GB2187919A

GB2187919A - Correcting magnetically induced raster distortion

Info

Publication number: GB2187919A
Application number: GB08704340A
Authority: GB
Inventors: Albert Kaufmann; Ulrich Reimers; Herbert Zettl
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1986-03-14
Filing date: 1987-02-24
Publication date: 1987-09-16
Also published as: JPS62220085A; FR2595892A1; DE3608542A1; GB8704340D0

Abstract

In the vicinity of the camera tubes 4, 5, 6 there is provided a magnetic field sensor 16, whose output signals x, y, z influence the deflection signals of the camera tubes via correction function generators 32 to 37 in such away that geometry and picture superimposition errors caused by interfering magnetic fields are reduced. The use of a microprocessor 45 enables the correction of other disturbing factors e.g. the temperature or the position of the camera. <IMAGE>

Description

SPECIFICATION Colour television camera This invention relates to a colour television having a plurality of camera tubes.

As is known, external magnetic fields have a disadvantageous effect on the electro-optical imaging system in a television camera tube, and in the case of a multi-tube (colour) television camera even the weak geomagnetic field is sufficientto bring about different deflection characteristics ofthe scanning beams in the case of camera movement and these lead to interference in particular if the camera tubes used are not precisely parallel to one another. In orderto eliminate this interference by external magnetic fields, in the past the camera casing has been constructed as a Faraday cage, which although successfui to a certain extent, was not sufficient to completely remove the disadvantageous image interference.

The object of the present invention is therefore to mitigate the adverse effect of interfering magnetic fields on the geometry and picture superimposition in a colourtelevision camera.

Accordingly, the present invention provides a colourtelevision camera with a plurality of camera tubes each ofwhich has an electron beam deflecting means controlled by deflection signals, wherein a magnetic field sensor is positioned in the vicinity of the camera tubes and the output signal(s) thereof are used to modify the deflection signals ofthe camera tubes in such a way that deflection errors caused by external magnetic fields are at least reduced.

The invention has the advantagethatthe geometry and picture superimposition remains substantially stable independently of the influence of external magnetic fields.

An embodiment of the invention will now be described with reference to the accompanying drawing.

The drawing shows a colourtelevision camera 1 with a lens 2, together with those elements in the camera casing 3 which are necessary for explaining the embodiment ofthe invention. A colour television camera conventionally contains three camera tubes 4, 5, 6for producing three primary colour signals R, G, B which are available at the outputs 7,8,9 respectively ofthe three camera tubes. A colour-separating prism system 11 is positioned in frontofthe signal electrodes ofthe camera tubes 4,5,6 for separating the primary colours ofthe external sceneto be televised.

Deflecting systems 12, 13, 14forthe K and V deflection directions are provided in the camera tubes along the casingsthereoffordeflecting the electron beam ofthe tubes. The deflecting systems which generally comprise two deflection coils are supplied with deflection signals by a time-base generator 15.

To mitigate the influence of interfering magnetic fields on the geometry and picture superimposition in the colour television camera 1, in the immediate vicinity of the camera tubes 4,5,6 there is provided a magnetic field sensor 16, which can be constructed with one, two orthree axes. In the present embodiment a three-axis magneticfield sensor 16 is shown for measuring the interfering magnetic fields in three mutually perpendicular directions x, y and z. In each of the three coils ofthe sensor 16, which are mutually perpendicularto one another, variations in the flux coupling with external magnetic fields induce respective voltages,which voltages are proportional to the rate of change of the magnetic field or the produce of magnetic field intensity and frequency.The output signals of the magnetic field sensor 16 generated in respect of the three directions x, y and z are each amplified in a respective amplifier 17,18 and 19 and then digitized in a respectiveanalong-digital converter 21,22,23. The digital signals thus produced are supplied to a digital memory 25 which contains, e.g., empirically determined test (correction) data which is read out as a function ofthe measured magneticfield underthe control of a microprocessor 25. By means of respective digital-analog converters 26 to 31, this data is converted into analog values and in each case supplied to a respective correction function generator 32 and 37.By means of the analog values supplied thereto, the correction function generators 32 to 37 produce correction signals required for correcting the deflection signals of the camera tubes. These correction signals are supplied in an adder stage 38 or 39 to theVorH deflection signals fortube 4, in an adder stage 41 or42 to the Vor H deflection signals fortube 5 and in an adderstage 43 or44to the V or H deflection signals fortube 6. Thus, the geometry ofthe electrooptical imaging and the picture superimposition of the camera tubes remain substantially independent of external magnetic field influences.

An even more precise determination of interfering magneticfields is possible through an additional use ofthe microprocessor 25 in conjunction with the digital correction value memory 24. The access of the microprocessor 25 to digital memory 24 can be used for controlling the correction of other environmental factors, such as the location, use position, temperature, inclination angle of the camera, etc.

1. Acolourtelevisioncamerawitha pluralityof camera tubes each ofwhich has an electron beam deflecting means controlled by deflection signals.

wherein a magnetic field sensor is positioned in the vicinity of the camera tubes and the output signal(s) thereof are used to modify the deflection signals of the camera tubes in such a waythatdeflection errors caused by external magnetic fields are at least reduced.

2. A colourtelevision camera acclaimed in Claim 1 ,wherein the output signal(s) of the magnetic field sensor is/are digitized and supplied to a digital memory containing correction data, wherein as a function of the measured magnetic field correction data is read out of the digital memory and, following digital-analog conversion, is supplied to correction function generators, and wherein correction signals supplied by the correctionfunction generators are added to the deflection signals.

3. Acolourtelevision camera as claimed in Claim 2, wherein the or each output of the magnetic field sensor is connected via a respective amplifier and analog-digital converterto the digital memoru where intheoutputsignalsofthedigital memory are each connected to one input of a respective adder stage via

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Colour television camera This invention relates to a colour television having a plurality of camera tubes. As is known, external magnetic fields have a disadvantageous effect on the electro-optical imaging system in a television camera tube, and in the case of a multi-tube (colour) television camera even the weak geomagnetic field is sufficientto bring about different deflection characteristics ofthe scanning beams in the case of camera movement and these lead to interference in particular if the camera tubes used are not precisely parallel to one another. In orderto eliminate this interference by external magnetic fields, in the past the camera casing has been constructed as a Faraday cage, which although successfui to a certain extent, was not sufficient to completely remove the disadvantageous image interference. The object of the present invention is therefore to mitigate the adverse effect of interfering magnetic fields on the geometry and picture superimposition in a colourtelevision camera. Accordingly, the present invention provides a colourtelevision camera with a plurality of camera tubes each ofwhich has an electron beam deflecting means controlled by deflection signals, wherein a magnetic field sensor is positioned in the vicinity of the camera tubes and the output signal(s) thereof are used to modify the deflection signals ofthe camera tubes in such a way that deflection errors caused by external magnetic fields are at least reduced. The invention has the advantagethatthe geometry and picture superimposition remains substantially stable independently of the influence of external magnetic fields. An embodiment of the invention will now be described with reference to the accompanying drawing. The drawing shows a colourtelevision camera 1 with a lens 2, together with those elements in the camera casing 3 which are necessary for explaining the embodiment ofthe invention. A colour television camera conventionally contains three camera tubes 4, 5, 6for producing three primary colour signals R, G, B which are available at the outputs 7,8,9 respectively ofthe three camera tubes. A colour-separating prism system 11 is positioned in frontofthe signal electrodes ofthe camera tubes 4,5,6 for separating the primary colours ofthe external sceneto be televised. Deflecting systems 12, 13, 14forthe K and V deflection directions are provided in the camera tubes along the casingsthereoffordeflecting the electron beam ofthe tubes. The deflecting systems which generally comprise two deflection coils are supplied with deflection signals by a time-base generator 15. To mitigate the influence of interfering magnetic fields on the geometry and picture superimposition in the colour television camera 1, in the immediate vicinity of the camera tubes 4,5,6 there is provided a magnetic field sensor 16, which can be constructed with one, two orthree axes. In the present embodiment a three-axis magneticfield sensor 16 is shown for measuring the interfering magnetic fields in three mutually perpendicular directions x, y and z. In each of the three coils ofthe sensor 16, which are mutually perpendicularto one another, variations in the flux coupling with external magnetic fields induce respective voltages,which voltages are proportional to the rate of change of the magnetic field or the produce of magnetic field intensity and frequency.The output signals of the magnetic field sensor 16 generated in respect of the three directions x, y and z are each amplified in a respective amplifier 17,18 and 19 and then digitized in a respectiveanalong-digital converter 21,22,23. The digital signals thus produced are supplied to a digital memory 25 which contains, e.g., empirically determined test (correction) data which is read out as a function ofthe measured magneticfield underthe control of a microprocessor 25. By means of respective digital-analog converters 26 to 31, this data is converted into analog values and in each case supplied to a respective correction function generator 32 and 37.By means of the analog values supplied thereto, the correction function generators 32 to 37 produce correction signals required for correcting the deflection signals of the camera tubes. These correction signals are supplied in an adder stage 38 or 39 to theVorH deflection signals fortube 4, in an adder stage 41 or42 to the Vor H deflection signals fortube 5 and in an adderstage 43 or44to the V or H deflection signals fortube 6. Thus, the geometry ofthe electrooptical imaging and the picture superimposition of the camera tubes remain substantially independent of external magnetic field influences. An even more precise determination of interfering magneticfields is possible through an additional use ofthe microprocessor 25 in conjunction with the digital correction value memory 24. The access of the microprocessor 25 to digital memory 24 can be used for controlling the correction of other environmental factors, such as the location, use position, temperature, inclination angle of the camera, etc. CLAIMS

3. Acolourtelevision camera as claimed in Claim 2, wherein the or each output of the magnetic field sensor is connected via a respective amplifier and analog-digital converterto the digital memoru where intheoutputsignalsofthedigital memory are each connected to one input of a respective adder stage via a respective digital-analog converter and correction function generator, and wherein a respective deflection signal forthe V or H deflection of each camera tube is connected to the other inputof each adder stage, the outputs ofthe adder stage being connected to the deflection means ofthe camera tubes.

4 A colourtelevision camera as claimed in Claim 2 or 3, wherein the digital memory is controlled by a microprocessor.

5. Acolourtelevision camera as claimed in any preceding claim, wherein the magneticfield sensor has three mutually perpendicular axes.

6. Acolourtelevision camera substantially as described herein with reference to the accompanying drawings.