[zoky]

> Grain is independent frame-to-frame. It doesn't move with the objects in the scene (unless the video's already been encoded strangely)

That might seem like a reasonable assumption, but in practice it’s not really the case. Due to nonlinear response curves, adding noise to a bright part of an image has far less effect than a darker part. If the image is completely blown out the grain may not be discernible at all. So practically speaking, grain does travel with objects in a scene.

This means detail is indeed encoded in grain to an extent. If you algorithmically denoise an image and then subtract the result from the original to get only the grain, you can easily see “ghost” patterns in the grain that reflect the original image. This represents lost image data that cannot be recovered by adding synthetic grain.

[wyager]

It sounds like the "scaling function" mentioned in the article may be intended to account for the nonlinear interaction of the noise.

[creato]

> If you algorithmically denoise an image and then subtract the result from the original to get only the grain, you can easily see “ghost” patterns in the grain that reflect the original image. This represents lost image data that cannot be recovered by adding synthetic grain.

The synthesized grain is dependent on the brightness. If you were to just replace the frames with the synthesized grain described in the OP post instead of adding it, you would see something very similar.