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Looks like copier but
isn't WITH the advent of computers and the Internet a lot of interest is being shown by one and all in gaining knowledge and work experience related to the field of hardware of software. However we might not be familiar with the functioning of various peripherals in use, one of them being Desktop Scanner (DTS) that plays an important role in converting the image, data from the hard copies on to the computer. At the first glance, DTS looks much like a personal copier. It also shares much of the technology. A desktop scanner serves as the eye of the computer. It can see photographs, capture artwork and read other hard-copy text. Of course, this requires getting interfaced with the computer through appropriate software. By just placing the document on the glass and pushing the desired buttons, the scanner copies the image to the computer. What goes inside a scanner is quite complex. The scanner is equipped with an electronic digital camera coupled with Charge Coupled Device (CCD), which is composed of nearly 2600 photosensitive cells or elements and alight source. In most of the desktop scanners the CCD is only about an inch square and is fixed in place. How it works With the press of the button on the scanner or the command through the keyboard, a light bar moves across the object to be scanned and the light is reflected to the CCD by a system of mirrors. Each cell produces an electrical signal proportional to the strength of the reflected light that hits it. The signal that represents one pixel in the original image is converted into binary numbers and sent to the computer. Darker portions beam less light and are given lower numbers. This image is converted into a digital image that is understandable by a computer. Thus a scanned image is created. Formation A scanned image comprises of a group of dots that join together and form an image. Such an image is called a Raster Image. A raster image is classified in terms of resolution at which it was scanned and the resolution is expressed in DPI (Dots per Inch). More the DPI, the higher the quality of the scanned image. DPI is a fixed number based on the number of cells in the array and the total areas scanned. An array with 2590 cells covering 8.5 inches gives a resolution of 300 dpi. The smaller the area, the better the resolution. Many of images that need scanned are present in different hardware media like paper, transparency, RTFs can be old and may be in poor condition. Technical drawings require high image quality because of the important data present in the media. Hence scanner is provided with a contrast setting. This allows the scanner to distinguish between the faded background of the document and the actual drawing or readable text. In early scanning
devices, the scanners were limited to one value per pixel. Most desktop
scanners today have CCDs that can differentiate 256 shades of grey or
levels of brightness. This is about the same brightness range as a black
and white photograph and roughly twice what the human eye can
distinguish. Since CCDs capture brightness levels, it makes sense that
they can be found in gray-scale scanners, which are used for reproducing
both continuous tone and line art originals. But how does a scanner
capture colour with the same CCD? It is indeed an interesting process
and is based upon the principle that all colours are the combination of
red, green and blue. The CCD creates three separate versions of the
image, one for each if three primary colours of light reflected by the
target. Most colour scanners do this in three passes, one pass with a
red filter records the red component, a second pass with the green
filter records the greed light and a final pass with a blue filter
records the blue. |
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