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The Obsession with the 24fps Frame Rate

Photo & Video

One of the biggest criticisms to the Movie mode of the Canon 5D mark II according to the concensus of the web is the lockdown to a fixed framerate of 30 frames per second. The critique seems to stem from the fact that since american NTSC video is captured using 30fps and Hollywood film are shot using 24fps, the video output from the 5D mark II resembles sitcoms from the 80′s rather than high quality film. Can this be true?

In a word, no. A higher frame rate will only lead to smoother playback and is uncorrelated to image quality. The film like qualities sought is smooth movements of the subjects, something attributed to the fixed shutter speed (1/48s) of many 24fps film cameras which results in motion blur. Some believe that this motion blur is close to how our eyes perceive motion and that video captured using faster shutter speeds is just too clear.

As a result it’s not the 24fps that we’re chasing, but rather 1/48s shutter speeds. The 5D mark II varies its shutter speed from 1/30s to 1/125s resulting in some parts that resembles film and some that resembles video. Is it so?

In a word, no. That would mean that slow motion sequences in big-budget movies would look like video since they’re shot using shorter shutter speed than 1/48s. No matter of how the effect is perceived, the slow motion parts of the movie 300 doesn’t look like video to me.

There’s so much more that separates video from 35mm film; contrast, dynamic range, depth of field, resolution, colors and so on. Basically, the same parameters that separate our D-SLR’s from the compact cameras. The 5D mark II won’t be transformed to a 35mm film camera if a 24fps Movie mode is added through firmware. It’s not a film camera just as it isn’t a digicam. It’s something else, a new breed of movie camera along with the RED ONE that’s neither.

Just as some prefer the distortion added by valve amplifiers in high-end audio reproduction some prefer the added motion blur captured by film. In my opinion it’s preferable to start with the cleanest and clearest source possible and then degrade it by choice rather than capturing it muddy from the start. Who knows, maybe it’s possible to add a motion blur filter to the next generation of our playback devices?

EDIT 20081218: It has been brought to my attention that the different types of shutters in film and digital movie cameras cause one more difference in how motion blur shows up. The 180 degree rotary shutter in most film cameras exposes the film for half of the time for each cycle and blocks the film the other half (to allow the advance to the next frame). This leadsto the 1/48s shutter speed for 24fps film and also motion blur streaks which aren’t consistent between each frame, there will be gaps between the ends of a motion blur streak between two frames since the exposure is blocked for 1/48s.

The 360 degree (or fully open) electronic shutter of digital cameras means that there will be no gaps in the motion blur trails from one frame to the next. This creates a more theoretically correct motion blur, just something that we don’t associate with high-end movies, yet.

Shorter shutter speeds than 1/48s is seen in the landing scene in Saving Private Ryanand Gladiator, for example. Shutter angles such as 90 and 45 degrees produces shutter speeds of 1/96s and 1/192s, respectively. This freezes the motion and reveals much more details while also introducing a “staccato” effect when objects moving at high speed are clear and full of detail. One of the oldest tricks in the book to show the speed of a fast moving object is to introduce motion blur. When the motion blur isn’t there it makes us think that something is wrong since we aren’t used to it. It isn’t wrong, just something we needs to be accustomed to and which can be used to creative effect if it can be set manually (which the RED cameras can but 5D can’t).

The big benefit with 24fps frame rates is not the film like quality then, since it doesn’t exist. More frame rate options helps to reduce light flicker from lights running on mains electricity by synching frame rate and frequency. It is also much easier to convert to other frame rates suitable for broadcast and DVD’s around the world. 24 fps can be converted to 30 fps through a 3:2 pull down which introduces extra frames, the other way around is much harder. However, most (if not all) DVD/Blu-ray players, HD-TV sets and computers can show all common frame rates which makes this a solely theoretic advantage. Film in 30fps, edit in 30fps, distribute in 30fps and show in 30fps and the problem is solved.

EDIT 20090105: I just read an article on Variety where James Cameron describes his views on 3-D movies (and cinemas) and he also discusses resolution and framerates for normal movies. Turns out I’m not the only one who don’t like judders during pans:

“For three-fourths of a century of 2-D cinema, we have grown accustomed to the strobing effect produced by the 24 frame per second display rate.”
[...]
The DLP chip in our current generation of digital projectors can currently run up to 144 frames per second, and they are still being improved. The maximum data rate currently supports stereo at 24 frames per second or 2-D at 48 frames per second. So right now, today, we could be shooting 2-D movies at 48 frames and running them at that speed. This alone would make 2-D movies look astonishingly clear and sharp, at very little extra cost, with equipment that’s already installed or being installed.

Increasing the data-handling capacity of the projectors and servers is not a big deal, if there is demand. I’ve run tests on 48 frame per second stereo and it is stunning. The cameras can do it, the projectors can (with a small modification) do it. So why aren’t we doing it, as an industry?

Because people have been asking the wrong question for years. They have been so focused on resolution, and counting pixels and lines, that they have forgotten about frame rate. Perceived resolution = pixels x replacement rate. A 2K image at 48 frames per second looks as sharp as a 4K image at 24 frames per second … with one fundamental difference: the 4K/24 image will judder miserably during a panning shot, and the 2K/48 won’t. Higher pixel counts only preserve motion artifacts like strobing with greater fidelity. They don’t solve them at all.”
[...]
“I would vastly prefer to see 2K/48 frames per second as a new display standard, than 4K/24 frames per second. This would mean shooting movies at 48 fps, which the digital cameras can easily accommodate. Film cameras can run that fast, but stock costs would go up.”
[...]
“Of course, the ideal format is 3-D/2K/48 fps projection. I’d love to have done Avatar at 48 frames. But I have to fight these battles one at a time. I’m just happy people are waking up to 3-D.

Maybe on Avatar 2.”



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