التلفزيون الملون - كيف يعمل جهاز استقبال التلفزيون .. الإلكترونيات

Color TV - How does a TV receiver work .. Electronics

Color TV

It is possible to obtain all colors, except black, by mixing three primary lights, which are red, green and blue.

It is known that mixing colored lights is completely different in its results from mixing dyes, as the absence of all colors gives us black, while we get yellow by mixing red and green together. As for the crimson color, we get it by blue and red, while the bluish-green color is produced by mixing blue with green (177). It is known that mixing red, blue and green colors by 40%, 26% and 34% respectively is sufficient to give the white color again.

In order to send a color image, the scene must be scanned by cameras sensitive to the three primary colors, blue, green and red, which can be reproduced in the receiver. Other colors are produced by changing the intensity of the red, blue, and green channels appropriately.

Figure (178) shows a color imaging system, which includes mirror A, which allows red to pass through it, but reflects green and blue, and mirror B, which allows blue to pass through but reflects green, which in turn is reflected by mirror C.

177 - Color mixing.

178 - How to obtain color signals for transmission.

In this way, the scene can be scanned and separated into its three colors, each of which gives its own signal. There are other arrangements for these mirrors by which the scene can be scanned and the same results obtained.

As for reproducing the image in the receiving device, it is done by using three projection tubes, one for red, the second for blue, and the third for green, and each of them receives the color signal assigned to it (179).

Another method of reproducing a color image is by using a valve containing what is called a shadow mask, which is characterized by three separate cathodes (180), each of which emits a beam controlled by a signal whose intensity is proportional to one of the three primary colors: red, green, or blue. Inside this valve and on the path of the rays, a mask containing many small holes is placed, and it is mounted so that all the rays of the cathodes, entering from different levels, intersect and all pass through the same hole, so that each one falls on the phosphorescent point or grain that lights up in the color corresponding to the ray falling on it. In addition, the screen is painted so that the colored beam collides with the signal of the same color. It is worth noting that these phosphorescent points are small so that they dissipate on the screen relative to the eye, mixed with the desired color degrees.

179 - A system with three valves for receiving colored signals.

180 - Color device valve.