You can say it captures and convert documents and images to a digital form.After getting softcopy of your image you can publish it on the internet. It’s all simple. Plug you scanner and throw any photo onto glass, push one button without even starting software and result would be appear. I am using Acer ScanPrisa 640.
Scanner has an array of photosensitive cells that can detect light reflection throw the object. This array of receptors is called charge-coupled device (CCD), which measures light intensity and convert this intensity into an electronic charge.
For digitise the information, An analogue to digital converter (ADC) is required. There are so many cells in CCD array. Each cell creates one pixel. And for each pixel a certain number bits are stored. For better image quality, more information assigned to each pixels.
There are a few but important parts which used to make scanner are given below –
(1) CCD ( Charged coupled devise)
(2) Lamp
(3) Scan Head
(4) Glass Plate
(5) Lens/Mirror
(6) Stepper motor
CCD – CCD (Charged coupled devise) is very important part of scanner. It is made of an array of photo diodes, which sense the light coming from image (after reflection). And convert this light to electronic signal.
Lamp – The lamp used in scanner is basically cold cathode fluorescent lamp. This lamp lights up the area of photo (or document) to be scanned with white light. This light reflected back from document. CCD is captured this reflected light.
Glass plate – This is where document or photo is placed. It is larger in size than the document. If there is dirt over or under the glass, the scanned image will have artifacts and smudges. The scan quality depends a fair deal on glass.
Scan Head – Scan head is used to hold CCD (Charged coupled devise) and the florescent lamp. The head assembly is mounted on the stabiliser bar. This stabiliser moves from end to end while scanning.
Lens/mirror – There are two or three mirrors in a scanner. These mirrors reflect the light to the lens. If mirrors and lens are not properly placed, some areas of the scanned image will be cut.
Stepper motor – The CCD (Charged coupled devise), lamp, mirror and lens are all placed on the same head assembly (Scan Head). This assembly is moved by the stepper motor which takes its control signal from circuitry placed at the bottom of the scanner.
So how to choose a scanner –
Well you can choose a scanner on the basis of scanner’s feacture and the capabilities of the scanner. Before buy any scanner you should look for-
(1) Maximum color resolution support
(2) Document Scan area
(3) Color depth
(4) Bundled accessories such as power adapter and interface cable.
