9/22/2008

09-22-08 - 1

It's interesting to me the way H264 is designed. The coder is so simple, it really relies on the good motion compensation + bit allocation to do a good job, and it does very well. What this means is that the when image is easily predicted from motion vectors, you get a very high quality reproduction. When the image does not map to motion vectors, you get noise until it settles down. This is exactly the right way to create error from a human visual point of view. As long as there are still or simple translation elements that our eyes can track, we are very sensitive to error, and H264 does very well in those cases. When something changes in a non-linear way, like it rapidly changes direction randomly, or a new object is created via explosion or expulsion or whatever, then it appears distorted until it becomes linear, but that's exactly when our own visual system sort of fuzzes out the object anyway!

You can see my point better perhaps if you contrast with the opposite way of doing things. Something like motion-jpeg2000 might have roughly the same CPU usage, but it's not doing any motion comp and instead spends that CPU time on a better transform & still image coder. The total error rate is the same (pretend), but the motion-jpeg2000 coder is putting error all over the place, and we'll see horrible wiggles in still spots or simple translating spots.

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