A scanner works by dividing an image into microscopic rows and columns and measuring, like the film in a camera, how much light (or lack thereof) reflects from each individual intersection of the rows and columns. Each reflection is recorded as a dot, or picture element (pixel). After the scanner collects information from each dot, it compiles the result into a digital file on the computer.
There are a wide variety of scanners that work in a number of different ways, but the technology behind them is essentially the same. The following sections discuss the more popular types of scanners available today.
ON THE WEB:Two excellent Internet resources for more information on scanners and scanning techniques can be found at: http://www.scanshop.com http://www.cis.ohio-state.edu/~sking/Scanners.html
Flatbed scanners look and behave a lot like a photocopier. You lay the item to be scanned on a glass plate and the scanning head passes below the glass.
Flatbed scanners are very versatile: you can scan objects in a variety of sizes and shapes, including pages from a book, without damaging the original. While flatbed scanners are the best choice for a wide variety of uses, if you plan to do a lot of text scanning (called OCR for Optical Character Recognition) work, keep in mind that flatbeds only accommodate one page at a time. Scanning multi-page documents can be a slow, tedious process, because you have to manually remove one page and insert the next.
Sheetfed scanners look and act more like fax machines. The page or item is fed into the machine, scanned, then spit out on the other end . A sheetfed scanner is a good choice for large volumes of text, but not for handling delicate original photographs. Scanning directly from a book or other three-dimensional object is impossible.
Hand scanners are a low-cost alternative to their larger, more sophisticated cousins. As their name implies, hand scanners are manual devices you move over a flat surface, just as you do your PC's mouse
The hand scanner's advantages are many, but so are its disadvantages. Generally, hand scanners work best for small, uncomplicated images such as company logos or small black-and-white photographs. You might want a hand scanner if you don't plan to use it on a regular basis, because it usually doesn't require adding internal cards to your CPU, and it's easily disconnected and stored away. Most hand scanners can only scan a four-inch wide image at one time and require a steady hand. You're usually provided with software that helps you "sew up" a series of these 4-inch, side-by-side scans into one image, but this is obviously not as convenient as getting the full image at once.
NOTE: Other types of scanners also exist, such as barcode readers (like the ones at the grocery checkout) and slide scanners; however, because these are specialty items primarily used for commercial purposes, they are not covered here.
Color versus Grayscale Scanners
Scanners that can scan images in full color have become much more popular as their prices have dropped. Just a few years ago, color scanners cost several thousands of dollars, but can now be bought for a few hundred, depending on resolution and type.
Even so, grayscale (meaning shades of black and white only, no color) scanners are still available and are significantly cheaper. In many cases, they are perfectly adequate for the average user. Unless you have a color printer, or use your scanner to create artwork that will only be viewed on-screen (such as for a Web page), there's no point in having a color scanner. Consider this carefully before buying; however, what you think you'll never do now could change as you grow more experienced and interested in computer technology.
Understanding Resolution and Dots Per Inch
Like printers, the technical capability (optical resolution) of a scanner is measured in dots per inch (dpi). The higher the dpi, the sharper your on-screen printable image will be. The reason for this is that the more dots that can be placed in the same area (in this case, one square inch), the smoother and more detailed the overall image will look.
On the other hand, the higher its resolution, the longer the scanner takes to scan the image, and the larger the resulting image's data file will be (more dots equals more information; more information equals a larger file). Typical flatbed scanners range from 300 dpi to more than 3,200 dpi; The most affordable resolution for the average consumer is 1,200-1,600 dpi.
NOTE: Don't be fooled by ads touting astronomical resolutions like 6,400 dpi interpolated or enhanced resolution. Interpolated resolution (as opposed to optical or true resolution) is just another term for the scanner's ability to guess at how the image would look at a higher resolution by adding new dots in between the old ones. For most uses, this process adds no value--and can often actually reduce the scan quality. The exception is that interpolated resolution can improve the quality of scanned line art images that will be output at very high resolution, such as magazines or commercially produced documents.
Before you buy or try to install a scanner, make sure that your computer can actually run it. Scanners can really stretch the limits of a mid-range PC--and may not work at all on low-end ones. Carefully review the manufacturer's stated system requirements and verify that your system has at least the minimum amount of RAM, CPU speed, and hard drive space listed. For best results, exceed the minimum requirements by as much as possible. Most manufacturers require nothing less than a 486/33 processor (if you have a Pentium or better, you should be safe). Most experts recommend a minimum of 16-24M of RAM even if the manufacturer claims less.
Connecting a Scanner to Your PC
Like all peripheral devices, your scanner must be connected to your computer in some way. Most likely, your scanner came with all the equipment required to hook it up.
SCSI Cards and Cables
The vast majority of flatbed and sheetfed scanners use SCSI (Small Computer System Interface, pronounced "skuzzy") connections. If you're lucky, your computer already has a SCSI card installed and all you'll have to do is connect the provided cable to the SCSI port at the back of your computer. But most computers don't come that way, so you might need to open the system case and install a new card in one of your computer's expansion slots. If so, follow the instructions that came with the scanner, and check your computer system's manual to make sure you're installing it in the right place. See Chapter 27, "Upgrading Your Hardware," for details on how to install add-in cards.
NOTE: Hand scanners typically do not require SCSI connections; They usually connect to parallel ports, like the one used by your printer.
The great thing about SCSI devices is that one SCSI card can support up to seven different devices connected together in a "SCSI chain." You might, for example, have a scanner plugged into the SCSI port, a Jaz drive connected to the scanner, an external hard drive connected to the Jaz drive, and a CD-ROM drive connected to the external hard drive. Not only does this give you more flexibility in configuring your system, it also saves the few expansion ports in your computer for other devices that aren't able to share.
CAUTION: Be careful when comparing scanners and the SCSI cards included with them. Some manufacturers cut corners (and offer lower prices) by including a proprietary SCSI card, or one that only works with that particular scanner and does not support other devices. The card will work, of course, but it's not a very efficient use of the technology. If you think the scanner is right for you but it comes with a proprietary card, you can always buy a general-purpose SCSI card separately.
NOTE: Most scanners and SCSI devices require a cable length of 12 feet or less--keep this in mind when you're setting up your system.
Every hardware device, whether internal or external, requires a software program called a driver to help it communicate with your computer's operating system. For scanners, the standard driver type is a TWAIN driver (supposedly, TWAIN stands for Technology Without An Interesting Name). By using TWAIN drivers, scanners can communicate with any TWAIN-compatible applications. Most of today's popular drawing and graphics applications such as CorelDRAW!, Paint Shop Pro, Adobe Photoshop, and even Microsoft Office 97 all support TWAIN, and thus use very similar steps, buttons, and the like. You don't have to learn a different method for every application you scan from. (If you're not sure, check the application's File menu for an item labeled Acquire, or look in the manual.)
Getting Windows 95 to Recognize Your Scanner
After you've made the physical connections, install the TWAIN driver according to the instructions that came with the scanner. If instructions for using the scanner under Windows 95 are not included, follow these steps:
- 1. Shut down the computer and wait 30 seconds. Power up the scanner, wait 10-15
seconds, then reboot your PC.
2. From the Start menu, choose Settings, Control Panel. When the Control Panel window opens, double-click Add New Hardware.
3. Click Next. The wizard will ask if you want Windows 95 to search for your new hardware; choose No and click Next again
- 4. At the next screen, click Other Devices from the list of items click
5. Look through the Manufacturers list and the Models list. If you find your scanner (you probably won't), click Next. If not, click Have Disk.
6. In the Install from Disk dialog box, show the wizard where your install program is (usually on a floppy disk that came with the scanner), either by typing in the path name or clicking the Browse button and navigating to the proper location. Click Next twice.
7. When you get to the final wizard screen, click Finish. Windows will continue the setup process, and may ask you for your Windows 95 CD-ROM.
8. When the setup process is complete, restart your computer by choosing Shut Down from the Start menu, then choosing Restart the Computer?.
- 9. As Windows 95 restarts, you may notice a message on the screen indicating it
has found a new device and is installing drivers for it, or other similar messages.
Respond and follow any directions if necessary.
10. To confirm that Windows has found and set up your scanner, double-click the System icon in the Control Panel folder.
11. Click the Device Manager tab, and look for the Other devices entry on the list of devices. Click the + next to Other devices; your scanner should be listed. Click OK to clear the dialog box. Your scanner is now ready to use.
Scanning a Document
Most scanners come with some kind of image-editing software such as Adobe Photoshop or Photoshop LE. Even if not, there are some excellent programs available for a relatively inexpensive price--some you can even download from the Internet, such as Paint Shop Pro or Graphics Workshop.
If the program is TWAIN-compliant, its scanning features will work about the same no matter which program you choose. The main differences will come from the TWAIN driver supplied by your scanner's manufacturer. You'll want to review the program's documentation or check its online Help system to learn exactly how to use that particular program.
Regardless of the program, the general tips and techniques that follow will help you produce better scans and get the most out of your image-editing software:
|Always keep the glass on your
flatbed scanner clean and free of smudges and fingerprints. Be sure to use special
lens-cleaning cloths, not household tissues or paper towels--these can permanently scratch
your scanner's glass. You can get lens-cleaning cloths at most computer or office supply
|If you have to move your
flatbed scanner, make sure you lock the scanning head in place first. If you don't, it can
become dislodged from its track and be costly to repair. If the locking mechanism isn't
obvious, check the scanner's documentation for help.|
|Know the desired result before
you scan. How will the image be used--for a letterhead? On a Web page? In a newsletter?
Different jobs require different approaches, so plan ahead.|
|Use the lowest resolution
possible that will still provide the quality you want. "Overscanning" only
serves to make larger files and slower scans.|
|Scan photographs at about
twice the resolution of the expected output. If you're not sure what that will be, ask
your print shop. Magazines are traditionally printed at 133 lines per inch (lpi), so scan
the photo at 266 dpi.|
|For line art images
(hand-drawn artwork, mechanical drawings, and so on), always use the highest resolution
|Don't overscan an image if
it's only going to a laser or inkjet printer. Laser printers generally output at about 50
or 100 lpi, so a simple 200 dpi scan will do just fine.|
|Images intended only for
on-screen viewing need even less: 80 to 100 dpi is adequate.|
|For OCR (see the next
section), use 300-400 dpi.|
|Get to know your image-editing software. Experiment with the various filters and effects you can apply to your scanned images--they can make all the difference in the world. If you're really interested in mastering image editing or you need to learn a lot quickly, consider taking a class or buying a book especially on that software program. Inside Adobe Photoshop from New Riders Publishing would be one recommendation. An edition of the book is available for each of the two current releases (3 and 4).|
Using OCR, scanners can also be used to convert hardcopy text to a text file you can then edit in your word processor, saving hours of retyping. In addition to stand-alone programs like IBM's TextBridge, many of the better fax/modem software programs such as Delrina WinFax PRO also include OCR capability.
Keep in mind that while most OCR programs have a 95 percent or higher accuracy rate, they are not perfect. For best results, you need to start with a clean hard copy (preferably on white paper), in a simple typeface, such as that produced by a typewriter. Handwritten words, unless very neatly printed, usually don't translate very well. If your original is messy, or the print is too small or fancy for the scanner to read easily, you might end up spending as much time cleaning up the scanned text as you would retyping it after all.