NAME
ra_ppm - convert RADIANCE picture to/from a Poskanzer Portable Pixmap
SYNOPSIS
ra_ppm [ -r ][ -a ][ -b ][ -s maxv ][ -g gamma ][ -e +/-stops ] [ input
[ output ] ]
DESCRIPTION
Ra_ppm converts between RADIANCE and Poskanzer Portable Pixmap formats.
The -g option specifies the exponent used in gamma correction; the
default value is 2.2. An exponent of 1 turns gamma correction off.
The -e option specifies an exposure compensation in f-stops (powers of
two). Only integer stops are allowed, for efficiency. The -r option
invokes a reverse conversion, from a Pixmap to a RADIANCE picture. If
the output file is missing, the standard output is used. If the input
file is missing as well, the standard input is used.
The -a option produces a standard ASCII Pixmap representation instead
of the default binary file. The file is much larger and the conversion
is much slower, which is why this format is not normally used. The -b
option forces greyscale output. The -s option controls the output
scale, which is 255 by default. If this value is set above 255, then
two bytes will be output for each component in binary mode. This may
not be understood by some PPM readers, which do not understand files
with maximum values greater than 255. The maximum allowed setting for
this parameter is 65535.
With the -r option, the type of the Pixmap input file is determined
automatically. Ra_ppm will read either greyscale or color Pixmaps,
with any precision up to a maximum scale of 65535.
NOTES
The Poskanzer Portable Bitmap Plus package contains translators between
the Pixmap format and many of the dozen or so image file "standards"
that exist. At the time of this writing, the software is free and
available by anonymous ftp from export.lcs.mit.edu (18.30.0.238) in the
file "contrib/pbmplus.tar.Z".
AUTHOR
Greg Ward
ACKNOWLEDGEMENT
Work on this program was initiated and sponsored by the LESO group at
EPFL in Switzerland and Silicon Graphics, Inc.
SEE ALSO
pfilt(1), ra_bmp(1), ra_bn(1), ra_pr(1), ra_pr24(1), ra_t8(1),
ra_t16(1), ra_tiff(1), ximage(1)