HFR on SGU

I’m planning on heading to Sydney early in the new year to catch The Hobbit in its high frame rate version. I’ll be writing something about it for Sound and Image magazine.

Now Steven Novella from the Skeptics’ Guide to the Universe has given some interesting thoughts on it on SGU’s most recent podcast. I had a couple of minor quibbles, which I posted on the SGU forums here (it’s the 10th comment).

Here it is cross-posted:

Thanks for the impressions on the HFR Hobbit (it’s not here in Aus for a little while yet). A couple of technical corrections, though.

First, Steve, your high refresh rate TV is only slightly comparable to HFR film, digital. Yes, if you’re watching Blu-ray movies at their native frame rate of 24fps (actually, 23.976, thank you very much NTSC!) then your TV will be showing 48 or perhaps even 72 or 96fps. But only the original 24 frames are actually from the source. The rest are generated by the TV itself, interpolating from the actual source frames.

This processing can often improve the viewer’s ability to see things during moving scenes, but only some things. A cinematographer has to balance when filming moving things at 24fps between a fast shutter speed to keep the image sharp, and a slow shutter speed to allow sufficient motion blur to eliminate visible ‘judder’. Judder is where you can see the picture jump from frame to frame.

Motion interpolation systems are very good at eliminating judder, but can do nothing about motion blur.

Unfortunately they have side effects. First, there are often clear distortions introduced into the picture. I normally refer to these as looking like a heat haze surrounding moving objects. Second, they tend to wash out things like random film grain (since basically the interpolating is showing frame averages half or more of the time). It is this which gives a glossy sheen to the image.

I’ve been reviewing TVs with this kind of processing for over a decade (it started back in 2000 with something called ‘Digital Natural Motion’ from Philips). When I’m reviewing a TV, after checking out the processing to see whether it works and how much damage it does, I switch it off since it does not let you see the movie or whatever as it was originally shot. An occasional exception is Sony, which has a motion smoothing system that somehow avoids these problems, particularly on its home theatre projectors.

The Hobbit of course involves no interpolation, but actually captures double the number of frames from scratch. It should make everything clearer. Because of the higher frame rate the cinematographer can go for shorter exposure times without introducing judder, so there’s less motion blur.

One correction: a TV with a higher refresh rate does not require a new cable for that reason alone. The refresh rate is purely internal to the TV. You may actually have changed to a lower frame rate. American analogue TV connection standards are at 60 hertz. If you moved to Blu-ray via HDMI, then you’ve likely dropped back to 24 hertz for a lot of content.

Rebecca: why don’t digital projectors show HFR stuff? There’s no reason in principle why they can’t. But in practice projectors are designed for a specific set of input signals, and until recently 48fps content wasn’t among them. Remember virtually everything for the cinema has been shot at 24fps since the late 1920s when the introduction of sound forced the adoption of a standard. HFR is truly revolutionary.

Home digital projectors and TVs should, likewise, be able to cope with 48fps … except that it wasn’t designed into them. I would expect future models to start supporting it, but then there’s no 48fps source. A new version of Blu-ray could perhaps be developed, but that’s unlikely to happen just for one movie. If 48fps becomes popular, though …

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2 Responses to HFR on SGU

  1. Craig Mecak says:

    48p is very close to 50p, which most TVs and Projectors can already handle. So, a filmmaker could simply speed up the feature to 50p and have all display devices able to cope with it, just as any feature shot at 24 has been made compatible with PAL TV frame rates (+4%). But with blu-ray, at 50p the resolution tops out at 720p. Or they could easily do 50i at 1080.

    A better method would be to firmware update blu-ray players and TVs/Projectors to handle 48p. It is slower than 50p/60p after all. All 3D compatible blu-ray players should be able to do this, as 3D on blu-ray is essentially two 24p streams, but doubled. So they would simply be doing 2D @ 48p (1080 x 1920) instead of 3D @ 24p (2 x 24p).

  2. Hi Craig. A speed up is I suppose technically possible, but I suspect that commercially it won’t happen. These things are driven by the US, Japanese and Korean markets primarily, and there’s a lot of equipment in the US that simply won’t work at 50 hertz. Even today.

    As you say, 50 hertz in progressive tops out at 720p on Blu-ray anyway, so gaining temporal resolution at the cost of lateral and vertical doesn’t seem too good an idea.

    No, my guess is (and my guesses are very often totally wrong!) that if 48fps catches on in the cinema then a new format will appear.

    As it happens, current Blu-ray players have the bandwidth for 1080p48 since that is simply a variation on 1080p24 frame packed 3D. But The Hobbit is, of course, both 48fps and 3D, so a further bandwidth enhancement would be required, probably with a greater storage capacity as well (eg. four layer Blu-ray).

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