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.\" RCSid "$Id"
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.TH RA_XYZE 1 5/30/96 RADIANCE
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.SH NAME
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ra_xyze - convert between RADIANCE RGBE and XYZE formats
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.SH SYNOPSIS
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.B ra_xyze
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[
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.B \-r
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][
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.B "\-e exposure"
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][
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.B \-c
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.B \-u
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][
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.B "\-p xr yr xg yg xb yb xw yw"
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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_xyze
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converts between RADIANCE RGBE (red,green,blue,exponent) and XYZE
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(CIE X,Y,Z,exponent) formats.
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The
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.I \-e
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option specifies an exposure compensation, which may be given as
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a decimal multiplier or in f-stops (powers of two).
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By default,
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.I ra_xyze
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produces a flat XYZE RADIANCE picture file from any type of RADIANCE
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input picture.
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To override these defaults, the
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.I \-c
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option may be used to specify run-length encoded output,
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or the
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.I \-u
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option may be used to specify a flat output.
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.PP
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The
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.I \-r
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option causes
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.I ra_xyze
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to produce a run-length encoded RGBE file instead.
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The
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.I \-p
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option may be used to override the standard RADIANCE RGB primary
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colors to tailor the image for a particular output device or
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representation.
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The eight floating-point arguments to this option are the 1931
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CIE (x,y) chromaticity coordinates of the three RGB primaries
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plus the white point, in that order.
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The new primaries will be recorded in the header of the output file,
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so that the original information may be fully recovered later.
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It is not necessary that the input file by in XYZE format.
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Th
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.I \-r
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option may therefore be used to convert from one RGB primary
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representation to another using the
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.I \-p
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option.
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.PP
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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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.SH NOTES
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The CIE standard used is the 1931 2-degree observer, and the
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correct output representation relies on the original RADIANCE
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input description being defined properly in terms of the standard
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RADIANCE RGB primaries, whose CIE (x,y) chromaticity values are
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defined in the header file in src/common/color.h.
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In this same file is a standard for the luminous efficacy of white
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light (WHTEFFICACY), which is used as a conversion between lumens
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and watts throughout RADIANCE.
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This same factor is applied by
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.I ra_xyze
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when converting between the radiometric units of the RGBE format
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and the photometric units of the XYZE format.
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The purpose of this factor is to ensure that the Y component of
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the CIE representation is luminance in units of candelas/meter^2.
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.PP
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Most of the RADIANCE picture filters should work uniformly on either
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RGBE or XYZE files, so it is not necessary to convert back to RGBE
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format except for conversion or display, in which case the correct
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primaries for the chosen output device should be specified with the
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.I \-p
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option if they are known.
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.SH EXAMPLES
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To convert RGBE output from
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.I rpict(1)
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into run-length encoded XYZE format:
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.IP "" .2i
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rpict [options] scene.oct | ra_xyze -c > scene_xyz.pic
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.PP
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To prepare a RADIANCE picture for display on a calibrated NTSC monitor:
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.IP "" .2i
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ra_xyze -r -p .670 .330 .210 .710 .140 .080 .333 .333 stand.pic ntsc.pic
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.SH AUTHOR
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Greg Ward
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.SH BUGS
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Any color correction applied to the original image is not removed
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or translated by
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.I ra_xyze,
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and it may result in color shifts in the output.
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If color preservation is important and the correction is unwanted,
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it is best to remove it with
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.I pfilt(1)
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using the
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.I \-er,
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.I \-eg
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and
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.I \-eb
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options first.
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(Simply look at the header and apply the reciprocal primaries of all
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COLORCORR= lines multiplied together.)
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Better still, get the picture before color correction is applied.
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.SH "SEE ALSO"
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pfilt(1), ra_rgbe(1), rpict(1)
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