What Exactly Is a Digital Image?

Whether you take a picture with a digital camera or use a scanner to bring a photo (or other artwork) into Photoshop, you are digitizing the image. That is, digit not as in a finger or toe but as in a number. Computers do everything — absolutely everything — by processing numbers, and the basic language of computers is binary code. Whether it's a photo of a Tahitian sunset, a client's name in a database, or the latest box score on the Internet, your computer works on it in binary code. In a nutshell, binary code uses a series of zeros and ones (that's where the numbers part comes into play) to record information. (In Photoshop, this is a critical concept for color, as you can see in Chapter 6.) Binary code might look like this:

00100101 01010011 00011011 11010100 11101000 11000110 10101001 10010011 11010101 01011010 00101100 11101110

This example, of course, would be complete gibberish to a computer — if those two lines turn out to be the launch code for some missile, it's just a coincidence.

So what does binary code have to do with the wedding photos that you took this weekend or the masterpiece you must print for your thesis project? An image in Photoshop consists of tiny squares of color called pixels (short for picture element), as you can see in the close-up to the right in Figure 2-1. Each pixel is recorded and processed by the computer in binary code. These pixels replicate a photo the same way that tiles in a mosaic reproduce a painting.

Figure 2-1: That's not really an ugly old dog; it's a bunch of tiny colored squares.

A tile in a mosaic isn't face or sky or grass; rather, it's beige or blue or green. The tiles individually have no relationship to the image as a whole; rather, they require an association with the surrounding tiles to give them purpose, to make them part of the picture. Without the rest of the tiles, a single tile has no meaning.

Likewise, a single pixel in a digital image is simply a square of color. It doesn't become a meaningful part of your digital image until it's surrounded by other pixels of the same or different color, creating a unified whole — a comprehensible picture. How you manipulate those pixels, from the time you capture the image digitally until you output the image to paper or the Web, determines how successfully your pixels will represent your image, your artwork, your dream.

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