Color and Image ProcessingFaculty of Electrical Engineering and Information Technology

University of AachenD-52056 Aachen, Germany

Univ. Prof. Dr.-Ing. Bernhard HillTel. +49 (0) 241 802 7703; E-mail: hill@ite.rwth-aachen.de

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Color and Image Processing:

Main Objectives

Multispectal Image Capture

Multiprimary Display

Softproof Workstation

Standards developed withinIEC 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-”

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 scanners

Colour printers

Colour cameras

Colour image projectors

From sRGB to opRGB

bluered

The story of the default RGB color space

nonlinear distortion

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

linear relation between XYZ und sRGB:

Primaries according to chromaticities ITU-R BT.709.3

green

X 0.4124 0.3576 0.1805 RsRGB

Y = 0.2126 0.7152 0.0722 GsRGB

Z 0.0193 0.1192 0.9505 BsRGB

matrix(3x3) RGBsRGBXYZ

RGB´sRGB

digitizationRGB8Bit

Linear transformation

0.0 1.0

-> RsRGB

0.0

1.0

0

255

R8Bit R´sRGB

RsRGB > 0.0031308

R´sRGB = 1.055 RsRGB(1/2.4) - 0.055

RsRGB > 0.0031308

R´sRGB = 12.92 RsRGB

RsRGB > 0.0031308

R´sRGB = 1.055 RsRGB(1/2.4) - 0.055

RsRGB > 0.0031308

R´sRGB = 12.92 RsRGB

Nonlinear distortion:

R8Bit = round[255 R´sRGB]R8Bit = round[255 R´sRGB]

550

600

500

chromaticity diagramand sRGB

typical location ofprimaries of LCD-displays

550

600

500

RGB-Cube and optimal color space

planes of constant lightness spaced Eab = 10 units

550

600

500

RGB-Cube and optimal color space

planes of constant lightness spaced Eab = 10 units

bluered

Scene-oriented and extended RGB colour spaceIEC 61966-2-2

linear relation between XYZ und sRGB:

Primaries according to chromaticities ITU-R BT.709.3

green

X 0.4124 0.3576 0.1805 RscRGB

Y = 0.2126 0.7152 0.0722 GscRGB

Z 0.0193 0.1192 0.9505 BscRGB

matrix(3x3) RGBscRGBXYZ

digitization 16 BitsRGBscRGB(16)

linear transformation

RscRGB

1.0

~7.5

8192

127

16384

RscRGB(16)

65535

4096

0

12288

4096

1.5

~ - 0.5

0.0

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

range brighter than the white point

the range from -0.5 to 1.5 covers thewhole space of visible surface colors

(optimal color space)

the range from -0.5 to 1.5 covers thewhole space of visible surface colors

(optimal color space)

1.0RscRGB -->

0

Optional RGB Colour SpaceIEC 61966-2-5

matrix(3x3) RGBsRGBXYZ Linear transformation

550

600

500

chromaticity diagramand sRGB

wide gamut colour space!

bluered

Optional RGB Colour SpaceIEC 61966-2-5

nonlinear distortion

linear relation between XYZ und sRGB:

Primaries according to CIE 122:1996 chromaticities

green

X 0.5767 0.1856 0.1882 RsRGB

Y = 0.2973 0.6274 0.0753 GsRGB

Z 0.0270 0.0707 0.9913 BsRGB

matrix(3x3) RGBsRGBXYZ

RGB´sRGB

digitizationRGB8Bit

Linear transformation

0.0 1.0

-> RopRGB

0

255

RopRGB(8)

0.0

1.0

R´opRGB

R´opRGB = RopRGB(1/2.2)R´opRGB = RopRGB

(1/2.2)

Nonlinear distortion:

R8Bit = round[255 R´sRGB]R8Bit = round[255 R´sRGB]RopRGB(N) = round[(2N-1) R´opRGB]RopRGB(N) = round[(2N-1) R´opRGB]

1.0

Luma-Chroma Color Space sYCCIEC 61966-2-1 Appendix

nonlinear distortion(extended gamut)

transformation from sRGB´ into sYCC´components:

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

matrix(3x3) RGBsRGBXYZ

RGB´sRGB

digitization 8 BitYCC´sYCC

linear transformation

matrix(3x3) linear transformation

YCCsYCC(8)

0.0 1.0

-> RsRGB

extended nonlinear distortion:

1.01.0

R´sRGB

0.0

-0.5

1.0

0.5

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

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

0

255

YsYCC(8)

YsYCC(8) = round[255 Y´sYCC]YsYCC(8) = round[255 Y´sYCC]

CbsYCC(8) = round[255 Cb´sYCC] + 128CbsYCC(8) = round[255 Cb´sYCC] + 128

CrsYCC(8) = round[255 Cr´sYCC] + 128CrsYCC(8) = round[255 Cr´sYCC] + 128

- digital values below 0 and above 255 are clipped

- the color space covered by sYCC is larger than that of sRGB

but smaller than the optimal color space!

digitization of sYCC´ components:

Extended gamut YCC colour space xvYCCIEC 61966-2-4

nonlinear distortion(extended gamut)

matrix(3x3) RGBXYZ

RGB´

digitization 8 Bit

YCC´601

linear transformation

matrix(3x3)linear transformation

YCC´709

matrix(3x3)

ITU-R BT.6014:3 and 16:9 TV

ITU-R BT.709HDTV

YCCxyYCC(8) YCCxyYCC(8)

0.0 1.0

-> R

extended nonlinear distortion:

1.01.0

R´

0.0

-0.5

1.0

0.5

1.086

-0.758

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

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

Transformation from RGB´ to xvYCC´ components

transformation according to R BT.601

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 according to R BT.709

0

235

YxyYCC(8)

YxyYCC(8) = round[219 Y´nnn + 16]YxyYCC(8) = round[219 Y´nnn + 16]

CbxvYCC(8) = round[224 Cb´sYCC] + 128CbxvYCC(8) = round[224 Cb´sYCC] + 128

CrxvYCC(8) = round[224 Cr´sYCC] + 128CrxvYCC(8) = round[224 Cr´sYCC] + 128

digitization of YCC´ components:

16 black

255

white point

- the complete optimal color space is covered

- higher quantization in 10 Bits or 16 Bitsis defined as well

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