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The Good, the Bad, and the Ugly Subs???


Derbyshire Dave

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Hi,

 Subs have been very hard to come by recently, the weather has just been shocking, and even when there has been some clear spells, there often has been some high cloud about .. or if not that dang moon.

 

 Got me to thinking about the best way to rate subs. I tend to use Deep Sky Stacker for my stacking, and during the 'Register Checked Pictures' process, there is a rating system. On the 'Advanced' tab, there is a 'Compute the number of detected stars' button. I normally change the threshold so that I have a few hundred stars visible.

 The registration process then gives a score and a number of stars and sorts the good one to the top of the list. The score seems to be proportional to the number of stars you have chosen. i.e if you choose to have more visible stars, you will get higher scores, even from the same pictures.

 

 I normally choose about 90% or more of the subs, discarding the lowest scores.

 

 I wondered whether there are other, more scientific perhaps, mean of choosing the best subs. I use PixInsight, and the Blink facility is great, allowing you to easily turf out subs with aeroplane or satellite trails etc, but doesn't, I don't think, allow me to compare sub quality other than that..

 

 So, how do you do this guys, It would be interesting to see what methods people think is the best....

 

Cheers

 

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I use Maxim.

It has its own way of sorting the subs by only allowing subs that pass a set criteria to be stacked.

The main criteria that I use is " roundness ".

Maxim measures the stars in each sub for roundness and rejects any sub where the stars are slightly out of round, elongated or trailed ect above your set limit. 

It is pretty brutal but very accurate in its decisions sometimes removing subs for very minor imperfections.

 

Edited by Graham
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Hi Dave

I use the subframe selector batch process in Pixinsight. Good accurate measurement of all the usual metrics - produces a plotted graph so you can see subs relative to each other which I find useful

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40 minutes ago, Chris P. said:

Hi Dave

I use the subframe selector batch process in Pixinsight. Good accurate measurement of all the usual metrics - produces a plotted graph so you can see subs relative to each other which I find useful

Chris, thanks, that's exactly the kind of information I was after. Much appreciated, I'll have a look at that...

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Chris, thanks for the heads up on Subframe Selector. Spent the morning having a good look through and ran some tutorials. It really is an amazing comprehensive way of selecting and rating images, you can choose different ways of selecting, roundness, FHWM, noise, number of stars etc etc.

 

I probably only confirms what you can see by visually inspecting the images in blink, but it is really good to know the capabiliity is there. Also interesting to comapre statistics between different nights, although again, quality will depend on conditions and the objects position in the sky.

 

At the end of the day, subs are so hard to come by, I guess the general rule will always tend to include, rather than reject, as many as you can.

 

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