Polychromatic Graphic Visual Display And Control System Assembly

Abstract

Polychromatic visual display and control system assembly, characterized by a main memory receiving graphic data corresponding to traces of various colors and/or various color portions to be displayed on a polychromatic cathode tube, and a selection system for sequentially selecting one of the various colors and for controlling the read-out from the main memory of all the data corresponding to the selected color such that the display of the traces and/or portions of the traces of each of the various colors is enabled in a sequential manner to form a composite display of the traces of various colors.

Description

The present invention concerns a polychromatic graphic visual display assembly enabling, more particularly, the traffic of various craft or the trace of various mathematical curves to be observed on a screen.

Various data relating to craft moving in the region of space considered and concerning, more particularly, their position, their identity, their speed or their altitude, in the case of aircraft, are transmitted to the observer installation, for example by a radar or other detection or telemeasuring devices. The vectors which are to be traced on the panoramic indicator screens are intended, for example, to indicate the direction and the speed of the craft, or of the cartographic elements. These vectors are linked together and thus form broken lines or polygonal contours. They have well-defined origins and ends. It is particularly interesting to be able to observe the traffic of these various craft according to traces of different color, in order to avoid any possible confusion between the trajectories of the various craft.

Known devices enabling such results generally comprise

A POLYCHROMATIC CATHODE TUBE WHOSE SCREEN IS SUITABLE FOR RECEIVING TRACES OF SEVERAL COLORS, THESE TRACES BEING RENEWED IN SUCCESSIVE CYCLES;

A MAIN MEMORY COMPRISING A MEMORY BLOCK, AN ADDRESS REGISTER AND AN OUTPUT REGISTER, FROM WHICH ARE EXTRACTED THE GRAPHICAL DATA RECEIVED FROM A CALCULATOR OR COMPUTER (THIS DATA IS RECORDED BY THE MEMORY BLOCK AND CLASSIFIED ACCORDING TO ITS ADDRESS IN THAT BLOCK AND IT CONCERNS THE DIRECTING PARAMETERS AND THE COLOR OF EACH VECTOR FORMING A PART OF THE POLYCHROMATIC TRACES);

A DATA PROCESSING MEANS OR ELEMENT FOR ENABLING THE GENERATION OF TRACES ON THE SCREEN OF THE CATHODE TUBE IN ACCORDANCE WITH THE OUTPUT REGISTER OF THE MAIN MEMORY;

A VECTOR GENERATOR CONTROLLED BY THE DATA PROCESSING ELEMENT AND SUITABLE FOR AFFECTING THE DEFLECTION OF THE CATHODE BEAM SO AS TO MAKE TRACES APPEAR ON THE SCREEN (Generally, the vector generator is connected with a character generator enabling characters to be made to appear on the screen); and

MEANS FOR CAUSING CHANGES IN COLOR OF THE VECTORS, THESE MEANS BEING CONTROLLED BY THE CONTROL BLOCK AND ALSO FORM A PART OF THE DEVICES.

Generally, the polychromatic visual display assembly is equipped with a cathodic penetration tube which enables a polychromatic adding synthesis, controlled by the energy in the electrons of the beam. That is, by switching the acceleration voltage of the electrons, the color on the screen is changed. Such voltage switching requires high power, for example, with a conventional switching device, the average power dissipated is on the order of 100 watts for a cathode tube having a diameter of 40 centimeters and with a switching time not exceeding a millisecond.

The loss of time, when tracing figures, which results from such relative slowness, causes stresses for programming pictures. Indeed, only 25 milliseconds at the most are available for tracing the picture, since the light revival frequency must not go below 40 Kc/s as this would cause a disagreeable flickering. If the color is not counterbalanced by a reduction in the representing capacity, the total duration assigned to the color switching operations during a cycle must remain small with respect to the period of each cycle of traces. With a switching time in the order of a millisecond, this necessitates a grouping together of the elements of the picture according to color to be effected by programming in order to require of the visual display assembly only the minimum of four color changes per picture (in the case where the polychromatic visual display assembly is a four-color assembly, for example).

The programming requirement is, when analized, a very serious matter. In the first place, it makes the rearranging and transferring of a new visual display program compulsory for the least change in color of a simple vector of the traces, since the place of each vector in the main memory depends on its color. If the link with the computer has a low output, the operator must wait a long time for the complete message to be transmitted. What is more serious is that the rearranging requires a great amount of work by the calculator. Considering, for example, a curve traced in a certain color by means of a sequence of vectors; the simple changing of the color of a small part of the curve requires the breaking of that sequence and hence, not only transferring the element in question to another memory zone, but also inserting two further positioning instructions, the one at the outset of the element which has changed color, and the other at the resumption, on the curve of the interrupted chain.

There are even more serious problems. For example, performing graphic systems generally enable the simultaneous display of several pictures. Thus, it is possible to feed four cathode units, for example, with distinct pictures. The memory, the vector generator, the character generator and the connected circuits are common and used on a time-sharing basis. In principle, the four pictures are traced successively, extinguishing, for each, the beams of the screens which are not concerned. The program requirement for grouping together according to color, necessitates that with multi-screen systems, the four pictures are dissociated and that at the least change made to one of the pictures, the complete message of the four pictures must be reorganized by the computer and transferred to the assembly.

A programming facility afforded to known assemblies is the subprogram call instruction by means of which a picture element capable of being repeated needs to be written only once, in a "corner" of the memory, from where it may be called through the "main program." It is quite evident that the sorting out according to color requirement prevents any change in color within a sub-program. These sub-programs must be written in an achromatic way and will compulsorily be visually displayed in monochromatic form.

With regard to power dissipation problems in the color switching elements, a known device enables very fast switching without permanent power dissipation to be ensured. The duration of the color changes may thus be reduced to 50 microseconds. In a great number of applications, that solution is satisfactory and enables the color to be treated as a variably selected parameter, in the same way as the brightness of the traces, for example. Unfortunately, one requirement limits, at present, the number of color changes allowed per picture. Technological imperatives limit the average power exchanged between the color switching device and the reactive charge which the anode of the cathode tube represents. In present technology, that limit is reached at 20 color changes per cycle of traces and per screen (the screens not concerned remaining at rest). That limit is rarely reached, but it may happen, in certain applications, that the limit is insufficient.

A conventional solution enabling the requirement for programming according to color to be obviated consists in having the sorting out of the vectors effected by the visual display assembly and not by the computer. That solution does not, however, rid the programmer of all requirements pertaining to color. That is, with this solution it is not only necessary to record a list for the sorting out of the vectors according to color, but moreover, it is necessary to:

1. Dissect each assembly of traces into "isochromatic elements or vectors." That is, determine all the elements whose color is liable to be modified.

2. Make the trace of each isochromatic element thus determined practically autonomous, that is, independent from what may be traced beforehand. Thus, not only the color, which is the cause of that dissociation, but all the other parameters, as well as the original positioning of each vector, must be specified at the beginning of each element.

3. Organize in a quite particular manner the visual display program. That is, each isochromatic element must be recorded in the form of an achromatic sub-program and the main program then takes the form of a list of sub-programs, each being preceded by the indication of its color. If there are four distinct colors, these requirements then being satisfied, the main program must be read four times in succession, by cycle of traces, that is, calling only the sub-programs which are in the processed color.

The part of the requirements imposed by the above solution present problems when analized. For example, considering a curve traced quite naturally by a sequence of small vectors, if it is required to be able to show the operator any element of the curve and to modify its color, this simple method of tracing is no longer possible, since each elementary vector must be preceded by a positioning and the specification of its color. It must, moreover, be transmitted in the form of a sub-program with the jump and return to main program instructions which this entails. This is the equivalent of saying that it is an impossible task. It is therefore possible to have doubts about the advantage of a solution which sacrifices, to avoid a programming requirement which might be troublesome but not impossible to overcome, the true possibilities of using color.

It is therefore an object of the present invention to avoid these various programming and technologically limiting requirements.

In accordance with the present invention, there is provided a polychromatic graphic visual display assembly comprising:

a polychromatic cathode tube whose screen is suitable for receiving traces having portions of various colors, these traces being renewed in successive cycles;

a main memory comprising a memory block, an address register and an output register from which the graphic data received from a computer are extracted, the main memory being suitable, for each portion of traces, for recording a group of data items relating to that portion, the group of data items being classified in the memory in a group of addresses, the first of these data items relating to the color of the portion and being classified at a first address, called the "color" address, in the group of addresses, the other data items relating to the parameters of the vectors constituting the portion being classified at the following addresses in the group of addresses;

a data processing element for enabling the generation of the traces on the screen of the cathode tube, in accordance with the output of the output register;

a vector generator and a character generator controlled by the data processing element and capable of influencing the deflection of the cathode beam so as to make traces and characters appear on the screen;

means for causing changes in color of portions of the traces, the means being controlled by the control block; and

the assembly being characterized in that it comprises a color change address selecting element controlled by the memory block and its address register, the selecting element listing the color addresses of the various groups and recording the corresponding color data, and the selection element being capable of controlling the reading of the main memory, so as to extract successively from that memory the data corresponding to the groups of addresses of the main memory containing identical color change data.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing, which shows, for purposes of illustration only, two embodiments in accordance with the present invention, and wherein:

FIG. 1 is a schematic block diagram illustration of an embodiment according to the present invention; and

FIG. 2 is a schematic block diagram illustration in another embodiment according to the present invention.

Referring now to the drawings wherein like reference numerals are utilized to designate like parts throughout the several views, the visual display assembly shown in FIGS. 1 and 2 are provided with a polychromatic cathode tube 1 whose screen 2 is suitable for receiving traces of several colors, these traces being renewed in successive cycles. A main memory is also provided and includes a memory block 3, an address register 4 and an output register 5. The geographical data concerning the directing parameters and the color of the vectors forming a part of the polychromatic traces are received from a calculator or computer 6 by the block 3. This data is classified according to its address by means of the address register 4. A data processing element 7 for enabling the generation of the traces and controlling the traces on the screen 2 of the cathode tube 1 is connected to the output register 5 and controlled thereby. A vector generator 8 and a character generator 9 controlled by the processing element 7 and suitable for influencing the deflection of the cathode beam are provided so as to make traces and characters appear on the screen. These vector and character generators control the horizontal deviation plates 10 and vertical deviation plates 11 by means of analog voltages supplied by a binary-to-analog convertor 12. It has been supposed, by way of an example, that one of the horizontal deviation plates 13 and one of the vertical deviation plates 14 are brought to a fixed reference potential.

The assembly comprises, also, means 15 for causing changes in color of the traces. These means consist of a switching element for the high voltage applied to the cathode 16 of the cathode tube 1 and they are controlled by the element 7. It has been supposed, by way of an example, that the wehnelt 17, as well as the anode 18 of the cathode tube, is brought to the fixed reference potential.

Lastly, the assembly includes an address selection element or system 19 for selecting by change in color, and controlled by the memory block 3, by the address register 4 of the main memory and by the processing element 7. The selection element is controlled so as to receive, from the memory block 3 and from its address register 4, the data relating to each change in color of the traces and enables all the addresses in the main memory where color change data is stored to be listed. The selecting element 19 then controls the address register 4 of the main memory, so that, for each cycle of traces of several colors, the data items extracted from the main memory is classified into several groups of addresses comprising identical color change data. Thus, in the example of a chosen embodiment, for which the visual display assembly enables red, orange, yellow and green traces to be effected, the selection element 19 which has received data concerning the address and the color of the various color changes contained in the main memory, controls the reading of the main memory, so that, for example:

Only data concerning the red-colored traces are extracted from the main memory. That is, only the addresses preceded by a change in the red color will be selected and consequently occupied by data concerning red-colored traces. For that cycle of traces, the red-colored traces effected through the data processor 7, the vector generator 8, the character generator 9 and the switching system 15 will appear in the first instance on the screen.

The processing then continues by means of element 19 for selection by color change address, in an identical manner for the other colors for the cycle of traces considered. That is, all the orange-colored traces, then all the yellow-colored traces and lastly all the green-colored traces are formed.

The operation of the selection element 19 will be better understood by way of the following description. The selection element includes an auxiliary memory 20 controlled by the memory block 3 and by the address register 4 of the main memory. It is this auxiliary memory 20 which records the address and the color of each change in color in a same cycle of traces. There is also provided an address sorting out system 22 which includes a reference element 24 capable of sending out, successively, for each cycle of traces and for each color of traces, a reference signal characteristic of that color. The reference element may be a counter, having four states, in the case, for example. of a visual display system having four colors of traces. The counter will be placed in the first, second, third and fourth states, respectively for red, orange, yellow and green, during a cycle of traces. It will therefore supply, at the output, successively, four reference signals, each of these signals relating to a color of the traces. The counter may receive, on one of its inputs 25, a signal for resetting to zero at the end of the cycle, coming from the auxiliary memory 20 through a referencing element 26. The reference element 24 receives, on one input 27, a signal indicating the end of a reading pass of the auxiliary memory, each time a group of addresses concerning a same color is exhausted. The end of reading pass signal causes the change in states of the counter.

The color change address sorting out system also includes a color comparator 28, which receives, on one input 29, the reference signal of the reference element 24. The comparator receives, simultaneously, on another of its inputs 30, the "color" signals sent out by an output of the auxiliary memory 20, relating to the various changes in color listed in the auxiliary memory and coming into play during a cycle of traces. If the "color signal" 30 corresponds, at the instant considered, to the reference signal 29, a signal which may be qualified, for example, as a "successful test" signal, appears at the output 31 of the comparator and causes the blocking of an "AND" gate 32, one of whose inputs receives pulses from a clock 37. If, on the other hand, the color signal 30 does not correspond to the reference signal, a negative test signal appears at the output 32 of the comparator and makes the "AND" gate 32 conductive. An address counter 33 for the auxiliary memory 20 is connected by an input 34 to the output of the gate 32. Reading or recording in the auxiliary memory is effected through a recording and reading element 23, controlled by an output 39 of the data processor 7.

The selection system 19 enables the reading of the contents of the auxiliary memory 20 by the sorting out of the groups of color change addresses. Thus, at the instant considered in the example, only the successive addresses in the main memory preceded by a change in the red color, then the addresses preceded by a change in the orange color, the addresses preceded by a change in the yellow color, and then in the green color, will be retained for the traces. For each address of the auxiliary memory, for which a successful test signal has been sent out by the comparator 28, there appears at an output of that auxiliary memory corresponding to that address, an operand which enables the reading of the main memory at the address considered. In a first operation phase of the visual display assembly, the graphic data, for a cycle of traces coming from the calculator, are charged in the main memory. In a second operation phase, the charging of the auxiliary memory 20 is effected by the data concerning the address and color of each color change, a recording order having reached an input 35 of that memory. Lastly, the third operation phase is the auxiliary memory reading phase, controlled by the selection system 19, as has previously been described. Each time an address forming a part of a same color change group in the auxiliary memory is selected, an operand appears at one of the corresponding outputs of the buffer 21 of that memory, this causing the graphic data contained at that address to be extracted from the main memory. The trace corresponding to that data then appears in the color of the color change group selected by means of the reference element 24;

If a "successful test" signal is applied at the output 31 of the comparator, there is no signal at the input 34 of the address counter 33. In that case, the address counter 33 does not change states, this causing the appearance of an operand at an output corresponding to the address considered in the auxiliary memory and thus, the reading of the contents of the main memory 3 at the address considered, when the input 36 of the address register of the main memory has received the reading signal corresponding to that address. A trace corresponding to the data contained at that address of the main memory is then effected on the screen in the color determined by the reference element 25 affecting the switching element 15.

If a negative test signal appears at the output 31 of the comparator 28, this is because the color comparison test is unsuccessful, the color signal reaching an input 30 of the comparator not corresponding to the reference signal, the gate 32 then supplies a pulse to the address counter 33 which changes states and thus causes the passing to the following address of the auxiliary memory while a new comparison of the color signal with the reference signal is established. Comparison tests are thus effected at the successive addresses of the auxiliary memory until an address where a successful comparison test may be established is detected, this causing the appearance of a new operand on an output of the auxiliary memory and the subsequent reading of the corresponding address in the main memory.

According to FIGS. 1 and 2, the assembly therefore enables the traces to be effected separately according to successive colors, during a cycle. In the case of a four-color system, the auxiliary memory is passed through four times, each pass corresponding to a color. The programming requirements relating to the colors are thus avoided and the color switching system does not operate in prohibitive switching speed conditions. With the color change sorting out system, there is no longer any limit in the number of changes in the colors of the traces. The system operates without modification of the aspect of the message transmitted by the calculator.

FIG. 2 illustrates another embodiment of the present invention which is intended, moreover, to avoid programming requirements relating to the operating of the spot when there are color changes. In the visual display assembly in FIG. 2, the address register 4 is forced by the calculator or computer 6, at the beginning of the transfer, towards the memory block 3 at the address considered and is incremented at each word of the graphic message. The selection element 19 is moreover controlled by the binary outputs 38 and 40 of the assembly 12 comprising a binary-to-analog converter supplying the analog control voltages of the horizontal deviation plates 10 and vertical deviation plates 11. Thus, for each color change address, the data concerning the positioning of the light spot which generates the traces from each color change, are supplied to the selection element 19, which records them. The controlling of the selection element 19 by the binary outputs 38 and 40 of the assembly 12 is applied to the auxiliary memory 20 which records, besides the address and the color of each change in color in a same cycle of traces, the data concerning the position of the light spot at the instant of the change in color.

In operation, the selection element 19 which has received data concerning the address, color, various changes in color and the data concerning the positioning of the spot when the color changes, contained in the main memory, will control the reading of the main memory so that, for each cycle of traces having the same color, all the traces of that color are then effected by selection, in the main memory, of the address preceded by a change in that color, the data concerning the coordinates of the light spot being extracted from the main memory at the same time as the data concerning the change in color by means of the selection element which has previously recorded them. The programming requirements relating to the positioning of the spot are thus avoided due to the extra information supplied by the auxiliary memory for each change in color, besides the address and the color in the main memory, the coordinates of the spot at the instant of the change in color are shown. These coordinates, at each change in color, are calculated by the data processing element during the original reading cycle which is used for seeking color change addresses. During that original scanning of the main memory, the various instructions are carried out as in a normal cycle of traces, but the spot remains extinguished as long as the charging of the auxiliary memory is effected. During that scanning, each time there is a change in color, the various data concerning the address and the color of the change in color is recorded in the auxiliary memory, but moreover, it is easy, at that instant, to record, also, in the auxiliary memory, data concerning the coordinates of the light spot when that change in color takes place.

During trace presentation cycles, the auxiliary memory is scanned and the isochromatic assemblies are traced by successive colors; nevertheless, before the trace of each assembly, the light spot is positioned according to the data recorded in the auxiliary memory. If, at a given instant, a block of traces forming a part of an isochromatic assembly is analyzed in the main memory, then traced and if a color change instruction then appears, this indicates the end of the isochromatic block. This is interpreted by the data processing element as a reading order at the outgoing address of a block of the same color in the auxiliary memory. Therefore, before jumping to that outgoing address of the following block, the spot is positioned according to the positioning data contained in the auxiliary memory.

While I have shown and described only two embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as are known to those skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

Claims

What is claimed is:

1. Polychromatic graphic visual display assembly comprising:

a polychromatic cathode tube having a screen for receiving traces having portions of various colors, the traces being renewed in successive cycles;

a main memory means including a memory block, an address register and an output register from which graphic data items entered into the memory are extracted, the main memory means for each portion of traces recording a group of data items relating to that portion, the group of data items being classified in the memory means in a group of addresses, the first of the data items relating to the color of the portion and being classified as a first color change address in the group of addresses, the other data items relating to the parameters of the vectors constituting the portion being classified at following addresses in the group of addresses;

data processing means for enabling the generation of the traces on the screen of the cathode tube in response to the output register;

vector generator means and character generator means responsive to the data processing means for influencing a cathode beam deflection control element means so as to make traces and characters appear on the screen;

means for causing changes in color of the portions of traces in response to said data processing means; and

color change address selecting means responsive to said memory block and said address register thereof for listing the color change addresses of the various color groups and recording the corresponding color data thereof, the color change address selecting means selecting in sequence one of the various colors and controlling the reading of the main memory means for extracting successively from the main memory means all of the data corresponding to the groups of addresses of the main memory means containing identical color data for the selected color so as to extract the data corresponding to the various colors in sequence.

2. Visual display assembly according to claim 1, wherein the color change address selecting means includes auxiliary memory means responsive to the memory block and the address register for listing the color change addresses and recording the corresponding color data, and color change address sorting system means controlling the auxiliary memory means to sort out the addresses in the auxiliary memory means which contain identical color data at the reading outputs of the auxiliary memory means and for controlling the reading inputs of the main memory means.

3. Visual display assembly according to claim 1, wherein the cathode beam deflection control element means provides an output of digital signals indicative of light spot positioning data on the screen of the cathode tube, the color change address selecting means being responsive to the digital signals for listing for each color change address the light spot positioning data generating the traces from each color change, the color change address selecting means controlling the reading of the main memory means to extract the corresponding light spot positioning data from the main memory means at the same time as the extraction of the data of each color change.

4. Visual display assembly according to claim 1, wherein the digital signals are binary signals.

5. Visual display assembly according to claim 4, wherein the color change address selecting means comprises:

auxiliary memory means responsive to the memory block, the address register and the outputs of the cathode beam deflection control element means for listing the color change address and for recording the corresponding color change and positioning data; and

color change address sorting system means controlling the auxiliary memory means to sort out the addresses in the auxiliary memory means which contain identical color data at the reading outputs of the auxiliary memory means and for controlling reading inputs of the main memory means.

6. Visual display assembly according to claim 2, wherein the color change address sorting out system means comprises:

reference element means for providing successive outputs for each cycle of traces and for each of the colors of a reference signal characteristic of the color;

color comparator means for comparing, at each instant, the reference signal with a color change signal provided at one of the outputs of the auxiliary memory means, the color change signal being characteristic of the color change data existing in the auxiliary memory means in the color address corresponding to the output at the instant, the comparator providing an output of one of a positive test signal when the color change signal corresponds to the reference signal and of a negative test signal when the color change signal does not correspond to the reference signal;

an address counter for the auxiliary memory means;

incrementing means responsive to the comparator means for providing an output to the address counter of the auxiliary memory means, the incrementing means incrementing the said address counter in response to a negative test signal, the auxiliary memory means providing at one of the reading outputs thereof an operand signal when a positive test signal is obtained for the color address corresponding to such output, the operand signal controlling the main memory means so that a trace corresponding to the data contained at the corresponding address in the main memory means is effected on the screen.

7. Visual display assembly according to claim 6, wherein the reference element means is a counter capable of changing states for each cycle of traces in accordance with the number of colors in each of the cycles.

8. Visual display assembly according to claim 7, wherein the incrementing means includes an AND gate having one input connected to the output of the comparator means and another input connected to receive clock pulses.

9. Visual display assembly according to claim 5, wherein the color change address sorting out system means comprises:

reference element means for providing successive outputs for each cycle of traces and for each of the colors of a reference signal characteristic of the color;

color comparator means for comparing, at each instant, the reference signal with a color change signal provided at one of the outputs of the auxiliary memory means, the color change signal being characteristic of the color change data existing in the auxiliary memory means in the color address corresponding to the output at the instant, the comparator providing an output of one of a positive test signal when the color change signal corresponds to the reference signal and of a negative test signal when the color change signal does not correspond to the said reference signal;

an address counter for the auxiliary memory means;

incrementing means responsive to the comparator means for providing an output to the address counter of the auxiliary memory means, the incrementing means incrementing the said address counter in response to a negative test signal, the auxiliary memory means providing at one of the reading outputs thereof an operand signal when a positive test signal is obtained for the color address corresponding to such output, the operand signal controlling the main memory means so that a trace corresponding to the data contained at the corresponding address in the main memory means is effected on the screen.

10. Visual display assembly according to claim 9, wherein the reference element means is a counter capable of changing states for each cycle of traces in accordance with the number of colors in each of the cycles.

11. Visual display assembly according to claim 10, wherein the incrementing means includes an AND gate having one input connected to the output of the comparator means and another input connected to receive clock pulses.

12. Graphic visual display assembly comprising:

polychromatic cathode tube means for displaying a picture composed of traces of various colors in accordance with binary data items supplied by a computer in groups of data items, each group defining successive traces having the same color;

main memory means for recording the groups of data items at successive groups of addresses wherein the first address is the color data item of the corresponding traces;

processing unit means responsive to the main memory means for generating signals for controlling the cathode tube means in accordance with data read-out from the main memory means; and

selection circuit means for sequentially selecting one of the various colors and for controlling the read-out from the main memory means of all the groups of data items preceded by the color data item of the selected color, the data read-out being supplied to the processing unit means for enabling the display, one color after another, of the traces having the same color to form a composite picture.

13. A visual display assembly according to claim 12, wherein the selection circuit means includes an auxiliary memory means for recording the color addresses and recording the corresponding color data.

14. A visual display assembly according to claim 13, wherein the selection circuit means also includes color sorting means for controlling the auxiliary memory means to sort out the addresses in the suxiliary memory means which contain identical color data at the reading outputs of the auxiliary memory means and for controlling the reading inputs of the main memory means in accordance therewith.