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MAY 4 2026: APP 2.0.0-beta44 has been released !

New improved internal memory controls should now work on all computers

May 1 2026: APP 2.0.0-beta43 has been released !

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Update on the 2.0.0 release & the full manual

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Once 2.0.0 is released, the price for APP will increase. Owner's license holders will not need to pay an upgrade fee to use 2.0.0, neither do Renter's license holders.

 

CRITICAL WARNING: flat-field calibration can not be performed correctly.

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(@gtdulaney)
Molecular Cloud
Joined: 1 year ago
Posts: 3
Topic starter  

Received warning below during integration.

"CRITICAL WARNING: flat-field calibration can not be performed correctly!

To be able to perform accurate flat-field calibration,
the provided flats need to be calibrated by either

- a MasterBias, of the same ISO/gain value as the flat frame, or
- a MasterDarkFlat of the same ISO/gain value and the same exposure time as the flat frame, or
- both "

I am using Bias data only.  The bias and flat frames were both taken a a gain 75, offset 100.  When I review the FITS header data the flats have both gain and offset.  The bias frames only have gain.

Could the missing offset field in the FITS header cause this error?  If it is can I manually add the offset field and data to the files?



   
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(@gtdulaney)
Molecular Cloud
Joined: 1 year ago
Posts: 3
Topic starter  

Link to example files...APP Flat Calibration



   
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(@jhart)
Neutron Star
Joined: 6 years ago
Posts: 75
 

I get the same warning.  I am using Dark Flats captured with NINA flat wizard that captures the Dark Flats with the same settings as the Lights.



   
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(@mabula-admin)
Universe Admin
Joined: 9 years ago
Posts: 5254
 

Posted by: @gtdulaney

Received warning below during integration.

"CRITICAL WARNING: flat-field calibration can not be performed correctly!

To be able to perform accurate flat-field calibration,
the provided flats need to be calibrated by either

- a MasterBias, of the same ISO/gain value as the flat frame, or
- a MasterDarkFlat of the same ISO/gain value and the same exposure time as the flat frame, or
- both "

I am using Bias data only.  The bias and flat frames were both taken a a gain 75, offset 100.  When I review the FITS header data the flats have both gain and offset.  The bias frames only have gain.

Could the missing offset field in the FITS header cause this error?  If it is can I manually add the offset field and data to the files?

Dear Greg @gtdulaney,

Thank you very much for sharing your issue.

I understand correctly that you are using flats and bias, right?

Then the warning will appear if you are using multi-channel/filter mode in 1)LOAD and the bias/masterbias has not the same filter assignment as the flats. Can you double check that? You can see the filter assignment in the frame column in the frame list panel.

What happens if you disable multi-channel/filter mode, load the flats and bias and run calibration again?

Mabula

 



   
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(@mabula-admin)
Universe Admin
Joined: 9 years ago
Posts: 5254
 

Posted by: @gtdulaney

Link to example files...APP Flat Calibration

Dear Greg, @gtdulaney

Thank you, I have checked the data, the flat has incompatible dimensions with the lights and the darks, bias. The dark and bias have same dimensions as your light, but even the bias is different from the dark in the sense that the bias has no CFA indication in the FITS header, whereas the dark (and flat) have.

data is incompatible created with different capture software

You can see that the flat has dimension 6240x4174, the other frames have dimension 6248x4176. So the flat can not be used unless you know how to change the image dimensions properly.

The biggest issue here is that the frames are created with different capture software. Issue like this are then very common especially with CFA/color data.

Light created with SharpCap v4.1.13332.0

flat created with N.I.N.A. 3.2.0.1046

dark created with SharpCap v4.1.13332.0

bias created with Sequence Generator Pro v4.4.1.1441

For proper data calibration and to ensure that everything goes as expected, you really want to to use the same capture software and even the same capture software version for all the lights and calibration frames. If you can change the image dimension of the flat to match with the others or vice versa, your issue will be solved.

Hope this explains it?

Mabula

 



   
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(@mabula-admin)
Universe Admin
Joined: 9 years ago
Posts: 5254
 

Posted by: @jhart

I get the same warning.  I am using Dark Flats captured with NINA flat wizard that captures the Dark Flats with the same settings as the Lights.

Hi @jhart,

Do your frames have the same dimensions? The same filters assigned in multi-filter/channel mode? And are you adding bias or darflats for the flats?

Mabula

 



   
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(@gtdulaney)
Molecular Cloud
Joined: 1 year ago
Posts: 3
Topic starter  

@mabula-admin 

Thanks for the through response.

I took additional flats the following night and integration worked very well.  I was having software issues and used different app to capture flats that didn’t work.

New flats, APP for integration, light pollution correction and some Pixinght resulted in this.

APP had no issues integrating the data, where pixinsight WBPP failed.

Greg Dulaney

NGC6960 Final

 



   
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(@jhart)
Neutron Star
Joined: 6 years ago
Posts: 75
 

Hi Mabula,

I am using DarkFlats instead of Bias frames for the Flats.  They have the same exposure, gain, bias, and binning as the Flats and the same reported dimensions.  (While the Flats and DarkFlats have identical exposure times per each filter, the Lights are different). Even though I get the pop up warning the Flats seem to calibrate the Lights well.

The FITS headers for the Flats and DarkFlats have the filter used, exposure time, gain, binning, and sensor temp, but not the camera bias setting even though it is the same for all.  Could  the absence of the bias information in the FITS header be what is triggering the warning?

Thanks, Jeff


This post was modified 11 months ago 2 times by jhart

   
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