The International Color Consortium (ICC) is an organisation which was founded by Adobe, Agfa, Apple, Kodak, Microsoft, Silicon Graphics and Sun, whom about another 60 companies have since joined.

ICC has been operating since 1993, and its aim is to develop and maintain a standard multi-platform color management system at operating system level. ICC specifications concern norms of construction and use of profiles.

The absolute space for converting colors, known as Profile Connection Space (PCS), supported the ICC standard are the space XYZ (CIE 1931) and the space Lab (CIE 1976). Every profile must be based on one of these PCS and every color engine must support both.

There are seven classes of profiles defined by the ICC standard. Three of these concern the devices and are the most common ones:

• input (scnr), for scanners and digital cameras;
• display (mntr), for monitors, both CRT and LCD;
• output (prtr), for printers and video recorders.

The other four classes include ICC profiles for special purposes:

• device link (link), direct connection of devices;
• color space conversion (spac), conversion between color spaces;
• named color (nmcl), spot colors, e.g. Pantone;
• abstract (abst), abstract spaces.

The device profiles, apart from scnr type, are two-directional. In other words, they have the information to convert from device to PCS and vice versa. The scnr type profiles are one-directional, having only the part which converts from device to PCS.

A device profile can memorize its information in two ways:

• using algorithms based on matrices and linearisation curves (matrix profile);
• using lookup tables (table profile).

An ICC profile also contains other information, such as the preferred CMM, the preferred rendering intent, the PCS used and the version.

As well as existing as independent files, ICC profiles (apart from abst and link) can be embedded into images saved in the following graphic forms:

• PICT;
• EPS;
• TIFF;
• JFIF (JPEG graphic format);
• GIF

and can be inserted into the print stream created by an application and directed at the print driver.

The ICC standard makes provision for the four rendering intents, which we examined in detail in the previous pages:

• perceptual;
• relative colorimetric;
• saturation;
• absolute colorimetric.

The information regarding rendering intents is memorized in the profiles. Absolute colorimetric rendering is not implemented directly (i.e. it does not have a table or an algorithm of its own); it is constructed by modifying the relative colorimetric information, bearing the white point in mind.

In a table profile, there will be up to three device to PCS conversion tables (one for each type of rendering intent), and up to another three for the reverse. In ICC terminology, these tables are referred with the following tags:

• from device to PCS (e.g. from CMYK to Lab):
  • AtoB0: perceptual;
  • AtoB1: relative colorimetric;
  • AtoB2: saturation;
• from PCS to device (eg from Lab to CMYK):
  • BtoA0: perceptual;
  • BtoA1: relative colorimetric;
  • BtoA2: saturation.

Thus, A denotes the device color space and B the profile connection space (PCS). 0 denotes perceptual rendering, 1 relative colorimetric and 2 saturation. When it is necessary to denote the absolute colorimetric rendering, 3 is used. (Note that AtoB may also be written A2B.)

The ideal case is one in which one tag corresponds to one table, but the same table can almost always be refferred to by more than one tag. The tag and the table to which it refers are two separate things and if a profile contains a tag for a specific rendering intent, it does not necessarily contain the table for that rendering intent. There are normally more tags than tables.

Every profile contains the tag for the preferred rendering intent (normally perceptual or relative colorimetric). This is generally ignored by the applications. Nevertheless, if it were respected, the tables or algorithms chosen in both the source and destination profiles would be those of the source profile's rendering intent.

ICC standard conformant color management occurs on-host, that is, within an application or in the print driver (i.e. before printing).

It consists of a conversion (carried out by a color engine) from a source profile (read from device to PCS) to a destination profile (read from PCS to device) using the relevant rendering intent data.

The conversion is carried out by the color engine or CMM (color management module/method).