- Odds are, you have used a scanner either at work or at home recently. These devices are inexpensive, and they have become a mainstay of most office environments. Whether the scanner is part of a printer, is a stand-alone flatbed unit or even a handheld unit, the basic idea of a scanner is easy to understand. The scanner takes a picture of your document or photo and digitizes it for use on a computer. While most people understand this intuitively, most don't really know what goes on inside a scanner. Fortunately, by understanding a few common components inside every scanner, you can get a better idea of how this common appliance works.
- The core component in a scanner is the charge-coupled device, or CCD, which is actually the same device contained within a digital camera. A CCD is a collection of tiny light-detecting diodes in an array. Each of these diodes, called a photosite, converts light into an electrical charge. Photosites will generate a greater amount of electricity when exposed to more light, allowing the CCD to accurately reproduce images.
- When scanners operate, they are working to expose the document being scanned to the CCD as smoothly and predictably as possible. A light is shined on the document, which will then reflect the light back at the CCD to capture the details of the document. Since a CCD doesn't know what it is looking at, scanners rely on a slow, methodical process to capture all information about a document.
- Different scanners accomplish this feat in different ways. Some scanners move the backlight behind the document, while others may move the document and leave the scanner hardware in place. In either case, the light reflected from the document is bounced off of a mirror, which reflects it onto the CCD. Software keeps track of the timing and position of the process and extrapolates this information to determine what part of a document is currently being scanned.
- To accomplish color scanning, scanners use a multi-pass system, where the scanner makes a single pass using a filter for each color. By detecting levels of red, green, and blue in a document, the scanner can merge the images to accurately reproduce photos with millions of colors. Newer scanners sometimes use different parts of the CCD for each color and use only a single pass, but the basic idea remains the same. Using these simple techniques, a scanner can create an image of virtually any document in only a few seconds.
