Making Stuff Up

According to LCD TV manufacturers, we've got a massive problem with what we watch: it's not smooth enough. In particular, they'll argue, films are incredibly jerky. In some respects, they've got a point. Films are shot at just 24fps, which is fine for most scenes, but looks jerky when there's a wide-angle panning shot.

At least, that should be: looks jerky on a TV. In the cinema, you'd be hard pushed to notice it for a couple of reasons. First, the screen's so big that it's hard to take in everything, let alone focus on a bit of jerky motion. Secondly, it's the way that cinema projectors work. Film is passed frame-by-frame at high speed in front of a light-source that projects the image onto the screen. Synchronised with this is the projector's shutter, which cuts the light off as the film moves to the next frame (if it didn't, you'd just get a blur of light caused by the moving film). The result is that you see frame layered upon frame, creating the illusion of movement. Persistence of vision, where the eye retains an image for a brief moment of time, helps blend the short gap between frames, making the final image smoother.

In addition, most cinema projectors have a higher shutter speed to reduce the perception of flicker on the screen. So, for each frame of video that's displayed, the shutter will open and close twice (48Hz) or three times (72Hz). You can even look out for this next time you go to the cinema by blinking at different speeds until you see the black 'gaps' in the film. Well, either that or people near you will think you've gone bad.

With LCD TVs, there's a constant backlight and a smaller screen. Without the shutter, films played at their native frame rate can become noticeably jerky. The answer to this problem is for TVs to create some extra frames to create smoother motion.

So, in a panning shot the TV can insert a frame or two of interpolated data to smooth the movement. It's a brilliant idea, but perhaps one that's gone too far with the new TV sets, capable of running at 200Hz (200fps). To put this in context, for every frame of real footage, the TV has to make up 7 1/3 frames itself. To put it another way in the final image that you see on screen, only 16 per cent of the video ever actually physically existed, the other 84 per cent has been made up by your TV.

That is a ludicrous amount of data to just add, and not entirely successful. At this year's consumer electronics show we were lucky enough to see one manufacturer showing off its standard TV, 100Hz TV and 200Hz TV with Iron Man. The regular TV looked gritty and real; the 100Hz TV's motion looked a bit strange; the 200Hz TV made it look like a Benny Hill episode directed by an MTV music video producer. People's legs moved in unnatural, comically fast ways, while a helicopter landing looked as though it was made of Lego and the footage sped up.

These systems also get it wrong quite a lot, as they have to predict the path of movement in an object. If something's moving erratically and unpredictably, you end up with a stuttering mess on screen.

I'm all for technology improving what we see and watch, but in this case it appears as though the TV manufacturers are playing a numbers game and we're getting worse-quality video as a result.