DE2852213B2 - Fast convergence adjustment system for colour TV camera - uses min. energy content of colour difference signal and needs no special test scene - Google Patents

Abstract

Position controllers allow the position of the second colour channel's raster to be displaced w.r.t. the third colour channel's raster as reference such that the best convergence in vertical and horizontal directions is attained. The position controllers are adjusted by hand to minimise a display of the energy contained in a colour difference or equivalent signal. The min. is shown by an instrument, l.e.d. indicators or a monitoring screen. A normal scene can be used to adjust the camera. No special test scene is needed so that adjustment is rapid.

Description

The invention relates to a method for automatic Kotwergenzabgleich for a color television camera according to the preamble - ', as per claim 1.

The methods used so far for automatic convergence comparison use Is criterion for the congruence is preferably a test image which has a steep black-and-white transition in the Displays TV picture This black-and-white jump is generated in the three image pick-up tubes of the color TV camera and thus a corresponding signal jump in the three color channels, which is used as a criterion for the Control loops for mutual shifting of the scanning grid is used.

The signal for the green color channel and thus the corresponding scanning raster represents the reference value for the other two color signals (color channels red and blue) and their scanning raster. These two Scanning rasters are shifted in their raster position by an assigned control loop until the generated signal jump results in clear coverage

In one direction, ζ. B. the horizontal direction, corrected image is provided by an arrangement similar to that of in the other preferred direction, e.g. B. the vertical direction, works, fully optimized.

The clear generation of the is important for the proper functioning of this known arrangement Jump signal, since the jump edge is preferably used to compare the signals. This is done in the generally this jump signal is converted into a digital signal and then in the subsequent control loop further processed.

If, for example, the test image is recorded out of focus, this can be done by blending the Jump signal lead to a misalignment.

DE-OS 20 57 540 describes a method for detecting the misregistration of two television tubes and a television camera having at least two television pickup tubes. It is about however, a complicated and cumbersome solution that is expensive to implement. The prospecting the minimum of the energy content in the horizontal direction takes place here on a rather complicated basis Way as major precautions have to be taken to get the correct signal vertically. at This known method or the television camera also shows an uncertainty factor in

ίο that when there are intense colors, for the minimum Shifts arise and the minimum can no longer be clearly identified it is assumed that the mean colors are desaturated.

For example, H is a saturated color area in the image present, then the two signals do not cancel each other out exactly. That is, if before by lateral displacement of the images against each other (i.e. storage of the convergence) a signal was obtained, then becomes this signal is falsified by this saturated color area, which is included in it. Accordingly, there is none clear minimum determination guaranteed; the evaluation circuit according to the known device is then overwhelmed in this case

According to the features of also an automatic grid or color coverage in color video cameras relevant Auslegesphriften DE-AS 22 24 143 and DE-AS 24 14 0) 3 is constantly during operation A dynamic correction of the coverage signals is sought, i.e. convergence. I.e. the picture will constantly evaluated whether there are any deviations; and as soon as an error signal occurs, it is activated by a motor controlled potentiometer or by shift register, etc. the image is immediately corrected in its position until again

J5 is optimal coverage

In the case of a circuit arrangement for the automatic correction of misregistration of the color component images DE-AS 24 11 815 relating to a multi-tube color television camera has a "measuring window" provided.

hen (»electric window«) to the video image area to zoom out and derive the vertical size. Characteristic feature of this known circuit arrangement is also a multiplication. By limiting the range, the aim is to increase the probability the wrong decisions are reduced. There is no uniqueness in the evaluated signals, if pine any scene is recorded or used; it is only unique when a black and white image (Test image) is recorded, with only one piece of information (a black and white jump) in each direction is available.

The invention is based on the object of a method for the automatic adjustment of the convergence for color television cameras to indicate which of the above-mentioned deficiencies of known alignment systems eliminated and a clear identification of the minimum of the energy content, especially with saturated colors, and allows the optimal convergence to be achieved safely

This object is achieved according to the invention by what is stated in the characterizing part of claim 1 Features solved.

For the implementation of the method according to the invention, the contrast transitions in

^ft5 normal, usual scenes of an image proved sufficient.

The convergence adjustment is advantageously carried out in an analogous manner for both the horizontal and the

performed for the vertical grid shift.

The inventive method is a convergence adjustment on hand can be a normal image Halbtonj§, ie without special test image, perform fi which so far only conditionally possible. For evaluation) ä processing of the signals are therefore no jump signals Sj but the energy content of a differential signal, which fö from the compared color signals i; is obtained, relied on and around unambiguously

¹ Vt to find out wu the optimal setting, ie the I main minimum is present, according to the invention a measurement

; phase interposed before final adjustment

t ·. will.
': It is now needed for the invention for the adjustment

the convergence no strips of a defined test pattern are used, but can ., a normal, usual scene can be used. Kick

the main minimum in the horizontal direction, then it is certain that here an absolutely congruent H This is the point of the preceding H measuring phase. D. Il, it is first in the horizontal H measured where the maximum minimum lies. During the H run, the main minimum or its value is determined P determined and stored. The main minimal of the first run is used as the second run g adjustment variable used and so the convergence jf completed immediately.

t 'The adjustment process in the

other direction (V direction or image direction) £ j carried out and the main minimum sought in the K direction jo yj If this minimum is found, the convergence p is precisely matched to it in the H second phase, the alignment phase

j / Since in the method according to the invention the adjustment

$ Process in the horizontal direction and in the » fe vertical direction runs in the same way and additional '< Measures are not required, proves a

¹ circuit arrangement according to the invention opposite

the known circuit arrangements as simpler and at the same time more advantageous. A special preparation for the vertical direction is not required in the invention. Mh a single circuit will both Directions "edited".

The shortcomings that add to uncertainties in the known facilities, since the minimum is not is to be clearly identified, do not occur in the invention 4. There - even with saturated colors - ,, ·, 'with the measuring phase according to the invention, the main mini-ΐ; mum is determined and \.! ie -i optimal «; Convergence achieved To store the Γ The grid position can be used for any length of time

: determined values for the grid coverage in one

'Analog or digital memory can be saved.

An exemplary embodiment of the invention is shown in the ■ drawing and will be described in more detail below described. It shows

F i g. 1 the deviation of the grid of two different color channels to explain the invention Procedure, and

^r Fig. 2 is a schematic functional diagram of a & o

electronic control circuit for carrying out the method according to the invention.

According to Fig. 1, which shows the deviation of the grid represents two different color channels, is used to facilitate understanding of the invention with the camera (not shown) an original image was added, which has a black bar on a white The background represents, for example, the position of the grid of the image pickup tube for the color channel Green with a solid line and the position of the grid of the image pickup tube for the red color channel shown with a dashed line If you subtract one signal from the other, you get that under the in the F i g. 1 indicated grids indicated additional signal. If both grids are congruent, then the signal to zero. If the grid is shifted in the opposite direction, the signal increases again. One Correct convergence therefore occurs when the energy content of the difference signal is at a minimum will. This applies both horizontally and vertically Direction, for black / white as well as for colored original images and for halftone images as well as for extreme high-contrast images.

In other words, it shows that every deviation or offset of the grid generates additional signals that occur as disturbing color fringes in the picture and are known. Are the disturbing signals by optimizing the Eliminated grid position, the energy content of the Difference signals a minimum.

This in conjunction with the description of FIG. 1 of the above-mentioned knowledge can become an electronic Control circuit can be used to carry out the method.

An exemplary embodiment for such an electronic control circuit is shown schematically as a functional circuit diagram in FIG. 2, which in turn is explained in more detail below with reference to the green and red channel of a color camera. From the in the respective deflection units 1,2 or image pickup tubes of the color television camera (not shown) generated Color signals for the color channels green and red are in a unit 5 for the difference formation Difference signal obtained, which in turn is fed to a minimum identification circuit 6. One starts the adjustment by a start button 8, then the red raster runs, controlled by a shift signal generator and memory 7, first in one of the lateral end positions and is then subsequently with constant Speed shifted in the opposite direction.

As soon as the minimum of the difference signal is found, the grid is held in this position and the Values are stored in memory 7 (shift signal generator) via a STOF signal on the Output of the minimum identification circuit 6. This means that the position of the red grid is fixed for any length of time

In practice, the case may arise that the original image or scene has areas that also can result in low values in the energy content of the difference signal. So that the convergence comparison does not already takes place when a first minor minimum occurs, according to the invention by twice Passing through the scanning area, the main minimum of the energy content of the difference signal is determined and used as a control variable, the main minimum being determined in the first run and in the the second run, this value is found again and the final adjustment is carried out.

The method described above in connection with a horizontal grid shift or the described electronic control circuit for carrying out the method can be analogous Can also be used for a vertical grid shift.

1 sheet of drawings

Claims (2)

Patent claims: 1, A method for automatic convergence adjustment for a color television camera with at least two color channels and with control circuits, which the shift currents of the grid of two color channels change compared to the third color channel grid as a reference value in such a way that there is an optimal one Convergence in vertical and horizontal image direction results, with the minimum of the control variable Energy content of the associated color difference signals or difference signals generated for this purpose, which from the color signals to be compared are used, characterized in that that a sufficiently wide scanning area is traversed twice and that The main minimum of the energy content of the differential signal in this area was determined and used as a control variable is used, the main minimum being determined in the first run and in the the second run, this value is found again and the final adjustment is carried out. 2. The method according to claim 1, characterized in that the convergence adjustment in an analogous manner is performed for both horizontal and vertical grid shifting.