Patent GB-1207740-A (GB)
Title: Cathode ray tube scanning systems
IPC: H04N1/409
Filed: 1968-12-16
Abstract: 1,207,740. Colour facsimile. PRINTING DEVELOPMENTS INTERNATIONAL S.A. 16 Dec., 1968 [22 Dec., 1967], No. 59618/68. Heading H4F. Specification describes a colour facsimile system, Fig. 1, of the type comprising a cathoderay tube 65 raster scanning in a main scan a colour transparency 40, a photodetector and colour analyser head assembly 80 producing yellow, magenta and cyan video signals, a computer 90 processing said signals and feeding the processed video signals plus a derived black (luminance) signal, to a reproducer/film exposer 20, comprising the films 37a-37d to be exposed mounted on a rotating drum 21 and illuminated by respective brilliance modulated light sources 35a-35d moving along the drum in step fashion, the cathode-ray tube scan and the drum and light sources movement being in synchronism, wherein to increase local contrast in the reproductions the transparency is scanned in an area centred on and moving with the main scan spot and the resulting area video signals allow the determinations of local contrast between a scanned spot and the surrounding area and the use of such to produce the aforesaid increase reproduced contrast. In the embodiment of Figs. 2 and 3, the area 175 is scanned in a series of radial sweeps 173 with one sweep per 50 Ásec, the outer sweep taking 3<SP>1</SP>/ 8  Ásec. and return sweep (during which the tube is blanked also taking 3<SP>1</SP>/ 8  Ásec. Between the radial scans the spot returns to the main raster scan. The main scan video signals and the area scan video signals occur alternately and are directed to the correct channels by means of gates 215a- 215c and gates 216-216c respectively closed and opened by gating signal C, Fig. 3. The gating signal C, the tube blanking signal B and the beam intensification signal A, are produced by a pulse generating assembly comprising a 320 kHz. oscillator 130 feeding square waves to a chain bi-stable divider circuit 132a-132d and diode decoders 135a-135c receiving the outputs of the dividers. The X and Y deflection signals for the radial area scan are shown at H and J and are produced by ramp generations 160 and 161 from the signals A and B. So that successive radial scan shall rotate, the amplitudes of the signals A and B are modulated by sine waves D and E in quadrative, whereby the deflection signals become as at M and N and the radial area scan rotates as shown at O. These deflection signals are added to the normal raster scan deflection signals and lines 59 and 61. The amplitudes of the composite deflection signals may be varied together to vary the ratio between the sizes of the original and the reproduction. The area scan video signals are integrated in four pass filters 225 and combined in mixer 230 to produce an area scanning signal for said contrast increase. The colour analyser head assembly 80 comprises a known arrangement of mirrors, image splitters 201, 202, dichroic filters 205-208 and photomultiplier detectors 204a-204c. In the embodiment of Figs. 4 and 5 the area 176 is scanned in a succession of 360-degrees spirals, the corresponding deflection signals GG, HH being two single oscillations in quadrature progressively decreasing in amplitude. The whole of the area may be simultaneously scanned by simply deforming the spot, Figs. 6, 7a, 7b (not shown), or by applying noise signals as the deflection signals, Figs. 8, 9a, 9b (not shown). By employing a two-gun cathoderay tube 280, Fig. 10 (not shown), the main scan and the area scan may be carried out simultaneously, the two scanning spots being brightness modulated at different frequencies, to produce distinguishingly different carriers In the resulting scan and area video signals.