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r.out.ppm.1grass

NAME

r.out.ppm

DESCRIPTION

r.out.ppm converts a GRASS raster file 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 file, 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

SEE ALSO

d.out.png
r.out.ascii
r.out.mpeg
r.out.png
r.out.ppm3
r.out.tiff

AUTHOR

Bill Brown, UIUC

Last changed: $Date: 2007/01/28 22:18:17 $

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