M31 Re-processed

[imakebeer]

One thing I always seem to struggle with is noise, particularly in the farfield of my DSO images. I'm not ready to bite the bullet and fork out for software to do this so in the meantime I've been having a play with some free tools. Below is a with/without or before/after comparison of my last M31 capture from January 2023 - stacking and initial processing was done in Siril.

@Elp mentioned to me in another thread about trying StarNet to make a starless image. This worked really well and I found it much easier to stretch the histogram in GIMP when dealing with just the galaxy on it's own and so bring out more detail 👍

I added the stars back on a separate later and made them only 25% opaque. I'm pleased with the result as they seem less stark and don't dominate the image so much.

Following that I found AstroDenoisePy - maybe paid tools like noiseXTerminator are better but for a freebie and never having used a de-noise tool before it seemed easy enough and did a pretty good job I think.

( @WolfieGlos I saw in another thread you had tried it, I'm interested to get your take on ADnPy)

I found it changed the colour quite a lot until I dialled back the de-noise level from the default 0.9 to 0.25.

Also I'm not sure if I'm doing these processing steps in the right/best order??? It also looks like the latest beta of Siril had some new de-noise capability so I'll be trying that out too.

Anyhow a comparison of the images below. I'm pleased with the outcome of these new techniques, though I've still got loads more to learn and perfect.

Any comments, tips or feedback would be most welcome!

Original: Siril + GIMP

Re-processed: Siril + StarNet + GIMP + AstroDenoisePy

[ollypenrice]

First impression: in the first one, too much green and in the second too little (turning things magenta.) The reduced stars look great.

Olly

[WolfieGlos]

7 hours ago, imakebeer said:

Following that I found AstroDenoisePy - maybe paid tools like noiseXTerminator are better but for a freebie and never having used a de-noise tool before it seemed easy enough and did a pretty good job I think.

( @WolfieGlos I saw in another thread you had tried it, I'm interested to get your take on ADnPy)

I found it changed the colour quite a lot until I dialled back the de-noise level from the default 0.9 to 0.25.

Also I'm not sure if I'm doing these processing steps in the right/best order??? It also looks like the latest beta of Siril had some new de-noise capability so I'll be trying that out too.

AstroDenoise I’ve only just started using and I found the same regarding colour, but also brightness. It took me a while before I started changing the STF sliders at the top to realise that these were stretching the image, so I brought them both right down. I used this for my recent HorseHead image. Seems obvious to me now!

I’ve since found that you can untick the “Normalise” box at the top which greys these out and prevents any stretching, and I then try it with 0.9 denoise. I usually change the tiling to 4 (no idea what it does; there’s no help that I can find, but I have noticed a small difference zoomed right in), but I also run several versions with varying degrees of noise reduction, down to about 0.6, and see which I prefer. The results can look quite “plasticky” so I try not to take it too far. I’ve used it at the end of my non-linear processing. 

As for Siril, I’ve tried the new noise reduction in the beta but I haven’t been that impressed with the results. In their defence they have said it works better on mono images. I forget their names, but the second noise reduction option took 30minutes to run on my system, and it looked no different to the first one! I’d be interested to see what result you get though. 

[imakebeer]

8 hours ago, ollypenrice said:

First impression: in the first one, too much green and in the second too little (turning things magenta.) The reduced stars look great.

Olly

Thanks for the feedback Olly, this is helpful. I agree with you - I'll take a look at the histogram and see if I can tweak in a bit more green/less magenta 👍

[ollypenrice]

7 minutes ago, imakebeer said:

Thanks for the feedback Olly, this is helpful. I agree with you - I'll take a look at the histogram and see if I can tweak in a bit more green/less magenta 👍

That's always the tricky axis in AP...

Olly

[imakebeer]

1 hour ago, WolfieGlos said:

I’ve since found that you can untick the “Normalise” box at the top which greys these out and prevents any stretching

Thanks for the feedback @WolfieGlos. Yeah I switched off the stretching which improved things. I'll let you know about Siril but based on what you've said I'm not too optimistic, but we'll see.