Irani-Peleg Renderer

ALE implements an iterative image reconstruction algorithm based on Michal Irani and Shmuel Peleg's paper "Improving Resolution by Image Registration", published in Graphical Models and Image Processing, Vol. 53, No. 3, May, pp. 231-239, 1991, or available at:

http://www.wisdom.weizmann.ac.il/~irani/abstracts/superResolution.html

This algorithm iteratively performs two steps: first, an approximation of T is projected, based on a filter approximating d_j, and data collected during alignment, to create a set of simulated input frames; second, the per-pixel error -- between these simulated input frames and the actual input frames -- is calculated, backprojected, and subtracted from the approximation of T, resulting in a new approximation of T.

Initial Image Approximation

ALE uses the results of previous rendering steps as the initial image approximation.

Projection and Back-projection filters

ALE provides command-line options for selecting forward-projection filters, including box filters (release 0.4.2 and later) and custom filters (release 0.4.7 and later). The back-projection filters are constructed so that the normalized back-projection weight between a given pixel in the approximation of T and a given pixel in an input frame is always equal to the corresponding normalized forward-projection weight. This differs from the approach taken by Irani and Peleg.

Box Filter

ALE versions 0.4.2 and later implement a box filter with user-specified diameter. This is somewhat similar to the 'blur' operator used by some image editing applications, and in some cases, may be an adequate approximation for d_j.

Custom Filters

ALE versions 0.4.7 and later implement support for device-specific custom filters, including a filter calibrated for the IBM PC Camera Pro (XVP610) in 320x240 mode. Configurability by color channel and pixel position in the input frame is also supported, although the latter is not currently used by any filter included with ALE.

`stdin` Filter

ALE versions 0.4.7 and later support limited configuration of filters at runtime from standard input, implemented through a custom filter called 'stdin'. This filter can be used with a script included in the source distribution to calibrate filters for devices with unknown properties.

Transformation details

ALE's method of transforming pixel areas between coordinate systems approximates transformed pixel boundaries with axis-aligned rectangular regions. Since boundaries are transformed into the coordinate systems of the input frames, this approximation can be improved by using larger scale factors (and hence reducing the size of transformed pixels).

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