Determination of chroma mapping functions based on hue angular sectors partitioning the gamut mapping color space

A method of determination of a chroma mapping function allowing to map at least the chroma C of source colors of a content from a source color gamut into a target color gamut in a 3D gamut mapping color space allowing to define 2D constant-hue leaves having axes for lightness and chroma, comprising:

• defining in said gamut mapping color space a plurality of key constant-hue leaves, each of them characterized by a specific key hue corresponding to the hue of one of the primary and secondary colors defining said source color gamut, or/and to the hue of one of the primary and secondary colors defining said target color gamut, such as to partition said gamut mapping color space into a plurality of angular hue sectors, each of them being delimited in hue direction by two different key constant-hue leaves,
• for each of said key constant hue leaves, defining a key hue leaf chroma mapping function gh*( ) allowing to map the chroma of any of said source colors belonging to this key constant-hue leaf, such that, when applied to the chroma C of any source color of lightness L that belongs to the corresponding key constant hue leaf of hue h*, this chroma C is mapped into a chroma
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• where, in said key constant hue leaf:
• Cmax-h*SOURCE is the chroma of a color at the intersection of a line of constant lightness L with said source color gamut,
• Cmax-h*TARGET is the chroma of a color at the intersection of said line of constant lightness L with said target color gamut,
• for each angular hue sector, defining a continuous angular hue sector chroma mapping function g(h,) allowing to map the chroma of any of said source colors belonging to this angular hue sector, such that, for any source color belonging to one of the two key constant-hue leaves delimiting said angular hue sector, said continuous chroma mapping function allows to map the chroma of said source color according to the key hue leaf chroma mapping function of the key constant-hue leaf to which said source color belongs.