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Old 05-08-2016, 07:47 PM
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Atmos (Colin)
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Processing a large moasic

I was on the ride on mower this afternoon about 4pm and I came to the conclusion that I would like to, when my new mount arrives soon, do something on the order of a 200 panel mosaic.

My plan is to put my Nikon D700 onto my frac, FX OSC camera at ~670mm FL. The plan is to just do single 120s frames at ISO 1600 starting at the centre of the Milky Way and basically spiralling outwards from there. If I can organise it better I'd prefer to start from the west side and slowly work my way east so that I am fighting the Earth's rotation. The whole lot can be done in one night.

My question is however, would I be better using software like PTGui to create the super file to begin with or process every frame individually and slowly add it onto a master mosaic?

This whole idea may eventually just end up falling into the "too hard basket" but who knows
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Old 05-08-2016, 07:58 PM
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Sounds like an exciting plan.

PTGui is good but for that to work the files would have to be kept small. PTGui can handle it but Photoshop can't handle Sony A7r2 files at about 80mb each x 8.

I also find PT Gui does not lining up star only scenes. It works best when there are landscape items in the image. But if you made sure your camera was on a panorama rig it would help.

What is a frac?

Greg.
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Old 05-08-2016, 08:45 PM
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Years ago I did use PTGui to do a 360 Pano of the sky, cannot remember if I had any landscape in it though. Was more of a test of software than anything, ended up with something like 50 files and it did it okay.

Currently planning on having it on a EQ mount on my refractor (frac). If I put in my camera and telescope FL into MaximDL it can tell it to spiral out from a central point (galactic centre).
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Old 06-08-2016, 08:15 AM
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Hi Colin,
I have two suggestions which you may have already considered. Sequence Generator Pro has an awesome Mozaic wizard for creating the sequence. It would work very well for what you are proposing.

As for the processing, Pixinsight has some really good tools such as mozaic by coordinates for registering the files and Gradient merge mosaic for integrating them. I use both these tools quite often and work really well. Hope you go ahead with it, sounds like an amazing project.
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Old 06-08-2016, 09:00 AM
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Hi Colin,
I have two suggestions which you may have already considered. Sequence Generator Pro has an awesome Mozaic wizard for creating the sequence. It would work very well for what you are proposing.

As for the processing, Pixinsight has some really good tools such as mozaic by coordinates for registering the files and Gradient merge mosaic for integrating them. I use both these tools quite often and work really well. Hope you go ahead with it, sounds like an amazing project.
I've just put in a 30 FOV around M8 to see if SGP can handle such a large region. It was something that I had considered attempting but didn't think it would be able to handle. It did! It has gathered nearly 50 panels and stitched them together for me
Apparently it would take 172 panels to do 30 around M8. This would be at 2.77"/pixel with 15% overlap and full colour. Thanks for making me test it Rex

Where my main questions stems from is whether I should be doing some basic processing on each individual image and then stitching them OR stitching them and then doing basic processing. Considering that my current plan is just single 120s exposures out of an unmodified DSLR, it is going to be noisy as all getup. Processing is not going to be anything fancy as the data just isn't going to take it.

FYI, doing the aforementioned would end up with a 1.75 gigapixel image
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Old 06-08-2016, 10:30 AM
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Where my main questions stems from is whether I should be doing some basic processing on each individual image and then stitching them OR stitching them and then doing basic processing. Considering that my current plan is just single 120s exposures out of an unmodified DSLR, it is going to be noisy as all getup. Processing is not going to be anything fancy as the data just isn't going to take it.
In this case, since you're stitching single exposures, I suspect you can get away with processing after the stitching. As you note, it's going to be fairly noisy anyway. If you process each one individually, you may have different levels or other issues to deal with when trying to piece them together. Although, as I wrote that, it's possible you'll have that anyway...
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Old 06-08-2016, 10:40 AM
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In this case, since you're stitching single exposures, I suspect you can get away with processing after the stitching. As you note, it's going to be fairly noisy anyway. If you process each one individually, you may have different levels or other issues to deal with when trying to piece them together. Although, as I wrote that, it's possible you'll have that anyway...
I think no matter what I do... My computer is not going to like me
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Old 06-08-2016, 12:07 PM
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Just guessing here, but I think you would at least have to calibrate each frame before stitching.
Apply darks and flats or the mosaic would look weird if each frame had vignetting.

Cheers
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Old 06-08-2016, 12:20 PM
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Just guessing here, but I think you would at least have to calibrate each frame before stitching.
Apply darks and flats or the mosaic would look weird if each frame had vignetting.

Cheers
You are correct Bill. If I use MaximDL I can have it auto calibrate every image as it is taken.
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Old 06-08-2016, 12:22 PM
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As others have said, the challenge you've set yourself Colin goes up exponentially depending on:

- sky quality (gradients)
- vignetting
- coma/curvature
- noise versus number of shots per panel


Sounds exciting - do keep us updated!
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Old 06-08-2016, 12:39 PM
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Atmos (Colin)
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Originally Posted by RobF View Post
As others have said, the challenge you've set yourself Colin goes up exponentially depending on:

- sky quality (gradients)
- vignetting
- coma/curvature
- noise versus number of shots per panel


Sounds exciting - do keep us updated!
Gradients are my biggest concern but hopefully not too noticeable comparable to other issues (background noise) from single images. I get about 25% vignetting which is easy to correct for with flats. Curvature should be almost negligible, the telescope has a corrected field of 55mm and an FX camera only hits 42mm so well within capabilities (theoretically).

I hope to be able to program it to go North to South starting in the West and working my way east. HOPEFULLY with only 120s exposures I'll be able to more or less keep up with it moving across the sky.
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Old 06-08-2016, 12:49 PM
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I would stitch together and then process.

But you can batch process for the some standard type processing in Lightroom. Things like a tweak to white balance, some noise reduction, increase saturation a little.

So long as each panel gets the same treatment you should be fine. Then final colour processing at the end.

A lot of the noise may be reduced by the large overlap and also so many panels will mean the noise will go to the background I would think.

Greg.
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Old 06-08-2016, 01:06 PM
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Quote:
Originally Posted by Atmos View Post
I've just put in a 30 FOV around M8 to see if SGP can handle such a large region. It was something that I had considered attempting but didn't think it would be able to handle. It did! It has gathered nearly 50 panels and stitched them together for me
Apparently it would take 172 panels to do 30 around M8. This would be at 2.77"/pixel with 15% overlap and full colour. Thanks for making me test it Rex

Where my main questions stems from is whether I should be doing some basic processing on each individual image and then stitching them OR stitching them and then doing basic processing. Considering that my current plan is just single 120s exposures out of an unmodified DSLR, it is going to be noisy as all getup. Processing is not going to be anything fancy as the data just isn't going to take it.

FYI, doing the aforementioned would end up with a 1.75 gigapixel image
Your welcome Colin. 1.75 gigapixel image, now that's awesome. Colin, with the SGP sequence you created from the wizard, you can change the order that the panels are taken quite easily, so programming the order from North to South will be no problem for you. Like Greg said, I usually stitch then process. After calibration etc. Another thing I do that helps with varying sky conditions is I make sure I take the entire mosaic in one night. Meaning that if it is a 6 panel mosaic, I work out how many subs I can take but still get every panel. The following night I rotate the order so that each panel gets taken at a diferent part of the sky. In this way over several nights each panel gets taken at different altitudes and when you combine them they average out a lot better between panels. That might be hard for your situation because of the amount of panels you are planning, but you may be able to work it in somehow.
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Old 06-08-2016, 01:17 PM
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Originally Posted by gregbradley View Post
I would stitch together and then process.

But you can batch process for the some standard type processing in Lightroom. Things like a tweak to white balance, some noise reduction, increase saturation a little.

So long as each panel gets the same treatment you should be fine. Then final colour processing at the end.

A lot of the noise may be reduced by the large overlap and also so many panels will mean the noise will go to the background I would think.

Greg.
Planning on doing all the processing in PI, I have done some attempts in Lightroom (on my second last trial day! Love it for general purpose) but ended up preferring PI.

I am hoping with the sheer scale of the mosaic the noise will just end up being swamped visually by everything else around it. Having never really done a mosaic before (my first and only attempt stitched well but was terribly done overall, no real processing) I am hoping that it'll become vanishingly small (visually) and therefore become non-existent hehe

Quote:
Originally Posted by Rex View Post
Colin, with the SGP sequence you created from the wizard, you can change the order that the panels are taken quite easily, so programming the order from North to South will be no problem for you. Like Greg said, I usually stitch then process. After calibration etc. Another thing I do that helps with varying sky conditions is I make sure I take the entire mosaic in one night. Meaning that if it is a 6 panel mosaic, I work out how many subs I can take but still get every panel. The following night I rotate the order so that each panel gets taken at a diferent part of the sky. In this way over several nights each panel gets taken at different altitudes and when you combine them they average out a lot better between panels. That might be hard for your situation because of the amount of panels you are planning, but you may be able to work it in somehow.
I'll have to have a deeper look at the SGP wizard. I have found that when grabbing a 30 FOV using the wizard it is nigh impossible to actually see what I am selecting so I think I may be better off finding the wide field in Astrobin (as I think SGP reads all its data) and selecting it that way.

One of the reasons I won't attempt it until my new mount arrives is that my current one is too slow. Slewing speed isn't important but when it comes to guider settling and what not, will just lose FAR too much time in settling periods for it to be practical.

Taking 200 panels at 120s, being generous with 15s for slewing and mount stabilisation (should theoretically be closer to 5s) plus adding in the 30 seconds or so for several battery changes (will be charging them throughout the night) it comes to about 7.5 hours which is definitely manageable this time of year.
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Old 06-08-2016, 04:02 PM
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I'll have to have a deeper look at the SGP wizard. I have found that when grabbing a 30 FOV using the wizard it is nigh impossible to actually see what I am selecting so I think I may be better off finding the wide field in Astrobin (as I think SGP reads all its data) and selecting it that way.
Hey Colin, you don't reorder it during the wizard, you just pick the area and let it make the panels etc. Once you tell it to make the sequence, each panel is a separate target and you can change the order of targets by selecting the one you want to move and using the up down arrow icon just under the target section in the sequence window. SGP will just number the panels however it sees fit, but when it creates the sequence the panel number will be on each target so you know which one you are selecting. I have attached a screen shot, you can see I have selected panel 3 (says so just above to the right), and you can see panel 3 is the top right of the mosaic. I have the mouse on the up arrow, which will move it up the order. This is what I meant by you could order them however you wanted. Hope that helps.
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