Abstract:
The invention relates to a multi-layer display ( 1 ) for displaying coloured images comprising a light source ( 2 ), a first image screen ( 3 ), arranged for displaying a first image ( 8 ), whereby the first image screen ( 3 ) overlaps with and is placed substantially parallel with the light source ( 2 ), and a second translucent image screen, arranged for displaying a second image ( 8 ), whereby the second image screen ( 4 ) is placed spatially separated along a viewing axis perpendicular to the light source ( 2 ) and placed substantially parallel to and overlapping with the first image screen ( 3 ), whereby the first image screen ( 3 ) is controllable to alternate at least part of the first image ( 8 ) between transparent and a first appearance and the second image screen ( 4 ) is controllable to synchronously with the first image screen ( 3 ) alternate at least part of the second image ( 8 ) between occluded and a second appearance.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a multi-plane display for the display of images. The invention further relates to a method of displaying images on a multi-plane display.  
       BACKGROUND  
       [0002]     Multi-plane displays are presently known in the art. Usually they comprise a light source, which can be planar, and a plurality of interspaced, overlapping, translucent image screens, which can be simultaneously controlled to display images that have a spatial or three-dimensional character.  
         [0003]     An example of a multi-plane display is described in the patent publication WO0115127.  
         [0004]     Such displays can be used for various purposes like for amusement, games, but also for showing complex information like in military applications, where it is desirable to show overlapping graphical information in one three dimensional view.  
         [0005]     Usually the plurality of image screens comprises liquid crystal displays (LCD&#39;s). These LCD&#39;s can be black-and-white or colour displays.  
         [0006]     The plurality of image screens can be viewed using a light source, whereby the image screens are placed between the light source and the viewer. The light source can be planar such as a LCD backlighting device, placed in parallel close to the image screens, but the light source can also be the daylight or a daylight lit background placed in the line of sight and viewable through the image screens.  
         [0007]     When displaying colours on a multi-plane display each image screen may present a plurality of images. A first image, having a first appearance on a first image screen, may be occluded by a second image having a second appearance on a second image screen. An appearance may be a colour or a grey tone. An appearance may have a brightness ranging from transparent to full saturation, so for example in case of the colour red from transparent to fully saturated red, or in the case of grey tones from transparent to black, where black means that the light source is fully occluded by the image screen. An appearance may also include a pattern and the pattern may represent a texture.  
         [0008]     The resulting image, when viewed from a viewpoint mainly perpendicular with respect to the front plane of the display, then shows, where the first and second image overlap, an appearance which corresponds to the mixed appearance of the first and second appearance.  
         [0009]     In colour, the mixed appearance arises from the absorption or subtraction of colour components of the first image by the colour of the second image. In grey tone, the appearance of the overlapping image parts is darker.  
         [0010]     In pattern, the overlapping parts appear to have a mixed pattern.  
         [0011]     While displaying images on different planes or image screen in this way the appearances of overlapping image parts thus interfere because of the interaction of the translucent screens. For example, it is not possible to display a white image on top of a black image.  
       SUMMARY OF THE INVENTION  
       [0012]     It is an object of the present invention to provide a multi-layer display capable of simultaneously displaying images on at least two image screens that may overlap from a viewing position and that retain their appearance regardless the overlap of the images.  
         [0013]     The object is achieved according to the invention by means of a multi-layer display that may comprise a light source, a first translucent image screen, whereby the first image screen can overlap and be placed substantially parallel with the light source, arranged for displaying a first image, having a first appearance, e.g. at least one of a colour, grey tone and a pattern, and wherein the first screen is capable of displaying the first image in one of a transparent state, a normal appearance state and an occluded state, the display further comprising a second translucent image screen, whereby the second image screen can be placed spatially separated along a viewing axis perpendicular to the light source and placed substantially parallel to and overlapping with the first image screen, arranged for displaying a second image, having a second appearance, e.g. at least one of a colour, grey tone and a pattern, wherein the second screen is capable of displaying the second image in one of a transparent state, a normal appearance state and an occluded state, and wherein the first image screen is controllable to alternate at least part of the first image between transparent state and a normal appearance state and the second image screen is controllable to synchronously with the first image screen alternate at least part of the second image between an occluded state and a normal appearance state, and wherein the normal appearance state of the first image occurs simultaneously with the occluded state of the second image and the transparent state of the first image occurs simultaneously with the normal appearance state of the second image.  
         [0014]     According to this embodiment according the invention, displayed images on the first and second image screen that overlap from a viewing point, which is usually more or less along an axis perpendicular to the light source, retain their correct appearance. Images appear as opaque. No undesired interference occurs. So even a white image can appear correctly on top of a black image.  
         [0015]     The alternation of images or part of the image screens has to be fast, preferably at rates from 20 Hz or more in order to minimize the perceived flicker by a viewer. The phenomenon of flicker is well known form for example television sets or data monitor using cathode ray tubes.  
         [0016]     A first embodiment according to the invention, wherein the first image screen can be controllable to occlude at least part of the first image screen not belonging to the first image, while displaying the first image in the normal appearance state, has the advantage that the background of the images when viewed together appears darker. In this way a trade-off is achieved between image brightness and appearance preservation of the overlapping images.  
         [0017]     A second and preferred embodiment according to the invention, wherein the second image screen can be controllable to occlude at least part of the second image screen not belonging to the second image, while displaying the second image in the normal appearance state, also has the advantage that the background of the images when viewed together appears darker. In this embodiment the best perceived result is obtained. The luminance ratios between first and second images and images and background are best preserved, since all features visible through the combined image screen are mixed with occluded or “black”.  
         [0018]     The first and second embodiment combined give when viewed together an occluded or black appearing background, whereas the first and second image appear overlapping with their appearance preserved. The colour saturation of overlapping images is preserved optimally, and also there is less flicker, because the background remains occluded.  
         [0019]     In yet a further embodiment according to the invention, wherein the first and second image screen are arranged to synchronously alternate only the overlapping part of the first and second images, as viewable along the viewing axis perpendicular to the light source, the area that needs alternation is minimised thereby substantially reducing flicker of the image screens.  
         [0020]     In yet a further embodiment according to the invention, further comprising an at least one intermediate image screen, placed between the first and the second image screens, wherein the at least one intermediate image screen is controllable for displaying a third image, which overlaps at least in part with the first image on the first image screen, and which is overlapped by at least in part by the image on the second image screen, it is possible to display even more complex image combinations in more than two layers or image screens.  
         [0021]     In yet a further embodiment according to the invention, wherein the third image is displayable in an occluded state simultaneously with the first image in a normal appearance state and the second image in an occluded state, and wherein the third image is displayable in a normal appearance state simultaneously with the first image in a transparent state and the second image in an occluded state, and wherein the third image is displayable in a transparent state simultaneously with the first image in a transparent state and the second image in a normal appearance state and wherein the simultaneous states of the first second and third images are alterable synchronously, it is possible to display more than two overlapping images retaining their appearance.  
         [0022]     The object is also achieved according to the invention by means of a method for displaying coloured images on a multi-layer display, the multi-layer display having a light source, a first translucent image screen, whereby the first image screen overlaps with and is placed substantially parallel with the light source, arranged for displaying a first image, having a first appearance, e.g. at least one of a colour, grey tone and a pattern, and wherein the first screen can be capable of displaying the first images in one of a transparent state, a normal appearance state and an occluded state, and a second translucent image screen, whereby the second image screen can be placed spatially separated along a viewing axis perpendicular to the light source and placed substantially parallel to and overlapping with the first image screen, arranged for displaying a second image, having a second appearance, e.g. at least one of a colour, grey tone and a pattern, wherein the second screen can be capable of displaying the second image in one of a transparent state, a normal appearance state and an occluded state, the method comprising alternating at least part of the first image between a transparent state and a normal appearance state and synchronously alternating at least part of the second image between an occluded state and a normal appearance state.  
         [0023]     According to this embodiment according the invention, displayed images on the first and second image screen that overlap from a viewing point, which is usually more or less along an axis perpendicular to the light source, retain their correct appearance. Images appear as opaque. No undesired interference occurs. So even a white image can appear correctly on top of a black image.  
         [0024]     In an third embodiment according to the invention, further comprising occluding at least part of the first image screen not belonging to the first image, when the first image is displayed in the normal appearance state. In this way a trade-off is achieved between image brightness and appearance preservation of the overlapping images.  
         [0025]     In an fourth embodiment according to the invention, further comprising  
         [0026]     occluding at least part of the second image screen not belonging to the second image, when the second image is displayed in the normal appearance state, also has the advantage that the background of the images when viewed together appears darker.  
         [0027]     The third and fourth embodiment combined give when viewed together an occluded or black appearing background, whereas the first and second image appear overlapping with their appearance preserved. The colour saturation of overlapping images is preserved optimally.  
         [0028]     In a further embodiment according to the invention, further comprising  
         [0029]     synchronously alternating in the first and second image screen only the overlapping part of the first and second images, as viewable from the viewpoint, the area that needs alternation is minimised thereby substantially reducing flicker of the image screens.  
         [0030]     In a further embodiment according to the invention, further comprising  
         [0031]     displaying a third image on an at least one intermediate image screen, placed between the first and the second image screens, whereby the third image overlaps at least in part with the first image on the first image screen, and which is overlapped by at least in part by the image on the second image screen, it is possible to display even more complex image combinations in more than two layers or image screens.  
         [0032]     In a further embodiment according to the invention, further comprising displaying the third image in an occluded state simultaneously with the first image in a normal appearance state and the second image in an occluded state,  
         [0033]     displaying the third image in a normal appearance state simultaneously with the first image in a transparent state and the second image in an occluded state,  
         [0034]     displaying the third image in a transparent state simultaneously with the first image in a transparent state and the second image in a normal appearance state and wherein the simultaneous states of the first, second and third images are alterable synchronously, it is possible to display more than two overlapping images retaining their appearance. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]      FIG. 1  shows a basic construction of a multi-plane display according to the state of the art.  
         [0036]      FIG. 2  shows a basic architecture for controlling a multi-plane display according to the state of the art.  
         [0037]      FIGS. 3   a - 3   c  show the display of two images on two image screens according to the state of the art.  
         [0038]      FIGS. 4   a - 4   e  show the display of two images on two image screens according to the invention.  
         [0039]      FIGS. 5   a - 5   e  show the display of two images on two image screens according to the preferred embodiment of the invention.  
         [0040]      FIGS. 6   a - 6   e  show the display of two images on two image screens according to another embodiment of the invention.  
         [0041]      FIGS. 7   a - 7   j  show the display of three images on three image screens according to another embodiment of the invention. 
     
    
       [0042]     In all drawings, an appearance, colour or grey tone, is for technical reasons represented by a pattern. The embodiments given should be read with an appearance in mind and not the pattern in the drawing.  
       DETAILED DESCRIPTION  
       [0043]     The invention can be embodied in any multi-plane colour display known in the art, where each plane comprises a image screen which can be a liquid crystal display. However the invention applies to any type of multi-plane display whereby each image screen is transparent.  
         [0044]      FIG. 1  shows a basic construction of a multi-plane display  1  according to the state of the art.  
         [0045]     A light source  2  may constructively be part of the display  1 , but this is not necessarily the case. The light source  2  may also be a light emitting or light reflecting surface remote from the display  1 .  
         [0046]     The display  1  further comprises at least a first  3  and a second image screen  4 , placed more or less parallel and overlapping from a viewer&#39;s position  13 . The relative positions of the image screens  3 , 4  are between the viewer&#39;s position  13  and the light source  2 . The image screens  3 ,  4  are placed substantially perpendicular to the viewing axis  14  between the viewing point  13  and the light source  2 .  
         [0047]     The image screens  3 ,  4  are transparent and fit for displaying images having an appearance in at least one of colour and grey tone. Furthermore the image screens  3 , 4  can in whole or in part be occluded, which means that viewed from a viewers position towards the light source  2 , the occluded part of either of the image screens  3 , 4  appears as black. Such image screens  3 ,  4  can be liquid crystal displays (LCD&#39;s), but other technologies can be possible.  
         [0048]     The image screens  3 ,  4  can be constructively integrated into a display by means of supporting means  5 . The supporting means  5  may comprise supports, props, frames etc. The relative distance between the image screens may vary depending on the image screen diameters and is not essential for the invention. Essential is that images can be viewed as overlapping.  
         [0049]     Additional image screens may be mounted to the image screens  3 ,  4  using additional supporting means  5 .  
         [0050]      FIG. 2  shows a basic architecture for controlling a multi-plane display.  
         [0051]     Each image screen  3 , 4  is electronically controllable, by means of a control device  6 , connected to and cooperating with each image screen respectively. Control devices  6  may be shared between image screens  3 ,  4 . The control devices  6  can be connected to an image generator  7 . This image generator  7  may be a computer or PC arranged for generating images. A computer has a processor, memory and a graphics adaptor, whereby the processor can be programmed to perform control of the graphics adaptor. The connection between display  1  and image generator  7  may be hard-wired or wireless. Various implementations are possible, readily available for the person skilled in the art.  
         [0052]      FIG. 3   a - 3   c  show the display of two images on two image screens according to the state of the art.  
         [0053]      FIG. 3   a  separately shows a first image  8  having a first appearance, depicted by a first pattern, displayed on the first image screen  3 ,  FIG. 3   b  separately shows a second image  9  having a second appearance, depicted by a second pattern, displayed on the second image screen  4 .  
         [0054]      FIG. 3   c  shows the two image screens  3  and  4  overlapping, viewed from the viewer&#39;s position  13 , whereby the images  8  and  9  also overlap. The image  9  appears as being on top of image  8 , but the appearances of the image  8  in the overlapping part  10  is interfered by the appearance of image  9 , since both image screens  3  and  4  are transparent.  
         [0055]      FIGS. 4   a - 4   e  show the display of two images on two image screens according to the invention.  
         [0056]      FIG. 4   a  shows the first image  8  having a first appearance, in a normal appearance state depicted by the first pattern, displayed on the first image screen  3 .  
         [0057]      FIG. 4   b  shows the second image  9  having a second appearance, but in an occluded state, displayed on the second image screen  4 .  
         [0058]      FIG. 4   c  shows the first image  8  having a first appearance, but in a transparent state, displayed on the first image screen  3 ,  
         [0059]      FIG. 4   d  shows the second image  9  having the second appearance, in a normal appearance state depicted by the second pattern, displayed on the second image screen  4 .  
         [0060]     The screens  3  and  4  are controlled such that the states of the images  8  and  9  as shown in  FIGS. 4   a  and  4   b  occur simultaneously in a first timeframe.  
         [0061]     The screens  3  and  4  are further controlled such that the states of the images  8  and  9  as shown in  FIGS. 4   c  and  4   d  occur simultaneously in a second timeframe.  
         [0062]     The timeframes with the states of the images  8  and  9  in  FIG. 4   a  and  FIG. 4   b  are synchronously alternated with the timeframes with the states of the images  8  and  9  in  FIG. 4   c  and  FIG. 4   d.    
         [0063]      FIG. 4   e  shows the two image screens  3  and  4  overlapping, viewed from the viewers position  13 , whereby the images  8  and  9  partially overlap, the image  9  is viewed as being on top of image  8 , and the appearances of the two images in the overlapping part  10  no interfere.  
         [0064]      FIGS. 5   a - 5   e  show the display of two images on two image screens according to the preferred embodiment according to the invention.  
         [0065]      FIG. 5   a  shows the first image  8  having a first appearance, in normal appearance state depicted by the first pattern, displayed on the first image screen  3 .  
         [0066]      FIG. 5   b  shows the second image  9  having a second appearance, but in an occluded state, displayed on the second image screen  4 .  
         [0067]      FIG. 5   c  shows the first image  8  having a first appearance, but in a transparent state, displayed on the first image screen  3 .  
         [0068]      FIG. 5   d  shows the second image  9  having the second appearance, in normal appearance state depicted by the second pattern, with an occluded background displayed on the second image screen  4 .  
         [0069]     The screens  3  and  4  are controlled such that the states of the images  8  and  9  as shown in  FIGS. 5   a  and  5   b  occur simultaneously in the first timeframe.  
         [0070]     The screens  3  and  4  are further controlled such that the states of the images  8  and  9  as shown in  FIGS. 5   c  and  5   d  occur simultaneously in the second timeframe.  
         [0071]     The timeframes with the states of the images  8  and  9  in  FIG. 5   a  and  FIG. 5   b  are synchronously alternated with the timeframes with the states of the images  8  and  9  in  FIG. 5   c  and  FIG. 5   d.    
         [0072]     A variant, not shown here but also an embodiment according to the invention, is to occlude the background of screen  3  in the case of  FIG. 5   a  having image  8  in the normal appearance state. The combined image in  FIG. 5   e  would then appear as having a black or occluded background with the images  8  and  9  whereby image  9  appears on top of image  8 .  
         [0073]     The difference of this embodiment with the invention as disclosed in  FIGS. 4   a - FIG. 4   e  is that the non-image part  11  of image screen  4  is alternated between transparent as shown in  FIG. 5   b  and occluded as shown in  FIG. 5   d.    
         [0074]     The result as shown in  FIG. 5   e  is that 1) what is perceived as background, the non-image parts of image screens  3  and  4  combined is darker and 2) the objects appear with the proper occlusion.  
         [0075]     In order to reduce the alternating part of the image screen  4  it is possible to alternate only part of the non-image part of image screen  4 . By this reduction of the alternating part of image screen  4  a reduction of flicker can be perceived.  
         [0076]     If part of the non-image part of image screen  4  is alternated, the non-alternating and non-image part of image screen  4  can be kept at a brightness level comparable with the brightness level of the alternating non-image part  11  of image screen  4 .  
         [0077]      FIGS. 6   a - 6   e  show the display of two images on two image screens according to another embodiment of the invention.  
         [0078]      FIG. 6   a  shows the first image  8  having a first appearance, in normal appearance state depicted by the first pattern, displayed on the first image screen  3 .  
         [0079]      FIG. 6   b  shows the second image  9  having a second appearance, but the overlapping part of image  9  in an occluded state, displayed on the second image screen  4 .  
         [0080]      FIG. 6   c  shows the first image  8  having a first appearance, but the overlapped part of image  8  in a transparent state, displayed on the first image screen  3 .  
         [0081]      FIG. 6   d  shows the second image  9  having the second appearance, in normal appearance state depicted by the second pattern, displayed on the second image screen  4 .  
         [0082]     The screens  3  and  4  are controlled such that the states of the images  8  and  9  as shown in  FIGS. 6   a  and  6   b  occur simultaneously in the first timeframe.  
         [0083]     The screens  3  and  4  are further controlled such that the states of the images  8  and  9  as shown in  FIGS. 6   c  and  6   d  occur simultaneously in the second timeframe.  
         [0084]     The timeframes with the states of the images  8  and  9  in  FIG. 5   a  and  FIG. 5   b  are synchronously alternated with the timeframes with the states of the images  8  and  9  in  FIG. 6   c  and  FIG. 6   d.    
         [0085]     In this embodiment only the overlapping parts of images  8  and  9  are alternated, thereby minimizing the area per image screen  3 ,  4  to be alternated.  
         [0086]     The non-overlapping parts  12  of the images  8 ,  9  can be corrected for brightness, so that a uniform brightness distribution can be perceived for each of the images  8 ,  9 .  
         [0087]     The invention can be used with more than two image screens.  
         [0088]      FIGS. 7   a - 7   j  show the display of three images on three image screens according to another embodiment of the invention.  
         [0089]     An intermediate image screen  15 , with its own controller can be placed in between the first  3  and second  4  screen.  
         [0090]      FIG. 7   a  shows the first image  8  having a first appearance, in normal appearance state depicted by the first pattern, displayed on the first image screen  3 .  
         [0091]      FIG. 7   b  shows a third image  16  having a third appearance, but in an occluded state, displayed on the intermediate image screen  15 .  
         [0092]      FIG. 7   c  shows the second image  9  having the second appearance, but in an occluded state, displayed on the second image screen  4 .  
         [0093]      FIG. 7   d  shows the first image  8  having a first appearance, but in a transparent state, displayed on the first image screen  3 .  
         [0094]      FIG. 7   e  shows the third image  16  having a third appearance, in normal appearance state depicted by a third pattern, displayed on the intermediate image screen  15 .  
         [0095]      FIG. 7   f  shows the second image  9  having the second appearance, but in an occluded state, displayed on the second image screen  4 .  
         [0096]      FIG. 7   g  shows the first image  8  having a first appearance, but in a transparent state, displayed on the first image screen  3 .  
         [0097]      FIG. 7   h  shows the third image  16  having a third appearance, but in a transparent state, displayed on the intermediate image screen  15 .  
         [0098]      FIG. 7   i  shows the second image  9  having the second appearance, in normal appearance state depicted by the second pattern, displayed on the second image screen  4 .  
         [0099]     The screens  3 ,  4  and  15  are controlled such that the states of the images  8 ,  9  and  16  as shown in  FIGS. 7   a,    7   b  and  7   c  occur simultaneously in the first timeframe.  
         [0100]     The screens  3 ,  4  and  15  are further controlled such that the states of the images  8 ,  9  and  16  as shown in  FIGS. 7   d,    7   e  and  7   f  occur simultaneously in the second timeframe.  
         [0101]     The screens  3 ,  4  and  15  are further controlled such that the states of the images  8 ,  9  and  16  as shown in  FIGS. 7   g,    7   h  and  7   i  occur simultaneously in a third timeframe.  
         [0102]     The timeframes with the states of the images  8  and  9  in  FIGS. 7   a,    7   b  and  7   c  are synchronously alternated successively with the timeframes with the states of the images  8  and  9  in  FIGS. 7   d,    7   e  and  7   f  and with the timeframes with the states of the images  8  and  9  in  FIGS. 7   g,    7   h  and  7   i.    
         [0103]     The resulting image is shown in  FIG. 7   j,  where image  9  appears on top of images  16  and  8  and where image  16  appears on top of image  8 .  
         [0104]     The order in which the image states are altered can be chosen arbitrarily.  
         [0105]     A person skilled in the art can easily derive the general case with at least two intermediate screens  15  having intermediate overlapping images  16 .  
         [0106]     The alternating only has to take place between overlapping images.  
         [0107]     On an intermediate screen  15  an image  16  is shown in an occluded state when a screen behind the intermediate screen is showing an image in normal appearance state.  
         [0108]     On an intermediate screen  15  an image  16  is shown in a transparent state when a screen before the intermediate screen is showing an image in normal appearance state.  
         [0109]     On an intermediate screen  15  an image  16  is shown in normal appearance state when no other screen before or behind the intermediate screen is showing an image in normal appearance state.  
         [0110]     The notions ‘before’ and ‘behind’ are to be interpreted from the viewer&#39;s point of view  13 .  
         [0111]     The invention can be realised by arranging the image generator  7  to perform the alternating function required. It is also possible to arrange, in case of the use of a computer, to arrange the graphics adaptor for the alternating function. Furthermore it also possible to arrange the control devices  6  for the alternating functions according to the here above described embodiments.  
         [0112]     By alternating images or parts thereof, the viewer may perceive the alternating images or parts thereof as flickering.  
         [0113]     In order to counteract this phenomenon, the alternating frequency should be as high as possible. It is known in from experiments with the invention that an alternating rate of approximately 20 Hz suffices to adequately perform such that displayed overlapping images no longer interfere. At this rate however flicker is perceived strongly. At higher rates, for 2 image screens preferably at 70 Hz or higher, a common viewer perceives no flicker.  
         [0114]     In the case that a plurality of overlapping images pairs is to be displayed, each pair can be alternated at a different timing or at a different rate. Also the alternating rates of the various couples can vary in time, for example at random.