Computer scanners

Computer Scanners

Computer scanners have become an integral part of the home and the offices over the last few years has they can be used in many ways. Computer scanners is the computing device that analyses any image or an object like photograph, printed text and then coverts these into digital images. The Computer scanners can be of several kinds. The different types of Computer scanners are drum scanners, desktop or flatbed scanners, handheld scanners, sheet-fed scanners rotary scanners, fingerprint scanners, planetary scanners and 3D scanners.

Drum Scanners are the oldest of all the computer scanners. These scanners have a photomultiplier tube that moves back and forth on a single axis in order to scan. The document or the image which needs to be scanned is wrapped around the drum after soaking the image or document in the oil and this is referred to as wet mounting. These drum scanners are only used for high end applications like magazine advertisements as they have been replaced by the desktop or the flatbed scanners which are much cheaper as compared to the drum bed.

Today only a few companies manufacture the drum scanners and these are expensive. Though drum scanners have the ability to produce superior scans with better resolution, brightness and color gradation due to the photomultiplier tube which is much sensitive to light than the charge coupled device such as flatbed scanners. If the scanned image is to be enlarged too much then the performance of drum scanners is good. But today high quality flatbed scanners have replaced the drum scanners as the oil-mounted transparencies cannot be found easily.

The flatbed scanners work on the charge couple. A flatbed scanner consists of a platen or a glass pane and the pane gets illuminated by the bright light present underneath it and a moving optical array. The three arrays of sensors having green red and blue filters are present in color scanners. The document or the image which is to be scanned is placed face down on the glass pane which is sensed by the sensor array while the light keeps moving across the glass in order to read the entire area. So the image is visible to the charge coupled their eyes as it reflects the light. Transparent Images need certain special accessories that help illuminating them from the upward side.

Some flatbed scanners may have automatic document feeder where a stack of pages can be placed into a hopper from where the pages are automatically taken up by the scanner individually. During the automatic document feed scanning the sensor array does not move as the page moves through the scanner at the constant speed by the rollers. The Pages are collected in the separate exit tray.

The Sheet-fed Scanners are similar to the flatbed but they differ in that their scan head does not move and the document moves. It resembles a small portable printer.

Handheld scanners make use of the same technology at the flatbed scanners but they have to be moved by the user. Their image quality is not good but they are useful for scanning text quickly.

The rotary scanners are used for high speed scanning of a document. This is similar to drum scanner but it makes use of a CCD array and not a photomultiplier.

Planetary scanners photograph the books and documents. The 3D scanners are used for the production of three-dimensional pictures of the objects.

These computerized fingerprints scanners were previously could be seen only in the spy thrillers but with the changing times not they can be found in the police stations, in this high security areas, and even on certain computer keyboards. Today the personal USB fingerprint scanners can be bought within hundred dollars. To make use of these fingerprint scanners, the fingerprint in addition to the password is needed.

The red green blue color data is read by the scanner from to array and processed using certain algorithms to correct this scan for different exposure conditions and then it is sent to the computer through the input/output into this of the device. The color depth is generally 24 bits though it varies according to the array characteristics of the scanner. Another parameter to see to the quality of the scanner is resolution of the scanner which is measured in pixels per inch or these may be commonly referred to as samples per inch. Manufacturers usually speak of the interpolated resolution and forget about the meaningful parameter known as optical resolution. Normally of a good flatbed scanner has 1600-3200ppi of optical resolution, high end flatbed scanners have 5400ppi, and a good drum scanner has 8000-14,000ppi of an optical resolution. As the resolution gets higher the file also becomes larger. Another important parameter is the density range for the scanner. If a scanner has a high density range then it can produce shadow details and brightness details in a single scan.

The document or the image that is scanned can be transferred to the memory of the computer. Some scanners make use of the embedded firmware to compress and clean the image. When the image reaches the computer it can be processed with raster graphics and can be saved on any storage media. Usually the scans are Stored in hard disk in the JPEG, TIFF, PNG and bitmap formats. Editable text can be scanned by the process called optical character recognition.

Infrared cleaning is the method of removing scratches and dust from the film and is present in most of the available scanners. It scans the film with infrared light which makes dust and the scratch detection easy as it cuts off the infrared light and then it can be easily removed by looking at their size, position, surroundings and shape.

The basic task of a computer scanner is to analyze an image or a document and process it. This helps the user to save the information in the computer which can be changed or enhanced of printed or maybe used on the on the web page.