Scanner

Scanners allow a pc to convert a picture or object into digital code that allows the computer to display and use an image. A scanner's sophistication is the ability to translate an unlimited number of analog voltage levels to digital values. The computer is not able to use graphics unless they are in a form that they can understand. The scanner takes the information it sees on a page and converts into code that the computer can use. A picture once scanned can be edited, printed, or used in an application. Scanners can come with specialized software called optical character recognition (OCR). This software can read text as printed or written. The information can then be manipulated in the computer.

Important Note: A feature of the scanner is the resolution. This is how sharp and detailed the scanner can read. Scanners are measured in dots per inch. The higher the resolution, the more the memory that is required to scan the file. The bigger the file that is produced. Larger files take longer scanning time. If a file is big and you need to fit it on a diskette, you may run into a problem storing it unless you store it to the hard drive or another high capacity drive. Therefore, if you are wanting to produce a file for screen output, you should scan at 72 dpi because that the best resolution that the monitor can display. It is the same of the printed output. If you only have a 300 dpi printer, do not scan the file at a higher resolution since the printer will only print it at that resolution.

Types of Scanners:

Sheet-Fed ScannerSheet-fed scanners have mechanical rollers that move the paper past the scan head.

Flatbed ScannerFlatbed Scanners have a glass window where the item to be scanned is placed on top of a while the head moves past the item. This method is similar to a xerox machine.

Hand Held ScannersHand held scanners are small, portable scanners that depend on a human operator to move the head across the the object or image to be scanned. .

Color vs Grayscale

Gray Scale: Using black and white and shades of gray, the scanner is able to translate the image into gray scales. Why would you use a gray scale scanner? If you plan to print on a black and white printer, it is most cost effective since color ink is so expensive. Text is best done on a grayscale scanner.

Color: A color scanner scans images in red, blue, and green shades. This scanner is more expensive in terms of final print output . A color scanner usually costs more than a gray scale scanner. If you plan on doing presentation work, work with color photographs, or any sort of task that requires a color output, then use a color scanner. With this scanner you can also choose options of scanning such as line art (scanning the image only in black or white), grayscale (black, white, and shades of gray, or color (shades of red, blue, and green).

How a Flatbed Scanner Works

1: A light source underneath the picture or document illuminates the image. Spaces white or blank reflect more light than do inked and colored areas.

2: A motor moves the scan head underneath the page. when the scanhead is moving it captures light that was reflected from individual areas of the page about 1/90,000 of an inch

3: Light from this page is bounced through an intricate system of mirrors that must continually pivot to keep the light beams aligned with a lens.

4: A lens focuses the beams of light into light sensitive diodes that translate the amount of light into an electric current. The amount of the current depends on the amount of light reflected, the greater the amount of light reflected the greater the current.

5: The analog to to digital (A-D) converter stores each analog reading of voltage as a digital pixel representing either a black or white area. Scanners that are more sophisticated can translate the voltage into shades of gray. In a color scanner, the scan head makes 3 passes under the image and the light on each pass is directed through a red, green or blue filter before it strikes the original image.

6: The digital information is sent to the pc where it is translated into a format that a graphics program can read.

How A Hand-Held Scanner Works

1: On the majority of handheld scanners when you press the scan button a light-emitting diode (sometimes called a LED) illuminates the image below the scanner. An inverted, angled mirror that sits right above the scanner's window reflects the image onto a lens in the back of the scanner.

2: The lens focuses a single line of the image onto a CCD (known as a charge coupled device), which is a component designed to detect subtle changes of voltage. As the light shines onto sever rows of light detectors located on the CCD, each registers the amount of light as a voltage level that equals to black,white or gray.

3: Special analog chips receive light voltage generated by the CCD for gamma correction. This process enhances the black tones into an image that is that the eye will have be able to recognize the shades of the image easier.

4: The line of the image now is moved to the analog-digital converter. In a gray scale scanner, the converter assigns 8 bits to each pixel, or 256 shades of gray.

5: As the disk turns, a light shines through the slits and is detected by a photomicrosensor on the other side of the disk. When light strikes the sensor it throws a switch that sends a signal to the A-D converter. This signal tells the converter to send the line of bit generated to the computer. Then the converter clears itself of the old data.

6. The computer then moves to the next line.