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Lobster Claw & Bubble Nebula


souls33k3r

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10 hours ago, wimvb said:

Noise reduction in PI:

Extract luminance and apply stf as permanent stretch, if you're working on the unstretched image

Make a copy of this luminance, and with curves bring the background up to 50% intensity. Apply this copy inverted to the original image as a mask. This way, noise will be reduced rather than obliterated. And it will only be applied where needed; the dark areas of your image.

Select a preview of the image background and use Image | statistics. Note the standard deviation number.

Open tgvdenoise. Use the extracted luminance as reference, and the measured standard deviation as edge protection value. Lower the exponent of edge protection one unit. Since you're doing luminance noise reduction and not colour noise reduction, set mode to Lab and uncheck chrominance. Reduce L strength to 1.

Increase number of iterations to taste.

Apply tgvdenoise to image.

My preferred method to battle chrominance noise (colour noise and colour mottle) is Multiscale Median Transform applied to Chrominance, because as the name says, it can reduce colour noise over multiple image scales (from pixels to blobs).

Legend! 

Thanks Wim. 

I will see if I can reprocess some of my old data with this knowledge. 

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I'm confused - isn't the Bubble in Cassiopeia and the Lobster all the way over in Scorpio ?  What's the official designation of the large nebula in that pic ?

 

Re PI noise reduction, as Wim says for TGV, I usually do it on the stretched image and do trial and error on both the edge protection setting and the strength setting - though I think the strength setting I use is much less than 1, more like an exponent of -2 iirc.

Multiscale Linear Transform works very well for noise reduction too, and settings are much less than are generally touted on the internet - here's my trick for doing it - *linear*, masked as per Wim's post above, open up MLT, 6 layers, and turn off layers 1-5 inclusive, run on small dark area previews first, open a live preview with a strong stretch - it'll just look like a blurry nothing.  Then turn level 1 back on - the noise will jump out at you, kind of looks like etched glass.  Turn on the noise reduction for that layer, amount 0.75, iterations 3 and fine tune the threshhold till the noise *just* disappears.  Then turn that layer off again, and repeat for levels 2 and 3, maybe 4.  Finally turn all layers back on and apply it to the full image.

Whether MLT or TGV, I usually dial back the settings till the noise starts showing a little bit, rather than removing it completely.  Just need to take the fizz off, not make it look plastic.   Can run a stronger denoise on chrominance than on luminance.

 

*edit, I apply MLT at linear stage, not non-linear

Edited by glowingturnip
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22 minutes ago, glowingturnip said:

I'm confused - isn't the Bubble in Cassiopeia and the Lobster all the way over in Scorpio ?  What's the official designation of the large nebula in that pic ?

 

Re PI noise reduction, as Wim says for TGV, I usually do it on the stretched image and do trial and error on both the edge protection setting and the strength setting - though I think the strength setting I use is much less than 1, more like an exponent of -2 iirc.

Multiscale Linear Transform works very well for noise reduction too, and settings are much less than are generally touted on the internet - here's my trick for doing it - non-linear, masked as per Wim's post above, open up MLT, 6 layers, and turn off layers 1-5 inclusive, run on small dark area previews first, open a live preview with a strong stretch - it'll just look like a blurry nothing.  Then turn level 1 back on - the noise will jump out at you, kind of looks like etched glass.  Turn on the noise reduction for that layer, amount 0.75, iterations 3 and fine tune the threshhold till the noise *just* disappears.  Then turn that layer off again, and repeat for levels 2 and 3, maybe 4.  Finally turn all layers back on and apply it to the full image.

Whether MLT or TGV, I usually dial back the settings till the noise starts showing a little bit, rather than removing it completely.  Just need to take the fizz off, not make it look plastic.   Can run a stronger denoise on chrominance than on luminance.

Sorry yes you're right, this was Lobster Claw nebula. I have now amended the topic

Super useful on the processing technique, have saved it now and will put this in to action on a new target :)

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