by Glyn Sheridan
A flatbed scanner is useful in copying documents and photographs into a digital format that allows you to read, edit or transmit images to others over the Internet. With so many flatbed scanners on the market, in a wide range of prices, you may be wondering how to choose a flatbed scanner that will meet your needs. Here are some tips to help you compare features and choose a scanner that works for you.
Check the resolution. Digital images are classified by how many dots per square inch (dpi) they contain. The higher the dpi, the better the image resolution. If you need high resolutions in your digitally scanned images, you will benefit from a scanner with a high dpi scanning ability. Understanding the scanner's dpi number can be confusing, so keep in mind that the lower of the two numbers indicates the true optical resolution. For example, the scanning resolution may read "1200 x 2400," but only the lowest number represents true optical resolution. The higher number represents the scanner's ability to interpolate the image by combining two adjacent pixels and inserting a blended pixel between them.
Scanners use different image-sensing technology. A flatbed scanner captures an image by directing light onto the image and then recording the reflected information. A contact image sensor (CIS) document scanner records the information directly from the document to the sensor. While this is fine for most text documents and small photographs, a better image quality is obtained when a scanner uses charge coupled device (CCD) technology, which records a mirror image of the photograph or document.
Consider the dynamic range and tonal range. Represented by a single "D" on the manufacturer's specification sheet, the dynamic range varies from 0 to 4. A higher number corresponds to a better scan. The dynamic range of a document scanner is the depth of shadow from pure white to total black and all the shades in between. A flatbed scanner's tonal range ability is listed in "bits." The higher the bits, the more discerning the scanner. Graphic editing programs require at least 24 bits, but 30 bits or 36 bits offer an even better image. If the scanner box lists the bits "per channel," multiply the number by three to arrive at the total bits. For example, eight bits per channel offers a total of 24 bits of tonal range-scanning ability.
Compare cost versus quality. An expensive, high-quality flatbed scanner performs very well, but you may not always need such powerful capability. Cheap scanners with 600 dpi that utilize CIS technology are sufficient for most office and home scanning tasks. A high-end flatbed scanner is ideal if you need high-resolution and great color quality from your scans. Mid-range and high-end flatbed scanners come with decent price tags, but graphic artists and those who must have high-resolution images for photo editing will spend the money for a scanner with CCD technology, 32 bits or higher tonal range and a dynamic range of at least 3.2 to get high-quality scanned images.