PamRubber User Manual(0) PamRubber User Manual(0)
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NAMEpamrubber - a rubber-sheeting utility that stretches an image based on
control points
SYNOPSISpamrubber {-tri | -quad} [-linear] [-frame] [-randseed=N] cp1x cp1y
[cp2x cp2y [cp3x cp3y [cp4x cp4y]]] cp1x cp1y [cp2x cp2y [cp3x cp3y
[cp4x cp4y]]] [filename]
Minimum unique abbreviation of options is acceptable. You may use dou‐
ble hyphens instead of single hyphen to denote options.
DESCRIPTION
This program is part of Netpbm(1).
The pamrubber utility converts a pam image into a new image with the
contents moved around. The transformation is often called 'rubber
sheeting': you identify control points (CP) on the source image and
specify new positions for those points in the new image. pamrubber
moves all the pixels around, stretching and compressing as necessary,
as if the original image were on a sheet of rubber and you pulled on
the sheet to make the control points move to their new locations.
The new image has the same dimensions and format as the original.
The transformation can happen in two very different ways, called 'quad'
and 'tri.' With the former, you must specify four control points (for
both source and target). These are the corners of two quadrilaterals
that will act as the coordinate system for both source and target
images. Consider them as non-orthogonal (0,0), (0,1), (1,0) and (1,1)
points. This transformation comes close to the one pamperspective
does, however that program does other corrections as well.
When you specify less than four control points, the program adds con‐
trol points in the following way. With three control points, pamrubber
chooses the fourth one such that the four points form a parallelogram.
With two points, pamrubber considers them the opposite corners of a
rectangle. When you specify only one control point, pamrubber uses a
rectangle from the top left corner of the image to the single control
point.
In 'tri' mode, pamrubber conceptually cuts up the source and target
image into triangles. It Transforms within each corresponding pair of
triangles in a stretching fashion. It's like pulling on the three cor‐
ners of the triangle. In this mode, each pixel in the source image
gets mapped to a position in the target image. No pixels are lost.
When, in 'tri' mode, you specify only a single control point in the
source and target image, pamrubber creates four triangles from this
point to the four corners of the image. With two points, the program
creates six triangles from the two endpoints of the line connecting the
two points, again to the four corners of the image. Three control
points is in a way the core of this utility in 'tri' mode. Between the
three edges of the central triangle and the four edges of the image,
pamrubber constructs another seven triangles. Four control points
define two central connected triangles. In total this results in cut‐
ting the source and target image up into ten triangles.
In this case clearly a picture says more than a thousand words. There
is a graphical illustration of these various modes at
www.schaik.com/netpbm/rubber ⟨http://www.schaik.com/netpbm/rubber⟩ .
An example of how to use this type of rubber sheeting in cartography is
in the article
Visualizing the Landscape of Old-Time Tokyo
⟨http://www.isprs.org/proceedings/XXXVI/5-W1/papers/21.pdf⟩ .
PARAMETERS
The parameters are control points (cp) in pairs of x and y. The source
and target image must have the same number of control points. The min‐
imum number of values specified here is 4 for a single control point in
the source and target image. The maximum is 16 for four control points
in each image.
filename is the name of the input file. If you don't specify this, pam‐
rubber reads the image from Standard Input.
OPTIONS
<dl compact="compact">
-tri | -quad
This selects the type of rubber sheeting done. You must specify
exactly one of these options.
-linear
This determines whether pamrubber uses nearest neighbor interpo‐
lation or bilinear interpolation of four source pixels.
-frame
This option causes pamrubber to overlay the target image with
the edges of the quadrilaterals, respectively the triangles used
for the rubber sheeting. To get the same overlay for the source
image, use a pamrubber transformation with identical control
points for source and target.
-randseed=N
pamrubber randomizes some of its output. So that you can pro‐
duce repeatable results, you can choose the seed of the random
number generator with this option. If you use the same input
image and the same random number generator seed, you should
always get the exact same output. By default, pamrubber uses
the time of day as the seed, so you get slightly different out‐
put when you run the program twice on the same input.
SEE ALSOpam(1)and pamperspective(1)HISTORYpamrubber was new in Netpbm 10.54 (March 2011).
AUTHORS
Willem van Schaik wrote this program in February 2011 and contributed
it to Netpbm.
netpbm documentation February 2011 PamRubber User Manual(0)
