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OSC red and blue hot pixels in integration result  

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(@mxcoppell)
Brown Dwarf Customer
Joined: 2 years ago
Posts: 6
August 19, 2019 18:07  

Hello All,

It's my first time to integrate OSC frames with APP. In the final integration result, there are red and blue hot pixel everywhere in the integration frame. 

I am just using the default parameters. Loaded lights, darks, biases and flats, then launched integration with "Quality/Average" directly. Just wondering if there is any settings that could help me get rid of these hot pixels. 

WechatIMG138

 

  • Camera: QHY168c  (with Optolong l-eNhance filter)
  • Lights: 88, Unity Gain 10, 300s, Temp 0C
  • Darks: 40, Unity Gain 10, 300s, Temp 0C
  • Biases: 60, Unity Gain 10, 0s, Temp 0C
  • Flats: 40, Unity Gain 10, Temp 0C

 

Thanks!

-Min

This topic was modified 1 month ago by mxcoppell
This topic was modified 1 month ago by Vincent Groenewold - Moderator

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(@wvreeven)
Red Giant Customer
Joined: 1 year ago
Posts: 60
August 19, 2019 19:34  

Hot pixels normally get identified when using darks but you already do that. Can you zoom in to a region with those hot pixels? All I see in your image are very red or blue stars, which is odd, but those aren’t hot pixels because they cover more than one adjacent pixel.

 

Wouter


(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 725
August 19, 2019 19:46  

These still look like hot pixels though, if they are stars that would be very weird. With darks, bias and flats you can make a nice bad pixel map btw, just select it when you have loaded in all the calibration files and use it during the process (also for later sessions). Could you upload a 1:1 picture here (jpeg form is fine as it has to fit 30 MB) so we can zoom in nicely?


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(@mxcoppell)
Brown Dwarf Customer
Joined: 2 years ago
Posts: 6
August 19, 2019 20:00  

Vincent is right. These are not stars. They are hot pixels. 

Discussed this with QHY technical support, they are suggesting that the offset value is too small to create good calibration frames (dark and bias frames). QHY suggests that the offset value should be higher to prevent calibration frame from clipping. That's next I am going to try.

Just trying to see if there is a way to save the existing data. Especially if I want to do Ha-OIII/Ha extraction and Ha-OIII/OIII extraction, this will be more important. 

Vincent, are you asking for 1:1 calibration master frames or the integration result? I can upload them when I get home. 

Thanks!


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(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 725
August 19, 2019 20:18  

Did you try do perform some, maybe a bit aggressive, sigma clipping? Like LN MAD and then kappa 2.0 and 2 iterations. It may be less nice for some details, but if that helps to get rid of them, it might save the frames. Did you dither when capturing? That will help as well.

Just a 100% jpeg of the result as you posted above would be nice.


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(@mxcoppell)
Brown Dwarf Customer
Joined: 2 years ago
Posts: 6
August 19, 2019 20:32  

Thanks Vincent!

No I didn't try with Sigma Clipping. Actually that's what I want to learn from here. I will definitely give it a test (Sigma Clipping / LN MAD / Kappa 2.0 w/ 2 iterations). Any more ideas that I could try?

As of dither, yes and no. I did dither every single frame. But I didn't adjust the dither settings from the mono setup so it won't work. The OSC scale on my system is 2.18 and the main camera scale is 1.708. I only did the small dither (0.5 pixel) and dither scale of 1.0. It's not even close to remove the hot pixels. That's another thing I want to see how it could help - pushing up Offset value and increase dither size. Only concern I have is how much time it will cost the mount to settle with large dithers. 

I will post the 100% JPEG when I get home. The picture I posted is actually 1:1 crop from the integration result. 


(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 725
August 19, 2019 21:49  

I'd try the clipping first, might already help quite a bit.

Dithering will help a lot! Especially if you dither randomly and maybe at normal to somewhat higher setting. Yes, it will need to settle, but my experience is it usually takes about 5-10 seconds for a high dithering. I only do that every 2-3 frames and since I know the benefit, I'm happy to take a bit of time for it.


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(@mxcoppell)
Brown Dwarf Customer
Joined: 2 years ago
Posts: 6
August 20, 2019 06:03  

Vincent, I am happy to report that following your suggestion the red and blue hot pixels are now successfully removed. Here is 100% comparison. 

ln mad sigma clipping comparison

Thanks! 


(@mxcoppell)
Brown Dwarf Customer
Joined: 2 years ago
Posts: 6
August 20, 2019 06:05  

Want to ask a quick one that is totally not related to hot pixel. How do I change the "greenish" O3 color to nice blue color in APP? 🙂


(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 725
August 20, 2019 17:47  

Great! So now you can try to dial that setting back to maybe kappa 2.5 or 3.0 with 1 or 2 iterations, so it will do less "damage" if at all seen.

The green you can dial back with the "HSL selective color" tool, I would try to change "Cyan", drag the G<->MA (green-magenta) to magenta a bit, B<->YE (Blue-Yellow) to blue a bit. Maybe the same on the "Magenta"...


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