Color managed embedding system for embedding signals in color artwork

A non-transitory computer readable medium comprising instructions stored therein that, when executed by one or more processors of a computer system, cause said computer system to perform operations comprising:

• accessing a color image comprising original Cyan (C), original Magenta (M), and original Yellow (Y), collectively, original CMY;
• obtaining information represent a contour representing a constant L* for different values of the original CMY;
• at a starting location on the contour represented by an original CIELAB a*, b* that is associated with the original CMY, determining L* gradient information to find a direction in CMY-space which moves towards a target CIELAB a*, b*, the target CIELAB a*, b* residing on the contour;
• determining a scalar representing the distance between the original CIELAB a*, b* and the target CIELAB a*, b*;
• and
• applying the determined scalar to the original CMY to yield a scaled CMY, the scaled CMY carrying the encoded signal, thereby encoding a signal in the color image by making changes in CIELAB a* and b* while maintaining L* within a predetermined tolerance.

An apparatus comprising:

• an input to obtain a reflectance value representing an image pixel or group of image pixels within a wavelength range, the image pixel representing artwork including a cyan value, a magenta value, and a yellow value;
• means for altering the reflectance value according to an information carrying signal, said means for altering yielding a target reflectance value within the wavelength range;
• means for changing, in a first direction, the cyan value to achieve the target reflectance value, said means for changing yielding changed pixel color values;
• means for evaluating a luminance (L*) value of the changed pixel color values relative to a luminance (L*) value of the image pixel or group of image pixels;
• means for changing, in a second direction opposite of the first direction, a magenta value of the changed pixel color values to minimize a change in luminance (*L) between the luminance (L*) value of the changed pixel color values relative to the luminance (L*) value of the image pixel or group of image pixels while maintaining the target reflectance value within 0-5%.

A non-transitory computer readable medium storing instructions that, when executed by one or more processors of a computer system, cause said computer system to perform operations comprising:

• obtaining original CIELAB L*, a*, b* values representing a color image comprising CMY channels;
• generating a a L* contour;
• determining a direction along the L* contour to introduce a change to carry a signal in the color image, said determining a direction yielding a determined direction;
• determining an amount of change in the determined direction, said determining an amount yielding a determined amount;
• applying the determined amount to achieve new CIELAB L*, a*, b* values, the new CIELAB L*, a*, b* values carrying the signal.