GB1509975A - Recording apparatus coding circuit for an image signal and corresponding decoding circuit - Google Patents

Abstract

1509975 Television THOMSON-CSF 21 Oct 1975 [22 Oct 1974] 43230/75 Heading H4F A coding circuit for processing a television image signal before the recording thereof, comprises a clock 2, Fig. 1, of frequency f, where f is the frequency bandwidth of the image signal; means 3, synchronized by said clock, for generating brief sampling pulses of frequency f/2, whose instants of occurrence, relative to the start of the active line duration, are during one frame period out of two shifted by a period T = 1/f relative to their occurrence during the other frame periods; a sampling and holding device 5 having an input for receiving the image signal, and a control input for receiving said sampling pulses; a low-pass filter 6 having a cut-off frequency equal to f/2; means 13 for generating a burst signal formed by a train of sampling pulses in each horizontal blanking interval; and a mixer 19 receiving the output signal from said filter and the burst signals. The circuit may code an image signal directly from a camera, a sync. generator 7 being provided for supplying horizontal and vertical sync. signals both to said camera and to said mixer, said sync. generator having a synchronizing input coupled to clock 2 through a gating circuit 12 having a control input, and comprising means for delivering to said control input a pulse at half the frame frequency for blocking circuit 12 for this pulse so as to shift by T the image signal delivered by the camera for the duration of one frame period out of two. There is provided also a decoding circuit, Fig. 2, comprising two input channels 21, 22 for respectively receiving the signals from two pick-up units simultaneously reading recorded signals relative to two consecutive frames. Two sampling and holding devices 31, 32 are coupled respectively to said channels. A separator 28 extracts the burst signals included in the signal from channel 21. A generator 30, synchronized by a clock 27 in turn synchronized by the burst signals, delivers two series of sampling pulses of frequency f/2, shifted by T, respectively to control inputs of devices 31, 32. A common output channel including an amplifier 35 is coupled to a common output of devices 31, 32.