LHE and Ringing

Alan Karty

I am attempting to apply Local Histogram Equalization with a starless mask to protect background sky and bright stars.  Range Mask - Star Mask = Starless Mask.  I still get ringing around the bright stars.  Any tips?  Adjust the masks?

Thank you.

Alan

BlockHead

HI Alan,

These kinds of questions are tough to answer without seeing the data and masks. In short...I don't know. Likely it is a question of generating the right kind of mask. LHE is also a fairly aggressive operation- which raises the difficulty of creating a mask to do what you want. 

Your description of the masks doesn't quite make sense to me... though I suspect you are doing it correctly. The areas that have your bright stars should be 100% black in the mask right? Why aren't they?? You might consider using Morphological Transformation Closing to capture the big things that need to be subtracted (I demonstrate this in my star de-emphasis tutorial). Or... simply apply convolution to your Star Mask to bloat the stars more before you subtract to create the starless mask. You might not be fully encompassing the stars to begin with. If you do apply convolution.. you will want to using HistrogramTransformation to brighten those stars... or just straight up use Binarize to make sure they are absolutely white... and then subtract.

-the Blockhead

Alan Karty

I believe I figured this out.  The clue was your word "aggressive".  I reduced the Amount from 0.5 to 0.25 and the ringing went away.  Thought I would let you know.