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The True Nature of Pixels

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 Here are some basic truths about pixels that you really need to know. Although reading this next section probably won’t improve your love life, let you speak to the dead, or give you the winning lottery number, it will help you understand what’s happening to your image as you work with it in Photoshop.


Each pixel can be exactly one color. That color can change as you edit or alter the image, but each pixel consists entirely of a single color — there’s no such thing as a two-tone pixel. Figure 2-2, at 1600% zoom, shows each pixel distinctly.
 
Each pixel is independent. You might think that you see a car or a circle or a tree or Uncle Bob in an image, but the image is actually only a bunch of little colored squares. Although you can read about various ways to work with groups of pixels throughout this book, each pixel exists unto itself.

Each pixel is square (except on TV). Really! Each pixel in a digital image is square except when creating images for television, which uses nonsquare pixels. (That’s a rather specialized field, which I very briefly address in Chapter 3.) It’s important that you understand the squareness (totally, like L7, Daddy-O) of pixels because you sometimes have to deal with those pointy little corners.

Smaller is better (generally speaking). The smaller each pixel, the better the detail in an image. (However, when preparing images for the Web, you need smaller images that invariably have less detail.) If you capture an image of a dog in a park with two million pixels and capture the same shot with only 30,000 pixels, it’s pretty obvious which image will better show the individual blades of grass and the fur. Take a look at Figure 2-3 for an example of this critical concept. Smaller pixels also help hide those nasty corners of pixels that are sometimes visible along curves and diagonal lines. When the corners of pixels are noticeable and degrade the image, you call it a bad case of the jaggies.




Figure 2-3: More pixels (top) means better detail.

Pixels are aligned in a raster. The term raster appears regularly when you discuss images created from pixels. Raster, in this case, refers to the nice orderly rows and columns in which pixels appear. Each image has a certain number of rows of pixels, and each row is a certain number of pixels wide — the columns. Within the raster, the pixels perfectly align side-to-side and top-to-bottom. 

Every picture created with pixels is rectangular. Some images might appear to be round, or star-shaped, or have a hole cut from the middle, but they don’t unless you print them out and grab your scissors. The image file itself is rectangular, even if it appears round. There are actually pixels in those seemingly empty areas; the pixels are, however, transparent.

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What Exactly Is a Digital Image?

Posted on 10:23 PM No Comments Labels: , ,
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.

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.


Figure 2-1: 


That’s not really an ugly old dog; it’s a bunch of tiny colored squares

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