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[Solved] Stacking with sub frame

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(@outer-space)
Main Sequence Star
Joined: 4 years ago
Posts: 15
Topic starter  

Hello APP devs,

my  full-frame sensor size is 6338x9576. When I capture a Light image and view the metadata, it lists the size correctly as:

HDU1 - NAXIS1 = 9576 / length of data axis 1
HDU1 - NAXIS2 = 6388 / length of data axis 2

 

In my capture program, I am able to set a smaller frame size for capture from this camera. This is helpful when a reducer doesn't produce a full-frame image and I have to crop in. In my recent session, I set the frame size to be  4168x6224 (the middle area). The Light from this session shows the correct metadata as:

HDU1 - NAXIS1 = 6224 / length of data axis 1
HDU1 - NAXIS2 = 4168 / length of data axis 2

[ref:A] the 4168x6224 images were captured at (1110,1676) location. I have also captured my flats using these dimensions.

I have a library of calibration images (Darks, bias etc.) that were captured with the full sensor size. The metadata for these files show correctly as:

HDU1 - NAXIS1 = 9576 / length of data axis 1
HDU1 - NAXIS2 = 6388 / length of data axis 2

 

Q1. using [ref:A] above, can I extract the  4168x6224  subframe in APP from the full-size calibration files (Darks, Bias) to apply to my 4168x6224 sized lights? How can I do that? I understand BPM may be re-calculated with the cropped Darks / Bias frames. Does APP allow me to crop with exact pixel range and location? AFAIK, batch crop doesn't let me do this.

Q2. Is it a sound approach? will it work? Yes/no why? 

All in all, I am trying not to redo my entire calibration library for my cropped capture of Lights.

 

Looking forward to your thoughts & many thanks for your time!

 

 

 


This topic was modified 3 years ago by outer space

   
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(@mabula-admin)
Universe Admin
Joined: 9 years ago
Posts: 5056
 

Hi @outer-space,

The approach is sound I would think, you need to crop away 1676 on the left and 1110 from the top from your original masters with dimensions 6338x9576 and make sure that the resulting masters have the correct dimensions of 4168x6224. Best check to know if it works correctly, is to check if the Bad Pixel Map properly removed the hot pixels in a light. You can check this with the calibrated image viewer 😉

The Batch Crop tool should allow you to do this, you can simply add the correct offsets in the offset fields like this (APP 2.0.0-beta17) and the crop will show correctly on those masters to crop:

BatchCrop set crop offsets

So left offset would be 1676, right offset would 1562, Top offset would be 1110 and bottom 1060, then the resulting dimensions would show 6224x4168 (width x height) for your data 😉 (I loaded a different image with different dimensions so my resulting dimensions are off... )

Mabula

 

 



   
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(@outer-space)
Main Sequence Star
Joined: 4 years ago
Posts: 15
Topic starter  

Many thanks Mabula, this works!



   
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(@mabula-admin)
Universe Admin
Joined: 9 years ago
Posts: 5056
 

Excellent @outer-space !



   
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