Format of analog video

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There are three types of analog video formats: The NTSC system used in North America, Japan, etc., for PAL systems in Western Europe and China, and for the use of SECAM systems in Eastern Europe, Russia and other place. The following main introduction of the domestic application of a wide range of PAL video signal formation principle. According to the three-color principle, the use of R (Red), G (green), B (blue) Three different proportions of the mixture can represent a variety of colors. The camera converts the light signal to an RGB tri-primary signal by means of a photosensitive device such as a CCD: charge-coupled device. In the television or monitor, the RGB signal is used to control the electron flow of the impact screen of the three electronic guns respectively, so that the image is generated by the light. Since the original signal in the camera and the final signal in the TV and monitor are RGB signals, the use of RGB signals as video signal transmission and recording will undoubtedly have a higher image quality. In practice, however, this is often not the case, because it greatly widens the bandwidth of the video signal, increases the cost of the associated equipment, and the second is incompatible with the current black and white. The three primary colors are combined into luminance (Y) and chroma (U,V) signals in a certain proportion, and the relationship between them is as follows: In order to enable U, V and Y to transmit in one frequency band, to achieve the purpose of receiving compatibility for the black/white/color video signal, the two chroma signals need to be modulated in quadrature amplitude. Set U (t), V (t) is the chroma signal, Y (t) is the luminance signal, then the modulated two chroma signal is: U (t) =u (t) sin (ΩSCT) V (t) =v (t) Φ (t) cos (ΩSCT) (1.2): ωsc= The 2ΠFSC is the subcarrier angular frequency of the chroma signal, and Φ (t) is the switching function. The resulting quadrature amplitude modulated chromaticity signal is: C (t) =u (t) +v (t) =c (t) sin[ωsct+θ (T)] (1.3) wherein: θ (t) =φ (t) TG-1[v (t)/U (t)]C (t) = φ (t) is a switching function, such as φ (t) = 1, can represent the color signal of the NTSC system, such as φ (t) =+1 (even line) or 1 (odd line), can represent the color subcarrier progressive inverted phase of the PAL system chroma signal. In PAL system, chroma secondary carrier frequency Fsc=283.75fh=4.43mhz, line frequency fh=15.625khz, Frame frequency =25hz, field frequency =50hz. In the NTSC system, the chromaticity subcarrier Fsc=227.50fh=3.589545mhz, the line frequency fh=15.75khz, the frame frequency =30hz, the field frequency =60hz. The image aspect ratio is 4:3 for both formats. From the spectrum of the video signal, the sub-carrier of the chroma signal is located at the high frequency of the luminance signal spectrum, as shown in Figure 1. In this way, the high-frequency portion of the luminance signal is inserted through the orthogonal modulation of two Chroma components to form a color TV baseband signal, also known as composite TV signal or full TV signal: E (t) =y (t) +c (t) = Y (t) +c (t) sin[ωsct+θ (T)] (1.4) Figure 1 The spectrum of composite video signal (PAL system) The application of composite video is mainly for the convenience of transmission and television signal transmission. In order to ensure the stable reproduction of the transmitted image, the actual full-TV signal includes the composite synchronization signal (including the line field synchronization, the line field blanking) and the color synchronization signal. Described above is the color TV signal, black and white signal can be regarded as a special case of color TV signal, the condition is that at this time C (t) = 0. Recently, many video devices have added S-video output terminals In addition to the composite video output. The s-video signal outputs the luminance Y (t) and Chroma signal C (t) in two lines, so that Y and C are combined to output and then output to another device and then the Y and C are separated. Such a repetitive process is detrimental to image quality. Like movies, video images are made up of a series of individual stills that are called frames. Generally when the frame rate between 24~30 frames per second, the video image motion feeling is relatively smooth and continuous, and less than 15 frames per second, continuous motion image will have a sense of animation. Our country's TV standard is PAL system, it stipulates 25 frames per second, each frame has a horizontal direction of 625 scan line. As a result of interlaced scanning, 625 lines of scanning lines are divided into odd and even lines, which constitute odd and even two fields of each frame. This creates a 50/s field frequency, further reducing the flicker of the TV screen. Since the electron beam is scanned from top to bottom in each frame, there is a scanning inverse of the electron beam from the right to the left of the screen, and from the bottom-right corner of the screen to the beginning of the upper-left corner of the screen. During this period the hidden scan line is impossible to carry the image content, the field scan inverse period accounts for about 8% of the total vertical scan time. Similarly, in the entire 64μs scan cycle, the effective scan time (carrying information) is approximately 52μs.

Format of analog video