Patent ID: 11962733
Assignee: DIGIMARC CORPORATION
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G  H | IPC G  H

Claim 4:
5. An apparatus configured for encoding a signal in a PDF file, the PDF file comprising a first element including a color image comprising original Cyan (C), Magenta (M), Yellow (Y), said method comprising:
means for rasterizing the first element to yield a rasterized first element;
means for determining gradients of L*, a*, b* with respect to changes in the original CMY at a rasterized first element location to be encoded;
means for using determined L* gradient information to find a direction in CMY-space which moves towards a target a*, b* value while keeping L* unchanged within a predetermined tolerance;
means for using determined a*, b* gradient information to find a scale value for a*, b* in a determined L* gradient direction to reach the target a*, b* value, yielding a found scale value;
means for applying the found scale value to the original CMY, yielding scaled CMY, and using the scaled CMY as replacements for the original CMY within the rasterized first element to yield an embedded rasterized first element, the scaled CMY carrying the signal;
means for replacing the rasterized first element with the embedded rasterized first element.