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Interpolation and HFR48

This part was originally just going to be one long, continuous angry hiss, but that doesn’t play nearly as well in writing as it does in speech. Truth be told, it doesn’t play that well in speech, either.

Interpolation and HFR (which stands for High Frame Rate) are lumped together as two very different technologies, because their end result is very similar, if not identical. This has to do with the number of frames per second that are projected onto the screen. Movies are traditionally shot at 24 frames per second. This frame rate was originally due to nothing more than the advent of sound in movie theaters; early silent films, using hand-cranked film cameras and hand-cranked projectors, would display movies with anywhere between 16 and 26 frames per second. When sound came along, and once it became possible to print an audio track directly onto the film itself, it became necessary to pick a standard and go with it…with the fewer frames used and the less money spent, the better.

A frame rate of 16 did not produce workable sound, and the lowest frequency that did was 24. Thus, 24 frames per second in film (and 24p in digital cinema) became an industry standard on the back of a decision that was entirely motivated by cost control…and in the current environment, where frame rate does not affect cost at all if you’re shooting digitally, a frame rate of 24 is an entirely arbitrary decision mathematically.

There was a side effect to 24 frames per second being an industry standard for decades, though: it didn’t depict motion very fluidly. Any part of a film where the subjects were exhibiting significant movement, or if the camera was moving, exhibited a trait known as frame judder - or more colloquially, motion blur. This was a visual characteristic that was only present in film, and the association of cinema with that unique judder was total. Film trained the human eye to perceive its world in a certain way, one that was very different from how the human eye processes the signal of a TV show or a video game (or real life, for that matter). 24 frames per second is just slightly fast enough for the eye to recognize what it’s seeing as motion, instead of a series of photographs.

This causes a slight but unmistakable disconnect between how we perceive the reality of life and the reality of movies, and everything about a film shot at 24 frames per second - the sets, the lighting, the dialogue, the music, and especially the actors - possesses a certain mystique. To use a rather artful expression, there is a veil of mysticism between the audience and what is happening onscreen. This is a psychological trick more than anything else, but you’d be hard-pressed to find someone not invested in the form who could deduce why a movie looks like a movie.

The theoretical advantages of going higher than 24 frames per second are fairly obvious: with more frames in the same amount of time, judder or blur on motion is diminished or removed. This produces a much clearer and cleaner image. Projection systems operating off of a higher frame rate give the impression of having a far higher resolution.

And with the advent of 3D into theaters in the mid-2000s, there was a refreshed opportunity for HFR systems to establish themselves. With the right amount of planning during preproduction and production, the kind of strobing/ghosting effect we’ve talked about could be minimized - but as we’ll see in the next section, planning for 3D exhibition was not generally done very successfully. HFR was tremendously beneficial to 3D visuals: quick movement and motion could be depicted in full 3D with no strobing or motion blur.

There is perhaps no better example of HFR in a mass-market setting than Peter Jackson’s Hobbit films. The movie itself may have been shot with the Red Epic, with all of that 3D system’s disadvantages against something like Fusion, but it was shot in 3D for exhibition in 3D, and the camera movements and edits were orchestrated with this in mind. The use of HFR-48 on the movies is what set it apart, and what initiated a rather intensely love-it-or-hate-it reaction among test audiences, with most of the reaction coming down firmly in the “hate it” column.

The points for and against using HFR weren’t really any different from what we’ve identified here in our controlled environment; it was the totality of the response that garnered attention. With fantasy films like The Hobbit, where effects and makeup and costuming and set design combine to create an artificial reality, the immediacy of the visuals - arrived at by shooting at a frame rate much closer to the 60 interlaced “fields” per second we get on reality TV shows and news broadcasts - have the effect of decisively removing the viewer from the world of the film.

This may be partially due to culture. We have been exposed to 24 frames per second for generations; movies and TV shows with higher frame rates enjoy greater acceptance and prevalence in other countries. Here, though, it’s unlikely that we’ll see HFR advertised theatrically to nearly the degree that we saw with the initial Hobbit film (promotion for HFR for both of the sequels was noticeably diminished). In marked contrast, frame interpolation is omnipresent in home cinema; it generally presents itself as something like TruMotion or Smooth Motion or Cinemotion or some other portmanteau of two terms.

Motion interpolation on an HDTV is generally a matter of a processor within the TV artificially creating frames in between those already present: if the original media has Frame A, Frame B, and Frame C, motion interpolation would create an intermediary image between each of these actual ones. If you put them in sequence, the frames would look like this: A-AB-B-BC-C. Frame interpolation is a fairly common way to optimize a video sequence, and it’s been around long enough for most HDTVs to accomplish it with little to no artifacting of the image. If HFR does gain a wider acceptance down the road, it’s likely to be due to frame interpolation making inroads in the home-theater space.

It’s still awful, though.

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