Best way to tidy up background in starless image?

[edarter]

Hi,

I'm still using my Veil Nebula stack to try and learn more about post processing, and could do with some advice on what is the best way to tidy up a starless image from Starnet++ within photoshop. My Veil one comes out VERY blotchy, I took a couple of hours yesterday with the spot healing brush to get it to this point but to my eye its still far too blotchy. I appreciate care needs to be taken to not wipe out faint nebula detail and to make sure that the background in not just a uniform colour but I feel my image is quite a long way from even being close at the moment. I even tried using Star Xterminator to see if that gave better results but it didn't, I'm hoping the new version due shortly for Photoshop will be a bit better.

I even considered adding the nebula in to the stars only image I have as that background is far better!

[raadoo]

I tried my hand at cleaning it up:

I intentionally didn't resort to either Topaz, Astronomy Tools Actions or any of the myriad of other add-ons one can employ with Photoshop and instead focussed on using just the default toolset. I also attached a screenshot of what the layers panel looks like, for reference.

The basic approach

Although noisy, the original image has some pretty clear separation between the Veil's nebulosity and the background. Initially, I thought this contrast may be stronger in the green channel, but it turns out to be fairly similar across all three colour channels.

As such, the approach here is to create a separation between background and nebulosity via a mask based on luminosity. So I grayscaled the original and used that as a layer mask to separate background from nebulosity. This mask needed further levels and a low powered Gaussian Blur to achieve the right level of separation.

Edits

With the background and nebulosity separated, I approached each of them in a different way, but using the same Adobe Camera Raw editor to keep it simple.

For the background I lowered the contrast and highlights, upped the shadows and blacks, desaturated slightly, lowered the texture, clarity and dehaze sliders all while adjusting the expoure slider to try and maintain the same black level as the original. I also ran a quick noise reduction while in the same ACR module. Essentially this step is about reducing detail in the background as the only detail to be found here is noise. One must be careful not to go hog wild on this, though - you're right that using a solid colour for the background would look off and certainly isn't in line with your (and mine) keep it natural philosophy.

For the nebulosity, I also resorted to ACR, but this time paying attention to just the Veil itself. So this time it was about increasing contrast, upping the highlights and lowering the shadows slightly, increasing saturation (slightly) in the reds, oranges, yellows and greens and reducing the saturation in aquas, blues, magentas and violets, increasing clarity and texture a smidge, all the while toggling the defaults (\) to make sure I'm keeping true to the original luminosity and colour.

I spent maybe 10min on this, so you can certainly expect even better results from taking the time but hopefully the way I approached it helps. It certainly doesn't help that I edited a compressed JPG 😆

 

[edarter]

Raadoo - that is amazing, thank you for the very detailed response. It certainly gives me new hope that I can get something from it!!
I shall be trying your techniques over the next few days, again many thanks for this it really helps a lot to see what others can do as its very easy to fall in to a pit of despair and thing you're never going to improve or that the data is fundamentally flawed.

Ed

[raadoo]

Fundamentally, all data is flawed by one thing or another. Even the best data we can acquire from Earth is flawed by the atmosphere.

Personally, that helps me psychologically because it means my data is just slightly messier (sic!) than others'.

And even if it's not the best outcome in the world, it's your time, effort, knowledge, skill and passion that were poured into making it, so never let anyone say it's bad, especially not yourself!

[Clarkey]

I would add that the veil is particularly difficult to reduce the stars using starnet+. I processed by reducing the star luminosity rather than removal as it gave a cleaner result. Many other subjects are easier.

[edarter]

On 15/12/2021 at 14:49, Clarkey said:

I would add that the veil is particularly difficult to reduce the stars using starnet+. I processed by reducing the star luminosity rather than removal as it gave a cleaner result. Many other subjects are easier.

How did you do that? produce a star mask?

 

Thanks
Ed

[Clarkey]

1 hour ago, edarter said:

How did you do that? produce a star mask

In effect. Using an intensity mask to reduce the stars only and then blend the layers together. You can also use a starnet starless image and mix it with a full star image. Also works quite well and hides a lot of the 'damage' done by starnet.

[edarter]

Well for now at least I think I'm done trying to process this stack. Reasonably happy with this result after the tips here, but still plenty that could be improved. Think I will come back to it in a few months when I've hopefully honed a number of techniques a bit more. Would love to have a go at this target with a dedicated astro camera rather than a DSLR!