Color space

A color space is a specific way of representing colors as tuples of numbers, typically as three or four values. 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:

• Pantone
• Munsell color system
• NCS color system

Reference color spaces:

• CIE color spaces

Obsolete colorspaces:

• RG[?] for early Technicolor film
• RGK[?] for early color printing

Note: this article needs expert input: at the moment, it is extremely informal, and needs lots of work by experts in the field to give a good account of this highly technical field.

Table of contents 1 Commonly used color spaces 2 Commercial color spaces 3 Reference color spaces 4 Obsolete color spaces

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.

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. It was (is?) used in older(?) hardware by Tektronix[?].

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

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.

Commercial color spaces

to be written

Reference color spaces

There are also a number of reference color spaces, used in more serious applications.

The reference standard usually used is the CIE Lab color space[?].

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

External links:

• Charles Poynton's Color FAQ (http://www.poynton.com/ColorFAQ)
• FAQ about color physics (http://www.colourware.co.uk/cpfaq.htm)
• Dan Bruton's Color Science (http://www.physics.sfasu.edu/astro/color)
• Color-Scheme - open source color space management package written in Scheme (http://www-swiss.ai.mit.edu/~jaffer/Color/index)