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Combining Flag images?
11-18-2007, 00:54
Post: #1
Combining Flag images?
Hi,

I intent to produce flag images in addition to the weights as I hope this could further improve our sextractor detections for astrometry and photometry.

But I don't want this information to vanish after reduction, so I thought about creating a combined flag image which would contain the information of all the input flags and then be another source of information in addition to the weight image created by SWarp.

The question is: How to do this? As far as I've seen, SWarp does not know about flags images, only about input weights. So I might have to coadd the flags in a separate run using the same astrometric solution as for the scientific images. If that makes sense at all (I hope so :rolleyesSmile, I think I have to specify -COMBINE_TYPE MAX in this coaddition. Any clue on this?

Thanks in advance! Big Grin

Best regards Jan
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11-19-2007, 15:55
Post: #2
RE: Combining Flag images?
Hi Jan.
This is tricky matter. The right way to combine pixels for flag-maps would be an arithmetical "OR". The problem is that SWarp handles all input image pixels as floats. I could certainly add an "OR" combine-type, converting (small) floats to int. Obviously combining flag maps would only make sense if background-subtraction is turned off (SUBTRACT_BACK N), flux scaling is 1, and resampling is done using nearest-neighbour interpolation (RESAMPLE_TYPE NEAREST) .
What do you think?
- Emmanuel.
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11-20-2007, 12:44
Post: #3
RE: Combining Flag images?
Your right, that sounds reasonable.

If I read correctly, I would then have to remove the FLXSCALE parameter out of the header for this coaddition process. Just to clearify my mind: Weighting would be senseless, too for this combining process, is that true?

Best regards Jan
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11-20-2007, 13:42
Post: #4
RE: Combining Flag images?
Well I could do the same as for COMBINE_TYPE MIN (or MAX), that is only consider the pixels associated with non-zero weights. Sure it would not make much sense, but it would be consistent Toungue .
- Emmanuel.
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02-09-2009, 23:51
Post: #5
RE: Combining Flag images?
Hi-

I'm also looking to coadd flag images. Has the 'OR' function been implemented in SWARP?

Cheers,
Doug
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03-06-2015, 02:45
Post: #6
RE: Combining Flag images?
I think I have to specify -COMBINE_TYPE MAX in this coaddition. Any clue on this?

idbtaoo
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