New watershed and other things Nov 28, 2018 9:45:38 GMT 8
Post by asgr on Nov 28, 2018 9:45:38 GMT 8
I thought I’d get in touch with some important user accessible features in ProFound.
The main bottleneck for large images on the previous version of ProFound appears to be the deblender (taken from Medical Imaging software). After a bit of effort I wrote (and Rodrigo Tobar re-wrote) a C++ variant that has more options that are appropriate for astronomy. This is both much faster and much better (qualitatively) at deblending astronomical images. The default option is still the old version (watershed='EBImage') to access the new one you need to specify it: (watershed='ProFound’). The new option exists from version 1.3.1 (so you might have it, and not realise).
Attached are some before and after run on setting that are chosen for global quality (so we don’t merely want to set the deblend threshold too high or we merge together way too many faint sources). Because of the new reltol option it can now keep prevent very extended sources from fragmenting too much. As a suggestion, if using the new options tolerance = 20, reltol = -10 and cliptol = 100 are a good starting point.
Cliptol controls how *really* bright things are treated. basically when CCD start to get saturated you expect glitches that can erroneously start fragmenting sources (usually and issue for stars). Cliptol can prevent this by auto-merging very bright touching segments even if they would otherwise be fragmented. The attached shows this for an extreme case. Not perfect, but we basically get the bright star number counts right now.
These new features are currently only on the GitHub variant: github.com/asgr/ProFound.
PastedGraphic-6.tiff (213.6 KB)