| 摘要 |
1290720 Television THOMSON CSF 30 Dec 1969 [30 Dec 1968 20 Jan 1969] 63378/69 Heading H4F [Also in Division H1] To impart relative adjustments, in gain, black level, or gamma correction exponent, to three primary colour signals whilst maintaining the overall signal level constant, three linear rotary potentiometers PR, PB, PV, one in each channel and controlling, e.g. the gain or black level thereof as a linear function of angular setting, are arranged at the corners of an isosceles triangle and are coupled to a single lever 10 by arcuate slotted slides 4-6 so that when the lever is moved about a ball joint 11 the total variation of impedance presented by the potentiometers is at least approximately zero. For relative adjustment of the gamma factor, each signal is fed to a circuit with a logarithmic transfer function which is variable by means of one of the potentiometers, and then fed to a circuit with a constant antilog transfer function. The potentiometer shafts 1-3 may extend radially of the slides at their points of connection and they may intersect equi-angularly and be coplanar or relatively inclined, or they may be parallel. It is possible to visualize the correction made to the signals from the position of the lever with respect to the showing of a colour triangle centred on the joint 11, Fig. 3 (not shown), but a clearer representation is obtained using the circuit of Fig. 4. The potentiometers are provided with a source of constant potential and the variable potentials at the taps are used to adjust the relevant parameter, e.g. gain, of a corresponding circuit. Resistors 18, 19 and galvanometers 16, 17 give an indication of the potential between pairs of the taps. The galvanometer needles 13, 14 rotate about two apices of a displayed equilateral colour triangle and lie along symmetry axes thereof when no current flows, so that the point of intersection of the needles shows the relative adjustment effected. |
