Patent GB-1401637-A (GB)
Title: Encoding system and method
IPC: H04N1/419
Filed: 1972-07-05
Abstract: 1401637 Digital transmission: facsimile run length coding ADDRESSOGRAPH MULTIGRAPH CORP 5 July 1972 [9 July 1971] 31515/72 Headings H4P and H4F The total number of successive black or white elements in any scanned portion of a document (for facsimile transmission) is represented by a corresponding 3-bit code word or, if the number is large enough to require it, by a following 5-bit code word, one of the possible 3-bit words being reserved to indicate whether such a 5-bit word follows. The system additionally uses 8- and 11- bit code words, each larger code being similarly heralded by a selected 5-bit word. Coding.-Of the seven possible non-zero code words using 3-bit coding, six are chosen to represent black runs of 1-6 elements, the seventh indicating that a 5-bit word follows. Of the thirty one possible non-zero 5-bit code words, 28 are chosen to represent black or white runs of 1-28 elements (or 29-56 elements); the 29th indicating that the next code word is another 5-bit word representing the above numbers 29-56; the 30th indicates that an 8- bit word follows representing numbers of elements between 57-256; and the 31st indicates that an 11-bit word follows representing numbers greater than 256. The 11-bit words represent numbers between 1 and 2046, the 2047th indicating that another 11-bit word follows. Encoder system, Figs. 1, 1A.-The operation of the symbol input system 13, receiving the document scan signals from 14 and feeding a counter 16, and of the code word generator and sender 18, are governed by twomultistate circuits 10, 11. The "minor" state generator 11 cycles through nine states (M1-M9, Fig. 2, rows) and consists (Figs. 4, 4A, not shown) of a pulse generator (47) counter (43) count decoder (44) and a gate (46) feeding back the nine outputs of the decoder (44) to the generator (47); there being two further gates (63, 75) arranged to temporarily halt the generator at states M5, M9 respectively. The major state generator 11 (details, Figs. 3, 3A, not shown) has thirteen states (S1-S13) and consists of two shift registers (31, 32) and gating circuits which set the first register (31) in accordance with document scan symbols being monitored, during the M2 state (of the minor state generator 10). During M1, the input register (31) has been cleared; during M3 the output register 32 is cleared; and during M4, output register 32 is loaded with the contacts of input register (31), to produce the corresponding major state output S1-S13. Fig. 2 indicates how given major-minor state combinations control encoder operation.  Decoder system (Figs. 9, 9A, not shown).- This operates along generally similar lines, and has major and minor state generators (222, 218) controlling the operation of input register and counter subsystems (214, 221) which recognize the received code words, and derive an output count at (211) from those code words identified as being the actual conveyers of facsimile information. The decoder again starts at S2, M2 by assuming the first signal is white, thereafter responding only to changes between black and white, so that correspondence between colour of the transmitted and received facsimile information is ensured.