126 lines
5.1 KiB
XML
126 lines
5.1 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN"
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"file:///usr/share/xml/docbook/schema/dtd/4.4/docbookx.dtd">
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<chapter id="user-chains"><title>Rendering Chains</title>
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<p>The ALE incremental renderer is configured using rendering chains. Rendering chains are
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constructed hierarchically from: invariants, SSFEs (scaled sampling filters
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with exclusion), SSFs (scaled sampling filters), and sampling filters. Each of
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these components is described in a section below. Defaults are outlined in the
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final section.</p>
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<s><t>Chains</t>
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<p>The chain is the top level of the rendering chain hierarchy, and is composed of a
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sequence of invariants. Syntactically, a chain is specified as a number of
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invariants separated by commas:</p>
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<p><code>invariant<sub>1</sub>,invariant<sub>2</sub>,invariant<sub>3</sub>,...,invariant<sub>n</sub></code></p>
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<p>Each rendered pixel is assigned a value at the first invariant whose weight
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exceeds the weight threshold, or otherwise at the last invariant in the sequence.</p>
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<s><t>Chain Options</t>
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<pre>
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--wt <w> Set weight threshold for defined pixels [default is 0.8 in v0.8.0; 0.1 in v0.8.1 and later]
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--dchain <g> Use chain <g> to render the default output.
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--ochain <g> <o> Use chain <g> to render output file <o>.
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--achain <g> Use chain <g> to render the alignment reference image.
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--3d-chain <g> Use chain <g> by default to render 3d output. [0.8.4 and later]
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</pre>
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</s><s><t>Chain Examples</t>
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<pre>
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triangle:2 ALE 0.6.0 merging (roughly)
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fine:box:1 Drizzling (roughly)
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fine:sinc*lanc:8 High-frequency preservation
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last:nex:sinc*lanc:8 Useful for video stabilization
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fine:box:1,triangle:2 Multi-resolution rendering
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fine:sinc*lanc:8,sinc*lanc:8 Multi-resolution rendering
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</pre>
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</s></s><s><t>Invariants</t>
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<p>Invariants determine whether the rendered pixel value should be taken from a
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single frame, or from an average of all frames. If from a single frame, it can
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be the first, last, minimal, or maximal pixel value. Averages include mean
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and, in versions 0.8.1 and later, the median. By default, the mean is used.
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(Note that using the median value may require allocation of a quantity of
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memory linear in the number of frames.) The syntax is as follows:</p>
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<table>
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<caption>Invariant types</caption>
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<tr><th>Syntax</th><th>Description</th></tr>
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<tr><td>avg:<SSFE></td><td>Mean value</td></tr>
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<tr><td>median:<SSFE></td><td>Median value</td></tr>
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<tr><td>max:<SSFE></td><td>Maximum value</td></tr>
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<tr><td>min:<SSFE></td><td>Minimum value</td></tr>
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<tr><td>first:<SSFE></td><td>First value</td></tr>
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<tr><td>last:<SSFE></td><td>Last value</td></tr>
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<tr><td><SSFE></td><td>Same as avg:<SSFE></td></tr>
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</table>
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</s><s><t>Scaled Sampling Filter with Exclusion (SSFE)</t>
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<p>SSFEs qualify SSFs, indicating whether exclusion regions should be honored.</p>
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<table>
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<caption>Scaled sampling filter with exclusion (SSFE) types</caption>
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<tr><th>Syntax</th><th>Description</th></tr>
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<tr><td>ex:<SSF></td><td>Honor exclusion regions</td></tr>
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<tr><td>nex:<SSF></td><td>Don't honor exclusion regions</td></tr>
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<tr><td><SSF></td><td>Same as ex:<SSF></td></tr>
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</table>
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</s><s><t>Scaled Sampling Filter (SSF)</t>
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<p>SSFs indicate whether filtering should occur at the resolution of the output
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image, or at the minimum of input and output image resolutions. The former prevents loss
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of details; the latter prevents aliasing.</p>
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<table>
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<caption>Scaled sampling filter (SSF) types</caption>
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<tr><th>Syntax</th><th>Description</th></tr>
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<tr><td>fine:<SF></td><td>Filter at full output image resolution</td></tr>
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<tr><td>coarse:<SF></td><td>Filter at minimum resolution</td></tr>
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<tr><td><SF></td><td>Same as coarse:<SF></td></tr>
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</table>
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<s><t>SSF Options</t>
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<pre>
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--afilter <s> Use SSF <s> to interpolate points in alignment.
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</pre>
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</s></s><s><t>Sampling Filter (SF)</t>
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<p>SFs are used to limit bandwidth. Primitive functions and pointwise multiplication of these
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functions (windowing) are available.</p>
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<table>
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<caption>Sampling filter (SF) types</caption>
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<tr><th>Syntax</th><th>Description</th></tr>
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<tr><td>sinc</td><td>sinc filter</td></tr>
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<tr><td>lanc:<x></td><td>Lanczos, diameter x.</td></tr>
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<tr><td>triangle:<x></td><td>Triangle, diameter x.</td></tr>
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<tr><td>box:<x></td><td>Box, diameter x.</td></tr>
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<tr><td>zero</td><td>Zero function</td></tr>
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<tr><td><f>*<f></td><td>Pointwise multiplication (windowing)</td></tr>
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</table>
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</s><s><t>Defaults</t>
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<p>ALE defaults are as follows:</p>
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<pre> dchain Varies by <a href="../../defaults/">default setting</a>
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achain Varies by <a href="../../defaults/">default setting</a>
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afilter internal (approximates triangle:2)
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</pre>
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</s>
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</chapter>
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