GB2134348A - Method and apparatus for colour simulator - Google Patents

Abstract

Method and apparatus for effecting colour simulation in which an object having variable brightness is photographed with a monochrome television camera (1) to give a picture image in the form of brightness signals which is converted in an RGB separator into colour signals comprising an R signal, a B signal, and a G signal of mutually substantially equal levels. These are fed into a cut-off circuit to produce colour signals of mutually different magnitudes which, in turn, are fed to a television tube display unit (5) to produce a colour image which is a composite of the three signals. The shades of colour then represent levels of brightness in the original picture. The method can be applied to the visualisation of fluid flow in which injected bubbles reflect light. <IMAGE>

Description

SPECIFICATION Method and apparatus for colour simulation This invention relates to a method and apparatus for colour simulation in which a picture image input in the form of brightness signals is converted into given corresponding colour signals with attendant brightness and then formed into a colour picture image.

As means for visually displaying a flow of fluid, the tracer method is available which by a simple procedure enables the trend of an entire region of fluid flow to be observed at one glance. Among other forms of the tracer method, the air bubble tracer method which uses air bubbles as the tracer can be used with great simplicity without affecting the fluid flow under observation. Thus, it is suitable for observation of complicated fluid flows. The air bubble tracer method as adopted heretofore, however, lacks means of quantitative measurement and has been used only for qualitative measurement.

The present inventors made various studies on the air bubble tracer method with a view to achieving quantitative measurement of the density of a fluid.

They have consequently acquired a knowledge that, when the fluid is made to contain densely therein fine, homogeneous air bubbles and a beam of light is projected onto this fluid, the light on hitting the air bubbles in the fluid is irregularly reflected to give rise to scattered beams of light suitable for measurement and that the intensity of the scattered beams of light is thought to be directly proportional to the number of affected air bubbles in the unit volume of the fluid and, consequently, the intensity of the scattered beams of light corresponds to the density of the fluid. Although these changes in brightness permit visual observation of generally rough distribution of density or change of density, they are not suitable for observation of partial or detailed condition of the density.

In visualizing in a readily discernible manner such quantitative information as pertains to density and mixture manifested in terms of changes in brightness, the practice of displaying the information in changes of colour corresponding to variation in the intensity of brightness, constitutes one of the most effective methods. This method contributes to promoting study and comprehension of the phenomena of turbelent mixture of fluid, particularly in the aforementioned fluid flow model.

One of the conventional rnethods proposed for colour simulation is based on a procedure which, as illustrated in Figure 1, comprises converting an incoming analog image signal at at image transmission side (television camera) conversion unit A into a digital image signal in accordance with a fixed sampling mode, committing the digital image signal temporarily to a computer B, subjecting the digital image signal, while subsequently being read out of the computer B, to a treatment of stepwise colour designation corresponding to the intensity of brightness, and thereby allowing the digital image signal to be produced on a display C in the form of an image of simulated colours. Here, the intensity of the brightness of individual picture element is divided by the number of memory bits involved.A picture element of 4 bits, for example, is divided into 24 = 16 steps. The image signals and the brightness signals converted into digital signals, therefore, can be given a colour designation depending on their respective numbers of steps. The colour designation may be effected, for example, by assigning red to a certain range of brightness, blue to a lower range of brightness, and green to a higher range of brightness. In this case, variation of brightness is represented simply by differences in colour hue and is not attended by intensity of brightness such as bright red or dark red. One given colour embraces brightness or density spread over a range of certain width and does not represent the information with definite accuracy.Further, this method of colour simulation involves converting an analog image signal into a digital image signal by sampling in a fixed mode, storing the digital image signal temporarily in the computer B, and subjecting the digital image signal, while subsequently being read out of the computer, to the treatment of color disignation, thereby producing the digital image signal as a colour picture image on the display C. This is the so-called static image communication system which calls four processing time. It can be used effectively on a static image but cannot be used advantageously for observation of continuous change in density of a flow field in a fluid flow model. To be more specific, sampling generally is made of a total of 126 to 512 points on one scanning line.An effort to decrease the number D of sampling points, shorten the processing time on the image reception side, and approxiamte the reproduced image to the real image in motion results in coarsening the image surface and impairing the accuracy of colour simulation. A desire to enhance the accuracy of colour simulation by increasing the number of sampling points inevitably necessitates use of a high-speed large computes for heightening the processing speed. In spite of the efficiency of the computer, the increased number of sampling points calls for several seconds to several minutes of time even in obtaining a static image. Thus, the conventional method of colour simulation under discussion can hardly be expected to effect colour simulation on an image in continuous motion.Thus, this method cannot be used for the aforementioned visually displaying of density which is required to display an image of delicate motion by colour simulation.

Although a system of colour simulation capable of converting, on real time, an imput image into an image of desired colour has been a prominent desideratum, no technique has succeeded in producing such a system to date.

This invention is aimed at meeting this desideratum. The first object of this invention is to provide a method and apparatus for colour simulation capable of converting an input image in the form of a brightness signal, on real time, into a desired colour image. A second object of this invention is to provide an inexpensive apparatus for effecting colour simulation of an image in motion.

According to the present invention there is pro vided a method for colour simulation which comprises forming an image input composed of brightness signals; converting the brightness signals into colour signals comprising an R-signal, a B-signal, and a G-signal of mutually substantially equal levels in an RGB separator; cutting off portions of at least one of the resulting three colour signals at a level corresponding to a particular brightness level to produce colour signals representative of mutually different brightness ranges; and reproducing on a colour display a colour image which is a composite of the three colour signals obtained in the cutting off step.

According to a second aspect of the present invention there is provided apparatus for colour simulation which comprises means for producing a picture image input composed of brightness signals, an RGB separator arranged to convert the brightness signals into colour signals comprising an R-signal, a B-signal, and a G-signal of mutually substantially equal levels; cut-off means for cutting off portions of at least one of the resulting three colour signals at a level corresponding to a particular brightness level to produce colour signals representative of mutually different brightness ranges and a display device for reproducing a colour image which is a composite of the three colour signals obtained in the cutting off step.

In such a method and apparatus, the intact signals may be cut off at low cut-off points, cut off at high cut-off points, or cut off at both low and high cut-off points. Furthermore, one of the cut off signals may be amplified to a level above the other two.

Preferably, the reproduced image comprises a triangular-shaped area the legs of which constitute an ordinate and an abscissa and in which the colour bands formed from the cut off colour signals extend from the ordinate along the abscissa so that one colour overlaps one other colour and the third colour overlaps the other two. Alternatively, the reproduced image may comprise a triangular-shaped area the legs of which constitute an ordinate and an abscissa and in which each colour band formed from the cut off colour signals has a portion which is not overlapped by any other colour band. In a preferred form, adjacent blue and green bands overlap to form a narrow cream-coloured band and adjacent blue and red bands overlap to form a narrow purplecoloured band.

The apparatus and method of the invention may be used for colour simulation and a visual display of the flow of a fluid in which a slit of light is projected onto the flow field of a fluid containing a large volume of fine, homogeneous gas bubbles so that the light is reflected irregularly by the bubbles to produce the said image in which the intensity or brightness of the reflected light is representative of the density of the bubbles, and in which the image is displayed as a colour simulation in which the colours are representative of the brightness and so the air bubble density in the fluid.

While the method and apparatus thus described is particularly useful in connection with the air bubble tracer method described above, in that the density of the fluid flow field, i.e., the concentration of air bubbles therein is displayed on a display unit in colour patterns corresponding to the intensity of the scattered beams of light reflected from the air bubble, it is nonetheless useful for analysing images of variable brightness however produced.

The invention may be carried into practice in various ways and some embodiments will now be described by way of example with reference to the accompanying drawings, in which Figure 1 is a block diagram illustrating a conventional simulating colour image system; Figure 2 is a schematic block diagram of one embodiment of a simulating colour picture system in accordance with the present invention; Figure 3 is a circuit diagram of the coloursimula- tion circuit of Figure 2; Figure 4 is a diagram showing the principle of the colour simulation; Figure 5 is a schematic block diagram of a second embodiment of a colour simulation system; Figure 6 is a circuit diagram for the colour simulation circuit of the embodiment of Figure 5; Figure 7 is a diagram showing the principle of the colour simulation of the embodiment of Figures 5 and 6;; Figure 8 is a schematic block diagram illustrating a third embodiment of simulating colour image system; Figure 9 is a circuit diagram for the colour simulation circuit of the embodiment of FigureS; Figure 10 is a diagram illustrating the principle of the colour simulation of the embodiment of Figures 8 and 9; and Figure 11 is a circuit diagram illustrating an inverter circuit to be inserted in the simulating colour circuit.

In Figure 2, a system for the colour simulation of an image is schematically depicted in a block diagram with respect to an industrial television system. This simulating colour image system is a manifestation of base band transmission using a coaxial cable 2. It comprises a television camera for photography, an amplifying circuit for amplifying feeble image signals and brightness signals, a colour simulating circuit 4 serving to convert brightness signals into colour signals, and a colour display unit 5. Of course, the system may rely on modulation transmission in which case, the system requires circuits such as an amplitude modulation circuit and a demodulation circuit which are necessary to the processing of image signals.

As the TV camera 2 mentioned above, an industrial black and white TV camera may conveniently be used because the system of this invention involves the use of brightness signals. A colour TV camera may be used provided that it is used to derive only brightness signals. Use of a colour TV camera, however, is expensive and is not necessary.

The colour simulating circuit 4, as illustrated in Figure 3, comprises RGB separator circuits 6 for converting the brightness signals into an R colour signal (herein referred to as R signal), a G colour signal (herein referred to as G signal), and a B colour signal (herein referred to as B signal), of mutually equal levels, and low cut-off circuits 7 for cutting off colour signals below mutually different specific low voltage levels in colour signal circuits located between the RGB separator circuits 6 and the colour display unit 5. Thus, the colour simulating circuit 4 serves to convert the RGB signals of mutually equal levels fed out corresponding to the brightness signals into different voltage levels, producing a colour image.

These low cut-off circuits 7 may be of a type which is shown in Figure 3, comprising a transistor8 adapted to receive a colour signal at its base, a variable resistance network comprising the potentiometer 9 and fixed resistors 11 inserted between the emitters of the transistors 8 and the ground, and a bias network. The operating point or cut-off point of the transistor 8 is set by the magnitude of the voltage applied to the emitter side, as determined by the variable resistance, and the transistor 8 is actuated only when the colour signal arriving at the base has a level exceeding the prescribed limit, namely, the voltage level to be fixed based on the corresponding operating point. The magnitude of the voltage applied to the emitter of transistor 8 is set by the variable resistance and bias networks.Thus, the low cut-off circuit 7 actuates the transistor 8 only when the base receives a colour signal with a voltage level exceeding the emitter side voltage level set by adjusting the potentiometer 9. By suitably changing the magnitude of its voltage level, the low level region of the colour signal corresponding to the varied magnitudes is cut off and prevented from being fed out as an output.

The collector of the transistor 8 is directly connected to the emitter of drive transistor 12 so that the colour signal which has gone through the cut-off circuits may be amplified and fed to the colour display unit 5. To the emitter of the transistor 8 is connected the above mentioned bias network formed of condensers 13 and resistors 14. This bias network and the standard power source 10 are connected to the base of the drive transistor 12 through a diode 15 and a resistor 16 in parallel. In the present embodiment, NPN transistors are used as the cut-off circuits 7. These circuits may alternatively be formed of other transistors or other devices such as, for example, operational amplifiers.

A cut-off circuit 7 as described is associated with each of the colour signal circuits and is located between each of the RGB separator circuits 6 and the colour display unit 5. They are given varying operating points (cut-off points or levels) by the operation of the variable resistors (potentiometer) 9. Since the colour signals which have gone through the low cut-off circuit 7 possess varying cut-off regions when they are amplified and fed into the colour display unit 5, they assume the state of all three, a combination of any two, or any one, of the RGB signals corresponding to the brightness levels to give rise to a colour picture. As the colour display unit 5, a braun tube functions most advantageously from the practical point of view. Any of various types of braun tubes can be used. The braun tube of a colour TV set can be used in an unmodified form, for example.Of course, a colour display unit using liquid crystals may be used.

In the simulating colour image system described above, the object to be photographed is reproduced on the display unit 5 in the form of a colour image by having light reflected from the object fed in as a picture image in the form of brightness signals corresponding to the brightness of the object, then causing the brightness signals to be converted in an RGB separator into separate RGB signals of mutually equal levels, and in accordance with the additive colour mixing process, allowing desired colour signals, after being cut off with desired levels, to be reproduced on a display unit, thereby artificially producing colour image signals.The brightness signals fed out of the TV camera 1 corresponding to the brightness of the object are first converted in the RGB separator circuits 6 into colour signals comprising an R signal, a G signal, and a B signal of mutually equal magnitudes or levels. Then, the colour signals are forwarded to the cutoff circuits 7 disposed in the respective colour signal circuits and, in the cutoff circuits 7, the portions of the colour signals falling below respective preset cutoff levels are cut off. At least two of the signals must be cut off if it is desired to provide three signals of different magnitudes.

For the R signal, the cutoff value can be fixed at 0 so that this signal is fed out intact to the image or display tube 5. For the G signal, the low cutoff level may be fixed at one-half the maximum value of the brightness level. And for the B signal, the low cutoff level may be set at about four-fifths the brightness level. Thus, the three signals will have mutually different magnitudes, for example, the R > the G signal > the B signal. The invention, however, is not limited to this particular sequence, as any of the colour signals can have a greater magnitude than any other. The portions of the colour signals which exceed the respectively fixed low cutoff levels are allowed to be fed out as output.Since the signals initially have mutually equal levels, they will have different magnitudes according to the amounts cut off and will be reproduced as a triangular image having an ordinate and an abscissa. Since only the low portion, or portions, is cut off, the images will have the same bases, which, as shown in Figure 4, start at the ordinate and extend along the abscissa, according to their respective magnitudes. Thus, there will be overlapping of the three colors in the B region and of the green and red in the G region.

Thus, the image on the colour receiver tube 5 will be a simulated colour display of three colours, red, yellow and white corresponding to the brightness levels as illustrated in Figure 4. These colours have the degrees of brightness corresponding to the brightness levels. Take the colour of red, for example. In the region of red, there exists bright red, dark red, and a red colour intermediate between bright and dark red. When the brightness level is extremely low, the red appears to be black. To the human eyes, therefore, the simulated colour image appears in a total of five colours, black, dark red, red, yellow, and white. Even by setting the low cut-off level of the R signal at below about one-fifth the maximum value of the brightness level forthe purpose of permitting a clear distinction between the portion appearing in black and that appearing in dark red, the desired repression of the colour signal output within the low brightness region may be obtained.

Here, the cut-off levels are set by suitably changing the magnitudes of resistance of the variable resistors (potentiometer) 9 in the respective cut-off circuits 7. In other words, the operating points (cut-off levels) of the transistors are changed by changing the magnitudes of resistance of the emitter sides of the transistors 8. Hence, by adjusting the variable resistors 9 in the three cut-off circuits 7, any desired relation between the three colour signals can be obtained.

When an interesting aspect of the phenomenon under consideration produces a low brightness signal which, for example, is reproduced on the display unit as dark red, it is sometimes desirable to invert that signal by means of an inverter circuit, such as illustrated in Figure 11 at 44.

The simulating colour image system constructed as described above can be advantageously utilised in applications which require given objects to be displayed in colours corresponding to changes in brightness of the objects. For example, an apparatus for visually displaying or simulating a fluid flow by reproducing a flow field in a fluid flow model by the use of a fluid containing a large volume of fine, homogeneous air bubbles and projecting a slit of light onto the flow field, thereby allowing the light to be irregularly reflected on the air bubbles in a given cross section of the fluid flow and displaying that flow field with the resultant scattered beams of light, has been proposal by the present inventors and is shown in the present Applicants' copending British Patent Application No. 8330046 (Publication No. ).

The combination thereof with the simulating colour image system of this invention, may also therefore form part of the general inventive concept of the present inventicn. In this apparatus for depicting fluid flow, when the fluid contains a large volume of air bubbles which are sufficiently fine and homogeneous, the intensity of the scattered beams of light is believed to be directly proportional to the number of such air bubbles in a unit volume of the fluid, i.e., the density of air bubbles. This postulation implies that the intensity of the scattered beams of light is proportional to the density of air bubbles. By causing changes of brightness of the scattered beams of light to be displayed in colours proportionate to the brightness levels therefore, the continuous changes of density can be shown visually relatively and continuously.

As described above, this embodiment of the present invention can produce a color image of an uninterrupted motion picture in colour, hue and brightness corresponding to the brightness level of a given object directly from an analog image signal in its unaltered form by a procedure which comprises causing brightness signals fed out of the TV camera corresponding to variations of brightness of the object to be converted in the RGB separator circuits into colour signals comprising an R signal, a G signal and a B signal of mutually equal levels, cutting at least two of the resultant three signals with different cutoff levels set in advance, thereby eliminating the portions of these signals below the cutoff levels, and feeding the remaining portions of colour signals to the colour display unit, thereby allowing any of the R signal, G signal, and B signal to be selected and combined according to brightness levels to produce colours. Moreover, this invention can convert an analog black-and-white image signal into a colour image signal of desired colours without being converted in advance into a digital image signal, by disposing in each of the different colour signal circuits laid between the RGB separator circuits and the colour display unit, the low cutoff circuit permitting variation of the operating point and serving to cut off the portion of a colour signal falling below a prescribed low operating voltage and, at the same time, providing the RGB separators with means for feeding thereto brightness signals from the TV camera.By means of the present invention, therefore, a form of colour simulation, which has previously been barely capable of achieving a static image in colour even with the aid of a high-speed, large computer, can now be effected quite inexpensively without the use of any computer.

It is sometimes desirable to avoid or minimise the overlapping of the colour signals. Suitable circuitry for this is illustrated in Figures 5 and 6. This circuitry includes low cut-off circuits 7 as described above with the addition of high cut-off circuits 17 interposed between the RGB separator and the low cut-off circuits 7.

The high cut-off circuit 17 may be of a type which, as illustrated in Figure 6, causes portions of the colour signal exceeding fixed levels to be grounded.

This is accomplished by feeding the colour signal into the collector through a resistor 20 and through a resistor 21 to a variable resistor (potentiometer) 19, which is a base bias for a transistor 18. In the high cut-off circuit 17, the RGB separator 6 side of the resistor 20 is grounded via the resistor 21 and the variable resistors 19 in series, while the low cut-off circuit 7 side of the resistor 20 is connected to the collector of the transistor 18. Further, the transistor 18 has its emitter side grounded and its base side connected to the variable resistor 19. When the magnitude of the resistance of the variable resistor 19 is changed and set to a certain value, the drive level between the base anci the emitter are determined, based on these values.When the colour signal rises and reaches a voltage level exceeding the drive level, the transistor 18 is actuated to ground the colour signals. As the resultthe high level portion of the colour signal determined bythe aforementioned preset values of resistance of the variable resistor 19 is cut off. These high cut-off circuits 17 are disposed one each in the colour signal circuits and they have different drive levels or high cut-off levels set respectively. The low cut-off circuits 7 are disposed one each in the colour signal circuits between the high cut-off circuits 17 and the colour display unit 5 and are given different operating points by operation of the variable resistors 9.

Optionally, the low cut-off circuits 7 may be located before the high cut-off circuits 17 so that the colour signals will be subjected to high cut-off and then fed out to the colour display unit 5.

When the colour signals which have gone through the aforementioned high cut-off circuits 17 and low cut-off circuits 7 are amplified and fed to the colour image tube 5, therefore, they produce a colour picture image on the tube because they have mutually different cut-off regions and are fed out with the coloured regions varying with the original brightness levels (including the case in which these regions overlap). By selecting suitable settings for the potentiometers 9 and 19, it is possible to give each colour signal a separate region or area in the display, extending away from the ordinate and along the abscissa, according to their respective low and high cutoff points, as shown in Figure 7. If desired, the overlapping areas (GfB-cream and B/R-purple) can be enlarged as desired or entirely eliminated by adjusting the cutoff points.

In the present embodiment, NPN transistors are used as the cutoff circuits 7, 17. These circuits may be formed of other transistors or other devices such as, for example, operational amplifiers. They may be other cutoff circuits.

In the simulating colour image system constructed as described above, the object to be photographed is reproduced in the form of a colour picture image on the colour display unit 5 by the additive colour mixing process with colour image signals which are artificially produced by having the object fed in as a picture image in the form of brightness signals corresponding to the brightness of the object, causing the brightness signals to be connected into RGB signals of mutually equal levels, and allowing the RGB signals to be cut off with mutually different high cutoff levels and low cutoff levels and distributed to mutually different brightness levels.

The brightness signals fed out of the TV camera 1 corresponding to the brightness of the object are first converted at the RGB separator circuits 6 into an R signal, a G signal, and a B signal of mutually equal levels. Then, in the cutoff circuits 7, 17 formed in the respective colour signal circuits, the portions of the colour signals falling above and below respectively preset different high and low cutoff levels are cut off.

Designation of the high brightness region with green colour, for example, is effected by setting the high cutoff level at the maximum value of the brightness level and, at the same time, raising the low cutoff level -o the high brightness side, designation of the medium brightness region with blue colour is effected by setting the high cutoff level at about two-thirds the maximum value of brightness level and, at the same time, raising the low cutoff level to the medium brightness side, and designation of the low brightness region with red colour is effected by setting the high cutoff level at about one-third the maximum value of the brightness level and, at the same time, setting the low cutoff level at the minimum value of the brightness level. Consequently, the picture image on the colour image tube 5 is displayed in a form simulated with the three colours, red, blue and green.In this case, otherwise possible occurrence of a portion devoid of signal, namely a black portion in the colour boundaries is precluded and desired observation of changes in brightness is consequently facilitated by setting the low cutoff level slightly below the lower region of the high cutoff level. In this case, the picture image is displayed as simulated with six colours i.e., black, dark red, purple, blue, cream and green. Any desired repression of the colour signal output in the low brightness region may be attained by setting the low cutoff level of the R signal slightly above the minimum value of brightness level,thereby ensuring clear distinction between the portions appearing in black and those appearing in dark red.Here, the high cutoff levels and the low cutoff levels can be set by suitably varying the magnitudes of the resistances of variable resistors 19, 9 in the respective cutoff circuits 17,7.

As described above, this embodiment of the present invention can produce a colour image of an uninterrupted motion picture in colour, hue and brightness corresponding the the brightness level of a given object directly from an analog image signal in its unaltered form by a procedure which comprises causing brightness signals fed out of the TV camera corresponding to variations in brightness of the object to be converted in the RGB separator circuits into an R signal, a G signal, and a B signal of mutually equal levels, cutting the resultant three signals with mutually different low cutoff levels and high cutoff levels set in advance, thereby eliminating the portions of these signals respectively below and above the low and high cutoff levels, and feeding the remaining portions of the colour signals to the colour display unit, thereby allowing the R signal, G signal, and B signal to be distributed to different regions corresponding to the brightness levels to produce colours. Moreover, this invention can convert an analog black-and-white image signal into a colour image signal of desired colours without being converted in advance into a digital image signal by including in each of the different colour signal circuits, between the RGB separator circuits and the colour display unit, the low cut-off circuit permitting variation of the operating point and serving to cut off the portion of a colour signal falling below a prescribed low operating voltage and the high cut-off circuit permitting variation of the operating point and serving to cut off the portion of a colour signal falling above a prescribed high operating voltage and, at the same time, providing the RGB separators with means for feeding thereto brightness signals from the TV camera.By means of the present invention, therefore, a form of colour simulation which previously has been barely capable of achieving a static image in colour even with the aid of a high-speed, large computer, can now be obtained quite inexpensively without the use of any computer.

It is sometimes further desirable to provide a variable gain amplifying circuit for a colour signal from one or both of the cut-off circuits. This embodiment of the invention will be described with reference to the examples illustrated in Figures 8, 9, and 10 in which, in addition to the low and high cut-off circuits 7 and 17 of Figures 5, 6, and 7 there is provided an amplifying circuit 22.

The colour simulating circuit 4, as shown in Figure 8, comprises RGB separator circuits 6 for converting brightness signals into colour signals, high and low cut-off circuits 7 and 17, adapted to cut off the portions of the colour signals falling above or below mutually different prescribed voltage levels and the colour display, as fully described above. In this embodiment, a variable gain amplifying circuit 22 is disposed between the cutoff circuits and the colour display in order to confer a higher degree of amplification on any one of the R signal, G signal, and B signal distributed in different brightness level regions in the cutoff circuits 7 and 17, than on the other two remaining signals.This colour simulating circuit 4 inherently functions to produce a simulating colour image by causing RGB signals of mutually equal levels fed out in response to brightness signals to be distributed as divided by prescribed brightness levels and to amplify a selected colour signal with a higher gain than the remaining colour signals.

The aforementioned high cutoff circuits 17 may be of a type described above, in which colour signals are fed as input to variable resistors (potentiometer) 19, base biases of NPN transistors 18, and to collectors and allow the colour signals to be grounded when they have voltage levels exceeding prescribed levels.

The low cutoff circuits 7, desirably, are of a type which, as illustrated in Figure 9, feed colour signals as inputs to the variable resistors 9, base biases for the NPN transistors 8, and to the collectors ofthe NPN transistors 12 and allow the colour signals to be grounded when they have voltage levels not exceeding the prescribed levels. In the low cutoff circuits 7, the collectors of NPN transistors 8, connected with colour signal at the base sides, interconnect with the bases of NPN transistors 12 connected with colour signals at the connector sides wherein both emitter sides of transistors 8 and 12 are grounded, and the collector sides of transistors 8 and base sides of transistors 12 are connected with the standard power source 10 through resistors 13to permit application of bias voltage.When colour signals having voltage levels exceeding the operating points of transistors to be determined by the variable resistors 9 as base biases are received in the lower cutoff circuits 7, therefore, the transistors 8 are actuated to ground the base voltages and the transistors 12 are left unactuated. Consequently, the colour signals are fed out without being grounded.

When colour signals having voltage levels not exceeding the operating points are received, however, the bias voltages are applied to the transistors 12 to actuate these transistors 12 because the transistors 8 are not actuated. Consequently, the colour signals are grounded and are not fed out. The resistors 11 and corresponding variable resistors 9 are disposed in series on the base sides of the transistors 8 and the resistors 13 are located between the base sides of the transistors 12 and the standard power sources 10.

The aforementioned variable gain amplifying circuits 22 may be of a type which, as illustrated in Figure 9, comprise complementary Darlington circuits having variable resistors 20 disposed on their input base sides so that the degrees of amplification effected on the final output colour signals will be altered by suitably changing the voltages of input signals. The variable gain amplifying circuits 22 serve to alter the voltages of output signals by changing the magnitudes of the resistance of the variable resistors 23 at the input side bases of the complementary Darlington circuits which are formed by connecting the collectors of NPN transistors 24 through the medium of bias resistors 26 to the bases of PNP transistors 25 and, at the same time, connecting the emitters of the NPN transistors 24 to the collectors of the PNP transistors 25.As the result, the circuits 22 permit variation of amplification. The symbol 27 denotes emitter grounding resistors.

The colour signals which have gone through the aforementioned high cut-off circuits 17, low cut-off circuits 7, and variable gain amplifying circuits 22 are forwarded through other necessary circuits and fed out to the colour display unit 5. As the colour display unit 5, a braun tube, particularly a braun tube for a colour television is preferably used for reasons of economy, through a liquid crystal display device or other similar device may be used.

In the simulating colour image system shown in Figures 8, 9, and 10, the object to be photographed is reproduced in the form of a colour picture image on the colour display unit 5 by the additive colour mixing process, as described above in connection with Figures 5, 6 and 7. There is thus obtained a colour image having a variation of brightness and formed of a desired set of colours corresponding to the original brightness levels. There is a possibility however, that in this colour image, the low brightness level region will detract from brightness to a point where the variation of brightness ceases to be clearly discerned.To avoid this danger, therefore, the colour signal of the low brightness region, namely, the R signal, will be amplified in the variable gain amplifying circuit 22 to a greater extent than the other colour signals so as to have its brightness emphasised. Specifically, this preferential amplification of the R signal is effected by raising the magnitudes of resistance of the variable resistor 23 in the G signal circuit and the B signal circuit and lowering the input signal voltage and, at the same time, lowering the magnitude of resistance of the variable resistors 23 in the R signal circuit, thereby increasing relatively the input signal voltage. As the result, the R signal is amplified more than the G signal and the B signal. Of course, where the magnitudes of resistance of the variable resistors 23 in the respective colour signal circuits are set in advance at rather high levels, this selective emphasis may be effected only by lowering the magnitude of resistance of the R signal. By this arrangement, a colour image can be formed in which the image of the low brightness region is made to appear with prominence, as shown in Figure 10.

In this embodiment, a desired one of the three colour signals is selectively amplified to a greater extent than the other colour signals by feeding into the variable gain amplifying circuit 22 the appropriate colour signals after undergoing the cut-off treatment. Optionally, the embodiment may be modified so that the preferential amplification will be carried out by feeding to the variable gain amplifying circuit 22, the colour signals which have undergone the high cut-off treatment or the low cut-off treatment, instead of both high and low cut-off treatments. The cut-off treatment, particularly the high cut-off treatment, is effected only with great difficulty on colour signals which have undergone amplification.Thus, the preferential amplification is desired to be effected by injecting into the variable gain ampliying circuit, colour signals which have already undergone the high cut-off treatment. In this case, the colour signal circuit through which the preferentially amplified colour signal is passed, is required to have its low cut-off point raised proportionately to the increase in the extent of amplification.

The simulating colour image systems produced according to this embodiment can be advantageously utilised in applications which require given objects to be displayed in colours corresponding to changes in brightness of the objects, as more particularly described above, and can produce a colour image of an uninterrupted motion picture in colour hue and brightness representing the brightness levels of a given object directly from an analog image signal in its unaltered form and, at the same time, can emphasise the brightness of a colour corresponding to a specific brightness.This is achieved by a procedure which comprises causing brightness signals fed out of a television camera representing the brightness of an object being photographed to be converted in RGB separator circuits into an R signal, a G signal, and a B signal on mutually equal levels, cutting the three signals with mutually different low cut-off levels and high cut-off levels set in advance, thereby eliminating the portions of the three signals respectively below and above the low and high cut-off levels, and distributing the resultant RGB signals to different regions proportionately to the brightness levels.At the same time, one of the three colour signals is amplified more than the remaining two colour signals and is fed out in conjunction with the remaining colour signals to a colour display unit, thereby causing the R signal, G signal, and B signal to be distributed to regions of different brightness levels and allowing the desired colour signal to be amplified to a greater extent than the other colour signals.

Further, this invention can convert an analog black-and-white image signal into a colour image signal of desired colours without being converted in advance into a digitial image signal and, when desired, can cause a desired colour signal to be amplified to a greater extent than the other colour signals by disposing in each of the different colour signal circuits between RGB separator circuits and a colour display unit, a low cut-off circuit permitting variation of the operating point and serving to cut off the portion of a colour signal falling below a prescribed operating voltage, a high cut-off circuit permitting variation of operating point and serving to cut off the portion of a colour signal falling above a prescribed operating voltage and, when desired, a variable gain amplifying circuit for receiving a colour signal having gone through at least one of two cut-off circuits and, at the same time, providing the RGB separator circuits with means for feeding brightness signals from a TV camera.

Claims (17)

1. A method for colour simulation which comprises forming an image input composed of brightness signals, converting the brightness signals into colour signals comprising an Signal, a B-signal and a G-signal of mutually substantially equal levels in an RGB separator; cutting off portions of at least one of the resulting three colour signals at a level corresponding to a particular brightness level to produce colour signals representative of mutually different brightness ranges; and reproducing on a colour display a colour image which is a composite of the three colour signals obtained in the cutting off step.

2. A method as claimed in Claim 1 in which the intact signals are cut off at low cut-off points.

3. A method as claimed in Claim 1 or Claim 2 in which the intact signals are cut off at high cut-off points.

4. A method as claimed in any preceding claim in which one of the cut off signals is amplified to a level above the other two.

5. A method as claimed in Claim 2 in which the reproduced image comprises a triangular-shaped area, the legs of which constitute an ordinate and an abscissa in which the colour bands formed from the cut-off colour signals extend from the ordinate along the abscissa, so that one colour overlaps one other colour and the third colour overlaps the other two.

6. A method as claimed in Claims 2 and 3, or Claim 4 in which the reproduced image comprises a triangular-shaped area the legs of which constitute an ordinate and an abscissa and in which each colour band formed from the cut off colour signals has a portion which is not overlapped by any other colour band.

7. A method as claimed in Claim 6 in which adjacent blue and green bands overlap to form a narrow cream-coloured band and adjacent blue and red bands overlap to form a narrow purple-coloured band.

8. A method for colour simulation substantially as herein specifically described with reference to and as shown in Figures 2 to 4, Figures 5 to 7, or Figures 8 to 10 of the accompanying drawings, or any of these embodiments modified in accordance with Figure 11.

9. A method as claimed in any preceding claim forthe colour simulation and visual display of the flow of a fluid in which a slit of light is projected onto the flow field of a fluid containing a large volume of fine, homogeneous gas bubbles so that the light is reflected irregularly by the bubbles to produce the said image in-which the intensity or brightness of the reflected light is representative of the density of the bubbles, and in which the image is displayed as a colour simulation in which the image is displayed as a colour simulation in which the colours are representative of the brightness and so the air bubbles density in the fluid.

10. Apparatus for colour simulation which comprises means for producing a picture image input composed of brightness signals, an RGB separator arranged to convert the brightness signals into colour signals comprising an 11-signal, a B-signal, and a G-signal of mutually substantially equal levels; cut-off means for cutting off portions of at least one of the resulting three colour signals at a level corresponding to a particular brightness level to produce colour signals representative of mutually different brightness ranges; and a display device for reproducing a colour image which is a composite of the three colour signals obtained in the cutting off step.

11. Apparatus as claimed in Claim 10 in which the cut-off means are arranged to cut off the intact signals at low cut-off points.

12. Apparatus as claimed in Claim 10 or Claim 11 in which the cut-off means are arranged to cut off the intact signals at high cut-off points.

13. Apparatus as claimed in any of Claims 10 to 12 including an amplifier arranged to amplify one of the cut off signals to a level above the other two.

14. Apparatus as claimed in Claim 11 in which the reproduced image comprises a triangularshaped area the legs of which constitute an ordinate and an abscissa and in which the colour bands formed from the cut off colour signals extend from the ordinate along the abscissa, so that one colour overlaps one other colour and the third colour overlaps the other two.

15. Apparatus as claimed in Claims 11 and 12, or Claim 13, in which the reproduced image comprises a triangular-shaped area the legs of which constitute an ordinate and an abscissa and in which each colour band formed from the cut off colour signals has a portion which is not overlapped by any other colour band.

16. Apparatus as claimed in Claim 15, in which adjacent blue and green bands overlap to form a narrow cream-coloured band and the blue and red bands overlap to form a narrow purple-coloured band.

17. Apparatus for colour simulation constructed and arranged substantially as herein specifially described with reference to and as shown in Figures 2 to 4, Figures 5 to 7 or Figures 8 to 10 of the accompanying drawings, or any of these embodiments modified in accordance with Figure 11.