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Color and Image Processing: Standards and Transformations for Display Technologies

Learn about default and optional RGB color spaces, nonlinear distortion, and optimal color spaces for displays. Explore the transformation matrices and digitization techniques for improved color accuracy.

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Color and Image Processing: Standards and Transformations for Display Technologies

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  1. Color and Image Processing Faculty of Electrical Engineering and Information Technology University of Aachen D-52056 Aachen, Germany Univ. Prof. Dr.-Ing. Bernhard Hill Tel. +49 (0) 241 802 7703; E-mail: hill@ite.rwth-aachen.de Sl jl

  2. Multispectal Image Capture Multiprimary Display Softproof Workstation Color and Image Processing: Main Objectives

  3. Standards developed within IEC TC 100 - TA2: “Color Measurement and Management in Multimedia Systems and Equipment” Represented in Germany by: DKE (Frankfurt) Committee 742.06 “Multimedia Systeme und Geräte -Farbmessung und Farbmanagment-”

  4. Projects and standards: Default RGB colour space - sRGB Extended precision RGB colour space Default YCC colour space - sYCC Equipment using cathode ray tubes Eqipment using liquid crystal display panels Eqipment using plasma displays Colour printers Colour scanners Colour cameras Colour image projectors

  5. From sRGB to opRGB

  6. X 0.4124 0.3576 0.1805 RsRGB Y = 0.2126 0.7152 0.0722 GsRGB Z 0.0193 0.1192 0.9505 BsRGB red green blue The story of the default RGB color space (sRGB: a display color space IEC 61966-2-1) Linear transformation XYZ matrix(3x3) RGBsRGB nonlinear distortion RGB´sRGB digitization RGB8Bit linear relation between XYZ und sRGB: Primaries according to chromaticities ITU-R BT.709.3

  7. R8Bit 255 0 Nonlinear distortion: R´sRGB 1.0 -> RsRGB 0.0 RsRGB > 0.0031308 R´sRGB = 1.055 RsRGB(1/2.4) - 0.055 RsRGB > 0.0031308 R´sRGB = 12.92 RsRGB 0.0 1.0 R8Bit = round[255 R´sRGB]

  8. chromaticity diagram and sRGB 550 500 typical location of primaries of LCD-displays 600

  9. RGB-Cube and optimal color space 550 500 600 planes of constant lightness spaced DEab = 10 units

  10. RGB-Cube and optimal color space 550 500 600 planes of constant lightness spaced DEab = 10 units

  11. X 0.4124 0.3576 0.1805 RscRGB Y = 0.2126 0.7152 0.0722 GscRGB Z 0.0193 0.1192 0.9505 BscRGB red green blue Scene-oriented and extended RGB colour space IEC 61966-2-2 XYZ matrix(3x3) RGBscRGB linear transformation digitization 16 Bits RGBscRGB(16) linear relation between XYZ und sRGB: Primaries according to chromaticities ITU-R BT.709.3

  12. 65535 the range from -0.5 to 1.5 covers the whole space of visible surface colors (optimal color space) RscRGB(16) 16384 12288 8192 range brighter than the white point 127 4096 4096 0 ~7.5 RscRGB(16) = round[8192 RscRGB]+4096 RscRGB 1.5 1.0 0.0 0 1.0 RscRGB --> ~ - 0.5

  13. Optional RGB Colour Space IEC 61966-2-5 Linear transformation XYZ matrix(3x3) RGBsRGB

  14. chromaticity diagram and sRGB 550 wide gamut colour space! 500 600

  15. X 0.5767 0.1856 0.1882 RsRGB Y = 0.2973 0.6274 0.0753 GsRGB Z 0.0270 0.0707 0.9913 BsRGB red green blue Optional RGB Colour Space IEC 61966-2-5 Linear transformation XYZ matrix(3x3) RGBsRGB nonlinear distortion RGB´sRGB digitization RGB8Bit linear relation between XYZ und sRGB: Primaries according to CIE 122:1996 chromaticities

  16. R´opRGB RopRGB(8) 255 1.0 0 0.0 Nonlinear distortion: 1.0 -> RopRGB 0.0 1.0 R8Bit = round[255 R´sRGB] RopRGB(N) = round[(2N-1) R´opRGB] R´opRGB = RopRGB(1/2.2)

  17. Y´sYCC 0.2990 0.5870 0.1140 R´sRGB Cb´sYCC = -0.1687 -0.3312 0.5000 G´sRGB Cr´sYCC 0.5000 -0.4187 -0.0813 B´sRGB Luma-Chroma Color Space sYCC IEC 61966-2-1 Appendix XYZ matrix(3x3) RGBsRGB linear transformation nonlinear distortion (extended gamut) RGB´sRGB matrix(3x3) linear transformation YCC´sYCC digitization 8 Bit YCCsYCC(8) transformation from sRGB´ into sYCC´components:

  18. R´sRGB 1.0 1.0 0.5 0.0 -0.5 extended nonlinear distortion: RsRGB > 0.0031308 R´sRGB = 1.055 RsRGB(1/2.4) - 0.055 -0.0031308 <= RsRGB >= 0.0031308 R´sRGB = 12.92 RsRGB RsRGB < -0.0031308 R´sRGB = -1.055 RsRGB(1/2.4) + 0.055 1.0 -> RsRGB 0.0 1.0

  19. YsYCC(8) 255 - digital values below 0 and above 255 are clipped 0 digitization of sYCC´ components: YsYCC(8) = round[255 Y´sYCC] • the color space covered by sYCC • is larger than that of sRGB • but smaller than the optimal color space! CbsYCC(8) = round[255 Cb´sYCC] + 128 CrsYCC(8) = round[255 Cr´sYCC] + 128

  20. Extended gamut YCC colour space xvYCC IEC 61966-2-4 XYZ matrix(3x3) RGB linear transformation nonlinear distortion (extended gamut) RGB´ linear transformation matrix(3x3) matrix(3x3) YCC´601 YCC´709 ITU-R BT.601 4:3 and 16:9 TV ITU-R BT.709 HDTV YCCxyYCC(8) YCCxyYCC(8) digitization 8 Bit

  21. R´ 1.086 1.0 1.0 0.5 0.0 -0.5 -0.758 extended nonlinear distortion: RsRGB > 0.081 R´ = 1.099 R0.45 - 0.099 -0.081 <= R>= 0.081 R´ = 4.5 R RsRGB < -0.081 R´ = -1.099(-R)0.45 + 0.099 1.0 -> R 0.0 1.0

  22. Y´601 0.2990 0.5870 0.1140 R´ Cb´601 = -0.1687 -0.3312 0.5000 G´ Cr´601 0.5000 -0.4187 -0.0813 B´ Y´709 0.2126 0.7152 0.0722 R´ Cb´709 = -0.1146 -0.3854 0.5000 G´ Cr´709 0.5000 -0.4542 -0.0458 B´ Transformation from RGB´ to xvYCC´ components transformation according to R BT.601 transformation according to R BT.709

  23. - the complete optimal color space is covered digitization of YCC´ components: YxyYCC(8) 255 white point 235 YxyYCC(8) = round[219 Y´nnn + 16] 16 black • higher quantization in 10 Bits or 16 Bits is defined as well 0 CbxvYCC(8) = round[224 Cb´sYCC] + 128 CrxvYCC(8) = round[224 Cr´sYCC] + 128

  24. If you like to experience the standards of the default RGB and YCC colour spaces, look to your TV and DVD multimedia home equipment ! Details of the standards are available from the publications of IEC Thank you for listening !

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