Graphic Design and Print Production Fundamentals by Graphic Communications Open Textbook Collective

Author:Graphic Communications Open Textbook Collective [Graphic Communications Open Textbook Collective]
Language: eng
Format: epub
Tags: DES000000 DESIGN / General, DES007000 DESIGN / Graphic Arts / General, DES007010 DESIGN / Graphic Arts / Advertising, DES007050 DESIGN / Graphic Arts / Typography, DES012000 DESIGN / Reference, COM012000 COMPUTERS / Computer Graphics
Published: 2015-11-12T16:00:00+00:00

Perceptual and saturation intents use gamut compression, where the overall gamut space is adjusted. Relative and absolute colorimetric intents use gamut clipping, where colour matching is maintained throughout the available gamut, and out-of-gamut colours are moved to the available extremes of the destination gamut.

The perceptual intent is used mainly for RGB to CMYK transformations, which are typically image conversions. Since we are moving from a larger gamut (RGB) to a smaller gamut (CMYK), it makes sense to employ a rendering intent that preserves the overall relationship rather than one that emphasizes one-to-one colour matching within the gamut.

The saturation intent is the least relevant for colour-managed workflows. When you use this intent, colour saturation is preserved as much as possible at the expense of hue and luminance. The result is a bad colour match, but the vividness of pure colours is preserved. This intent is usually used for documents such as presentations, charts, and diagrams, but not for graphic arts jobs.

The two colorimetric intents, relative and absolute, are closely related. They are both used for CMYK to CMYK conversions where the gamuts of source and destination are closely matched or the destination is larger (typical of a proofer compared to the press it is matching). They emphasize exact colour matching for in-gamut colours and clip out-of-gamut colours.

The only difference between the two colorimetric rendering intents is in white point handling. The absolute intent pays attention to the colour of white in the source and reproduces that in the destination. Think of newspaper printing where the whitest colour is the paper that has a dull and beige tone. With an absolute rendering intent, a proofer matching the newspaper would add that beige colour to all of the white areas of the proof. This matching of white destination to white source colour is not usually necessary due to the chromatic adaptation or colour constancy that we discussed earlier. We have a built-in mechanism for adjusting to judge the overall colour relationship independent of the appearance of white. For this reason, the relative colorimetric intent is used most of the time and the white of the destination is not adjusted to simulate the white point of the source.

With all of the pieces of the colour management process clearly delineated, we can put them to use in our standard graphic arts workflow applications.

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