These scanners have a scanners have a stationery scanner head. Sheetfed scanners can scan only one paper at a time. These accessories are provided as option by many flatbed scanner manufacturers today. It is not possible to scan transparent image with this as they will need special accessories that illuminate them from the upper side. It is then covered with an opaque cover so that no ambient light is able to cross through the opaque cover. In this type of scanner the object to be scanned is placed face down on the glass. Contact image sensors (CIS) scanners have a moving set of red, green and blue LEDs strobes for illumination and a connected monochromatic photodiode array for light collection. The CCD scanners have three rows or arrays of sensors with red, green and blue filters. Under the glass pane, there is a bright light that illuminates the glass pane, and a moving optical array in charge coupled devices (CCD) scanning. The flatbed scanners comprise of a glass pane called the platen. Many fine-art photographers still buy drum scanners because the pre-owned scanners are easily available. The second type of scanners are flatbed scanners that have replaced the drum scanners in most of the scanning jobs except for the high ended applications like museum-quality archiving of photographs where scanning of high quality books and magazine advertisements are needed. Drum scanners become advantageous when a very large scanned image is needed due the capability of drum scanners having resolutions up to 24, 000 PPI. The superior resolutions, value structure and colour gradation of the drum scanners make their demand felt in certain sectors. Although the prices of drum scanners have come down but they are still costlier than the flatbed and film scanners. Drum scanners are manufactured only by a very few companies these days. Nevertheless, the drum scanners are still a matter of choice with regard to scanning of films since films can wet-mounted on the drum and due to the exceptional sensitivity of the photomultiplier tubes. However, with coming into existence of the inexpensive flatbed scanners, the use of drum scanners have become obsolete. The drum scanners could control the aperture and sample size separately. However the output size of the scanned image differed from manufacturers. The original document of maximum 11"x17" size could be mounted on the drum. These scanners derived their name from the clear acrylic cylinder called drum. These scanners scanned the images by using photomultiplier tubes (PMT). The first kind of scanners called drum scanners were first introduced in 1957. Let us discuss these features of scanners in detail. The scanners are most commonly used in modern offices. Digital cameras are based on the concept of reprographic cameras. In the more recent times, digital camera scanners are available as alternatives to the traditional scanners due to their anti-shake, portability and high speed features. 3D scanners take three dimensional models of objects with full colours. There are also planetary scanners to photo books and documents. Rotary scanners are types of drum scanners for scanning documents at high speed. Old drum scanners used photomultiplier tubes as image sensors, whereas the modern scanners make use of charge coupled devices (CCD) and contact image sensors (CIS). The different types of scanners used in modern offices are desktop or flatbed, hand-held and 3D scanners. The image so scanned is then turned into a digital image by the scanner. The image to be scanned may be text whether typed, printed or handwritten, or a picture, diagram of an object. The purpose of an image scanner is to optically scan an image.
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