Patent GB-1467243-A (GB)
Title: Scan conversion arrangements
IPC: H04N7/00
Filed: 1973-06-20
Abstract: 1467243 Scan conversion EMI Ltd 4 June 1974 [20 June 1973] 29333/73 Heading H4F Signals from a line scan system carried by an aircraft, in which movement of the aircraft provides the frame scan, are fed to storage means, 10, 11 operating to store input signals at the rate at which they are produced and read them out at a rate compatible with a television display, the signals prior to this storage, being processed at 3, 7, 8 so that the signals corresponding to a number l of lines from the line scan system are combined to form a single line of the signals to be stored, the number l being varied in response to variations in the ratio of the velocity V of the aircraft to the height h of the aircraft so that the quantity and hence the display resolution in the frame scan direction, is maintained substantially constant. In the embodiment shown in Fig. 1 for converting signals from an infra-red scanner having a line period of 2 ms into interlaced television signals of 625 lines per frame, 50 fields per second, the input signals are applied to an analogue-to-digital converter 2 and then to a low-pass filter 3, including a one-line delay 5, acting as an integrating circuit, a divider 7 and a switch 8 closed for one line period of the input signal in every l (e.g. ten) such periods. The signals from switch 8 are fed via switch 9 to store 10 or 11, each store storing n (e.g. 2, 4 or 6) line signals from switch 8; when store 10 or 11 is full switch 9 is changed to supply the following n line signals to the other store and switch 12 is changed to read, from the full store the stored signals at television line rate. These signals are fed via switch 13, changed over at the end of each television line period, and switches 14 15 (which are in their positions * when signals are being read from store 10 to 11) alternately to field stores 16, 17, which store the signals representing the respective interlaced fields for the television display, the signals from the store 10 or 11 being inserted at the top of the display and replacing signals at the bottom of the display. In the period between application of signals from stores 10, 11, the signals in stores 16, 17 are recirculated via switches 14 15 and are read-out via switch 18 operated at the end of each field period to terminal 19 and thence to a low-pass filter 21, including a one picture point delay 22, and a divider, providing averaging in the line scanning direction, a switch 23 closed for one picture point period in every p (e.g. two) such periods, random access memories 25, 26 and digital-to-analogue converter 20 to an output terminal 28. To perform zooming in the frame scan direction the rate of operation of switch 8 is changed to alter l, factors k and k<SP>1</SP> applied to multiplying and dividing circuits 6 and 7 respectively being altered correspondingly. For zooming in the line scan direction the rate of operation of switch 23 is changed to alter p with corresponding alteration of factors c and c<SP>1</SP>, and the position of writing in memories 25, 26 is altered; e.g. p is two and signals are written in memories 25, 26 in positions “-¥ of the way along the memories. In an alternative embodiment (Fig. 2, not shown) for providing a 1700 line display the signals from l lines are combined in an integrator (30) having an adder receiving the input signals and the output of a shift register, the adder output being fed to the shift register; when the signals from l lines have been added the sum is divided by l and this signal is fed to an intermediate memory (31) from which signals are transferred to the main memory (33) once per television frame period. In this embodiment zooming in the line-scan direction is carried out by controlling the operation of the analogueto-digital converter (29) by adjusting the starting point, in each line, of the sampling, and the sampling frequency.