Radiance pfilt program

PFILT(1)                                                              PFILT(1)

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  expo-
       sure  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 resolu-
                 tion  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 specifica-
                 tion 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 PIXAS-
                 PECT 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 exceed 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 pic-
                 ture above the hot level are not used in  setting  the  expo-
                 sure.

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)