g.pnmcomp(1)

NAME
g.pnmcomp - Overlays multiple PPM image files.

KEYWORDS
general, display

SYNOPSIS
g.pnmcomp
g.pnmcomp --help
g.pnmcomp input=name[,name,...] [mask=name[,name,...]] [opacity=float[,float,...]] output=name [output_mask=name] width=integer height=integer [bgcolor=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

  Flags:

--overwrite
    Allow output files to overwrite existing files

--help
    Print usage summary

--verbose
    Verbose module output

--quiet
    Quiet module output

--ui
    Force launching GUI dialog

  Parameters:

input=name[,name,...] [required]
    Name of input file(s)

mask=name[,name,...]
    Name of input mask file(s)

opacity=float[,float,...]
    Layer opacities

output=name [required]
    Name for output file

output_mask=name
    Name for output mask file

width=integer [required]
    Image width

height=integer [required]
    Image height

bgcolor=name
    Background color
    Either a standard color name or R:G:B triplet

DESCRIPTION
g.pnmcomp isn’t meant for end users. It’s an internal tool for use by wxGUI.

In essence, g.pnmcomp generates a PPM image by overlaying a series of PPM/PGM pairs (PPM = RGB image, PGM = alpha channel).

NOTES
The intention is that d.* modules will emit PPM/PGM pairs (by way of the PNG-driver code being integrated into Display Library). The GUI will manage a set of layers; each layer consists of the data necessary to generate a PPM/PGM pair. Whenever the layer "stack" changes (by adding, removing, hiding, showing or re-ordering layers), the GUI will render any layers for which it doesn’t already have the PPM/PGM pair, then re-run g.pnmcomp to generate the final image (just redoing the composition is a lot faster than redrawing everything).

A C/C++ GUI would either have g.pnmcomp’s functionality (image composition) built-in, or would use the system’s graphics API to perform composition (for translucent layers, you would need OpenGL or the Render extension, or something else which supports translucent rendering).

Tk doesn’t support transparent (masked) true-colour images (it does support transparent GIFs, but that’s limited to 256 colours), and an image composition routine in Tcl would be unacceptably slow, hence the existence of g.pnmcomp.

SEE ALSO
g.cairocomp

AUTHOR
Glynn Clements

SOURCE CODE

Available at: g.pnmcomp source code (history)

Accessed: Tuesday Jun 16 04:04:24 2026

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