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