X Window System Protocols and Architecture - Core Protocol - Color Modes

Color Modes

The way the X Window System handles colors can sometimes confuse users, and historically several different modes have been supported. Most modern applications use TrueColor (24-bit color, 8 bits for each of red, green and blue), but old or specialist applications may require a different color mode. Many commercial specialist applications use PseudoColor.

The X11 protocol actually uses a single 32-bit unsigned integer - called a pixelvalue - for representing a single color in most graphic operations. When transferring the intensity of primary colors, a 16 bit integer is used for each colour component. The following representations of colors exist; not all of them may be supported on a specific device.

• DirectColor: A pixel value is decomposed into separate red, green, and blue subfields. Each subfield indexes a separate colormap. Entries in all colormaps can be changed.
  • TrueColor: Same as DirectColor, except that the colormap entries are predefined by the hardware and cannot be changed. Typically, each of the red, green, and blue colormaps provides a (near) linear ramp of intensity.
• GrayScale: A pixel value indexes a single colormap that contains monochrome intensities. Colormap entries can be changed.
  • StaticGray: Same as GrayScale, except that the colormap entries are predefined by the hardware and cannot be changed.
• PseudoColor (Chunky): A pixel value indexes a single colormap that contains color intensities. Colormap entries can be changed.
  • StaticColor: Same as PseudoColor, except that the colormap entries are predefined by the hardware and cannot be changed.