Eliminate subs with satellite trails?

[abillionnewstars]

Is there a way to filter out subs with pesky satellite trails? Some trails are bigger than others and force a longer total integration to make them dissappear from the final image. A filter with a tolerance slider would be amazing to have. Or maybe it already exists?
Or maybe there is a way to remove them manually? (other than saving all subs and restack them later)

[admin]

There are a couple of ways to do this...

Firstly you can use the option in live stacking for using a 'sigma clipped' stack - this means that the stacking will exclude unusual values when adding a new frame, like a satellite trail that is much brighter than that particular region of the image was previously. The slight gotcha is that this only kicks in after the first 10 frames - SharpCap has to stack a few frames without this turned on to get an idea of what the typical brightness values are in different parts of the image. If you get a satellite trail in that establishment phase then it will show up.

The second option is to use the satellite trail detection and removal feature in the pre-processing controls on the right. It's usually best to set this up with some saved images that have satellite trails in them (using either the folder monitor virtual camera or the deep sky test camera to show those images in SharpCap as though a camera had just captured them). You can adjust the sensitivity and other parameters for the satellite detection in 'highlight trails mode' , then switch to 'remove trails' mode. When that's all set up, SharpCap will try to detect satellite trails in each image, and when it finds one it 'paints out' that area of the image with nearby background - a bit like you can erase unwanted objects from photos on your phone.

The gotcha with the satellite trail detection and removal option is that it is quite hard to set up the sensitivity correctly to actually pick up all the trails and to not falsely detect other things in the image as trails - it's a particular problem if you only get a short length of trail in a particular frame.

cheers,

Robin

[abillionnewstars]

Thank you Robin.

I tried the detection feature on raw PNG subs, 2 of which had bad trails. It didn't work even at the highest sensitivity. The 2 frames with the trails went by and nothing happened.

And for some reasons, the PNGs were black and white. The session was ran with a OSC.

[abillionnewstars]

""SharpCap has to stack a few frames without this turned on to get an idea of what the typical brightness values are in different parts of the image. If you get a satellite trail in that establishment phase then it will show up.""

Does this mean I have to start the stack without Sigma clipping and remember to turn it on later on?

Does it also mean that if I get a satellite trail in the first few minutes, it is there to stay even after sigma clipping is turned on after?

[Jean-Francois]

Hello,

If you start a stack without the Sigma-Clipping activated and activate it during the stack, SharpCap will stop the actual stack and start a new one with the Sigma-Clipping activated. The same if you deactivate the Sigma-Clipping during a stack.

SharpCap remembers ... so it uses the last settings with or without Sigma-Clipping for the next observation session.

You can set the minimum number of frame for the Sigma-Clipping, the Initial Frame Count is 5 (you can change it with larger number).
That means SharpCap needs the initial images for the statistic calculation.
Yes, if you have one satellite trace during these first frames, it will stay in the stack.

So ... with Sigma-Clipping activated ... it is better to stay in front of the monitor and "Unstack" manually one image during the capture of the initial frames in the case of a trace on the image.

Regards,
Jean-Francois

[abillionnewstars]

Thank you for the tips and tricks Jean-François. Je vais chercher ce fameux bouton "unstack".

.Merci!

[admin]

Hi,

yes, Jean-Francois is right - watch the first 10 or so frames in sigma clipping mode and unstack any noticeable trails.

Your saved PNG files are mono because you are looking at the RAW images from the camera which have the colour information encoded in the individual pixel values (there will be a chessboard pattern at the pixel level if you zoom in). There are also parameters on trail width and minimum length that you may need to adjust - if you still can't get anything to work, please send me the PNG files and I will add them to my collection of files to test with.

thanks,

Robin

[abillionnewstars]

Where is that "unstack" button? I don't see it and can't find an interface picture online where it is shown. It is supposed to be at the bottom left.

[Gfischer]

Unstack button in actions group right under save button. Looks like your running an older version of sc

[abillionnewstars]

It is the latest version.