GB2089168A - The display of coloured images on a screen - Google Patents

Abstract

A system for displaying coloured images on for example a TV monitor indicating the results of e.g. ultrasonic tissue scanning utilises a novel form of signal processing. The instantaneous value of a monochrome signal derived from the scan is represented as one of a number of discrete colours on the screen. The same coloured area on the screen is controlled in luminosity also in dependence on the instantaneous value of the signal. Information can therefore be resolved within a colour level and echo perspective is maintained.

Description

SPECIFICATION The display of coloured images on a screen This invention relates to the display of coloured images on a screen.

In one of its applications the invention may be included in the processing of signals produced by ultrasonic scanning of human tissue. The signal received from the ultrasonic scanner may represent a scan across an area of tissue which is to be represented on the screen. The received signal varies in intensity according to the intensity of the reflected ultrasonic waves from corresponding parts of the scanned-area. This signal is usually compensated for path attenuation so that its intensity represents changes in acoustic impedance within the tissue.

There are known imaging systems in which a cathode ray oscilloscope has been used to display the signal from the scanner. In such cases distance along the X and Y co-ordinates represents time and spatial distances in one of a number of ways and the intensity of the received signal modulates the brilliance of the spot on the screen. The image appears as grey-scaled, black-to-white with the largest echoes appearing as the brightest points on the screen.

This system has the merit of displaying most of the available information, but this is not readily appreciated by the human eye since regions of similar but not identical levels separated by black or white areas are not readily discerned.

A coloured display aids appreciation and it has been proposed to grade the intensity of the signal, i.e. what previously represented greyness, into one of eight colours. Each colour is presented at full luminance, but it results in an overall display which is coarse. Whilst the amount of information conveyed could be improved by increasing the number of colour levels, a rather speckled image would be produced. Furthermore the human eye has difficulty in recognising small changes in colour and hence important clinical information can be lost and furthermore the areas representing greatest amplitude are not necessarily the most prominent to the eye.

Other systems in which colour coding and luminance control are combined have been proposed, but these have their own respective disadvantages.

In particular these systems result in a reduction in the colour information that can be provided. For example one system uses signal averaging to eliminate much of the local signal information in the coloured representation.

The present invention seeks to provide a system for representing the value of signals on a visual display system with colour facility which uses the signal which controls luminance to also determine colour.

According to the present invention there is provided a system for representing a monochrome data signal in a visual display system with colourfacility comprising: means for sensing the instantaneous value of the data signal and operating colour control circuitry such that successive values of the data signal are represented on the display in a colour code, wherein each colour represents a single range of data signal values, and means operative to vary the luminance of each coloured representation on the display in dependence on that value of the data signal which also determines the colour.

It will be appreciated that unlike prior discrete level display systems the invention enables information to be resolved within a level by the variation in the brilliance of the image whilst maintaining the hue appropriate to that level, and in so doing maintains echo perspective.

The invention may find particular application in representing scans of human tissue.

In a preferred form of the invention circuitry is provided such that the hue and/or saturation level corresponding to a signal level can be preselected as desired, but for ultrasonic body scanning the display has been found particularly effective when the colours are displayed at full saturation.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

In the drawings: Figure lisa block circuit diagram of part of an apparatus for processing composite video signals in accordance with the present invention; Figure 2 is a block circuit diagram of another part illustrating subsequent stages in that process; Figure 3 is a block circuit diagram of an alternative circuit for controlling the luminance of the display.

Referring to Figures 1 and 2 an input terminal 1 receives a composite video signal from an ultrasonic scanner and a range of successive amplitude values of this data signal are required to be represented on a television screen. The input terminal 1 is connected to a line termination and buffer unit 2 which terminates the video signal cable at its characteristic impedance. The terminated signal is fed to a voltage follower and then a dc restoration circuit 3. The output from the circuit 3 is fed to a first video amplifier 4which amplifies the signal to a level of +2.5 volts. The video signal includes synchronisation pulses and the first video amplifier 4 has its output offset such that all negative signals at its output terminal represent synchronisation pulses only.

The output terminal of the amplifier 4 is connected to a sync pulse amplifier 5 which amplifies the synchronisation pulses from the amplifier 4 and feeds them to a comparator 6. The comparator 6 compares these pulses with a reference voltage and produces a noise free synchronisation signal. This synchronisation signal is fed via a buffer 7 and a circuit for selecting polarity 8 to an output socket 9.

The output from the buffer 7 is also fed to integration and comparison units 10 and 11 and thence to an external field synchronisation output 12 which is used to facilitate synchronisation of photographic equipment such as cine-cameras. The output from the buffer 7 is also fed via an OR gate 13 whose other input comes from the comparator 11 and whose output provides a blanking signal.

The output terminal of the first video amplifier 4 is also connected to a circuit 14 which operates to remove the synchronisation pulses from the signal.

The signal thus stripped is then fed to a further video amplifier 15 having an offset adjustment for setting the correct black-level on the video screen. The output signal from this video amplifier 15 is fed via a mode switch 16 to weighting circuits of the video output amplifiers as will be described below. The output terminal of the amplifier 4 is also connected to a set of seven comparators, each of which has a comparison signal fed to it from a reference ladder chain voltage source 18. The reference voltage source 18 has the facility for adjustment in overall level set by a calibration unit 19 and also has the facility for switching between a linear ladderfunction and a logarithmic ladder function.Each of the comparators in the unit 17 produces an output logic signal when the video signal exceeds the reference voltage provided for that individual comparator on the voltage ladder source 18. The maximum value of signal voltage, i.e. that which would produce an output from all of the video comparators in the set 17, is that which corresponds to a video signal which on a black and white screen would be intended to produce a peak white image. The output of each of the comparators in the set 17 is fed to a corresponding level priority logic circuit in a unit 20.

Each priority circuit in the unit 20-comprises an inverting gate 21 feeding one input of an AND gate 22. The other input of the AND gate is connected to receive the non-inverted signals from the comparator at the next highest threshold level. Thus the AND gate 22 will only produce a logic 1 output signal when its associated comparator produces a logic 0 signal and the next highest comparator produces a logic 1 output signal. In this way the greatest of the comparison voltages that the video signal exceeds is detected. It follows therefore that only one of the AND gates will produce an output logic 1 signal.

The signals from the AND gates in the level priority logic unit 20 are fed along separate channels on a priority bus 23.

A colour television screen associated with the described apparatus is controlled in the normal way by three separate colour signals corresponding to red, blue and green; and the respective output stages for these three signals are shown as 24, 25 and 26 in Figure 2. Each output stage has a corresponding hue-mix selector unit 27,28 and 29 which controls its associated colour output stage in accordance with the position of the logic 1 signal in the 7-bit signal from the priority unit 20 and determines whether and to what extent that stage operate to colourthe signal on the screen.

The hue-mix circuits receive the signals on the priority bus 23 after extraction via a buffer 30, provided for each of the hue-mix selector circuits.

Each hue-mix circuit has a series of switches, each switch being connected to one channel of the priority bus, such that by preselection of those switches, a particular 7-bit code is arranged to produce a desired effect on the associated colour output stage. Each of the colour output stages 24, 25 and 26 also has an associated hue ratio and saturation control circuit 31,32 and 33. These ratio and saturation control circuits are also preconditioned and controlled by the signal from the priority bus 23 via a respective buffer 30. The saturation control effected by these circuits is achieved by adding amounts of the missing colours for a particular selected colour displayed so that the overall colour becomes less saturated and hence moves towards the white part of the colour triangle.

Most significantly, with regard the present invention, each colour output stage 24, 25 and 26 includes an associated weighting circuit 34,35 and 36 to which is fed the video signal from the video amplifier 15. The amplitude of the video signal fed via the switch 16 and a respective weighting circuit modifies equally each colour output stage to vary the luminance of the signal in accordance with the amplitude whilst not affecting the selected hue and saturation.

As a result a non-discrete brightness variation, producing a brighter display for larger amplitude signals, is imposed on the discrete hues selected.

Thus the information which would previously have been lost because of the discrete 8 level characterisation of the signal is now included by virtue of the gradation of luminance, and hence within one hue level the human eye will be able to preceive important differences. A practical advantage of the overall luminosity variance is that the echo amplitude perspective is retained throughout the displayed image. This is particularly noticeable in moving pictures. It should be appreciated that the human eye is more adept at distinguishing intensity variations than it is of saturation or hue changes. It is preferable that those colours which are used to denote signals of least intensity, and therefore which themselves will be reproduced less brilliantly on the screen, are those to which the human eye is most sensitive; and these are the colours centred around green.

Another advantage given by this system is that medical information may be obtained by counting the number of pixels of one colour in the display.

This exact information may not be appreciated by the eye but is nevertheless present and useful. In ultrasonic scanning such information is generally not spurious and is lost if the signal that is colour coded is subjected to some form of local averaging.

The apparatus may include the facility on switch 16 to switch off all the hue-mix and saturation control circuits such that only a black-to-white grey-scaled image appears. Alternatively the switch 16 may be operated to maintain the colour facility while disconnecting the weighting circuits 34 to 36 from the video signal and connecting them to a source of maximum luminance.

Referring now to Figure 3, in an alternative embodiment of the invention the luminance of the display areas is additionally controlled by the differential of the data signal at the point which is represented on the screen. This enhances peak signals to partly compensate for the non-linear response of the eye to luminosity. In this embodiment the signal from the sync stripper 14 which is fed to the video amplifier 15 to control the luminance of the display is also shunted via a differentiator 40 and an attenuator 41. The resultant signal is then combined additively in an adding circuit 42 with the signal from the sync stripper 14 before being fed to the video amplifier 15. The attenuator 41 is set to deliver a signal from the differentiator which is only approximately 20% of the signal at the input of amplifier 15 directly from the syne stripper 14. Thus the main control of the luminance of the display is the value of the amplitude of the received signal, but augmented or reduced as the case may be by the differential of the received signal.

It will of course be appreciated that whilst reference has particularly been made to the use of the invention for representing ultrasonic tissue scanning it is neither limited to ultrasonic scans nor to representing features of tissue, although it is in the latter field that the invention may prove particularly advantageous.

Claims (8)

1. A system for representing a monochrome data signal in a visual display system with colour facility comprising: means for sensing the instantaneous value of the data signal and operating colour control circuitry such that successive values of the data signal are represented on the display in a colour code, wherein each colour represents a single range of data signal values, and means operative to vary the luminance of each coloured representation on the display in dependence on that value of the data signal which also determines the colour.

2. A system as claimed in claim 1 including means operative to differentiate the data signal and to modify the luminance of each coloured representation in dependence on the differential of the data signal at said value in addition to the control of luminance imposed by said value alone.

3. A system as claimed in claim 1 or claim 2 wherein said means for sensing the value of each data signal operates to compare the value of each data signal with a series of incremental reference signals to produce a comparison signal representing correlation with a particular one of the reference signals, the comparison signal causing the colour control circuitry to display the data signal in one of a discrete number of colours corresponding to the reference signals.

4. A system as claimed in any one of the preceding claims forming part of a scanning system wherein said data signal represents signals received from parts of a scanned area.

5. A system as claimed in claim 4 wherein the scanning system represents the amplitudes of returned ultrasonic echoes.

6. A system as claimed in claim 4 or claim 5 wherein the scanning system is adapted to scan the or parts of the human body.

7. A system as claimed in claim 5 wherein each coloured area on the display is displayed at full saturation.

8. A system for representing a monochrome data signal in a visual display system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.