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Can’t get rid of hot pixels for only one session  

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(@th-van-driessche)
White Dwarf Customer
Joined: 4 years ago
Posts: 14
April 3, 2021 14:26  

I’m using APP, version 1.083-beta1, with default settings for stacking. The only changes: tab 0 pattern RGGB choosen and force bayer checked, tab 6 1st degree LNC choosen and enable MBB checked.

I am using 2 different setups with the same camera: ASI294MC Pro.

My darks, flats and darkflats have been taken in the same way for the 2 setups: darks at the same temperature and gain as the lights, flats taken using the same conditions and environment for both setups (room temp, same tools used and same gain as darks and lights) with exposure time above 1 seconds and same conditions for both setups for the darkflats (same gain as lights, darks and darkflats and same exposure time as the flats).

For one night, I was shooting with one of both setups at a gain of 120, -15°C, 180sec. For the other night I was using the second setup but with a gain of 250, -10°C, 240sec.

When using APP for the first setup using the gain of 120 I don’t have any hot pixels in my stack, see picture. For the other night using the second setup and with a gain of 250, I can’t get rid of a lot of hot pixels, see picture. (pictures are at 225%). APP has been used in the same way for both sessions.

Any help appreciated.

No hot pixels nova NGC4414
Hot pixels nova NGC4414

 


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3569
April 6, 2021 09:35  

Hi,

So, higher gain and more hotpixels. That at least makes sense. 🙂 What you can try is to load such a sub in (with gain 250), zoom into the region with hot-pixels, load in the dark for that sub and the BPM and then switch to "l-calibrated" on top of the preview window, that should apply the dark and BPM to that sub and you can check to see if they actually have proper bad pixels at those locations.


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(@th-van-driessche)
White Dwarf Customer
Joined: 4 years ago
Posts: 14
April 6, 2021 16:15  

@vincent-mod

Hi,

I did as told. Indeed, I am finding the hot pixels on those locations, see attached picture.

I checked all of my lights and all of my darks and they are all taken at the same temperature and gain as well.

Is there anything I can do in order to get rid of those after the integration? Change one or another parameter while integrating or in another step?

Hot pixel 3
Hot pixel 2
Hot pixel

 Thank you and best regards.


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3569
April 6, 2021 19:06  

And can you also load 1 of those in, zoom in and then load the dark or the BPM to check if they have that bad pixel on the same location? That would tell you if the darks may have a problem somehow.


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(@th-van-driessche)
White Dwarf Customer
Joined: 4 years ago
Posts: 14
April 8, 2021 11:23  

@vincent-mod

When loading 1 light and 1 dark, less hot pixels are removed in the l-calibrated picture compared to when I load the BPM. What I will do is add some more darks, I have only 30 of them, and then make the stacking again. I will see what more darks will do by creating a new BPM.

I will keep you posted.

Best regards,

Thierry


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(@th-van-driessche)
White Dwarf Customer
Joined: 4 years ago
Posts: 14
April 8, 2021 13:42  

@vincent-mod

Here are for the same area the stack using 30 darks and 50 darks. It looks like there is no difference between both.

The problem remains. What's next I could do? Thank you for further assistance.

Hot pixels met 50 darks ipv 30 en nieuwe flats histo ABE cr
Hot pixels met nieuwe flats histo ABE cr

 


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3569
April 9, 2021 12:01  

Next step will be to send some of the data to us for analysis. Please provide a minimum of data that still shows the issue;

Go to https://upload.astropixelprocessor.com and use upload1 as username and upload1 as password.

Create a directory named “th-van-driessche-darksIssue” and upload in there. Thank you!

 


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(@th-van-driessche)
White Dwarf Customer
Joined: 4 years ago
Posts: 14
April 9, 2021 20:00  

@vincent-mod

I created the directory and uploaded following files:

the BPM file, the MF, MDF and MD as well as the final stack with 50 darks (Met_50_darks_ipv_30.fits). Other files that I uploaded are: 5 lights (Supernova NGC4414 met Celestron_240sec_-10C_gain_250 **.fits), 5 darks, 5 flats and 5 darkflats.

Please let me know if you need eventually more files.

Thank you for your support. Hopefully something comes out from your analyse.

Best regards,

Thierry

 


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3569
April 13, 2021 11:19  

Sorry for the delay, downloading now!


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(@th-van-driessche)
White Dwarf Customer
Joined: 4 years ago
Posts: 14
April 13, 2021 11:52  

@vincent-mod

Thanks no problem. Please be aware I have been using "small dither" in SGPro.


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(@th-van-driessche)
White Dwarf Customer
Joined: 4 years ago
Posts: 14
April 13, 2021 14:59  

@vincent-mod

I meanwhile checked the dither I have been using for those lights. Apparently the “small dither” seems to be too small. I took lights yesterday using “medium dither”, and on those ones dithering can easily been seen using blink in PI.

On the other hand, I found following article meanwhile: https://www.skyatnightmagazine.com/astrophotography/astrophoto-tips/guide-cmos-camera-deep-sky-astrophotography/

At the end of the article: “If the darks are captured on a short cable connected to a local computer the resulting subtraction can contain lots of coloured hot pixels and a digital rain across the image.”

I am using a USB cable of 10m with build in amplifier for taking the lights but a cable of 1.5m for taking the darks. Would that be an explanation of my problem?


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3569
April 14, 2021 09:57  

Mmm, not sure, electrical problems can cause all kinds of weird issues, but usually not just a few hot pixels that are not calibrated out. I would indeed advice to go for a high dither, that should definitely get rid of a few more, but I'll have a close look at your masterdark en a light to check if that one is ok.


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3569
April 14, 2021 10:05  

Ok, had a look and I see a lot of light in your masterdark. 3 light sources apparently, it could be amp-glow, but I usually don't see multiple glows, is that the case for your sensor indeed? The dark also seems to correct bad pixels, so that's good, I think you indeed need some extra dithering to get rid of them completely. Maybe the amp-glow also cause some of this, not sure.


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(@th-van-driessche)
White Dwarf Customer
Joined: 4 years ago
Posts: 14
April 14, 2021 14:53  

@vincent-mod

Thank you very much for your feedback. Once weather is OK, and if I have time, I will once again try with the same setup and settings to take lights from another object but using “medium dither” in SGPro. I’m quite confident that this will be the solution of the problem I had.

As far as I know, ampglow looks not to be a real problem as darks very probably removes them (all?).

Once again, I appreciate your help. Best regards.


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