ColourSpaceConversions.pdfAdrian Ford (ajoec1@wmin.ac.uk <defunct>)
and Alan Roberts (Alan.Roberts@rd.bbc.co.uk).
August 11, 1998(b)
Contents
1 Introduction 3
2 Some Colour Definitions and Explanations. 3
2.1 What is the correct way to describe colour? . . . . . . . . . . . . . . . . . . . 3
2.2 What is a colour space? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3 Why is there more than one colour space? . . . . . . . . . . . . . . . . . . . . 4
2.4 What’s the difference between device dependent and device independent? . . . 5
2.5 What is a colour gamut? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.6 What is the CIE System? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.7 What colour space should I use? . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.7.1 RGB (Red Green Blue) . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.7.2 CMY(K) (Cyan Magenta Yellow (Black)) . . . . . . . . . . . . . . . . 6
2.7.3 HSL (Hue Saturation and Lightness) . . . . . . . . . . . . . . . . . . . 6
2.7.4 YIQ, YUV, YCbCr, YCC (Luminance - Chrominance) . . . . . . . . . 6
2.7.5 CIE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Gamma and linearity. 7
4 Grassman’s Laws of additive colour mixture. 8
5 Tristimuli, Chromaticity, and Colorimetric systems. 9
5.1 CIE XYZ (1931) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2 CIE YUV (1960) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.3 CIE YU’V’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4 CIE L*u*v* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.5 CIE L*a*b* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.6 Colour Difference. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6 Computer Graphics Colour Spaces. 11
7 Computer RGB colour space. 12
8 CMY(K) (Cyan Magenta Yellow (Black)) 14
9 HSL (Hue Saturation Lightness). 15
9.1 Hue Saturation Value (Travis). . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.2 Hue Saturation and Intensity. (Gonzalez and Woods). . . . . . . . . . . . . . . 17
10 TV and allied non-linear systems 18
10.1 European Y’U’V’ (EBU) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.2 American Y’I’Q’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.3 SMPTE-C RGB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.4 ITU.BT-601 Y’CbCr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.5 ITU.BT-709 HDTV studio production in Y’CbCr . . . . . . . . . . . . . . . . 24
10.6 SMPTE-240M Y’PbPr . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11 Kodak PhotoYCC Colour Space. 26
12 Colour appearence. 28
13 The Colour Reproduction Index. 28
14 Some references and bedtime reading. 29
14.1 On–line references. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
14.2 Real Paper References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
14.2.1 General Colour Theory. . . . . . . . . . . . . . . . . . . . . . . . . . 29
14.2.2 RGB to CIE conversion. . . . . . . . . . . . . . . . . . . . . . . . . . 29
14.2.3 Colour in TV and Computer Graphics. . . . . . . . . . . . . . . . . . . 30
14.2.4 Colour and printing. . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
14.2.5 Gamma and transfer functions. . . . . . . . . . . . . . . . . . . . . . . 30
14.2.6 Colour in Digital Image Processing and Computer Graphics. . . . . . . 30
14.2.7 Other Colour Related. . . . . . . . . . . . . . . . . . . . . . . . . . . 30
15 Footnotes & Disclaimer. 31