NAME

       pinterp - interpolate/extrapolate view from pictures

SYNOPSIS

       pinterp  [ view options ][ -t threshold ][ -z zout ][ -f type ][ -B ][ -a|q ][ -e exposure
       ][ -n ] pictfile zspec ..

DESCRIPTION

       Pinterp interpolates or extrapolates a new view from one or  more  RADIANCE  pictures  and
       sends  the  result  to  the standard output.  The input picture files must contain correct
       view  specifications,  as  maintained  by  rpict(1),   rvu(1),   pfilt(1)   and   pinterp.
       Specifically, pinterp will not work on pictures processed by pcompos(1) or pcomb(1).  Each
       input file must be accompanied by a z specification, which  gives  the  distance  to  each
       pixel  in  the  image.   If  zspec  is  an existing file, it is assumed to contain a short
       floating point number for each pixel, written in scanline order.   This  file  is  usually
       generated by the -z option of rpict(1).  If zspec is a positive number rather than a file,
       it will be used as a constant value for the corresponding image.  This may be  useful  for
       certain transformations on "flat" images or when the viewpoint remains constant.

       The  -n  option  specifies that input and output z distances are along the view direction,
       rather than absolute distances to intersection points.  This option is usually appropriate
       with a constant z specification, and should not be used with rpict(1) z files.

       The  -z  option  writes  out  interpolated z values to the specified file.  Normally, this
       information is thrown away.

       Pinterp rearranges the pixels from the input pictures to produce a reasonable estimate  of
       the  desired view.  Pixels that map within the -t threshold of each other (.02 times the z
       distance by default) are considered coincident.  With the -a  option,  image  points  that
       coincide will be averaged together, giving a smooth result.  The -q option turns averaging
       off, which means that the first mapped pixel for a given point will be used.   This  makes
       the  program  run  faster  and  take less memory, but at the expense of image quality.  By
       default, two or more pictures are averaged together, and a single picture is treated  with
       the  faster  algorithm.   This  may  be  undesirable  when  a quick result is desired from
       multiple input pictures in the first case, or a single picture is being  reduced  in  size
       (anti-aliased) in the second case.

       Portions  which  were hidden or missing in the input pictures must be "filled in" somehow,
       and a number of methods are provided by the -f option.  The default value for this  option
       is  -fa,  which  results  in  both foreground and background filling.  The foreground fill
       algorithm spreads each input pixel to cover  all  output  pixels  within  a  parallelogram
       corresponding  to  that  pixel's projection in the new view.  Without it, each input pixel
       contributes to at most one output pixel.  The background algorithm fills in those areas in
       the  final  picture  that  have  not  been filled with foreground pixels.  It does this by
       looking at the boundary surrounding each blank area and picking  the  farthest  pixels  to
       each  side,  assuming that this will make a suitable background.  The -ff option tells the
       program to use only the foreground fill, the -fb option says use only background fill, and
       the -f0 option says not to use either fill algorithm.

       Even  when  both  fill  algorithms  are used, there may still be some unfilled pixels.  By
       default, these pixels are painted black and assigned a z distance of zero.  The -fc option
       can  be  used to change the color used for unfilled pixels, and the -fz option can be used
       to set the z distance (always along the view direction).  Alternatively,  the  -fr  option
       can  be  used  to  compute these pixels using rtrace(1).  The argument to this option is a
       quoted string containing arguments for  rtrace.   It  must  contain  the  octree  used  to
       generate  the  input  pictures,  along  with  any  other  options  necessary  to match the
       calculation used for the input pictures.  The -fs option can be used to place a  limit  on
       the  distance  (in  pixels) over which the background fill algorithm is used.  The default
       value for this option is 0, which is interpreted as no limit.  A value of 1 is  equivalent
       to  turning  background  fill  off.   When  combined  with the -fr option, this is roughly
       equivalent to the -ps option of rpict(1).

       In order of increasing quality and cost, one can use the -fa  option  alone,  or  the  -fr
       option  paired  with  -fs  or  -ff  or  -f0.   The  last  combination  will  result in the
       recalculation of all pixels not adequately accounted for in the input  pictures,  with  an
       associated  computational  expense.  It is rare that the -fs option results in appreciable
       image degradation, so it  is  usually  the  second  combination  that  is  used  when  the
       background fill algorithm results in objectionable artifacts.

       The  -B  option  may be used to average multiple views read from the standard input into a
       single, blurred output picture.  This is similar to running  pinterp  multiple  times  and
       averaging  the  output  together  with a program like pcomb(1).  This option is useful for
       simulating motion blur and depth  of  field.   (See  pmdblur(1).)   The  input  views  are
       reported  in the information header of the output file, along with the averaged view.  The
       picture dimensions computed from the first view will be the ones used, regardless  whether
       or  not  the  subsequent  views  agree.  (The reported pixel aspect ratio in the output is
       determined from these original dimensions and the averaged view.)  Note that  the  expense
       of  the -fr option is proportional to the number of views computed, and the -z output file
       will be the z-buffer of the last view interpolated rather than an averaged distance map.

       In general, pinterp performs well when the output view is  flanked  by  two  nearby  input
       views,  such as might occur in a walk-through animation sequence.  The algorithms start to
       break down when there is a large difference between  the  view  desired  and  the  view(s)
       provided.  Specifically, obscured objects may appear to have holes in them and large areas
       at the image borders may not be filled by the foreground or background algorithms.   Also,
       specular  reflections and highlights will not be interpolated very well, since their view-
       dependent appearance will be incompletely compensated for by the program.  (The -a  option
       offers some benefit in this area.)

       The -e option may be used to adjust the output image exposure, with the same specification
       given as for pfilt.  The actual adjustment will be rounded to the nearest  integer  f-stop
       if the -q option is in effect (or there is only a single input picture).

EXAMPLE

       To  interpolate two frames of a walk-through animation, anti-alias to 512x400 and increase
       the exposure by 2.5 f-stops:

         pinterp -vf 27.vf -a -x 512 -y 400 -e +2.5 30.hdr 30.z 20.hdr 20.z > 27.hdr

       To extrapolate a second eyepoint for a stereo pair and recalculate background regions:

         pinterp -vf right.vf -ff -fr "-av .1 .1 .1 scene.oct" left.hdr left.z > right.hdr

       To convert an angular fisheye to a hemispherical fisheye:

         pinterp -vf fish.hdr -vth -ff fish.hdr 1 > hemi.hdr

AUTHOR

       Greg Ward

SEE ALSO

       getinfo(1), pdfblur(1), pfilt(1), pmblur(1), pmdblur(1), rpict(1), ranimate(1), rtrace(1),
       rvu(1)