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ra_ppm (1)
NAME
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ra_ppm - convert RADIANCE picture to/from a Poskanzer Portable Pixmap |
SYNOPSIS
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ra_ppm [ -r ][ -a ][ -b ][ -s
maxv ][ -g gamma ][ -e +/-stops ] [
input [ output ] ] |
DESCRIPTION
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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. |
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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. |
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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
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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
ACKNOWLEDGEMENT
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Work on this program was initiated and sponsored by the LESO
group at EPFL in Switzerland and Silicon Graphics,
Inc. |
SEE ALSO
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