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Preserving weight-map information
08-11-2010, 20:10
Post: #1
Preserving weight-map information
I'm using an exposure time map as a weight map, and when I resample it using swarp, swarp seems to apply an arbitrary re-normalization. It seems like this is mentioned in the manual:

Quote:Relative variances or weights are scaled internally using local variance measurements made directly on the input images.

Basically I want to know if swarp could not do this. My weight map is an exposure time map, and (unless I'm mistaken) the resampling process hasn't changed the exposure time of the image. So a re-normalization of my weight image is counter productive for me. I want to know what the exposure time is for each pixel in my resampled image, but I don't know how to get this info out of the new weight map.

I also have a suspicion that I'm highly confused. Thoughts?
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08-13-2010, 19:13
Post: #2
RE: Preserving weight-map information
So I'm thinking that the thing to do is to run the weight maps through swarp as if they were themselves an image. Any reason why this shouldn't give me what I'm looking for?
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08-21-2010, 22:17
Post: #3
RE: Preserving weight-map information
Hi
I guess you must have set COMBINE_TYPE to WEIGHTED? You are making a good point. There are many cases where the automatic weight-map rescaling is just making things more confusing (and slightly sub-optimal). I was already thinking of adding an option to SWarp to switch off this automatic rescaling. Please allow me a few days to implement this option!
- Emmanuel.
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08-25-2010, 23:25 (This post was last modified: 08-25-2010 23:26 by Emmanuel Bertin.)
Post: #4
RE: Preserving weight-map information
Hi,
I just added a new RESCALE_WEIGHTS config switch in SWarp which turns off the automatic rescaling of weights (or variances) if set to N (the default is Y). You might want to check out the latest development version.
- Emmanuel.
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08-26-2010, 17:05
Post: #5
RE: Preserving weight-map information
Thanks!
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