Patent GB-1235007-A (GB)
Title: Improvements in or relating to redundancy reduction systems
Inventor: CANDY JAMES CHARLES
IPC: H04N7/36
Filed: 1969-11-11
Abstract: 1,235,007. Television. WESTERN ELECTRIC CO. Inc. 11 Nov., 1969 [13 Nov., 1968], No. 65042/69. Heading H4F. General.-In a redundancy reduction television transmission system for matching the transmitted signal to the limited bandwidth of a channel 403 and/or to enable TDM over the line of a plurality of different video transmissions, the framed video signals are sampled and digitally encoded on to lines 101. A digitized sample or word is fed to comparison circuit 13 and also via gate 14 to a frame memory 21. The word at the same position in the previous frame is read out from the memory 21 and fed via gate 17 to the other input of comparison circuit 13. Each word lasts a period T A , defined by sync. and address generator 11 which also produces pulses # 1 , # 2  and # 3  defining the final, second and last third of T A , and also the coded address A (line and element in that line) of the word on line 101. When the circuit 13 detects a significant difference between the real time and stored words, the real time word is read into the frame memory and a matrix flag memory 22 is energized at a location address corresponding to that of the new word. An entire line of memory 22 is read out during periods # 1 , or # 3 , into group flag register 29 and is there searched for an energized location (i.e. an indication of a new " new word "). Detection of such a location causes the read out of the word from memory 21 into data register 27 for subsequent transmission at the next " transmit order " from transmitter 40. Details.-During # 1  the word in memory 21 at location A from the previous frame is read out to comparison circuit 13 via enabled gate 17. If there is a change, signal on line 131 enables gate 14 to write in new video during # 2 . If there is no change, absence of signal on line 131 enables gate 15 and the word from the memory is re-stored. When there is a change, signal on 131 enables gate 18 such that during # 2 , address A in flag memory 22 (identified by the address signal A at input 228) is energized. During # 2 , a " ready " signal is on line 330 such that if a " transmit " order appears on 401, gate 37 gives a 1 setting bi-stable 31 and enabling gate 32. The word stored in register 27 is thus read through to the transmitter. During # 3 , bistable 31 is cleared and the 1 to 0 transient at the " zero set " input clears register 27. Gate 32 is also closed and bi-stable 33 set. The " ready " signal is removed and gate 34 receives a 1 signal. If input 351 of gate 34 is enabled, bi-stable 35 is set indicating that a new flagged (changed) word has been found during a previous search. Gate 34 gives a " read-restore " order pulse, which sets bi-stable 28 and is fed to the " read-restore " input of memory 21. The " read-restore " order also enables gate 25 and gate 20 via gate 43. The address of the flagged word to be read out of memory 21 at # 3  is F, as generated by 38, 39 and is fed to " address input " of 21 via gate 20. The word at this address is read out by the " read-restore " order, together with the address F, through gate 25 into register 27, provided that during # 2  a " transmit " order was received and acted upon. The " read-restore " order sets bi-stable 28 to enable gate 44. At the next # 1 , the enabled gate 44 gives a signal clearing bistables 33, 28, 35. Bi-stable 28 is now ready to receive the next " read-restore " order and bistable 33 produces the " ready " signal such that register 27 is " ready " to transmit its newly stored data during the next # 2  in response to a " transmit order". The cleared bi-stable 35 gives a #1 signal on 352 which is an order to search for a new flagged word in memory 22. Generator 41 feeds very high-frequency stepping pulses through enabled gate 26. Gate 26 is inhibited during # 1  and # 3 , but not # 2  by " read " order from bi-stable 30 which gives said " read " order when set at the end of a line when element counter 38 gives an " end of line " pulse on 381. The " read " order is fed to the " read " input of memory 22 during # 1  and # 3 . An entire line G in memory 22 is read out into register 29. Number G is fed into memory 22 via gate 24. When the read out is complete " read " order from 42 is fed via delay 36 to clear bi-stable 30 and prepare it for the next end of line pulse from 38. The clearing of 30 removes the inhibit signal from gate 26 such that the " search " " order and the stepping pulses can pass to the register. Each element is read out in turn until an energized flag address is detected, setting bi-stable 35. The stepping pulses also advance counter 38 such that the number of the address F is given. The setting of 35 removes the " search " order such that no further stepping pulses advance the register or counter. The detected " changed " word is read out of memory 21 during the next # 3  provided register 27 has been emptied. Transmitter 40 may be connected to a plurality of systems like that shown, and may transmit then as a TDM basis. The rate of the " transmit " orders is 1/10 that of the word frequency.