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In order to convert RGB or CMYK values to or from L*a*b*, the RGB or CMYK data must be linearized relative to light. The reference illuminant of the RGB or CMYK data must be known, as well as the RGB primary coordinates or the CMYK printer's reference data in the form of a color lookup table (CLUT).
An ICC profile defines the bidirectional conversion between a neutral "profile connection" color space (CIE XYZ or Lab) and a selected colorspace, in this case both RGB and CMYK. The precision of the conversion depends on the profile itself, the exact methodology, and because the gamuts do not generally match, the rendering intent and ...
Most image editing programs accept this range. Therefore, RGB should be entered into image editing programs wherever possible because it rarely (if ever) requires conversion. It is assumed that the exact meaning of the primary colors ("red" for example) is that of the sRGB standard, and that the sRGB gamma function is in use.
A "color model" is an abstract mathematical model describing the way colors can be represented as tuples of numbers (e.g. triples in RGB or quadruples in CMYK); however, a color model with no associated mapping function to an absolute color space is a more or less arbitrary color system with no connection to any globally understood system of ...
To see how this works in practice, suppose we have a particular RGB and CMYK color space, and want to convert from this RGB to that CMYK. The first step is to obtain the two ICC profiles concerned. To perform the conversion, each RGB triplet is first converted to the Profile connection space (PCS) using the RGB profile.
It was designed to encompass most of the colors achievable on CMYK color printers, but by using RGB primary chromaticities on a device such as the computer display. The Adobe RGB color space encompasses roughly 50% of the visible colors specified by the Lab color space, improving upon the gamut of the sRGB color space primarily in cyan-greens.
These formulas allow conversion between YIQ and RGB color spaces, where R, G, and B are gamma-corrected values. Values for the original 1953 NTSC colorimetry and later SMPTE C FCC standard. The following formulas assume:
Color RGB CMYK Gray 128 128 128 Black 0 0 0 White 255 255 255 Red 255 0 128 Orange 255 83 0 Yellow 255 255 0 Lime 83 255 0 Green 0 255 128 Sea blue 0 172 255 Blue 0 0 255 Purple 172 0 255 66.32.71.96 02:21, 2 Apr 2004 (UTC) Note: (or note to self :-P ) we need an RGB -> CMYK conversion formula, like on HSV color space, that'd be handy.