Decimating Ghost interlaced frames

[JClement]

I have been playing around with various algorithms for removing ghost interlaced frames. I have been using a modified Fdecimate as the original source.

To set the stage, I have an old movie that I want to use Spot Remover, so I first deinterlaced it. But it seems the original had been ghost interlaced, and then 3/2 interlaced by another program, so I ended up with 4 good frames and 1 50/50 ghost interlaced. I suspect the ghost interlacing was done mechanically with a double exposure of 2 frames to create a 30fps film for easy TV broadcasts.

Basically I have found that the original decimation algorithm only found some of the ghost frames. Just putting in a search for current - 1/2 last - 1/2 previous worked somewhat better, but not good enough. Then I tried changing the metric to looking at the standard deviation. Discarding pixels that only had a very small difference also helped. The metric strongly identified ghosted images. The big problem is of course the random noise in the old video which can mess up the algorithm.

OK, now I am trying to rewrite it to just discard the ghosted images. The threshold is useless. Actually fdecimate misbehaves for a high threshold and puts frames out of order.

So the basic question is in the logic of avisyth. Is there some documentation on the logic of plugins, especially ones that can decimate frames. Actually I only want to quinquemate 1 in 5 rather than decimate 1 in 10.