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Processing a mosaic


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I'm about to dip my toe into doing a mosaic of the veil nebula.

I just wondered if there is some sort of 'standard operating procedure' to processing? 

I'm guessing the way to go is process each panel then stitch together?

 

Any advice to point me along the right path would be greatly appreciated.

 

Am using DSS, Siril and Gimp currently. Also have Startools.

 

Thanks 

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Originally yes. I was going to bring each panel in as a layer and adjust the transparency and line them up.

But, 

I have now found Microsoft ICE which seems a far easier (and probably better) way.

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I do lots of mosaics and don't have a standard method because each one is different. The biggest division comes between stitching the linear data and stitching the stretched. On smaller mosaics, say up to 4 panel or maybe even 6, I will give the linear files a go and hope to be lucky. First, though, the images must be edge-cropped and have gradients removed. The background sky has to be as close to perfect as you can get it, so the same brightness per panel and the same colour balance. I always go for parity in R,G and B. In Photoshop I'm looking for 23/23/23 in R,G and B. I use Pixinsight's DBE to get rid of gradients.

Next I go into Registar, a wonderful program. Sometimes it will give a perfect stitch of the linear. If so I can just treat it as I would a single image from there.

When the linear stitch doesn't work I do a partial stretch of each panel (say about 2/3 of a full stretch.) I get the backgrounds equal in brightness and colour balance and feed those into Registar. Sometimes it's perfect, sometimes not. Maybe a couple of edge lines show? If so, I go back to the individual sub frame from Registar, the frame which covers the joint that's showing, and I paste that over the joint and adjust manually, like a patch, using a feathered eraser to blend it.

In ICE I'd be inclined to use this 2/3 stretch method and give those to the program.

Does GIMP have an 'Equalize' adjustment as Photoshop does? If so, it's a brilliant diagnostic tool. Run 'Equalize' on the mosaic and it will show all the defects of the stitch in gory detail!! If one panel is too green and another too magenta, you'll see it. Go back to the originals, adjust them, and try again in ICE. You don't keep or permanently apply Equalize, it's just there to exaggerate the problem areas so you can fix them.

Olly

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Brilliant help, thanks!

I haven't really had a chance to try again since my initial go but my issue was getting each panel the same brightness. I had used Siril to do a background extraction and a colour calibration, but I hadn't stretched them. I opened these up in Gimp and applied the same stretch to each panel but they weren't exactly the same. I didn't think of getting R, G, B all the same so that's a top tip. I'll also see if Gimp has an equivalent of equalise.

 

Really appreciate the advice. Thanks again.

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