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<title>Drizzling 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>Drizzling Renderer</h1>
<p>ALE versions 0.4.1 and later implement a drizzling algorithm based on that
outlined in research by Richard Hook and Andrew Fruchter.<sup>1</sup>
<h2>Algorithm</h2>
<p>In the drizzle rendering method, pixels from source images are considered to
span an area smaller than the original source pixel (a 'reduced footprint');
these source images with reduced pixel footprint are transformed for alignment,
and the reduced-area pixels from all transformed source images are combined to
form the target image, where each source pixel contributes to each target pixel
linearly with the area of overlap after transformation.
<p>ALE uses an approximation to the above approach, wherein the area of overlap
is calculated in the coordinates of the source image and then multiplied by a
factor approximating any difference in scale between the source and target
images; for the purpose of these calculations, the region of the target pixel
is approximated by a rectangle in the source coordinate system having all sides
parallel to the source image coordinate axes.
<h2>Properties</h2>
<p>Assuming small drizzling radius, drizzling is approximately the same as
convolution of discrete pixel data with a box filter having the same radius as
the chosen drizzling radius. For a very large, uniform input sequence, point
sampling with simple optics, and sufficiently small radius, drizzling should
provide an acceptable approximation of <b>T</b>.
<small>
<p><sup>1</sup> More information on drizzling can be found in the paper by Hook and Fruchter,
"Variable-Pixel Linear Combination", published in vol. 125 of the ASP
Conference Series (eds. Gareth Hunt and H. E. Payne). This paper was also
published on-line at:
<p><a href="http://www.cv.nrao.edu/adass/adassVI/hookr.html">http://www.cv.nrao.edu/adass/adassVI/hookr.html</a>
</small>
<hr>
<i>Copyright 2002, 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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