US2246631A - Scanning method for television image analyzers - Google Patents

Description

June 24, 1941. u. KNICK 2 I SCANNING METHOD FOR TELEVISION IMAGE ANALYZERS Filed March 3, 1938 Patented June 24, 1941 SCANNING METHOD FOR TELEVISION IMAGE ANALYZERS Ulrich Knick, Berlin-Steglitz, Germany, assignor to the firm of Fernseh Aktiengesellschaft, Zehlendorf, near Berlin, Germany Application March 3, 1938, Serial No. 193,797 In Germany March 4, 1937 2 Claims. (01. 25036) In the use of image analyzers containing a storage member, a non-uniform distribution of intensity of the received image is encountered also with a non-illuminated mosaic plate, for reasons which are not as yet completely understood. In order to compensate for this defect, suitable auxiliary voltages are introduced and mixed with the picture signals in an amplifier stage of the transmitter. These auxiliary voltages are derived from the deflecting voltages for frame and line deflection. The disadvantage of this method is that the magnitude and the wave shape of these compensating voltages must be adjusted according to the current value of the scanning beam. This current value in turn, however, is again preferably matched to the light intensity of the optical image to be transmitted. Hence, if the transmission is changed from a bright to a darker image, the method described calls for readjustment of the magnitude of the scanning beam current, as well as for readjustment of the auxiliary voltages. This makes operating complicated and slow.

It is the object of this invention to compensate for the non-uniformity of the distribution of intensity by scanning the storage electrode at a rate of speed which is no longer constant, but varies over certain portions of the image. The variation in scanning speed may take place in the horizontal or line scanning, or in the vertical or frame scanning. A deviation of only 2% to of the rate of scanning speed from an average value produces strong picture signals. These signals, caused by the non-uniformity of the rate of scanning speed, superimpose themselves upon the normal picture signals predetermined by varying charges of the mosaic elements and can be utilized for compensation of the interfering voltages. A change in the rate of scanning speed in the aforementioned order of magnitude is practically without influence upon the fidelity of transmission of the image. The advantage of the method described lies in the fact that the picture signals produced in varying the velocity of scanning depend upon the electron beam current in the same manner as the interfering signal, so that compensation need not to be readjusted if the beam current is varied.

In order to efiect such a scansion, the deflecting saw-tooth voltage waves must possess a degree of non-linearity, whereby, however, the average value of scanning velocity, that is, the time required for scansion of one line, or of one frame, respectively, usually remains unchanged.

An embodiment of the invention is represented in the single figure of the drawing. This figure shows a circuit arrangement for producing a sawtooth voltage, the linearity of which can be adjusted by means of a variable resistance.

The circuit contains a triode I and a condenser 2 in the anode circuit of the triode. The anode is connected furthermore through a resistor 3 to the contact 9 of the potentiometer 8. The anode of valve I is furthermore connected to the grid of an amplifier tube 4 and the anode circuit of this tube 4 is connected to the grid of the further amplifier tube 6. The anode circuits of tubes 4 and 6 are connected to the deflecting plates I0 and I I of a B-raun tube and bridged by the potentiometer 8. They are furthermore connected by way of resistors 5 and I to the positive pole of a source of potential.

For the operation of this device the input circuit of the tube I is connected to a source of rectangular short impulses of the form a. The condenser 2 which is continuously charged through resistor 3 is periodically discharged over the tube I. The tube 4 amplifies the saw-tooth voltage produced in the anode circuit of tube I. This amplified voltage is applied to one deflecting plate. A counter-phased voltage is produced by tube 6 and. applied to the other deflecting plate I I. Potentiometer 8 is used to change the rate of charging condenser 2. In the center position of contact 9 the voltage at resistor 3 is constant so that also the charge current remains constant. By moving contact 9 away from the central position, the charge current becomes dependent on the saw-tooth voltage so that the slope of the saw-tooth voltage is curved in the desired manner.

It is, for instance, also possible to obtain a substantially uniform and adjustable curvature of the deflecting voltage curve by connecting a variable resistance in series with a condenser which is large in comparison with the charging condenser, and to connect the series combination of said resistor and said condenser in parallel with the charging condenser. In order to obtain further variations in the wave shape of the deflecting voltage curve, suitable sinusoidal voltages, particularly the fundamental and the harmonics of the Kipp oscillation, can be superimposed upon the Kipp voltage curve.

I claim:

1. The method of controlling the wave shape of the output of a saw-tooth wave generator, generated by charging and discharging a condenser through different impedances which comprises impressing saw-tooth wave potentials of by charging and discharging a condenser through 10 different impedances, a potentiometer so connected in the output circuit of said generator that its center point is substantially at zero potential for alternating voltages and. across which a saw-tooth voltage wave is developed, and means for selecting and utilizing a portion of said last-named voltage of an adjustable phase and amplitude for altering the rate of charge of said condenser.

ULRICH KNICK.

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