Mosiac clips data a...
 
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Mosiac clips data and changes the colour balance  

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(@sharkmelley)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
May 19, 2019 09:38  

I'm having a problem assembling a 36 pane mosaic of part of the Cygnus region in natural colour.  As usual APP has aligned the panes flawlessly with a high degree of accuracy, which is great!    Each pane of the mosaic had already been carefully white balanced with the camera's colour correction matrix already applied.  The data was still linear and I was very careful not to clip the black level.  They were loaded into APP as 32bit floating point TIFFs for Registration followed by Integration.  However, I have noticed two strange issues in the final mosaic:

1) Colour channels were black clipping in certain regions of the final mosaic

2) The white balance was substantially altered - specifically the green channel had been significantly boosted and the red channel had been significantly attenuated

You can see these effects in the attached screenshot.  I also saved the individual registered panes and these looked perfectly normal.  Why is this happening - is there some setting I have overlooked?

APP Mosaic Issue

Mark

 

 


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(@dav78)
Main Sequence Star Customer
Joined: 9 months ago
Posts: 39
May 19, 2019 17:22  

Hi Mark,

Have you tried to load the different integrated panes of your mosaic before doing anything (color balancing, etc...).

Where those pictures taken with your A7S ?

 

David.

 

 

This post was modified 1 month ago by Dav78

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(@sharkmelley)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
May 19, 2019 18:19  
Posted by: Dav78

Hi Mark,

Have you tried to load the different integrated panes of your mosaic before doing anything (color balancing, etc...).

Where those pictures taken with your A7S ?

 

I probably wasn't being very clear.  Each pane of the mosaic was created, white balanced and background subtracted in another piece of software (Pixinsight) and saved as 32bit TIFFs.  I am now loading those TIFFs into APP to run the registration and integration steps.  The registration works perfectly - I can see the registered panes and no colour alteration has happened (APP can save the registered panes).  The colour alteration and the clipping of the darker areas happens in the integration step.

The data all comes from my Sony A7S.

Mark

This post was modified 1 month ago 2 times by Mark Shelley

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(@dav78)
Main Sequence Star Customer
Joined: 9 months ago
Posts: 39
May 19, 2019 18:44  

You should try to make the color balancing and the background extraction in the final mosaic instead of doing this step in each files.

That's the way I make my mosaic taken with my A7S : each tile is preprocessed and integrated in Pix or APP (I've similar results with both software), if the gradients are strong, I remove them in the different tiles, and then I create the mosaic with APP. And after that I make the background extraction and color calibration.

Here is the topic where I asked for some advice in APP settings for creating a mosaic.

https://www.astropixelprocessor.com/community/main-forum/some-questions-for-creating-a-mosaic/#post-5805

😉


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(@sharkmelley)
White Dwarf Customer
Joined: 2 years ago
Posts: 14
May 19, 2019 19:14  
Posted by: Dav78

You should try to make the color balancing and the background extraction in the final mosaic instead of doing this step in each files.

That's the way I make my mosaic taken with my A7S : each tile is preprocessed and integrated in Pix or APP (I've similar results with both software), if the gradients are strong, I remove them in the different tiles, and then I create the mosaic with APP. And after that I make the background extraction and color calibration.

Here is the topic where I asked for some advice in APP settings for creating a mosaic.

https://www.astropixelprocessor.com/community/main-forum/some-questions-for-creating-a-mosaic/#post-5805

😉

Thanks - that's a very useful thread.

In any case, I've just found my mistake.  I had accidentally used the default settings in step 5) Normalize

In the Normalize step if I set method to "none" and uncheck "neutralize background" then the mosaic works as expected, without altered colour balance and without clipping of blacks.

Mark

This post was modified 1 month ago by Mark Shelley

(@dav78)
Main Sequence Star Customer
Joined: 9 months ago
Posts: 39
May 19, 2019 20:51  
Posted by: Mark Shelley

In any case, I've just found my mistake.  I had accidentally used the default settings in step 5) Normalize

In the Normalize step if I set method to "none" and uncheck "neutralize background" then the mosaic works as expected, without altered colour balance and without clipping of blacks.

Thanx for the information.

In step 5, I allway let the default settings. But it's maybe a mistake, as I usually remove the gradient before making the mosaic...

I'll have to try that because in my last mosaic of Orion, the blacks were a little clipped too.

Let's see the final result of your mosaic, great picture for sure 😉 

Cheers,

David


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(@vincent-mod)
Black Hole Moderator
Joined: 2 years ago
Posts: 383
June 5, 2019 11:32  

Sorry for the late reply, but that's all very valuable, thanks for posting the fix. I normally do the corrections all per panel indeed so might not have encountered this issue as such yet.


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