Patent GB-799491-A (GB)
Title: Improvements in or relating to the electrical reproduction of pictures or originals
IPC: G03F3/08
Filed: 1955-04-25
Abstract: 799,491. Local copying by scanning. ADALIA, Ltd. April 25, 1955 [April 26, 1954], No. 11898/55. Class 40 (3). In an arrangement in which corrected colour separations are produced from the photo-electric scanning of an original, portions of the picture are subjected to correction different from the overall correction by means of a mask scanned simultaneously with the original, but having at each of the specified areas a transmission factor different from that at other parts of the mask so that signals derived from the scanning of the mask are used to effect colour corrections which are appropriate to those areas. The special corrections may be controlled by the combined operation of a mask having areas of different transmission factors conforming approximately to the areas to be corrected with a second control effected by signals having the values of the tristimulus or colour component signals of the colour of the areas to be corrected. The signals derived from photo-cells 5, 51, 5<SP>11</SP> by scanning an original 1 through filters 5a, 5a<SP>1</SP>, 5a<SP>11</SP> are amplified at 6, 6<SP>1</SP>, 6<SP>11</SP> and applied through switches 12d, 12d<SP>1</SP>, 12d<SP>11</SP> to computers 13 ... 13<SP>111</SP> providing outputs m, j, c, n controlling recorders 14 ... 14<SP>111</SP> producing three colour separation records 15 ... 15<SP>11</SP> and a record 15<SP>111</SP> to control a black printer. For the portions 1a, 1b, 1c of the original which are to be corrected, the exact corresponding areas 2<SP>1</SP>a, 2<SP>1</SP>b, 2<SP>1</SP>c on a mask member 2<SP>1</SP> are arranged to have different transmission values when scanned by a source 7 in conjunction with a photo-cell 8 and amplifier 9, and the appropriate control signals are passed to a switch arrangement 10 controlling switches 12a ... 12a<SP>11</SP>, 12b ... 12b<SP>11</SP>, 12c ... 12c<SP>11</SP> so that modified signals from precomputers 11a ... 11a<SP>1</SP>, 11b ... 11b<SP>1</SP>, 11c ... 11c<SP>1</SP> are fed to the computers 13 ... 13<SP>111</SP> to produce the corrected signals m, j, c, n for the four negatives 15 ... 15<SP>111</SP>. When the areas 1a, 1b, 1c are not accurately delineated by the areas 2<SP>1</SP>a, 2<SP>1</SP>b, 2<SP>1</SP>c of the mask 2<SP>1</SP>, approximate areas 2<SP>11</SP>a, 2<SP>11</SP>b, 2<SP>11</SP>c with the appropriate transmission factors are formed on the mask 2<SP>11</SP>, and the control of the switching arrangement for the computers 11a ... for the precise areas is effected by the values of the three colour components or tristimulus signals corresponding to those areas to be speci-. ally corrected. In the switching arrangement shown in Fig. 3 the control by the signals is effected by assigning upper and lower limits for the respective tristimulus signals corresponding to the areas to be specially corrected. The colour signals from the amplifiers 6, 61, 6<SP>11</SP> are fed to potentiometers 21a, 21b, 21c, 22a ... 23a ... from which tappings are taken to the windings of relays 24a, 24a<SP>1</SP> ... 25a ... , 26a ... 26c<SP>1</SP>. A potentiometer 27 connected to the output of the amplifier 9 has tappings connected to the windings of relays 29a, 28a in parallel with 29b, and 28b in parallel with 29c. According to the transmission value of the portion of the mask 2 in combination with the assigned values of the tristimulus signal values of the area to be corrected the signals b<SP>1</SP>, g<SP>1</SP>, r<SP>1</SP>, b<SP>11</SP> ... , or b<SP>111</SP> ... from the first, second or third sets of precomputers 11a ... 11a<SP>11</SP>, 11b ..., 11c ... are passed over switches 12a, 12a<SP>1</SP>, 12a<SP>11</SP>, 12b ..., 12c ... to the computers 13 ... 13<SP>111</SP>. The simplified modification for the control by the transmission values of the actual areas of Fig. 2a is described in connection with Fig. 4 (not shown). In a modification, Fig. 5 (not shown), using four computers giving four different outputs m, c, j, n for the same set of b, g, r signals, the switching arrangement selects one of the four separate computers utilized respectively to effect the normally corrected reproduction and the special correction of the three selected areas 1a, 1b, 1c. The switch member may be operated by signals from the mask, or by such signals in combination with colour signals of the areas concerned. In a further modification, Fig. 6 (not shown), in which the corrections for the various areas are derived by multiplying the b, g, r signals by predetermined factors, the signals are applied to three variable-gain amplifiers whose gain factors are respectively adjusted by sets of three potentiometers rendered effective by switch members controlled by a switching arrangement operated by the tristimulus signals and the signal corresponding to the transmission value of the area of the mask 2. A further arrangement, Figs. 7 and 8, employs cathode-ray tubes 51, 51<SP>1</SP>, 51<SP>11</SP>, to the deflecting coils of which the g, r signals are applied. The screens are focused on to shutters 53 having adjustable members 81, 81<SP>1</SP>, 81a, 81<SP>1</SP>a set according to the predetermined limits of the signals of the areas to be specially corrected. Photo-electric cells 55, 55<SP>1</SP>, 55<SP>11</SP> behind the screens control the grid potential of three further C.R. tubes 57, 57<SP>1</SP>, 57<SP>11</SP> to the coils of which are applied signals corresponding to the blue component signals and signals derived by the scanning of the mask. The screens of these tubes are focused on to further stop members comprising elements adjustable according to the prescribed limits of the blue signal and the transmission factors of the mask. Behind the screens 59, 591, 59<SP>11</SP> are photo-cells 61, 61<SP>1</SP>, 61<SP>11</SP> which control triodes 64, 641, 64<SP>11</SP> connected to the deflecting coils and control grid of a C.R.T. 65 having a screen 66 which is opaque except for one quadrant through which light can pass to a photo-cell 67 in circuit with a triode 69 connected to the control grid of an orthicon 73. The outputs of the triodes 64, 64<SP>1</SP>, 64<SP>11</SP> are similarly connected to orthicons 73<SP>1</SP>, 73<SP>11</SP>, 73<SP>111</SP>. The arrangement is such that the light passes through the transparent quadrant when the area not requiring special correction is being reproduced and the orthicons 73', 73<SP>11</SP> ... 73<SP>111</SP> are individually and selectively operative for the reproduction of the areas 1a, 1b, 1c of the original. Each orthicon 73, to a deflection coil of which the b signals are fed, is associated with a lenticulated memory screen 71, each combination acting as a computer as described in Specification 780,523 and being employed for the m signals. Additional sets of four computers may be employed for the c, j, n signals. Alternatively, the screens 71 ... 71<SP>111</SP> may be replaced by sets of four screens modified to produce the corrected values of the signals c, j and n.