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.\" RCSid "$Id: ra_ppm.1,v 1.2 2003/12/09 15:59:06 greg Exp $"
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.TH RA_PPM 1 2/10/99 RADIANCE
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.SH NAME
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ra_ppm - convert RADIANCE picture to/from a Poskanzer Portable Pixmap
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.SH SYNOPSIS
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.B ra_ppm
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[
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.B \-r
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][
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.B \-a
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][
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.B \-b
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][
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.B "\-s maxv"
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][
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.B "\-g gamma"
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][
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.B "\-e +/-stops"
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]
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[
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.B input
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[
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.B output
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]
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]
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.SH DESCRIPTION
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.I Ra_ppm
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converts between RADIANCE and Poskanzer Portable Pixmap formats.
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The
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.I \-g
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option specifies the exponent used in gamma correction;
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the default value is 2.2.
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An exponent of 1 turns gamma correction off.
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The
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.I \-e
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option specifies an exposure compensation in f-stops (powers of two).
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Only integer stops are allowed, for efficiency.
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The
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.I \-r
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option invokes a reverse conversion, from a Pixmap to
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a RADIANCE picture.
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If the output file is missing, the standard output is used.
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If the input file is missing as well, the standard input is used.
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.PP
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The
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.I \-a
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option produces a standard ASCII Pixmap representation instead of
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the default binary file.
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The file is much larger and the conversion is much slower, which is
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why this format is not normally used.
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The
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.I \-b
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option forces greyscale output.
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The
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.I \-s
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option controls the output scale, which is 255 by default.
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If this value is set above 255, then two bytes will be output for each
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component in binary mode.
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This may not be understood by some PPM readers, which do not understand
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files with maximum values greater than 255.
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The maximum allowed setting for this parameter is 65535.
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.PP
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With the
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.I \-r
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option, the type of the Pixmap input file is determined automatically.
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.I Ra_ppm
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will read either greyscale or color Pixmaps, with any precision up
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to a maximum scale of 65535.
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.SH NOTES
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The Poskanzer Portable Bitmap Plus package contains translators between the
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Pixmap format and many of the dozen or so image
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file "standards" that exist.
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At the time of this writing, the software is free and available by
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anonymous ftp from export.lcs.mit.edu (18.30.0.238) in the file
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"contrib/pbmplus.tar.Z".
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.SH AUTHOR
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Greg Ward
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.SH ACKNOWLEDGEMENT
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Work on this program was initiated and sponsored by the LESO
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group at EPFL in Switzerland and Silicon Graphics, Inc.
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.SH "SEE ALSO"
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pfilt(1), ra_bmp(1), ra_bn(1), ra_pr(1), ra_pr24(1), ra_t8(1), ra_t16(1),
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ra_tiff(1), ximage(1)
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