Scanners For Dummies
By Mark L. Chambers
John Wiley & Sons ISBN: 0-7645-6790-X
Chapter One Let's Get Digitized!
In This Chapter
* Understanding what a scanner does
* Finding material to scan
* Recognizing the different types of scanners
* Identifying parts common to all scanners
* Uncovering how your scanner works
* Explaining resolution
* Understanding bit depth
In medieval times, magicians known as alchemists used to weave tales of a wonderful box. In this box, they said, one could place an ordinary item (an egg, for example), close the lid, and - presto! - the egg would turn to pure gold or a flawless diamond. Many alchemists spent their lives trying to perfect this nifty little household appliance. In fact, some said that they actually did, and these people became the performers we know today as magicians. (A few politicians and used-car salesmen are probably in that group also.) Everyone knows that a machine like that is a fairy tale.
But, wait: What if I told you that such a box really does exist - one that can take ordinary paper and turn it into creative magic? Imagine a machine that can bring a smile to the faces of your friends and family or reshape opinions, safeguard your memories, and perhaps even help sell your '79 Pinto?
Computer scanners now can do all that and more, and you don't need a degree in the magical arts (in other words, a computer programming degree) to use one with your PC or Macintosh computer system. The facts get even better, too: The perfect scanner for most home and small business uses costs less than $150, and you can connect it and produce your first scanned image in less than five minutes. After all, the faster you get a picture of that '79 Pinto on your Web site, the better the chance that you can finally unload it!
In this chapter, I introduce you to the computer equivalent of the alchemist's magic box. You discover what you can do with a scanner, what types of scanners are available, what makes them tick (if you want to know), and the importance of resolution and color.
"Okay, I'll Bite - What's a Scanner?"
Although many different types of scanners are available - flatbed, sheet-fed, color, and black-and-white, just to name a few - they all perform the same function. Therefore, it's easy to define exactly what a scanner is:
Scanner. (n) A machine that reproduces an image from a source object, producing an identical digital image for display or processing.
There - that explains everything, at least for technotypes. In plain English, a scanner "reads" the image from an object (typically a piece of paper) and then creates a copy of that image as a picture file on your computer. (If you're curious about what goes on inside, I explain the process later in this chapter.)
Of course, my explanation also has exceptions. It figures, right?
You don't necessarily have to scan something from a sheet of paper. For example, your source image can be printed on fabric or some other material or can be a photographic negative.
A scanner doesn't necessarily have to create a picture file on your computer; if you've used a fax machine or a copy machine, you've been using a scanner. After the scanner read the image, it was simply sent somewhere else. The fax machine sent the image as data over the telephone line, and the copy machine sent the image to the built-in printer to create a duplicate.
You may not be scanning that original to create an image file on your computer. With the right software, scanners can now recognize the printed characters on a page and enter them into your word processor. I discuss this process, called optical character recognition (or OCR, for those who crave acronyms), in detail and show you how to use it later in this book. Another good example of a "rogue" scanning application is the familiar barcode, which has appeared on just about every inanimate object in your local shipping office and grocery store.
Most of the work you do with scanners these days, however, is performed as I describe in my definition: For example, you want an image from a magazine in a form you can use with a document you've created with Microsoft Word. Or perhaps you want to send that picture of Aunt Martha through e-mail to your folks living a thousand miles away.
What Can I Scan, Mr. Spock?
You won't be scanning the surface of an alien planet from the bridge of the starship Enterprise, so you won't hear me say "Fascinating!" Instead, we humans here on planet Earth scan these types of materials:
Sketches and original art
Cereal and pizza boxes
You get the idea: If it's reasonably flat and it has any type of image on it, it's likely to be scanner material. Scanners can record surface detail, too, but the results vary widely according to the material that makes up the object. (Naturally, the darker the material, the harder it is for your scanner to deliver a clear image.)
Different Breeds of Scanner
Over the past few years, different types of scanners have evolved for different jobs. Some types provide a better-quality scan, some take up less room, and some are designed especially for one type of original media. In Chapter 2, I get into the specifics of which type of scanner is perfect for you. For now, take a moment for a scenic overview of what's available. Sit back and enjoy the tour. (Have an hors d'oeuvre!)
Flatbed: Imagine the top of a copy machine. Cut off the rest of it, and you have a flatbed scanner, as shown in Figure 1-1. With a flatbed, you're likely to get the best resolution with the least distortion, and you can easily scan pages from a magazine or book. Sheet-fed: Limited space on your desk? A sheet-fed scanner may be the answer. The shortest models are about the size of a roll of aluminum foil, and other models look suspiciously like a fax machine. (As a matter of fact, a fax machine has a built-in scanner that it uses to create an image of the page.) Figure 1-2 shows you a typical sheet-fed scanner.
Photo scanner: Many photo scanners are internal computer components, which means they fit inside your computer's case, as shown in Figure 1-3. Photo scanners are specially designed to read individual pictures taken with a film camera (or even small printed items, such as business cards or a driver's license).
Handheld scanners: These portable scanners come in different shapes and sizes, ranging from a handheld model that can scan three or four inches at a time to a pen scanner that reads a single line of text. Handheld scanners don't offer the picture quality and convenience of a flatbed scanner. They can fit in a laptop case (or even a pocket), though, so they have their place with the road warriors among us. Barcode scanners are also typically handheld. Figure 1-4 shows a handheld scanner.
Negative scanners: The snobs of the scanner world, negative scanners are designed for only one purpose: to scan photographic slides and negatives. Although these scanners are usually hideously expensive, if the images you need are on slides or you want the best possible scan of a photographic negative, a negative scanner is the only way to produce a high-quality image. Figure 1-5 provides glimpse of a negative scanner.
Quite a lineup, eh? Darwin himself would have been proud of the way in which scanners have adapted to their environment.
Examining the Innards
Okay, I know what you're thinking. (Didn't know that little tidbit about computer book authors, did you?) You're wondering, "Do I really have to read about my scanner's anatomy?" Ladies and gentlemen, the answer is a big, emphatic "No!" None of the material in this section has any cosmic meaning, so if the closest you want to get to your scanner's mechanical side is plugging in the power cord to the wall outlet, feel free to jump ahead to the next section (which, come to think of it, you can skip as well)!
Hey, if you're still reading, you're curious about mechanical mysteries, like I am. Did you disassemble alarm clocks when you were a kid, too? (Dad eventually had to lock his up in the garage.) Read on while I explain the common parts shared by every scanner.
Crack open your scanner - no, don't grab a hammer, it's just a figure of speech - and you'll find that the sensor is the star of the show. The scanner sensor is comprised of an array of individual photosensitive cells. Wait - don't drift off yet - it gets better! Each of these cells returns a certain amount of electrical current to the scanner's brain; how much current is determined by the amount of reflected light the cell receives as it passes by the original image. Figure 1-6 illustrates how this process works.
If you're knowledgeable about your human anatomy (or, like me, you were able to stay awake in high-school biology class long enough to pass), you can see the parallels between this process and how the human eye works. In the eye, the photosensitive nerves perform the same function: They send impulses to your brain that depend on the amount of light they receive.
Each of the cells in the scanner's sensor reads a single dot of the image. And that basic building block, the pixel, is a unit of measure I return to time and time again in this book. Your computer monitor is also measured in pixels, as are digital cameras. All digital images are made up of individual pixels. Your eye and brain work together to combine them into the image you see.
Of course, the sensor doesn't do you a tremendous amount of good if it just sits in one place on the image. You would get a single line of pixels from the original! (That makes for a very bad scan, as you can imagine.) The designers of the first scanners knew that they needed to move the sensor across the surface of the original so that they could scan the entire thing, so they added the motor.
Figure 1-7 illustrates the two types of motors in today's scanners: In effect, one design moves the sensor head past the original, and the other moves the original past the scanner head (which is fixed in one spot). In later chapters, I explain which is better for you; both types of motor drives have their advantages.
A sensor that's sensitive to light needs illumination, and your scanner carries its own built-in "reading lamp" - the light that's reflected from the original is picked up by the sensor. Most scanners have this light mounted right next to the scanner head.
Like just about everything in the world of computers, your scanner has an electronic brain for processing image data. The brain isn't sophisticated compared to your computer's central processing unit (CPU), which has a master's degree in several subjects. A scanner's brain has at least passed the fourth grade, though. I talk more about this processing in the next section.
Every scanner needs a connection of some sort to your computer. In all their wisdom (and their surprisingly intermittent common sense), computer hardware designers have to have a separate word for this connection. For some reason, the word connection didn't hack it. Therefore, they call the type of connection your scanner uses an interface. Although most scanners made these days use the Universal Serial Bus (USB, for normal human beings), I introduce you to all the connections (whoops, there I go again) - the interfaces - found on scanners. As you'd expect, I also help you determine which is best for you.
Scanning Explained (for Normal Folks)
Here I go, trying to explain the alchemist's magic box. If you don't care how the box works and you would rather jump right to the next section, I can meet you there. This stuff is absolutely not necessary. If you're like me, however, and you stick your head into everything electronic from sheer curiosity, keep reading!
Here's the process your scanner uses to produce that spiffy digital image (use Figure 1-8 to follow along, if you like):
1. The scanner light is turned on.
2. The sensor head moves slowly past the original, or the original is moved slowly past the sensor head. (Anyway, movement and a motor are involved, as I mention in the preceding section.)
3. The sensor reads the amount of light reflected by the original in each pixel of the current scan line and sends those signals to the scanner's brain. 4. The signals are converted to binary data and sent to your computer through the interface.
5. The sensor head moves to the next line of pixels, and the process begins again with Step 2.
This process is repeated until the scanner has read each line of pixels in the original image. Depending on the type of scanner, the sensor head typically makes as many as three full transits across the original to capture a complete, full-color image. I tell you more about this process later in this book.
Although this operation sounds lengthy, things are moving at computer speeds. For example, most scanners can read an entire page of text in fewer than 10 seconds and can read an entire full-page image in fewer than 30 seconds.
If you've read the "Examining the Innards" section, earlier in this chapter, you may remember the array of photosensitive sensors I mentioned. (If not, don't worry about it; I don't give you a test on that stuff.) The sensor array in a typical scanner is comprised of hundreds of individual sensors. The density of these individual sensors leads to what's likely the most important single specification you should consider in a scanner: resolution.
Scanner resolution is commonly measured in dots per inch, or dpi - the number of individual dots scanned per inch of the original image. The dpi measurement is usually expressed as horizontal (the number of individual sensors in the array) by vertical (the distance the sensor head moves between individual lines), for example, 600 x 1200. I call this measurement the "common" dpi because most scanner manufacturers use it in their specifications.
Other scanner manufacturers may give you only one dpi figure. That's what I call the "true" dpi because it measures only the number of pixels horizontally.
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