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I have 7 video frames (saved as PNG) of a lightening strike who's main 'vein' persists over most of the frames but is also producing 'tendrils' that are different in each frame.
I want to make a single image that includes all parts of that strike over time.

I have imported each image in GIMP as a separate layer.
I have tried 'Merge Visible Layers', that basically gives me just the first image.
I have tried setting each image to 50% Opacity and then each image Mode to 'Merge' - which is the closest I can currently get to the desired end-point, unfortunately the grey in the clouds where the image does NOT include the 'tendril' tends to erase that from the image where that tendril IS present.

I have experimented with Add Subtract and Multiply but they all badly effect the overall background image.

I have no doubt that this has been done before, but Google and this forum search does not result in anything awesome.

Attached are a couple of the (reduced to 20%) frames that the effect is visible in.

It would have been better if you gave us the 6 image (at 20% is fine), because it could be needed to have an "order" to get all the burst/veins,

anyway with 2 images try Luma/Luminance lighten only
[attachment=9922]

Then do a New from Visible from right click on the top layer inside the layer dialog or go to Layer > New from Visible
Above the new "Visible" layer put the next layer you want to "fuse" and do the same put it in > Luma lighten only, and so on > New from visible... etc...

Or instead of new from visible, each time merge them down by 2 each time instead of new visible

There are many other solutions, like get a mask (very easy on this type of image) to protect the trees, the roof and even the sky and have only the bursts.

You can try puttin all layers (except the bottom one in "lighten only mode"):


To improve this, once you have done that:

• Get the image as a layer: Layer > New from visible
  
• Duplicate that, and Color > Desaturate > Desaturate (Luminance)
  
• Start the Curves tool, the idea is to tweak the image so that, the whole sky becomes white, the lighting becomes black, and the trees stay the same 
  
• [attachment=9924]
  
• Open the Channels list, right click any of the RGB channels; and Channel to selection
  
• Hide the desaturated layer, selected the first "New from visible", and decrease the brightness and increase the contrast.
  

Well I have gone roughly the same route. Five consecutive frames @ say 25 frames/second and the background should be identical.

Frame 1 and frame 2 differenced. 

[attachment=9926]

In a layer group and the difference layers over Frame 1 in Addition mode.

[attachment=9927]

Should be possible to create a combined image with succesive pairs of frames.  (or maybe not)

Another option is to also use one of the before/after frame **without** lighting (or to also combine all the frames in darken only mode) .

You can then subtract that frame from your lightning frames(*), and this leaves you with the lightning only. Then once you have these (added with lighten only mode) in a group, you can duplicate the  group for added contrast, and put it over a darkened version of the lightning-less frame (which is much easier to work with because you don't have to protect the lightning).



Final note: its likely useful to use high precision mode for all this.

(*) ofn-interleave-layers can blend a layer against all layers in a stack with any blend mode)

(06-13-2023, 01:57 PM)Ofnuts Wrote: [ -> ]You can try puttin all layers (except the bottom one in "lighten only mode"):



...

That's IT!, that's what I wanted, the Lighten Only mode was sufficient but I will experiment with your further suggestions when I have more time.
Attached is the result I was looking for.

Many thanks to all that replied, I will try each suggestion as a 'training exercise'.

'Grain merge' works too. So does 'inear burn' if you want the trees & rooftop dark