GB1019811A - Improvements in and relating to the conversion of television signals from one standard to another - Google Patents

Abstract

1,019,811. Television. BRITISH BROADCASTING CORPORATION. June 28, 1963 [June 22, 1962], No. 24191/62. Addition to,928,730. Heading H4F. The invention comprises a modification of the television line standards converter described in Specification 928,730 and is concerned with preventing degradation of picture quality when interlaced scanning is employed. In the apparatus described in Specification 928,730 the output derived from any one storage element is determined by input signals derived from adjacent lines of one interlaced field. According to the present invention the output is determined by input signals derived from adjacent lines of a picture, the general procedure being to delay the input signals by a period of the order of one field duration so as to make available by way of the direct and delayed signals information relating to adjacent picture lines. In one way of carrying out the invention, Fig. 6, the input switch 30 is provided with two inputs 29 and 32 which operate at points spaced apart by one half-line. The input signals are applied directly to input 29 and via a one field duration delay 31 to input 32. Each storage element 33 thus receives (during the scanning of one input signal line) two inputs corresponding to aligned picture points on adjacent picture lines. Another embodiment, Fig. 1, is based on the modification described in Specification 966,318 where the storage elements are capacitors 20 and the input signal is derived by an interpolating arrangement 12, 14, 15 whereby the contributions of the two input signals are varied by a function generator 27 which applies a signal r to modulator 12 and a signal 1-r, by way of inverter 28, to modulator 14. The function generator is controlled by a sawtooth generator 26 synchronized at the difference of the input and output line rates by signals from separator 23 and generator 25. For the purposes of the present invention the input B to modulator 12 is obtained via a unit having a delay of one field plus one-half line, whilst the input to modulator 14 is determined by switch SW and comprises either the original signal obtained directly or the signal A when delayed in unit 13 by one line. Signals at B, C and A thus represent respectively the information from a point in a line in one field and the information from aligned points in the adjacent lines in the next field, i.e. the points all occupy adjacent picture lines. The form of the signal from function generator 27 is illustrated in Fig. 4 where Tw denotes input writing (i.e. line) time and Tr output reading (i.e. line) time. The Figure also shows the operation of switch SW. The solid line curve shows the nature of the function where it is desired to simulate a sine-squared filter response (i.e. to simulate the operation of the basic system of Specification 928,730 where the filters have a sine-squared response); the dotted line shows the function where linear interpolation is required. A modification is described, Fig. 5 (not shown) where modulator 12 receives an undelayed signal and modulator 14 receives (via switch SW) signals delayed by one field minus one half-line and one field plus one half-line. The basic operation is similar to Fig. 1, but the arrangement may be adapted as described with reference to Fig. 7 (not shown) so as to permit each of signals A, B and C to have subtracted therefrom adjustable proportions of signals due to adjacent picture lines with the object of correcting for imperfect erasure in a camera supplying the original signal. Reference is made (without giving details) to the use of more than two input signals to determine the entry in each storage element. The need for two modulators 12 and 14 may be dispensed with by an arrangement in which the difference of the two input signals is derived and operated on in one modulator by function r and then combined with the second of the two signals. Fig. 1 illustrates an arrangement where conversion is to a smaller number of lines. Where the number of lines is increased, the number of switch input arms is increased together with a corresponding increase in interpolating arrangements. Magnetic recording and ultrasonic delay systems may be used for the delay devices with retro-active control in response to synchronizing pulses to stabilize operation of the precisely correct delays. The switches 'shown in Figs. 1 and 6 are in practice electronic switching systems.