Patent GB-998849-A (GB)
Title: Improvements in and relating to the production of photographic records
IPC: H04N1/207
Filed: 1962-03-23
Abstract: 998,849. Copying by scanning. CIBA Ltd. March 23, 1962 [March 24, 19611, No. 11303/62. Heading H4F. In a process for the production of photographic records, electric signals are produced by the point-by-point scanning of an original, the electric signals are modified and/or corrected and a light-sensitive material is exposed using a dark-field optical system in which the control medium is modulated point-by-point by the modified and/or corrected signals. Fig. 1 shows a first arrangement arranged for colour reproduction in which an original picture 12 produced by a camera 10 is scanned point-bypoint by a cathode-ray tube flying-spot scanner 14 operating in conjunction with photo-electric cells 18 to produce red, green and blue component colour signals which are applied to a unit 20 where desired modifications and/or corrections of the signals are effected. The modifications may, for example, involve conversion from three to four component colour signals and the corrections may involve contrast modification or a change from signals for negative to signals for positive reproduction. The resulting signals are applied to modulate the beam 24 of a cathode-ray tube which is scanned over a control medium 28 in synchronism with the scanning of the original picture 12. The control medium consists, for example, of a layer of highly viscous oil the surface of which is deformed by the action of beam 24. The medium is located in a dark-field optical system in which an image of an aperture 36 illuminated by a lamp 32 is formed by lens 34 on a stop 38 and an image of the control medium 28 is formed by lens 40 on a light-sensitive material 42 on which the desired reproduction is to be made. The component signals from unit 20 may control cathoderay tube 30 in sequence. Alternatively a plurality of separate cathode-ray tubes may be controlled simultaneously. Exposure of the light-sensitive material may be effected by single or repeated scanning. In the event of repeated scanning, the scanning patterns used in successive scans may differ. Reference is made to the use of curve-shaped scans, for example Lissajou's figures. In a second arrangement, Fig. 2 (not shown), the control medium is such that a permanent or semi-permanent recording may be effected on it. For example, the medium may consist of a polymerizable or hardness-reducing synthetic material which, after scanning by the cathode-ray beam, may be treated by washing off to reveal a recording in the form of thickness variations. Alternatively a thermoplastic material may be used which, when softened by heating, deforms in accordance with the change pattern resulting from the cathode-ray beam scanning. In this arrangement the medium is in the form of a strip which, after the recording is made, is either lead out of the cathode-ray tube via a vacuum trap directly to a dark-field optical system similar to that shown in Fig. 1, or is wound on to a roll and taken from the cathode-ray tube and used subsequently in a dark-field optical system to expose the light-sensitive material. In a third arrangement, Fig. 3, the original picture 100 is situated in the dark-field system in close proximity to the control medium 104 and a semitransparent mirror 118 is included in the light path to the light-sensitive material 116 so as to direct part of the light to a photo-electric cell 120. The signals from the cell are applied via a conversion or correction circuit 122 to modulate the cathode-ray tube. In this arrangement the reproduction is effected by direct photographic copying from the original 100 to the light-sensitive material 116 with the control medium 104 acting as a light mask. Reference is made to the use in the invention of dark-field optical systems of the type employing mirror bars. Reference is also made to arrangements in which the image is projected on a screen to which the light-sensitive material is exposed, corrections being effected by local variations of the albedo of the screen. Specifications 543,485 and 678,307 are referred to in the connection with dark-field optical systems.