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Summer Triangle Challenge

NGC7023 - The Iris Nebula


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This is my LRGB version of the Iris Nebula (also attached the full size TIFF file).  This represents a total of 25 hours of integrations comprising 9 hours Luminance, 5 hours Red, 5.5 hours Green and 5.5 hours Blue.  It was captured using my TS Optics 130 Triplet APO and QHY268M mounted on my Losmandy G11.  The data was acquired with SGP guided with PHD2.  It was processed in PixInsight (Pre-processing, Linear Fit on L, R, G and B, RGB channel combination, DBE on L and RGB, BTX on L and RGB, SPCC and SNCR on RGB, NXT on L and RGB, Masked Stretch on L and RGB, StarXT on L and RGB, Curves on L and RGB, LRGB combination and addition of stars with Pixel Math) and Photoshop (to tweak black point and saturation).  This data was a bit of a challenge to process as much of it was captured before, during and after the full moon under Bortle 5 skies.  Constructive criticism always welcome - I am really trying to improve my processing skills.





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I think you have a terrific image here with a wealth of dusty stuff around this difficult target, but a number of things could be done to make the best out of it.

First, an easy fix to the background that looks magenta: Invert the image and run SCNR green on it and invert again. Inverting an image turns magenta into green so SCNR green will work, inverting back restores the colours to where they should be. I think in this case you should not have done SCNR green since the result is too magenta (too much green lost). For what little i have tried SPCC on it doesn't nearly as often require an SCNR green afterwards compared to the older tools, so test that out too with the linear files.

Second issue is with the sampling. Looks like you have drizzled the image x2? What you should have done is gone the other way, binned x2. That will provide a very good sampling rate for your kit, 2x higher SNR (4x compared to drizzled) but still produce a healthy 3000x2000px image with your camera. The higher SNR will also allow you to sharpen much further and control noise in noisy parts of the image. In short, sampling went the wrong way x2, try without drizzle and integer resample x2 after stacking.

Other than these 2 points i think you have done a really good job with the processing, these dusty dark nebulae are very tricky to process.

Your attached file was not linear so a limited amount of stuff can be done with it but i tried anyway, also i was able to sharpen the image more since i binned it x4 but doing it from the linear phase would yield much better results:


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