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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Scanners. History of invention and production
Directory / The history of technology, technology, objects around us A scanner is a device used to enter graphic images into a computer: texts, drawings, slides, photographs, drawings. Most scanners use charge-coupled devices (CCDs) to convert images into digital form. Scanners differ in their scanning mechanism. There are systems with a movable mirror, when the original is stationary, with an integrated scanning head, and systems with a movable document holder, which have a mechanically independent scanning part. According to the method of moving the reading head and the image relative to each other, scanners are divided into manual, roll, flatbed and projection. A variety of projection scanners are slide scanners designed for scanning photographic films. In high-quality polygraphy, drum scanners are used, in which a photomultiplier tube is used as a light-sensitive element.
The principle of operation of the most common single-pass flatbed scanner is that a scanning carriage with a light source moves along the scanned image, located on a transparent fixed glass. The reflected light through the optical system of the scanner, consisting of a lens and mirrors or a prism, falls on three CCD-based photosensitive semiconductor elements arranged parallel to each other, each of which receives information about the image components. The light source used in the design of a particular scanner to a large extent affects the quality of the resulting image. Four types of light sources are currently in use. Xenon discharge lamps are characterized by extremely fast turn-on times, high radiation stability, small size and long service life. But, on the other hand, they are not very efficient in terms of the ratio of the amount of energy consumed and the intensity of the light flux, they have an imperfect spectrum, which can cause a violation of color accuracy. In addition, they require high voltage - about 2 kV.
Hot cathode fluorescent lamps have the highest efficiency, a very even spectrum (which can also be controlled within certain limits) and a short warm-up time (about 3-5 seconds). The negative aspects include not very stable characteristics, rather large dimensions, a relatively short service life (about 1000 hours) and the need to keep the lamp constantly on during the operation of the scanner. Cold cathode fluorescent lamps have a very long service life (from 5 to 10 thousand hours), low operating temperature, and a flat spectrum. The design of some models of cold cathode lamps is optimized to increase the intensity of the light output, which negatively affects the spectral characteristics. For the listed advantages, you have to pay for a rather long warm-up time from 30 seconds to several minutes. These lamps also have higher power consumption than hot cathode lamps. LEDs have very small dimensions, low power consumption and do not require warm-up time. In many cases, three-color LEDs are used, which change the color of the emitted light at a high frequency. However, LEDs have a rather low (compared to lamps) light intensity, which reduces scanning speed and increases image noise. A very uneven and limited emission spectrum entails an inevitable deterioration in color reproduction. To scan opaque originals and transparencies, slides and negatives, there are flatbed scanners with a slide module. Three or four years ago, these scanners were quite expensive. Relatively high prices were justified by the design complexity - after all, for scanning in transmitted light, an additional light source was used, located above the tablet in a special cover and moving synchronously with the carriage.
Currently, a new generation of low-cost "tablets" with slide modules has appeared, the main distinguishing feature of which is the use of a fixed light source to scan transparent originals. This solution eliminates the need for a cumbersome and expensive mechanical system, and, consequently, significantly reduces the cost and improves reliability. Of course, such a solution is not without drawbacks - to provide the required intensity of the luminous flux, a lamp of much greater power is required than in the case of using a moving light source, which, in turn, significantly increases energy consumption and the amount of heat generated during operation. Even more challenging is the need to provide stable and uniform illumination of the scan area. To meet these requirements, while maintaining reasonable prices for such products, it was necessary to come to some compromise. Realizing that the vast majority of transparent originals scanned at home are 35mm negatives and transparencies, manufacturers have reduced the maximum size of the area scanned in transmitted light. The lower intensity of the light flux was compensated by an increased exposure time, sacrificing scanning speed. Author: Musskiy S.A.
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