[alma-config] image fidelity, etc

[Mark Holdaway]

1) Dynamic range:  off source errors

Select an off-source region (you could do this by taking your model
image, convolving with Gaussian; then setting everything below
1e-5 to 1.0, everything above 1e-5 to 0.0), calculate the rms offsource,
divide that into the reconstructed peak.

2) on-source dynamic range:

Invert the region defined above to that it is "on-source".  may want
to change the clip level to emphasize "on-source" (ie, take out the
barely off-source region), calculate the on-source rms in the difference
image, divide that into the rconstrcuted peak

3) median fidelity:

Make error (difference) image, make a mask based on the convolved model
clipping below some level (ie, you now have a mask that defines the
on-source region of interest). divide the absolute error into the pixel
values of the convolved image.  As some pixel errors will accidentally be
very small, take the median of this fractional error image.

Often the median fidelity will reflect the fractional error level in
weak pixels.  To overcome this, you could set the clip value higher,
or you could weight the fidelity image by the pixel values:

4) moment fidelity:

Define mask as above; calculate the fidelity image within the masked
region: convolved model / abs( convolved model - reconstruction ).
Weight each pixel by the pixel value (in the convolved model);
Take the average, normalize.


	-mark