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<title>Irani-Peleg Renderer</title>
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<table align=right valign=top width=160>
<td valign=top height=600 width=160>
<a href="http://auricle.dyndns.org/ALE/">
<big>ALE</big>
<br>
Image Processing Software
<br>
<br>
<small>Deblurring, Anti-aliasing, and Superresolution.</small></a>
<br><br>
<big>
Local Operation
</big>
<hr>
localhost<br>
5393119533<br>
</table>
<p><b>[ <a href="../">Up</a> ]</b></p>
<h1>Irani-Peleg Renderer</h1>
<p>ALE implements an iterative image reconstruction algorithm based on Michal
Irani and Shmuel Peleg's paper "Improving Resolution by Image Registration",
published in <i>Graphical Models and Image Processing</i>, Vol. 53, No. 3, May,
pp. 231-239, 1991, or available at:
<p><a href="http://www.wisdom.weizmann.ac.il/~irani/abstracts/superResolution.html">http://www.wisdom.weizmann.ac.il/~irani/abstracts/superResolution.html</a>
<p>This algorithm iteratively performs two steps: first, an
approximation of <b>T</b> is projected, based on a filter approximating
<b>d<sub>j</sub></b>, and data collected during <a
href="../alignment/">alignment</a>, to create a set of simulated input frames;
second, the per-pixel error -- between these simulated input frames and the
actual input frames -- is calculated, backprojected, and subtracted from the
approximation of <b>T</b>, resulting in a new approximation of <b>T</b>.
<h2>Initial Image Approximation</h2>
<p>ALE uses the results of previous rendering steps as the initial image
approximation.</p>
<h2>Projection and Back-projection filters</h2>
ALE provides command-line options for selecting forward-projection filters,
including box filters (release 0.4.2 and later) and custom filters (release
0.4.7 and later). The back-projection filters are constructed so that the
normalized back-projection weight between a given pixel in the approximation of
<b>T</b> and a given pixel in an input frame is always equal to the
corresponding normalized forward-projection weight. This differs from the
approach taken by Irani and Peleg.
<h3>Box Filter</h3>
ALE versions 0.4.2 and later implement a box filter with user-specified
diameter. This is somewhat similar to the 'blur' operator used by some image
editing applications, and in some cases, may be an adequate approximation
for <b>d<sub>j</sub></b>.
<h3>Custom Filters</h3>
ALE versions 0.4.7 and later implement support for device-specific custom
filters, including a filter calibrated for the IBM PC Camera Pro (XVP610) in
320x240 mode. Configurability by color channel and pixel position in the input
frame is also supported, although the latter is not currently used by any
filter included with ALE.
<h3><code>stdin</code> Filter</h3>
ALE versions 0.4.7 and later support limited configuration of filters at
runtime from standard input, implemented through a custom filter called
'stdin'. This filter can be used with a script included in the source
distribution to calibrate filters for devices with unknown properties.
<h2>Transformation details</h2>
<p>ALE's method of transforming pixel areas between coordinate systems
approximates transformed pixel boundaries with axis-aligned rectangular
regions. Since boundaries are transformed into the coordinate systems of the
input frames, this approximation can be improved by using larger scale factors
(and hence reducing the size of transformed pixels).</p>
<hr>
<i>Copyright 2003 <a href="mailto:dhilvert@auricle.dyndns.org">David Hilvert</a></i>
<p>Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved.
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