Culling bad subs

In the integrate tab (6) there is a slider called "lights to stack". If you move it to the left it was start culling your subs based on quality. You can sort your subs by quality by right clicking and selecting sort by quality.

Posted by: @astrogee

In the integrate tab (6) there is a slider called "lights to stack". If you move it to the left it was start culling your subs based on quality. You can sort your subs by quality by right clicking and selecting sort by quality.

Thanks, @astrogee. Eric is my friend and kindly asked those questions on my behalf as I try to get oriented to APP. 

I am coming to APP from PixInsight. In that program, I first manually preview all of my light frames to remove any that are obviously bad (usually because of clouds). Then I run the light frames through the SubframeSelector process, which does a quality analysis and allows a "weighting" to be applied to each frame for the final stacking. 

I understand that APP can sort and stack subs based on quality. But how does it know which ones not to stack at all? If I give it a bunch of light frames with, say, 50% that are ruined by clouds, will APP know not to stack those? The "lights to stack" slider seems a little arbitrary. If I have 100 subframes and 50 of those are of poor quality due to clouds, and I put the "lights to stack" slider to 75%, will it still stack 25 of those bad frames? 

Thanks,

Glenn

What I do, and I am not 100% sure if this is the best way but after Registration, or Analyze stars from 1.075 onward I right click on the bottom list of subs and sort by quality.  I then right click again and select the Graph option. This graph will show clearly at what point quality starts dropping off severely.  I use this as a reference to set my slider in 6. If it is not 100% clear where the quality drops I use 0.5 in the graph as a reference to the number of subs I should stack. 

There maybe much better logic around this so hopefully other people will share how they decide how to select the number of subs to stack.

I have no idea how to select the number of subs to stack if it is a multi-channel image.

Thanks for the tip @lanties

It would be worthwhile to try loading all lights regardless to see what happens. Its likely that clouded over subs will be rejected at step 3 (analyze stars) because it won't find the required amount of stars. If the sub passes this stage then the other major factor is FWHM. The quality takes into account many factors but I think FWHM has the most weight as it seems to be highly correlated to quality - this may be selectable under the "lights to stack" slider but I'm not sure if it works with the slider or during stacking only. Anyway, I sort by quality and as I decrease the slider, I see subs with bad FWHM excluded from the stacking. (Cloudiness will reduce FWHM so FWHM is also a good measurement of sky clarity.) At the moment I filter out anything below FWHM=4 but I may refine this to FWHM=3 as I get my rig working better.

Thank you for the tips! 

Kind regards,

Glenn

@glenn

Oops. I got the FWHM level backwards but you probably know what I mean. Lower FWHM means better stars - so reverse what I said. Sorry!

So, I should have written: At the moment I filter out anything ABOVE FWHM=4 but I may refine this to FWHM=3 as I get my rig working better

EDIT: I should add that the FWHM is dependent on your scope and camera and may not fall in the same range as mine 

Posted by: @astrogee

At the moment I filter out anything ABOVE FWHM=4

In my case, that would be 100% of my subs.   🙁

Posted by: @cheetah

Posted by: @astrogee

At the moment I filter out anything ABOVE FWHM=4

In my case, that would be 100% of my subs.   🙁

 

Sorry, that value needs to be qualified because its dependent on the camera and scope, so for you it may be ok!