Future Tense: The Showscan Insight


Thirty-five years ago, Douglas Trumbull, the special effects wizard who created marvelous spaceships for Stanley Kubrick’s 2001: A Space Odyssey and not-so marvelous spaceships for Gene Roddenberry’s Star Trek: The Motionless Picture also worked on a process called Showscan .

Showscan used 70mm film projected onto a screen that curved 150 degrees around the audience—exactly like the Cinerama screens of the 50’s and 60’s. The difference between Showscan and 70mm Cinerama was that Showscan was photographed and projected at 72 frames per second. The impact on viewers was profound. The image was so clear it looked three-dimensional. All film grain disappeared. If there was dirt on the film, it wasn’t on the screen long enough to register. All that was left was the image. Even better, fast moving objects didn’t flicker, didn’t blur, didn’t shudder—they just moved smoothly. The inevitable roller-coaster demonstration was visceral .

Trumbull tested the Showscan process in front of several live audiences; he also had researchers from UCLA come in and measure the physical reactions of Showscan viewers. They found that viewers’ physical reactions were significantly affected by the frame rate. The higher the frame rate, the greater the impact. Above 60fps, the image stopped looking like a screen and started looking like a window.

Trumbull even filmed a movie intended to use the Showscan process for key sequences. Brainstorm starred Natalie Wood, Christopher Walken, Louise Fletcher and Cliff Robertson. Unfortunately, before the film was finished, Natalie Wood drowned in a boating accident and MGM, fearful of the publicity, cut back their investment in the film. The planned Showscan sequences were instead presented in 70mm, the rest of the film in 35mm. It just wasn’t the same. The film was a box-office disappointment, but it’s a good SF movie nonetheless because it’s actually about something .

(Look, I enjoy the eye-candy as much as the next nerd. But after the movie is over, when we all go out for coffee and talk about what we saw, I want to have a discussion about ideas—honest!)

Eventually, the Showscan process found a second life as an amusement park attraction . Simulators with jiggling seats showed point-of-view spaceship journeys or runaway mine-trains at 60fps on a small flat screen. What had previously been an awe-inspiring demonstration of a great technological possibility had been reduced to an unconvincing parlor trick.

Nevertheless, Doug Trumbull established once and for all that frames-per-second are a critical factor to your perception. The more sensory information presented to the brain, the greater the presence of the experience— the more it feels real .

This is true for all media. Not just moving images, but audio as well. You can test this yourself. (Hardcore audio-geeks already know what I’m talking about.) Find the highest quality audio track you have—something very well recorded, something with a lot of presence, a favorite piece of music you are intimately familiar with.

Now rip several MP3 copies at different bit rates. The lowest possible bit-rate, the highest possible, and even a few in between. Listen with headphones. You will hear audible differences between the low bit-rate material and the original. But as you work your way up toward higher and higher bit-rates, comparing each to the original source material, you will eventually pass a critical threshold. Somewhere above 160-bits or 192-bits, the differences will become virtually impossible to detect.

The issue isn’t bandwidth or bit-rate; that’s merely the medium of transmission. This is really about the amount of information you’re experiencing each moment. Greater bandwidth makes it possible to deliver more information per second, and as the sheer quantity of sensory information increases, so does the perception of realism. When the information channel surpasses what your senses can distinguish, it becomes indistinguishable from reality.

This is why HDTV looks so much better than NTSC. An NTSC analog signal gives you (at best) 500 lines of picture information at 29.97 frames per second (and 25 lines with no picture information at all). But interference measurably reduces the quality of an off-the-air analog broadcast, introducing ghosts and snow and ringing effects. Digital transmission of NTSC, via cable or satellite or broadcast DTV, eliminates the interference and provides clear stable images—better than you can receive with any off-the-air transmission, unless you’re living half a block from the transmission tower.

In 1994, a friend invited me over to see his new home theater. He had a 53” rear-projection set (with a built-in line-doubler) connected to a DirecTV receiver. It was a transformative experience. I was flabbergasted—and genuinely envious. Until that moment, I hadn’t believed it was possible to make a television picture look that good. The picture was stable, there were no visible scan lines, and the colors were bright. There was no snow, no ringing, and no artifacts of any kind. The picture was even better than a well-produced laserdisc, which until that moment set the standard for high-quality NTSC video.

Laserdiscs were the precursors to DVDs. They were optical discs the size of vinyl records and could hold only an hour of video on each side of the disc—but it wasn’t a digital signal, it was an analog signal delivered to your set as composite video. Laserdiscs were good, better than S-VHS or Beta, and noticeably better than a broadcast signal too. But they were large and heavy, inconvenient and expensive, and never achieved much market penetration.

But laserdiscs were essentially limited by their own analog technology. By contrast, DVDs encode the signal digitally which allows for a virtually unlimited dynamic range, dependent only on the bit-rate.

Analog transmission contains a virtual copy of the sound and picture impressed on a carrier wave. The carrier wave is modulated with the signal, so the dynamic range of the signal is limited by the dynamic range of the carrier medium. The practical maximum works out to about 60db, though the average achieved is usually 10db less.

Digital transmission is simply a stream of ones and zeroes. With the appropriate error-correction codes, the signal is much more resistant to fluctuations in signal-to-noise ratio. The digital signal doesn’t need a large dynamic range in the carrier medium, only enough to distinguish the difference between a zero and a one. The bitstream represents only the instructions for flawlessly reconstructing the sound and picture. As long as the bitstream arrives intact, the signal-to-noise ratio can be anything the designers choose to implement—usually around 95db.

A 95db s/n means the noise floor is essentially undetectable, while allowing for maximum dynamic range between bright and dark, loud and soft. The superior quality of digital NTSC was a critical factor in the growth of various cable and satellite systems—and that helped expand the market for HBO, Showtime, and various other cable-only networks.

The laserdisc market evaporated with the advent of DVDs. An NTSC-DVD stores video as an MPEG-2 stream with a resolution of 720/704×480—image quality that touches the lower range of what is considered high-definition video.

Today, the market is rapidly shifting to Blu-Ray discs, capable of delivering 1080p at 60fps. A state of the art Blu-Ray presentation on a large screen can look as good as the original Showscan. The image is bright, stable, and solid, there’s no grain, no blurring, no shudder. Viewed on a set that has motion interpolation at 120hz or 240hz, the image quality can (theoretically) even surpass Showscan for the smoothness of its motion. Consider it Home-Showscan, minus the Cinerama style screen. (That’s next year, after 3D.)

So what does all this have to do with overclocking?

Frame rates.

60fps is going to look a lot better than 30fps. You already knew that of course, but now you know why.

David Gerrold is a Hugo and Nebula award-winning author. He has written more than 50 books, including "The Man Who Folded Himself" and "When HARLIE Was One," as well as hundreds of short stories and articles.  His autobiographical story "The Martian Child" was the basis of the 2007 movie starring John Cusack and Amanda Peet. He has also written for television, including episodes of Star Trek, Babylon 5, Twilight Zone, and Land Of The Lost. He is best known for creating tribbles, sleestaks, and Chtorrans. In his spare time, he redesigns his website, www.gerrold.com

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