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November 21, 2009 |
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Created and Maintained by: The Photoimaging Information Council |
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Articles |
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As we discussed in Part I of this review of photo scanners, you’ll find two basic types of devices for digitizing your conventional photographs. Flatbed scanners are optimized for making digital files from large flat objects such as photographic prints, graphics, kids’ artwork, etc. Even the 600dpi models produce image files that are fine for sharing with friends via the Internet or for making 4x6” prints. Some models have a film drawer or accept a “transparency adapter unit” for scanning (the much smaller) slides and negatives with acceptably sharp focus. The better models can provide a file that’s suitable for making a good print if you scan a razor sharp image.
 Film/Negative Scanners Flatbed scanners are primarily intended for digitizing photographic prints and artwork but some models include a slot or transparency adapter for scanning film. However, if you need extremely high image quality from slides and negatives, consider a dedicated film scanner, available from most of the same manufacturers. Flatbed Scanners If you’re planning to use a scanner only occasionally, you’ll find the information in Part 1 adequate for selecting an affordable flatbed model. However, if you’re technically inclined and want the best digital files from numerous pictures – read on.
 Advanced Scanner Concepts A 4x6” print scanned with an affordable 1200dpi flatbed model (with 3.0 D-range and 24-bit color depth) produced this high quality digital image. Models with even higher resolution and greater color depth are available for those who need superior image quality.
Let’s take a look at some of the technical factors of flatbed scanners that you’ll want to consider before deciding on the model to buy. These concepts will also apply to film scanners (for slides and negatives only) although the recommended specs will be different. Review the following before moving on to the section on Film Scanners.
 Peter K. Burien Advanced Scanner Concepts If you want to scan slides or negatives, and plan to make excellent 4x6” prints from the digital files, consider a 1200dpi flatbed scanner with film drawer or transparency adapter. If you want to make excellent 5x7” prints or good 8x10” prints, look for a 1600+dpi, model preferably with D-range of 3.4 (Scan of color slide with 1200dpi scanner with transparency adapter, 3.0 D-range, 24-bit color depth.) True Optical Resolution: True Optical Resolution: Even the affordable scanners offer high optical resolution: 1200dpi (dots per inch) is becoming common. Actually, this refers to pixels per square inch (ppi), but dpi has become the common term. A 1200dpi flatbed model is adequate for scanning prints but if you’re really fussy about image quality, look for a 1600+ dpi scanner. Do you plan to scan three dimensional objects such as coins and collectibles? If so, look for a scanner – preferably a 1600dpi model -- that’s designed to accept thicker objects, including some Canon models with Z-Lid Expansion Top.
Note: The specs for optical resolution – the number of pixels that the CCD line sensor will see -- always include two numbers, such as 1200 x 2400dpi. That’s because a scanner offers higher resolution (more pixels) in the horizontal direction than in the vertical plane. Its processor then “interpolates” (generates extra vertical pixels) so you get a properly scaled image. In any event, it’s the first number that’s typically used for comparison purposes.  Interpolated Resolution: The technical specs also include a figure for “Maximum Resolution” or “Interpolated Resolution”, such as 9,600 x 9,600dpi. Internal software increase the number of pixels in the scan through interpolation, but this feature may not improve image quality very much if the optical resolution is low.
 Density Range: In a flatbed scanner that will be used to scan prints and artwork a D-range of 3.0 is plenty for reproducing detail from both highlight and shadow areas. If you need a scanner with a transparency adapter for slides and negatives, a higher D-range such as 3.2 or even 3.4 would be useful. It will reproduce more detail in a contrasty image and you’ll get less digital “noise” in dark areas Color Rendition: High color bit depth equals high amounts of color information stored with each pixel, important for accurately reproducing the subtle differences between similar colors. Inexpensive scanners record 8 bits of information per color channel (red, green, blue) for a total of 24-bits. Today, you can find affordable 30-bit scanners and for a bit more money, you can get a 36-bit model; pay even more and you can buy a 42-bit scanner. These produce richer and more faithful colors.
 Color Management: Some mid to high priced flatbed scanners support color management (Color Sync for Mac and ICM 2.0 for PC); check the Specs for this advanced feature. When used with image editing software, this produces more faithful color rendition. They may also offer color profiling software for calibrating your monitor and scanner, often as an extra cost accessory. If very high color accuracy is essential, this option is worth considering. Fast or Slow?: Scan speed is an important consideration if you plan to digitize a lot of pictures. Although the manufacturers’ specs are often optimistic as to pre-scan and actual scan times, the information is useful for comparison purposes. A scanner that is said to take 3 minutes with an 8x10” print might be preferable to one that takes 6 minutes – assuming that the optical resolution, color depth and other specs are similar.
 Connectivity: At one time, serial cables were commonly used for connecting a scanner to your computer. Today, most models also accept a USB cable for significantly faster image data transfer. With USB, you don’t need to shut down your computer to connect or disconnect the scanner (“hot-swappable”). Most recent Mac and PC’s include the necessary USB port; if yours does not, it can probably be upgraded.
Want lightning-fast speed? Look for a scanner with a SCSI connector. They’re a bit more expensive but should include a PCI SCSI board that you can install into your computer. Eventually, Firewire (IEEE1394) connection will become common; also super-fast, it’s hot-swappable.  Size and Weight: Scanners vary considerably in physical size. If you have little desktop space, or you plan to move your scanner around often, look for a slim model with small “footprint”.
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