multi-pag (sa-delta/beta calculation)

Behavior

This widget is used to compute the optimal \(\frac{\delta}{\beta}\) value for Paganin.

It run a serie of slice reconstruction for a set of \(\frac{\delta}{\beta}\) values and computes a score for each slice (see later).

If the autofocus is lock then it will automatically select the \(\frac{\delta}{\beta}\) generating the highest score.

If a center of rotation has already been computing upstream (from “axis” or “saaxis” widgets) then it picked for the reconstruction.

To speed up reconstructions you can increase “horizontal binning” on the nabu properties (on reconstruction settings tab) - binning and sub-sampling section.

Score calculation

For now there is two ways of computing a \(\frac{\delta}{\beta}\) reconstruction score (the same as for saaxis). This method can be set on the “results” tab

• standard deviation for readability purpose we multiply the by 100.

• total variation by the formula:

  \[tv = \sum{\sqrt{\nabla_{x}^2 + \nabla_{y}^2}}\]

  To avoid having very low score values we divide it by 10e5.

• 1 / standard deviation

• 1 / total variation

The score is computed on the circumscribed square of “biggest” common circumscribed circle of all reconstructed slices. Having a square roi simplify a lot calculation compared to having a disk (we have for example some gradient calculation)

Demo

There is several “video” demonstration for sa-delta-beta widget:

• as a standalone widget

• part of a workflow with user interaction during processing