NB accents - ugly issue?

[dx_ron]

Working on M31 OSC from a dark (for these parts, anyway) site plus narrowband (Antlia AlpT filter). Stacked each in Siril. Extracted the Red channel from the AlpT data. Aligned to each other using ASTAP. Loaded in Compose.

The aligned red-only stack from the AlpT looks OK.
(first image)

2022-09-02T00.58.08.jpg (246.49 KiB) Viewed 4318 times

In Wipe, Luminance and Color look good, but in Narrowband I see:


I find that disconcerting

(sorry about the odd formatting, I can't seem to get the images inline where I want them to be)

[Mike in Rancho]

Hi Ron,

Two things -- one, that really looks like your classic Wipe reaction to stacking or registration artifacts. I think more crop is needed. I'll take a wild guess at upper left corner.

Two - I don't think you need to extract R if you just want to use this for Ha NB Accent. If you tell it in compose that the NB Accent file is from a duoband, later when you get to the module, you can tell it whether you want to use it for accenting Ha, or OIII, or both. Might even be a continuous slider, I can't recall. Point is just throw the whole file in.

[dx_ron]

Ah thanks. Guess I've managed to never offend Wipe in such a manner. I shall trim more. And try loading the full file.

If you've not guessed, this is my first try at adding NB accents.

[Mike in Rancho]

Well, my data is far more offensive, no doubt.

Also, oops on upper right, I meant upper left of course. Edited it.

[dx_ron]

You were 100% correct, though - just trimming another 20 or so pixels off the left edge fixed it.

Took me a bit of playing around to catch on to the workflow of adding the NB. Once I did, I was so focused on tweaks to the color and stretching of the galaxy that it took quite a while for me to notice a fundamental flaw

align-oops.jpg (115.82 KiB) Viewed 4274 times

Oops. I was following some post from a while back where some guy (in Rancho, coincidentally enough) suggested using ASTAP to register the two images.

Back to the drawing board. I will probably go all the way back in Siril and register all of the individual AlpT subs to the original OSC reference sub rather than registering the stacks.

[Mike in Rancho]

Ha ha! Well, it wouldn't be the first time I've led people astray with my "tricks." Including you before. I swear though, they all work right in front of me on my computer!

The only times I've really had issues with ASTAP's registration is with JWST data, collaboration data with multiple sets of different resolutions and fields of view, and a two-panel three channel SHO mosaic. Though now I wonder if I unwittingly caused that last one myself - as I just discovered a cone error problem that I hadn't realized I had.

Did you even read through this thread a few months back? viewtopic.php?f=10&t=2568

There's some good combining conversation in there and NB Accent galaxy usage. Starts out with M81/82 and ends with M101. I think one revelation for me there was adjustment of the detail parameter - as I did not want the "stray Ha," which can be quite heavy in places, to be impacting the nice coloration already set for the galactic arms and core, but instead just the poke-through blobs of small Ha regions.

I believe we also discussed a quick undo/reversal on a star core mask right after NB Accent, because otherwise all the nicely RGB-balanced stars can end up pink.

[fmeireso]

Hi Ron,

Two things -- one, that really looks like your classic Wipe reaction to stacking or registration artifacts. I think more crop is needed. I'll take a wild guess at upper left corner.

How can this be avoided? I mean, you can't see the two stacks in NB accent like you see the two stacks if ones use Luminance and chrominance, so cropping becomes difficult. I had thesame issue yesterday, i immediately understood it, but it is a bit annoying.

[Stefan B]

How can this be avoided? I mean, you can't see the two stacks in NB accent like you see the two stacks if ones use Luminance and chrominance, so cropping becomes difficult. I had thesame issue yesterday, i immediately understood it, but it is a bit annoying.

If I remember correctly you can see both stacks in Crop (don't have access to ST at the moment). You can toggle between three views in Crop if you filled the RGB and the NBAccent slot in Compose:
- luminance (a b/w version of your RGB luminance)
- color
- Nrwbd (or something like that; this is your NBAccent stack)

Regards
Stefan

[fmeireso]

Aha, thanks Stefan, that is correct. First you see the color button in Crop but clicking it switches to the Luminance, then you see both stacks aligned.
I did not know that....

[Mike in Rancho]

There's a switching button in crop? Arg. And here I was just using my innate skills to know where the overlaps were.