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**Color and Image Processing**

Faculty of Electrical Engineering and Information Technology University of Aachen D Aachen, Germany Univ. Prof. Dr.-Ing. Bernhard Hill Tel. +49 (0) ; Sl jl

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**Color and Image Processing:**

Main Objectives Multispectal Image Capture Multiprimary Display Softproof Workstation

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**Standards developed within IEC TC 100 - TA2: **

“Color Measurement and Management in Multimedia Systems and Equipment” Represented in Germany by: DKE (Frankfurt) Committee “Multimedia Systeme und Geräte -Farbmessung und Farbmanagment-”

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**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

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From sRGB to opRGB

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**(sRGB: a display color space IEC 61966-2-1)**

The story of the default RGB color space (sRGB: a display color space IEC ) Linear transformation XYZ matrix(3x3) RGBsRGB nonlinear distortion RGB´sRGB digitization RGB8Bit linear relation between XYZ und sRGB: X RsRGB Y = GsRGB Z BsRGB red green blue Primaries according to chromaticities ITU-R BT.709.3

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**R´sRGB = 1.055 RsRGB(1/2.4) - 0.055 R8Bit = round[255 R´sRGB]**

255 R8Bit Nonlinear distortion: R´sRGB 1.0 -> RsRGB 0.0 RsRGB > R´sRGB = RsRGB(1/2.4) R´sRGB = RsRGB 0.0 1.0 R8Bit = round[255 R´sRGB]

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**chromaticity diagram and sRGB typical location of primaries of**

550 500 typical location of primaries of LCD-displays 600

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**RGB-Cube and optimal color space**

550 500 600 planes of constant lightness spaced DEab = 10 units

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**RGB-Cube and optimal color space**

550 500 600 planes of constant lightness spaced DEab = 10 units

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**Scene-oriented and extended RGB colour space**

IEC XYZ matrix(3x3) RGBscRGB linear transformation digitization 16 Bits RGBscRGB(16) linear relation between XYZ und sRGB: X RscRGB Y = GscRGB Z BscRGB red green blue Primaries according to chromaticities ITU-R BT.709.3

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**RscRGB(16) = round[8192 RscRGB]+4096**

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

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**Optional RGB Colour Space**

IEC Linear transformation XYZ matrix(3x3) RGBsRGB

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**wide gamut colour space!**

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

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**Optional RGB Colour Space**

IEC Linear transformation XYZ matrix(3x3) RGBsRGB nonlinear distortion RGB´sRGB digitization RGB8Bit linear relation between XYZ und sRGB: X RsRGB Y = GsRGB Z BsRGB red green blue Primaries according to CIE 122:1996 chromaticities

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**RopRGB(N) = round[(2N-1) R´opRGB]**

255 RopRGB(8) 0.0 1.0 R´opRGB 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)

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**Luma-Chroma Color Space sYCC**

IEC 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: Y´sYCC R´sRGB Cb´sYCC = G´sRGB Cr´sYCC B´sRGB

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**R´sRGB = 1.055 RsRGB(1/2.4) - 0.055 R´sRGB = 12.92 RsRGB**

-0.5 0.5 extended nonlinear distortion: RsRGB > R´sRGB = RsRGB(1/2.4) <= RsRGB >= R´sRGB = RsRGB RsRGB < R´sRGB = RsRGB(1/2.4) 1.0 -> RsRGB 0.0 1.0

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**digitization of sYCC´ components:**

255 YsYCC(8) digitization of sYCC´ components: - digital values below 0 and above 255 are clipped 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

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**Extended gamut YCC colour space xvYCC**

IEC 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

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1.0 R´ 0.0 -0.5 0.5 1.086 -0.758 extended nonlinear distortion: RsRGB > 0.081 R´ = R <= R >= 0.081 R´ = 4.5 R RsRGB < R´ = (-R ) 1.0 -> R 0.0 1.0

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**Transformation from RGB´ to xvYCC´ components**

transformation according to R BT.601 Y´ R´ Cb´ = G´ Cr´ B´ transformation according to R BT.709 Y´ R´ Cb´ = G´ Cr´ B´

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**digitization of YCC´ components:**

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

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**Thank you for listening !**

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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