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<chapter id="user-rendering"><title>Rendering</title>
<p>Rendering determines how an output image is constructed from a series of
aligned input frames, and occurs in two stages: incremental rendering and
Irani-Peleg rendering.  Additional rendering options include exposure
registration, certainty-weighted rendering, spatial extension, range extension,
scaling, and Bayer pattern specification.  Experimental options for video
stream processing are also available.</p>

<s><t>Incremental Rendering</t>

<p>The incremental renderer uses configurable rendering chains to determine the
output image.  It can increase resolution and reduce aliasing, but it cannot
reduce blur.  For more information on rendering chains, see <xref
linkend="user-chains"/>.</p>

</s><s><t>Irani-Peleg Rendering</t>

<p>The Irani-Peleg renderer uses configurable point-spread functions to model
blur, which is then reduced by an iterative backprojection technique.  By
default, mean correction values are used at each iteration step, but median
correction can also be specified.  For more information about point-spread
functions, see <xref linkend="user-psf"/>.  For iteration defaults, see
<xref linkend="user-defaults"/>.

</p>

<ll>--ips &lt;i&gt;         Run &lt;i&gt; iterations.
--ip-mean         Use the mean correction [default]
--ip-median       Use the median correction
</ll>

</s><s><t>Exposure Registration</t>

<p>By default, ALE adjusts an exposure model to minimize differences in tone
between frames.  The option <l>--exp-noregister</l> indicates that exposure
should be assumed uniform across all frames.  In this case, no adjustment is
performed.  The option <l>--exp-meta-only</l> indicates that only exposure
information included in the image files should be used for registration.
Currently, EPPM is the only type of exposure metadata supported by this option;
for more information, see <xref linkend="user-eppm"/>.</p>

<ll>--exp-register    Register exposure between frames.  [default]
--exp-noregister  Assume uniform exposure across all frames.
--exp-meta-only   Use only image metadata for registering exposure.
</ll>

</s><s><t>Color Adjustment</t>

<p>To adjust the color of the output image (e.g., for white balance), the
--exp-mult= option can be used.</p>

<ll>--exp-mult=c,r,b   Adjust all channels by &lt;c&gt;, red by &lt;r&gt;, and blue by &lt;b&gt;.
</ll>

</s><s><t>Certainty-weighted Rendering</t>

<p>The exposure model includes an associated certainty function, which
quantifies the reliability of sensor measurements.  By default, this function
is raised to the zeroth power, to obtain uniform certainty for all measurements.
To specify a different certainty exponent, the option <l>--cx</l> can be
used.  This option is best used in combination with <l>--exp-extend</l> (see
below) and <l>--ips</l>.  For defaults, see <xref
linkend="user-defaults"/>.</p>

<ll>--cx &lt;x>          Render with certainty exponent &lt;x>
--no-cx           Render with uniform certainty.
</ll>

</s><s><t>Scale factor</t>

<p>Rendering with a larger scale factor results in image output of the specified
larger scale.  Larger scales can improve alignment precision and output image
quality, but can also increase alignment and rendering times.</p>

<ll>--scale=x         Scale images by the factor x, where x > 0.     (1 is default)
</ll>

</s><s><t>Image extents</t>

<p>The --extend option records pixel data that falls outside of the region of the
first frame in the sequence.  This can be useful for providing additional
alignment constraints or creating panoramic image mosaics.  (For mosaics, see
also the description of the --follow option in <xref linkend="user-alignment"/>.)</p>

<ll>--extend          Increase image extents to accommodate all pixel data.
--no-extend       Don't increase extents; crop to original frame. [default]
</ll>

</s><s><t>Exposure extents</t>

<p>By default, ALE restricts the output range to that of the original frame.
To adjust the output range to accommodate the ranges of all input frames,
specify <l>--exp-extend</l>.  For defaults, see <xref linkend="user-defaults"/></p>

<ll>--exp-extend      Extend range to include all calculated values.
--exp-noextend    Restrict to the original frame's range.
</ll>

</s><s><t>Bayer pattern specification</t>

<p>Many cameras sample only one color channel per output pixel.  To ignore the
other channels, a Bayer pattern can be specified.</p>

<ll>--bayer &lt;b&gt;       Set the Bayer pattern to &lt;b&gt;, one of:
                    (clockwise from top left pixel)
                      rgbg      Red-green-blue-green
                      gbgr      Green-blue-green-red
                      grgb      Green-red-green-blue
                      bgrg      Blue-green-red-green
                      none      RGB-RGB-RGB-RGB
                  Default is none or device-specific.
</ll>

</s><s><t>Video stream processing (Experimental)</t>

<p>If a sequence of frames represents a video stream, then, in addition to
producing a single output image, ALE can also produce one or more sequences of
processed frames, corresponding to one or more occurrences of the
<l>--visp</l> option.  This option has its own associated scaling option,
as well as an option to show excluded regions as dimmed wherever possible.</p>

<ll>--visp &lt;args&gt;     Process a video sequence.
                     &lt;args&gt; are:
                         &lt;chain&gt; &lt;stabilization-type&gt; &lt;prefix&gt; &lt;suffix&gt;
                     &lt;chain&gt; is an incremental rendering chain.
                     &lt;stabilization-type&gt; is one of:
                         ma:&lt;x&gt;     Moving average over 2*&lt;x&gt; + 1 frames
                         sf:&lt;x&gt;     Stabilize to single frame number &lt;x&gt;
                         identity   Same as ma:0
                     &lt;prefix&gt; is an output file prefix
                     &lt;suffix&gt; is an output file suffix
--visp-scale=&lt;x&gt;  Use scale &lt;x&gt; for VISP output.  (default is 1.0)
--exshow          For single-invariant chains, show --ex regions dimmed.
</ll>

<s><t>Video stream processing example</t>

<p>To mimic the behavior of repeated applications of the 0.6.0
<l>--replace</l> option over a sequence of frames, the following
<l>--visp</l> option could be used.</p>

<ll>--visp last:nex:triangle:2 sf:0 frame .jpg
</ll>

<p>For better filtering, the following option could be used instead:</p>

<ll>--visp last:nex:sinc*lanc:6 sf:0 frame .jpg
</ll>

</s>
</s>

</chapter>