M27, think I've over processed it

[heathenwoods]

On reflection, this image owes a lot to the classifieds here and Astro Buy & Sell:
90x60s lights with a Canon 1000D through a 130PDS on a grumpy old Celestron CG5.
Also: An Altair Astro CCD-CLS filter but I'm not yet convinced it's a massive help. Bortle 5 skies
30 flats (I've assumed I leave the filter on for these?) [edit: had originally called them lights]
30 biases
Stacked in DSS and played with in Siril and PS. I think I've overdone it as the background looks quite uneven and gritty.

I'm coming to the conclusion that (i) I need to keep track of my processing workflow and (ii) I need to look into getting guiding worked out.

Edited July 13, 2022 by heathenwoods
correct 'lights/flats' error

[ollypenrice]

By 30 lights, did you meant 30 flats? If so, yes, the filter stays in. You need to replicate the light path of the lights.

My processing advice would be,

- don't stretch so far. The core of M27 is brighter than it needs to be and is losing contrast and detail as a result. The background sky is also very 'busy' and a softer stretch would help that. When you stretch, you might try this (in Photoshop.) Stretch in Levels till you get to a background brightness of 22 per colour. channel. Check this using the colour sampler tool. After that, continue to stretch - but in Curves.  Put a fixing point on the curve at 22 (Alt click on background sky.) Put another fixing point below that. Now stretch by lifting the curve only above these fixing points so as not to stretch the background and so increase its noise.

- Sooth the background sky by selecting it with the Colour Sample and reduce its colour saturation and try Reduce Noise set to colour noise.

- Colour balance. This looks very blue-green on my calibrated monitor. I use colour sampler in the Eyedropper menu to check the background is equal per channel.

On the capture side, are you dithering? A 12 pixel dither would help combat that diagonal walking noise.

It's already a very respectable image.

Olly

[heathenwoods]

Thanks very much, Olly. That is all very helpful.

Starting from your last comment, I'm not dithering - I'm just using the camera with an intervalometer. I'm guessing that I could set up the mount to dither with Phd2 or similar software? I don't have a guiding setup but this might be a god way of familiarising myself with the software before fully going down that route.

The blue/green balance is probably out because I tried to push the blue in the middle of the nebula with curves - possibly the source of a number of issues!
And, yes, I meant flats when I wrote lights for the second time.

I'll try reprocessing using those tips - again, thanks so much for taking the time to make these suggestions.

[heathenwoods]

Okay, I've tried to follow @ollypenrice's advice (as much as my data allows!) and I think this coming on a little...

[Adam J]

24 minutes ago, heathenwoods said:

Okay, I've tried to follow @ollypenrice's advice (as much as my data allows!) and I think this coming on a little...

better but still looking a little green in the background on my screen. 

[ollypenrice]

Yes, you've jumped from blue to green! Give red a little shove...

😁lly

[carastro]

I get the impression this is one of your first images, if not THE first.  You're not guiding, and I think you have done a magnificant job in the circumstances.  Yes, processing needs a bit of adjusting, but HEY this might be your first bit of processing too.  

Really well done.   Follow Olly's and others advice above and you'll do well.  

Hint, guiding makes one heck of a difference.

Carole 

[heathenwoods]

I've come to realise just how powerful levels and curves are! I think I've got all the curves more or less in the same place now and it's been fun trying to push just a little bit more detail out of the core. It's been amazing to see what a huge difference three astute tips made 🙂
(Although I'm not sure the background isn't a tiny bit too red now!)

Carole - not quite my first but my first for quite a while. Although I realise the CG5 is bordering on 'vintage' it looks as if guiding should be relatively straightforward to setup (🤞)

[AstroMuni]

14 hours ago, heathenwoods said:

've come to realise just how powerful levels and curves are! I think I've got all the curves more or less in the same place now and it's been fun trying to push just a little bit more detail out of the core. It's been amazing to see what a huge difference three astute tips made

Its looking good now. Try the new GHT (generalised hyperbolic transform) tool in Siril rather than the Histogram transform. You have better control and can get better results.

[Laurieast]

You can sometimes easily remove the green tint in one click with a plugin for PS and Affinity, Hasta La Vista, Green, from:

https://www.deepskycolors.com/archivo/2010/04/26/hasta-La-Vista-Green.html

As mentioned by AstroMuni, the new GHT (generalised hyperbolic transform) tool in Siril is way better than just levels and curves. 

Nice result already with your last image above!

 

Edited July 14, 2022 by Laurieast

[heathenwoods]

On 14/07/2022 at 14:56, Laurieast said:

You can sometimes easily remove the green tint in one click with a plugin for PS and Affinity, Hasta La Vista, Green, from:

https://www.deepskycolors.com/archivo/2010/04/26/hasta-La-Vista-Green.html

As mentioned by AstroMuni, the new GHT (generalised hyperbolic transform) tool in Siril is way better than just levels and curves. 

Nice result already with your last image above!

 

Thanks, Laurence! I haven't really looked at GHT and have continued to use the Asinh tool; I'll have a look at it tonight! I'll also have a look at Hasta La Vista. Cheers 🙂

 

[ollypenrice]

On 14/07/2022 at 15:56, Laurieast said:

 

As mentioned by AstroMuni, the new GHT (generalised hyperbolic transform) tool in Siril is way better than just levels and curves. 

 

 

I doubt this, though I haven't tried it. Levels gives a bog standard logarithmic stretch but any stretch done by any action can be replicated in Curves. In Curves you have total control - but you need to know how to use it. For a second dimension of control you can use Curves in Layers and use layer masked blending to combine the two (or more) layers. The great thing about doing it manually is that you're not using pre-ordained 'guesstimates,' you are looking at your own unique data and interacting with them as you see fit. Obviously I haven't tried all the pre-packaged stretches out there but, of those I have tried, none has tempted me away from individually constructed curves.

I reckon it's worth thinking through what you're doing in Curves because no ready made stretch can, in the end, beat one tailor-made to your data and to your own taste and intentions. On top of that, you learn what is really happening when you post-process an image.

Olly