The set of colors that the average human eye can see is known as the absolute color space and has been represented with various systems of absolute coordinates. The main ones are:

• L, a, b (CIE 1976 Lab space);
• X, Y, Z (CIE 1931 XYZ space);
• x, y, Y (CIE 1931 chromaticity diagram plus luminosity).

There is only one absolute color space; the conversion from one system of coordinates to another can be carried out mathematically, without loss of information.

The profile of a device is a means of describing its gamut in terms of this absolute color space. It consists of a set of information (memorised in a file, for example) which allows the gamut of the device to be located within the absolute color space by indicating the relationship between the device’s coordinates and one kind of absolute coordinates.

The profile of a particular device correlates the device’s color coordinates to the absolute coordinates. It consists of a table or an algorithm (or method) for constructing such a table.

For example, the profile of a monitor is a table (or a method for constructing a table) which, for every set of three RGB numbers, indicates the absolute coordinates of the color produced by that set of numbers on that monitor. Here is an example of such a table, which uses the L, a, b system of absolute coordinates.

From the above diagram we can ascertain that if the monitor is asked to display the color RGB (40, 72, 150), the monitor will produce a color whose absolute Lab coordinates are (32, 10, -47).

Similarly, the profile of a CMYK printer is a table which indicates, for every set of four CMYK numbers, the absolute coordinates of the color produced by the four CMYK inks in the ratio indicated.

In the case of a scanner or digital camera, for every color which is read in RGB, the table indicates the absolute color coordinates.

If the profile does not contain the table itself, it may contain an algorithm with gives the absolute coordinates for each of the device’s colors. The algorithm, in other words, is used to construct the table.