ICtCp

IC_TC_P, 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] C_T and C_P are the blue-yellow (named from tritanopia) and red-green (named from protanopia) chroma components.^[3]

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

Calculate LMS from BT.2100 RGB:

{\begin{aligned}L&=(1688\cdot R+2146\cdot G+262\cdot B)/4096\\M&=(683\cdot R+2951\cdot G+462\cdot B)/4096\\S&=(99\cdot R+309\cdot G+3688\cdot B)/4096\\\end{aligned}}

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

{\begin{aligned}L'&=EOTF_{PQ}^{-1}(L)\\M'&=EOTF_{PQ}^{-1}(M)\\S'&=EOTF_{PQ}^{-1}(S)\\\end{aligned}}

Calculate ICtCp:

{\begin{aligned}I&=(0.5\cdot L'+0.5\cdot M')\\C_{T}&=(6610\cdot L'-13613\cdot M'+7003\cdot S')/4096\\C_{P}&=(17933\cdot L'-17390\cdot M'-543\cdot S')/4096\\\end{aligned}}

IC_TC_P is near constant luminance, which improves chroma subsampling versus YCbCr.^[4] IC_TC_P also improves hue linearity compared with YCbCr which helps with compression performance and color volume mapping.^[5] When combined with adaptive reshaping IC_TC_P 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]

References

1 2 "BT.2100-0 : Image parameter values for high dynamic range television for use in production and international programme exchange". International Telecommunication Union.
↑ "ST 2084:2014". Society of Motion Picture and Television Engineers.
1 2 3 4 "ICtCp Dolby White Paper" (PDF). Dolby. Retrieved 2016-04-20.
↑ "Subsampling in ICtCp vs YCbCr" (PDF). Dolby Laboratories, Inc.
↑ "ITP Colour Space and Its Compression Performance for High Dynamic Range and Wide Colour Gamut Video Distribution" (PDF). ZTE.
↑ "Evaluation of ICtCp color space and an Adaptive Reshaper for HDR and WCG" (PDF). IEEE.
↑ Peng Yin; Chad Fogg; Gary J. Sullivan; Alexis Michael Tourapis (2016-03-19). "Draft text for ICtCp support in HEVC (Draft 1)". JCT-VC. Retrieved 2016-04-20.

Color space
List of color spaces Color models
CAM	CIECAM02 iCAM
CIE	CIEXYZ CIELAB CIECAM02 CIELUV Yuv CIEUVW CIE RGB
RGB	Color space sRGB RG chromaticity Adobe Wide Gamut ProPhoto scRGB DCI-P3 Rec. 709 Rec. 2020 Rec. 2100
YUV	YUV PAL YDbDr SECAM YIQ NTSC YCbCr Rec. 601 Rec. 709 Rec. 2020 Rec. 2100 ICtCp YPbPr xvYCC YCoCg
Other	CcMmYK CMYK Coloroid LMS Hexachrome HSL, HSV HCL Imaginary color OSA-UCS PCCS RG RYB
Color systems and standards	ACES ANPA Colour Index International CI list of dyes DIC Federal Standard 595 HKS ICC profile ISCC–NBS Munsell NCS Ostwald Pantone RAL list
For the vision capacities of organisms or machines, see Color vision.

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