Help Processing M57

[WolfieGlos]

I have been collecting data on M57 (Ring Nebula) with the L'enhance filter after I couldn't get any more on M8/M20 (https://stargazerslounge.com/topic/411320-m8-and-m20-mosaic/ ) after each session, and I'm having a lot of problems trying to process it without blowing out the nebula itself !

Does anyone have any tips or experience with this one? I know the target is a little small for my setup, but where there's a will and all that....

I'm wondering whether this requires a HDR type of process (similar to Orion) to bring this out correctly?

I've tried running Starnet on it to try processing separately...but it see's the Ring as a star and removes it !

Examples as below. Any help much appreciated (I use Siril and GIMP), below taken from Siril.

Here we have it straight from the stack...no processing at all...and the Ring is clearly visible in the middle:

 

And here it is with nothing more than just a histogram stretch, set to auto and the stretch toned right back.

 

...

 

Even at this stage, it is already clipping the highlights in the nebula itself, but none of the faint outer shell is even visible yet.... but it is in my data if I use the auto stretch: 

 

 

Any help appreciated 🙂 

Edited July 2, 2023 by WolfieGlos

[Elp]

1. Do a minor histogram stretch on the linear file in Siril a few times until some nebula detail starts to look okay.

2. Export and open in GIMP

3. Draw a selection mask around the nebula with the rectangle select, ellipse select or lasso tool (free select)

4. Only that which is encircled should now be active, you can now do any colour or levels adjustments accordingly independent of the surrounding background

5. To better mask and blend an area it's good to feather the selection edge first before doing any operations, so it blends in better

6. If needed you can always cut as a layer the edited nebula region once done and paste it over the stretched star field, then paint an opacity mask on the edges of the top layer with a soft brush so it blends in with any bottom layers better

I use PS more but GIMP works pretty much the same.

Edited July 3, 2023 by Elp

[WolfieGlos]

Thanks Elp, good idea with the mask in GIMP. I tried layering but it looked awful, and as I stretched the star layer the nebula grew and didn’t overlap with the dimmer nebula layer well at all. Works taken over at the minute so will try again when I get chance.

[Elp]

Regarding layering, you don't layer one full layer over the other in this case. You can either mask the nebula and process it individually from the rest of the image (in this case it will be a single layer), or copy the layer and process just for the nebula then select just the nebula with a bit of space around it and cut it out and paste it above the separately edited star field layer (this would be two layers), then blend the edge of the top layer with an opacity mask so it blends in seamlessly with the bottom starfield layer.

[AstroMuni]

On 02/07/2023 at 22:59, WolfieGlos said:

I've tried running Starnet on it to try processing separately...but it see's the Ring as a star and removes it !

Have you tried stretching the image a little bit so M57 is clearer and doesnt get confused as a star? If you are more interested in M57 rather than the full fov try cropping before you apply Starnet. M57 shows up as a small circle in my FOV so I crop heavily before processing. Here is one I took a few weeks ago (around 30mins worth). Processed in Siril no starnet.

Steps:

- Background extraction

- Crop (you could do background extraction after the crop too)

- Asinh stretch to bring out colour

- GHS stretches to gently tease out details.

- Noise reduction

- Remove green noise (if needed)

- Improve saturation (if needed)

Good luck!

 

Edited July 4, 2023 by AstroMuni

[WolfieGlos]

Back to trying to process this image, and still finding it frustrating! For such a small object 😕

On 04/07/2023 at 09:57, Elp said:

Regarding layering, you don't layer one full layer over the other in this case. You can either mask the nebula and process it individually from the rest of the image (in this case it will be a single layer), or copy the layer and process just for the nebula then select just the nebula with a bit of space around it and cut it out and paste it above the separately edited star field layer (this would be two layers), then blend the edge of the top layer with an opacity mask so it blends in seamlessly with the bottom starfield layer.

Hi Elp - I couldn't get this to work, due to the red ring expanding out when stretching. I just don't seem to be able to bring out both the bright central ring and the faint outer core properly. See below.

On 04/07/2023 at 10:42, AstroMuni said:

Have you tried stretching the image a little bit so M57 is clearer and doesnt get confused as a star? If you are more interested in M57 rather than the full fov try cropping before you apply Starnet. M57 shows up as a small circle in my FOV so I crop heavily before processing. Here is one I took a few weeks ago (around 30mins worth). Processed in Siril no starnet.

Nice star colours in your image! I take it that's RGB? My narrowband stars won't look so good. Maybe I'll try gathering some RGB after the non-stop cloud cover.

Anyway, it's odd, Starnet didn't work on a set of data in Siril and removed everything.....but exporting the very same image to TIF and running it through the stand alone version of Starnet worked! Never seen this before. Anyway, doing this, and then processing as usual I ended up with this:

I actually find it quite a pleasing image with very minimal stretching at all, which shows just how bright this object actually is.

But what I still can't get is the outer, fainter area to come through without blowing out the nebula.

The left-version below shows the faint outer regions, but the core is just too bright. The second is with the original overlayed and brushed in...horrible! The problem seems to be, that as a stretch is applied, so the nebula grows so I can't actually overlay it correctly without that horrible dark band. I get the same by using Elp's method using the lasso and keeping the core separate.

And here are the full widefield images of the above for comparison. If it wasn't for the fainter outer shell I would have probably stuck with the first image. Second one below shows how many stars are there.

 

This is an example of what I was trying to achieve: https://www.astrobin.com/unoexu/?q="M 57" - although I don't have the integration time of this - 6.5 hours vs 16.5 (or the scope, aperture or a mono camera...or even that other shell beyond what I have picked up!), the HDR range is what I was aiming for. If I could get this, I might pour in more hours to this target, but otherwise I might just call it a day and move to a new target.

Edited July 22, 2023 by WolfieGlos

[Elp]

An option to try, you can view each RG and B channel under the channels tab, copy the layer and work on each separately, then recombine into an RGB image. This is one advantage mono imaging has from the start as well as utilising every pixel on the sensor.

[ollypenrice]

You seem to be familiar with the HDR layer masking technique widely used to combine different exposure lengths in M42.

Instead of using different exposure lengths you can simply use different stretches, so a very soft stretch for the nebula and a harder stretch for the background sky.

Olly

[MartinB]

Sorry if you have already done this but I would process for the "usual" ring.  Then duplicate the layer and create a mask using the existing image.  Now invert the mask so that you have a negative image.  Use levels to make the core black and everything else approaching white.  Apply a gaussian blur (maybe around 13%).  Now return to your masked image and start gently stretching.  Hopefully your outer halo will start appear without ruining the core.  You may need a few tweaks to this routine's settings but hopefully you will get it as good as your data will allow

[WolfieGlos]

Thanks Elp, Olly and Martin, I will give these a go later this week.

[AstroMuni]

On 22/07/2023 at 23:59, WolfieGlos said:

Anyway, doing this, and then processing as usual I ended up with this:

That looks lovely 😍 Good luck with applying the techniques mentioned in the posts above, to extract the outer nebula and look forward to seeing final result.

On 22/07/2023 at 23:59, WolfieGlos said:

Nice star colours in your image! I take it that's RGB?

Thanks. I use an OSC camera (ASI533mc pro)

 

Edited July 24, 2023 by AstroMuni

[WolfieGlos]

On 23/07/2023 at 18:10, MartinB said:

Sorry if you have already done this but I would process for the "usual" ring.  Then duplicate the layer and create a mask using the existing image.  Now invert the mask so that you have a negative image.  Use levels to make the core black and everything else approaching white.  Apply a gaussian blur (maybe around 13%).  Now return to your masked image and start gently stretching.  Hopefully your outer halo will start appear without ruining the core.  You may need a few tweaks to this routine's settings but hopefully you will get it as good as your data will allow

Thanks Martin, I tried this method and it worked with a better result, but I still ended up with that horrible black ring. Not as bad, but still there.

So I decided to look at what workflow I had done previously right from the outset, and it included a deconvolution. I usually try it, don't like the result and undo...in this case it appears I must have kept it......so it looks like it was me all along....! 🤦‍♂️

Anyway I pulled in another 3 hours of narrowband subs on the target last night and used a mix of longer exposures, up from 3 minutes to a mix of both 5 and 10 minutes. I then combined the stacks which allowed quite an extreme stretch on the background and it gave me the below after NR, and the core brushed in with a mask and gaussian blur. It looks a little overprocessed and too saturated to my eye, but as a first pass it seems better. Thanks for all the help  

[MartinB]

Well that's looking pretty good!  You can always reduce the saturation if you think it is to much, the main thing is that there are no glaring artefacts.

[wimvb]

On 23/07/2023 at 18:06, ollypenrice said:

... you can simply use different stretches, so a very soft stretch for the nebula and a harder stretch for the background sky.

Olly

That used to be how I would tackle high dynamic range too. But recently I got good results without masks, using the newest kid on the block, GHS in PixInsight. For this type of target, it's like curves stretch on steroids.

 

[MartinB]

The trouble is Wim, GHS isn't available on Gimp.  However, I believe it is included with Siril which is free of course.  Definitely worth a try.

[WolfieGlos]

GHS did work to an extent, but not to bring the whole thing out. That might be my relative lack of processing experience to others though.

Still, I've finally got there and I've just posted it up in the DSO section.