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pcond (1)
NAME
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pcond - condition a RADIANCE picture for output |
SYNOPSIS
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pcond [ options ] input [ output
] |
DESCRIPTION
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Pcond conditions a Radiance picture for output to a
display or hard copy device. If the dynamic range of the
scene exceeds that of the display (as is usually the case),
pcond will compress the dynamic range of the picture
such that both dark and bright regions are visible. In
addition, certain limitations in human vision may be
mimicked in order to provide an appearance similar to the
experience one might have in the actual scene. |
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Command line switches turn flags off and on, changing
program behavior. A switch given by itself toggles the flag
from off to on or on to off depending on its previous state.
A switch followed by a '+' turns the option on explicitly. A
switch followed by a '-' turns the option off. The default
is all switches off. Other options specify output device
parameters in order to get more accurate color and
contrast. |
|
Mimic human visual response in the output. The goal of this
process is to produce output that correlates strongly with a
person's subjective impression of a scene. This switch is a
bundle of the -a, -v, -s and -c
options. |
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Defocus darker regions of the image to simulate human visual
acuity loss. This option will not affect well-lit
scenes. |
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Add veiling glare due to very bright regions in the image.
This simulates internal scattering in the human eye, which
results in a loss of visible contrast near bright
sources. |
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Use the human contrast sensitivity function in determining
the exposure for the image. A darker scene will have
relatively lower exposure with lower contrast than a
well-lit scene. |
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If parts of the image are in the mesopic or scotopic range
where the cone photoreceptors lose their efficiency, this
switch will cause a corresponding loss of color visibility
in the output and a shift to a scotopic (blue-dominant)
response function. |
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Use a center-weighted average for the exposure rather than
the default uniform average. This may improve the exposure
for scenes with high or low peripheral
brightness. |
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Set the relative importance of fixation points to
fixfrac, which is a value between 0 and 1. If
fixfrac is zero (the default), then no fixation
points are used in determining the local or global
adaptation. If fixfrac is greater than zero, then a
list of fixation points is read from the standard input.
These points are given as tab-separated (x,y) picture
coordinates, such as those produced by the -op option
of ximage(1). The foveal samples about these fixation
points will then be weighted together with the global
averaging scheme such that the fixations receive
fixfrac of the total weight. If fixfrac is
one, then only the fixation points are considered for
adaptation. |
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Rather than computing a histogram of foveal samples from the
source picture, use the precomputed histogram provided on
the standard input. This data should be given in pairs of
the base-10 logarithm of world luminance and a count for
each bin in ascending order, as computed by the
phisto(1) script. This option is useful for producing
identical exposures of multiple pictures (as in an
animation), and provides greater control over the histogram
computation. |
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Use a linear response function rather than the standard
dynamic range compression algorithm. This will prevent the
loss of usable physical values in the output picture,
although some parts of the resulting image may be too dark
or too bright to see. |
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Set the exposure adjustment for the picture to
expval. This may either be a real multiplier, or a
(fractional) number of f-stops preceeded by a '+' or '-'.
This option implies a linear response (see the -l
option above). |
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Specifies the top of the luminance range for the target
output device. That is, the luminance (in candelas/m^2) for
an output pixel value of (R,G,B)=(1,1,1). The default value
is 100 cd/m^2. |
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Specifies the dynamic range for the target output device,
which is the ratio of the maximum and minimum usable display
luminances. The default value is 32. |
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-p xr yr xg yg xb yb xw yw |
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Specifies the RGB primaries for the target output device.
These are the 1931 CIE (x,y) chromaticity values for red,
green, blue and white, respectively. Usually, the white
value is set to (.333,.333) to avoid color balance problems
in the display. |
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Use the given output file from macbethcal(1) to
precorrect the color and contrast for the target output
device. This does a more thorough job than a simple primary
correction using the -p option. Only one of -f
or -p may be given. |
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Put out the final mapping from world luminance to display
luminance to mapfile. This file will contain values
from the minimum usable world luminance to the maximum (in
candelas/m^2) in one column, and their corresponding display
luminance values (also in candelas/m^2) in the second
column. This file may be used for debugging purposes, or to
plot the mapping function created by
pcond. |
EXAMPLES
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To display an image as a person might perceive it in the
actual scene: |
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pcond -h final.pic > display.pic
ximage display.pic ; rm display.pic & |
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To do the same on a 24-bit display with known primary
values: |
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setenv DISPLAY_PRIMARIES ".580 .340 .281 .570 .153 .079
.333 .333"
pcond -h -p $DISPLAY_PRIMARIES final.pic | ximage
& |
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To prepare a picture to be sent to a film recorder destined
eventually for a slide projector with a minimum and maximum
screen luminance of 1.5 and 125 candelas/m^2,
respectively: |
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pcond -d 83 -u 125 final.pic > film.pic |
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To do the same if the output colors of the standard image
"ray/lib/lib/macbeth_spec.pic" have been
measured: |
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macbethcal -c mbfilm.xyY > film.cal
pcond -d 83 -u 125 -f film.cal final.pic >
film.pic |
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To further tweak the exposure to bring out certain areas
indicated by dragging the right mouse button over them in
ximage: |
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ximage -op -t 75 final.pic | pcond -i .5 -d 83 -u 125 -f
film.cal final.pic > film.pic |
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To use a histogram computed on every 10th animation
frame: |
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phisto frame*0.pic > global.hist
pcond -I -s -c frame0352.pic < global.hist | ra_tiff -
frame0352.tif |
REFERENCE
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Greg Ward Larson, Holly Rushmeier, Christine Piatko, ``A
Visibility Matching Tone Reproduction Operator for High
Dynamic Range Scenes,'' IEEE Transactions on
Visualization and Computer Graphics , December
1997. |
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http://www.sgi.com/Technology/pixformat/Larsonetal.html |
AUTHOR
SEE ALSO
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getinfo(1), macbethcal(1), normtiff(1), pcompos(1),
pflip(1), phisto(1), pinterp(1), pvalue(1), protate(1),
ra_xyze(1), rad(1), rpict(1), ximage(1) |
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