Abstract: In order to compensate for image distortion introduced into a digitally controlled raster-scan CRT by the finite video amplifier rise and fall times, the digital video drive waveform is subjected to selective pulse stretching to extend the duration of each pel which is immediately preceded by a pel of lower light intensity value (brightness). This is achieved by means of a comparator (14) which examines each current pel PEL(N) in the video data stream in relation to its immediately preceding neighbor PEL(N-1) in order to detect pel boundary transition therebetween representing an increase in brightness from the preceding pel to the current pel. Re-timing means (17, 19, 21, 22) is operably under control of the comparator output to cause advancement in time by a predetermined amount (dt) of any such pel boundary transition relative to remaining pel boundary transitions.

Abstract: An ultrasonic probe (1) for use with ultrasonic imaging apparatus for investigating the internal structure of a body contains a pair of pulse echo receivers (RA1, RB1; RA2, RB2; . . . ) for each pulse transmitter in a linear array of transmitters (T1, T2, . . . ). The two receivers (A,B) in each pair lie in a plane at right-angles to the pulse propagation axis of the associated transmitter and equidistant therefrom. The outputs from the two receivers in each pair are correlated by multiplying in multipliers (11.1, 11.2, 11.3) so that in use the time coincident components of the two waveforms in each receiver pair are emphasized, thus focussing the echo information in the longitudinal plane of symmetry (4) of the probe.