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pinterp (1)
NAME
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pinterp - interpolate/extrapolate view from pictures |
SYNOPSIS
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pinterp [ view options ][ -t threshold ][
-z zout ][ -f type ][ -B ][
-a|q ][ -e exposure ][ -n ] pictfile
zspec .. |
DESCRIPTION
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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),
rview(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. |
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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. |
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The -z option writes out interpolated z values to the
specified file. Normally, this information is thrown
away. |
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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. |
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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. |
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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). |
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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. |
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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 also pdfblur(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. |
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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.) |
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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
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To interpolate two frames of a walk-through animation,
anti-alias to 512x400 and increase the exposure by 2.5
f-stops: |
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pinterp -vf 27.vf -a -x 512 -y 400 -e +2.5 30.pic 30.z
20.pic 20.z > 27.pic |
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To extrapolate a second eyepoint for a stereo pair and
recalculate background regions: |
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pinterp -vf right.vf -ff -fr "-av .1 .1 .1
scene.oct" left.pic left.z > right.pic |
AUTHOR
SEE ALSO
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