Popular Products > Computers > Flatbed Scanners

The amazing power of modern technology enables us to instantly send a digital image of a photo or a document from one place to another. This is not possible without a scanner – a device that converts a regular picture or document into a digital one. The most popular of these scanners is the flatbed scanner, which is compact and affordable and yet manages to deliver high quality images.

Before flatbed scanners, drum scanners were used. These drum scanners used photomultiplier tubes to sense images. The drum scanners were useful because they controlled the aperture size, which in turn smoothened out the grains when scanning a black and white photo or a colour negative. Although drum scanners are capable of much higher resolutions, flatbed scanners are more common because they are inexpensive and compact. Drum scanners are now mostly used in scanning images from films.

Flatbed scanners use a “charge-coupled device” (CCD) or a “contact image sensor” (CIS). The CIS is a more recent invention and is useful in flatbed scanners because it makes almost direct contact with the image and does not use a mirror to make the light bounce off and reflect the image. However, a CIS cannot capture the depth of field as effectively as other scanning devices.

The most significant drawback of a flatbed scanner is that the image has to be completely flat. Photos or documents are placed on a flat pane of glass and a cover is lowered over it so that outside light does not interfere with the light source inside. This light source is usually xenon or cold cathode fluorescent. The CCD moves within the scanner to capture the image. The image sensors then convert the image into a digitized copy.

Colour scanners use red, green and blue filters to read the images correctly. Such scanners can scan transparencies like 35mm slides and also do reflective scanning of printing on materials like opaque paper. While a normal document requires a resolution of only 300 dots per inch (dpi), a photo image requires more than 2500 dpi. The technique involves scanning at a higher resolution and downgrading it for printing.

There are different types of flatbed scanners from a small postcard size to the regular A4 size. If the scanner is 24-bit, then it will only reflect 256 colours. Generally, scanners do their own computing while processing and transferring data. So, if the thickness of a scanner is less, like a CIS scanner, the resolution of the scanned image or document will also be less and this will produce an image of a lower quality.