Abstract: A digital television signal includes data sent as multilevel symbols in successive data segments each including a synchronizing sync character. The detected synchronizing sync character produces a characteristic having two opposite polarity levels separated by a zero reference level, with the levels occurring at successive sampling points of the television signal, and a detection signal that has a peak occurring in time coincidence with the zero reference level. The detection signal controls sampling of the received television signal. The gain of the received signal is controlled by an AGC circuit that also responds to the detection signal.

Abstract: Synchronization signals for a digital device are derived for an analog composite video source by computing during a "synch-up" phase the average duration of a low synchronization portion of the signal and the average duration of a high active portion of the signal over a predetermined number of lines separated by the synchronization portions. During subsequent operation, the duration of low times and high times as they are encountered in the unknown signal are compared with their respective average durations. If the duration of a low time is significantly longer than the average low time, a vertical synchronization signal is indicated, the vertical synchronization signal being about 20 times longer than the horizontal synchronization signal in a typical video format. Similarly, if the duration of a high time is significantly shorter than the average high time, a video half line is indicated.

Abstract: Picture quality is improved by reducing an influence such as an illumination unevenness caused on the low band side by providing an image signal correcting device comprising a logarithmic compressing device for logarithmically compressing an image signal, a two-dimensional filter device of a characteristic of suppressing the low band side and relatively enhancing the high band side of this logarithmically compressed image signal and an exponential converting device for converting the image signal having passed through this two-dimensional filter to be of an exponential characteristic.