Warning: The dark frame optimization threshold is probably too high

[Niall Saunders]

Hi Carlos,

Sorry to reactivate this thread
https://pixinsight.com/forum/index.php?topic=9704.msg61598#msg61598,
but I am also experiencing the same (or, at least very similar, issues):

Code: [Select]

ImageCalibration: Global context

Loading master calibration frames:
Loading calibration frame image:
C:/Users/Niall/Pictures/Astro/Darks/600s/2017 03 03/_PI/_MasterDark_600s_02.xisf
Loading image: w=3896 h=2612 n=1 Gray Float32
261 FITS keyword(s) extracted.

Dark frame optimization thresholds:
Td0 = 0.00345814 (6506 px = 0.064%)
[color=purple]** Warning: The dark frame optimization threshold is probably too high (channel 0).[/color]

Calibration of 30 target frames:
* Using 4 worker threads

Calibrating target frame 1 of 30
Loading target frame:
C:/Users/Niall/Pictures/Astro/Flats/Wall/1000ms/2017 04 08/RAW G30 O125 T-15/wFlat 1000ms 001.fit
Reading FITS image: 16-bit integers, 1 channel(s), 3896x2612 pixels: done
28 FITS keywords extracted
28 FITS keywords extracted
The remainder of the console output contains no errors.

I am not using Bias frames - my Flats and FlatDarks (30 of each) were all exposed at 1000ms, using an illuminated wall in the observatory, and the CCD has excellent temperature regulation at -15°C.

I am calibrating the Flats using a previously created MasterFlatDark using an Optimization Threshold of 3.000, an Optimization Window Size of 1024 and I am relying on PixInsight to detect CFA.

The MasterFlatDark was a simple ImageIntegration of 30 Darks which was executed in two passes. In the first pass I fully evaluate noise in order to be able to select the image with the highest noise result as the 'ReferenceImage'. The second pass, using the ReferenceImage, is then used to create the MasterFlatDark itself.

One question that immediately arises here is, "Should Weighting be left at 'NoiseEvaluation' for the second (final) pass, or should it be returnd to 'Don't Care, all Weights=1'?"

However, do you (or anyone else) have any ideas or suggestions?

[bulrichl]

Hi Niall,

I am a little bit confused, maybe I am missing some information. So I ask whether I understand it right:

1) The warning "The dark frame optimization threshold is probably too high..." occurs when you are calibrating your flat frames with a Master Dark.
2) You are not using bias frames.

That doesn't go well together: in order to apply dark frame optimization you need a Master Bias too. In the dark frame optimization process (Juan Conejero has described it in detail in topic 8839, "Dark Frame Optimization Algorithm") Master Bias is subtracted from both the light frames and the Master Dark, then the difference of Master Dark and Master Bias is scaled with a k0 that is iteratively optimized for minimum noise in the calibration result. So with dark frame optimization you have to use a Master Bias or you calibrate without dark frame optimization - but then no such warning should occur.

Bernd

[Niall Saunders]

Hi Bernd,

I am confused too - I am going to read and (try to) understand Juan's post that you mentioned.

I will reply further after I have done that.