Choosing best frame...
 
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Choosing best frames for integration, signal/noise, full-width-half-maximum  

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(@rickwayne)
Molecular Cloud Customer
Joined: 3 months ago
Posts: 4
26/06/2019 2:59 am  

Hi all,

I like that APP makes it pretty simple to set a quality threshold for my subs; just by yanking the "lights to stack" slider back and forth I can not only set the proportion, but also see the exact frames being culled in the list. Bravo!

A question, though: the "quality score" is a bit of a black box to me. I see that SNR and FWHM scores are also available, but apparently not till after integration. What goes into the "quality score", and can I obtain the other two for my subs either "in the raw" or after calibration? And should I have been able to find this information on my own?

TIA!

 


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(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 596
27/06/2019 8:35 pm  

Here's an answer from Mabula I found on the forum;

The quality scores are relative. There is no absolute score to indicate what a good score is actually.

The score is calculated with a special formula that consists of star density, noise and star shape.

Simply said, star density and star shape are relative in terms of imaging scale in pixels. If you register frames of different image scales, this will become clear.

In relative terms, frames with stars with a large FWHM value  in pixels will get a low score. But it does not mean that the frames are bad, it could simply mean that you are shooting with a very long focal lenght.


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(@rickwayne)
Molecular Cloud Customer
Joined: 3 months ago
Posts: 4
27/06/2019 11:38 pm  

Thanks Vincent! I actually saw that response linked beneath my query as a related topic -- AFTER I posted it. I'll try to pay a little more attention next time.

It will take a little more thought to use the score, rather than some arbitrary FWHM,  eccentricity number, or combination thereof. After all I don't care all that much about what percent I'm rejecting, I care about the quality of the frames. If I have a good, consistent night I might want 95% of them; a consistently bad night, perhaps 10%, and an inconsistent night maybe 50%. But perhaps I can suss that out by playing with the slider and seeing what frame-scores stay selected.

If there's an APP best practice for this, I'm all ears, as Ross Perot said.

Thanks again!

Thanks again!


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(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 596
27/06/2019 11:46 pm  

You're welcome. 🙂 As for the best practice, it comes down to personal preference a bit I think and some experimentation. I usually never look at the frames anymore (blinking through them) as I know my rig is very stable now and things like aircraft trails aren't a big issue at my location. I tend to always go for about 95% to stack, with quality as the selected method and it always works very nice. If you, however, are in an area with loads of aircraft or other disturbances, it might be better to first do a pass through the frames before going this route. If a particular session makes you want to throw the slider down to 10%... I, personally, would just call it a day and go for the next. 😉 Satellite trails usually aren't a problem when you take enough subs.


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(@rickwayne)
Molecular Cloud Customer
Joined: 3 months ago
Posts: 4
28/06/2019 12:36 am  

Sigh. I could only dream of a "very stable" rig, I'm afraid. I'm culling frames due to eccentricity, or even jagged trails from time to time when there's some kind of hiccup. That sort of thing shows of nicely in lower-level stats, I'll have to throw some of my special brand of horror frames at APP and check out how it scores them.


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(@vincent-mod)
Galaxy Moderator
Joined: 2 years ago
Posts: 596
28/06/2019 8:50 am  

Ow, sorry for that. Well those type of frames should be dealt with properly in APP using the quality method.


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