159 lines
6.5 KiB
XML
159 lines
6.5 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-rendering"><title>Rendering</title>
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<p>Rendering determines how an output image is constructed from a series of
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aligned input frames, and occurs in two stages: incremental rendering and
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Irani-Peleg rendering. Additional rendering options include exposure
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registration, certainty-weighted rendering, spatial extension, range extension,
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scaling, and Bayer pattern specification. Experimental options for video
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stream processing are also available.</p>
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<s><t>Incremental Rendering</t>
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<p>The incremental renderer uses configurable rendering chains to determine the
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output image. It can increase resolution and reduce aliasing, but it cannot
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reduce blur. For more information on rendering chains, see <xref
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linkend="user-chains"/>.</p>
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</s><s><t>Irani-Peleg Rendering</t>
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<p>The Irani-Peleg renderer uses configurable point-spread functions to model
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blur, which is then reduced by an iterative backprojection technique. By
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default, mean correction values are used at each iteration step, but median
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correction can also be specified. For more information about point-spread
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functions, see <xref linkend="user-psf"/>. For iteration defaults, see
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<xref linkend="user-defaults"/>.
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</p>
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<ll>--ips <i> Run <i> iterations.
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--ip-mean Use the mean correction [default]
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--ip-median Use the median correction
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</ll>
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</s><s><t>Exposure Registration</t>
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<p>By default, ALE adjusts an exposure model to minimize differences in tone
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between frames. The option <l>--exp-noregister</l> indicates that exposure
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should be assumed uniform across all frames. In this case, no adjustment is
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performed. The option <l>--exp-meta-only</l> indicates that only exposure
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information included in the image files should be used for registration.
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Currently, EPPM is the only type of exposure metadata supported by this option;
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for more information, see <xref linkend="user-eppm"/>.</p>
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<ll>--exp-register Register exposure between frames. [default]
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--exp-noregister Assume uniform exposure across all frames.
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--exp-meta-only Use only image metadata for registering exposure.
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</ll>
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</s><s><t>Color Adjustment</t>
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<p>To adjust the color of the output image (e.g., for white balance), the
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--exp-mult= option can be used.</p>
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<ll>--exp-mult=c,r,b Adjust all channels by <c>, red by <r>, and blue by <b>.
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</ll>
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</s><s><t>Certainty-weighted Rendering</t>
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<p>The exposure model includes an associated certainty function, which
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quantifies the reliability of sensor measurements. By default, this function
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is raised to the zeroth power, to obtain uniform certainty for all measurements.
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To specify a different certainty exponent, the option <l>--cx</l> can be
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used. This option is best used in combination with <l>--exp-extend</l> (see
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below) and <l>--ips</l>. For defaults, see <xref
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linkend="user-defaults"/>.</p>
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<ll>--cx <x> Render with certainty exponent <x>
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--no-cx Render with uniform certainty.
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</ll>
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</s><s><t>Scale factor</t>
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<p>Rendering with a larger scale factor results in image output of the specified
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larger scale. Larger scales can improve alignment precision and output image
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quality, but can also increase alignment and rendering times.</p>
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<ll>--scale=x Scale images by the factor x, where x > 0. (1 is default)
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</ll>
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</s><s><t>Image extents</t>
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<p>The --extend option records pixel data that falls outside of the region of the
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first frame in the sequence. This can be useful for providing additional
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alignment constraints or creating panoramic image mosaics. (For mosaics, see
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also the description of the --follow option in <xref linkend="user-alignment"/>.)</p>
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<ll>--extend Increase image extents to accommodate all pixel data.
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--no-extend Don't increase extents; crop to original frame. [default]
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</ll>
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</s><s><t>Exposure extents</t>
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<p>By default, ALE restricts the output range to that of the original frame.
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To adjust the output range to accommodate the ranges of all input frames,
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specify <l>--exp-extend</l>. For defaults, see <xref linkend="user-defaults"/></p>
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<ll>--exp-extend Extend range to include all calculated values.
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--exp-noextend Restrict to the original frame's range.
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</ll>
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</s><s><t>Bayer pattern specification</t>
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<p>Many cameras sample only one color channel per output pixel. To ignore the
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other channels, a Bayer pattern can be specified.</p>
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<ll>--bayer <b> Set the Bayer pattern to <b>, one of:
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(clockwise from top left pixel)
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rgbg Red-green-blue-green
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gbgr Green-blue-green-red
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grgb Green-red-green-blue
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bgrg Blue-green-red-green
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none RGB-RGB-RGB-RGB
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Default is none or device-specific.
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</ll>
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</s><s><t>Video stream processing (Experimental)</t>
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<p>If a sequence of frames represents a video stream, then, in addition to
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producing a single output image, ALE can also produce one or more sequences of
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processed frames, corresponding to one or more occurrences of the
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<l>--visp</l> option. This option has its own associated scaling option,
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as well as an option to show excluded regions as dimmed wherever possible.</p>
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<ll>--visp <args> Process a video sequence.
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<args> are:
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<chain> <stabilization-type> <prefix> <suffix>
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<chain> is an incremental rendering chain.
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<stabilization-type> is one of:
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ma:<x> Moving average over 2*<x> + 1 frames
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sf:<x> Stabilize to single frame number <x>
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identity Same as ma:0
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<prefix> is an output file prefix
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<suffix> is an output file suffix
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--visp-scale=<x> Use scale <x> for VISP output. (default is 1.0)
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--exshow For single-invariant chains, show --ex regions dimmed.
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</ll>
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<s><t>Video stream processing example</t>
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<p>To mimic the behavior of repeated applications of the 0.6.0
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<l>--replace</l> option over a sequence of frames, the following
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<l>--visp</l> option could be used.</p>
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<ll>--visp last:nex:triangle:2 sf:0 frame .jpg
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</ll>
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<p>For better filtering, the following option could be used instead:</p>
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<ll>--visp last:nex:sinc*lanc:6 sf:0 frame .jpg
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</ll>
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</s>
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</s>
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</chapter>
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