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How Television Works
Television is certainly one of the most influential forces
of our time. Through the device called a Television Set or TV,
you are able to receive news, sports, entertainment, information and commercials.
The average American spends between two and five hours a
day glued to "the Tube"!
Have you ever wondered about the technology that makes television
possible? How is it that dozens or hundreds of channels of
full-motion video arrive at your house, in many cases for free?
How does your television decode the signals to produce the picture?
How will the new digital television signals change things? If
you have ever wondered about your television (or for that matter
your computer's monitor), then you will love this edition of
How Stuff Works!
Two Amazing Things about the Brain
Start by watching the following video clip. Simply click on the picture and at
the dialog that appears select the "Open" option:
by Marshall Brain
Let's start at the beginning with a quick note about your brain. We
all take television for granted, but there are two amazing things about your
brain that make television possible. By understanding these two facts
you gain a good bit of insight into why televisions are designed the way
they are.
This is a standard piece of home video showing a happy baby playing with a toy. It is encoded as an MPEG file so that you can view it on your computer, and it embodies the two principles that make TV possible.
The first principle is this: If you divide a still image into a collection of small colored dots, your brain will reassemble the dots into a meaningful image. This is no small feat, as any researcher who has tried to program a computer to understand images will tell you. The only way we can see that this is actually happening is to blow the dots up so big that our brains can no longer assemble them, like this:
Most people, sitting right up close to their computer screens, cannot tell what this is a picture of - the dots are too big for your brain to handle. If you stand 10 to 15 feet away from your monitor, however, your brain will be able to assemble the dots in the image and you will clearly see that it is the baby's face. By standing at a distance the dots become small enough for your brain to integrate them into a recognizable image.
Both televisions and computer screens (as well as newspaper and magazine photos) rely on this fusion-of-small-colored-dots capability in the human brain to chop pictures up into thousands of individual elements. On a TV or computer screen the dots are called pixels. The resolution of your computer's screen might be 800 x 600 pixels, or 1024 x 768 pixels.
The human brain's second amazing feature is this: If you divide a moving scene into a sequence of still pictures and show the still images in rapid succession, your brain will reassemble the still images into a single moving scene. Take, for example, these four frames from the example video:
Each one of these images is slightly different from one to the next. If you look carefully at the baby's left foot (the foot that is visible) you will see that it is rising in these 4 frames. The toy also moves forward very slightly. By putting together 15 or more subtlety different frames per second, the brain integrates them into a moving scene. 15 per second is about the minimum possible - any fewer than that and it looks jerky.
When you download and watch the MPEG file offered at the beginning of this section, you see both of these processes at work simultaneously. Your brain is fusing the dots of each image together to form still images, and then fusing the separate still images together into a moving scene. It really is amazing, and without these two capabilities TV as we know it would not be possible.
Go to the next article about How Television Works or pick from the table of contents:
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