Optional outlier rejection during coaddition

[Emmanuel Bertin]

Quote:In our pipeline (THELI) we use weight maps which are based on the normalised flat field, i.e. they have not only weights of 1 and 0 but everything in between. I assume they are simply neglected when using the COMBINE_TYPE MEDIAN combination instead of the WEIGHTED option?

True.

Quote:Indeed the MEDIAN combination would throw away the cosmic, but if the number of images is small, the cosmic would bias the unfiltered median towards a higher value.

Well hopefully the fraction of pixels hit by cosmic rays is fairly small. I believe it is better to bias only those ones than the vast majority that does not suffer from cosmic rays!

Quote:What I have currently in place is a programme that I run after the input images have been resampled. It looks up all the resampled input pixels for a particular output pixel in the coadded image, detects any outliers, and sets the corresponding pixels in the previously resampled weight map to zero. I then combine using the WEIGHTED average method. However, that approach is rather inefficient for a larger number of exposures (likely due to my inferior programming), and I wondered if it was a simpler solution implementing it directly in Swarp since all the transformations etc are known there already.

OK what you want is basically a weighted average with rejection. Let me see what I can do, and I will come back to you!
Emmanuel.