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M33 with Blotchy Background

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#1 SilverLitz

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Posted 15 November 2019 - 05:46 PM

Here is my 1st M33. It was shot with my ASI183mm-Pro and ZWO 36mm Premium LRGB filters and Baader 7nm Ha, using my Esprit 100 with the TSAPORED075 FF/FR at 413mm.  I have not been able to get the background right, even with multiple DBE, ABE, PCC, etc....  The background has large blotches of red.  My only (inexperienced) guess is that I need more integration time, especially for Ha.  This is a HaRGB image, with Lum extracted by PI.  Extracted Lum was MUCH better than using my Lum data, with more detail; with the Lum data I got a bright haze around the core.

 

Ha     240sec x 42

R       120sec x 105

G       120sec x 74

B       120sec x 98

 

For this I stretched using MS.  The star color is not as good as AS, but AS was blowing out the Red Ha knots.  Using normal HT, the background was even more of a mess, and I had worse detail.    HDRXform and MLT Sharpening helped, but Dark Structure Enhance did not; the opposite of my M31.  

 

This is my 1st image that I semi-finished with Esprit 100 and the TSAPORED075 FF/FR, and this only has minor crops for stacking artifacts.  My opinion is that the TSAPORED075 FF/FR works well for the Esprit 100, and I very much like the 413mm framing with the ASI183 as well as the f/4.13 speed.

 

Any other suggestions on the background blotchiness?

 

Thanks!

 

M33_HaRGB_MS (LoRes).JPG


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#2 elmiko

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Posted 15 November 2019 - 06:04 PM

Did you try MSLT in the linear stage. I do it right after Color Calibration. And before the initial nonlinear stretch. Use a mask to protect everything but the background. 7 Layers  with fairly High settings. Set the target for chrominance noise.

Nice image by the way!


Edited by elmiko, 15 November 2019 - 06:06 PM.

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#3 SilverLitz

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Posted 16 November 2019 - 11:04 AM

Did you try MSLT in the linear stage. I do it right after Color Calibration. And before the initial nonlinear stretch. Use a mask to protect everything but the background. 7 Layers  with fairly High settings. Set the target for chrominance noise.

Nice image by the way!

Thanks!

 

I assume you mean, MLT (MultiscaleLinearTransform).  I did use MLT NR in linear stage, but 5 layers on RGB/K, not Chrominance.

 

I tried it, but it did not help.


Edited by SilverLitz, 16 November 2019 - 11:10 AM.

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#4 SilverLitz

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Posted 16 November 2019 - 11:29 AM

I still think my problem is the need for more Ha data.  The stretched Ha is basically black in the background, while the RGB has smooth grey background.  (All after DBE, MLT NR, ...)

 

Here is the HaR (90% Ha, 10% R) which shows a rough background with holes:

 

M33_HaR_9010.jpg


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#5 elmiko

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Posted 16 November 2019 - 11:56 AM

Okay, I use a osc,  but I thought it was worth a try. Sorry I couldn't help.



#6 SilverLitz

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Posted 16 November 2019 - 03:16 PM

Here is the result of a partial cosmetic fix:

1) add inverted elliptical bin mask (from GAME) covering the galaxy

2) Invert image

3) SCNR (green)

4) Invert image

 

Without the mask protecting the galaxy, the red of the Ha regions would altered.

 

The results are not perfect, but the background has MUCH less blotchiness.

 

M33_HaRGB_MS (LoRes).JPG


Edited by SilverLitz, 16 November 2019 - 03:18 PM.

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#7 SilverLitz

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Posted 16 November 2019 - 03:20 PM

Here is what has been subtracted (the blotchy background):

 

M33_HaRGB_MS_background.jpg


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#8 SilverLitz

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Posted 17 November 2019 - 12:18 PM

This still left some residual blotchiness, which was revealed in a further mild HT stretch, leaving some brown patches.  So I did the same process, but SCNR (blue) and then SCNR (green).  This improved the background, but bleached the star color.

 

Here is the result with the extra HT stretch and blotch removal.  There still is some residual.  

 

M33_HaRGB_MS_HT (LoRes).JPG



#9 SilverLitz

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Posted 17 November 2019 - 12:21 PM

Here is what has been subtracted (the blotchy background) with the 2nd process:

 

M33_HaRGB_MS_HT_background.jpg

 

Notice the spots where the star color was changed.



#10 bobzeq25

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Posted 17 November 2019 - 09:21 PM

Suggestion.  Desaturate the blotched background.  It will look much more natural if it's gray.

 

There are various methods, depending on your processing program.  PixInsight lets you desaturate anything below a certain value, using a Range Mask.  Using CurvesTransformation is another option.


Edited by bobzeq25, 17 November 2019 - 09:24 PM.



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