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# ALE Point Spread Functions

The ALE Irani-Peleg renderer uses a point-spread function to model the optical and electronic properties of the capture device used. The PSF can be specified in terms of one linear and one non-linear component.

### PSF specification

The PSF can be explicitly specified by using one or both of the psf options.

    --lpsf <p>        Set linear colorspace point-spread function to <p>
    --nlpsf <p>       Set non-linear colorspace point-spread function to <p>

Available explicit point-spread functions are as follows:

    box=<d>           Set the PSF to a box filter with diameter <d>.
    circle=<d>        Set the PSF to a circular filter with diameter <d>.  [ALE 0.7.1 and later.]
    stdin             Specify a custom filter at runtime.
    stdin_vg          stdin with vertically-oriented gaps after every 8th pixel.
    <p>+<p>           Summation of two functions
    <p>^<p>           Convolution of two functions.  [ALE 0.7.3 and later.]
    <n>*<p>           Multiplication by a scalar <n>.  [ALE 0.7.3 and later.]

If a device is known to ALE, then its PSF can be implicitly set with the `--device` option. (See the device page for more information.) If a device is not specified, then the default linear PSF component is `box=1`. The non-linear PSF component is disabled by default.

### Determining the PSF

The PSF can be approximated based on images of known scenes. The ALE source distribution includes an experimental script that numerically approximates the PSF in this way (`d2/render/psf/ale-psf-calibrate`). Other, more efficient methods for approximating the PSF are likely possible, however.

Copyright 2003, 2004 David Hilvert

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