Patent GB-1386905-A (GB)
Title: Apparatus for transmitting optically scanned information
IPC: G06V30/166
Filed: 1973-07-26
Abstract: 1386905 Television transmission systems INTERNATIONAL BUSINESS MACHINES CORP 26 July 1973 [16 Aug 1972] 35605/73 Heading H4F In a bandwidth reduction system for the transmission of optically scanned information the video pattern (e.g., a 20 x 30 bit matrix) resulting from the scanning of each character is compared with previously stored prototype patterns each of which is identified by a symbol such as a binary number and if a "match" occurs only the binary number is transmitted whereas if no match occurs the video pattern resulting from the scanning together with an assigned identifying binary number are stored and such pattern and number together with information specifying the position of the character in terms of its X-Y co-ordinates are transmitted. Fig. 1 shows the general arrangement in which alphanumeric textual data 12 is line scanned and digitized by a flying spot scanner 14 which produces, for each character, a video signal in the form of a binary pattern matrix, e.g. of 20 x 30 bits, representative of the character. This pattern is fed to a correlator 16 in which it is sequentially compared with each of prototype patterns previously stored in a store 18 each prototype pattern being associated with a stored prototype (identifying) number. If the correlation is high, e.g. 90%, a threshold device 20 produces a "MATCH" signal on line 22 which opens gate 24 and allows the (binary) number associated with the stored prototype to pass via line 26 to the output line 28. If correlation is below the predetermined threshold value, device 20 produces a 'NO MATCH" output on line 30 which steps on a binary counter 32 and opens a gate 24 to allow the video pattern produced by the scanning to pass along line 36 and together with its prototype (identifying) number from counter 32 to pass to the output line 28 and to pass along line 38 for storage in store 18 as a prototype pattern and corresponding number. Additionally, each pattern and its prototype number and each prototype number, solus, transmitted over path 28 has associated therewith the X and Y co-ordinates of the position of each character represented thereby on sheet 10 in coded form derived from the deflection circuits of the flying spot scanner. The signals supplied to the output line 28 may be stored on a tape or disc in a magnetic store 42 for subsequent reproduction of the scanned characters or they may be transmitted over a suitable medium such as a co-axial cable 44 to a receiving station 46. When the signals received comprise only prototype numbers these are compared in comparator with the prototype numbers of prototypes previously stored in store 48 from which the corresponding prototype is read out and employed via a flying spot recorder 50 to reproduce the corresponding characters in the correct positions on a recording medium 56. When the signals received comprise prototypes together with corresponding prototype numbers both are stored in 48 as protoypes and the prototype is then reproduced on the medium 56. Fig. 3 shows the various steps in the operation in which a line of text a is scanned to produce digitized character video and X and Y coordinate data b which, as shown at c, is transmitted by, initially transmitting the prototype video, the co-ordinate data and the prototype number for each of the first three characters whereas in the second word of the text only the prototype numbers (and co-ordinate data) are transmitted in place of the characters "t" and "e" since these now exist as stored prototype patterns, the other characters of this word, which are not stored, being transmitted in full. On the average, each prototype character may be represented by a 10 x 15 binary array and each non-prototype character by a 9 bit number, an additional 20 bits being required for the coordinate data. This is stated to produce an average compression factor of 16 and this may be improved to a factor of at least 40 : 1 by methods such as: (1) reducing the co-ordinate data to 8-bits by specifying only the spacing of one character from the previous characters; (2) Huffman coding; (3) Run-length coding of the video and (4).