| 摘要 |
In present video equipment for recording a colour video signal on a magnetic tape the what is commonly referred to as the "colour under" transmission method is used. Therein, starting from the composite colour video signal, luminance and chrominance signals are separated from each other and both bandwidths are considerably limited. The frequency band of the luminance signal is converted to a first transmission band by means of frequency modulation. The frequency band of the chrominance signal is converted by means of amplitude modulation to a second transmission band located below the first band and which does not overlap this first transmission band.
<??>In order to counteract considerable bandwidth limitation of these two signals and to reduce the influence of transmission noise on the chrominance signal, a transmission method is now proposed which will be denoted as the "color shift" method. Therein the composite colour video signal which is formed by a sequence of analogue line signals is sampled, as a result of which each analogue line signal is converted into a time-discrete line signal formed by a plurality of line signal samples occurring at a rate fs, each sample being formed from the sum of a luminance and a chrominance signal sample. Thereafter, these time-discrete line signals are submitted to a scrambling operation in which in accordance with a predetermined pattern a number of line signal samples is each time selected from the line signal samples of a group of time-discrete line signals for assembling time-discrete auxiliary line signals. This selection is effected such that of all those line signal samples which together represent a given time-discrete auxiliary line signal the associated chrominance signal samples all have the same polarities. As a result thereof the chrominance signal is converted without bandwidth limitation to a lower frequency band, while it continues to be located within the frequency band occupied by the luminance signal. This new composite colour video signal can now, after having been converted into an analogue signal, be transposed in its totality to a suitable transmission band by means of frequency modulation. |
