An ICC input profile describes typically a scanner or digital camera color gamut.

All scanners and digital cameras (monochrome apart) read colors in RGB. Some older professional scanners have a built-in algorithm which converts RGB to CMYK and cannot be disactivated. Hence the possibility that the input profile may be CMYK.

An input profile is one-directional, allowing the conversion from device coordinates to absolute, because the scanner or camera is always a source device, never a destination.

As the input profile is always a source profile, the rendering intent plays no part and therefore there is only one conversion. Such conversion can be specified with a table (from RGB or CMYK to Lab or XYZ) or with an algorithm (matrix profile, from RGB to XYZ).

Summarizing, the ICC input profile has the following characteristics:

• is one-directional, from device to PCS;
• only one rendering intent is required;
• may be either, depending on the type of device:
  • RGB, in which case may be either:
    • in matrix form (the PCS must be XYZ);
    • in table form (the PCS can be Lab D50 or XYZ);
  • CMYK, in which case must be
    • in table form (the PCS can be Lab D50 or XYZ).

Most scanner ICC profiles are RGB to Lab tables with the XYZ coordinates of the white point and a table as below.

The profile may also contain information about one-dimensional curves before or after the matrix or table.

There are no specifications for the purpose of these curves; their meaning is decided by the software which created the profile. They may be linear curves (which do nothing) or special curves which do something bizarre. The general structure of an RGB to Lab (or XYZ) input profile is illustrated below