Choosing the right flatbed scanner |
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30 different scanners and they all look about the same on the outside. What makes the €500 model better than the €50 one? Four main factors drive up the price of a scanner: resolution, colour depth, speed, and interface. This article helps you understand these factors and looks at other scanner elements that might affect your purchasing decisions.
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Resolution |
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Resolution is the maximum number of dots per inch (dpi) that the scanner can register. The higher the dpi, the finer the quality of the scanned image. generally, scanner resolution is advertised as either one number (1200 dpi) or two (1200x2400 dpi). If there are two numbers, the first one matters most -- it's the number of sensors in the scanning head. The second number tells you how many rows the scanner can register. If there's only one number, both measurements are the same.
Some scanners advertise two resolutions: optical and enhanced. Optical refers to the raw capability of the hardware itself, while the enhanced resolution identifies the resolution the scanner can achieve with the help of scanning software, for example, a high-end scanner might offer 2400 dpi optical and 9600 dpi enhanced (or "unlimited" enhanced). Even though software can enhance a scanner's capabilities, the optical resolution is the true measurement of the scanner's capacity, so use it as a guide when you are shopping.
Less expensive scanners typically have 1200 dpi resolution, while higher-priced scanners usually offer 2400 dpi. A 1200 dpi model is fine for most uses, because there's no point in scanning an image at a higher dpi than your printer will print, and most printers have a maximum resolution of between 600 and 1200 dpi. However, if you plan to regularly produce brochures or print ads that you will send to a professional printer, choose a 2400 dpi model.
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Color depth (bits) |
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Color depth defines how many colours a scanner can register, and is measured in bits: 30-bit, 36-bit, 48-bit, etc. A colour depth of 24-bit is known as "true colour," and uses a 24-digit binary code to represent each pixel. This bit depth provides for over 16 million possible colours for each pixel, which is more than the human eye can detect, so in theory 24-bit colour depth is the most a scanner would ever need. However, most scanners today advertise 36-bit support or more, up to 48-bit in high-end models. Why? It's all about colour correction. Scanners that start with more bit depth have more room to do colour correction.
For casual or occasional use, a 36-bit scanner is adequate. However, even inexpensive scanners nowadays offer 48-bit colour depth, so if it costs no more (or little more) for the extra quality, go for it.
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Speed |
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Speed refers to the time it takes to scan. However, the actual speed can vary greatly depending on factors like the size or resolution of a scan, whether it's colour or grayscale, and whether you're using Optical Character Recognition (OCR) software to import scanned text.
A low number (9 to 20 seconds) refers to the fastest possible speed at which a scanner's scanning head can move across the glass. This number helps you compare scanners, but it doesn't account for such variables as the operating system, scanner software, and image size and resolution.
A higher number (45 to 60 seconds) tells you how long a typical scan takes. This number isn't very meaningful unless it's related to resolution and image size. A scanner might take 60 seconds to scan a colour snapshot, 90 seconds for an OCR text page, and 150 seconds for anA4 colour photo.
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The importance of the interface |
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The interface connects the scanner to your computer and makes it possible for you to actually use the scanner with your computer. Pay attention to a scanner's interface type -- not all computers have all types of interfaces, and interface type affects the scanner's speed.
Note: The interfaces mentioned here are for Intel-based PCs, the kinds that run Windows. If you use a Mac, choose a scanner that's specifically advertised to work with Macs.
In the past, most low-end scanners used a parallel interface. Most computers have only a single parallel interface, and most computers use it for the printer. Therefore, a parallel scanner usually includes a pass-through that enables it to share the port with the printer. It's a good idea but it doesn't always work very well. Ink-jet printers in particular have a difficult time sharing a parallel port. You can make adjustments in BIOS to reconcile the two devices, or you can unhook the scanner and attach the printer every time you want to print. Parallel is also the slowest interface for scanning.
At the other end of the spectrum, the most expensive scanners typically have a SCSI (pronounced "scuzzy") interface. SCSI has been around for a long time and has many advantages, like high speed and the ability to daisy-chain several devices onto a single SCSI port. However, some PCs do not have SCSI ports built in, so you might have to add a SCSI expansion board to the PC to use a SCSI scanner.
In the middle is the most popular scanner interface today: Universal Serial Bus (USB). USB combines the advantages of SCSI and parallel. It's fast and it can chain several devices together on a single port -- like you can with SCSI -- and most computers already have a USB port -- as is common with parallel ports. The only requirements for USB are a USB port (which almost all PCs made in the last 4 years have) and Windows 98 or higher.
There are two USB specifications: regular USB and USB 2.0. USB 2.0 is backward compatible with USB. If both your PC's USB port and the scanner's USB interface support USB 2.0, the transfer between them is much faster than with standard USB. If buying a USB scanner for a new computer, make sure it has a USB 2.0 interface
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Some other factors to consider |
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While resolution, colour depth, speed, and the interface type are the primary features you will compare as you shop for a scanner, other factors may affect your final purchasing decision:
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Size: If desktop space matters, choose a smaller unit. If large scanning size is important, buy one with a larger scan area. |
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Software: If you need image-editing software, make sure you scanner comes with a program from a well-known software maker like Adobe or Corel. |
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Accessories: Some scanners have an optional slide/negative scanner and/or a sheet feeder. If either of these is important to you, make sure that you either buy the accessories at the same time as the scanner (preferred) or select a scanner that has them available for purchase at a later date |
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Operating system compatibility: Most scanner software works with most versions of Windows. If you have Windows Millennium Edition (Me), Windows 2000, or XP and you want a scanner that works directly with the your system's built-in Scanner and Camera Wizard, choose a scanner that's on Microsoft's Hardware Compatibility List. |
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