6.3 Color Conversion Contexts and Gamut Mapping

When Xlib converts device-independent color specifications into device-dependent specifications and vice-versa, it uses knowledge about the color limitations of the screen hardware. This information, typically called the device profile, is available in a Color Conversion Context (CCC).

Because a specified color may be outside the color gamut of the target screen and the white point associated with the color specification may differ from the white point inherent to the screen, Xlib applies gamut mapping when it encounters certain conditions:

Gamut handling methods are stored as callbacks in the CCC, which in turn are used by the color space conversion routines. Client data is also stored in the CCC for each callback. The CCC also contains the white point the client assumes to be associated with color specifications (that is, the Client White Point). The client can specify the gamut handling callbacks and client data as well as the Client White Point. Xlib does not preclude the X client from performing other forms of gamut handling (for example, gamut expansion); however, Xlib does not provide direct support for gamut handling other than white adjustment and gamut compression.

Associated with each colormap is an initial CCC transparently generated by Xlib. Therefore, when you specify a colormap as an argument to an Xlib function, you are indirectly specifying a CCC. There is a default CCC associated with each screen. Newly created CCCs inherit attributes from the default CCC, so the default CCC attributes can be modified to affect new CCCs.

Xcms functions in which gamut mapping can occur return Status and have specific status values defined for them, as follows:

Next: Creating, Copying, and Destroying Colormaps

Christophe Tronche, ch@tronche.com