[RCC] Improving detail & image quality - Forums

Topic starter

Jun 30, 2022 · Edited: Jun 30, 2022

Hello. Looking for community wisdom on how to improve my image of NGC7000. I've looked at images from similar equipment and feel my image still lacks in some areas. The areas that I've identified are:

Resolution/sharpness
Color (color deficient)
Stars. Trying to control the bloat from different filters upon combination. Maybe some lens flare issues with Oiii
I know this image was taken with my back focus slightly off so there are some oblong stars
Depth and controlling nebulosity. Kind of hand in hand with my sharpness issue. The yellowish nebulosity just blurs and isn't consistent with other images I've seen.

I would be interested in any solid references on advanced masks in PI or PS, and color mapping techniques.

Link to image, North America Nebula (NGC7000): https://astrob.in/1iz0uh/0/

Thank you for your time and attention.

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Wim van Berlo

Jun 30, 2022

I looked at your image, but not in full resolution (99 MB). Why so large, is it a mosaic? Also, you have a very small pixel scale (0.4 "/p) which you can only fully enjoy from a location with very low humidity and excellent seeing (read Atacama desert in Chile). Nebulae rarely require such a low pixel scale. If your local atmospheric conditions can't support such a pixel scale, binning 2x2 or 3x3 will give you much better SNR without losing detail. Once you have an image with high SNR, you can apply more aggressive processing to reveal colour and contrast.
If the image is a 4 panel mosaic, you only spent about 2 hrs in total on each panel, which may be too little for a reasonable signal in Oiii and Sii. If otoh, this is a drizzled image, try processing in its original resolution. Drizzle decreases SNR.
A good SNR is essential for creating a great image.

cs,

Wim

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Jneums87

Topic starter

Jun 30, 2022

@Wim van Berlo Thank you for looking at my image and providing comments. It is not a mosaic. This is one of my first images that I took with my new ASI 6200mm. I would say, I'm still learning the process of handling such a large sensor with file and pixel size. I uploaded the image and it said it was 50 MB so I'm not sure how it jumped to 99 MB?

I'll always be fighting humidity here so thanks for the tip and in the future I will test out binning at 2x2 or 3x3. Also, I was surprised that single 300s subs barely showed nebulosity. I usually see really good SNR with my Radian 61 w/ 1600mm, so I chalked it up to the fact that the Radian 61 is f/4.5 and my new WO FLT132 is f/7. But maybe it was due to binning as you mentioned? Thanks again.

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rhedden

Jun 30, 2022

It's actually looking like a fine image at a glance, without pixel peeping. To address the file size, you could try saving it as a 90% quality JPG before uploading. Chances are that you won't be able to tell the difference between the original and the compressed JPG vesrion.

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rhedden

Jun 30, 2022 · Edited: Jun 30, 2022

Here is a little more detailed CC.

In three of the corners, stars are elongated in the direction of the corner. In the lower right corner, stars are compressed rather than elongated. These aberrations could be due to a slight error in back-focus and/or tilt.

Some of the stars have bright rings around them, especially in the upper right hand corner. Are the halos in the raw data, or did they appear after deconvolution?

Some of the yellow stars appear to be slightly green upon closer inspection.

The brighter stars are stretched to the point that their cores are saturated.

The dark sky background at the upper right is actually dark blue - but I think it is a color balance issue, not so much that there is any Oiii emission there.

All of the four corners have a gradient problem - they are tinted purple. The purple color is not from the nebula - it's a leftover problem (perhaps with flats?) that needs to be addressed in processing.

These are some finer points that could help make your future images better. Overall, it's an impressive image when zoomed out, and I enjoyed seeing it very much.

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Jneums87

Topic starter

Jun 30, 2022

@rhedden Thank you so much for the finer points you observed. I knew early on that I was having a gradient issues. I didn't do any DBE on it because I was concerned with 90% or more of the image containing nebulosity. Any pointers on gradient removal with nearly 100% nebulosity image. Also, when I run DBE, it tends to generate even more noise and blotches all over. Thoughts on that?

I definitely agree with you about the back focus/tilt. I put on a WO 68III flattener and it has to be like 7.4mm offset to properly flattnen. I may have been just a hair off. May invest in a digital micrometer or caliper.

I think I started to see ringing around the stars after running an EZ Star Reduction with default 5 iterations.

I auto stretched using ScreenTransferFunction and HistogramTransformation. Then removed stars to process nebulosity. Not sure how cores are over saturated but star protection and halos/chromatic aberrations have been the bane of my existence in this hobby.

Thanks again for your time.

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rhedden

Jun 30, 2022

I'll leave your questions for a PixInsight user to answer, since I'm one of the holdouts who insists on using different processing software. Background extraction when the entire field is covered by nebulosity is a tricky business. It really helps to have some empty sky around the nebula!

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