CMOS Camera Dark Current Tutorial and Image Calibration -- article and questions

[rockenrog]

Hi,
In the below linked (English) article the author, Mr. Alessio Beltrame, reviews some ways for calibration for CMOS cameras using PI. And why CMOS camera (non linear ADU vs time) need some different attention than CCD cameras (linear ADU vs time). He uses is QHY163M as his study reference. The first part of the article he describes using the overscan area and how it is used for calibration subtraction preventing driving dark frames to zero ADU's. He then points out that this method does not take into account ADC heating.   
In the latter part of the article (p13 onward) he presents his recommended PI method for calibration. He makes no mention of overscan.

So my question is there need for utilizing the overscan areas in processing CMOS camera images, or not?

I wrote to the author twice, but no answers coming back. Probably I don't understand something that is obvious to those more skilled than I am. So your comments are welcome. I really appreciate Mr. Beltrame's work, and his passion, for understanding his equipment and processing for the best results.

http://www.alessiobeltrame.com/wp-content/uploads/2018/01/DC_tutorial.pdf?fbclid=IwAR0iBQrKgXKaiIhREdO3qcSI7rYgMpX4icN76Gejnh_f2_EM70g1MroTGsk

Thanks,
  Roger

[gianpri]

Alessio Beltrami cannot answer you: he died a year ago, at the age of 52.
R.I.P.

[bulrichl]

Hi Roger

I thought I answered your question already in the other thread, but obviously you didnt't understand:
There is no point in trying to do an overscan calibration in case of CMOS sensors.

For calibration of CMOS sensor data you'll need:
1) light frames,
2) dark frames (same gain, offset, temperature and exposure time as the light frames)
3) flat frames
4) flat-darks (same gain, offset, temperature and exposure time as the flat frames). Don't capture bias frames, they are not needed.

Don't pre-calibrate the darks, just integrate them to the MasterDark.
Similarly integrate the flat-darks to the MasterFlatDark
Calibrate the flat frames with the MasterFlatDark and integrate the calibrated flat frames to the MasterFlat.
Calibration of the light frames:
- uncheck the section 'Master Bias',
- in section 'Master Dark' select the MasterDark. Both options 'Calibrate' and 'Optimize' have to be unchecked)
- in section 'Master Flat' select the MasterFlat. Option 'Calibrate' has to be unchecked.

(Explained in detail in my guide https://pixinsight.com/forum/index.php?topic=11968 )

Bernd

[rockenrog]

Hi Bernd,
Sorry for the late reply... Too busy at this side for my favorite pastime.
I am sorry to hear of Mr. Beltrame passing. Just reading his website I can tell he was absolutely dedicated to expanding his and others knowledge of photography and astro photography.
I will use your just described and linked technique to process my CMOS images. I did not properly read your earlier reply, and also I did not state my original post correctly.
Thank you for your help to get me unstuck on this overscan issue.

Best regards,
      Roger

[rockenrog]

Hi Bernd,
I read the processing tutorial you wrote and believe it will get me doing it correctly. It was in depth, and I appreciate your knowledge/experience, and the effort and time you spent to write it down.

Now I have sets of raw lights, darks, and flats with overscan and without overscan. The without overscans had the overscan cancelled at the camera.

I want to process all the lights, but need to cancel the overscan area. Should I be using Dynamic Crop to get all the raw images to the 'without overscan' exact size? There is overscan on left, top, and right of the frames. Then I can proceed the calibration, alignment, and integrations. Your advice is appreciated.
Thanks,
    Roger

[bulrichl]

Hi Roger,

it is critical to crop the frames with overscan regions exactly, this is not only a matter of same size of the cropped frames. If not performed correctly, the cropped frames will be unusable. Can you please upload one dark frame each with and without the overscan area?

Bernd

[rockenrog]

Hi Bernd,
Below are Dropbox links to 2 of my raw darks. The -0004 file is without overscan. And -0002 is with overscan.
I think you are going to give me the crop settings. Thanks!

In my (now old) ImageCalibration with overscan I had this data for Image Region: 4  58  4952 3288 which results in image with size matching the without overscan raws. It also could not see any overscan rows or columns.

https://www.dropbox.com/s/89tyc5ggcg8yidy/Dark_-10C_600s_1x1_G10Off70-0004Dk.fit?dl=0
https://www.dropbox.com/s/kgfi8luciquyjsq/Dark-10C_600s_1x1_G10Off70-0002Dk.fit?dl=0

Thanks,
    Roger

[bulrichl]

The coordinates that you found out are correct. From the frames containing the overscan region you have to crop:
58 pixels at the top,
 4 pixels at the left,
84 pixels at the right,
 0 pixels at the bottom.

Appended is an archive with the PixInsight Crop process that does this job.

Bernd

[rockenrog]

Hi Bernd,
Thks for the quick reply. I extracted the process file and then loaded to PI. It does not show up, even checking all workspaces. If I open again it gives me the expected pop up... "The current process icon set has been modified.... Throw away all process Icons."
So click I click on yes, and it still does not show up. Any ideas?

Now I do the Crop myself....
After play around for awhile... I select the View Image I want to crop, put in -58, -4, -84 in Margin/Anchors, Original Pix is greyed out, and the Target Pix automatically changes to 4952, 3288 which matches the no overscan size of 4952, 3288.  The result is correct size, and no overscans. Sounds easy, but there are several ways to put in data.

Until you learn the logic of the Crop process, filling the data is not intuitive. When cropping something (ie vacation photos) you just highlight and it crops the excess.  Just my learning process with Powerful Pixinsight!

Thanks for all your help,
   Roger

[bulrichl]

Sorry I cannot reproduce your issue. I just verified again that the process file works:

You simply drag the extracted process file to the PI desktop, and a double-click on the process will open the Crop process with the right margin values.

Bernd