yielding second cyan values; changing the magenta values and the yellow values to offset luminance (L*) attributable to the second cyan values, the changing yielding second magenta values and second yellow values; and providing the second cyan values, the second magenta values and the second yellow values to represent the artwork, in which the information signal is detectable from image data representing the second cyan values under red-light illumination at or around 660 nm.

Additional features, combinations and technology will be readily apparent from the following description with reference to the accompanying drawings.

