US3792463A

US3792463A - Apparatus for producing graphic images on an image surface

Info

Publication number: US3792463A
Application number: US00224019A
Authority: US
Inventors: E Eriksson; O Nilsson
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-10-24
Filing date: 1972-02-07
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12
Also published as: DE1953725A1; SE341284B; GB1292327A; FR2021506A1

Abstract

An apparatus is provided for producing graphic images on an electronically controlled display surface, the images being subdivided into a plurality of area elements a number of which are filled with pattern elements which give each of said area elements a preselected surface representation. The apparatus is operative to store data defining the contour of successive area elements to be reproduced, along with informa-specifying the pattern density of the respective area element. A control circuit responsive to said stored information operates to determine the position of the first of said pattern elements within the respective area element, and thereafter successively determines the position of the remaining pattern elements within the respective area element. The apparatus further comprises means for modifying the surface representation of each area element by controlling the visual appearance of the pattern elements which fill said area element.

Description

United States Patent Eriks son et al.

APPARATUS 'FOR PRODUCING GRAPHIC IMAGES ON AN IMAGE SURFACE Inventors: Erik Arivd Rune Eriksson,

Faltskarsgatan 12, 42176 Vastra Frolunda; Olof Lars-Erik Nilsson,

Nordostpassagen 71, 4131 l Goteborg, both of Sweden Filed: Feb. 7, 1972 Appl. No.: 224,019

Related US. Application Data Continuation-impart of Ser. No. 868,061, Oct. 21, 1969, abandoned.

Foreign Application Priority Data Oct. 24, 1968 Sweden 14432/68 u.s Cl 340/324 AD, 178/D1G. 6 Int. Cl. G06f 3 14 Field of Search 340/324 A, 324 AD; l78/D1G. 6

References Cited UNITED STATES PATENTS Primary ExaminerJohn W. Caldwell Assistant Examiner-Marshall M. Curtis Attorney, Agent, or Firm-Fred C. Philpitt 57] ABSTRACT An apparatus is provided for producing graphic images on an electronically controlled display surface, the images being subdivided into a plurality of area elements a number of which are filled with pattern elements which give each of said area elements a preselected surface representation. The apparatus is operative to store data defining the contour of successive area elements to be reproduced, along with informaspecifying the pattern density of the respective area element. A control circuit responsive to said stored information operates to determine the position of the first of said pattern elements within the respective area element, and thereafter successively determines the position of the remaining pattern elements within the respective area element. The apparatus further comprises means for modifying the surface representation of each area element by controlling the visual appearance of the pattern elements which fill said area element.

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APPARATUS FOR PRODUCING GRAPHIC IMAGES ON AN IMAGE SURFACE This is a Continuation-inPart of application Ser. No. 868,061, filed Oct. 21, 1969, now abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to an apparatus, especially for use in visual data presentation, for producing graphic images on an image surface, said images comprising a plurality of area elements, each of which is filled with pattern elements in order to obtain a certain surface structure.

In the prior art the different pattern elements, which below will be referred to as symbols, have been positioned in dependence on coordinate values calculated in a computer. This method is disadvantageous as it involves at least two of the following three drawbacks, viz. an extended occupation of the computer, a comparatively slow reproduction rate and a need for high memory capacity. Further, it has not been possible to control the characteristics of the symbols or patterns.

The present invention has for its object to eliminate these drawbacks and to provide a reproduction apparatus permitting a rapid generation of the area elements. An apparatus made in accordance with the invention is primarily characterized in that it is provided with means for determining the positions of the symbols in dependence of stored data defining the edge of the respective area element and comprises means for modifying the surface structure of said area elements by controlling the pattern characteristics, such as size, shape, intensity, sharpness, colour, angular direction and density of the pattern elements.

Said apparatus, which below will be referred to as an area generator, can be arranged to produce images of desired structure by producing them in the form of area elements, each of which is filled with symbols of a certain density and appearance, i.e., size, shape, intensity, sharpness, colour and angular direction of the pattern elements can be individually varied. These symbols may for instance consist of parallel lines, dots, and geometrical figures, such as triangles, squares, circles and the like, which make it easier for an observer to perceive the different elements as areas. By varying the density or appearance of the symbols between different parts of an area element or between different area elements it may be possible to obtain a certain degree of three-dimensional impression. The area generator can be arranged to produce either a single type of symbol of a predetermined density and appearance or symbols of varying density and appearance. In the latter case i the choice of symbol density etc. can be controlled either by manually operated control means of the area generator or by external information supplied to the generator.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in greater detail reference being made to the accompanying drawings in which:

FIG. 1 shows, by way of example, a block diagram of an area generator according to one embodiment of the invention.

FIG. 2 shows a number of diagrams illustrating different signals appearing in the area generator as functions of time, when the apparatus is used to generate symbols in the shape of parallel lines.

FIG. 3 shows corresponding diagrams when the apparatus is used to generate symbols in the shape of triangles.

FIG. 4 and 5 show an area produced by means of the area generator according to FIG. 1, which area is filled with symbols in the shape of parallel lines and triangles, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 reference numeral 10 designates a saw tooth voltage generator the output signal of which through a memory 47 is fed on the one hand to a comparator l3 and on the other hand to an adder 44. In adder 44 the output voltage from generator 10 is added to a voltage from a pattern element or symbol generator 43. The resulting output from adder 44 is fed on the one hand as vertical deflection voltage to a cathode-ray tube 11, and on the other hand to a comparator 12. Each

comparator

12, 13 has two additional inputs. These additional inputs of comparator 12 are each supplied with the output signal from a control voltage source 14 and 15, respectively, while the corresponding inputs of comparator 13 are fed with variable D.C. voltages from two adjustable DC.

voltage sources

16 and 17. Reference numeral 18 designates a generator which through an adder 45 delivers the horizontal deflection voltage to cathode-ray tube 11 and reference numeral 19 refers to an intensity controlling circuit connected to the cathoderay tube. The input of generator 18 is connected to the output of a gate circuit 20 having two control inputs and one main signal input. The main signal input of said gate circuit is connected to the output of comparator 13. Reference numeral2l designates a further gate circuit of the same type as gate circuit 20 and having its main signal input connected to the output of comparator l2 and its output connected, on the one hand to one control input of gate circuit 20 and on the other hand to one input of the intensity controlling circuit 19. The output of gate circuit 20 is also connected to the input of a down counter 22. The output of this down counter is coupled, on the one hand to a terminal 23, and on the other hand to one input of an OR-gate 24, having its other input connected to a terminal 25. The output of gate 24 is coupled on the one hand to the second control input of each

gate circuit

20 and 21, and on the other hand to a further input of the intensity controlling circuit 19, and finally to one input of each control voltage source 14 and 15, respectively. Reference numeral 26 designates an AND-gate having its one input connected to a terminal 27 and its other input coupled to the output of comparator 13. The output of AND-gate 26 is connected on the one hand to the first control input of gate 21, and on the other hand to a further input of each one of the two control voltage sources 14 and 15, and finally to a register 42.

The control voltage sources 14 and 15 are identical and each of them contains two memories or

registers

28 and 29, respectively, which are connected each to one digital-

analog converter

30 and 31, respectively. The output signal from converter 30 is fed directly to one input of an adder 32, while the output of converter 31 is connected, over an electronic switch 33, to the input of an integrator 34, the output signal of which is supplied to a second input of adder 32. Switch 33 is controlled by the output signals from

gates

24 and 26. The output signal from adder 32 is fed to the input of a sampling circuit 35 supplied with trigger pulses from the output of comparator 13. The output signals from the two sampling circuits 35 are fed each to one input of comparator 12.

The horizontal deflection voltage generator 18 consists of an adder 36, two

memories

37 and 38, and a digital-analog converter 39. Adder 36 has a trigger input fed with the output pulses from gate circuit 20. Adder 36 also has two inputs connected each to one of the two

memories

37 and 38, and an output coupled to memory 37. Memory 37 is also connected to the input of converter 39, the output signal of which is added to the output from symbol generator 43 in adder 45. The resulting output from adder 45 forms the horizontal deflection voltage for the cathode-ray tube 11.

The intensity controlling circuit 19 comprises a flipflop circuit 40 having a trigger input connected to the output of gate circuit 21. Said flip-flop circuit is arranged to be supplied with the output signal from OR- gate 24 in order to assume a state to cut-off the electron-beam in cathode-ray tube 1 1 before each area generation.

The output signal from flip-flop 40 is fed to a control input of a controller 41. A second input of the controller is coupled to the intensity output of the pattern element or symbol generator 43. A third input of the controller is fed from a register 46 storing information relating to desired intensity and colour of the symbols. In controller 41 the information from generator 43 and register 46 are compared, and if the grey tone or colour of the pattern element do not correspond to the values stored in register 46, the grey tone or colour is controlled. The output of controller 41 is coupled to the cathode-ray tube 11. If the flip-flop 40 is in a state corresponding to energized electron-beam the output signal from controller 41 will be supplied to the cathoderay tube 1]. Otherwise this signal is blocked and the electron beam is cut-off.

Register 42 stores information relating to the desired shape and size of the pattern elements and space between the elements in vertical direction. The inputs of register 42 are connected to the outputs of AND-gate 26 and gate 21, and the output is coupled to symbol generator 43, in which a plurality of pattern elements are stored. It is also possible later on to store new pattern elements in generator 43 which has four outputs. Outputs for horizontal and vertical deflection voltages are connected to

adders

44 and 45, respectively, wherein said voltages are added to the outputs from the generators l and 18, respectively, to form the final deflection voltages for the cathode-ray tube 1 1. The third output controls the memory 47, which upon a control signal stores the instantaneous value of the output voltage from generator 10. The fourth output is an intensity output and as mentioned above this output is connected to the controller 19.

Reference numeral 51 designates a register storing information relating to variations of the size of the pattern elements. The output from this register is controlled from generator 18 in such a way that the output signal is increased or decreased as a function of the value stored in memory 37 of the generator 18. Each time the generator is stepped forward the output signal from register 51 will increase or decrease dependent on what type of information is stored in the register. The output signal from register 51 is supplied to register 42 in which it controls the information relating to the size of the pattern elements. Thus, the symbol generator is fed with a signal defining the size of the pattern element, which signal is dependent on the horizontal deflection voltage from generator 18 and will cause the generator to produce pattern elements of an increasing or decreasing size.

Naturally, the size of the symbols can also be dependent on for example the vertical deflection voltage. In this case register 51 is connected to memory 47 or directly to generator 10.

Below the function of the apparatus above described will be explained in greater detail. The arrangement is such that area elements reproduced on the screen of the cathode-ray tube will be filled with vertical lines or vertical rows of triangular symbols of a certain density. Any separate reproduction of the edge or periphery of the area does not take place. Further, the apparatus of FIG. 1 is restricted only to the reproduction of trapezoids having their parallel edges extending in vertical directions. Naturally, this includes the marginal case wherein the shortest one of the parallel edges has a negligible length, i.e., the area in question is a triangle.

FIGS. 4 and 5 show, by way of example, a reproduced area having the shape of a trapezoid and being filled with symbols in the shape of lines and triangles, respectively. The comers of the area are designated P P P and P respectively. The figures also show a coordinate system (X,Y) corresponding to the horizontal and vertical axes of the screen of the cathode-ray tube. The different corners of the area can be defined by means of the following coordinate expressions:

3 0; 0 s where X, and Y designate the Xand Y coordinates for P while A designates the horizontal distance between P and P -A is the difference between the Y coordinate for P and Y while A designates the difference between the Ycoordinate for P and the Y coordinate for P 'A is the difference between the Ycoordinate for P and Y In this connection it should be noted that A, and A can assume positive as well as negative values. The horizontal distance between adjacent parallel vertical lines has been designated D. Beyond the different designations used in FIGS. 4 and 5 a further designation L is introduced for the total number of parallel vertical lines defining the area in question. The relationship between A, D and L is determined by the equation A= D(L-l Below, the function of the apparatus will be explained when used for reproducing area elements filled with vertical lines, reference being made to the signal diagrams of FIG. 2. Before the generation of an area can be started one has to make sure that the

gate circuits

20 and 21 are closed and that the flip-flop circuit 40 is in a state corresponding to cut-off electron beam in the cathode-ray tube. Moreover, it is required that the electronic switches 33 in control voltage sources 14 and 15 are in such positions that the output signals from integrators 34 assume zero values. The necessary resetting of the apparatus is obtained at the beginning of thereproduction by means of a ready signal supplied to terminal 25. When the generation of an area has been completed the corresponding resetting is caused by a signal from down counter 22. When the apparatus is used for reproducing areas filled with lines the sawtooth voltage from oscillator 10 is supplied directly to adder 44, i.e., the unit 47 is inactive. The output signals from symbol generator 43 are zero which means that the signal from oscillator 10 is supplied to the cathoderay tube 11. As regards adder 45 also the voltage from generator 18 will be supplied directly to the cathoderay tube 11.

Before the generation of an area can be started values corresponding to the desired area have to be fed to and stored in

registers

28, 29, 37, 38, 42, 46, 51 and in down counter 22. Said values can suitably be calculated in a computer, although, in some special cases, it

may be possible to calculate and feed said values to the registers in a manual way. The values Y and A, are stored in

registers

28 and 29 of voltage source while the

corresponding registers

28 and 29 in control voltage source 14 are supplied wtih the values of Y +A and A respectively. At the same time'the corresponding values of X and D are stored in

registers

37 and 38, while the value of L is stored in down counter 22.

Register 46 is fed with information relating to colour and intensity of the symbols and register 42 is in this case supplied with information only indicating that an area element is to be reproduced whereupon it disconnects the symbol generator 43, as only parallel lines are to be reproduced.

When the different values have been stored in the respective memories and in down counter 22 the genera tion of the desired area is initiated by means of a starting signal u, supplied to terminal 27. This signal can suitably consist of a DC. voltage which is applied during a short period of time. The starting signal is fed to one input of AND-gate 26, theother input of which is connected to the output of comparator 13 as mentioned above. The output signal a from comparator 13 has the shape of equally spaced short pulses which serve as synchronization pulses. Such a pulse is generated each time the vertical deflection voltage u from generator 10 passes any of the existing values U and U respectively, for the output voltages 11,, and L4,; from

D.C. voltage sources

16 and 17. When the starting signal has been applied the first subsequent synchronizing pulse from comparator 13 will cause an output signal from AND-gate 26 opening gate circuit 21 which has previously been closed. The output signal from AND- gate 26 also serves as a control signal for the two switches 33 in the control voltage sources 14 and 15, whereby said switches close the connections between the respective digital-analog converters 31 and integrators 34. The output signal u from comparator 13 activates also the two sampling circuits 35 which serve as signal sources for comparator 12 and produce the output signals u and u respectively, the initial values of which have been designated Uy +A and Uy respectively, in FIG. 2.

The integrator 34 can for instance be of a capacitive type, i.e., its function can be based on the charging of an RC circuit. The output voltage from such an integrator will, when a DC. voltage is applied to the input, vary from the initial zero value and asymptotically approach the value of the applied voltage. As the output voltage from the integrator follows an exponential function it is, when said voltage is intended to represent a straight line, viz. one of the two dashed edge lines of the trapezoid shown in FIGS. 4 and 5, possible to use only the first portion of the voltage curve. The size of the part of the exponential curve that can be utilized is determined by the permitted deviation from a pure linearity. The above circumstances mean that the digital analog converters 31 which feed the integrators 34 have to deliver output voltages which have been amplified to a sufficient degree.

The sampling circuits 35 are such that each time they are supplied with a trigger pulse from comparator 13, they will instantaneously sense and store the resulting value formed in the respective adder 32. The resulting output voltage u and u respectively, from each one of the two sampling circuits 35 will thus be a step function according to FIG. 2.

After the first moment above described the conditions will be as follows: gate circuit 21 is open and gate circuit 20 is closed, the electron beam is cut-0K and the integrators have started. The next following moment is initiated when the vertical deflection voltage u,,, i.e., the output voltage from generator 10, passes any of the levels representing the instantaneous values of the output signals 14,, and a respectively, from the sampling circuits 35. When this happens comparator 12 is caused to deliver a pulse u which through gate circuit 2, now open, passes on the one hand to gate circuit 20 and opens said gate circuit, and on the other hand to flip-flop circuit 40 causing this circuit to shift to a position for brightening the electron beam of the cathoderay tube 11. After this moment the conditions of the apparatus are as follows:

gate circuits

20 and 21 are both open, the electron beam is energized, the horizontal deflection of said beam is proportional to the value X and its brightness and colour are determined from the values in register 42 which are fed to the controller 41. The electron beam will now, during the next period, move vertically upwards or downwards until the vertical deflection voltage reaches the other one of the two levels defined by signals u and a In this moment comparator 12 will generate a new output pulse which causes flip-flop circuit 40 to shift to a position for cutting-off the electron beam. The output signal from controller 41 has in FIG. 2 been designated u,. The conditions are now as follows: a first vertical line has been reproduced on the screen of the cathode-ray tube, the electron beam is cut-off,

gate circuits

20 and 21 remain open, down counter 22 is still set to value L originally stored therein and memory 37 contains the original value X which means that the horizontal deflection is unchanged.

The next change in the conditions of the different circuits is caused when the vertical deflection voltage assumes a value corresponding to the output voltage u, or u from any of the two DC.

voltage sources

16 and 17, which are set so that u, u and u u and so that the pulse spacing between the synchronizing pulses u from comparator 13 remains constant. The pulse now delivered from comparator 13 is transmitted on the one hand to AND-gate 26, and on the other hand to the two sampling circuits 35, and finally also through gate circuit 20 to down counter 22 and adder 36. The

AND-gate 26 does not cause any change in the conditions of the other circuits as switch 33 and gate circuit 21 are already open. The pulse fed to gate circuit 20 from comparator 13 instead causes a change of the condition of down counter 22 as well as of the horizontal deflection generator 18. The setting of the down from the respective adder 32 in the moment when the a pulse from comparator 13 appears at the trigger input of circuit 35. After this moment the conditions are as deflection voltage 11 has been changed from the prior value U and is now proportional to the value X 1 D, and the down counter is set to value L- 1.

The next moment will be initiated when the vertical deflection voltage reaches the level u or u respectively, when the electron beam is again energized due to a shift of flip-flop circuit 40. This initiates the reproduction of a second vertical line on the screen of the cathode-ray tube. In this connection it should be noted that it has been .assumed that the arrangement is such that two vertical lines are generated during each period of the vertical deflection voltage.

The described process is then cyclically repeated until down counter 22 reaches the zero value, at which time the down counter delivers a pulse to OR-gate 24 to close gate circuits and 21 and shift the position of circuit 40. Said pulse from down counter 22 is also fed to terminal 23 wherefrom it can be transmitted to any suitable means for indicating that the reproduction of the area in question has been completed. New values can then be fed into

memories

28, 29, 37, 38, 42, 46 and 51 and into down counter 22 whereupon the reproduction of another area can be initiated.

It is apparent that the illustrated arrangement can be used for producing other areas than trapezoids and triangles. These areas should then be divided into a number of subareas of the above kind, the division into subareas being made so as to satisfy the desired accuracy requirements. Moreover, the arrangement can easily be modified so that the areas will be reproduced filled with horizontal lines instead of vertical lines. Through pulse modulation of the intensity controlling signal one can also obtain dashed lines instead of full lines. The width of the lines can be varied on the one hand by changing the intensity and the focusing of the electron beam, and on the other hand by noise modulation of the horizontal deflection.

The area element can be reproduced utilizing other types of symbols as mentioned above. Below, the function of the apparatus will be described when it is used for reproducing area elements filled with triangular symbols arranged in vertical rows, reference being made to FIGS. 3 and 5. The area generator works generally as in the example above but with some exceptions. Information is stored in

registers

28, 29, 37, 38, 42, 46 and 51 and in the down counter 22. Symbol generator 43 which in the previous example has been inactive will now be active as register 42 indicates that the symbols shall be in the shape of triangles, i.e., not lines.

When register 42 has received a signal indicating that the value of the output voltage from oscillator 10 is within the values u and u a ready signal u is supplied to symbol generator 43. The generator 43 delivers a signal u, to the memory 47 indicating that the instantaneous value of the voltage u,, from oscillator 10 shall be stored and supplied to adder 44. The output signal u,, from memory 47 is shown in FIG. 3. When adder 44 spectively, from each sampling circuit is changed 5 into agreement with the value of the output voltage follows: the electron beam is still cut-off, the horizontal l0 LII has received the value of the output voltage from oscillator 10 symbol generator 43 is activated and delivers the signals u, and u Signal u, is added to the instantaneous value of the output voltage from oscillator 10 in adder 44. signal u, is added to the deflection voltage from generator 18 in adder 45 and signal u, which is the intensity of the pattern element, is supplied to the intensity control circuit 19.

FlGffsho ws an example in which a pattern element in the shape of a triangle is reproduced by means of signals u,,, u, and u',. When the reproduction of the symbol is started the values of U, and u' are zero but the intensity value u, has its maximal amplitude. The signal u, shows the voltage supplied to the cathode-ray tube 11. Normally as when the first pattern element in FIG. 3 is reproduced signal u, follows the signal u, delivered by the pattern generator 43. FIG. 3 shows that signal u I is increasing and reaches its maximal amplitude after one time-unit, during which period signal u' has remained on zero level. Accordingly, a horizontal line forming the base of the triangle is drawn. After the next time-unit the value of u, has decreased by one half and u, has reached its maximal amplitude. This results in one leg of the triangle. During the third time-unit both signal u, and signal u, are decreasing to zero values and the other leg of the triangle is drawn. As the initial values of u, and u, were zero a complete triangle has been reproduced. Further during the third time-unit the value of the intensity signal has been held at a level corresponding to half its maximal amplitude. Thus, the last side of the triangle is reproduced at a lower light intensity.

When a pattern element ha s been reproduced this is reported to the

registers

42 and 47. Register 47 releases the output voltage from oscillator 10. Register 42 comprises a controlled time-delay circuit which after a predetermined time period causes a new pattern element to be reproduced. The following symbols are reproduced in the same way as the first. But when the instantaneous value of the voltage from oscillator 10 becomes so high, see the signals defining the second pattern element in FIG. 3, that the deflection voltage from adder 44 will be higher than the value a when signal u, reaches its maximal value, comparator 12 will deliver a signal through gate 21 to controller 19 in order to cut-off the intensity signal. Thus, the electron beam in the cathode-ray tube 1 1 is cut-off and will not be reenergized until the value of signal u, is decreased to a value such that the output signal from adder 44 is lower than u This situation is detected by comparator 12 which delivers a ready signal to intensity regulator 19. Thus, the symbol will be truncated in such a way that the final area element will follow the imaginary boundary line as near as possible.

Naturally, the invention is not restricted to the embodiment above described and illustrated in the drawings. Especially, it should be noted that the arrangement can be such that it can be used for producing other areas than those which similar to trapezoids and triangles have straight edge lines. Moreover, the area generation can be obtained by other means than cathode-ray tubes or the like. Thus, it is for instance possible to use light-beams which by suitable control means are caused to move according to a desired pattern on a photographic film or the like.

9 What is claimed is:

1. An apparatus for producing graphic images which are subdivided into a plurality of area elements a number of which area elements are filled with pattern elements in order to obtain for each of said area elements a preselected surface representation, said apparatus comprising an electronically controlled display surface, register means for storing data defining the peripheral contour of successive area elements to be reproduced on said display surface, means for successively filling selected ones of said area elements with pattern elements of preselected configuration, said last-named means including density defining means for establishing the pattern element density to be produced in a selected one of said area elements, coordinate control means jointly responsive to the contour data in said register means and to said density defining means for determining the coordinate position of the first of said pattern elements within said selected area element on said display surface and for thereafter automatically determining the successively different coordinate positions of each of the remaining pattern elements to be filled into said selected area element, display control means responsive to said coordinate control means for successively reproducing said patterns at said successively determined coordinate positions, and visual control means for selectively modifying the surface representation of said each of said area elements by controlling a preselected visual parameter of the pattern elements in said area element.

2. An apparatus in accordance with claim 1, comprising means for varying the characteristics of the pattern elements within the area elements in dependence of the positions of the pattern elements within said area elements.

3. An apparatus in accordance with claim 1, comprising means for supplying a completion signal after each complete generation of an area element to bring the apparatus into a ready state for receiving information about a new area element.

4. An apparatus in accordance with claim 1, wherein the pattern elements are generated along parallel lines within area elements defined by data stored in said register means.

5. An apparatus in accordance with claim 1, wherein the graphic images are composed of a plurality of adjacent trapezoidal area elements and said pattern elements are generated along lines parallel to the parallel sides of said trapezoid.

6. The apparatus of claim 1 wherein "said visual 'e'dntrol means includes means operative to control the size of each of said pattern elements.

7. The apparatus of claim 1 wherein said visual control means includes means operative to control the intensity of each of said pattern elements.

8. The apparatus of claim 1 wherein said visual control means includes means operative to control the shape of each of said pattern elements.

9. The apparatus of claim 1 wherein said visual control means includes means operative to control the sharpness of each of said pattern elements.

10. The apparatus of claim 1 wherein said visual control means includes means operative to control the colour of each of said pattern elements.

11. The apparatus of claim 1 wherein said visual control means includes means operative to control the angular orientation of each of said pattern elements.

Claims

6. The apparatus of claim 1 wherein said visual control means includes means operative to control the size of each of said pattern elements.