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.\" RCSid "$Id: ra_xyze.1,v 1.5 2008/11/10 19:08:17 greg Exp $" |
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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 \-o |
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][ |
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.B \-c |
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| |
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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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The |
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.I \-o |
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option may be used to specify original units, to which the exposure |
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compensation is applied. |
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Otherwise, the multiplier is in addition to any previous exposure adjustment. |
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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, unless |
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.I \-u |
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is given, also, when it will produce a flat RGBE file. |
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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 be 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.hdr |
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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.hdr ntsc.hdr |
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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), pvalue(1), ra_rgbe(1), rpict(1) |
