A scanner analyses an image and processes it. Image and textcapture (optical character recognition or OCR) allow you to save information ina file on your computer. You can then either modify the file or print itaccording your needs. Scanners have a true hardware resolution of at least300x300 dots per inch
There are four types of scanners:
Flatbed scanners
Sheet-fed scanners
Handheld scanners
Drum scanners
Flatbed scanners are the most commonly used of the four andwe'll focus on a flatbed scanner in this How Things Work.
A CCD array is the most common technology for image captureand so forms the core component of a scanner. A CCD array is a collection oftiny light-sensitive photosites which convert light into electrical charge.When you scan the document, the light reaches the CCD array through a series ofmirrors, filters and lenses.
THE DIGITISING
1. A document is placed on the glass plate of the scannerand the cover lowered. The inside of the cover is flat white and it provides auniform background. This forms a reference point against which the scannersoftware determines the size of the document being scanned.
2. There is a lamp below the glass plate that illuminatesthe document. The lamp can be either a cold cathode fluorescent lamp (CCFL) ora xenon lamp.
3. The scan head comprises mirrors, lens, filter and a CCDarray which moves slowly across the document on a belt attached to a steppermotor. It is secured to a stabiliser bar to ensure there is no deviations inthe pass (or a complete single scan of the document).
4. The image of the document is reflected on to anothermirror by an angled mirror. Each mirror is slightly curved to slightly diminishthe image it reflects. The second mirror reflects the image on to a lens, whichfocuses the image through a filter to the CCD array.5. The lens splits the image into three smaller version ofthe original. Each smaller version passes through a colour filter (Red, Greenand Blue) in the CCD array to the analog-to-digital converter (ADC). After thepass is completed, the scanner software assembles the filtered images into asingle full colour image.
6. The scanned image needs to be transferred to a computerso that it can become usable. USB is the common method. The scanner driver mustbe installed in computer to be able to read the data.
