GB1327419A - Method of and means for recording line drawings on the screen of a cathode ray tube under computer control - Google Patents

Abstract

1327419 Cathode-ray tube displays DRING RUDOLF HELL GmbH 16 July 1970 [16 July 1969] 34632/70 Heading H4T In an arrangement for achieving uniform brightness in the tracing of line drawings on the screen of a cathode-ray display tube the lines are approximated by a plurality of straight lines of different lengths (Fig. 1) the co-ordinates of which are supplied by a computer as respective #x, #y, voltages which control respective deflection generators producing sawtooth waves of constant duration but with slopes proportional to #x and #y respectively, the #x and #y quantities being squared, added together and the square root of the sum extracted to provide a quantity for intensity control of the tube beam. Alternatively the latter quantity is formed by multiplying the sum and difference of #x, #y by constant respective factors and adding the resultant quantities. Fig. 2 shows one embodiment in which the sawtooth generators 63, 64 are controlled directly by the co-ordinate values #x, #y during equal intervals determined by a pulse generator 65 whilst the intensity of the tube beam is controlled as a function of deflection velocity by squaring #x, #y in respective operational amplifiers 53, 54, summing the outputs of the latter in adder 57 and employing the summed output to control an operational amplifier 59 producing the function ##x<SP>2</SP> + #y<SP>2</SP>. The latter quantity is then supplied to the intensity control means of the tube 22 via a correction circuit 61 which predistorts the control function voltage to compensate for the non-linear relationship between it and the light intensity produced by the tube. In a modification of the latter embodiment which avoids errors, particularly at low deflection velocities, in electronically squaring and subsequently forming the square-root, the function for controlling the beam intensity is produced by forming the sum and forming the difference of the co-ordinate values #x, #y and then adding such sum and difference to form the input to the correction circuit 61 (Figs. 3 and 4, not shown). In a further modification, the input to the correction circuit comprises, in addition to the sum and difference as in the last modification, further inputs derived by subtracing from the difference input predetermined fractions of the sum input. (Figs. 5 and 16, not shown.)