How Scanners Connect to your Computer
One of the most remarkable examples of how far prices have fallen in the computer industry is in the area of color scanners. Only a few years ago, a decent color scanner cost close to $2000; now, comparable units – with better software, in many cases – can be had for about $500. And with the image-editing software included with today’s scanners, you can not only capture photos, but retouch or radically alter them (Look -- It’s Dino-dad!) before printing them, publishing them in a newsletter or even posting them to the Internet. Sending artwork to Grandma will never be the same.
There are three main methods by which a scanner is connected to a computer. AT the high end, the most widely used method is SCSI, or Small Computer System Interface. The advantage of SCSI is its ability to support several devices by "daisy-chaining" one unit to the next (see the sidebar for details). SCSI is also capable of fast data transfers. The disadvantage is its propensity toward various PC-related configuration hassles, including a phenomenon known as a "SCSI ID conflict," and potential difficulties with SCSI termination and various Windows -- or Mac -- configuration issues. With that said, most experts would recommend a SCSI-connected scanner over other methods of connected. SCSI will give you the widest range of options, better performance and better compatibility with future operating systems. (SCSI scanners are also your best bet if you are running OS/2, Macintosh or other less mainstream operating systems.)
What can you connect to a SCSI interface?
One of the great things about having a SCSI interface in your computer is the way it allows you to add other devices without using up precious IRQs (interrupt requests, of which a PC has a very limited amount) or extra slots. In other words, all of the above devices could be added to a single SCSI interface, and would thus use up only one slot and one of your PC’s IRQs.
SCSI cards may be added to any available ISA or PCI bus slot on a PC (SCSI is built into many Macintosh models, too), or in the case of a portable PC, via a PCMCIA card slot. See the glossary at the end of this article for a description of these and other acronyms.
While Microsoft Windows 95, Windows NT and Windows 98 provide built-in support for several popular brands of SCSI interface (and virtually all SCSI-based scanners provide drivers on disk for Windows 3.x, 95/NT, and/or Macintosh), the fact remains: SCSI scanners can be a pain sometimes. Installing the interface card is, let's face it, tricky for those that aren't mechanically and technically inclined.
For PC owners who crave simplicity, another alternative is a scanner connected via a parallel or serial port. Many low-cost models from makers such as Hewlett-Packard, Microtek, Umax and a host of less well-known manufacturers connect via a parallel port, making them simple to attach to virtually any Windows-compatible PC – even a laptop model. Parallel-connected scanners don’t require you to open up the computer to insert or fiddle with interface cards – a definite plus for those adverse to such endeavors.
There are a few things to watch out for with parallel devices: It is fairly rare, but not unheard of, for a parallel device to include a passthrough connector, in case you connect another device. Fortunately, if your computer already has a device (say, a printer) connected to a parallel port, it is a simple and fairly inexpensive proposition to install a simple A/B switchbox to toggle between the devices. It is also possible to add a second parallel port to a PC, although, again, this is a task best left to the technically inclined.
Another consideration is the fact that parallel interfaces were designed primarily for printers. Although it is possible to add scanners, disk drives, tape backup units and other devices to a parallel port, compatibility problems occasionally arise as a result. For example, Windows 95 did not provide built-in support for storage devices, tape backup or scanners connected via a parallel port, although Microsoft has since provided an update to the Windows 95 backup program that provides limited support for some of these devices. Drives and tape units connected via SCSI, however, are well supported.
The third, and most recently popular option is to purchase a scanner with a USB, or Universal Serial Bus, port. USB has several advantages -- most notably, it's truly plug and play. You just attach a USB-compatible peripheral such as a scanner, camera, joystick, mouse, or keyboard (etc.), and your computer automatically recognizes it and, if necessary, prompts you to insert a disc if it needs to load any drivers. This of course requires that your computer's operating system support USB and that the PC or Mac actually has one or more USB ports. Most recent models do, but you generally need to be running Windows 98 (or, in the Mac world, running an iMac or blue G3 model) to use peripherals such as USB scanners or printers. Lastly, it's worth mentioning that to connect more than two USB devices, you will have to add an item with more ports known as a USB hub. With enough hubs, you can connect up to 127 USB devices -- more than enough, I think, for even the most elaborate computer setup.
Glossary
To help you choose the right scanner, here are descriptions of some of the terms and technicalities you are likely to encounter:
24-bit versus 30-bit color – briefly, the more bits captured, the better the dynamic range (and hence the quality) of the resulting image. A 24-bit scanner captures 8 bits worth of red, green and blue values. A 30-bit captures 10 bits of each, respectively. A 24-bit image can display up to 16.8 million colors.
Interpolation – see Resolution, below.
CCD – charge coupled device. An array of light-sensitive devices that capture images in scanners, video cameras, etc.
Cold Cathode Lamp – a type of fluorescent light source that lasts longer and generally produces better results than cheaper "hot" light sources.
Flatbed versus Sheetfed – Flatbed scanners are suitable for scanning books, magazines, and of course individual sheets of paper, card or other flat objects. Sheetfed scanners are only suitable for paper (without staples or curled corners!) in single sheets. Some flatbed scanners support documents up to legal size (8.5"x14"). This may be useful if you plan to use optical character recognition software to "read" text. OCR software, included with most scanners, can read printed pages and save the text in common word processor formats.
Resolution – usually described in terms of dpi, or dots per inch, most scanner manufacturers quote two figures: optical (true) resolution, and interpolated resolution. The higher the optical resolution, the more effectively you can scan small images. Most scanners use smoothing algorithms to reduce jaggies when capturing at higher resolutions – in effect, interpolation doubles or quadruples the optical resolution by smoothing. Although this method of saving higher quality images than the optics are capable of capturing may seem like faking, it works remarkably well – and thus nearly all manufacturers provide it.
Scanning Modes – All color scanners can also capture in black-and-white, halftone and grayscale modes. Black and white is sometimes referred to as "line art." There are no gray tones. Halftone mode in effect applies a screen to an image to produce dots of varying densities: the resulting image is well suited to photocopying or faxing.
Grayscale images are suitable for printing. Most of today’s laser printers and inkjet printers can reproduce a grayscale image quite well; however, an imagesetter at a prepress shop produces even better results. Thus, many publishers use their laser or inkjet printer to produce a "proof" and then send their disk(s) to a graphics service bureau for final imagesetter output to film or photographic paper.
One-pass versus three-pass – In a one-pass scanner, red, green and blue are all captured in a single movement of the scanning mechanism. This is generally much faster and more convenient than a three-pass scanner, in which the head must make three trips past your page.
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