Patent GB-1346507-A (GB)
Title: Television control circuit
IPC: H04N9/74
Filed: 1971-04-19
Abstract: 1346507 Television PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 19 April 1971 [25 March 1970 26 Jan 1971] 24850/71 Heading H4F The colour or shade of a colour or monochrome television picture is varied by a control circuit in which a threshold device, e.g. 1, in at least one of a plurality of video channels separates out video signal portions and which exceed a threshold level and applies these portions for control purposes via a pulse shaper 7 to a common clamping circuit 8, 9, 10 which establishes a reference level-e.g. black-for deviations of all of the above-threshold video signal portions. The output from the threshold device 1 is also applied to gated level control circuits 11-13 situated in each video channel after the common clamping circuit 8, 9, 10 so as to control the colour or shade of the portions of the displayed image corresponding to the abovethreshold video signal portions. Radical adjustments of coloration or shading are thus obtained, dependent upon the characteristics set for each of the level control circuits 11-13, which may, for example, comprise controlled transistors and may include signal generators to superimpose patterns on initially evenly coloured portions of the display or may use current sources charging or discharging capacitors to introduce colour gradations to initially evenly coloured portions of the display. In the colour system illustrated each of the three R, G and B video channels is provided with a threshold device 1-3, and there are in all nine gated level control circuits 11-19 to provide maximum hue variation. Fig. 2 (not shown) illustrates a more complex modification of the circuit of Fig. 1, in which a logical network of NAND gates and inverters is inserted between the threshold devices (1-3) and an array of twenty-one gated level control circuits (11-31) which separately control the hue of the portions of the displayed image corresponding to portions of the video signal for which only one of the three chrominance components is above-threshold, for which only two of the chrominance components are simultaneously above-threshold and for which all three of the chrominance components are simultaneously above-threshold. Each gate may be individually associated with a switch to determine whether or not it will contribute to the control of the level control circuits (11-31), and in addition an overall release or blocking signal may be used to switch in or by-pass the control circuit for all or part of the image. This signal may be generated electronically or by means of a television camera scanning a black- and-white image, the white parts of which generate a release signal to switch in the control circuit. The threshold devices may only produce an output r, g, b when the input R, G, B lies within upper and lower signal values. Each threshold device may then have a plurality of outputs corresponding to different signal value ranges. If only one of three video channels is provided with a threshold device, each of the three channels being supplied with the same video signal from a black-and-white camera, false colour may be generated in a colour display, dependent, for example, on variations in brightness in the black-and-white image. In the application of the invention to monochrome T.V. there may be provided two video channels supplied from the same video source with threshold devices provided in both channels but having different threshold levels so that the shading of certain white or grey tinted regions of the image can be controlled independently. The two channels may also be supplied from different video sources, grey control being achieved in the image corresponding to one of the channels so that the other image cannot be seen through the shading.