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[Sticky] A DSLR data calibration workflow by Mabula  

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(@mabula-admin)
Quasar Admin
Joined: 3 years ago
Posts: 2278
October 4, 2017 15:33  

Hi all,

This is a new video tutorial made possible by using data of Douglas Mason, thank you Douglas!

A DSLR data calibration workflow

Let me know if there are any questions 😉

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@frank_teunissen)
Hydrogen Atom Customer
Joined: 2 years ago
Posts: 1
February 19, 2018 18:00  

Hallo Mabula, zou het kunnen zijn dat er een foutje zit in deze video/handleiding?

Moet de iso waarde van de BIAS frames overeenkomen met de iso waarde van de DARK frames? Zo ja dan moet dus alle BIAS, DARK, FLAT en de LIGHT frames dezelfde iso waarde hebben. In de video wordt er mogelijk een onderscheid gemaakt: iso DARK = iso LIGHT en iso BIAS = iso FLAT (bij 1m:01s) . In het verhaal staat echter: iso DARK = iso FLAT. Wat is de juiste setting?

Mvg Frank  Teunissen

edit: translation by Mabula:

Does the ISO value of Bias frames need to be the same as the ISO value of dark frames? If that's the case, then there might be an error in your DSLR data calibration video tutorial. What's the correct value?

 


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(@mabula-admin)
Quasar Admin
Joined: 3 years ago
Posts: 2278
March 4, 2018 18:23  

Hi Frank @frank_teunissen,

No there is no error there. Let me explain:

It all depends on what you are trying to calibrate with the bias frames.

If you use bias frames to calibrate flats, the bias frames need to have the same ISO value as the flats.

If you use bias frames to calibrate lights, the bias frames need to have the same ISO values as the lights.

( and... If you use bias frames to calibrate darks, the bias frames need to have the same ISO as the darks.)

Other applications are less strict about this and fundamentally that's not a good thing in my opinion. If your Bias frames have a clear noise pattern to them (like horizontal or vertical stripes) then not following these rules will actually give you worse calibration. Currently APP forces these rules which confuses some users since other applications are not so strict. I do intend to make this easier in a next APP version though. The whole calibration engine will be upgraded soon.

Kind regards,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@hans_van_overzee)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 27
March 5, 2018 21:16  

Ha Mabula I have got a question.

For making  the master flat for instance an ISO for the flats of 400 is used.

As I understand it the Bias has to be also ISO 400. Both frames got to have  the same exposure time.

What about the bad pixel map used in this case has it also to be made of frames from darks and flats of ISO 400 with the same exposure time ?

 

If the lights have an other exposure time  and ISO for instance 800 the masterdark has to be made with the same exposure time and the ISO as the lights this is clear.

What about the bad pixel map in this case?

Have we got to make a second bad pixel map existing out of flats and darks with the same exposure time and ISO as the Lights and darks in this case?

 


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(@mabula-admin)
Quasar Admin
Joined: 3 years ago
Posts: 2278
March 21, 2018 12:44  
Posted by: Hans van Overzee

Ha Mabula I have got a question.

For making  the master flat for instance an ISO for the flats of 400 is used.

As I understand it the Bias has to be also ISO 400. Both frames got to have  the same exposure time.

What about the bad pixel map used in this case has it also to be made of frames from darks and flats of ISO 400 with the same exposure time ?

 

If the lights have an other exposure time  and ISO for instance 800 the masterdark has to be made with the same exposure time and the ISO as the lights this is clear.

What about the bad pixel map in this case?

Have we got to make a second bad pixel map existing out of flats and darks with the same exposure time and ISO as the Lights and darks in this case?

 

Hi Hans @hans_van_overzee,

As I understand it the Bias has to be also ISO 400. Both frames got to have the same exposure time.

Yes, If the flats are ISO400, then the Bias for the flats need to be ISO400, if you use darkflats for the flats, then they need to have the same ISO and exposure as the flats.

What about the bad pixel map used in this case has it also to be made of frames from darks and flats of ISO 400 with the same exposure time ?

No, the Bad Pixel Map is NOT ISO and exposure dependent. You can make a Bad Pixel Map using any ISO and exposure time and use it on data which have other ISO and exposure times. Just make one Bad Pixel Map using a set of darks with exposure times of several minutes (the longer the better) and an arbitrary ISO value. And the flats used in the BPM creation can have a different ISO and exposure time then those darks, no problem 😉

Have we got to make a second bad pixel map existing out of flats and darks with the same exposure time and ISO as the Lights and darks in this case?

So no, just make 1 BPM and use it on all Lights and Flats that you have 😉

Kind regards,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@hans_van_overzee)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 27
March 21, 2018 14:26  

Thanks Mabula for this clear explanation

Cheers,

Hans 


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(@hans_van_overzee)
Main Sequence Star Customer
Joined: 3 years ago
Posts: 27
March 21, 2018 14:27  

Thanks Mabula for this clear explanation

Cheers,

Hans 


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(@didi_sangye)
Molecular Cloud Customer
Joined: 3 months ago
Posts: 3
January 13, 2020 12:11  

@mabula-admin

Hallo Mabula,

as a beginner in astrofotography (but already a fan of APP and your work you have done!!) i want to ask you a  "basic" support to understand a little bit more what i'm doing, because there is still confusion and unclearity in my mind about the steps of the pre-processing in APP (and i didn't find any explanations). In the Internet i can find a lot about "Calibration", "Registration" and "Stacking" (i think that's what you call "Ingetration").

But can you please help me to understand what "Analayze Star" and "Normalize" is good for and what is happening in APP; and in which of the steps "Debuyering" occurs.

I know these are basic-questions of a beginner, but i want to understand the things a little bit better; so i'm asking you to give me some advices, tipps or explanations, so it can become "clearer" in my mind.

I'm starting with a astro-modified DSLR (Canon 80D); watched your tutorials; understood what darks, flats and bias are good for and how to get them. But i'm lacking understanding what the steps of pre-processing are doing in APP.

So thanks for your understanding and help

Dietmar

 


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(@mabula-admin)
Quasar Admin
Joined: 3 years ago
Posts: 2278
January 14, 2020 20:14  

Hi Dietmar @didi_sangye,

Welcome to our forum 😉

Analyse stars serves 2 purposes:

  • first of all, APP analyses the stars in your images and uses that for frame quality calculation.
  • Secondly, while analysing the stars, the star centroids are calculated. Star Centroids are the locations of the stars on your images in subpixel precision. These centroids are needed for registration of the images, registration means aligning the images to get very sharp and precise stacks/integrations.

And yes, stacks are also called integrations. If you combine multiple exposures by stacking them, you can also say that you are integrating their exposures into 1 image.

Debayering of color images happens after data calibration, APP will do this automatically at the right time in processing. So step 3) Analyse stars works on calibrated images which are debayered if they need to... 😉 In APP you won't need to concern yourself about when you need to do this, because APP handles this automatically.

Normalization is all about correcting your images for illumination differences in your dataset. This is very important to get good results.

Are you familiar already with data-calibration?

Kind regards,

Mabula

 

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@didi_sangye)
Molecular Cloud Customer
Joined: 3 months ago
Posts: 3
January 18, 2020 08:45  

@mabula-admin

Hey Mabula,

thank you very much for your explanations; they are helping me a lot and maybe a good topic for the upcoming manual as well 👌

concerning the calibration i studied your tutorial and your posts and through them i think it becoming clear, altough opposite to your dslr-workflow i decided to calibrate the flat-frames with a master-dark for flats (see your post „Data calibration principles/rules - must read !“) and the lights with a master-dark for lights and both additionaly with a BPM; so in this workflow i will do no bias. Is this okay??

 

kind regards

didi


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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1262
January 18, 2020 13:28  

So you can calibrate flats with a dark-flat (or whatever people call it 😉 ). It's simply a dark with exposure length and settings being the same as the flats. This is fine, it will contain the bias signal, some camera's even need this bit of extra dark exposure time to generate a proper bias signal.


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