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Bad Pixel Map shows characteristic IMX183 dark-current starburst pattern  

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(@rickwayne)
White Dwarf Customer
Joined: 1 year ago
Posts: 11
February 5, 2020 20:01  

Hello all,

I just happened to look at the bad pixel map for my ASI183MM-Pro camera.

If you're familiar with the camera, it has a very visible amp-glow pattern, including a big sunrise/starburst on the right side, with a ray that extends most of the way across the image.

Lo and behold, my BPM recognizably displays that pattern. That's incorrect, yes? Those aren't truly hot or cold pixels, they're just ones that are way brighter than the surrounding due to amp glow. This would seem to explain why I often have trouble calibrating out the last traces of the glow, and that long horizontal line is a particular bear!

What's your advice? Create a new BPM from my flat-darks, or from a bunch of bias frames? (I normally use the former rather than the latter.)

What are the best practices for creating APP BPMs?

Attached is a screenshot of the BPM in APP, it looks the same regardless of whether I select "image" or "linear" or anything else, and whether or not I click the "stretch" checkbox. I can upload the FITS if anyone wants to see that for some reason. For comparison, a SS of a stretched dark is below that. 

TIA,

rw

Screen Shot 2020 02 05 at 12.33.56 PM

 

Screen Shot 2020 02 05 at 1.00.57 PM

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(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1913
February 5, 2020 21:04  

Well first of all, wow.. that is some amp-glow indeed. Using darks gets rid of that for you? Did you make sure the "reduce amp-glow" setting is on in the calibrate-tab?

In general, a BPM can be made using flats (if you have cold pixels) and darks (long exposed dark is nice, at least 300 seconds). This should account for most of the bad pixels and work for a long time (depending on how much your sensor is used). You can at this stage play around with the kappa values, increasing it will have less pixels being recognised as hot. Maybe this can reduce that amp-glow bit. I haven't seen examples that this is particularly bad to have in a BPM though, I will try to find other examples.


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(@rickwayne)
White Dwarf Customer
Joined: 1 year ago
Posts: 11
February 6, 2020 01:24  

@vincent-mod

Thanks for the quick reply, Vincent. Yeah, stretching the dark frame really brings out the WOW for that sensor, doesn't it? That one was long exposures at a maxed-out gain for the camera, so it's pretty much worst-case.

It does calibrate out, at least almost all, usually. I do use the pedestal when I'm calibrating, which helps a lot. Or did you mean some option when I'm actually creating the BPM? But every once in a while I do see traces of the glow still there, and it's primarily the parts I see in the BPM.

I will try running a few iterations of making a BPM with various kappa values. I should also try processing an image or two with an without my current (weird) BPM, just to establish whether that's the problem.


(@vincent-mod)
Quasar Admin
Joined: 3 years ago
Posts: 1913
February 6, 2020 16:33  

That might be nice to know when you get those results back. If it doesn't help, I'll investigate further as well.


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