A basic PixInsight workflow for LRGB images

[RickS (Rick)]

I promised a few people that I would take my cryptic workflow mind map and make it into something more readable. The result is attached. I tried to keep it simple but still include some more advanced ideas. I hope it is helpful, especially to folks who have managed to tame some of the PI processes but are wondering how to connect them all together.

I don't claim this is the best way to do things but it mostly works for me. Each image will benefit from different treatment so don't treat this as something written in stone. Feel free to vary things and improvise. I usually do!

Cheers,
Rick.

[Spookyer (Brett)]

thanks Rick, appreciate that. I may actually have some data soon, this will give me a start on how to deal with it.


Do you a narrow band workflow as well?

Brett

[ozstronomer (Geoff)]

Cheers Rick, much appreciated. Will try it out next time I have some RGB data

Geoff

[RickS (Rick)]

Originally Posted by Spookyer

thanks Rick, appreciate that. I may actually have some data soon, this will give me a start on how to deal with it.


Do you a narrow band workflow as well?

Brett

I haven't written up a narrow band workflow, Brett, but you can use the same basic steps with a synthetic Luminance.

One simple way to generate a SynL is to do the LRGBCombination of the Ha, OIII and SII, get the colour about where you want it and then use ChannelExtraction to extract the CIE L* channel.

Another technique that has worked well for me is to use ImageIntegration (with no rejection) to combine the master Ha, OIII and SII frames into a SynL.

Originally Posted by ozstronomer

Cheers Rick, much appreciated. Will try it out next time I have some RGB data

Geoff

Hope it helps, Geoff!

[troypiggo (Troy)]

G'day Rick, great work!!

Mostly lines up with what I've been doing (when I get to image!).

I notice you independently stretch the L and RGB, then just combine them with tweaking the lightness and saturation sliders. For me, and possibly/probably because I take L 1x1 but RGB 2x2, I have trouble getting the LRGBCombination looking right. All washed out, not matter how much I tweak the sliders.

Solution I found was to do the individual stretching of the L and RGB, but then throw in some steps where I extract the CIEL from the RGB, then LinearFit it to the L, then combine it back into the RGB before the LRGBCombine of L and RGB. Rarely need to touch the lightness sliders when doing that because they're already matched.

Other thing I do at the cropping stage is before applying a DynamicCrop to the first image, I make a Process Icon out of it so can just drag and drop in on all the masters (or use Image Containers).

[RickS (Rick)]

Originally Posted by troypiggo

G'day Rick, great work!!

Mostly lines up with what I've been doing (when I get to image!).

Thanks, Troy. Small kids can get in the way of astro pursuits but they do grow up eventually

Originally Posted by troypiggo

I notice you independently stretch the L and RGB, then just combine them with tweaking the lightness and saturation sliders. For me, and possibly/probably because I take L 1x1 but RGB 2x2, I have trouble getting the LRGBCombination looking right. All washed out, not matter how much I tweak the sliders.

Solution I found was to do the individual stretching of the L and RGB, but then throw in some steps where I extract the CIEL from the RGB, then LinearFit it to the L, then combine it back into the RGB before the LRGBCombine of L and RGB. Rarely need to touch the lightness sliders when doing that because they're already matched.

Yeah, I've seen that done but never needed it myself. I always bin x1 so I guess my L and colour subs are reasonably compatible. A lot of the time I don't even need the sliders.

I have used LinearFit to match narrow band integrations where there is a big variation in intensity between Ha, OII and SII.

Originally Posted by troypiggo

Other thing I do at the cropping stage is before applying a DynamicCrop to the first image, I make a Process Icon out of it so can just drag and drop in on all the masters (or use Image Containers).

That's definitely the smart way to do it. You can also create a process icon by dragging from the HistoryExplorer after doing the first crop.

Cheers,
Rick.

[troypiggo (Troy)]

Didn't know about the HistoryExplorer creating Process Icons. Cool!

[multiweb (Marc)]

Cool - thanks for that Rick.

[gregbradley]

Thanks Rick.

Greg.

[pvelez (Pete)]

Rick

that is super helpful - thanks for that

Pete

[allan gould]

Thanks for the write up Rick. Will be super helpful for me when the weather clears up and I get some decent data.
Allan

[RickS (Rick)]

Thanks, chaps! If you have any feedback let me know and I'll update the document if needed.

[rogerg (Roger)]

Thanks everyone (especially Rick) for your suggestions and workflows.

I'm struggling with enthusiasm for astronomy right now (watching endless clear blue sky days and nights go by) and I think it's largely because LRGB processing is just such a struggle for me still. Battling new workflow with CCDStack and/or PixInsight. I'll get there eventually.

[DavidNg (David)]

Thanks Rick,

Any tips for the star mask? I've never got it right, always some small stars not covered as well as really big ones.

Regards

[Rod771 (Rod)]

Originally Posted by DavidNg

Thanks Rick,

Any tips for the star mask? I've never got it right, always some small stars not covered as well as really big ones.

Regards

This might help you David.

Click here for Pixinsight post

[RickS (Rick)]

Originally Posted by DavidNg

Any tips for the star mask? I've never got it right, always some small stars not covered as well as really big ones.

There's no magic bullet unfortunately, David. Building a good star mask can be hard work.

Here are some of the things that I've found helpful:

• if you have a colour image, extract the Lightness (CIE L*) and use that as the basis for the mask. If you have a mono image then just clone it.
• if you're still working with a linear image then apply a stretch.
• apply a heavy HDRMT dynamic range compression (as described in the PI Forum post that Rod mentioned.) Set the number of wavelet layers depending on the size of your largest stars and use several iterations (I usually try 4 or 6).
• grab a small but representative preview and use it to test different StarMask parameters to save waiting time.
• increase Noise Threshold if you're getting nebulosity or other non-star stuff in the mask. If you get really desperate there's always CloneStamp.
• set Scale big enough to capture the largest stars you want to mask.
• tweak the Structure Growth parameters to get the coverage you want and balance masking of small and large stars
• you can use MorphologicalTransformation for fine tuning of the mask (or to gradually adjust a mask when making iterative changes like multiple applications of MT to reduce stars).
• sometimes I do "fancy" stuff like: build a star mask, clone it, shrink the stars in one clone with MT Erosion, grow the stars in the other clone with MT Dilation, use PixelMath to "subtract" the little stars from the big stars making a donut mask that can be used to work on the outer edge of stars for fixing halos or reducing star size without dimming the cores too much.
• don't forget to apply the masks to your image and flick between normal and inverted view to get a feel for how well they fit
• sometimes a range mask (RangeSelection) can work better than a star mask.

Hope that helps... Experiment with the parameters and take your time.

Cheers,
Rick.

[RickS (Rick)]

Originally Posted by rogerg

I'm struggling with enthusiasm for astronomy right now (watching endless clear blue sky days and nights go by) and I think it's largely because LRGB processing is just such a struggle for me still. Battling new workflow with CCDStack and/or PixInsight. I'll get there eventually.

Hope you get your mojo back, Roger I quite enjoy the processing battle and I'm sure you will too once you climb the learning curve a little more!

[RobF (Rob)]

Great stuff Rick.

Interesting you do gentle noise reduction first thing on the Lum master. I wouldn't normally do any NR until the end depending on how good the data was and how hard it had to be stretched.

Anything like this that gets you thinking is good as no "right" way of course.

[RickS (Rick)]

Originally Posted by RobF

Great stuff Rick.

Interesting you do gentle noise reduction first thing on the Lum master. I wouldn't normally do any NR until the end depending on how good the data was and how hard it had to be stretched.

Anything like this that gets you thinking is good as no "right" way of course.

Thanks, Rob.

I think I first saw an example of noise reduction of linear data in a post by Juan introducing noise reduction using ATWT. It seems intuitively, to me at least, a good idea to tackle noise early and it does allow you to start with a slightly more aggressive stretch.

I use a clipped luminance mask to protect the bright areas and normally prefer ATWT or MMT with noise reduction only at the smallest wavelet scales. I work on a preview at 1:1 or higher zoom to check the effect and always err on the side of caution. It's really just a small scale smoothing of the background areas rather than full-on NR.

The thing I really can't decide is whether it is better to do this NR before or after deconvolution. I haven't been able to detect much difference so maybe it doesn't matter?

Cheers,
Rick.

[RobF (Rob)]

I just know I'm "bad" and always jump in the deep end stretching, teasing, pushing. Then way down the road often end up going back to look at deconv or NR if the data seems to be looking promising.

Mmmm. Sounds like my cooking too actually