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)

RADIANCE                                             11/8/96                                            PFILT(1)