SOON after men learned to broadcast sound, inventors wondered if they could also transmit live pictures. To appreciate the challenge, consider how television works today.
First, a TV camera focuses a scene onto a target device that “reads” the picture, similar to the way you read print. However, instead of scanning lines of letters on the page, it scans lines of spots (or pixels) in the picture. It converts what it sees into an electronic video signal that can be transmitted to another place. A receiver then converts the signal back into a live picture.
A Scotsman named John Logie Baird has been credited with being the first to demonstrate a television. When poor health caused him to give up his job as an electrical engineer, he turned to a subject that had interested him since he was a teenager—how to build a machine that could transmit live images.
Baird’s television camera used a disk (a hatbox, at first) perforated by about 30 holes arranged in a spiral. As the disk spun, the holes scanned successive lines of the picture and allowed light to fall on a photoelectric cell. The cell produced a video signal that was transmitted to a receiver. In the receiver the signal was amplified to illuminate a variable light behind a similar spinning disk to reproduce the picture. The challenge was to synchronize the disks. As Baird toiled on the project, he supported himself by shining shoes.
Baird transmitted the first television pictures from one end of his attic to the other on October 2, 1925. The first person ever to appear on TV was a frightened office boy from downstairs, who was pressed into service for half a crown. In 1928, Baird broadcast the first television pictures across the Atlantic. When John Baird arrived in person in New York, the timid Scotsman was acutely embarrassed when he was greeted by a pipe band. He was famous. But was he the first to transmit live pictures?
YOUR eyes are like tiny television cameras. They convert images into electrical signals and transmit these signals along the optic nerve to the back of your brain, where the actual seeing takes place.
The eye is a marvel in miniature. Just an inch [24 mm] in diameter and one fourth of an ounce [7.5 g] in weight, it is ingeniously engineered. For example, it has separate systems for dim and bright lighting, so that 30 minutes after entering a dark room, your eyes may become 10,000 times more sensitive to light.
In normal lighting, what gives you a clear picture? Your eye has over 100 times more light-sensitive cells (pixels) than most video cameras. Also, a large portion of those cells are packed into a small spot at the center of the retina called the fovea, which provides the sharpest vision. Since you shift your gaze several times a second, you get the impression that your whole field of vision is sharp. Remarkably, your eye’s fovea is about the size of the dot at the end of this sentence.
Electrical signals from the light-sensitive cells pass from one nerve cell to another toward the optic nerve. But the nerve cells do more than just pass the signals on. They preprocess them, enhancing vital information and suppressing unneeded detail.
The visual cortex of your brain is like a sophisticated video receiver. It sharpens images by enhancing edges and compares the signals from cells sensitive to primary colors, so you can distinguish millions of colors. Your brain also compares the tiny dissimilarities between what your two eyes see, so you can perceive distance.
Consider how your eyes scan faces in a distant crowd and send electronic impulses to your brain, which then transforms the signals into clear images. Consider, too, how subtle details of those faces are compared with ones in your memory, so that you instantly recognize your friend. Is that process not awe-inspiring?
Comments
Post a Comment