Noise Reduction in Deep Sky Images

[turfpit]

I recently had some sessions which were going to be potentially disrupted by intermittent cloud and decided to use the opportunity to capture some frames with a Luminance filter and experiment with different exposures - 40x120s and 60x60s in this case. At processing, many frames were rejected due to degradation by cloud. The resultant stacks were therefore noisy. I came across a piece of software, called Neat Image, which provides an automated workflow for reducing noise in images. https://ni.neatvideo.com/download - runs on Windows. MACOS, Linux and has a plug-in for Photoshop. The demo edition will only output 8-bit JPG files. On starting the software, there is a handy link to a tutorial video.

Here are the comparisons - the noise reduction took 4 or 5 clicks and no decisions needed to be made about settings. Click on the images to better see the comparison.

M51-Neat-Image-compare-120s-stack.jpg (212.1 KiB) Viewed 2756 times

M51_Neat-Image-compare-60s-stack.jpg (298.79 KiB) Viewed 2756 times

M51-Neat-Image-120s-stack.jpg (202.67 KiB) Viewed 2756 times

To date, I haven't been able to get close to these results using the noise reduction in GIMP, which is probably down to user ignorance rather than the software.

Neat Image is worth a look if there is a requirement to clean up some noisy images.

Dave

[oopfan]

Dave,

Great write up! I like your "compare and contrast" style.

I too have found noise-reduction to be woefully inadequate. I use GIMP's "selective Gaussian blur" followed by sharpening, not the other way around. I downloaded Neat a few months ago. My impression was that it did a fine job, better than GIMP, but the learning curve is steeper.

Perhaps you could put together a short tutorial on Neat for lame-brains like me.

Thanks!
Brian

[turfpit]

Here is a rapid tour. The image used was a stack of 40 x 120s exposures with a luminance filter, captured with thin cloud deteriorating over time. Hence the noisy image.

Start Neat Image and ensure Beginner Mode is selected at top right.

start.JPG (17.23 KiB) Viewed 2707 times

On the Input Image tab, click Open input image.

load-image.JPG (49.02 KiB) Viewed 2707 times

On the Device Noise Profile tab click Auto Profile then Auto Fine-Tune.

process.JPG (62.71 KiB) Viewed 2707 times

On the Output Image tab click Save output image. The image name will have _filtered appended.

save.JPG (40.28 KiB) Viewed 2707 times

By clicking on the Filtered image in the application it is possible to 'blink' between filtered and original.

By selecting Advanced Mode when loading the application a full set of controls become available. As far as i can work out, the Noise Levels presented in Advanced are related to the unsharp mask radius in PhotoShop & GIMP which again are related to Registax's pixel radius Layer 1 (small pixel sharpening) up to Layer 6 (larger pixel sharpening).

noise-levels.JPG (11.48 KiB) Viewed 2706 times

The tutorial videos at the Neat Image site give an interesting explanation of all of this.

Dave

[donstim]

Wow, thank you for this find, Dave. This does a much better job than wavelet denoise in GIMP (or at least the way I have been using it).

Don

[turfpit]

Thanks Don. Yes, a very useful piece of software which produces consistent results for little effort.

Dave

[Menno555]

Post is 6 months old but here now too on Neat Image Pro and it is indeed really great. It beats a program like Topaz Denoise AI by miles.
The results are way more natural due to the many settings. All in all it looks way less "synthetic" then Topaz.

Menno

[turfpit]

Menno

I select Advanced Mode at top right which gives more options in Noise Filter Settings. This seems to give me satisfactory results.

Dave

M27-RGB-in-Neat-Image.JPG (106.15 KiB) Viewed 1972 times

[Menno555]

Hi Dave

Yep, I use that.
And also no profiles but the Noise Filter Settings itself.
Btw, the current version is 8.6.0.

Menno

[Obelisk]

I have had good results with this on DSOs where there is a large enough area to place the sample box that has no image i.e. galaxies, clusters and so on. Where it will fall down is when the whole frame is image i.e. nebula and star fields. I have not tried this but I guess if you took a single frame close to the target in a clear area, you could take a sample from that and import it via the Load Profile tab? Could one build a noise library and if so what would be the defining variables?

Colin

[turfpit]

Colin

The denoise worked well for the M31 image below. I have found it doesn't work well on rich star fields (think NGC7000 region) and images captured with wide angle lenses (rather than scopes). Where Neat does complain I accept what is offered and take whatever improvement is given.

Could one build a noise library and if so what would be the defining variables?

There is a user donated library of noise profiles https://ni.neatvideo.com/download/noise-profiles plus some profiling info https://ni.neatvideo.com/download/calibration-target.

Dave

M31-denoise-comparison.JPG (58.56 KiB) Viewed 1947 times