images to work effectively in Photoshop?
The answers to those two questions are “Not as much as he/she should” and “Not as much as you might fear.” In this chapter, I give you some basic information about how digital images exist in Photoshop, a real understanding of that critical term resolution, and an overview of the different ways that you can save your images. But most importantly, I help you understand the very nature of digital images by explaining the world of pixels.
Welcome to the Philosophy chapter!
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.
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 (pixel is short for picture element), as you can see in the close-up to the right in Figure 2-1. The computer records and processes each pixel 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 Hugo the Bulldog; it’s a bunch of tiny, colored squares.
The True Nature of Pixels
Here are some basic truths about pixels that you really need to know. Although reading this section probably can’t improve your love life, let you speak with ghosts, or give you the winning lottery number, it can help you understand what’s happening to your image as you work with it in Photoshop.
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 you’re creating images for some television formats, which use nonsquare pixels. It’s important that you understand the squareness of pixels because you sometimes have to deal with those pointy little corners.
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 3,200 percent zoom, shows each pixel distinctly.FIGURE 2-2: Each pixel is monotone, containing a single color throughout the pixel.
Smaller is better (generally speaking). The smaller each pixel, the better the detail in an image. (However, when you are preparing images for the web, you need smaller images that invariably have less detail.) If you capture an image of a house with an older cellphone camera and capture the same shot with a new DSLR (digital single-lens reflex camera — you know, one of the cameras with interchangeable lenses) that captures 3 or 7 or 15 times as many pixels — it’s pretty obvious which image has better detail. Take a look at Figure 2-3, which illustrates how lots more smaller pixels present a better image than do fewer-and-larger pixels.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. Note the zoom factors in the lower left of each window. Keep in mind that the size at which an image can be printed — and still look good — depends on the number of pixels available. Sure, these days every cellphone seems to capture at least 10 megapixels, which is fine for 8-x-10 prints and perhaps even as large as 16-x-20 inches. But how about when your 10-megapixel pocket camera doesn’t have a long enough zoom to capture little Tommy’s exploits on the far side of the soccer field? That’s when you might need to crop and resample the image to increase the number of pixels. I cover resampling later in this chapter.
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 missing a hole from the middle, but they aren’t unless you print them and grab your scissors. The image file itself is rectangular, even if it appears round. Pixels actually exist in those seemingly empty areas; the pixels are, however, transparent. When printing, the transparent areas show the color of the paper you’re using.
How Many Pixels Can Dance on the Head of a Pin?
You hear the term resolution a lot when working with digital images. Digital cameras have so-many megapixels of resolution; inkjet printers have so-much by so-much resolution; to work in Photoshop, your monitor must have a resolution of at least 1,024 x 768 pixels; when printing your images, you must use 300 pixels per inch (ppi) as your resolution (wrong!), but your web images must have a resolution of 72 ppi (again wrong!); and don’t forget your New Year’s resolution!
Resolution revelations
In this wonderful world of digital imaging, you see resolution used in four basic ways:
Image resolution: Image resolution is the size of your image’s individual pixels when you print. I go into greater detail about this concept in the upcoming section, “Picking an image resolution.”
Camera resolution: Digital cameras capture each image in a specific number of pixels. Check your camera’s user guide or open one of the images in Photoshop and choose Image ⇒ Image Size. Take a look at the number of pixels that your camera records
