Patent GB-780523-A (GB)
Title: Reproduction method and computing apparatus
IPC: G03F3/08
Filed: 1955-04-01
Abstract: 780,523. Light utilizing; local copying. ADALIA, Ltd. April 1, 1955 [April 1, 1954], No. 9588/55. Class 40 (3). Three colour separations 1b, 1g and 1r (Fig. 2) obtained in the normal way from an original are scanned at corresponding points by light beams 5 from sources 6 and the signals obtained from the photo-cells 7 are amplified in the amplifiers 8b, 8g and 8r and fed to a computer 9. The outputs from the computer 9 are led to four electrooptical recording devices 11 which illuminate the four sensitized layers 12 in proportion to the input signals m, j, c and n and at positions corresponding to the scanning process of the separations 1. The layers 12 can then be used to make printing plates for the magenta, yellow, cyan and black. The computer 9 may comprise (Fig. 4) four CR tubes 16 the beams of which are deflected by voltages proportional to the g and r signals and iconoscopes 17 whose beams are deflected by the b signal so that the resulting voltages c, m, j and n may be used to control the recorders for the cyan, magenta, yellow and black printers. A spot on the CR tube 16 is imaged by lens 19 and 20 on to a memory screen 18 which has one surface of varied density and a lenticulated surface. The spot falls on the screen 18 at a position D (Fig. 7) corresponding to the r and g co-ordinates and the lenticulations and the lens 21 image the spot D on to a horizontal slot 23 in an otherwise opaque screen 24. The beam of the iconoscope 17 deflected by the b signal picks up the illumination from a position C in slots 23 so that the distance AC is proportional to b. The densities on the screen 18 are predetermined in such a way that the intensity of light passing through any spot is proportional to the r and g signals and thus the c signal from the iconoscope is a function of the r, g and b signals. To obtain the correct relationship between the input signals b, g and r to the computer 9 and the output signals m, j, c and n (so that the correct density distribution of the screen 18 may be deduced) the recorders 11 are separately energized by arbitrary voltages ml, j1, c1 and n1 from a suitable power pack 38 and separations 12m, 12j, 12c and 12n are made. These separations are used in the normal way to print a colour patch from which three b, g and r colour separations are made conventionally. These three colour separations are scanned in the same positions as 1b 1g and 1r in Fig. 2 and the signals from the amplifiers are measured say b1, g1 and r1. This process is repeated a number of times N so that N quadruplets m1, j1, cl and n1 and their corresponding triplets b1, g1 and r1 are obtained and an exact relationship between the colours for correct colour reproduction is obtained when the trichromatic co-ordinates of an original exactly correspond with one of the b1, g1 and r1 triplets measures as above. In the event of the co-ordinates not corresponding the correct value of the computer output signal is determined by one of the known interpolation formulµ. Instead of the arrangement shown in Fig. 4 each bank of the computer 9 for the c, m, j and n signals may comprise (Fig. 12) a light source 47 reflected by a mirror 48 pivoting on a vertical axis in response to the g signal and by mirror 49 pivoting about a horizontal axis in response to the r signal on to a memory screen 50 similar to screen 18 in Fig. 2. The beam from the screen 50 illuminates the horizontal slot 57a in the otherwise opaque screen 57. The mirror 60 which pivots about a vertical axis in response to the b signal deflects the illumination from the consequent position along the slot to the photo-cell 63.