Lacking in contrast!

[wimvb]

1 hour ago, Rustang said:

if so how can you tell!? 

Dark corners in your image. I'd say your flats are undercorrecting

[Rustang]

35 minutes ago, wimvb said:

Dark corners in your image. I'd say your flats are undercorrecting

I see, I get vignetting on all filters so I'm guessing they would also be produced on the flats for each filter!? Does make processing that extra bit of a pain in the back side but I can live with it. 

Edited June 26, 2021 by Rustang

[wimvb]

My take on your data.

Processed in PixInsight:

• Dynamic crop to remove most of the vignetting and stacking artefacts
• DBE to flatten the background. I used Sara Wagers image as a reference.
• 5 x histogram transformation with the gray pointer at 0.25. Instead of doing one bold stretch, I use several milder stretches. This gives me better control. I usually try to get the peak of the histogram past 0.1 (26 in PS), bringing in the black point when needed but avoiding clipping at all cost
• Multiscale Median Transform with a star mask applied to keep the stars from bloating. I used noise reduction on layers 1 - 3, which reduces noise on structures which are up to 4 pixels large. On larger structures I used a bias, which increases contrast. Like the local contrast enhancement that Olly wrote about, this darkens the darker areas and brightens the brightest areas, so I also added a bias to the residual layer (the whole image), brightening it a little. This way I avoided clipping the data.
• Star reduction
• Noise reduction
• curves transformation 

 

(click on the image to enlarge it)

This is the image just before local contrast enhancement with MMT (just stretched with histogram transformation, levels in PS)

 

Edited June 27, 2021 by wimvb

[ollypenrice]

13 hours ago, Rustang said:

Thanks for the heads up on this, I actually forgot I already have those actions so Ive taken a look at the 'Local contrast enhancement' and it works wonders. The images below show with and with out the preset and the areas it enhances are perfect!

This looks good. The stars look a bit hard, though, a bit too sharp. I always exclude stars when sharpening. Very easy with Noel's Actions. Use 'Select brighter stars,' expand and feather considerably and the select inverse in Ps. Sharpen that. I always sharpen a bottom layer with the original on top so I can use the eraser to let the sharpening through, paritally or fully, only where I want it.

Olly

Edit. Indeed, when very undersampled, as with my old Atik 4000 and focally-reduced Tak FSQ, I would sometimes select the stars and blur them to loose a slightly 'blocky' look.

Edited June 27, 2021 by ollypenrice
As stated

[wimvb]

10 minutes ago, ollypenrice said:

Edit. Indeed, when very undersampled, as with my old Atik 4000 and focally-reduced Tak FSQ, I would sometimes select the stars and blur them to loose a slightly 'blocky' look.

I found the stars in this image definitely not undersampled. In fact, they had a softer profile than what I usually have, almost as if focus was slightly off. But this can also be due to bad seeing and large guiding rms.

[ollypenrice]

Just now, wimvb said:

I found the stars in this image definitely not undersampled. In fact, they had a softer profile than what I usually have, almost as if focus was slightly off. But this can also be due to bad seeing and large guiding rms.

I agree, I think focus may have been a little soft. I think the hardness in Rustang's image may be from global sharpening?

Olly

[wimvb]

After I posted my version, I went back to the linear stage and applied deconvolution. That improved the stars and added a little sharpness to some of the finer details. I haven't finished processing the image yet, as it was getting too late. I will post it late this evening.

[Rustang]

Thanks again guys for all your help,im seeing some great processing on the data. In regards to softness, il keep an eye on the focus but one thing I've noticed is that all of a sudden I'm getting a very low RA OSC reading when guiding, it's always been sitting around 0.45 but during all of the imaging sessions for this target it's been going down to 0.06 so into the Red and barely goes higher than 0.18. Everything else has been the same and because the subs appeared ok I have carried on with the intention of finding out the problem later. Even when I tweaked a couple of settings that were mentioned online it had no effect on improving it. I put this down to seeing because of the bright nights but could be totally wrong, could this be adding to the focus issue/stars ? 

Edited June 27, 2021 by Rustang

[Rustang]

50 minutes ago, ollypenrice said:

I agree, I think focus may have been a little soft. I think the hardness in Rustang's image may be from global sharpening?

Olly

If you mean the images above where I was trying out the local constrat preset, I was only having a quick go to see what it could do so didn't worry about the stars while processing 😊

Edited June 27, 2021 by Rustang

[wimvb]

In the end, deconvolution didn't make much difference.

Btw, here's your star profile in the unstretched image. It's a bit wider and softer than what I'm used to. It looks oversampled, but with a SW 80ED and 5.4 um pixels it shouldn't be this soft, imo. I always thought that RA oscillation in PHD was a measure of seeing, but I never really looked further into it.

[Rustang]

30 minutes ago, wimvb said:

In the end, deconvolution didn't make much difference.

Btw, here's your star profile in the unstretched image. It's a bit wider and softer than what I'm used to. It looks oversampled, but with a SW 80ED and 5.4 um pixels it shouldn't be this soft, imo. I always thought that RA oscillation in PHD was a measure of seeing, but I never really looked further into it.

Thanks for having ago and for all your help. If the RA OSC is seeing then it could well be the brighter nights causing it its just strange how all of a sudden its not the reading it used to be but has only gone down since starting on this target during the 'non astro dark' nights. Il keep an eye on focus next time I'm imaging.

[Rustang]

So this thread has gone on for a little while but its definitely been helpful for a few reasons so thanks everyone. I'm comfortable with the fact my images arnt perfect, there are lots of factors that mean this is so but with all that being said I'm really pleased with the progression Ive made in this hobby with the new camera and Ive been amazed with what Narrowband imaging has opened up. So with help from all the above, here are two new processed versions of my HOO NGC7822 data that I'm much happier with. Ive not sharpened the images and I also haven't removed much of the noise either because I wanted to allow for the extra little bit of sharpness and details to show.