While there are many ways that you can capture digital images, scanners may be the most practical for many computer users because they let you produce computer-ready files from images created with the same cameras and film you're already using. What's more, scanners can be used to digitize all the images in your existing library of prints, negatives, and slides. How they work Scanners convert photographs into digital form by passing a light-emitting element across the original image, transforming it into a collection of pixels gathered as a digital file. The earliest scanning devices were drum scanners, which focus a light source onto an original transparency mounted on a rotating drum. This technology is capable of handling a wide range of image density and produces high-quality output, but the complexity of drum scanners makes them too expensive for the average computer user.
All desktop scanners use a lens to produce a digitized image.
The typical desktop scanner uses a CCD array consisting of several thousand CCD elements arranged in a row on a single chip. Because not all scanners can capture enough data in one pass, some use three passes. Single-pass scanners use three linear arrays, which are individually coated to filter red, blue, and green light. The same image data is focused onto each array simultaneously. CIS allows these scanners to be more compact.