Image Processing Apparatus Color Gamut Compression Degeneracy

The patent transforms color data from a uniform color space (L*a*b*) to a perceptual color space (JCh) that better represents human color perception. This parameter transformation allows the system to identify and correct color degeneracy by working with perceptually relevant parameters (J for lightness, C for chroma, h for hue) rather than uniform space parameters, thereby preserving perceived color differences while maintaining reproduciability.

The patent implements a feedback mechanism where color pairs are evaluated based on their perceived difference before and after compression. When color degeneracy is detected (colors that should be perceived as different become too similar), the system applies corrective processing to adjust the compressed colors, ensuring that perceptual color relationships are maintained throughout the compression process.

The patent changes the color space parameters from L*a*b* (uniform space) to JCh (perceptual space). In the JCh space, the hue angle (h) and chroma (C) parameters are designed to better reflect human perception, including the non-uniform effects described by MacAdam ellipses. This allows saturation-direction compression to proceed while maintaining hue perception accuracy because the compression operates on perceptually uniform parameters.

The patent applies different processing strategies to different color regions based on their perceptual characteristics. By evaluating color pairs in the JCh space and applying corrections specifically where hue perception would be affected, the system maintains local hue accuracy in critical regions while still achieving overall gamut mapping compression.