GB2126827A

GB2126827A - Electro-optical tube registration

Info

Publication number: GB2126827A
Application number: GB08225706A
Authority: GB
Inventors: Philip Rangecroft Groves; Hugh Kendal Littlejohn
Original assignee: Link Electronics Ltd
Current assignee: Link Electronics Ltd
Priority date: 1982-09-09
Filing date: 1982-09-09
Publication date: 1984-03-28
Also published as: GB2126827B

Abstract

Apparatus for calculating relatively small errors in spatial registration of an electro-optic tube comprises a reference generator which generates a plurality of reference picture elements, monitoring means which monitor the picture element signals of the tube derived from said reference picture elements, comparator means which compare picture element and reference picture element signals, displacement means which, for each picture element, displaces the picture element in a first direction to a position of relatively large registration error, as measured by the comparator means, and which displaces the picture element in a direction opposite the first direction to a position of corresponding relatively large registration error, as measured by the comparator means, and processing means for calculating, from the displacements effected by the displacement means, the position of optimum spatial registration (B) and an error signal (10) representing the initial error in spatial registration of the picture element. A correction signal generated from the error signals (10) is applied to control means to compensate images produced by the tube. The correction signal may be interpolated utilising the scaling function of digital to analog converters. <IMAGE>

Description

SPECIFICATION Electro-optical tube registration The present invention relates to a method and apparatus for calculating small errors in the spatial registration of an electro-optical tube. The invention also provides a method and apparatus for compensating for errors in the spatial registration of an electro-optical tube.

Where a camera contains a number of camera tubes it is necessary for the tubes to have a common spatial registration. For example, in a colour television camera it is necessary for the three colour tubes to have a common spatial registration. Such registration must be optimised in order to avoid blurring of the final image. A similar requirement exists for a colour television tube in which the electron guns require registration with each other.

According to a first aspect of the present invention there is provided apparatus for calculating relatively small errors in the spatial registration of an electro-optical tube, comprising a reference generator which generates a plurality of reference picture elements, monitoring means which monitor the picture element signals of the tube derived from said reference picture elements, comparator means which compare picture element and reference picture element signals, displacement means which, for each picture element, displaces the picture element in a first direction to a position of relatively large registration error, as measured by the comparator means, and which displaces the picture element in a direction opposite the first direction to a position of substantially the same relatively large registration error, as measured by the comparator means, and processing means for calculating, from the displacements effected by the displacement means, the position of optimum spatial registration and an error signal representing the initial error in spatial registration of the picture element.

According to a second aspect of the present invention there is provided a method of calculating relatively small errors in the spatial registration of an electro-optical tube comprising the steps of generating a plurality of reference picture elements, monitoring the picture element signals of the tube derived from said reference picture elements, comparing picture element and reference picture element signals, for each picture element displacing the picture element in a first direction to a position of relatively large registration error, displacing the picture element in a direction opposite the first direction to a position of substantially the same relatively large registration error and calculating, from the displacements effected, the position of optimum spatial registration and an error signal representing the initial error in spatial registration of the picture element.

The invention also provide apparatus for compensating spatial registration errors of an electro-optical tube comprising the apparatus of the first aspect of the invention together with processing means for calculating a correction signal from the calculated picture element error signals and control means for applying the correction signal to compensate images produced by the tube for spatial registration errors of the tube.

Similarly, the invention also provides a method of compensating spatial registration errors of an electro-optical tube comprising the steps of the second aspect of the invention together with the calculation of a correction signal from the calculated picture element error signals and the application of the correction signal to compensate images produced by the tube for errors in the spatial registration of the tube.

Preferably, calculation of the correction signal includes multiplying each of two adjacent picture element error signals by a respective reference signal, the reference signals being in anti-phase with each other and being equal in frequency to half the frequency of occurrence of the picture elements these errors are being multiplied and summing the multiplied signals, whereby calculation of the correction signal includes a smoothed interpolation.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 illustrates the spatial registration of a picture element signal compared with a reference picture element; Figure 2 is a diagrammatic representation of the interpolation of picture element error signals; and Figure 3 is a block diagram of a circuit for implementing the interpolation illustrated by Figure 1.

In a colour television camera it is necessary to ensure common registration of all of the camera tubes in order to avoid imperfections in the final television image. This is achieved by the projection of a test chart within the prism system of the camera. Registration of each of the tubes is measured against the test chart and a correction signal is calculated for each camera tube and applies so as to correct the output thereof.

The test chart consists of a regular matrix of fifteen rows and fifteen columns of identical rectangular areas of black shading. Each of the areas of black shading acts as a reference picture element.

A correction signal is provided for each of the camera tubes and since the process is the same for each tube a detailed description will be given with respect to one tube only.

The image produced by the camera tube is divided into 225 picture elements each of which should be in registration with a respective picture area of the test chart. For each of the picture elements in turn, the picture element signal is measured and is compared with the reference picture element. It will be appreciated that the reference picture elements are electronically generated and that the measured picture element signal is measured against the electronic signal of the respective reference picture element.

An error signal is generated corresponding to the error of registration between the picture element signal and the reference picture element.

Figure 1 illustrates variation of the error signal 1 0.

The above procedure is repeated for all of the 225 picture elements. Subsequently, a correction signal is calculated for the camera tube by interpolation of the picture element error values.

A circuit for monitoring valves from the picture elements may include gate location of the individual picture elements, bandpass filtering, analogue to digital conversion and storage in a RAM under the control of a CPU. The RAM stored valves can be interpolated in real time to provide a correction signal which is applied for real time correction of the image defects.

Convention interpolation techniques used in data processing utilise complex software. Such software can be extensive, difficult to maintain and will sometimes produce discontinuities in interpolation which would result in unacceptable positional changes in final television image.

Interpolation of the picture element error values in this embodiment of the present invention utilises the scaling function of digital to analogue converters.

Error values, in digital form, from each of two adjacent picture elements are multiplied by a respective reference signal. The reference signals have a frequency equal to half the picture element frequency and the reference signals are in antiphase with each other. The multiplied values are summed. A smoothed interpolation is obtained.

Figure 2 illustrates the interpolation of error values. Two reference signals are provided, V REF.

1 and V REF. 2. The frequency of the reference signals is half the frequency of the picture elements. V REF. 1 and V REF. 2 vary linearly between maximum and minimum and are in antiphase with each other.

Interpolation between two adjacent error values, value 1 and value 2, will now be considered. The reference signals vary between a minimum of 0 and a maximum of V. The first error value, value 1, is multiplied by V REF. 1 and the second error value, value 2.

Variations of the above embodiment will be evident to those skilled in the art. For example, in some circumstances it may be advantageous for the reference signals V REF. 1 and V REF. 2 to have a non-linear form.

Claims

1. Apparatus for calculating relatively small spatial registration errors of an electro-optical tube comprising a reference generator which generates a plurality of reference picture elements, monitoring means which monitor the picture element signals of the tube derived from said reference picture elements, comparator means which compare picture element and reference picture element signals, displacement means which, for each picture element, displaces the picture element in a first direction to a position of relatively large registration error, as measured by the comparator means, and which displaces the picture element in a direction opposite the first direction to a position of substantially the same relatively large registration error, as measured by the comparator means, and processing means for calculating, from the displacements effected by the displacement means, the position of optimum spatial registration and an error signal representing the initial error in spatial registration of the picture element.

2. Apparatus for compensating spatial registration errors of a camera tube including the apparatus of claim 1 and further including additional processing means for calculating a correction signal from the calculated picture element error signals and control means for applying the correction signal to compensate images produced by the camera tube for errors in spatial registration of the tube.

3. Apparatus as claimed in claim 2, wherein the additional processing means comprises two multipliers each of which multiplies one of two adjacent error signals by a respective reference signal which has a frequency equal to half of the frequency of occurrence of the picture elements whose error signals are being multiplied, the reference signals being in anti-phase with each other, and a summing circuit for summing the multiplied values, whereby processing of the error calculation of the correction signal includes a smoothed interpolation.

4. Apparatus as claimed in claim 3, wherein the error signals are in digital form and each muitiplier comprises a digital to analog converter.

5. Apparatus as claimed in claim 3 or 4, wherein the reference signals are linear between maximum and minimum.

6. Apparatus as claimed in any preceding claim, wherein the reference generator generates a regular matrix of identical reference picture elements.

7. Apparatus as claimed in claim 6, wherein the matrix is formed of fifteen rows and fifteen columns.

8. A television camera incorporating the apparatus of any preceding claim.

9. A method of calculating relatively small errors in the spatial registration of an electrooptical tube comprising the steps of providing a plurality of reference picture elements, monitoring the picture element signals of the tube derived from said reference picture elements, comparing picture element and reference picture element signals for each picture element, dispiacing the picture element in a first direction to a position of relatively large registration error, displacing the picture element in a direction opposite the first direction to a position of substantially the same relatively large registration error and calculating, from the displacements effected, the position of optimum spatial registration and an error signal representing the initial error in spatial registration of the picture element.

10. A method of compensating spatial registration errors of an electro optical tube including the steps of the method of claim 9 and including calculating a correction signal from the calculated picture element error signals and applying the correction signal to compensate images produced by the tube for errors in spatial registration of the tube.

1 A method as claimed in claim 10, wherein calculating the correction signal includes multiplying adjacent error signals by a respective reference signal which has a frequency equal to half the frequency of occurrence of the picture elements whose error signals are being multiplied, the reference signals being in antiphase with each other, and summing the multiplied values, whereby calculation of the correction signal includes a smoothed interpolation.

12. A method as claimed in claim 11, comprising multiplying the error signals, in digital form, and reference signals together in respective digital to analog converters.

13. A method as claimed in claim 11 or 12, comprising selecting the reference signals to be linear between maxima and minima.

14. A method as claimed in any of claims 11 to 13, comprising the provision of the reference picture elements in a regular matrix having fifteen rows and fifteen columns.

1 5. Apparatus for calculating relatively small errors in the spatial registration of a camera tube, substantially as hereinbefore described with reference to the accompanying drawings.

16. Apparatus for compensating spatial registration errors of a camera tube substantially as hereinbefore described with reference to the accompanying drawings.

17. A method of calculating relatively small errors in the spatial registration of an electrooptical tube, substantially as hereinbefore described with reference to the accompanying drawings.

1 8. A method of compensating spatial registration errors of an electro-optical tube, substantially as hereinbefore described with reference to the accompanying drawings.