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Of visible light rays - electromagnetic waves that occupy a narrow region of the range of electromagnetic waves from 0,4 to 0,76 microns. Electromagnetic fluctuations in the area of waves perceived by the human eye as the light of different colors human eye has different sensitivity to light of different wavelengths and equal power.
The main Lighting values are: luminous flux, luminous intensity, brightness and luminosity. Radiant flux characterizes the radiation energy per unit of time. It represents the radiation power measured in watts.
Luminous flux F - part of the radiant flux, perceived by the eye to light.
Often have diffuse reflection of incident light from the surface of objects as part of the light is absorbed by the reflecting surfaces Some items reflect nearly all incident light and appear bright, while others reflect little light and appear dark .. The human eye is an end device, the perceived image of the object being , so its properties and characteristics are taken into account when constructing television systems. Eye is an optical system. The role of the lens does the lens through which images of the surrounding objects are projected onto a photosensitive retina. Change the curvature of the eye's lens focuses the image on the retina of objects at different distances. Pupil, like the automatic diaphragm, Camera, shrinks or expands depending on the brightness of the light source (the eye is adapted). Retinal tissue is composed of many light-sensitive nerve endings. According to the theory of the dual view, there are two types of nerve endings - receptors: cones and rods. Cones have a low light sensitivity and cease to respond to light at low illumination, but are able to distinguish color and detail images. Sticks do not have the ability to distinguish colors, but have a much greater light sensitivity for black-and-white images. The central part of the retina contains mostly cone cells, and peripheral-cones and sticks. The density of cones is much lower at the periphery of the retina. Rods and cones through a complex nervous system, consisting of a set of nerve fibers associated with the visual center of the cerebral cortex. Light stimulation of retinal cones and rods are transmitted to the brain separately from each end of the optic nerve. From the description of the structure of the retina that of visible image of the object can be decomposed into many tiny elements. The main characteristics of view, which should be agreed upon parameters and properties of the television system are: visual acuity, spectral sensitivity, inertia, contrast sensitivity. Visual acuity (resolution of the eye) is characterized by limiting the eye's ability to see fine detail. There is a two-dimensional and three-dimensional visual acuity. Two-dimensional visual acuity as a resolution of the eye for planar imaging, three-dimensional - for the bulk (stereoscopic).
. Visual perception of a person can change the brightness of the object obeys the logarithmic 'law, which can be explained as an example. Inertia is the eye's ability to maintain visual sensation of a single light pulse for about 0.1 sec.
Only modern electronic television allows the most qualitative to transmit images over long distances.
Principle of the television system is easier to consider the example of the transfer of black and white images. Optical image of the object being through the lens is transferred to a photosensitive surface - sensor video, in which the conversion of optical images in the image signal (video signal).
The law of electric charge distribution under the influence of light rays in the plane of the photocathode is determined by the different light of its individual sections and the relevant laws of the brightness distribution of the object being. Transfer process on the elements of an electronic television image is called interlaced images, and the sequence of transfer elements - the way the sweep. Education video is three scan electron beam electron image at the target transmission tube. Instantaneous values of voltage (or current) proportional to the video brightness values of individual elements of the transmitted image. The more elements of the expansion of the image in a television system, the above can be obtained from the reproduced image clarity, and the closer it is to the original. Over a communication channel consisting of radio images, lines of communication and a television receiver, is transmitted at each time an electrical signal only one element of the expansion of the image. In the enhanced video introduces additional signals necessary to generate enough high-quality images: sync, blanking interval, as well as others, which will be discussed below. This signal is called a complete television signal.
In the receiving device selected composite television signal is amplified and fed to the input of electron-beam receiver cabin (CRT) that converts electrical energy of video signal in the optical image. The device synchronization television set from a complete television signal allocated synchronization pulses, which are used to operate the scanner CRT. Synchronicity scanning electron beams in the transmission and reception is a precondition for proper imaging, the sequence of transmission of television signals is determined by the method of scanning, the easiest way to scan - by the line at which the electron beam at the target transmission tube and on the background picture tube makes a uniform motion of parallel lines, lines, collection of all lines is called frame
Movement of the beam from the beginning to the end of each line forms a right turn. The return beam from the end of the previous line to the beginning of the next call Recoil sweep Similar definitions are given for the field sweep. The duration of backward moves horizontal and personnel developments significantly less than direct, as the image of these intervals is not transmitted. TV scan following parameters: number of lines per frame and number of frames per unit time ..
In the systems of television frame rate is chosen exactly equal to the frequency of power supply, which reduces the impact on image noise from the mains. Exact equality frame rate frequency network is called "binding" the frame rate to the frequency of the network.