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ASI071MC processing  

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(@jarbi58)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 30
June 10, 2017 22:23  

Hi Mabula,

After succesfull processing of my Canon CR2 frames I was taking images with the ASI071MC cmos camera. I have created flats and darks as well. 

After multiple attempts I am still not getting correct debayering, the resulting image is always pixelated somehow. Could you please take a look at it what went wrong here ?

The bayermask on this camera is theoretically the same as the Canon sensor. One more important info: I have used an Idas LPS P1 filter in front of the camera, and I took the flats with the filter on as well.

I have uploaded some frames on my Google drive:  https://drive.google.com/open?id=0B5rc5Ssg9hE-Yi0wOXhLS1J1Tjg

 

cheers,

Janos

 


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2081
June 11, 2017 01:03  

Hi Janos,

I'll have a look tomorrow 😉

Did you enable "force CFA" for these frames in 0) RAW/FITS ? Do you get different results when applying RGGB or GBRG as CFA pattern for instance?

If you set another CFA pattern and reload the current image in the image viewer, by using the image viewer dropdown box (above the image viewer panel) then the newly chosen CFA pattern is automatically applied.

(The asi071MC has the same sensor as the Nikon D5100 I believe)

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@jarbi58)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 30
June 11, 2017 12:53  

Hi Mabula,

Thanks for the tip, I have now reprocessed the image set with Force CFA on and RGGB, now it gives good calibration and integration results. I will post the final image when I finished it in PS CC. I am still curius about your findings with this camera based on the frames I provided,

Cheers,

Janos

 


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2081
June 11, 2017 13:25  

Hi Janos,

I will definitely took a look later today 😉

Looking forward to your result!

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2081
June 11, 2017 23:51  

Hi Janos,

I am looking at your data.

I have one advice:

You provided darks with the same exposure as the lights. That's fine

But the flats need either bias frames or dark frames with the same exposure as the flat frames to correctly remove the bias pedestal form the flats.

But the calibration does seem to work fine still. If you were to add bias frames or dark frames (so called dark flats) for the flat frames then I think the data calibration should improve.

The combined master dark looks rather odd though, (but no problem when applying it). But what's really odd is that the R,G,B channels seemed to be scaled for some reason.

First image, the master dark, second image the master dark with BG-N applied (neutralised background) in the preview filter. Third screenshot showing strange patches on the masterdark:

MD ISO gain 90.0 exp 300.0s 10subs ASICamera(1) NR avg St 1
darkStreaks
MD ISO gain 90.0 exp 300.0s 10subs ASICamera(1) NR avg St

I created a bad pixel map, masterdark and masterflat and a calibrated frame looks fine:

m51 300sec 1x1  frame3 St

Integration of the 10 light frames that you provided with a quick post processing using

  • remove light pollution
  • calibrate background
  • calibrate star colors
  • selective color

looks pretty good to me 😉

M51 Janos St

 

 

Main developer of Astro Pixel Processor and owner of Aries Productions


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 Heno
(@heno)
White Dwarf Customer
Joined: 2 years ago
Posts: 17
October 4, 2017 20:57  

Hi all. This is my first post at this forum.

@ Mabula: You wrote above: "But the flats need either bias frames or dark frames with the same exposure as the flat frames to correctly remove the bias pedestal form the flats."

This statement really confused me. I was always under the impression that flats were included to remove imperfections in the optical train and that exposure time and ISO/gain was irrelevant as long as the flat frames were normally exposed.

Bias frames I have always taken with the camera's shortest exposure time (1/4000 sec on my DSLR) and the same ISO (not sure if that matters) as my lights.

I know that this tread is not about DSLR, but generally it would be the same,  would it not?

Please explain.

Helge.


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2081
October 4, 2017 22:11  

Hi Helge,

Welcome to the forum 😉

Yes, I can understand why it can be confusing in the way this was written..., to be absolutely clear, it is:

"But the flats need either

  • bias frames of the same iso/gain as the flat frames or
  • dark frames with the same exposure and the same iso/gain as the flat frames(these are called flatdarks or darkflats..)

to correctly remove the bias pedestal form the flats."

Indeed the exposure time of the flats is irrelevant, although longer exposed flats tend to be of better quality and usually give less problems. Just make sure the histograms don't clip on the right side of the histogram.

And yes, the iso/gain of the flats is irrelevant, but lower iso/gain tend to give better results and less problems because the exposure time can be made longer without clipping the histogram on the right side.

So for correct flat-field calibration, the flats need to be corrected with either

  • bias frames of the same iso/gain as the flat frames or
  • dark frames with the same exposure and the same iso/gain as the flat frames

And yes, there is only one way to make bias, that is with the shortest exposure time your camera has. But the ISO needs to be the same as the ISO of the frames that you calibrate.

So if you use bias frames for your lights, the bias frames need to have the same ISO as the lights, but if you use bias frames for your flats (that might have different ISO/gain) you need to make sure the bias have the same ISO/gain as the flats. So if the flats have different ISO/gain than the lights, you need 2 different masterbias frames. One for the lights and one for the flats.

Yes, data calibration rules are the same for different types of cameras, but depending on the sensor characteristics, different calibration paths can give better results, really depens on the sensor and also the ability of your gear to apply dithering between frames.

All rules can be found in this thread:

https://www.astropixelprocessor.com/community/tutorials-workflows/astronomical-data-calibration-priciples-must-read/

Let me know if this clears the confusion for you 😉

Kind regards,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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 Heno
(@heno)
White Dwarf Customer
Joined: 2 years ago
Posts: 17
October 5, 2017 11:00  

Hi Mabula.

Thank you for the extensive explanation. You have made it all very clear and it is pretty much as I thought it was except that I need bias frames for both lights and flats. That was new to me. Then again, if I shoot using ISO 200 (or whatever) for all three types of frames I should get away with one set of master bias. Correct?

I will sit down and read the info your link and watch the videos. Looking forward to learning and using this piece of software.

If only we could have a clear night or two. 🙂

Helge

 


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2081
October 5, 2017 11:30  

Hi Helge,

You're most welcome 😉

that I need bias frames for both lights and flats. That was new to me. Then again, if I shoot using ISO 200 (or whatever) for all three types of frames I should get away with one set of master bias. Correct?

Yes that would be correct.

Yesterday, I added a new tutorial on calibration for a DSLR, that is probably interesting to watch 😉

https://www.astropixelprocessor.com/a-dslr-data-calibration-workflow/

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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 Heno
(@heno)
White Dwarf Customer
Joined: 2 years ago
Posts: 17
October 5, 2017 13:35  

Hi Mabula.

Just watched the video, very informative.

Thanks for your help so far.

Agreeing with Terminator; "I'll be back". 🙂

Helge


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2081
October 7, 2017 23:22  

You're most welcome Helge 😉

Main developer of Astro Pixel Processor and owner of Aries Productions


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