Understanding Motion Resolution

[Balthazar2k4]

I read somewhere on some forum either here or elsewhere about motion resolution and its importance to converting 1080p to 720p. The jist of what got out of the thread was that most Blu-Ray discs that are encoded at 1080p do not have 1080 lines of motion resolution, but far less (the exception being animated/computer animated movies). Can anyone shed any light on this? I have been considering the move to strictly 720p encodes to save some space, but understanding this subject better would help to provide some needed perspective.

[RunningSkittle]

Most of the time its 1080p movies are low passed and dont have enough detail to justify archiving in 1080p. (ie you cant tell the difference between upscaled from 720 and original 1080)

[julius666]

most Blu-Ray discs that are encoded at 1080p do not have 1080 lines of motion resolution, but far less (the exception being animated...

Animations (well, at least animes) are the worst :p

Anyway, compare the 1080p and the downscaled videos, and decide it by eyes. It varies per source.

[Lyris]

I've actually seen a lot of movies on BD that have escaped lowpass filtering (almost anything from Disney) or have only been mildly affected. I would dispute that down-rezzing to 720p is harmless in a lot of those cases.

[RunningSkittle]

I've actually seen a lot of movies on BD that have escaped lowpass filtering (almost anything from Disney) or have only been mildly affected. I would dispute that down-rezzing to 720p is harmless in a lot of those cases.

Thats a small minority of the bluray thats available.

[Blue_MiSfit]

I agree. There are definitely exceptions, but I'd say "as a rule" most BluRay discs do not gain much from keeping them at 1080p.

More of the newer discs I've processed have been better, and maybe with x264 finally having NAL-HRD in the GIT, we will see someone build an encoding workflow using x264 ;) WTB the first disc encoded professionally with x264!

~MiSfit

[Balthazar2k4]

Thanks guys for the clarification on the subject. Out of curiosity, how can you tell if a BD has been processed with a low pass filter or that it is limited in motion resolution?

[benwaggoner]

Also, in many cases film wouldn't have been low-passed explicitly. It's just that most movie content doesn't have that much detail, particularly older stuff shot on older film stocks.

I'm not sure what the phrase "motion resolution" means as opposed to normal resolution. If anything, you need less resolution when things are moving since motion blur reduces your detail further. The VC-1 encoder for VBR Smooth Streaming takes good advantage of that, dynamically reducing the resolution of GOPs with a lot of motion in order to avoid video artifacts.

[LoRd_MuldeR]

Out of curiosity, how can you tell if a BD has been processed with a low pass filter or that it is limited in motion resolution?

Maybe like this:

src = FFmpegSource("C:\Some 1080p Source.mkv")
res = src.Lanczos4Resize(1280,720).Lanczos4Resize(src.Width,src.Height)
Interleave(src.Subtitle("Original Source"),res.Subtitle("Downsized Version"))

If the original 1080p source doesn't look much different than the version that was first downscaled to 720p and then upscaled back to 1080p, then it's probably not worth keeping it at 1080p.

[Blue_MiSfit]

Yup. That's how I do it, more or less :)

~MiSfit

[Balthazar2k4]

Maybe like this:

src = FFmpegSource("C:\Some 1080p Source.mkv")
res = src.Lanczos4Resize(1280,720).Lanczos4Resize(src.Width,src.Height)
Interleave(src.Subtitle("Original Source"),res.Subtitle("Downsized Version"))

If the original 1080p source doesn't look much different than the version that was first downscaled to 720p and then upscaled back to 1080p, then it's probably not worth keeping it at 1080p.

I see. So if I take the source file and rescale it to 720p on the fly it would give me some idea. So there isn't some empirical formula, but purely based on personal viewing. I'll give it a try. Thanks everyone for the assistance!

[Lyris]

Out of curiosity, how can you tell if a BD has been processed with a low pass filter or that it is limited in motion resolution?
I just look for the artefacts (ringing)...

The little "wrinkle" you get around (what were once) high frequencies, like the small amount of letterboxing at the top and bottom of the frame, are a dead giveaway.

[Balthazar2k4]

I just look for the artefacts (ringing)...

The little "wrinkle" you get around (what were once) high frequencies, like the small amount of letterboxing at the top and bottom of the frame, are a dead giveaway.

Interesting. I did not realize that was caused by low pass filtering. I have always heard that ringing is caused by DNR & Edge Enhancement, is that the same thing as low pass filtering?

[Blue_MiSfit]

Low pass filtering is a fairly sadistic form of noise reduction (DNR). :devil:

~MiSfit

[Balthazar2k4]

Low pass filtering is a fairly sadistic form of noise reduction (DNR). :devil:

~MiSfit

I like the way you put that. I'll keep that in mind and thanks again for the insight.