Facsimile compression system
Номер патента: CA1131344A
Опубликовано: 07-09-1982
Автор(ы): Robert D. Widergren
Принадлежит: Compression Labs Inc
Опубликовано: 07-09-1982
Автор(ы): Robert D. Widergren
Принадлежит: Compression Labs Inc
Реферат: FACSIMILE COMPRESSION SYSTEM Abstract of the Disclosure Disclosed herein is a data compression system for compressing binary facsimile data to reduce transmission times over standard telephone system circuits. At the transmit end of the circuit a segment of adjacent scans of, e.g., a white or light background document having, e.g., black typewritten characters or other symbols thereon is stored in a binary format in a buffer memory. A scanner scans the memory to locate the position of a beginning point of each individual character. A block definer circuit then defines a rectangular block closely enclosing the character. A block mapping circuit then scans the block following a pre-determined pattern and provides a binary sequence of the black and white portions thereof. A run length encoder may then encode the binary sequence by run length or by Huffman code. A modem connected to the telephone lines sends data corresponding to the location, size and contents of each character block to a receiving modem at the receive end of the telephone circuit. There the coded binary sequence is decoded by a run length (or Huffman) decoder. A signal restoration memory receives and stores each character block according to sent location, size and binary sequence. A restoration scanner then scans the restoration memory to provide a reconstructed binary facsimile signal in conventional foxmat. For additional compression, the system may include a transmit library memory for storing initially scanned blocks of different individual characters. A receive library memory at the receive end of the circuit is loaded with the same character blocks. Thereafter, a character identifier circuit compares each subsequently scanned block against the characters in the library. Upon a parity detection, an abbreviated library address is sent in lieu of the run length encoded block data. The character data stored in the receive library memory at the sent address is then output to the signal restoration memory in place of the unsent block data for that character. The system repeats the foregoing func-tions until all portions of original documents have been sent and received. - b -
Method and apparatus for adaptive facsimile compression using a two dimensional maximum likelihood predictor
Номер патента: US4325085A. Автор: Robert P. Gooch. Владелец: DIGITAL COMMUNICATIONS CORP. Дата публикации: 1982-04-13.