Provided by: radiance_4R1+20120125-1.1_amd64 
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)