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)