GB1328266A - Digital data coding system - Google Patents

Abstract

1328266 Cathode-ray tube displays; facsimile systems INTERNATIONAL BUSINESS MACHINES CORP 30 Oct 1970 [4 Nov 1969] 51646/70 Heading H4F and H4T In a photocomposing system in which typographical images are produced on the screen of a cathode-ray display tube (and recorded on photographic film) under the control of a digital data code derived from a remote location or from a computer the code is produced in a "compressed" form by employing run-length coding for both the X and Y co-ordinates of each image the "compressed" code being "expanded" for controlling the production of the display. Thus, the lower case character "e" shown in Fig. 2 is coded in terms of the grid pattern (in practice a much finer grid is employed) by initially deriving a count (counting upwardly from the bottom of the grid) of the number of bits in vertical column 4 of the white portion of the display, i.e. 13 bits and a count of the number of bits of the black portion of the display (the first vertical segment of the character), i.e. 7 bits. Vertical column 5 is then analysed and a count of the difference between the white and black portions, i.e. - 3 and + 5 respectively is derived. Vertical columns 6 and 7 are analysed in similar manner giving count differences of - 2, + 4 and - 1, + 2 respectively. When, however, the number of White-Black transitions changes (columns 4 to 7 each have two such transitions whereas column 8 has four and column 9 has six transitions) it is necessary to derive a full count of the bits, i.e. column 8 has 6, 7, 3, 10 and column 9 has 5, 6, 5, 3, 2, 6 after which difference are produced for columns 10 to 24 all of which have six transitions. Column 25 which has four transitions is derived in a full length count 6, 6, 4, 10, columns 26 to 28 as difference count and columns 29 which has two transitions as a full length count 16, 4. Character data coded in the manner described is stored in a computer 10 (Fig. 1) and when required is sent to a data expander 12 in an eight bit per byte binary code the expander and the display control 13 (detailed in Fig. 3, not shown) supplying the beam blanking and unblanking signals which are required to reproduce successively the vertical column 4 to 29 of Fig. 2 during successive fixed position vertical scans on the display tube 14 the horizontal positions of each column on the photographic film 16 being controlled by a moving lens responsive to display controls 13. The detailed operation is described.