Patent GB-1275621-A (GB)
Title: Graphical data processor
IPC: G09G1/10
Filed: 1969-04-28
Abstract: 1275621 Cathode-ray tube displays XEROX CORP 28 April 1969 [29 April 1968] 21442/69 Heading H4T In an arrangement comprising a symbol generator for displaying symbols each of which is defined by a plurality of parallel visible linear traces on the screen of a cathode-ray tube under the control of beam deflection and beam intensity control signals specified by a sequence of bindary data words the number of words is less than the number of traces in a symbol and the deflection and intensity control signals are generated simultaneously. Fig. 1, shows the general arrangement in which data from a computer 5 is processed in 4 and utilized to produce the symbols on a cathode-ray tube 3 the image on the screen of which may be recorded on photographic film 1 from which a printing plate may be produced. The system is also capable of operating in other modes such as for the production of vectors (line drawing) and in a direct analogue mode such as in response to signals from a monoscope source 6. Referring to Fig. 2, data comprising 24 bit binary words is supplied from the computer to a main input register 10 and to a PC (Photocompose) input register 11, the former register being always operative whilst the latter register is employed only in the mode (Photocompose) of operation (i.e. the drawing of high quality Alpha-Numeric symbols) which forms the invention. Some of the bits of each word specify command functions and these bits are decoded in respective command decoders 14, 15 the outputs of which are utilized to gate other bits in each word in the input registers to various circuits as identified by the letters specifying the outputs of the decoders adjacent the various "blocks". Figs. 3 and 4 show in tabular form the functions performed by these outputs. In the Photocompose mode the command PC1 (A, Fig. 4) output of decoder 14 selects an initial address in the computer which is specified by the thirteen most significant digits of the word. The IJMP command (B, Fig. 4) output of decoder 15 directs the five most significant bits of this word into an increment register 30 the value set up in which indicates the required spacing between adjacent horizontal traces (i.e. the vertical resolution). The next command output of decoder 15 JMP (Jump) (C, Fig. 4) routs the first nine most significant bits, which indicate the amount of horizontal deflection required to position the beam (were it unblanked) at a desired horizontal co-ordinate position, together with the next bit (HD) which indicates the sign of this deflection, to a horizontal OFFSET register. The fourteenth bit (BD) represents the horizontal position at which the beam is unblanked in the next data word (specifying the first line trace) and this bit together with the next nine bits (i.e. bits 13 to 5), ), which indicate the amount of vertical deflection to position the beam (were it unblanked) at a desired vertical co-ordinate position), and bit VD (the fourth bit) which represents the sign of such vertical deflection are fed to the vertical velocity register 21 which in the P.C. mode also serves as a vertical offset register (i.e for beam positioning). The command JMP thus positions the (blanked) beam at a desired location on the tube screen which is referenced to a fixed point such as 40 (Fig. 5) and may be any of the positions 41, 42, 43, 44, 45 or 46 (Fig. 5). The next command BW (Black-White), D, Fig. 4, indicates two horizontal traces bits 24- 22 indicating the amount of "White" space, W.AMT, bit 21 indicating the sign of the direction of this space and bits 20-14 indicating the amount of "Black" space the sign of this latter space having been indicated by the fourteenth bit BD in the previous command JMP. (The terms BLACK and WHITE are used in the Specification to describe the result produced by a printing plate made from the photographic reproduction of the image on the tube screen. Thus, a BLACK line is printed where the trace on the tube screen is illuminated-unblanked- and vice versa in the case of WHITE). Bits 13-7 may also specify a BLACK-WHITE trace if required otherwise all of these bits must be indicated by binary "ONES". The next command RPT (Repeat), E, Fig. 4, specifies a BLACK-WHITE horizontal trace which may include vernier spaces (i.e. small increments to be added to the WHITE spacee.g. to produce a slant vertical effect) the command also including bits 7-3 which specify the number of times such trace is to be repeated. Command EPC (End Photocompose) F, Fig. 4, specifies the width of the previous symbol by bits 24-16 and bits 15-10 and 9-4 specify the left and right kern dimensions of the previous symbol. Figs. 5, 6, 7A and 7B show the sequence of steps utilized in the production of a symbol comprising e.g. a 36-point Bodoni Roman L and the Specification includes a table of the various data words required to trace the symbol by the sequential production of the portions A to N (Fig. 5). Thus, the beam is positioned initially at point 41 (all points being referenced to the point 40) and a succession of horizontal scans extending horizontally to point 42 and vertically to the upper limit of the base of the horizontal portion are produced to trace the portion A. The portions B, C, D and E are produced in similar manner with the exception that small "vernier" increments are added to the horizontal traces during the production of portions C, D, and E (see Fig. 7B) to produce the vertical slant. These portions A to E and portions G to N which are produced in a similar manner are specified by JUMP (JMP) commands, to position the beam at the points 41, 42, 43, 45, 46 followed by REPEAT (RPT) commands so that only about 20 command words are required. The portion F, however, requires a JMP command to position the beam at point 44 followed by 29 BW words since each horizontal trace is of a different length. Overall, however, because of the "compressed" coding employed a significant increase in the speed of operation is stated to result. The tube control circuitry includes known means for producing dynamic focus and deflection corrections and when operating in the line drawing mode the beam may be deflected at constant velocity or during constant time intervals the intensity of the beam being controlled in the latter case to ensure uniformity of brightness. The size of the symbols may be varied by ZOOM control circuits 27 (Fig. 2) which are also operative when signals produced by a monoscope are utilized (analogue mode). The specification includes detailed logic circuit diagrams of the block circuits of Fig. 2.