Introduction to Color Management System (CMS / CMM) and ICC Profiles

Color Management System / Module (CMS/CMM)

In digital printing combining RGB (matrix-based) or CMYK (LUT based) source ICC profiles with CMYK (LUT based) or RGB (LUT-based) destination ICC profiles leads to the most common profile chain for the color-managed transformation. Display destination profiles use matrix-based ICC profiles. CIE Lab (D50/2°) serves as the profile connection space.

RGB matrix-based and CIE Lab D65/10° (other illuminant/observer) used as so-called working color space (source) exist but are rare.

Device Link Profiles define the final color transformation table from the source to the output color space and not using the PCS of the CMS, therefore. In the Ergosoft RIP, Device Link Profiles are selected under the input color management sections. The printer profile of the activate Print Environment is ignored when selected.

A first additional loop in the profile transformation chain is inserted when an intermediate color space for e.g., proofing or color normalizing (or PDF-X Output Intent) is activated.

A second transformation loop is applied to generate more color-accurate soft proofs shown in the print preview pane within the Ergosoft RIP.

Matrix And LUT Based ICC Profiles

A matrix profile is a mathematical model made up of the three primary colorants of the device and some simple tonal curves, referred to as a 3 x 3 matrix.

A LUT-based profile contains much more information, consisting of a table of numbers that allows you to find an input value and its corresponding output value.

Matrix based profiles are used for simpler devices, such as scanners and monitors, while LUT-based profiles are used for more complex devices, such as printers. There are many different color spaces available, and most of them are matrix based. The advantages of a matrix-based profile are conversion speed and the ability to convert back and forth.

Ergosoft’s device ICC color profilers (ColorGPS RGB and ColorGPS CMYK++) generate LUT-based profiles. The most important lookup tables and contents are:

Lab to device (B2A) known as forward tables: Three lookup tables exist (Perceptual, Saturation, Colorimetric). These main tables are used to transform colors from the PCS to output. Each table consists of an additional output channel curve, normally set to linear.

Device to Lab (A2B) known as backward tables: Three lookup tables exist (Perceptual, Saturation, Colorimetric). These tables are used to transform colors back from output to PCS. These tables are also used to generate previews in cases in which no preview tables exist.

Preview tables: Ergosoft profilers are always calculating and writing high-precision preview tables into the ICC profiles. Three preview lookup tables exist (Perceptual, Saturation, Colorimetric). All Ergosoft preview modules and preview views are using these dedicated preview tables whenever available in the profile. Within the Ergosoft RIP, these preview tables are also used for gamut previews and out of gamut estimations, rather than the Gamut table or the A2B tables, which normally lead to less accurate results.

Media White Point tag: The measured and stored media white point is being applied to the Colorimetric output table (B2A) when Absolute Colorimetric Rendering Intent is used. The default content of the Colorimetric tables is Relative Colorimetric.