Artifact in Movie Colors Images

I’m looking at your movie colors multiple exposures project:

And I notice that many of the images have a vertical line down the center of them:

What causes this artifact? Is it a bug in the code, or something to do with the video encoding?

It’s a leftover of the end credits.

These images are formed by combining every frame (more accurately, 1 frame per second) into a single image. Each frame leaves a little bit of a “burn in” behind.

The end credits of most movies have two columns of text separated by some black space:

end creidts

This averages out to a darker line in the middle, with lighter sections to the left and right. Here’s the average of just the credits:

end credits average

You can see this in the final image, especially for movies with long credit sequences.