A vertical synchronization signal detector for detecting a vertical synchronization signal in a composite video signal. The detector comprises an input (1) for receiving the composite video signal, a first detector (4,16,22) for detecting equalization pulses occurring in the composite video signal and for generating a first detection signal upon detection of an equalization pulse, a second detector (4,16,20) for detecting horizontal sync pulses occurring in the composite video signal and for generating a second detection signal upon detection of an horizontal sync pulse, a third detector (4,12) for detecting negative going pulses occurring in the composite video signal that have a longer duration than the horizontal sync pulses and for generating a third detection pulse upon detection of such a pulse, a first signal combination unit (FF1) for generating a fourth detection signal (VBI) in response to at least one first and second detection signal generated by the first and second detector respectively, a first counter (58) for counting, when being enabled, the number of occurrences of second detection signals generated by the second detector and for generating a first control signal upon the detection of n occurrences of such second detection signals, where n is a constant integer larger than 1. Further, a second signal combination unit (AND) is provided for combining the third and fourth detection signals so as to obtain a second control signal. A third signal combination unit (FF2) receives the first control signal generated by the first counter and the second control signal from the second signal combination unit and generates in response thereto an output signal which is indicative of the occurrence of the vertical synchronization signal. The first counter is in an enabled state upon the presence of the output signal of the third signal combination unit (FF2).
A method assesses the quality of a television image. In diversity reception installations including several receivers, it is necessary to establish a criterion for selecting the receiver with the best image quality. For this purpose, the five vertical connection impulses are first detected in the video signal. The detection of the five equalization impulses initiates only after the vertical connection impulses have been detected. Then, the detection of the horizontal synchronization impulses, interfering impulses and the echo impulses is carried out only after the equalization impulses have been detected. The number of horizontal synchronization impulses, interfering impulses, and echo impulses detected is used as criterion for selecting the best receiver. The invention is applicable to diversity reception installations including several television receivers, in particular, for mobile installations.
A video signal reproducing apparatus and method for adjusting a change in a horizontal synchronous signal. The video signal reproducing apparatus transforms a format of an input video signal, generates horizontal and vertical synchronous signals, and displays the video. The video signal reproducing apparatus includes a measurer, a comparator, and an adjustor. The measurer measures a period of the horizontal synchronous signal, the comparator compares the measured period of the horizontal synchronous signal with a predetermined reference range, and the adjustor adjusts a period of a clock signal for producing the horizontal synchronous signal, if the measured period of the horizontal synchronous signal fails to fall within the predetermined reference range.
