تشكيل الصورة على الشاشة ١_a .. كتاب التلفزيون الملون والعادي

As for a drawing of its points on 1-4 forming the image on the screen, when the device is turned on on a channel that does not have television transmissions, the screen lights up in a white color called the linear structure of the image (raster), and we have mentioned that this illumination is formed by a single point that scans the screen, and is directed by the deflection coils horizontally and vertically. The image is controlled by this beam at each point of the screen, so the color of the bright point changes between complete darkness, which is the black color, and between full light, which is the white color. The beam was a pen or brush that draws point after point with the appropriate color for each point between black and white. As for the colored device, each point is drawn by three colors - red, green and blue, according to the chromaticity given by the color pigment corresponding to the image sent from the station. If each of the lines from the top to the bottom of the screen corresponds to the image broadcast by the station, and puts it in its correct place, as well as the movement of synchronized images, it is secured by special pulses called synchronization pulses, which are pulses for horizontal synchronization and pulses for vertical synchronization. And the horizontal and vertical extinguishing pulses that erase the impact of the rebound or return of each line. The formation of each image on two fields is followed in all television systems, because it makes the image stable and free from flicker and vibration. Each frame consists of (3125 horizontal lines.. and the number of images per second (25) (image) and in some systems (30 images per second). The number of image points can be calculated as follows according to the European System (CCIR)

526 3/4 526 = 526025 points

The aspect ratio is the ratio of the width to the height of the screen. As for the number of points or image details per second, it is: 520625 25 = 13,015,625 points or statement, i.e. about 13 million points, detail or statement per second. And let us not forget that the phenomenon of impression and permanence are all that is depended on in seeing scenes and animated images close to living reality, although it is a single point that moves quickly. very,
Its trace in the eye does not disappear until after 1/16 of a second. Also, the illumination of this point on the screen does not disappear after the movement of the beam that caused it, except after a certain time.

Figure (10-1) The number of image details is 625 points, which is the number of horizontal scan lines. 833 points represent the image length details, because the screen ratio is 3/4 - screen length / screen height .

Figure (1-11) The process of scanning the horizontal manuscript on two fields for each image. The black line represents the first field and the dashed line represents the lines of the second field. Note the way the line returns from the bottom of the screen to the top after the first and second frame.

Requirements for a good image In order for the details and elements of the image to be acceptable, good, and close to the living reality, and to the image or scene broadcasted by the transmitting station, the following must be achieved: 1- The accuracy of the beam as possible, and this is achieved with the appropriate voltage of the focus electrodes and the components of the screen coating.

2- The number of raster lines is very large, and it is 625 lines in the European system used in Europe and the countries forming the former Soviet Union, and some Arab countries, including Syria, Lebanon and Jordan, in America 525 lines, and in the French system 819 lines, and in the French system 819 lines.
Al-Britani has 405 lines, and increasing the number of lines enables sending and receiving more details in a single image. Correct synchronization of the image and free from distortion, vibration, volatility and ripples. 4 - Lighting, appropriate contrast and accuracy of the details of the elements between the transmitter and the receiver. e - Color matching with reality in color TV.

1-5 The composite visual signal and its components

The television camera at the transmitting station decomposes each image into lines similar to a horizontal raster. The image elements are transformed into electric charges whose voltage is identical to the levels of the image elements in terms of lighting and color between black and white. As for the other signals, they are blacker (blacker than black) so that they do not appear on the screen; Rather, it only passes through its designated circuits, and the station carries all these signals on a high-frequency wave, and the receiver receives them through the antenna, the voter, and the various circuits, to retrieve these signals as they were sent, so pictures and scenes appear on the screen, just as the sound appears from the speaker in the audio section of radio or television. Figure (1-12) the composite visual signal contains the following:

1- Image signal: (Video) which is the changes in the lighting of the image elements, so that the voltage of the cathode or the grid governing the screen LED changes, according to each point in the image or its level of illumination. The white color is generated by the largest positive voltage on the cathode - or the largest negative voltage in the governing grid. This is consistent with the adjustment method used in the screen valve. .

As for the black color, it is generated by the weak positive voltage on the cathode or the weak negative voltage of the governing network - and the frequency of the image signal ranges between 5 Hz to h megahertz.

2- SYNCHROPULSES:

It is sent with the composite visual signal to adjust the synchronization of the scanning and beam movement in the transmitter and receiver. Without any progression or delay in place or time, these pulses have a rectangular waveform. It is also generated in the receiver when it is turned on, even on a channel in which there is no transmission, by means of the horizontal oscillator and the vertical oscillator, and it is divided into:

A - Horizontal synchronization pulses: They determine the beginning of each horizontal line and the moment of its return after the end of the scan, and the amplitude of the pulse is between 75-100% of the amplitude of the composite visual signal, while the largest amplitude of the visual signal of the image does not exceed 75% only (Fig. 1 - 13). The pulses are located in a black area of ​​(black, that is, their effect is not visible on the image on the screen. The frequency of the horizontal scan lines is the frequency of the horizontal synchronization pulses, which is 15625) (Hz). The pulse width is equal to (9) times. Single line scan i.e. 1 x : 15625 - 5.76 microns (sec) and scan time per line (64 microns)
B - Vertical synchronization pulses: They are the ones that determine the moment of the ray bounce after the end of scanning each field - and they are located in the black area of ​​the black - and the amplitude of these pulses ranges between (75% to 100%)