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6 <appendix id="user-psf"><title>Point Spread Functions</title>
7 <p>The ALE Irani-Peleg renderer uses a point-spread function to model the optical
8 and electronic properties of the capture device used. The PSF can be specified
9 in terms of one linear and one non-linear component.</p>
11 <s><t>PSF specification</t>
13 <p>The PSF can be explicitly specified by using one or both of the psf options.</p>
15 <ll>--lpsf <p> Set linear colorspace point-spread function to <p>
16 --nlpsf <p> Set non-linear colorspace point-spread function to <p>
19 <p>Available explicit point-spread functions are as follows:</p>
21 <ll>box=<d> Set the PSF to a box filter with diameter <d>.
22 circle=<d> Set the PSF to a circular filter with diameter <d>.
23 stdin Specify a custom filter at runtime.
24 stdin_vg stdin with vertically-oriented gaps after every 8th pixel.
25 <p>+<p> Summation of two functions
26 <p>^<p> Convolution of two functions.
27 <n>*<p> Multiplication by a scalar <n>.
30 <p>If a device is known to ALE, then its PSF can be implicitly set with the
31 <l>--device</l> option. (See the <a href="../../device/">device</a> page
32 for more information.) If a device is not specified, then the default linear
33 PSF component is <l>box=1</l>. The non-linear PSF component is disabled
36 </s><s><t>Determining the PSF</t>
38 <p>The PSF can be approximated based on images of known scenes. The ALE source
39 distribution includes an experimental script that numerically approximates the
40 PSF in this way (<l>d2/render/psf/ale-psf-calibrate</l>). Other, more
41 efficient methods for approximating the PSF are likely possible, however.</p>