GRASS GIS manual: r.out.ppm

NAME

r.out.ppm - Converts a GRASS raster map to a PPM image file at the pixel resolution of the currently defined region.

KEYWORDS

raster, export

SYNOPSIS

r.out.ppm
r.out.ppm help
r.out.ppm [-qG] input=name [output=name] [--verbose] [--quiet]

Flags:

-q: Run quietly
-G: Output greyscale instead of color
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

input=name: Name of input raster map
output=name: Name for new PPM file (use '-' for stdout); Default: .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 rast=[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_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

Last changed: $Date: 2008-05-16 12:09:06 -0700 (Fri, 16 May 2008) $

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