Pixel maps are a feature of base OpenGL which allow certain look-up operations to be performed. OpenGL maintains tables which map:
Tables that map color indices to RGBA values are used automatically whenever an image with a color index format is transferred to a destination which requires an RGBA image. For example, performing a glDrawPixels() of a color index image to an RGBA framebuffer would result in application of the I to RGBA pixel maps. Other tables are enabled with the commands glPixelTransferGL_ MAP_COLOR, 1(GL_ MAP_COLOR, 1) and glPixelTransferGL_ MAP_STENCIL, 1(GL_ MAP_STENCIL, 1).
Pixel maps are defined using the glPixelMap() command and queried using the glGetPixelMap() command. Details on the use of these commands may be found in . The sizes of the pixel maps are not tied together in any way. For example, the R to R pixel map does not need to be the same size as the G to G pixel map.
Each system provides a constant, GL_ MAX_PIXEL_MAP_TABLE, which gives the maximum size of a pixel map which may be defined.