Color Rendering Intents

Rendering Intent is a transformation that describes how colors both inside and outside the gamut of the printer are mapped into the colors available on the printer. In general, the effect of rendering intents has more impact on colors that fall outside the gamut of the target output device than those colors inside the gamut.

http://www.normankoren.com/Gamut_mapping.jpg
Gamut Mapping is carried out by one of the following rendering intents. There is no standard algorithm on how the rendering intent is handled by the application creator.

1) Perceptual (Picture or Maintain Full Gamut)

The source gamut is compressed to fit into the destination gamut. It affects all colors and not just out-of-gamut colors. It aims to reduce out-of-range colors that might result in banding artifacts, and to produce pleasing colors with adequate gray balance.

2) Relative Colorimetric (Proof or Preserve Identical Color and White Point)

White point will be mapped to the theoretical white point (L=100, a=0, b=0)  and all other colors will be mapped relative to the white point, hence resulting in more precise color rendering for in-gamut colors, as they remain unchanged.

Rendered from the same image and displayed with the same scale
Top: Relative Colorimetric     Bottom: Absolute Colorimetric



 3) Absolute Colorimetric (Match or Preserve Identical Colors)

Absolute Colorimetric rendering behaves the same as Relative Colorimetric rendering except that no compression or stretching of the lightness occurs to fit the gamut of the printing material. In other words, white point will be mapped to the measured white point or paper tint  whereas relative colorimetric maps the white point to the theoretical white point.

If the source image contains colors that are lighter than the printing material, they will be clipped to the color of the printing material. If the source image's white is darker than the printing material, it will be printed with some ink in order to simulate the input white as precisely as possible. It is the most effective rendering intent for hard-copy proofing of spot colors.

4) Saturation (Graphic or Preserve Saturation)

Color is rendered to its most saturated equivalent within the gamut of the output profile. It produces appealing colors that are saturated but with poor color match, and is mostly used for business graphics (illustrations, charts, graphs, etc).

References:
www.normankoren.com/color_management.html

www.gamutvision.com/docs/gamutvision.html