Originally Posted by djbluemax1
I have no idea what that animation is supposed to show
The first video shows what the car is supposed to be doing and where it is supposed to be at 12 fps. The interpolated version (3 fps -> 12 fps) shows that interpolation puts the car at the wrong places and also that interpolation isn't precise and causes bad artefacts. If you don't see the car in the interpolated video appearing to speed up/slow down, look at the still frames of the car. The top image shows the front of the car not much after position 600. The interpolated version shows the front of the car (even though part faded) starting past position 625. The back of the car also is at the wrong position in the interpolated version (the faded part starts before the back of the car in the non-interpolated version). So you could say interpolated version of the car shows it both sped up and slowed down.
doesn't appear to be what happens with a good interpolation algorithm.
hopefully they'll eventually be able to do per-pixel interpolation which should eliminate most visible artifacts
The algorithm used for my example was
a per-pixel algorithm "pixel motion" and a good algorithm but like all algorithms for interpolating video it will generate artefacts. It might have done better if the car had more points (detail) it could match. I interpolated from 3 fps to 12 fps. Obviously if it had more frames to work with it would have done a better job, but doing it that way showed the artefacts more clearly as well as the motion artefacts. It still had less of a ratio of frames to generate than 24->120 fps interpolation - though with the lower frame rate you see the artefacts more clearly.
A decent algorithm simply adds intermediate frames between each successive real frame i.e. if they add 4 additional frames, then the created frames between frames 1 and 2 simply show the car at unit 1.2, 1.4, 1.6, 1.8. Between frames 4 and 5, they simply add frames that place the car at unit 6, 6.5, 7, 7.5 etc.
The fact that the car is accelerating and not traveling at a constant rate is not a problem for any decent algorithm.
You're assuming and possibly basing it off the promotional material of TVs that feature interpolation instead of basing it on evidence of what actually happens with and the results of interpolation algorithms. I've shown what actually happens with interpolation - using pixel motion - the type of interpolation you think will give the best interpolation - and shown - it causes motion artefacts - as well as can interpolate things wrong in other ways (eg. the shape of the objects, as well as ghosting type artefacts - and the ghosting is one thing that could make something appear to be at the wrong position/sped up - by placing it ahead of where it should be because it is showing part of something from a frame ahead of the current frame).
then the created frames between frames 1 and 2 simply show the car at unit 1.2, 1.4, 1.6, 1.8
And if the true position of the car or other thing in real life wasn't
1.2, 1.4, 1.6., 1.8 at those points in time between the real frames it's still either sped up or slowed down (or both) the true motion of the car/object - even if no other artefacts (such as ghosting - placing the object ahead of it's true position) are generated.
Here's another link which shows some of the artefacts of interpolation from the Red camera site (see interpolated 24 fps example towards the bottom of the page) - though they don't say what frame rate it was interpolated from or what algorithm they used (might be just frame blending):
There will also be youtube videos that show actual TV motion interpolation artefacts.
It proves that motion interpolation can speed up/slow down the true motion of something in video (as proved by the start/end positions of the car in the example frames, both from the same point in time, which show the time code and an X coordinate) - which you said didn't happen with frame interpolation, as well as shows the sort of artefacts it can add.