GB2146198A - Improvements in or relating to visual displays - Google Patents

Abstract

A visual display system includes a visual display, e.g. a television display, arranged to present a composite colour image of a viewed scene to viewer. The system includes image enhancement means adapted to interchange 7, 8, 9 the component colours of the scene whereby the colour difference between an object and a background can be adjusted so as to improve the sensitivity of perception of the object i.e. each of the red, green and blue colour generators 4, 5, 6 of the display system may be switched to receive any of the red, green and blue colour signals from respective signal generators 1, 2, 3. <IMAGE>

Description

SPECIFICATION Improvements in or relating to visual dis plays This invention relates to visual displays such as colour television screens where a colour visual image of a scene is presented to an operator and is particularly concerned with modifying the image displayed to allow the operator readily to perceive an object against a background.

Where a colour scene is recorded by a television camera and displayed by a television screen, this is done by a plurality of sensors in the camera, each responsive to a particular spectral region to generate a colour signal; the colour signals are then transmitted to a television screen having a plurality of visual colour emitters related in spectral characteristics to the sensors of the camera, to be reconverted into a visual colour image of the scene. Instead of receiving the colour signals directly from the camera, they may be received from a store, or indeed be generated by some other means.

A well-known technique is the trichromatic system in which a camera having sensors which are responsive to red, green and blue spectral regions produces signals which are fed to a television screen to produce a composite colour image of the scene viewed by the camera, the television screen having emitters emitting light from the red, green and blue spectral regions respectively. In this system, the red receptor effectively controls the red emitter and so on, and thus the television screen produces a realistic colour reproduction of the scene viewed by the camera.

When a scene includes a coloured object set against a coloured background, it is found that the sensitivity with which it can be perceived depends on various factors. One of these is the difference in colour between the object and the background and the sensitivity to this colour difference depends on the actual colours of the object and the background. As an illustration, for some background colours, sensitivity to objects of a slightly more red colour than the background is greater than the sensitivity to objects that are slightly more yellow than the background. For ther background colours, the variation can be for a different combination of colours.

In the one to one relationship arrangement described above, if the object and background colours are such that colour discrimination is worst, then the colour discrmination on the screen between the object and the background will also be poor. We have found, however, that if the component colours of the display are not represented in the one to one relationship with the object and the background, the colour discrimination between the displayed object and background can be improved.

According to one aspect of this invention, there is provided a visual display system for displaying a colour image to a viewer, said system comprising image display means, e.g.

a television display, for receiving an input signal and converting it toform a composite colour image including at least two component colours, and image enhancement means operable for interchanging at least some of the component colours, thereby to enhance the sensitivity of perception by the viewer of an object against a background.

Preferably, said system operates on the trichromatic basis so that said image display means receives said input signal and converts it to form a composite colour image including three component colours.

Preferably, the image display means includes respective colour generating means, and the image enhancement means comprises switch means for receiving colour signals from a picture signal source, said switch means being operable to switch said colour signals between said colour generating means. Alternatively, the image enhancement means may comprise, or be incorporated in, a suitably modified matrix decoder.

The system preferably further includes weighting means for weighting at least some of the colour signals supplied via the switch means, whereby the colour of the background may remain unaltered even though the component colours have been interchanged.

In a further arrangement, the system may include data base means containing data relating to the sensitivity of perception of the viewer and processor means adapted to sample the colour signals from the picture signal source and to select appropriate weighting and switching of the colour signals in accordance with said data, whereby the colour of an object in the image is changed in the most appropriate way but the colour of the background remains substantially unchanged. In an alternative arrangement, the colour of both the object and the background may be changed to give the optimum discrimination.

In another aspect of this invention, there is provided a target acquisition system for displaying a colour image of a viewed scene to an operator, said system comprising image display means, e.g. a television display, for receiving an input signal from a picture signal source and for converting it to form a composite colour image including at least two component colours, and image enhancement means operable for interchanging at least some of said component colours, thereby to enhance the sensitivity of perception by the operator of a target within the viewed scene.

In yet another aspect of this invention, there is provided a method of improving the sensitivity of perception of an object against a background in a composite colour image, said method comprising interchanging at least two of the component colours forming said composite image, whereby the colour of the object relative to the background is altered.

Further features will become apparent from the following description of various visual display systems by way of example only, reference being made to the accompanying drawings, in which: Figure 1 is a schematic view of a first embodiment of visual display system incorporating switch means, Figure 2 is a schematic view of a second embodiment of visual display system incorporating switch means and a weighting arrangement, Figure 3 is a schematic view of a third embodiment of visual display system incorporating switch means and selectable weighting networks appropriate for images including known backgrounds, Figure 4 is a schematic view of a fourth embodiment of visual display system incorporating a microprocessor for effecting switching and for selecting appropriate weighting values.

In each of the figures, there is shown a system in which a viewed scene is recorded by a camera or like apparatus which converts the view received into three signals, namely, the red, green and blue signals. Naturally, the system will also include synchronising signals for ensuring line and frame synchronisation between the camera and the image screen, but these are not material in understanding the arrangements of Figs. 1 to 3. The systems also include an image display screen which receives red, blue and green colour signals and converts them to form a composite colour image.

Referring now to Fig. 1, the visual display system is shown schematically as comprising a picture signalsource having picture signal generators 1, 2 and 3 which generate signals corresponding to the red, green and blue components of the image to be displayed, and an image display screen having colour generators 4, 5 and 6 which generate red, green and blue colours. The manner in which an image to be viewed is converted into colour signals and then reconverted into a visual image on a screen is believed to be well within the competence of one skilled in the art and therefore will not be described in detail.

In a conventional display system, the colour signals are fed to their appropriate colour generators. In this embodiment, however, switch means 7, 8 and 9 associated with the red, green and blue colour generators respectively allow each colour generator to receive any of the red, green or blue colour signals, there thus being several permutations of connection between the picture signal generators 1, 2, 3 and the colour generators 4, 5 and 6.

An example of how this arrangement may be used to increase the perception of an operator observing the image screen will now be given. Consider a white background with a small blue object of equal luminance to the background, which is displayed in realistic colour representation on the screen. The sensitivity of human perception of colour difference in the blue sense is poor and the small object must be of a strong blue colour before it is seen against the background. If the scene is analysed when the object is just visible using a conventional triochromatic system, the white background will give equal signals in the red, green and blue picture signal generators 1, 2 and 3. The object will give equal signals in the red and green picture signal generators 1 and 2 and a much stronger signal in the blue picture signal generators 3.

In order to heighten the sensitivity of perception of the target, the signal from the blue picture signal generator 3 is switched to either the red or green colour generator 5 or 6, and the signal from the red or green picture signal generator, as the case may be, is switched to the blue colour generator. When this done, the white background is essentially the same colour as before, but the object is now reproduced with a strong red or green colour (depending on the switching). The object will now be readily perceived because of the human eye's greater sensitivity to red or green against a white background, as compared to blue against the same background.

In the basic system just described, the colours of both object and background for natural rather than hypothetical scenes will be changed on switching. Occasionally, this could give less than optimum improvement to colour difference sensitivity. The problem can be eased by arranging that the background colour is approximately correct even after switching has been done. Fig. 2 shows a system in which this can be achieved. The colour generator 4, 5 and 6, receive signals from the picture signal generators 1, 2 and 3 via switches S,, 52, S3 repectively which are ganged. Ohen they are switched to other than the realistic, one to one colour representation, each colour signal is given an appropriate weight by means of pre-set attenuators or preset gain amplifiers P1, P2 and P3 respectively. These weights are related to the colour of the background of the scene and can be calculated by those skilled in the art. The appropriate components for defining the background colour can be derived from the picture signal generators themselves, or they may be measured separately for background types such as sea. sky, grass, etc. The results of these calculations are included as the values of the preset attenuators P1, P2 and P3 which may be switched ratio potentiometers.

Fig. 3 illustrates a system similar to that of Fig. 2 but having two selectable weighting networks, for example pre-set attenuators. The first network PlA, P2A, P3A, might be chosen so that in a sky view, when the picture signal generators are switched to a different combination, the sky background still remains fairly realistic in colour, and the second network PiB, P2B, PsB, may be chosen so as to give a realistic colour representation of a grass background when the picture signal generators have been switched.

Those skilled in the art will readily see how such a set of pre-set attenuators could be included in the matrix decoding of a colour television system. A re-arrangement of the decoding signals could also give the desired colour transformation for the object.

In a third approach, the weights may be made continuously variable according to appropriate rules, so that the decoder can arrange that the background colour is reproduced correctly but that the difference in colour between object and background can be changed to any desired colour sense. In this way, the viewer can adjust the relative colour of a small object to give best discrimination.

An example of such an arrangement is shown in Fig. 4, in which the red, green and blue colour signals pass via a three channel video switch 10, each to be fed through a variable gain amplifier P1, P2, P3 to a swtich matrix 1 2 where each signal may be fed to either the red, green or blue colour generators 4, 5 or 6. A microprocessor 1 3 analyses the colour of one complete frame of the television image sampling the red, green and blue colour signals. From this analysis, the microprocessor determines the background colour, obtains data from a data-base 1 4 containing a look-up table of visual sensitivity which contains, for each of a plurality of background colours the switching permutation that will give optimum discrmination of a known object.Having done this, the microprocessor then sets each preset gainamplifier P1, P2, P3 to the appropriate level and sets the switch matrix to the appropriate permutation, so that the background of the scene viewed by the operaor is reproduced in a realistic colour but that the object is presented in the colour which allows best discrimination. Alternatively, the information in the data base may be used to alter the colour of both the background and the object, so as to give optimum discrimination for the observer.

The systems described have particularly application where it is wished to perceive an object within a scene which, when viewed in a realistic colour representation, may be virtually indistinguishable from the background, but which has sufficient spectral differences from the background that if the colours forming the image are interchanged, the object will be more likely to be perceived. Such applications would include target acquisition, where the object may be camouflaged or earth resources surveillance where the object to be perceived may be very small relative to the viewed scene or the colour difference between the object and the background may be small.

Claims (10)

1. A visual display system for displaying a colour image to a viewer, said system comprising image display means, e.g. a television display, for receiving an input signal and converting it to form a composite colour image including at least two component colours, and image enhancement means operable for interchanging at least some of the component colours, thereby to enhance the sensitivity of perception by the viewer of an object against a background.

2. A system as claimed in Claim 1, wherein said image display means receives said input signal and converts it to form a composite colour image including three component colours.

3. A system as claimed in Claim 1 or Claim 2, wherein the image display means includes respective colour generating means, and the image enhancement means comprises switch means for receiving colour signals from a picture signal source, said switch means being operable to switch said colour signals between said colour generating means.

4. A system as claimed in Claim 3, which further includes weighting means for weighting at least some of the colour signals supplied via the switch means.

5. A system as claimed in Claim 3, which further includes data base means containing data relating to the sensitivity of perception of the viewer and processor means adapted to sample the colour signals from the picture signal source and to select appropriate weighting and switching of the colour signals in accordance with said data, whereby the colour of an object in the image is changed but the colour of the background remains substantially unchanged.

6. A system as claimed in Claim 5, wherein weighting and switching of the colour signals is selected such that the colour of the object and the background are changed.

7. A target acquisition system for displaying a colour image of a viewed scene to an operator, said system comprising image display means, e.g. a television display, for receiving an input signal from a picture signal source and for converting it to form a composite colour image including at least two component colours, and image enhancement means operable for interchanging at least some of said component colours, thereby to enhance the sensitivity of perception by the operator of a target within the viewed scene.

8. A method of improving the sensitivity of perception of an object against a background in a composite colour image, said method comprising interchanging at least two of the component colours forming said composite image, whereby the colour of the object relative to the background is altered.

9. A system substantially as hereinbefore described, with reference to, and as illustrated in, any of the accompanying drawings.

10. A method substantially as hereinbefore described, with reference to, and as illustrated in, any of the accompanying drawings.