r.out.ppm.1grass - Man Page

Converts a GRASS raster map to a PPM image file.

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=nameÂ [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.

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=-Â >Â 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

Author

Bill Brown, UIUC

Source Code

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

Accessed: Tuesday Mar 19 11:01:58 2024

Info

GRASS 8.3.2 GRASS GIS User's Manual