PINTERP(1) General Commands Manual PINTERP(1)
pinterp - interpolate/extrapolate view from pictures
pinterp [ view options ][ -t threshold ][ -z zout ][ -f type ][ -B ][ -a|q ][ -e exposure ][ -n ] pictfile zspec ..
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. With-
out 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 argu-
ment 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 com-
bination will result in the recalculation of all pixels not adequately accounted for in the input pictures, with an associated computa-
tional 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 anima-
tion 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).
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
getinfo(1), pdfblur(1), pfilt(1), pmblur(1), pmdblur(1), rpict(1), ranimate(1), rtrace(1), rvu(1)