Printers And Scanners : Types And Introduction To Scanners
3.Introduction to Scanners
Scanner is a device that scans images, printed text, and handwriting etc and converts it to digital form or image. It is so named because the data is converted one line at a time or scanned down the page as the scanning head moves down the page.
Components inside a scanner are the following
i. Glass Plate and Cover
The glass plate is the transparent plate wherein the original is placed so that the scanner can scan it and the cover keeps out stray light that can affect
the accuracy of the scan
ii. Scanning head
Scanning head is the most important component because it is the one which does actual scanning. It contains components like
1. Light source and mirror : It is the bright white light that is used to illuminate the original as it is being scanned and which bounces off the
original and reflected off several mirrors
2. Stabilizer bar: It is a long stainless steel rod that is securely fastened to the case of the scanner and it provides a smooth ride as the scanner
scans down the page
3. CCD (Charge Coupled Device) or CIS (Contact Image Sensor) : A CCD array is a device that converts photons into electricity. Any scanner that uses
CCD use lens to focus the light coming from the mirrors within the scanning head.
Another technology used in some cheaper scanners is CIS wherein the light source is a
set of LEDs that runs the length of the glass plate.
iii. Stepper Motor
The stepper motor in a scanner moves the scan head down the page during scan cycle and this is often located either on the scan head itself or attached to a belt to drive the scanner head.
3.1 Flatbed Scanners
The most commonly used scanner is a flatbed scanner also known as desktop scanner. It has a glass plate on which the picture or the document is placed. The
scanner head placed beneath the glass plate moves across the picture and the result is a good quality scanned image. For scanning large maps or toposheets wide
format flatbed scanners can be used.
3.3 Sheetfed Scanners
Sheet fed scanners work on a principle similar to that of a fax machine. In this, the document to be scanned is moved past the scanning head and the digital form
of the image is obtained. The disadvantage of this type of scanner is that it can only scan loose sheets and the scanned image can easily become distorted if the
document is not handled properly while scanning.
3.4 Handheld Scanners
Hand-held scanners although portable, can only scan images up to about four inches wide. They require a very steady hand for moving the scan head over the
document. They are useful for scanning small logos or signatures and are virtually of no use for scanning maps and photographs.