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31 July 2020 - Comet Registration video tutorial using APP 1.083-beta1 released.

30 July 2020 - APP 1.083-beta1 has been released introducing Comet processing! This 1st beta has comet registration. The stable release will also include special comet integration modes.

9 July 2020 - New and updated video tutorial using APP 1.081: Complete LRGB Tutorial of NGC292, The Small Magellanic Cloud by Christian Sasse (iTelescope.net) and Mabula Haverkamp

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[Sticky] Tricky Mosaic workflow, alignment problem  

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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 5, 2020 17:14  

I have four green data panels that where made following the workflow you outlined earlier. Each panel looks fine both visually and from the various analysis tools in APP but I cannot get them to form a mosaic. I have had no issues with this procedure with Red and Blue data shot at the same time with the same rig and within days of each other.  Analysis of the individual subs and the subsequent panels both visually and using the APP file analysis options all indicates the data is good. 

Is there anything that can be done in APP to get past the distortions I'm getting or is the data bad?

Kind regards

Chris

This topic was modified 6 months ago by ChrisPeace

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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 06:50  

Anyone want to have a go at stacking these four panel files into a mosaic and report how you get on? I keep getting distortions in the final mosaic following Mabula’s tutorial exactly and any number of other variations on that workflow. 

Chris

This post was modified 6 months ago by ChrisPeace

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(@ralph)
Red Giant Customer
Joined: 1 year ago
Posts: 78
May 10, 2020 12:55  

Works just fine for me.

What I did:

  • Fresh start of APP 1.079
  • Load the fits files, no multi-channel, no multi-session
  • Set registration mode in 4) Resister to "mosaic"
  • Click "integrate" in 6) Integrate, and use the proposed modifications when asked to change from the default settings.
test

(@minusman)
Neutron Star Customer
Joined: 3 years ago
Posts: 174
May 10, 2020 13:45  

I think the problem with the registration, is the under sampling of the data. When you zoom in, the stars look very blocky. I would suggest to integrate the panels with another pixel interpolation method (e.g. Cubic B-Spline). Or to take much more pictures per panel to use Drizzle.
Did you calibrate the images with Masterflat? The panels still have vignetting.

 

 

Mosaik Green session 1 4thLNC it1 mod St

 

This post was modified 6 months ago 3 times by minusman

(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 2484
May 10, 2020 14:04  

Excellent stuff Ralph and Minusman!


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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 14:06  
Posted by: @ralph

Works just fine for me.

What I did:

  • Fresh start of APP 1.079
  • Load the fits files, no multi-channel, no multi-session
  • Set registration mode in 4) Resister to "mosaic"
  • Click "integrate" in 6) Integrate, and use the proposed modifications when asked to change from the default settings.
test

Ralph, please do me one more favour and post a zoomed in section from the top centre join. I have been able to get close using your suggested technique but the stars at the top centre join are doubled. I know this because I have the R and B mosaic to compare against.

thanks for responding 

Chris


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(@ralph)
Red Giant Customer
Joined: 1 year ago
Posts: 78
May 10, 2020 14:09  

Hm, with more careful inspection there are some alignment mismatches in the right hand scarf.

And with 1400 stars instead of 500 I get worse registration RMS and can reproduce your warped space artefacts in the upper left hand quadrant.

I increased the number of stars detected to 5000 (actually detected stars about 1500 per panel) and played around a bit with the settings. With mosaic registration, scale start 4 and scale stop 6, and dynamic optical distortion on I get decent registration results. For the integration task I set 2nd degree LNC with 10 iterations (yes I know, probably overkill).

There is still some small misalignment visible in the center of the image where the 4 frames overlap, but it's only visible when I search for it. The rest of the alignment looks OK.

It is in my experience unusual to run into these problems, I think you happen to have a bit of bad luck with the way your data turned out for this channel. Advice for future integrations: increase the overlap between the images, or acquire more or deeper subs in order to identify enough stars in the overlap regions.

Alternatively, using the original exposures, select a handful of them per panel and detect the stars and do the alignment of all 4 panels. Have the "same camera and optics" option on, and save the distortion model. Then, use the distortion model for the registration of all the frames for each panel. I think this will reduce the artificial warping you seem to have introduced in your stacked panels.

Comparing the image in the previous answer to the one here, I see a lot of (visibly acceptable) distortion in the centres of the individual panels. This is of course possible for the registration routine since there are no stars in other panels to constrain the positions of the stars there or constrain the deformation. But it is at a first glance unexpected behaviour for the registration outcome.

@vincent-mod do you happen to have anything to add?

test2
This post was modified 6 months ago by Ralph Snel

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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 14:12  

@minusman Thanks for responding. I did use a master Dark, Flat and Bias for the panels. 
I’ll try your suggested pixel interpolation method and post my results. 

Chris


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(@ralph)
Red Giant Customer
Joined: 1 year ago
Posts: 78
May 10, 2020 14:14  

I have no experience yet with APP and multi-channel processing, so hopefully somebody else can jump in here.

Since stars should end up at exactly the same place irrespective of their colour, I would do the registration of all colours at the same time in one go. This way, it should be ensured that all stars in all colours are properly aligned, and that you don't run into the problem of one colour behaving in an odd way, as is the case here.

This post was modified 6 months ago by Ralph Snel

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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 14:27  

@ralph

I’m incredibly relieved to hear someone else has run into the issue. I used 2x2 binning 300sec subs and one hours worth of data in all three colour channels as there isn’t much colour in 95% of this IFN mosaic. Strangely, despite having precisely the same overlaps only the green channel is doing this. I reshot 11 subs Friday night and they stacked fine but had the same distortion when combined into a mosaic. 

thanks for the workflow break down. I’m learning all the time on this one. 

Kind regards

Chris

This post was modified 6 months ago by ChrisPeace

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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 14:37  

@ralph

As you may have seen from my linked thread on this forum ‘Pig and Fish images’ (under General) I have worked for days on this issue. I initially tried putting all the subs in together as you suggested but the integration ran overnight and then gave me the images you can see in my previous post. Mabula helped by restating the process and successfully integrated the Lum mosaic. His technique has not yet worked for me in the case of green. I’m frustrated as it’s not logical and looks like I’m at fault as all the other mosaics have worked and new data made no difference, so I cannot finish of this project until I crack green. 

Thanks for the continued help.

Chris


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 2484
May 10, 2020 14:45  

Ok, so distortion issues in this case it seems as well as undersampling. You will have a lot better results when you dither and use drizzle integration.

So, maybe I missed it, but did you select to use distortion correction? And what % is your overlap? I will give it a go later as well, so thanks for your data and thanks @ralph for your valuable input!


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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 15:28  

Vincent, 

Panel overlap was set at 10% for all subs in the entire HaLRGB mosaic. I have tried with and without DDC in all possible combinations with Same Camera Same optics (both following and ignoring APP warnings and Mabula's workflow guidance) including not having either selected.

My personal closest result (much to my surprise) to something I could put together with the other mosaics and get 95% star alignment apart from in an area I could crop out (but would impact M81 framing) was achieved this morning with the following workflow:

3) 3000 stars

4) start scale 1, stop scale 15  DDC and SC&O enabled (I know that's not recommended), mode: Mosaic

5) Advanced and Neutralise

6) Automatic, Full, 2nd Degree LNC, 3x Iterations, MBB 45%

 

Very non-standard but as I told Mabula I have tried everything else.

Thanks for offering to give this your time.

 

Chris


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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 16:34  
Posted by: @minusman

I think the problem with the registration, is the under sampling of the data. When you zoom in, the stars look very blocky. I would suggest to integrate the panels with another pixel interpolation method (e.g. Cubic B-Spline). Or to take much more pictures per panel to use Drizzle.
Did you calibrate the images with Masterflat? The panels still have vignetting.

 

 

Mosaik Green session 1 4thLNC it1 mod St

 

I have just tried the Cubic B-Spline setting as you kindly suggested with Mabula's recommended settings other than that. You'll see that I got the same 'plug hole' distortion in the middle of the bottom left hand panel as you did plus a tail on the upper left. Generally the stars did fatten up and became much less blocky. I wonder how that would integrate with the Ha, Lum, Red and Blue (green halos perhaps?).

20200508 Green P1 4 Cubic B Spline 2ndLNC it3 St

That's not vignetting by the way, its the consistent LP I have from this site.

Master Flat:

Chris


(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 2484
May 10, 2020 17:22  

Thanks for your patience Chris, it might be the data itself, but hopefully I can get something out of it. If not, it'll be very interesting for Mabula as he always wants to optimize things to make tricky situations work as well. If possible.


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(@minusman)
Neutron Star Customer
Joined: 3 years ago
Posts: 174
May 10, 2020 19:28  

The exposure time of the masterflat is extremely short.
Mabula has always recommended exposure times of at least 1s or more. Because some sensors do not behave linear at short exposure times. This can lead to an overcorrection in the lights. I have experienced this myself.

 


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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 20:26  

@minusman  That's an interesting point but are you or Mabula referring to CCD's or CMOS sensors or both?  I have used the following system for nearly three years and have never had issues before with distortion or with vignette or dust mote repair.  I guess the exposure is shorter because I'm using 2x2 binning. 

I used the Flats tool in APT. It dictates the exposure against the light source, in this case a light panel and the full well, which I set at 20K as suggested by ATIK for the 460EX mono.  So, if I understand you correctly I should be using a dimmer panel as the other parameters are automatic or driven by the manufacturer.

I'll see if I can find any threads on Flats timing on here.

 

regards

Chris


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 2484
May 10, 2020 21:05  

These longer exposures are indeed advised especially of the new CMOS sensors which seem to have an issue with this. Dark flats are also a fine alternative.


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(@chrispeace)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 40
May 10, 2020 21:24  

@vincent-mod                   So over 1 sec is also recommended for the ATIK 460EX CCD?  Given that my current exposure for 2x2 bin is 0.01 that's a x100 variance on my current Flats illumination. It's a dim flats panel already. Surely that's not reasonable?

This post was modified 6 months ago by ChrisPeace

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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 2484
May 10, 2020 21:26  

That's a CCD and I don't think they had that issue. If you do have trouble though, it still won't hurt to go to a higher exposure.

When you've dimmed a lot already, you can always add an extra layer to the panel or something like that.


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