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The simple trick that makes television possible

technofile  by al fasoldt

Columns and commentaries in a life-long dance with technology
 

Simple gray rule



The simple trick that makes television possible 


By Al Fasoldt

Copyright © 1990, The Syracuse Newspapers

It's all a trick of the eye.

When you look at a television picture, your brain is playing fast and footloose with the truth. In reality, the picture is shifting and flickering, but what you end up seeing is something that's steady and crisp.

That's nothing new, of course. The ability of our eyes and brain to freeze motion has made billions of dollars for Hollywood producers over the last eight decades. Motion-picture film is just a series of still pictures placed in front of our eyes so quickly that everything seems to be moving.

The process works so well that we usually don't pay any attention to it. The only time we are reminded of this optical trick is when the wagon wheels look like they are spinning backwards in those old cowboy movies—a phenomenon that happens when the spokes turn less than one full revolution between motion-picture frames.

Luckily for TV viewers, the inventors of television saw those wagon wheels going the wrong way, too. They knew that if they turned the flicker factor up a little higher, the problem would pretty much go away.

So American TV started life with a 30-frames-per-second flicker rate, about 50 percent faster than the motion-picture rate.

(Trivia fans may want to know that the picture is actually drawn 60 times a second, but each of those pictures is only filled in half way. So it takes two passes of the electron gun's picture-painter to make one whole frame.)

Another trick of the eye that lets us enjoy color TV is our amazing ability to forgive bad pictures as long as they are moving. Color pictures seldom have good color in each frame. Usually, the bright colors—the reds, especially—keep fading in and out, and the color also gets in the way of the detail that we're used to in black-and-white-pictures.

But never mind, the brain tells our eyes. Just keep feeding me those moving images and nobody will complain.

Well, your brain may not be so forgiving in the next year or so. Some of the people who are struggling to bring us high-definition TV have found a shortcut that you might object to.

They've come up with a way to pack a giant, fully detailed picture into the same broadcast-signal space as our present TV pictures—by leaving out everything that doesn't move from one frame to the next.

In other words, if you're watching a baseball game, this new type of TV system would save transmission space by sending just one image of home plate a second instead of 30 (after all, home plate's not going anywhere, right?), and it would freeze the pitcher's image, too, any time he's staring down the batter.

And unless there's a good breeze blowing in Candlestick Park, the grass might not be moving either. Why keep showing the same little green things all over again, frame after frame?

The inventors of this process believe they have opened the door to HDTV as much as three years ahead of time. Our broadcast channels could remain just as they are, with the newest sets picking up these tricked-up HDTV signals and all other sets showing regular video.

So far, the decision makers in the U.S. and Japanese television industry haven't shown much interest in the new system. The Japanese are committed to a full HDTV system, and most of the American research appears to be headed in the same direction.

But anything is possible in the race for HDTV, and we'll keep you posted if this odd way of faking a moving picture gains any headway.


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