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.\" RCSid "$Id: pfilt.1,v 1.6 2023/12/08 17:56:26 greg Exp $"
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.TH PFILT 1 11/8/96 RADIANCE
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.SH NAME
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pfilt - filter a RADIANCE picture
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.SH SYNOPSIS
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.B pfilt
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[
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.B options
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]
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[
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.B file
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]
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.SH DESCRIPTION
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.I Pfilt
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performs anti-aliasing and scaling on a RADIANCE picture
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or hyperspectral image.
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The program makes two passes on the picture file in order to
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set the exposure to the correct average value.
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If no
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.I file
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is given, the standard input is read.
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.TP 10n
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.BI -x \ res
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Set the output x resolution to
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.I res.
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This must be less than or equal to the x dimension
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of the target device.
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If
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.I res
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is given as a slash followed by a real number, the input resolution
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is divided by this number to get the output resolution.
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By default, the output resolution is the same as the input.
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.TP
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.BI -y \ res
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Set the output y resolution to
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.I res,
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similar to the specification of the x resolution above.
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.TP
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.BI -p \ rat
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Set the pixel aspect ratio to
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.I rat.
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Either the x or the y resolution will be reduced so that the pixels have
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this ratio for the specified picture.
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If
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.I rat
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is zero, then the x and y resolutions will adhere to the given maxima.
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Zero is the default.
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.TP
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.BI -c
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Pixel aspect ratio is being corrected, so do not write PIXASPECT
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variable to output file.
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.TP
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.BI -e \ exp
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Adjust the exposure.
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If
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.I exp
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is preceded by a '+' or '-', the exposure is interpreted in f-stops
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(ie. the power of two).
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Otherwise,
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.I exp
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is interpreted as a straight multiplier.
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The individual primaries can be changed using
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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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Multiple exposure options have a cumulative effect.
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.TP
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.BR -t \ lamp
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Color-balance the image as if it were illuminated by fixtures of
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the given type.
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The specification must match a pattern listed in the lamp
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lookup table (see the \-f option below).
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.TP
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.BR -f \ lampdat
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Use the specified lamp lookup table rather than the default (lamp.tab).
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.TP
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.BR \-1
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Use only one pass on the file.
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This allows the exposure to be controlled absolutely, without
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any averaging.
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Note that a single pass is much quicker and should be used whenever
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the desired exposure is known and star patterns are not required.
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.TP
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.BR \-2
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Use two passes on the input.
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This is the default.
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.TP
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.BR \-b
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Use box filtering (default).
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Box filtering averages the input pixels corresponding
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to each separate output pixel.
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.TP
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.BI -r \ rad
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Use Gaussian filtering with a radius of
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.I rad
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relative to the output pixel size.
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This option with a radius around 0.6 and a reduction in image width and
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height of 2 or 3 produces the highest quality pictures.
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A radius greater than 0.7 results in a defocused picture.
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.TP
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.BI -m \ frac
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Limit the influence of any given input pixel to
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.I frac
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of any given output pixel.
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This option may be used to mitigate the problems associated with
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inadequate image sampling, at the expense of a slightly blurred
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image.
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The fraction given should not be less than the output picture dimensions
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over the input picture dimensions (x_o*y_o/x_i/y_i), or blurring
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will occur over the entire image.
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This option implies the
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.I \-r
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option for Gaussian filtering, which defaults to a radius of 0.6.
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.TP
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.BI -h \ lvl
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Set intensity considered ``hot'' to
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.I lvl.
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This is the level above which areas of the image will begin
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to exhibit star diffraction patterns (see below).
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The default is 100 watts/sr/m2.
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.TP
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.BI -n \ N
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Set the number of points on star patterns to
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.I N.
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A value of zero turns star patterns off.
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The default is 0.
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(Note that two passes are required for star patterns.)\0
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.TP
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.BI -s \ val
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Set the spread for star patterns to
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.I val.
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This is the value a star pattern will have at the
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edge of the image.
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The default is .0001.
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.TP
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.BR \-a
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Average hot spots as well.
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By default, the areas of the picture above the hot level
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are not used in setting the exposure.
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.SH ENVIRONMENT
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RAYPATH directories to search for lamp lookup table
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.SH FILES
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/tmp/rt??????
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.SH AUTHOR
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Greg Ward
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.SH "SEE ALSO"
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getinfo(1), ies2rad(1), pcomb(1), pcompos(1), pflip(1), pinterp(1),
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pvalue(1), protate(1), rad(1), rcomb(1), rmtxop(1),
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rpict(1), ximage(1)
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