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Black output image and "WARNING: Null or negative global weighting factor".
01-10-2014, 11:57 (This post was last modified: 01-10-2014 12:45 by tlehmann.)
Post: #1
Black output image and "WARNING: Null or negative global weighting factor".
Hi,

I attempt on using swarp for an implementation of the "Bayer drizzle" algorithm (ref: http://deepskystacker.free.fr/english/te...rdrizzle).
During this process I'd like to stack for example all red pixels of BGGR bayer matrix images. To achive this I mask out all B and G channel pixels by creation of weight maps with a 2x2 pixel 0-0-0-1-pattern.

Now I run swarp (2.19.1) on the science images with some options:
swarp -weight_type map_weight -blank_badpixels Y -subtract_back N -combine_type average -resampling_type bilinear ??.fits

and get
> Filtering background map(s)
> WARNING: Null or negative global weighting factor:defaulted to 1
on each input image and the coadded image is pure black.

I suspect that the background statistics routine in src/back.c goes wild because 3/4 of all pixels are internally set to 0 (because of zero weight). If this routine would just ignore those "bad pixels" and do background statistics on the remaining pixels I believe the stacking process should succeed.
(Side note: I have seen other threads dealing with the same swarp warning but those were likely related to weird background distribution in the science images itself - which is different from my case.)

Any idea?

Thomas
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