How do you sort out a large number of subs prior to stacking?

[swag72]

I took some luminance subs last night and have now got about 65 of them. The old addage of rubbish in, rubbish out springs to mind, so is there a way to easily sort through the data to prevent the rubbish going in?

I will stack in Maxim, so can have a look at the roundness and FWHM figure of each one for some idea, but is there a programme that can be used to determine if something is a good or bad sub? When narrowband imaging, it's not an issue to go through each sub as there's no more than about 20. But once you start getting to the 60 mark and more, is there something out there that can help? Or do you all physically plough them them all?

[steppenwolf]

I always manually check mine by combining them in manual 1 star (if captured in a single session) or manual 2 star (if I have moved the camera at all between sessions) in MaxIm DL. This allows me to set my own criteria as each frame pops up automatically allowing me to quickly scan it for errors (including satellites!). This also gives me the opportunity to choose a different reference sub. (one ion the middle of the session) if I notice any differential flexure has crept in.

Sorry, I don't immediately know any software that would grade the images as a stand alone product.

[Komet]

Sorry, I don't immediately know any software that would grade the images as a stand alone product.

Try FITS Image Grader - its free from http://www.mainsequencesoftware.com - in the Downloads section

[swag72]

I'll have a look at that Mick, thank you - Do you use it for this purpose?

[Komet]

I'll have a look at that Mick, thank you - Do you use it for this purpose?

Yes I do ... it does help. It should be borne in mind that it grades only the images you have loaded relatively against each other. It does not categorically say that this image is good or this image is bad. It will however put them in some sort of order so you can decide. It will also rename with Good or Bad if required. I find it pretty useful. Part of SGPro anyway (which I love)

[ollypenrice]

Steve, satellites? I leave 'em in and let Sigma clipping remove them. In AA5 it's incredibly effective. In my Witch Head I had several in every single sub but they all vanished under Sigma. Tom had the same issue and upgraded from AA4 to AA5 and it worked for him as well. So clearly not all Sigma routines are born equal. You'd expect Maxim to be good, though.

I look at all mine unless I've seen them come in. AA5 lets you 'confirm each image.' How strict to be on criteria is a moot point. Suppose you have some slightly eggy stars on a target with lots of faint dusty stuff. If you are going to throw a lot of these away I wouldn't. Instead, make a stack with all the subs and another with only the good ones. Use the deeper but flawed stack for noise reduction on the faint stuff in the pristine set. You'd obviously just do this in Layers. (I have done something similar with some Bin2 luminance I shot for the infernal Praying Ghost. I only used the dust from the binned luminance, not the detail.)

[martin_h]

I use Nebulositys Preview Files section - select the files you wish to view and flick through them one by one - forwards and backwards - rename or delete as required.

[steppenwolf]

Steve, satellites? I leave 'em in and let Sigma clipping remove them

So do I if I am short on subs. but if I have a wealth of them, I remove them even though I use SDMask.

[r3i]

CCD Inspector can analyse images in a folder, either restrospectively or as they being saved during an imaging session. Gives data on FWHM, Aspect Ratio, Background ADU, tilt, curvature etc..

Just one problem - it aint cheap.

[ollypenrice]

So do I if I am short on subs. but if I have a wealth of them, I remove them even though I use SDMask.

I'm surprised. I leave mine in as long as I have sufficient subs to reject the outliers. In a way we are taking opposite views; in a short set I will not include them because the Sigma won't correct them, but once I have over a dozen I'm confident that it will so I leave them in. Veery interestink...

Olly