Color space

Color space

A color space is a specific way of representing colors as tuples of numbers, typically as three or four values or color components. Color spaces lend themselves to (in principle) reproducible representations of color, particularly in digital representations, such as digital printing or digital electronic display.

Some colorspaces in wide use are:

RGB for computer graphics
- RBGA for computer graphics with variable transparency
CMYK for printing
YUV and YIQ for television
HSV for graphic design

Commercial color spaces:

Specialised application color spaces:

CIE color spaces
RG Chromaticity for Computer vision applications

Obsolete colorspaces:

RG for early Technicolor film
RGK for early color printing

Table of contents

1 Commonly used color spaces
2 Commercial color spaces
3 Specialised application color spaces
4 Obsolete color spaces
5 Also see
6 External links
7 Weblinks

Commonly used color spaces

Additive color mixing

Subtractive color mixing

RGB is typically used to describe additive color. Light is added together to create form from out of the darkness. RGB stores individual values for red, green and blue.

RGBA is used similarly as RGB, but it has an additional channel, alpha, to indicate transparency.

CMYK is a subtractive color space used in the printing process. One starts with a white canvas, and uses ink to subtract color from white to create an image. CMYK stores ink values for cyan, magenta, yellow and black.

YIQ is used in NTSC (North American) television broadcasts for historical reasons. YIQ stores a luminance value with two chrominance values, corresponding approximately to the amounts of blue and red in the color. It corresponds closely to the YUV (also called YCC or more accurately YCbCr) scheme used in PAL television and JPEG image compression, except for the fact that the YIQ color space is rotated 33� with respect to the YUV color space.

HSV is often used by artists because it is often more natural to think about a color in terms of hue and saturation than in terms of additive or subtractive color components. HSV stores a hue value, a saturation value and an intensity value.

HLS is quite similar to HSV, with lightness replacing intensity value.

There's an overview of the differences between RGB and CMYK at http://www.pixelphoto.com/htdocs/html/rgb_cmyk.html

Once you've decided which color space you want to work in, if you are working on a computer, you must then address the problem of color space encoding.

Specialised application color spaces

The reference standard usually used is the CIE Lab color space. This is the most accurate color space but too complex for every day uses.

The RG Chromaticity space is used in Computer vision applications, and shows the color of light (red, yellow, green etc.), but not it's intensity (dark, bright).

Obsolete color spaces

Early color spaces had two components. They largely ignored blue light because the added complexity of a 3-component process was much less of a marginal increase in fidelity than the jump from monochrome to 2-component color.

References:

R. W. G. Hunt, The Reproduction of Colour in Photography, Printing & Television, 5th Ed. Fountain Press, England, 1995. ISBN 0863433812
Mark D. Fairchild, Color Appearance Models, Addison-Wesley, Reading, MA (1998). ISBN 0-201-63464-3