Things to Look For
Jul 23 '01
The Bottom Line There is a lot to look for in a flatbed scanner. Here is a breakdown of important facts.
First, there are two kinds of flatbed scanner available.
Contact Image Sensor, or "CIS" scanners are really cheap these days. They use an array of sensors directly mounted on the scanhead to pick up the image. Since these eliminate the complicated optics of CCD scanners, they tend to be lighter, thinner, and cheaper. Beware, however, since these scanners tend to give poor image quality. These scanners can be great for home use, but are not for the graphics professonal.
Charge-Coupled Device or "CCD" scanners contain a little CCD chip, similar to the chip found in camcorders and digital cameras. The scanner uses a complicated optical system to direct the image from the scanhead to the sensor. This makes the scanner thicker and heavier. CCD scanners are a well-worked-out technology, and tend to provide high-quality images. If you are a professional graphic artist, you will want to invest in one of these.
Color scanner technology has matured quite a bit. The next two items cover technologies that have become standard on most scanners.
Make sure a scanner has single-pass color scanning. Most scanners do today. Older scanners would scan a color photo with three passes, one for red, one for green, and one for blue. Modern scanners do all of this in one pass, saving time.
Cold Cathode technology allows a scanner to turn on its light only when necessary. Older scanners would leave their light on to avoid warmup time, but this ate electricity and wore out the bulb. Most modern scanners use this technology as well.
Here are important things to consider when looking for a scanner.
Check the scanner's Dots Per Inch rating carefully. Ignore interpolated ratings, and look for the actual optical rating. The optical rating is the scanner's true hardware resolution. Interpolation just takes the scan and fills in the missing pixels. This method doesn't give more detail, but just a larger, fuzzy image.
The interface can be important in your decision. Parallel-Port and USB scanners are cheaper, but they also tend to be slower. SCSI and FireWire (or 1394) scanners are more expensive, but faster.
Image quality, of course, is very important. Most well-known brands of CCD scanners have excellent image quality. You will almost always need to adjust the image once scanned due to problems with the source material. It is the rare photo that produces a perfect scan. If you can't try out scanners before you buy, then look for reviews on the models that you are considering.
Bit depth is the number of bits used per pixel within the scanner's hardware to define the image. Most computers and graphics programs can only handle 24 bits of color information (8 bits per primary). Scanners tend to use more bits so that they can make automatic adjustments to the image data, and still provide the computer with a true 24-bit image with little or no data loss.
If you get a scanner with more that 24-bit bit depth, then you will get the best quality scans by adjusting image quality while you are still in the scanner utility. Most scanners have an "automatic" setting, but you can also override this and adjust the image quality manually. Sometimes this requires multiple scans until it looks just right. Adjusting the image afterward in a 24-bit graphics program can lead to loss of data in the image. In extreme cases, this can be seen as extra noise or banding. If you are scanning for a low-quality medium such as the web, this becomes rather unimportant. If you are scanning for professional-quality media, then you will want a scanner with lots of bits.
Other things to look for are the size of the scanner's scanning window, which limits the size of the documents that it can scan. The speed of the scanner limits how many documents you can scan in a given time. Some scanners have optional accessories that you can purchase now or later, such as automatic sheet feeders for scanning multiple documents. Other scanners can scan transparencies and film. Be aware that most flatbed scanners cannot provide a sharp, high-resolution scan of 35-mm film. It's just too small.
A final consideration is the software that comes with the scanner. Some scanners come with a limited version of a graphics program, such as Adobe Photoshop LE. Once installed, most scanners can be accessed through a graphics program's "Acquire" function.
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Member: Greg Searle
Location: Nashua, NH
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About Me:
Computer graphics designer and software developer with interests in technology, home improvement, and family life.
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