I don’t think there’s anything unique about
human intelligence. All the neurons in the
brain that make up perceptions and emotions
operate in a binary fashion.
Bill GatesTHEreal difference between a film camera and a digital camera is not how the cameras take pictures, but how
they store them. After a picture is stored on film, there is only so much that can be done with it. How the film is
processed can change the image—once. Then the picture is frozen in the form of chemical molecules that have
clumped together to form microscopic dots of color. There’s no subtle way to manipulate those molecules. Sure, you
can disguise the information stored on the film. When you make prints from the negative, you can burn here and
dodge there, and use a special paper for a silvery look. You can...well, that’s about it. It’s purely cosmetic. The fact
remains that once visual information is stored on film, it is fixed for all time...or until the chemicals deteriorate so
much that the information is lost entirely.
But with a digital camera, or with film-based photos scanned into your computer, there’s no limit—none whatso-
ever—to what you can do with an image after it’s stored on a memory card, CD, or hard drive. That’s because the
image is stored as a huge array of numbers. And as you learned early on about numbers, they stretch to infinity.
Not that we need an infinity’s worth of numbers. Truthfully, for most photo purposes, there are only 256 numbers that
really count—no pun intended. But you may be surprised what you can do with such a meager supply of integers.
Each of the three colors used in digital photography—red, blue, and green—can have any of 256 shades, with
black as 0 and the purest rendition of that color as 255. The colors on your computer monitor or the little LCD screen
on the back of your camera are grouped in threes to form tiny full-color pixels, millions of them. When you change
the values of adjoining colors in the pixels, you suddenly have 17 million colors at your disposal for each pixel. (Or
thereabouts: 256 × 256 ×256 = 16,777,216.)
With colors now expressed as numbers, it’s much easier changing hues and shades with grade school arithmetic
than by mixing cans of paint. To lighten a photograph, all anyone has to do is add 25 or so to the color values of
every pixel in the picture—all 3–5 million of them. If you want to lighten only the shadows, just choose those pixels
that have a value under 125 and add 25 only to them. Or, go wild and rip out entire sections of the photograph
and replace them with entirely different constructs of numbers that represent anything from comets to cattle.
The math is simple, in principle, at least. The tricky part is converting all the possible combinations of colors into
numbers. Here, we’ll show you how your digital camera pulls that off.
CHAPTER 7 HOW LIGHT BECOMES DATA^99