Patent GB-966319-A (GB)
Title: Improvements in and relating to equipment for television and like purposes
Inventor: DAVIES ROBIN EVAN
IPC: H04N7/12
Filed: 1962-01-25
Abstract: 966,319. Television. BRITISH BROADCASTING CORPORATION. Jan. 25, 1963 [Jan. 25, 1962], No. 2846/62. Heading H4F. A mean line signal (r), Fig. 1, suitable for interpolation between two input line signals (a) and (b) containing edges (i.e. brightness changes) at times t 1  and t 2 , is derived with an edge which occurs at a time tm equal to the mean (t 1 +t 2 /2) of the times of the original edges and which has a height equal to the mean of the heights of the original edges. To perform the operation the input signals are rendered concurrent in time by delaying the earlier by one line-scanning period. Since the mean time cannot be determined until both edges have appeared, the mean line-signal is made available after a constant-delay time T. In Fig. 2 the original signals, which appear at terminals 1 and 2 are combined in a circuit 3 to give an arithmetic mean line-signal (i) and this signal is delayed by a time T in a device 7 to give signal (q) which is applied to an adder 15. The signal (i) is also differentiated in a circuit 4 to give signal (j) which is applied to a gate 6 via a device 5 producing a short delay a. The original signals are each differentiated in circuits 16 and 17 and the resulting pulses (c) and (d) applied to control gate 6 via OR gate 20. If either pulse has a height greater than a predetermined value, i.e. if either edge has a slope greater than a predetermined value, gate 6 is opened and signal (j) passes to a charge-discharge device 10. Delay a corresponds to the delay introduced by circuits 16, 17, 20 and 6. Device 10 functions to produce a pulse (1) which when integrated is equal to the sum of the integrals of the pulses in signal (j). Pulse (1) is released from device 10 at the correct mean time 1=tm (see below) and is combined in adding circuit 12 with a signal (n) corresponding to signal (j) delayed in device 8 by a time T - a and reversed in polarity in circuit 9. The resulting combined signal (0) is integrated in circuit 13 to form a signal (p) which when added to signal (q) will produce the desired mean line-signal (r). Signal (p) is applied to adder 15 via a gate 14. Gate 14 is controlled via an AND gate 26 from pulses (c) and (d) which are lengthened in circuits 24 and 25. The purpose of gate 14 is to inhibit the addition of signal (p) to signal (q) unless pulses (c) and (d) both have a height greater than the said predetermined value. Release of signal (1) from device 10 at the mean time is effected by applying pulses (o) and (d) to control constant-current sources 18 and 19 to produce signals (e) and (f) which are added in circuit 21 and integrated in circuit 22. The resulting potential variation (h) operates device 10 via a level discriminator 23 set to respond at a level V such that signal (1) is released at a time determined by the mean of the edges in signal (e) and (f) plus the constant delay time (T). If desired, the control exercised by either gate 6 or gate 14 may be dispensed with. According to a modification, the input line signals need not be equally weighted when added in circuit 3. The rates at which sources 18 and 19 feed current to integrator 22 may be correspondingly weighted with the result that the edge in signal (r) does not occur at the mean time of the input edges. Such an application of the invention may be employed when it is desired to interpolate a line at other than the midway position. Reference is also made to the use of weighting where more than two lines are combined to derive a mean signal and it is desired to attach more importance to lines immediately adjacent the position of the line to be interpolated. Reference is made to the application of the invention with conventional parallel line scanning, radial line scanning and spiral scanning. Specification 966,318 is referred to in connection with the application of the invention to a standards converter system.