How can I overlay many frames from a video into a single merged image?

Question

I am looking for a simple way to turn a video into one image. I want each frame to be added to together to create one (over exposed) image. The point of this is I am trying to convert a video of me using a light to write in the air into a picture of 'Light Graffiti'. At the moment I can export each frame into a folder called 1.jpg, 2.jpg, 3.jpg ect. But I need a way to merge (Adding) these images literally on top of each other.

I don't have Photoshop but I can use Paint.net or Gimp.

What is the easiest way to batch merge a folder of images using add or is there an easier way to do this?

Answer

You could use ImageMagick to merge the images:

convert -compose lighten 1.jpg 2.jpg -composite 3.jpg -composite 4.jpg ... -composite result.jpg

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