[daip] Regarding an issue in using 'spectral index' image with AIPS task IMAGR {External}

[egreisen]

On 2023-05-22 05:42, Subhashis Roy wrote:
> Hi Eric,
> 
> IMAGRPRM(17) in IMAGR is a very useful option for imaging wideband
> data, for which spectral index image has already been made by imaging
> from each sub-bands.

I have reached the conclusion that IMAGR is doing the best it can.
When I made a model without the second central source and corrected
UVMOD (it did bad things if FQCENTER > 0) and lowered FLUX, the
IMAGR with SPIX gave an rms 4-5 times better than without SPIX.
There are still low level rings around the north and south points
but they are significantly reduced.  I noticed that IMAGR had some
trouble with these sources even when doing a single channel so I
am not surprised that some trouble remains.  The FLUX level you chose
made the random noise a significant contributor to the image rms
with both SPIX choices.

Some of the issues I reported regarding SPIXR were due to my not 
remembering
to run CONVL on the cube in advance.  Of course, my IMMOD spectral index 
image
was guaranteed to be better than from the IMAGR cube.

Eric Greisen