نظام سيكام ( SECAM) الفرنسي ١_a .. كتاب التلفزيون الملون والعادي

9-3 The French SECAM system: It is called the Séquential Couleur à Memoire system, and it is a system developed by the French scientist Henri Dufrance. It relies on sending the luminance signal continuously, Figure (3) - (26). While the two differential signals (BYR-Y) are transmitted alternately with the scan lines. In the first line, for example, the luminance signal is sent () + (R-Y)), and in the second line, the luminance signal is sent (BY) + (Y), so
This system is the reciprocal system. In each scan line, there is one coloring sign - so the single lines have the first sign ((R-Y) and the double lines have the sign called
(B-Y)
We have mentioned in the (NTSC) system and the PAL system that the three signals. They are the luminance l and the chromatic aberration I and are correlated with each other in each raster. Therefore, let the simultaneous system (Fig. - 4 - 6 - 8 But the color image requires the three signs (E- LE, E - , (Y) or (DY, DR) in almost every element of the color image.
In order to achieve the convergence of the three signals (the color difference signal + the luminance signal (Y) in each scan line, the delay line delays the switch output signal for a period of (64) microseconds), which is the scan time.

The signal carrying the color difference takes two paths. A - A direct way to accompany the luminance signal not in the scan line B - The delay line way to accompany the second color difference signal and the luminance signal is a horizontal line Y Also in the next line

. That is, if we assume that in the first line you enter (R-Y). And the luminance signal also. In the second line, (BY) and the (R-Y) signal entered and exited the delay line after (64 microseconds) along with the luminance signal as well. In the third line, the (R-Y) signal, the rear (B-Y) signal, and the luminance signal L enter. And so in the rest of the lines - the delay line was a measure of memory that preserves the color difference signal information for each line for a period of (64 microseconds) to return the color information to it to be added to the next line

It is noted by this process that the color information is repeated for each two consecutive lines, as if in the picture the color information has been reduced to half - that is, about (300) lines) of color, so the effect of this reduction is not felt by the human eye. And it appears correct - and with the image, the colors and clarity are acceptable - but the luminance signal is not, it is continuous as in the rest of the systems. The main advantage of this system (SICAM) is that interference between the two color signals does not occur because they do not meet together in the transmission channel. Y is not affected much The resulting nonlinearity in the device.
The block diagram of the coding unit in the SECAM system. The shapes that show the shapes of signs in each of the designated places on the drawing are shown below.