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Dark library for guiding - do I create a master dark?

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Hi,

Quick question about creating a dark library for guiding. How many should I take and do I create a master darts file like we do for subs?

Also will an ASI290MM mini Gove me better guiding than an ASI120MM mini?

Rene
3 years 2 months ago #66237

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This isn't support now, the current method just captures one dark and saves it.

There is an issue open about this topic now: invent.kde.org/education/kstars/-/issues/50

Hopefully we can get time to work on it or another developer steps in to claim the task.
3 years 2 months ago #66243

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Ok thanks Jasem. So only 1 dark frame for each different exposure/binning etc.
3 years 2 months ago #66244

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And what if I capture one using the current method, then create manually master dark and finally replace the one from dark library with created master dark. Will it work then? Which parameters needs to match? Name is sufficient?
3 years 2 months ago #66256

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Not familiar with that code, but a quick look shows that this is the method that compares things:
invent.kde.org/education/kstars/-/blob/m.../darklibrary.cpp#L58
and it looks like the two options referenced there are set in KStars -> Settings -> Configure KStars -> Ekos -> Dark Library
3 years 2 months ago #66259

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Ok, so what I can see in the code, and if I understand it correctly, I need to match these parameters:
1) name of the CCD is the same
2) binning mode is the same
3) temperature is within a configured range
4) duration is within a configured range
I expect that these parameters are stored in FITS, and then it can be easily changed to match needed values
3 years 2 months ago #66262

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The way I see the code, those parameters are not stored in the FITS header. They are store in a side database.
See saveDarkFile: invent.kde.org/education/kstars/-/blob/m...darklibrary.cpp#L139

So, I think, the system has a record in its permanent storage of the CCD, binning, temperature, duration, filename.
When it wants a dark, it looks through all of the possibilities in this storage for a match. If it finds one, it tries to load the fits file from the filename.
If that fails, it destroys the record. If that succeeds, it uses the file it loaded.

To hack around the lack of a good dark-frame estimate, I think you'd
- capture a single dark frame with KStars using existing code with the right name, binning, temperature and duration.
- capture other files somehow, outside the KStars dark-frame framework.
- generate your averaged (or median'd) dark frame outside the KStars framework.
- replace the KStars file with your new file.
- adjust those options related to temperature range and longevity.
- give it a try!

BTW--just looking this over again, I'm worried that the dark estimate and the light frames you'd later want to improve need to be the same data format (e.g. you might not be able to have a 16-bit light frame and a floating point dark frame). See invent.kde.org/education/kstars/-/blob/m...darklibrary.cpp#L222. Since your lights are likely 8-bit or maybe 16-bit unsigned integer format, If I were you, I'd start with generating a similar dark-frame fits.


For sure, this is a hack, and the right thing to do is implement an improved dark-frame scheme. [Also, I can't be sure I'm right
about the above procedure, as I just looked at this quickly.]

The better solution may happen at some point. One of the developers (or you if you can) could implement things could pick up this project.
However, doing this hack and demonstrating improved performance with a good dark estimate would be valuable in motivating
someone to do the work.
The following user(s) said Thank You: hades
Last edit: 3 years 2 months ago by Hy Murveit.
3 years 2 months ago #66290

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I have just "hacked" it to use my master dark created in PixInsight. Here is how i have done it (some steps are the same as you just mentioned):
1) Go to guiding tab of Ekos and enable Dark checkbox
2) Click on Capture button. This will create one dark
3) Go co Capture tab, select your guiding camera. Create sequence for 20 (or more if you want) darks with the same exposure time used in first step. Dont forget to select Type: Dark. Execute the sequence
4) Stack these 20 captured darks in your favourite software. Resulting image must have the same bit depth as single sub (in my case it is 8bit)
5) Possibly optional step: change content of FITS header for stacked master darkto be exactly the same as has the one dark from step 2
6) Go to /.local/share/kstars/darks/ folder and rename the original dark from step 2. For example from "darkframe_2021-01-21T20-28-28.fits" to "darkframe_2021-01-21T20-28-28.fits.old"
7) To the folder above copy stacked master dark and change its name to be the same as the dark from step 2 (in my case "darkframe_2021-01-21T20-28-28.fits")
Go to KStars/Settings/Configure KStars/Ekos/Dark Library. Now if you double click on the record for dark from step 2 it will open the stacked master dark.
Most of guiding cameras are uncooled, so take the darks in step 3 in similar conditions as you will have during real-time guiding.
This is still a theory, I currently don't have conditions to test it outside, but I will report once done so :)
3 years 2 months ago #66301

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