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COMBINE_TYPE WEIGHTED
02-27-2009, 11:19
Post: #1
COMBINE_TYPE WEIGHTED
So far, I have been using COMBINE_TYPE AVERAGE and MEDIAN with SWarp without flux scaling, and would like to try flux scaling and weighting to improve the signal-to-noise ratio of co-added images. This because my input images frequently exhibit sizeable differences in background noise and signal levels as they are taken at different elevations (often there is a combined effect of both, a lower signal level due to increased atmospheric extinction and a brighter sky background as I move closer to the horizon).

Reading through the documentation, I believe that the following “configuration parameter recipe” is correct, and was wondering if somebody could confirm this for me:

- Provide flux scale factors in the FITS headers (keyword FLXSCALE)
- Set COMBINE_TYPE to WEIGHTED
- Supply the filenames of normalized flats (i.e. with an average pixel value of 1.0), after WEIGHT_IMAGE
- Set WEIGHT_TYPE to MAP_WEIGHT

Also, as a simplification opportunity, if I supply only a single weight-map file (as the flat field will be the same for all images), will SWarp assume that this is the file to use for all input images?

Thanks in advance for any confirmation/input

Robert
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02-07-2010, 23:09
Post: #2
RE: COMBINE_TYPE WEIGHTED
Hi Robert,

my answer comes a bit (!) late, but yes, your guess was 100% correct. You don't even need to normalize flats (except for possible gain jumps in the case of multiple readout ports) when WEIGHT_TYPE is set to MAP_WEIGHT.
- Emmanuel.
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02-10-2010, 19:57
Post: #3
RE: COMBINE_TYPE WEIGHTED
Thanks Emmanuel, in the mean time I've got everything working just fine.


(02-07-2010 23:09)Emmanuel Bertin Wrote:  Hi Robert,

my answer comes a bit (!) late, but yes, your guess was 100% correct. You don't even need to normalize flats (except for possible gain jumps in the case of multiple readout ports) when WEIGHT_TYPE is set to MAP_WEIGHT.
- Emmanuel.
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