TheSkySearchers

I'm working on a 4 panel widfield mosaic of the Cass/Ceph border. I have the wizard at bottom right and the cave and lobster claw middle and top.

When I stretch the image the wizard is blowing out before the other parts have got bright enough. I'm thinking to use GAME script to put a mask over him but not sure if that will work.

Any suggestions?

Try HDR Multiscale Transform. Takes a bit of tweaking.

Your problem sounds similar to the problem that is common in NB imaging. Here is a possible approach:

• 1) Complete linear processing on each panel separately.

• 2) Perform a moderate stretch on the brightest panel (the panel with the Wizard in your case).

• 3) For each of the other panels I use the HistogramTransformation left and middle adjusters to approximately match the star brightness and background level to match the brightest panel.

• 4) Remove stars from all four panels. I use StarXTerminator and check the Generate Star Image box.

• 5) Use the RangeSelection process with the settings shown below to select the nebulae in each of the three dimmer panels. Only adjust the Lower limit slider. This will produce three RangeSelection masks, one for each of the dimmer panels.

• 6) For each of the dimmer panels apply the corresponding RangeSelection mask. Stretch each panel so that the nebula brightness is what you want (approximately equal to the nebula in the brightest panel?). Adjusting the left hand HistogramTransformation slider can help to blend the boosted nebula into the surrounding background.

• 7) Reapply the stars to each of the panels.

• 8) Assemble the panels together.

Continue processing the assembled image.

Hope this makes sense. Let me know if you have any questions.

Steve

Thanks @STEVE333 - yes that makes perfect sense. Unfortunately I already combined the panels - there is quite a variance in SNR and gradients between the panels as they were taken over several nights, and what I read about Photometric Mosaic script said that in these circumstances its best to build the Mosaic before any adjustments. (photometric Mosaic works brilliantly by the way - I was previously using Gradient merge mosaic which was a bit hit and miss)

But your method above gives me good direction that I think I can see a way to to achieve what I want on my current mosaic - if it doesn't work I'll go back to uncombined panels.

Thanks again.

You're welcome David - I've never tried the Photometric Mosaic script. If I ever get ambitious enough to try another mosaic I'll give it a try.

Good luck. I really like that region of the sky and am looking forward to your results.

Steve