NAME
ra_xyze - convert between RADIANCE RGBE and XYZE formats
SYNOPSIS
ra_xyze [ -r ][ -e exposure ][ -o ][ -c | -u ][ -p xr yr xg yg xb yb xw
yw ] [ input [ output ] ]
DESCRIPTION
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). The -o option may be used to specify original units,
to which the exposure compensation is applied. Otherwise, the
multiplier is in addition to any previous exposure adjustment. 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.
The -r option causes ra_xyze to produce a run-length encoded RGBE file
instead, unless -u is given, also, when it will produce a flat RGBE
file. 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.
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
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.
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
To convert RGBE output from rpict(1) into run-length encoded XYZE
format:
rpict [options] scene.oct | ra_xyze -c > scene_xyz.hdr
To prepare a RADIANCE picture for display on a calibrated NTSC monitor:
ra_xyze -r -p .670 .330 .210 .710 .140 .080 .333 .333 stand.hdr
ntsc.hdr
AUTHOR
Greg Ward
BUGS
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
pfilt(1), ra_rgbe(1), rpict(1)