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CALIBRATE: we have detected a possible sensor offset issue between the MasterBias and the Masterdark !  

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(@stefan-b)
White Dwarf Customer
Joined: 2 years ago
Posts: 11
August 6, 2019 23:42  
Hello!
Apparently there is a problem with my dark frames and BIAS frames in module 2) Calibration. The pictures were taken with a CANON EOS 750D (astromodified). In the console output window the warning "we have detected a possible sensor offset issue between the MasterBias and the Masterdark !" appears.
I also suspect that the MasterBias is not subtracted from the Masterdark. The median values of both files are identical.
The file attachment contains the respective FITS header of the MasteBias and of the Masterdark as well as the error message.
Is there an explanation for this?
 
Greetings
Stefan B.
 

Warning Sensor Offset
Master Dark Header
Master Bias Header

This topic was modified 2 months ago by Vincent Groenewold - Moderator
This topic was modified 1 month ago 2 times by Mabula Haverkamp - Admin

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(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 725
August 7, 2019 10:55  

Mmm, that is interesting. Maybe the console logs a rounded number while in reality they are slightly different. It  only seems to be the case in channel 3. I don't see anything really strange in the fits data either. How do integrations look like and do you see the mention of darks and bias being applied to the light frames when looking on the overview list?


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(@stefan-b)
White Dwarf Customer
Joined: 2 years ago
Posts: 11
August 7, 2019 12:59  
Hello, Vincent!
Many thanks for the quick feedback. I quickly integrated 3 lights again. Once calibrated only with BPM and the second time with BPM+MD+MB. The visual difference in the integration file is very small. How can I check that the BIAS has been subtracted from the MD? In the FITS header the MEDIAN value is identical for MD and MB.

In the thread "How to correct a stack/integration for vignetting" ( https://www.astropixelprocessor.com/community/tutorials-workflows/how-to-correct-a-stackintegration-for-vignetting/ ), Mabula described that the ADU of the MD is approximately 0 if the BIAS was subtracted. I am a bit irritated now because the MEDIAN values of my data contradict this.
 
Overview list
FileList

 
Integration of 3 Lights only with BPM-calibration
Intergration 3 Lights only with BPM

 
Integration of 3 Light with BPM+MD+MF calibration
Intergration 3 Lights MD MB BPM

This post was modified 2 months ago by Stefan-B.

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(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 725
August 7, 2019 19:38  

It looks like the masters are all used, so then it should be substracted yes, it's also a warning and not necessarily a problem, otherwise APP would not continue. Personally I think it's totally fine, but Mabula has the deep know-how that I require in this case so I'll give him a notice. @mabula-admin

ps. never get irritated about data, if I did that I would be very grey by now. 😉


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(@stefan-b)
White Dwarf Customer
Joined: 2 years ago
Posts: 11
August 7, 2019 22:08  
It seems that in an earlier version of APP, the BIAS was subtracted when creating the MasterDark during calibration. In the current version this is probably no longer the case. I am sure that @mabula-admin has an explanation for the warning message. Many thanks for the help.
 
ps. unfortunately my hair is already grey, more is not possible anymore. But this is not due to APP!  😀 APP is an ingenious program and I like to work with it very much.
This post was modified 2 months ago by Stefan-B.

(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2127
August 13, 2019 18:30  
Posted by: @stefan-b
Hello!
Apparently there is a problem with my dark frames and BIAS frames in module 2) Calibration. The pictures were taken with a CANON EOS 750D (astromodified). In the console output window the warning "we have detected a possible sensor offset issue between the MasterBias and the Masterdark !" appears.
I also suspect that the MasterBias is not subtracted from the Masterdark. The median values of both files are identical.
The file attachment contains the respective FITS header of the MasteBias and of the Masterdark as well as the error message.
Is there an explanation for this?
 
Greetings
Stefan B.
 

Warning Sensor Offset
Master Dark Header
Master Bias Header

Hi @stefan-b & @vincent-mod,

Let me try to clarify what is happening here 😉

Indeed, the console will throw a warning if the median value of the masterdark is lower than the median value of the masterbias. Normally, this would indicate an issue with either gain/iso value or the sensor offset, meaning: perhaps they are not compatible between the masterdark and the masterbias, which would warrent a warning off course.

In this case however, there should be no problem. The newer cmos sensor techonology is reponsible for this to happen on some camera's now. And as you can see, the values are nearly identical so all should be fine.

It seems that in an earlier version of APP, the BIAS was subtracted when creating the MasterDark during calibration. In the current version this is probably no longer the case. I am sure that @mabula-admin has an explanation for the warning message. Many thanks for the help.
 
ps. unfortunately my hair is already grey, more is not possible anymore. But this is not due to APP!  😀 APP is an ingenious program and I like to work with it very much.
Indeed, you are totally right here, in older versions of APP, the MasterDark was already subtracted by the MasterBias if it was present in creating the Masterdark. In the latest versions of APP, this is no longer the case for several good reasons. The entire calibration module was rewritten and was made a lot smarter internally. Now the MasterDark can always be used, whether you want to use bias frames or not. The actual subtraction of the masterbias from the Masterdark is done dynamically when the frames are calibrated and now there will not be any clipping on the black point anymore, which in the old calibration engine could happen as well... so with the new calibration engine, you are now ensured of correct calibration, whichever calibration path you follow 😉
 
Thanks for your nice compliment, I hope this answers your concern about the warning issued in the console panel 😉
 
Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@stefan-b)
White Dwarf Customer
Joined: 2 years ago
Posts: 11
August 13, 2019 19:08  
Hello Mabula!

Many thanks for the feedback and the extensive explanation. My concerns that something is wrong with the calibration frames or that something is wrong with my camera have fortunately not come true.
 
Greetings and clear skies 😉 

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