Patent GB-859017-A (GB)
Title: Improvements in or relating to picture scanning and recording apparatus
Inventor: NUTTALL THOMAS CAYTON
IPC: H04N1/46
Filed: 1958-03-05
Abstract: 859,017. Copying by scanning. RANK CINTEL Ltd. March 5, 1959 [March 5, 1958], No. 7055/58. Class 40(3). A single cathoderay tube acts alternately as a flying-spot scanner to generate video signals and as a picture reproducing tube for the latter signals the alternation of function being effected cyclically with a periodic time which is short compared with the time which the scanning spot takes to traverse a distance equal to its own width. The invention is described as applied to an arrangement for producing a copy of an original transparency (&c.) by exposing photographic material to the picture reproduced by the tube from the signals generated when the tube operates as a flying-spot scanner in cooperation with a photo-electric device to scan the transparency. Fig. 1, shows one embodiment in which the signals derived from a photoelectric cell 15 as the result of scanning a transparency 11 by the raster on the screen of a cathode-ray tube 1 are supplied via an amplifier 18 and gate circuit 19 to a storage device 21 and thence via a second gate circuit 20 to the beam intensity control electrode of tube 1. The gates 19, 20 are always in different conditions (open or closed) and these conditions are cyclically reversed by a device 22 with a periodic time which is short compared to the time taken by the scanning spot to traverse a distance equal to its own width. In this manner video signals are stored in device 21 during brief intervals (gate 19 open and gate 20 closed) during which the beam of tube 1, which has an intensity determined by the bias source 23, acts as a flying spot scanner. During other, alternate, brief intervals (gate 19 closed and gate 20 open) the stored signals are applied to the intensity control electrode of the tube which then operates to reproduce a corresponding picture and this picture is imaged via a half-silvered mirror 18 on to the photographic material 13 on which a photograph the characteristics of which (contrast etc.) are determined by the characteristics of amplifier 18 is produced. Since the "feedback" loop from the photo-electric cell 15 to the intensity control electrode of tube 1 is never closed "positive feed-back" (i.e. the reproduced image may be the same as the transparency 11, either a photographic positive or negative) may be employed. In a second embodiment applied to the production of corrected colour-separation transparencies signals derived simultaneously from three colour separation transparencies during the scanning portion of the cycle are supplied to a computer which supplies "corrected" signals to the tube during the picture reproducing portion of the cycle the reproduced picture being imaged on photographic material to produce the required corrected colourseparation (Fig. 3, not shown). In this latter embodiment the cycle of operation has, in addition to the scanning and picture reproducing portion, a third portion during which the scanning beam has a predetermined constant intensity (e.g. zero) and during this portion a datum level signal is produced in amplifiers in the photoelectric cell circuits for each of the three original colour transparencies.