Unable to get proper Flat Integration with Canon R

giuseppepenzo

New member
Good morning.
I am a new user and I am trying to learn PI.
I am facing an issue that I am not able to solve.
I have a Canon R camera and I am shooting RAW frames (*.CR3).

Setting the "RAW Format Preferences" to "Pure Raw", with the default settings, and running the BatchPreProcessing script, the Bias and the Dark are integrated, the Flat calibrated with a warning "No correlation between the Master Dark and the target frames (Channel 0)", then the script stops on ERROR at the starting of the Flat Frames Integration. The Error is "..../flat/FrameName_c.xifs: Zero or insignificant signal detected (empty image)".

Setting the RAW Format Preferences to the "Demosiced RGB" the integration of the Flat proceeds, but then I get completely white calibrated Lights, because a totally black MasterFlat.

Here is the link to some of the Bias, Dark, Flat and Light frames that bring to the Error.

Without the Flats Frames the BatchPreProcessing script runs successfully to the end.
Is someone able to give me an hint to solve the issue?
Thank you in advance.

Giuseppe
 
Hi Giuseppe,

the bias, dark and light frames were captured at ISO 3200, but the bias frames at ISO 100.

At ISO 3200, the bias offset for this camera is 2048 ADU. However, the minimum intensity in the ISO 100 flat frames is only about 647 - 655. When subtracting the bias from the flat frames, images result which are empty. Only about 70 pixels (of a total of 30 million pixels) of the calibrated flats have an intensity > 0.

Take new flat frames at the matching ISO of 3200. Aim for a mean intensity of about 8000 ADU.

Bernd
 
I
Hi Giuseppe,

the bias, dark and light frames were captured at ISO 3200, but the bias frames at ISO 100.

At ISO 3200, the bias offset for this camera is 2048 ADU. However, the minimum intensity in the ISO 100 flat frames is only about 647 - 655. When subtracting the bias from the flat frames, images result which are empty. Only about 70 pixels (of a total of 30 million pixels) of the calibrated flats have an intensity > 0.

Take new flat frames at the matching ISO of 3200. Aim for a mean intensity of about 8000 ADU.

Bernd

Thank you Bernd.
I took the Flat frames at ISO 100 and with auto-exposure of 1/500 s, to have an histogram peak between 1/3 to 1/2 of the full range, assuming that this would have been what needed.
Many texts are stating to take the perfect Flat Frame (being the subject strongly illuminated) with low ISO and camera auto-exposure to have the perfect histogram.
I can see that the mean ADU of my flat frames is very low, while it should be between 4000 and 8000.
I will correct it by exposing for a time longer that 1/500s to obtain an over-exposed histogram, with an average ADU above 4000.
Thank you for the hint.
Best regards
 
Auto exposure without exposure correction will always underexpose your flat frames. I don't know in which software you looked at the histogram - in any case itwas not the histogram of an unstretched raw file. Your flat frames were severely underexposed.

If you want to use auto exposure you will have to set exposure correction in a way that the unstretched histogram has a mean intensity of about 8000 - 9000 ADU. If you once found out the necessary exposure correction you can use this setting for the flat frames.

Bernd
 
it is OK to take the flats at a different ISO than the lights, but it means that you must have matching ISO bias or flat-darks to calibrate the flat frames. it also complicates things for a beginner because you need to make sure WBPP does the right thing with the various darks/bias loaded - you need to check that the flat darks / flat bias got matched up properly with the flats and only the flats.

if you are doing everything manually (not using WBPP) then it is probably a little easier to be using different ISO flats as you need to calibrate the flats separately and then it's just a matter of making and choosing the appropriate flat dark or bias when calibrating.

rob
 
Auto exposure without exposure correction will always underexpose your flat frames. I don't know in which software you looked at the histogram - in any case itwas not the histogram of an unstretched raw file. Your flat frames were severely underexposed.

If you want to use auto exposure you will have to set exposure correction in a way that the unstretched histogram has a mean intensity of about 8000 - 9000 ADU. If you once found out the necessary exposure correction you can use this setting for the flat frames.

Bernd
I was just looking the histogram proposed by the camera.
In any case you are right. I should have had considered the average and the minimum ADU to be in the range you indicate.
Thank you again.
This solved the issue.
 
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