Comment by ErroneousBosh
18 days ago
You're not "throwing out half the motion".
Given that PC monitors these days don't have an interlaced mode, how would you display it? Line doubling, so you're throwing out half the vertical resolution?
18 days ago
You're not "throwing out half the motion".
Given that PC monitors these days don't have an interlaced mode, how would you display it? Line doubling, so you're throwing out half the vertical resolution?
> You're not "throwing out half the motion".
Yes, you are. The odd and even lines from proper interlaced footage belong to two separate moments in time, and so when you deinterlace from 60i to 30p you are unavoidably losing half of those moments.
> Given that PC monitors these days don't have an interlaced mode, how would you display it?
You deinterlace it to 60fps. There exist several algorithms to do so without losing motion fluidity.
> Line doubling, so you're throwing out half the vertical resolution?
Losing half of the vertical resolution of a 60i video is losing half the motion.
> You deinterlace it to 60fps. There exist several algorithms to do so without losing motion fluidity.
So what does "deinterlace it to 60fps" do? How does it work?
The most basic method is to "bob" deinterlace, which is more of a form of "interlace simulation" - you take the original fields, place each one in the appropriate image lines of a separate frame of video, then perform some type of interpolation of each frame for the in-between lines. More advanced algorithms exist like yadif, that do some amount of motion detection to determine which parts of the image require deinterlacing, and which parts can be essentially done with a "weave", which is just taking part of the image data from a combined 30fps frame containing two fields.
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AFAIU it is possible to get nearly full resolution and full frame rate by using motion tracking to merge the fields. I.e. if the motion is regular enough, lines from the previous and / or next frame can be inserted instead of doubling the current lines. Which is almost the same process required to achieve best image quality at half the frame rate, just without throwing away frames.
You're not throwing away frames, though. You're blending the lines from the odd and even frames so that you get the full vertical resolution, with a certain amount of motion blur on moving vertical edges.
Analogue video is 25 frames per second, 50 fields per second. You could guess at what the "missing" lines in a field are, but that doesn't magically make it 50p video.
The effective rate for 50i or 60i video, in terms of motion fluidity, is 50 or 60fps. Just because it's half the resolution per field doesn't mean that it's not a "frame" of video in abstract terms, just that it's not a "frame" in the jargon (because fields by definition are half a frame).
It is impossible to decimate a video from 50/60i to 25/30p without losing half of the motion fluidity, even if the properly interlaced source video is technically 25/30fps.