Mosaic Construction Experience Sharing - Forums

Topic starter

Jun 28, 2021 · Edited: Jun 28, 2021

Hi everyone,

I am reaching out to share my recent experience to build a mosaic.

The object was Rho Ophiucus and I had a top and a bottom panel. I have used PixInsight's GradientMergeMosaic, initially in non-linear image and one thing that puzzled me was the lack of the red hues in the bottom (see photo below, with strong selective color saturation), visible in so many other photos of the same object. I have re-done it several times with some modifications, either on non-linear and linear stage,but nothing seemed to work.

I reached out for help and then I was approached by John Murphy (the NGS script creator) who suggested me to use the PhotometricMosaic script, available by default at PI. Well, the script is a bit intimidating, with several "levers" to adjust, but documentation available at the script is really detailed. The harder here was to make the seam as disguised as possible (I found fairly easy to do this in GradientMergeMosaic) but when I nailed it, result was great. And by great I mean a disguised seam AND the presence of the said red hues. You can find the final result here: https://astrob.in/qp9ezb/0/

Long story short: if you're building fairly complex mosaic, give a try to this script (BTW, I am not sponsered by it

).

Does anybody else have used this script? What's your opinion about it?

Cheers,
André

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Wei-Hao Wang

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Jun 28, 2021

Hi,

Thank you for sharing.

One thing I noticed about GradientMergeMosaic is that it sometimes tries to minimize the overall gradient. For the large red nebula here, it can be identified as gradient and removed by GradientMergeMosaic. From this point of view, a new mosaic script that does not attempt to do too much on the gradient indeed should improve things.

Cheers,
Wei-Hao

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Andre Vilhena

Topic starter

Jun 29, 2021

Wei-Hao Wang:
Hi,

Thank you for sharing.

One thing I noticed about GradientMergeMosaic is that it sometimes tries to minimize the overall gradient. For the large red nebula here, it can be identified as gradient and removed by GradientMergeMosaic. From this point of view, a new mosaic script that does not attempt to do too much on the gradient indeed should improve things.

Cheers,
Wei-Hao

Hi,

I think you may be right. I don't have much experience with mosaics but indeed looking at these two panel, they're quite different - the lower is bright while the one on top is darker - and maybe that confuses GradientMergeMosaic. I tried to saturate the reds before merging, making it brighter than the one on top and nothing worked.
This script works using star photometry, which is a different concept.

Cheers,
André

Björn Arnold

Perfect post

Jun 29, 2021

Hi André,

Don't know if my post is interesting for you: I haven't tried mosaics for DSOs and don't have PixInsight experience. However, different people have told me that AstroPixelProcessor seems have a very good mosaic feature.

CS!
Björn

andrea tasselli

Frequent contributor

Jun 29, 2021

I have used all the mosaic scripts in PI and I've found PhotometricMosaic the one most reliable.

Andre Vilhena

Topic starter

Jun 30, 2021

Björn Arnold:
Hi André,

Don't know if my post is interesting for you: I haven't tried mosaics for DSOs and don't have PixInsight experience. However, different people have told me that AstroPixelProcessor seems have a very good mosaic feature.

CS!
Björn

Hi,

Actually I have heard good things about APP but for the time being I'm planning to stick with PI. But nevertheless it's a good input for anybody else seeing this thread and thanks for it!

Cheers,
Andre

Björn Arnold

Perfect post

Jun 30, 2021

I have not done any mosaic of DSO also . But i have a desire to start with Moon. Please share your methodology of planetery mosaic and post processing in any other software except PI as I don’t owe that. I saw in some other forums, many people have used a software called “imerge” .. is that a good one? please tell me.

For my moon mosaics, I‘ve used Affinity Photo. It will align the images which it did very well. However, the rest is all manual which includes background normalization etc.

Norman Hey

Aug 9, 2021

My first try at a mosaic was with GMM; got pinch artefacts and a not-bad seam. Tried PMM after reading the very comprehensive documentation and just ran defaults–miles better result! Next time, I got brave enough to look at the seam and adjust it a bit–even better! Thank you, John Murphy!

I have no experience with any of the other mainstream processing programs (although I did get started with Nebulosity) so can't comment on pros and cons of different approaches, but PI's PMM is like magic to me. It is stopping me (so far!) from spending money on a wider FOV rig! The downside is the extra time needed to gather the data on 2, 3, 4, 6, whatever frames, but I like the whole process, so it really isn't an issue.

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Brian Boyle

Aug 10, 2021 · Edited: Aug 10, 2021

I gave up using the mosaic tools in PI. Despite reading all the documentation and spending hours of my life trying to get it right, I gave up. It is borderline passable for merging two images along one seam, but anything more complex (e.g. 2x2), it simply wasn't worth my time.

Matthew Maclean pointed me to APP which is simple to use and very straightforward. Other non-astro programs e.g. PTGui also work well. I now use these, despite doing everything else in PI. Mosaicing is a real let-down in an otherwise brilliant package. PI really ought to do something about it.

CS Brian

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SemiPro

IOTD Staff

Perfect post

Aug 10, 2021

APP works for DSO mosaics. Like, it works really well. I found the best way was to stack each panel like you normally would a single image, THEN add them together. Things tended to get freaky in the final image like all kinds of warpage and what not if you just tossed in all your lights and tried to stack them all at once. It also seemed to handle the seams better so you didnt have this odd band of better SNR across your image. It also helps if you stack two at a time, then stack them together. For my 3x2 panel of the Virgo cluster that makes me cry every day because I never finished it (there is always next year I guess...) I did the above and worked like a charm.

2 Panel IC1396

Motest for the forum post.

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SemiPro

IOTD Staff

Perfect post

Aug 10, 2021

Andre Vilhena:
Does anybody else have used this script? What's your opinion about it?

Sorry for the double post, but I might have to give the script a try for my next one!

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andrea tasselli

Frequent contributor

Aug 10, 2021

Brian Boyle:
I gave up using the mosaic tools in PI. Despite reading all the documentation and spending hours of my life trying to get it right, I gave up. It is borderline passable for merging two images along one seam, but anything more complex (e.g. 2x2), it simply wasn't worth my time.

I wonder how difficult can it be? I did a 28 panel mosaic at my second attempt so definitely doable. Even better now with the photometric mosaicking.

Tim Hutchison

Aug 10, 2021 · Edited: Aug 10, 2021

My first experience with PMM was with a 4 panel mosaic from a QHY600 camera (60MP per panel). The resultant image is HUGE with lots of opportunities for bad seams. PMM handled everything perfectly. I thought the results were great. I've never used APP so I won't comment on a comparison but PMM in PixInsight yields great results for me.

Here is the image: https://astrob.in/ra9tw8/0/

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Andre Vilhena

Topic starter

Aug 11, 2021

Tim Hutchison:
My first experience with PMM was with a 4 panel mosaic from a QHY600 camera (60MP per panel). The resultant image is HUGE with lots of opportunities for bad seams. PMM handled everything perfectly. I thought the results were great. I've never used APP so I won't comment on a comparison but PMM in PixInsight yields great results for me.

Here is the image: https://astrob.in/ra9tw8/0/

Hi Tim,

This os a great result - absolutely seamless!

André

Norman Hey

Aug 11, 2021

I should have either pointed out which of my images are mosaics or provided a link. I have only done a couple or three maybe and have had no issues with PMM in PI. My biggest issue: getting "enough" integration time per panel! That and sorting out my various flatteners and/or reducers--natively or with accessories, my corners and edges still show issues and there may be (probably is) tilt as well. But at the usual scale I look at the images, it really isn't an issue.

https://astrob.in/z4fj2e/0/ plus my Andromeda image.

Norm

Related discussions

NGC 6726, etc

This is an interpretation of the image posted here https://astrob.in/0p7p5j/0/, done in Studio2. To quote the Topaz folks, "Topaz Studio is a artistic expression studio." And so it is.

Relevant for astrophotography project sharing and mosaic construction techniques discussion.

Jun 7, 2020