Scanners
** Hardware Guide Home **
Defining Scanner Types
Scanners are peripheral devices
used to digitize (convert to electronic format) artwork, photographs,
text, or other items from hard copy. In a sense, a scanner works as a pair of
eyes for your PC. Your eyes see an image and translate the image into electrical
impulses that travel to and are interpreted by your brain. Similarly, a scanner
captures images and converts them to digital data that travel to and are
interpreted by the computer.
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.
Flatbed Scanners
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
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
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.
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.
System Requirements
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.
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.
TWAIN
Drivers
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 Next again.
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:
| 1. |
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 stores.
|
| 2. |
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.
|
| 3. |
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.
|
| 4. |
Use the lowest
resolution possible that will still provide the quality you want. "Overscanning"
only serves to make larger files and slower scans.
|
| 5. |
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.
|
| 6. |
For line art
images (hand-drawn artwork, mechanical drawings, and so on), always use
the highest resolution possible.
|
| 7. |
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.
|
| 8. |
Images
intended only for on-screen viewing need even less: 80 to 100 dpi is
adequate.
|
| 9. |
For OCR (see
the next section), use 300-400 dpi.
|
| 10. |
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). |
OCR Software
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.
