GB524443A - Improvements in or relating to television systems - Google Patents

Abstract

524,443. Television ; cathode-ray tubes. VALENSI, G. Jan. 16, 1939, Nos. 1424, 1425 and 1426. Convention dates, Jan. 17, 1938, April 30, 1938, and June 1, 1938. [Classes 39 (i) and 40 (iii)] In colour television, the value of a signal representing an elementary area of the picture is dependent upon the colour' predominating in that area, or upon the colour which it is necessary mainly to suppress in order that the predominating colour may remain. In some modifications, additional signals dependent on the mean brilliance of the elementary area and/or on the "degree of saturation" of the colour, are also transmitted. In system shown in Figs 1 and 2, voltages t1, t2, t3 which correspond respectively to purple, yellow and green, are combined in a differential circuit 6 to give a voltage T, which is applied at the receiver to a Kerr cell 9. If t 1 -t 2 and t 1 -t 3 are positive, the applied voltage T should be zero to give purple. Otherwise, if t 3 -t 2 is positive, T should increase to give green, and if t 3 -t 2 is negative T should decrease to give yellow. The rate of variation should be inversely proportional to t 1 . For this purpose, the voltages t 1 -t 2 , t 1 -t 3 are applied to two triodes 19, 20, Fig. 2, which are so biassed that the combined 'output is constant while t 1 -t 2 and t 1 -t 3 are positive. Otherwise the output increases or decreases and is applied to a variable-mu valve 26, the amplification of which is so controlled, by a voltage across a resistance 25, as to be inversley proportional to t 1 . System utilizing spectrum analysis.-Fig. 4a. A spectrum of the elementary area of the image being scanned is thrown on an iconoscope I through a slit and prism, and an ordinary image is simultaneously projected on an iconoscope i. The output T# of the iconoscope I corresponds to the spectrum of the point scanned and the output Tm of the iconoscope i corresponds to the mean ordinate of that spectrum. The outputs are applied differentially to vertical deflecting plates K...K 1 <SP>1</SP> of a cathode-ray tube OC, and a time base voltage is applied to a horizontal deflecting coil B<SP>1</SP>h. A spectrum curve, Fig. 4b (not shown) is therefore traced on the fluorescent screen Fl, and all but the minimum (or maximum) is cut off by a blackened portion of a screen E1, Fig. 4c (not shown). The remainder of the screen is so shaded in vertical steps that the amplitude of the output from a photo-electric cell represents the colour mainly suppressed (or that predominant). An additional signal from a third iconoscope representing the brilliance of the elementary area may be transmitted over a separate channel to the receiver. The " colour signal" is applied in parallel to three cathode-ray tubes with screens which fluoresce in the primary colours, Fig. 5 (not shown), and the " brilliance signal" to an ordinary tube. The colour signals are applied through a circuit which has no output when the amplitude of the signal corresponds to the suppression of that colour, for example, a dynatron, Fig. 6a (not shown), or the circuit of Fig. 7a. When the applied voltage T is such that the voltage across the resistance R1 is equal to that of the battery E, there is no output across a resistance Wr. On departure from this voltage, the output increases up to a maximum. The shape of the output curve can be reversed by placing a voltage in series with the output, Figs. 6c, 7d (not shown). According to a modification of Fig. 4a, a voltage proportional to dT#/dt is applied to the oscillograph OC to cut off the ray except at maxima ur minima of the spectral curve. The unblackened part of the screen E 1 has 24 areas of different transparency, which represent six possible dominant colours of four possible intensities, Figs. 14-16 (not shown). Systems utilizing Maxwell colour triangle, Fig. 10. A line being scanned is incident on the mosaics Cx, Cy, Cz of iconoscopes Ix, Iy, Iz, and the points on it are spread out in spectra by prisms Sx, Sy, Sz. The iconoscopes have strip filaments parallel to the spectra. The screens Ex, Ey, Ez in front of the mosaics are graduated. The outputs X, Y, Z, from amplifiers Lx, Ly, Lz, are mixed and reduced to one third by amplifiers L'x, L<SP>1</SP>y, L'z. Voltages x+y+z/3, X, x+y+z/3, -Y are applied respectively to pairs of deflecting plates 1 ... 4<SP>1</SP> in cathode-ray tubes O, O<SP>1</SP>, in which the pairs of plates 1...2<SP>1</SP> are at 60 degrees to the plates 3...41. The cathode ray is then incident on a spot on the fluorescent screen which represents in a colour triangle the colour of the element being scanned. A screen e in front of the fluorescent screen fl is divided in six areas of different transparency, which correspond to six main colours, Fig. 11 (not shown), and a screen e<SP>1</SP> in front of the fluorescent screen fl<SP>1</SP> has five areas of different transparency corresponding to intensities of the colour, Fig. 11a (not shown). The outputs T, T<SP>1</SP> from photoelectric cells ph, ph<SP>1</SP>, and light intensity signals from an ordinary iconoscope are transmitted over three separate channels and operate a receiver similar to that described 'above. The second cathode-ray tube O<SP>1</SP> can be dispensed with, and the screen e then has 24 areas of different transparency, Fig. 12 (not shown). To separate the signal representing the intensity of colour at the receiver, the combined signal deflects a cathode ray, which is incident on one of 24 studs, which are connected in groups of six to four tappings on a battery (none being necessary for zero intensity). The Specification as open to inspection under Sect. 91 also describes the following systems :- (1) Signals corresponding to the three primary colours are obtained from iconoscopes Ib, Ij, Ir, Fig. 2 (Cancelled), are regulated by amplifiers Ab, Aj, Ar, and applied to deflecting coils Bb, Bj, Br of a cathode-ray tube C. A screen E in front of the fluorescent screen Fl is divided in 36 divisions, each of which has a different transparency and corresponds to one combination of three possible intensities of red and blue and four of yellow. The light is incident on a photo-electric cell P, which transmits a signal to deflecting coils B<SP>1</SP>b, B<SP>1</SP>j, B<SP>1</SP>r of cathode-ray tubes C'b, C<SP>1</SP>j, C<SP>1</SP>r at a receiver. The transparencies of associated screens E<SP>1</SP>b, E<SP>1</SP>j, E'r are so stepped that the resultant light on photo-electric cells P<SP>1</SP>b, P<SP>1</SP>j, P<SP>1</SP>r is proportional to the intensity of blue, yellow and red respectively, which is represented by the received signal. The progression of the shading of the squares on the coding screen E may be irregular for secrecy. The photoelectric coding and decoding devices may be replaced by secondary emitters, in which the screens E, E<SP>1</SP>b, E<SP>1</SP>j, E<SP>1</SP>r are replaced by mosaics, the parts of which have different secondary emissions when struck by the cathode rays. (2) At the receiver, coded signals representing colour, shading, and brilliance, are decoded by a cathode ray commutator with three contacts connected to tappings on a battery, no contact being necessary for zero intensity, Fig. 20 (Cancelled) (not shown). This subject-matter does not appear in the Specification as accepted.