Friday, June 12, 2009

Averaging Image Channels

Here is a good question from Sanch:

I am trying to average spectral channels in an image cube. Can anyone suggest what's the best way
to do it in AIPS?
I don't want to go back to the UV data and re-reduce it to get the image, as the data I am
working on is huge (VLBI data).

And some more details:
She wants to average together channels in a channel map. In other words, she has a channel map with, say, 100 channels and she wants to turn it into a map with 50 channels. Channels 1 and 2 would be averaged together and become the new "Channel 1," channels 3 and 4 would be averaged together and become the new "Channel 2," and so on.

Thoughts, AIPS gurus?


sillywolf said...

when you use the task 'IMAGR'
it is possible to use
AIPS 1: NCHAV -1 Number of chan. to average.
AIPS 1: CHINC 1 Channel incr. between maps.

If you set both NCHAV and CHINC to be 2,
then you will average channels 1-2 3-4 5-6.. 99-100 etc. to be channel 1 2 3 ... 50.

I guess it's the best way.

Sanchayeeta said...

I am sharing Eric Greisen's suggestion of binning spectral channels in an image cube.
He said " ..transpose the cube: task TRANS with TRANSCODE='312'
and then run SUBIM with XINC > 1. It gives you options of what is done with the pixels - select every XINC'th, average, take the MAX and take the MIN."

Thanks to everyone for brainstorming !