r.out.ppm(1)

NAME
r.out.ppm - Converts a GRASS raster map to a PPM image file.

KEYWORDS
raster, export, output

SYNOPSIS
r.out.ppm
r.out.ppm --help
r.out.ppm [-gh] input=name [output=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

  Flags:

-g
    Output greyscale instead of color

-h
    Suppress printing of PPM header

--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 [required]
    Name of input raster map

output=name
    Name for new PPM file (use ’-’ for stdout)
    Default: <rasterfilename>.ppm

DESCRIPTION
r.out.ppm converts a GRASS raster map into a PPM image at the pixel resolution of the CURRENTLY DEFINED REGION. To get the resolution and region settings of the raster map, run:

g.region -p raster=[mapname]

before running r.out.ppm.

By default the PPM file created is 24-bit color, rawbits storage. You can use the -g flag to force r.out.ppm to output an 8-bit greyscale instead. The greyscale conversion uses the NTSC conversion:

Y = .30*Red + .59*Green + .11*Blue

One pixel is written for each cell value, so if ew_res and ns_res differ, the aspect ratio of the resulting image will be off.

NOTES
A few ppm file comments are written: the name of the GRASS raster map, resolution, etc. Although these are perfectly legal, I’ve found one PD image utility that chokes on them, so if you need a commentless PPM file, use ’out=- > outfile.ppm’. (When sending output to stdout, no comments are written.)

HINTS
You can create a PNG image with NULL values represented by a transparent background by using the PNG driver with GRASS_RENDER_TRANSPARENT set to TRUE. Alternatively, you can use the pnmtopng program from netpbm to do this:

r.out.ppm raster
pnmtopng -transparent white raster.ppm > raster.png

SEE ALSO
d.out.file, r.out.ascii, r.out.gdal, r.out.mpeg, r.out.png, r.out.ppm3

AUTHOR
Bill Brown, UIUC

SOURCE CODE

Available at: r.out.ppm source code (history)

Accessed: Wednesday Feb 04 00:58:55 2026

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