| 摘要 |
1,268,899. Television. WESTERN ELECTRIC CO. Inc. 24 April, 1970 [30 April, 1969], No. 19718/70. Heading H4F. In transmission apparatus for reducing the redundancy in a video signal consisting of frames and lines, the signal (102, Fig. 1) is sampled in amplitude and digitized at 103 at regular intervals during each frame and each digitized amplitude sample is compared in subtractor 109 with a stored sample from memory 111 corresponding to the amplitude at the same spatial point location in the previous frame. If logic 114 detects a significant difference between the new and previous samples, the new sample is selected for feeding as an amplitude word to update the contents of a buffer memory 204 coupled to "parallel to serial" transmitter 207 and a transmit signal is fed from logic 114 to group word assembler 201. An address word from generator 105 is generated with each sample indicating the location of the sample within a line, but is only transmitted with its sample's amplitude word, if the selected sample is not immediately preceded by another selected sample. Thus if a run of consecutive samples all undergo a change in one frame, the address word of only the first is transmitted. A unique flag word from generator 213, is transmitted at the end of such a run. To maintain line synchronism with the receiver, synchronization words are transmitted during the blanking intervals. A counter 205 determines the fullness of the buffer memory 204. If the memory is overloaded, means 123 blocks the output of logic 114 so that the memory will not be updated even if the sample is sufficiently changed. Conversely, means 124 detects if the rate of updating the memory is too low and sends a signal via OR gate 118 to cause the memory to be updated by an amplitude sample even if the sample is unchanged. Group word assembler 201 which detects that a new selected sample is the first of a new run (the number in the run being one and upwards) and causes the appropriate transmission of both the address and amplitude words thereof, is shown in detail in Fig. 3. The sampling intervals are defined by pulses # on line 107. These are delayed by onethird sampling interval in delay 302 to give pulses # 1 and by a further one-third sampling interval in delay 303 to give pulses # 2 . When no selected samples have been produced for some time bi-stable 306 will be in a "clear" state and the inhibiting input of gate 307 having the enabling logic. TRANSMIT SIGNAL (TRANS). CLEAR 306. # 1 , is clear. Thus when the next transmit signal occurs, lasting for the whole of an inter # pulse interval, a "start run" (SR) pulse will be produced at the occurrence of the next # 1 pulse. The tiansmit signal and the next # 2 pulse set bi-stable 306 via AND gate 304. Bi-stable 306 will remain set until the # 2 pulse following the end of the transmit signal(s). If only one sample is selected for transmission, the "trans" signal will have ended before the next # 1 pulse, thus enabling gate 309, having the enabling logic NO TRANS . SET. # 1 , to give an end of run (ER) pulse. If, however, there are a plurality of consecutive "TRANS" signals, gate 308, having the enabling logics. TRANS . SET . # 1 will be enabled instead of gate 309 to give a "continuing run" (CR) pulse. The SR pulse passes the first amplitude and address words through gates 310, 311, respectively, to the first and second cells of shift register 321. The SR pulse is delayed for about 1/9th sampling period in delay 316 and a further 1/9th sampling period in delay 317. The delayed SR pulse from 316 and from 317 successively shift to the register and enable gate 377 so that the amplitude and address words are read out of the register into the buffer memory. If the run is continuous, a CR pulse appears which, via gate 311 and/or circuit 315 passes the amplitude word to the second cell of the register 321. The delayed CR pulse from delay 319 shifts out the amplitude word only to the buffer amplifier. For the last sample selected, the "end of run" (ER) appears and this gates through the flag-word to the second cell of the register via gate 314 and OR circuit 315. The "flag word" is then read out by the shifting of the delayed (ER) pulses from delay 319. |
