NAME

       pfilt - filter a RADIANCE picture

SYNOPSIS

       pfilt [ options ] [ file ]

DESCRIPTION

       Pfilt  performs  anti-aliasing  and  scaling on a RADIANCE picture.  The program makes two
       passes on the picture file in order to set the exposure to the correct average value.   If
       no file is given, the standard input is read.

       -x res    Set  the  output  x resolution to res.  This must be less than or equal to the x
                 dimension of the target device.  If res is given as a slash followed by  a  real
                 number,  the  input  resolution  is  divided  by  this  number to get the output
                 resolution.  By default, the output resolution is the same as the input.

       -y res    Set the output y resolution to res,  similar  to  the  specification  of  the  x
                 resolution above.

       -p rat    Set  the  pixel  aspect  ratio to rat.  Either the x or the y resolution will be
                 reduced so that the pixels have this ratio for the specified picture.  If rat is
                 zero, then the x and y resolutions will adhere to the given maxima.  Zero is the
                 default.

       -c        Pixel aspect ratio is being corrected, so do not  write  PIXASPECT  variable  to
                 output file.

       -e exp    Adjust  the  exposure.   If  exp  is  preceded  by a '+' or '-', the exposure is
                 interpreted in f-stops (ie. the power of two).  Otherwise, exp is interpreted as
                 a  straight  multiplier.  The individual primaries can be changed using -er, -eg
                 and -eb.  Multiple exposure options have a cumulative effect.

       -t lamp   Color-balance the image as if it were illuminated by fixtures of the given type.
                 The  specification must match a pattern listed in the lamp lookup table (see the
                 -f option below).

       -f lampdat
                 Use the specified lamp lookup table rather than the default (lamp.tab).

       -1        Use only one pass on the file.   This  allows  the  exposure  to  be  controlled
                 absolutely,  without any averaging.  Note that a single pass is much quicker and
                 should be used whenever the desired exposure is known and star patterns are  not
                 required.

       -2        Use two passes on the input.  This is the default.

       -b        Use   box   filtering  (default).   Box  filtering  averages  the  input  pixels
                 corresponding to each separate output pixel.

       -r rad    Use Gaussian filtering with a radius of rad relative to the output  pixel  size.
                 This  option  with a radius around 0.6 and a reduction in image width and height
                 of 2 or 3 produces the highest quality pictures.   A  radius  greater  than  0.7
                 results in a defocused picture.

       -m frac   Limit  the influence of any given input pixel to frac of any given output pixel.
                 This option may be used to mitigate  the  problems  associated  with  inadequate
                 image  sampling, at the expense of a slightly blurred image.  The fraction given
                 should not be less than the output picture dimensions  over  the  input  picture
                 dimensions  (x_o*y_o/x_i/y_i),  or  blurring  will  occur over the entire image.
                 This option implies the -r option for Gaussian filtering, which  defaults  to  a
                 radius of 0.6.

       -h lvl    Set intensity considered ``hot'' to lvl.  This is the level above which areas of
                 the image will begin to exhibit star  diffraction  patterns  (see  below).   The
                 default is 100 watts/sr/m2.

       -n N      Set  the  number  of  points  on star patterns to N.  A value of zero turns star
                 patterns off.  The default is 0.  (Note that two passes are  required  for  star
                 patterns.)

       -s val    Set  the spread for star patterns to val.  This is the value a star pattern will
                 have at the edge of the image.  The default is .0001.

       -a        Average hot spots as well.  By default, the areas of the picture above  the  hot
                 level are not used in setting the exposure.

ENVIRONMENT

       RAYPATH        directories to search for lamp lookup table

FILES

       /tmp/rt??????

AUTHOR

       Greg Ward

SEE ALSO

       getinfo(1),  ies2rad(1),  pcompos(1), pflip(1), pinterp(1), pvalue(1), protate(1), rad(1),
       rpict(1), ximage(1)