Scanners

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It is a device that is used for producing an exact digital image of a photo, text written in paper, or even an object. Digital image can be saved as a file on PC. The most common scanner is the flatbed scanner. The image and text are obtained through the process of optical character recognition (OCR). Types of scanners are discussed.

Drum Scanners – They were the first scanner developed in 1957 and mainly used in the publishing industry. In it a drum type cylinder on the top of which the image/document to be scanned is mounted and as cylinder rotates and the object placed on it will deliver the image copy with the help of precision optics which send the reflected light from the image to a sensor Modern drum scanners also recognize color images. The size of the image produced depends on the design of the drum by the manufacturer. It is used in publishing field due to capture of smallest details. Their scans are high in resolution, color gradation and value structure.

Flatbed Scanners – It is most widely used scanner and also called desktop scanner. In it paper is put on a flat glass plate and the scanner head moves up and down the page inside the body of the scanner. They are cheap and give good output for single photographs or documents. They use Charge-coupled device (CCD) to scan the object.

Sheet-Fed Scanners – They are similar to a flatbed scanner, but scan head remains stationary and the paper is moved over the head. Sheet-feeder attachments for flatbed scanners can turn them into sheet-fed scanners. It has high scan speed of 50–150 pages per minute, but at lower quality.

Handheld Scanners – It is a scanning head which is held in your hand and is moved down the page by person holding it or flat surface. They are cheap but the image quality is low as human hand can not be steady as a stepper motor.

Various components of a scanner are discussed

Glass Plate and Cover – Glass plate is the transparent plate on which document is placed for scanning and can be glass or clear acrylic plate. The cover comes down on the document to scan (in flatbed scanners) and keeps out light from outside and is usually white so that any part of glass plate is scanned as blank.

Scanning Head – It is the most important part as it does the actual scanning. It moves down the page below glass plate, controlled by PC and moved by motor.

Light Source and Mirrors – It is the bright white light which illuminate document as it is being scanned. It can be a fluorescent bulb, a cold cathode fluorescent lamp (CCFL), or a xenon lamp.

Stabilizer Bar – Scanning head rides on it in the scanner. It is a long stainless steel rod fastened to case of the scanner for giving smooth ride to scanning head as the scanner scans down the page.

Charge Coupled Device (CCD) Array or Contact Image Sensor (CIS) – Most scanners use one of these two devices to convert the light energy into a data stream. A charge coupled device (CCD) array is a device inside a scanner that converts photons (particles of light) into electricity. The more

light that falls on it, the more electricity it produces and thus the brighter the representation of the image on PC. CCD needs a lens to focus the light coming from mirrors in scanning head. CIS is used in low end scanners cheaper scanners as it replaces the mirrors and CCD array with a sensor as long as the glass plate is wide and light source is set of LEDs that runs the length of the glass plate. CCD or CIS determine the resolution of scanner or how many pixels a scanner can use to make up a square inch of an image so, in a 300 × 300 dpi scanner 90,000 dots are in one square inch. Higher the number, the higher the quality of the scan but higher file size.

Stepper Motor – It moves the scan head down the page during the scanning in scanner.

Interface

Scanners often use some of the same interfaces as printers. Interfaces used today are USB, Parallel,  SCSI and IEEE 1394/FireWire

Working of Flatbed Scanner

After placing the document on the glass bed and closing the cover. The lamp brightens up the text to be scanned. Stepper motor moves the scanner head from one end to other slowly and is controlled by a belt. As scan head moves, light from the lamp hits the document and is reflected back with the help of mirrors to be focused on CCD sensors. CCD sensors convert the light to electrical signals according to its intensity. The electrical signals will be converted into image format.

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