GB2024487A

GB2024487A - Multicolour Image Projection System

Info

Publication number: GB2024487A
Application number: GB7920737A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-06-29
Filing date: 1979-06-14
Publication date: 1980-01-09
Also published as: GB2024487B; DE2924101A1

Abstract

A large flat-display on a screen 48 is provided by projection, using reflection or transmission, e.g. by lens 47, from a liquid crystal display cell 46, possibly in series in the beam with a controlled colour or grey filter 44 comprising multiple liquid crystal elements associated with coloured or grey filter elements. Three beams in different colours from separate sources may be projected on to the same screen to provide a coloured display. Frequency modulation provides convenient control of the display intensity. <IMAGE>

Description

SPECIFICATION Multicolour Image Projection System The present invention relates to a multicolour image projection system.

More particularly, the present invention provides a possibility of obtaining very large liquid crystal panels of high information capacity and suitable for rapid switching and multiplexing and of obtaining very large and bright moving pictures, in monochrome or colour, using very simple and inexpensive techniques. Such pictures may find application in advertisement systems or as a background in theatre, in cinema or television studios or as data and graphic screens in computers instead of the conventional cathode ray tubes.

In accordance with the present invention, there is provided an image projection system comprising a light source, liquid crystal means positioned to receive light from the light source, a plurality of electrodes operatively associated with the liquid crystal means, means for applying voltages selectively to individual ones of the electrodes to make selected portions of the liquid crystal means transparent or reflective, screens means and lens means for projection light passing through or reflected by the liquid crystal means on the screen means.

Embodiments of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a front schematic view of a first type of electronically controlled colour or grey filter, using a liquid crystal, which may form a part of an image projection system embodying the present invention, Figure 2 is a sectional view of the filter of Fig. 1 on the line Y-Y, to a larger scale, Fig. 3 is a coloured mask of the controllable colour filter, Fig. 4 is a view of the counter-electrodes of a second type of liquid crystal display colour filter, Fig. 5 is a front view of a pattern panel also of a colour filter which is in radial form, Fig. 6 illustrates a liquid crystal display together with an electronically controlled colour filter, illuminated by externally reflected light and using mirrors, Fig. 7 is a front view of an electronically controlled slide, Fig. 8 is a side view of an arrangement, in which a liquid crystal display pattern panel is assembled together with a controlled grey filter, Fig. 9 shows an image projection system to project bright colour figures from a small liquid crystal display, Fig. 10 shows an image projection system to project bright multicolour figures from three small liquid crystal panels, Fig. 11 shows a very large electronically controlled slide built as an array of many very small liquid crystal cells, and Fig. 12 shows the relationship between the light transmitted by a liquid crystal display and frequency of the voltage applied to it.

Referring now to the drawings, the image projection system, as illustrated in Fig. 9, includes a large transparent or reflective screen 48, a lens 47, a liquid crystal display pattern panel 46, a frosted glass or translucent plastic member 45 or a suitable lens, an electronically controlled colour filter 44, a bright light source 43, a reflecting mirror 42 and a motor-driven blower fan shown generally at numeral 49. Light from the source 43 including that reflected by the mirror passes through the electronically controlled colour filter 44, which can have its colour changed as desired. A particularly suitable example of the colour filter 44 is to be described in greater detail further below.The light, which has in effect been coloured in passing through the filter 44, passes the frosted glass or translucent plastics member 45 or a suitable lens and becomes diffused and substantially of uniform intensity. The uniform light illuminates the transparent liquid crystal display pattern panel 46. The lens 47 magnifies and projects the image or picture from the pattern panel 46 onto the large screen 48. The blower fan 49 is effective to maintain a desired temperature of the liquid crystal display panel 46 and the colour filter 44.

The panel 46 may for example comprise a conventional alpha-numeric or seven-segment type of liquid crystal display. Such types may be used to provide data information on middle size screens for computers and the like instead of the conventional complicated systems which use cathode-ray tubes. Other possible uses include advertisement systems which include very large screens. Either moving or stationary images or fixed or changing data may be projected. For magnified graphic images, a small flat panel screen based on an m.n matrix of two liquid crystal displays may be used in the place of the liquid crystal display panel 46 in Fig. 9. In this case, "m" is the number of horizontal narrow strip segments on one liquid crystal display panel, while "n" is the number of vertical narrow strips on the other panel, the two panels being overlaid.

Fig. 7 illustrates another example of a pattern panel using a liquid crystal display. The front glass of the liquid crystal display of Fig. 7 carries electrodes in the form of vertical narrow strips, with the leads 21 to 36 being shown, while the rear glass carries counter-electrodes in the form of narrow horizontal strips with the leads a to i being shown. In practice, a considerably greater number of electrodes would of course be used depending on the resolution desired in any given case. Normally, the panel is opaque. When the voltage is applied between one vertical front segment, for example to lead 26 and one horizontal counter-electrode for example lead c, one point on the panel marked in Fig. 7 by an x becomes transparent and the light from the light source 43 passes through the point x, but not at any other point.By electronically addressing a desired group of different points, a user may create graphical images. The pattern panel shown in Fig. 7, when applied in the magnifying system of Fig. 9 provides a new component which may be referred to as an electronically controlled slide (ECS).

Fig. 5 illustrates another embodiment of an electronically controlled slide, in which the pattern panel is in a radial form. The front electrodes are narrow sectors, while the counterelectrodes are narrow parallel rings or vice versa.

This electronically controlled radial slide (ECRS) provides an image, which when magnified on bright large screen, may find many useful applications.

Another component especially useful in a system embodying the present invention is an electronically controlled colour filter, which together with the controlled slide allows a user to obtain coloured bright graphical figures on a screen, particularly a large screen.

Two types of the controllable filters are disclosed in the present application. The first type is very simple and may be driven by very simple electronic circuitry, but is suitable for data purposes only. This filter is explained with reference to Figs. 1 to 3.

As shown in Fig. 2, the colour filter includes two glass plates 11 and 13, which are held and separated from each other by a frame 12 and between which is disposed a liquid crystal 14.

The front plate 13 carries electrodes in the form of respective pluralities of narrow vertical strips marked in Fig. 1 as 1, 2, 3 and 4, while the rear plate 11 carries a plurality of counter-electrodes 1 6 also in the form of vertical narrow strips situated opposite the front electrodes of the plate 13. The front electrodes, as shown in Fig. 1, are connected internally or externally in four groups. The electrodes marked 1 are connected to a lead 5, the electrodes marked as 2 are connected to a lead 6, the electrodes marked 3 are connected to a lead 7 and the electrodes marked with 4 are connected to a lead 8. All the counter-electrodes 1 6 are connected together and to a lead marked "BP" on the glass plate 11 in contact with the liquid crystal 14.A striped colour filter 1 5 is disposed at the downstream surface of the glass plate 13 spaced from the crystal 14, as shown in Fig. 2. A front view of the striped colour filter is shown in detail in Fig. 3. It comprises a thin layer composed of four groups of transparent colour strips. The strips marked "R" are red, the strips marked "G" are green, the strips of the "B" group are blue and the strips of the "W" group are white. The coloured strips cover exactly the electrodes 1, 2, 3 and 4 of the liquid crystal display of Fig. 1. Normally, this panel is opaque.

When a voltage is applied between the lead BP and any of the leads 5,6,7 or 8, one group of the strips R, G, B or W becomes transparent. For example, when a voltage is applied between electrodes BP and the lead 6, all of the strips marked as 2 become transparent. In this case, light passes through only the green strips and a field of green luminous strips appears. The frosted glass 10 or similar element makes the light uniform on all surfaces. From Figs. 1 and 3, it is clear that a voltage on lead 5 causes red light, a voltage on lead 7 causes blue light and a voltage on lead 8 causes white light. It is possible to obtain 1 3 different colours by mixing the colours red, green and blue together with the white saturation colour. For example, red+white=pink and so forth.In Fig. 2, a second frosted glass or similar element 10-a is provided to obtain uniform white light before it reaches the colour filter.

Fig. 6 illustrates an example, in which the first type of colour filter 1 8 is used together with a conventional seven-segment liquid crystal display 20 activated by external reflected light. The external light for example day light, is reflected by mirrors 17, passes through a controllable colour filter 1 8 and becomes a desired colour. After passing through a frosted glass 19, the light becomes uniform and illuminates the liquid crystal display 20. This arrangement may be used in devices such as panel meters, watches or the like. The second type filter may be obtained when the coloured mask of Fig. 3 covers exactly the pattern plate of Fig. 7. In this case, it is possible to control the colours of all the regions of the picture selectively and independently by electronically addressing the vertical and horizontal electrodes 21 to 36 and a toj.In this case, the resolution of the colour filter is about one quarter of the resolution of the pattern panel, but this is often acceptable for colour pictures. The second type of controllable colour filter may be used more widely, but requires greater complexity in its associated electronic circuitry.

A further embodiment of a filter is an electronically controlled grey filter (ECGF), which may be obtained when in place of the four coloured strips in Fig. 3, four groups of grey filters with four different levels of grey are arranged. A mixing of the four groups of grey allow a user to obtain 13 levels of grey.

Fig. 8 illustrates a device, in which a controllable pattern plate 41 is arranged together with a frosted glass pane 40, a controllable colour filter 39, a controllable grey filter 38 and a light source 37. This arrangement allows a user to obtain artistic pictures and images in a.wide range of colour on a bright and large screen, when operatively associated with a screen and lens, such as the screen 48 and lens 47 shown in Fig.

9. This information content of the artistic pictures and images may be stores in electronic memories, recorded on tapes or on gramophone discs. Such information may also be received from radio transmitters which could also broadcast audio signals such as music. The present embodiment provides a visual picture art, as well as display techniques.

For professional devices, in which high resolution of colours is desirable, the projection may be transformed as illustrated by Figs. 10 and 11.

The projection system, as illustrated in Fig. 10, includes a large screen 65, three lenses 62, 63 and 64, three preferably identical liquid crystal displays 50, 51 and 52, three colour filters 53, 54 and 55, preferably of the colours red green and blue, and three light sources 56, 57 and 58 with the corresponding reflectors 59, 60 and 61. All three liquid crystal panels 50, 51 and 52 have the same pattern and are focussed by means of the lenses 62, 63 and 64 exactly in the same place on the screen 65. The composite portions of the picture which must be in red colour is addressed by energizing the liquid crystal panel 50, behind which is disposed a red filter 53, which is a red transparent glass or plastics material. Clearly, the colour filter may also be disposed in front of the liquid crystal panel 50 or even in front of the lens 62.The composite portions of the picture which must be in green colour is addressed to the liquid crystal panel 51, which has a green filter 54, and composite portions of the picture which must be in blue colour is addressed to the liquid crystal panel 52 which has a blue filter 55. Behind the light sources 56, 57 and 58, there are reflectors 59, 60 and 61 for improved light efficiency. The light from the source 56 passes through the red filter 53 and the liquid crystal panel 50. The lens 62 magnifies and projects all energized portions of the liquid crystal panel 50 onto the screen 65 in a red colour. Light from the source 57 passes through the green filter 54 and the liquid crystal panel 51. By means of the lens 63, the green composite portions of the picture are projected onto the same screen 65.Light from the source 58 passes through the blue filter 55, then the liquid crystal panel 52 and is projected onto the screen 65 by means of the lens 64 to create the blue composite parts of the picture. The mixture of the three coloured composites on the screen 65 creates a multicolour image or picture of high resolution of the colours. Coloured pictures may also be obtained by only two projection systems with two colours: orange and cyan-blue. Better results may be obtained with four projection systems of the colours, red, green, blue and white. Using opaque projection methods (by mirrors), reflective liquid crystal displays may be applied. Using mirrors or prisms, the 3-way projection system may be realized with one lens only, but with lesser light efficiency.

A large liquid crystal display (LLCD) is suggested in Fig. 2, which is suitable for high information capacity and rapid switching. This display is formed from many small liquid crystal cells 67-A, 67-B, 67-C, 67-D, 67-E, 67-F, 67-G, 67-H and 67-1. In practice, many more cells are likely to be used, the cells being assembled on one common transparent surface 66, which may be of glass or any suitable kind of plastics material. All cells are connected together with transparent conductors as shown in Fig. 11. Other methods of connections are of course possible.Small liquid crystal cells may be produced with very small spacing between the two pieces of glass thereby to permit rapid switching times suitable for multiplexing.The gaps between the individual cells may be made sufficiently small not to be visible from a normal viewing distance. When the liquid crystal cells are assembled on a surface of transparent plastics material, it has the additional advantages of being less fragile and manufacturable in larger sizes, though nevertheless not manifesting known phenomenona, such as Newton's rings or discoloured areas; moreover, it may be suitable for rapid switching so as to permit the multiplexing of large liquid crystal panels. The switching time may be additionally shortened by maintaining the liquid crystal panels near to the high end of their operation temperature at about 600C to 800C.This may be done as in Fig. 10 by a blower 68 with a heater element 69 and a thermostat 70. Results may be improved by energizing the liquid crystal panels at higher voltages and/or by n-way multiplexing and by interlacing methods.

For creating artistic pictures, like photographs, it is important to be able to modulate the light intensity of all elements of the picture independently. Such a possibility is given by an effect in liquid crystal devices described with reference to Fig. 12. It has been found that the intensity of light which passes through a transmissive liquid crystal device and the intensity of light reflected from a reflective liquid crystal display falls with increasing frequency of the applied voltage. As shown in Fig. 12, the relation between light intensity and frequency of the applied voltage is sufficiently linear to enable a liquid crystal device to be applied as a frequency to light-intensity converter or even as an optically coupled isolator for very high output currents with small consumption of energy from the switching circuitry.It has also been found that the application of higher voltages to the liquid crystal display causes the "frequency to light-intensity characreristic", which is shown in Fig. 12, to shift to higher frequencies, which may be significant for rapid light modulation or multiplexing. It is thus possible to modulate the intensity of light passing through or reflected by the liquid crystal means, by changing the frequency of the applied voltage. The light may also be modulated by changing the amplitude of the applied voltage between the threshold and saturation levels, but this method requires a nonlinear amplifier and may be less reliable.

In another variant, the large liquid crystal pane may also be provided without an additional common surface 66, as in Fig. 2. In this case, one of the glasses of the liquid crystal display, for example the front glass, with all front electrodes and connections may be in common integral large glass and only the opposite electrodes be disposed on individual small pieces of glass. It is to be appreciated that each individual liquid crystal element may be provided with its individual connections to circuits which prove voltages of variable frequency and/or amplitude thereby allowing one to provide highly detailed images of variable brightnesses for different portions and/or colours thereof.

Claims

Claims

1. An image projection system comprising a light source, liquid crystal means positioned to receive light from the light source, a plurality of electrodes operatively associated with the liquid crystal means, means for applying voltages selectively to individual ones of the electrodes to make selected portions of the liquid crystal means transparent or reflective, screen means, and lens means for projecting light passing through or reflected by the liquid crystal means on the screen.

2. A system as claimed in claim 1 , wherein the screen means is a large screen and the lens means is a cinema lens.

3. A system as claimed in either claim 1 or claim 2, comprising motor-driven blower means for maintaining the liquid crystal means in a predetermined temperature range.

4. A system as claimed in either claim 1 or claim 2, wherein the liquid crystal means comprises at least one electronically controllable liquid crystal filter.

5. A system as claimed in either claim 1 or claim 2, wherein the liquid crystal means comprises at least one electronically controllable liquid crystal colour filter.

6. A system as claimed in either claim 1 or claim 2, wherein the liquid crystal means comprises at least one electronically controllable liquid crystal display means.

7. A system as claimed in either claim 1 or claim 2, wherein the liquid crystal means comprises an electronically controllable colour filter and a liquid crystal display means positioned between the light source and the screen means, the liquid crystal display means being positioned between the screen means and the colour filter, and the colour filter being positioned between the liquid crystal display means and the light source.

8. A system as claimed in claim 7, wherein the liquid crystal means further comprises an electronically controllable grey filter means positioned between the light source and the liquid crystal means.

9. A system as claimed in claim 7, wherein the electronically controllable colour filter comprises a.

liquid crystal device having a number of electrodes in the form of narrow strips or at least one major surface of the crystal device and at least one coloured strip and including a light scattering means positoned between the colour filter and the light source.

10. A system as claimed in claim 9, wherein the light scattering element is a pane of frosted glass or of plastics material or a condenser lens, 1 A system as claimed in claim 7, wherein the electronically controllable colour filter comprises a liquid crystal device having electrodes in the form of narrow strips on at least one major surface of the crystal device, on which is disposed a layer of coloured strips of the colours red, green, blue and white, and includes light scattering means positioned between the colour filter and the light source and between the colour filter and the liquid crystal display means.

12. A system as claimed in claim 1 wherein the light scattering element is a pane of frosted glass or of plastics material or a condenser lens.

13. A system as claimed in either claim 1 or claim 2, wherein the liquid crystal means comprises an electronically controllable grey filter and a liquid crystal display means positioned between the light source and the screen means, the liquid crystal display means being positioned between the screen means and the grey filter and the grey filter being positioned between the liquid crystal display means and the light source.

14. A system as claimed in claim 13, wherein the electronically controllable grey filter comprises a liquid crystal device having electrodes in the form of narrow strips on at least one major surface of the crystal device, on which is disposed a layer of grey strips of different shades of grey, and including light scattering means positioned between the grey filter and the light source.

1 5. A system as claimed in claim 14, wherein the light scattering means is a pane of frosted glass.

1 6. A system as claimed in either claim 1 or claim 2, wherein the liquid crystal means comprises an electronically controllable liquid crystal pattern panel in a radial form, based on an m by n matrix defined by m electrodes in the form of narrow sectors and n electrodes in the form of narrow concentric rings, the n and m electrodes being positioned on opposite surfaces on the panel.

17. A system as claimed in either claim 1 or claim 2, wherein the light source comprises mirror means which reflects light toward the liquid crystal means.

18. A system as claimed in either claim 1 or claim 2, comprising means for feeding datarepresenting voltages to the electrodes.

1 9. A system as claimed in claim 18, wherein the means for feeding voltages comprises electronic memory means.

20. A system as claimed in claim 18, wherein the means for feeding voltages comprises recording tape playback means.

21. A system as claimed in claim 18, wherein the means for feeding voltages comprising gramophone playback means.

22. A system as claimed in claim 18, wherein the means for feeding voltages comprises radio receiving means to receive and demodulate signals from at least one radio transmitter.

23. A system as claimed in claim 1, comprising a plurality of light sources, a corresponding plurality of liquid crystal means positioned to receive light from the light sources, a plurality of filters, at least two of the filters passing different colours to colour respective corresponding light beams which are to pass respectively through the liquid crystal means from the light source, screens means, and projecting means for projecting light beams passed through the liquid crystal means and the colour filters onto the screen.

24. A system as claimed in claim 23, wherein the projecting means comprises three projecting devices of the colours red, green and blue.

25. A system as claimed in claim 23, wherein the projecting means comprise lens means.

26. A system as claimed in claim 25, wherein the lens means comprise a plurality of lenses each operatively associated with a respective one of the filters.

27. A system as claimed in claim 23, wherein the projecting means comprises four projecting devices of the colours red, green, blue and white.

28. A system as claimed in claim 23, wherein the projecting means comprises two projecting devices of the colours orange and cyan-blue.

29. A system as claimed in claim 23, comprising heater means to heat the liquid crystal means and comprising a blower, a heating element and a thermostat.

30. A system as claimed in claim 23, wherein the liquid crystal means are in the form of an array of liquid crystal cells assembled on a single common transparent surface.

31. A system as claimed in claim 30, wherein the common transparent surface is of a plastics material.

32. A system as claimed in claim 30, wherein the common transparent surface is provided on one of two liquid crystal plates, which is integral while the opposite plate is assembled from very small pieces of glass.

33. A system as claimed in claim 23, further comprising voltage supply means coupled to the liquid crystal means for energizing the same with voltages of changeable frequency to modulate the respective intensity of individual elements of the image.

34. A system as claimed in claim 23, further comprising voltage supply means coupled to the liquid crystal means for energizing the same with voltages to effect optically coupled isolation.