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ICTCP, ICtCp, or ITP is a color space used as a part of the color image pipeline in video and digital photography systems for high dynamic range (HDR) and wide color gamut (WCG) imagery and is specified in Rec. 2100.[1] I is the intensity luma component encoded using the Perceptual Quantizer (PQ) or Hybrid Log-Gamma (HLG) non-linearity.[2] CT and CP are the blue-yellow (named from tritanopia) and red-green (named from protanopia) chroma components.[3]

ICtCp top view.png

ICtCp is defined from Rec. 2100 RGB as follows:[1]

Calculate LMS from BT.2100 RGB:

Calculate L'M'S' using the PQ inverse EOTF (or the HLG OETF):

Calculate ICtCp:

ICTCP is near constant luminance, which improves chroma subsampling versus YCbCr.[4] ICTCP also improves hue linearity compared with YCbCr which helps with compression performance and color volume mapping.[5] When combined with adaptive reshaping ICTCP can improve compression performance by 10%.[6] For CIEDE2000 color quantization errors 10-bit ICtCp would be equal to 11.5 bit YCbCr.[3] Constant luminance is also improved with ICtCp which has a luminance relationship of 0.998 between the luma and encoded brightness while YCbCr has a luminance relationship of 0.819.[3] An improved constant luminance is an advantage for color processing operations such as chroma subsampling and gamut mapping where only color information is changed.[3] A draft document for ICtCp has been released by the JCT-VC.[7]