Perceptual and Relative Colormetric Intents

Perceptual and Relative Colorimetric Rendering Intents

Perceptual and relative colorimetric rendering are probably the most useful conversion types for digital photography. Each places a different priority on how they render colors within the gamut mismatch region. Relative Colorimetric maintains a near exact relationship between the in gamut colors, even if this clips out of gamut colors. In contrast perceptual rendering tries to also preserve some of the relationship between out of gamut colors, even if this results in inaccuracies for in gamut colors.
Perceptual maintains smooth color gradations throughout by compressing the entire tonal range, whereas relative colorimetric clips out of gamut colors.
Even though perceptual rendering compresses the entire gamut it does remap the central tones more precisely. The exact conversion depends on what the CMM is used for
Adobe ACE Microsoft ICM and Apple color sync are some of the most common

Absolute colorimetric Intent
Absolute is similar to relative colorimetric in that it preserves in gamut colors and clips those out of gamut, they differ in how each handles the white point, The white point is the location of the purest and lightest white in a color space. If we drew a line between the white point and the black point in a color space this would pass through the most neutral colors. The location of this lines changes between color spaces. Relative colorimetric skews the colors within the gamut so that the white point of one aligns with that of the other. While absolute colorimetric preserves colors exactly without regard to changing the white point. Absolute colorimetric preserves the white point while relative displaces the colors so that the old white point aligns with the new one. The exact preservation of colors may sound appealing, however relative colorimetric adjusts the white point for a reason. Without this adjustment absolute colorimetric results in unsightly color shifts and as such is rarely of interest to photographers.
The color shift results because the white point of the new color space usually needs to align with that of the light source or paper tint used. If one was printing to a color space for a paper with a bluish tint. Absolute colorimetric would ignore this tint change. Relative colorimetric would compensate to account for the fact that the whitest and lightest point has a tint of blue.
-Saturation rendering intent tries to preserve saturated colors, and is most useful when trying to retain color purity in computer graphics when converting into a larger color space. If the original RGB device contained pure (fully saturated) colors, then saturation intent ensures that those colors will remain saturated in the new color space — even if this causes the colors to become relatively more extreme.
Saturation intent is not desirable for photos because it does not attempt to maintain color realism. Maintaining color saturation may come at the expense of changes in hue and lightness, which is usually an unacceptable trade-off for photo reproduction. On the other hand, this is often acceptable for computer graphics such as pie charts.