xstdcmap

xstdcmap [-best | -default | -gray | -red | -green | -blue | -delete] [-namestoo] [-verbose] [-display display]

-best
    Installs an RGB_BEST_MAP standard colormap. This map provides the best visual approximation for the display.

-default
    Installs an RGB_DEFAULT_MAP standard colormap. This is typically a basic colormap providing a good range of colors.

-gray
    Installs an RGB_GRAY_MAP standard colormap, optimized for grayscale representation.

-red
    Installs an RGB_RED_MAP standard colormap, providing a ramp for red intensity.

-green
    Installs an RGB_GREEN_MAP standard colormap, providing a ramp for green intensity.

-blue
    Installs an RGB_BLUE_MAP standard colormap, providing a ramp for blue intensity.

-delete
    Deletes the specified standard colormaps (or all if no colormap type is explicitly given).

-namestoo
    Creates standard colormaps for all known standard colormap atoms, including those beyond the primary RGB_*_MAP types.

-verbose
    Prints verbose messages during execution, showing details about the colormap operations.

-display display
    Specifies the X server to connect to. The display argument should be in the format hostname:displaynumber.screennumber.

xstdcmap is an X Window System utility designed to manage and install standard colormaps for an X display.

In older X setups, particularly those with pseudo-color (8-bit) displays, applications often relied on predefined colormaps (like RGB_BEST_MAP or RGB_DEFAULT_MAP) to correctly render colors. xstdcmap allows a user to explicitly install one of these standard colormaps, making it available for applications that query for them via specific X atoms.

While less crucial in the era of true-color (24-bit or 32-bit) displays, it remains relevant for legacy applications, specific scientific visualization tools, or niche environments that still utilize indexed color models. The utility can install various types of standard colormaps, such as optimized "best" maps, default maps, or grayscale maps, as well as separate red, green, and blue ramp maps. It can also be used to delete existing standard colormaps.

xstdcmap is primarily useful for pseudo-color (8-bit) X displays. It is less relevant for modern true-color (24-bit or 32-bit) displays where applications typically manage their own colors directly without relying on shared colormaps. Misuse or incorrect application of standard colormaps can potentially affect color rendering for other legacy applications on the same display.

Standard colormaps are specific shared colormaps defined by the X Consortium, identified by atoms like RGB_BEST_MAP, RGB_DEFAULT_MAP, etc. They allow applications to share a common set of colors, which was essential on pseudo-color displays where only a limited number of colors could be displayed simultaneously. By installing a standard colormap, xstdcmap makes a predefined color palette available for applications that expect or request it.

Applications often query for standard colormaps through the XDGA_STANDARD_CMAP atom on the root window of the X display. When xstdcmap installs a standard colormap, it sets this property, making the installed colormap discoverable and usable by applications designed to look for it.

xstdcmap is an integral part of the X.Org (and previously XFree86 and X11R5/X11R6) distribution. Its functionality predates widespread true-color displays, originating in an era where shared colormaps were crucial for efficient color management on hardware with limited color capabilities. While its primary use case has diminished with modern display technology, it remains available for compatibility with legacy software and specific industrial or scientific applications that rely on indexed color models and standard X colormaps. The command has not undergone significant development or changes in recent years, maintaining its original purpose.

xdpyinfo(1), X(7)