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[Sticky] What is a Mosaic and when do I need to use the Mosaic Registration mode ? Or... Why does registration take forever ?  

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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2071
March 15, 2018 13:03  

Hi all,

There clearly is some confusion in the community about what a mosaic technically is and what not I think, so this FAQ is created to give a better understanding of what a mosaic is and when to approach it like that in registration.

Several users, especially users that have used Deep Sky Stacker (DSS) a lot, (but also other applications) are using APP's mosiac registration mode when it's not needed at all 😉 It will only complicate things a lot and it will slow things down hugely if you need to register and integrate 100s of frames.

DSS' mosaic function is really not a mosaic as far as I am concerned.

It's a composition mode that just shows all pixels in the integration of all frames. But DSS makes no attempt whatsover to register a mosaic. It simply can't.

The DSS mosaic setting has no influence on the registration so calling it a mosaic is bad naming (I think).

In APP this is called the full composition mode in 6) integration, which is used by default.

So what's a mosaic then?

Technically, a mosaic is a dataset that has some frames that have 0% overlap with the chosen reference frame. Then you can call it a mosaic technically and the registration can only solve that in the mosiac registration mode. A dataset like that can not be registered by DSS at all.

So if you have data that is spread over a  large field of view, but where all frames have some overlap with 1 of the  frames in the dataset (so that would be one of the frames in the center of the field of view), then this can and should simply be registered in the normal registration mode without using the mosaic mode.

Here is good example, this would be called a mosaic by a lot of DSS users, but it really isn't a mosaic and it was registered in APP using the normal registration mode.

It's data shot with a Nikon D5100 and a 50mm objective using a simple tripod without tracking. Iso 1600 and exposure of only 2.5 seconds.

So it's a wide field of view, a nice panorama, but

all frames have overlap with the frames in the center of the field of view, so this is technically NOT a mosaic ! and approaching it as a mosaic will only complicate things without a reason to do so.

in 4) register, use,

  • same camera and optics on
  • dynamic distortion correction on
  • registration mode normal (so not mosaic!)
  • projective model

Registration is then fast, optical distortion correction is very accurate as well, even with 100s of frames.

The first image shows registration & integration of 20 frames of the dataset, the other 2 images show 200 frames.

THIS IS NOT A MOSAIC 😉

20 frames full composition
200frames full composition
200frames crop

 

So what's a mosaic then ?

A mosaic has frames that don't have overlap with whatever frame you choose as a reference in registration:

This then clearly is a mosaic. several mosaic panels have 0% overlap with whatever frame you choose as a reference:

Data courtesy of André van der Hoeven @andre_van_der_hoeven , H-alpha exposure in Cygnus:

THIS IS A MOSAIC 😉

9 panel mosaic Andre Van Der Hoeven

 

Addtional and very important : if you do have a mosaic, don't try to register all frames of all panels all at once, that is very inefficient and not as robust as it could be!

If you have 9 panels of 30 frames each = 9x30 = 270 frames,

then registering 270 frames in the mosaic registration mode will take very long ! as some users have experienced. This is not efficient and also not the best method for precision.

You need to register (normal registration mode) and integrate the 9 panels separately first using both LNC and MBB in integration. LNC and MBB will strongly prevent any stack artefacts so chances are good that you won't need to crop (more data is always better for robustness of registration and SNR over the whole mosaic) any mosaic panel for a good mosaic registration & integration 😉

The integration of the mosaic itself needs to be done with LNC and MBB as well to prevent seams and illumination differences in the mosaic.

My recommendations currently would be:

For the individual mosaic panels:

  • LNC 1st degree 3 iterations
  • MBB at 5-10%

For the mosaic:

  • LNC 2nd - 4th degree 3 iterations (only increase iterations and degree if needed) A higher degree can cause more illumination waves in the mosaic. (LNC upgrade for this is being worked on)
  • MBB at 10-25% (depends on the amount of overlap between the mosaic panels, 10% overlap -> 10% MBB, 20% overlap -> 20%MBB)

Then the mosaic calculation is reduced to only 9 frames and calculating that is done in a couple of minutes on most hardware. So that will reduce the amount of time needed for registration greatly and it will even give better and more robust registration for your mosaic 😉

Kind regards,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@kees_scherer)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 32
March 24, 2018 11:06  

So first make a stack per panel using LNC and MBB. Then make the Mosaic with no LNC/MBB? With LNC/MBB? I am going to start over with the processing of my 72 Panel Orion Mosaic and need to know the best method before making the 72 stacks....


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2071
March 25, 2018 11:02  
 
Posted by: Kees Scherer

So first make a stack per panel using LNC and MBB. Then make the Mosaic with no LNC/MBB? With LNC/MBB? I am going to start over with the processing of my 72 Panel Orion Mosaic and need to know the best method before making the 72 stacks....

Hi Kees @kees_scherer,

Yes, integrating the individual panels with both LNC and MBB is highly recommended. If you don't you will need to crop the created panels to remove integration artefacts and the more data that you have for the mosaic, the better 😉

For the individual panels, use LNC 1st or 2nd, but not higher. The current LNC implemtation might gave waves with a higher degree, which you don't want, especially in the individual panels.

I have added the following information in the main post to be more complete:

The integration of the mosaic itself needs to be done with LNC and MBB as well to prevent seams and illumination differences in the mosaic.

My recommendations currently would be:

For the individual mosaic panels:

  • LNC 1st degree 3 iterations
  • MBB at 5-10%

For the mosaic:

  • LNC 2nd - 4th degree 3 iterations (only increase iterations and degree if needed) A higher degree can cause more illumination waves in the mosaic. (LNC upgrade for this is being worked on)
  • MBB at 10-25% (depends on the amount of overlap between the mosaic panels, 10% overlap -> 10% MBB, 20% overlap -> 20%MBB)

 

In addition to the LNC implementation, as you know, a new LNC implementation will come using several adjustments that should prevent the waves from appearing in the higher degrees. And I will work on making the calculations faster.

Kind regards,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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