94 lines
3.4 KiB
HTML
94 lines
3.4 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>Drizzling Renderer</title>
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<style type="text/css">
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TABLE.ba { max-width: 678; text-align: center; padding-bottom: 15; padding-top: 5}
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TABLE.inline { padding-right: 300; clear: left}
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TD.text_table {padding-left: 2; padding-right: 2; border-width: 1}
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H2 {clear: left}
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P {max-width: none; padding-right: 300; clear: left}
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BLOCKQUOTE {padding-right: 400 }
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LI {max-width: 640; clear: left}
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P.footer {max-width: none; width: auto; padding-left: 0}
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P.header {max-width: none; width: auto; padding-left: 0}
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HR.main {max-width: 640; clear: left; padding-left: 0; margin-left: 0}
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HR.footer {clear: both}
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</style>
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</head><body>
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<table align=right valign=top width=160>
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<td valign=top height=600 width=160>
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<a href="http://auricle.dyndns.org/ALE/">
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<big>ALE</big>
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<br>
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Image Processing Software
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<br>
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<br>
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<small>Deblurring, Anti-aliasing, and Superresolution.</small></a>
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<br><br>
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<big>
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Local Operation
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</big>
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<hr>
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localhost<br>
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5393119533<br>
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</table>
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<p><b>[ <a href="../">Up</a> ]</b></p>
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<h1>Drizzling Renderer</h1>
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<p>ALE versions 0.4.1 and later implement a drizzling algorithm based on that
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outlined in research by Richard Hook and Andrew Fruchter.<sup>1</sup>
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<h2>Algorithm</h2>
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<p>In the drizzle rendering method, pixels from source images are associated
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with a square region of given radius in the source image coordinate system.
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Similarly, each pixel in the accumulated image, or target image, is associated
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with a square region, such that each square region coincides with its neighbors
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exactly at its edges. The source regions are then transformed according to the
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known alignment between source and target, and the regions from all transformed
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source images are combined to form the target image, where each source pixel
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region contributes to each target pixel region linearly with the area of
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overlap between the regions (as calculated in the target coordinate system).
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<p>ALE uses an approximation to the above approach, wherein the area of overlap
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is calculated in the coordinates of the source image and then multiplied by a
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factor approximating any difference in scale between the source and target
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images; for the purpose of these calculations, the region of the target pixel
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is approximated by a rectangle in the source coordinate system having all sides
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parallel to the source image coordinate axes.
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<h2>Properties</h2>
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<p>Assuming small drizzling radius, drizzling is approximately the same as
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convolution of discrete pixel data with a box filter having the same radius as
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the chosen drizzling radius. Given the box filter approximation, jittering
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assumption, point sampling, and sufficiently small radius, drizzling should
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provide an acceptable approximation of <b>T</b>. Until this is proven,
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however, this result should be considered unreliable.
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<small>
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<p><sup>1</sup> More information on drizzling can be found in the paper by Hook and Fruchter,
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"Variable-Pixel Linear Combination", published in vol. 125 of the ASP
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Conference Series (eds. Gareth Hunt and H. E. Payne). This paper was also
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published on-line at:
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<p><a href="http://www.cv.nrao.edu/adass/adassVI/hookr.html">http://www.cv.nrao.edu/adass/adassVI/hookr.html</a>
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</small>
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<hr>
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<i>Copyright 2002, 2003, 2004 <a href="mailto:dhilvert@auricle.dyndns.org">David Hilvert</a></i>
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<p>Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved.
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</body>
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</html>
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