Just when I think I've got my head around this whole de-interlacing thing....
I've been experimenting with some filtering today while encoding a PAL DVD. It's a very old one. The effect of de-interlacing is confusing me a little. Best that I can tell, the video is a combination of progressive and interlaced. I thought I'd experiment with "full frame rate" de-interlacing, assuming the progressive bits would just result in repeated frames. However there's color differences I don't understand. To illustrate:
Screenshot number 1:
Screenshot number 2:
It mightn't be immediately obvious, but the color is a little different. Number 1 seems a little more "greenish".
The above screenshots are two consecutive frames. The video is progressive during that section, but when de-interlacing to 50fps the result is effectively 25p with each frame repeated, only they alternate between "greenish" and "not as greenish". I've tried different de-interlacers with the same result. I've stepped throlugh frames looking for blemishes which only appear in a single frame, and when de-interlacing progressive sections to 50fps they're repeated, but the color of the frames continues to alternate.
Deciding to use QTGMC for de-interlacing to 25fps I added the following to the script:
Each successive frame was now the same color: "greenish".
Changing the script to this:
Each successive frame was now the same color: "not so greenish".
So the end result is when it comes to de-interlacing, for the progressive sections, I can choose "greenish" 25fps or "not so greenish" 25fps by adding either SelectEven or SelectOdd to the script.
If I de-interlace to 25fps with Yadif, for the progressive parts I can choose between "greenish" and "not so greenish" by changing the field order.
I'm not sure I've ever seen that sort of thing before and have no idea how it'd come about, or whether there is some sort of normality to it and I'm just not very observant.
Anyone understand the how/why?
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It's quite common for video tape sources to have slightly different levels/colors on each field (one field per tape head).
To alleviate the problem you could adjust the colors of one field or Merge(SelectEven(),SelectOdd()).
Thanks guys. I kind of like knowing the "why" if I can. The quality is fairly poor and the goal was really just to make it "watchable" so the color thing wasn't a problem as such, it was just the "why" part. It's not something I'd noticed before. I'll have a play with both your suggestions. Cheers.