Technical Field

The present invention relates to the field of three dimensional (3D) displays, and more specifically to projection array light field displays capable of providing visual cues associated with natural depth perception without the need for visual aids such as glasses, goggles, or headsets.

Background

Viewing an image of a three-dimensional object or scene in 3D conveys more information than viewing two-dimensional (2D) views of that object or scene. This can be particularly important in medical diagnosis, scientific research, military applications, industrial applications, and entertainment applications. One known approach to generating a 3D image is to employ a stereoscopic method in which two 2D images are overlaid to produce an illusion of depth. However, stereoscopic methods do not provide all the visual depth cues associated with 3D viewing; for example convergence, accommodation, and motion parallax are not reproduced.

Light field displays are a class of 3D display technology capable of reproducing the visual cues of 3D vision by controlling the direction of light rays leaving the display. A projection array light field display is a type of light field display that utilises an array of projectors to project overlapping light field components onto a diffusion screen in order to emulate light rays from a real 3D object or scene. At each position on the diffusion screen, the angle of incidence of light rays from each projector is different than for the other projectors. By providing a diffusion screen for which the diffusion of a light ray from its angle of incidence is restricted within an angle corresponding to the angular separation of the projectors, a light ray from one point on the diffusion screen at a particular viewing angle generally originates from a single projector. Accordingly, and in contrast with conventional stereoscopic displays, multiple light rays can originate from a single point on the diffusion screen with the multiple light rays being distinguishable by varying the viewing position.

The light field components can be generated by taking many 2D images of a real object or scene, or many renders of a computer-generated object or scene, and performing a transformation to map the different light rays from the object or scene to a position (or pixel) on the diffusion screen and a direction at which the light ray leaves that position on the diffusion screen. The combination of the diffusion screen position and the direction for a light ray determines the projector that is to emit the light ray for display purposes. Accordingly, for each projector a corresponding light field component is generated that reproduces at the diffusion screen the light rays associated with that projector. By simultaneously projecting the light field component for all the projectors onto the diffusion screen, a viewer at a viewing position receives light originating from the projectors from respective different portions of the display in such a way as to reproduce the light field from a real 3D object or scene.

US patent number 7,959,294 discusses a projection array light field display which uses a linear array of projectors to illuminate a diffusion screen in order to produce an image with horizontal parallax. The projectors are configured to illuminate the diffusion screen from a discrete range of horizontal angles, and the diffusion screen has anisotropic diffusion properties such that the horizontal diffusion of individual light rays is comparable to the horizontal angular separation of the projectors and the vertical diffusion acts to maximise the allowable vertical field of view. In this way, as the viewing position moves horizontally around the display, light viewed from the same point on the diffusion screen originates from different projectors. Although there is no vertical parallax, in practice viewers typically maintain their eyes in a horizontal orientation and at a substantially constant vertical height, and therefore displaying vertical parallax is not necessary for a natural viewing experience of a 3D object or scene. By implementing horizontal only parallax using a linear array of projectors, significantly fewer projectors are needed than for a full-parallax light field display.

To increase the operable field of view of the display, current projection array light field displays must increase the number of projectors or otherwise decrease the angular resolution of the 3D image, making it appear less natural. Accordingly, projection array light field displays often have in excess of 70 projectors, and are therefore large, consume much power, and are expensive. In order to achieve sufficient separation angles between projectors, for example an angle of one degree to produce a natural 3D effect, the projectors must be positioned far away from the screen, which acts to increase the size of these systems further. In configurations using pico- projectors to compensate for these issues there is often a reduction in resolution. Other solutions to these issues are to constrain viewers to small observation areas and employ fewer projectors.

It is desirable to be able to produce a projection array light field display with good resolution and field of view but which does not require a large number of projectors.

Summary

According to a first aspect of the present invention, there is provided light field display apparatus for displaying an image having one or more projectors for projecting light field components for a 3D image, a diffusion screen to diffuse incident light rays through a diffusion angle, and an angular modulator arranged to deflect light rays from the or each projector through an angle of deflection and onto the diffusion screen. A controller applies a control signal to the angular modulator in order to vary the angle of deflection in order to vary the angle of incidence of light rays from the or each projector onto the diffusion screen synchronously with the projection of different light field components in order to emulate an array of projectors projecting respective light field components at respective angles onto the diffusion screen. Each projector in the array is separated by an angular separation substantially equal to the diffusion angle so that viewers from different viewing angles see light rays passing through a point in the diffusion screen from different virtual projectors, and accordingly different light field slices.

Advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 schematically shows a light field display according to the present invention.

Figure 2 schematically shows a projector and an angular modulator of the light field display illustrated in Figure 1 emulating an array of projectors. Figure 3a schematically shows image data processing by a conventional light field display to generate a 3D image by decomposing a 3D scene into image data for light field components and simultaneously sending the image data to respective projectors in an array.

Figure 3b schematically shows image data processing by the light field display illustrated in Figure 1 to generate a 3D image by decomposing the 3D scene into image data for light field components and sequentially sending the image data a projector.

Figure 4 schematically shows a viewer observing two parts of a 3D scene from different angles associated with the angular position of the virtual projector projecting each part of the 3D scene.

Figure 5 schematically shows an alternative light field display having extra optics in the path of the light ray for folding the optical path and magnification of the image.

Figure 6 schematically shows an alternative light field display having a transmissive angular modulator.

Figure 7 schematically shows an alternative light field display having a moveable projector.

Figure 8 schematically shows a macropixel of a holographic optical element configured in a sub pixelated structure with an intensity modulator for selecting one subpixel at a time.

Figure 9 schematically shows an alternative light field display having eye tracking cameras to allow the system to alter vertical parallax for different users.

Detailed Description

In a first embodiment, there is provided a light field display 1 comprising a controller 2, a projector 3, an angular modulator 4, and a diffusion screen 5 as shown in Figure 1. As will be discussed in detail hereafter, in this embodiment the light field display 1 reproduces horizontal parallax but not vertical parallax. As shown in Figure 1 , the horizontal direction x is parallel to the page and the diffusion screen 5 and the vertical direction y is perpendicular to the page.

The controller 2 provides image data for a sequence of images to the projector 3, which forms the corresponding sequence of images in the object plane of the projector 3 using a light modulator 7 so that light rays 9 produced by a light source 6 within the projector 3 are modulated in accordance with the image data. The light rays 9 leaving the projector 3 are imaged using focussing optics 8 at the diffusion screen 5. In this embodiment, the light rays 9 from the projector 3 are reflected by the angular modulator 4 and directed to the diffusion screen 5.

The diffusion screen 5 is a holographic optical element (HOE) that provides anisotropic diffusion of the light rays 9, such that the horizontal diffusion angle a is significantly smaller than the vertical diffusion angle. Such a diffusion screen is known from previous projection array light field displays and are readily available from manufacturers such as Luminit LLC (see www.luminitco.com).

The angular modulator 4 has a rotation mechanism (not shown in Figure 1) which enables the angular modulator 4 to be rotated about a vertical axis so that the horizontal angle through which the angular modulator 4 deflects the light rays 9 can be varied over a range of deflection angles. The controller 2 sends an actuation signal to the rotation mechanism of the angular modulator 4 to cycle the deflection angle over the range of deflection in equal angular steps in a manner that is time-synchronised to the supply of image data for the sequence of images to the projector 3, such that each image in the sequence of images is displayed in synchronism with a respective deflection angle.

In this embodiment, the angular modulator 4 is rotated in angular steps of cp/2, each angular step corresponding to a f change in deflection angle, with the angle f being substantially the same as the horizontal diffusion angle a of the diffusion screen 5. Having light rays 9 incident on the diffusion screen 5 at multiple angles produces the same effect as having an array of angularly separated projectors. In this way the projector 3 and the angular modulator 4, under the control of the controller 2, emulate an array of projectors. In other words, the projector 3 and the angular modulator 4, under the control of the controller 2 form a virtual projector array 21 formed by multiple virtual projectors 22a-22c, only three of which are shown in Figure 2 for ease of illustration.

The rate of variation of the deflection angle, and accordingly the rate at which the sequence of images is displayed by the projector 3, is sufficiently high that the angular modulator 4 cycles through the range of deflection within the persistence time of human vision, and accordingly it appears to a viewer that the light rays 9 for images displayed within a cycle exist simultaneously. For the projector 3 to change the image in the object plane of the projector time-synchronous ly with the time varying angular modulation, the image data for the sequence of images must be supplied to the light modulator 7 at a rate equal to the number of virtual projectors 22 multiplied by the number of frames which need to be projected per second to simulate a smooth image, based on the persistence time of human vision.

Each image in the sequence of images corresponds to a light field component for a corresponding virtual projector. By synchronising the supply of image data to the projector 3 to the deflection angle of the angular modulator 4 such that each light field component is, in effect, displayed by the corresponding virtual projector, a horizontal- parallax light field display is produced. The horizontal field of view is determined by the range of deflection of the angular modulator 4, with the limited horizontal diffusion angle providing for horizontal parallax. The vertical diffusion angle establishes the vertical field of view (without vertical parallax) and is made as large as possible to allow viewing over the largest possible range of vertical positions.

If light field components for a single image are cycled continuously, then a static 3D image is produced. Alternatively, if the sequence of images is formed by concatenating a series of sub-sequences of images, with each sub-sequence of images corresponding to the light field components for a separate 3D image, then a dynamic 3D image is produced.

As schematically shown in figures 3a and 3b, image data 31 corresponding to many 2D images of a real object or scene, or many 2D renders of a computer-generated object or scene, where each image or render represents the object or scene viewed from a different angular position, is processed to generate image data 32 for light field components to be projected by respective projectors 33. Each light field component must be projected such that the light rays 9 leave the diffusion screen 5 with a unique combination of position and angle corresponding to the position and angle of the light rays in the light field of the object or scene 31. In Figure 3 a, which is representative of conventional projection array light field displays, the image data 32 corresponding to a plurality of light field components for a single 3D image is sent to a respective projector 33 to be projected simultaneously. In Figure 3b, which represents an example of the projection array light field display 1 of the present invention, the image data 32 corresponding to a plurality of light field components for a single 3D image is sequentially sent to a single projector 3. By using only one projector 3 and one angular modulator 4, the size of a projection array light field display 1 can be smaller than when using an array of real projectors, and the energy use during normal operation can be reduced. Using a projector 3 and an angular modulator 4 to generate an array 21 of virtual projectors 22 in conjunction with a tracking sensor for detecting the position of a viewer can further increase performance by allowing the dynamic reallocating of resources in dependence on detected viewing positions, thereby decreasing the size and energy use of the projection array light field display 1.

In this embodiment, the diffusion screen 5 is a holographic optical element (HOE) that provides anisotropic diffusion of the light rays 9. Creating diffusion screens 5 with anisotropic properties from holographic optical elements is known. Anisotropic diffusion as provided by the HOE described in examples herein is a diffusion characteristic such that when light passes through the HOE, the resulting diffusion angle a is not the same in ah directions. In this example the diffusion angle a along the horizontal axis x is significantly smaller than the diffusion angle in the vertical axis y. The angular separation f of the virtual projectors 22 is the angle between the virtual projectors 22 when viewed from a point on the diffusion screen 5. This has the effect that within a viewing angle substantially similar to the angular separation f of the virtual projectors 22 the light rays 9 transmitted through a point on the diffusion screen 5 will be coming from only one virtual projector 22, the one virtual projector 22 being whichever is substantially in line with the viewer and the point on the diffusion screen 5. By using virtual projectors 22 having a controllable position and framerate, the display can be dynamically reconfigured using software to trade-off between angular resolution, framerate and field of view. The horizontal diffusion angle a being substantially equal to the horizontal angular separation f of the virtual projectors 22 allows the system to build up a 3D pixel where at each viewing position separated by an angle equal to the diffusion angle a the light rays 9 leaving the diffusion screen 5 come from a single virtual projector 61. This means that as an observer moves around a point 64 on the diffusion screen 5, the observer will see light rays 9 from different virtual projectors 22 through the point 64 depending on their position. If the horizontal diffusion angle a through each point on the diffusion screen is smaller than the horizontal angular separation f of the virtual projectors 22 then there will be a streaking effect as there is a drop in the intensity of light rays 9 leaving a point on the diffusion screen 5 between viewing angles. If the horizontal diffusion angle a is greater than the horizontal angular separation f of the virtual projectors 22 then there will be blurring of the edges between viewing angles as the light rays 9 leaving a point 64 on the diffusion screen 5 at an angle will overlap with light rays leaving the point 64 at a different angle.

Figure 4 schematically shows light rays 9 coming from two virtual projectors 61, 62 incident on a viewer’s eye 67 according to an example of the projection array light field display 1. While a comparatively small region of overlap of the light rays from the two virtual projectors 61,62 on the diffusion screen 5 is shown in Figure 4, it will be appreciated that in practice there will be a substantial region of overlap.

The first virtual projector 61 projects a first light field component on to the diffusion screen 5. The first light field component is composed of multiple rays which are each incident on a different point on the diffusion screen 5 and with a different angle of incidence. The second virtual projector 62 projects a second light field component on to the diffusion screen 5, the second light field component also being composed of multiple rays each incident on a different point of the diffusion screen 5 at a different angle of incidence. A human viewer 67 beyond the diffusion screen 5 sees only light travelling substantially towards the viewer 67 from the virtual projectors 61 , 62 due to the narrow horizontal diffusion angle a of the diffusion screen 5. Hence in one viewing position the light rays 69 incident on the viewer’s eye from the first virtual projector 61 are transmitted through a first point 64 on the diffusion screen 5, while the light rays 70 incident on the viewer’s eye 67 from the second virtual projector 62, pass through a different point 65 on the diffusion screen 5. The light rays 9 from each light field component pass through the points on the diffusion screen 5 at angles which correspond to the position and angles of the light rays from the light field of the object or scene 31. In this way the light field components passing through the diffusion screen 5 recreate the light field of the object or scene 31.

The light source 6 within the projector 3 may be light emitting diodes (LEDs), lasers, halogen lamps, or other suitable light sources for generating light rays 9 suitable for projection. However, because the light rays 9 from the light source 6 are to be distributed over a large volume at a high sample rate to emulate an array of projectors, the brightness must be greater than that of a standard projector used in a conventional projection array light field display.

The light modulator 7 is a device capable of encoding light rays 9 coming from the light source 6 with information such that when the exiting light rays 9 are imaged using the focussing optics 8, an image is be formed on the diffusion screen 5. As the projector 3 is being used to generate an array 21 of virtual projectors 22 with each of the virtual projectors 22 producing a different image, the framerate of the light modulator 7 must be sufficient to generate multiple videos running at standard framerates. The light modulator 7 may use Ferroelectric Liquid Crystal on Silicon (FLCoS), Liquid Crystal on Silicon (LCoS), or Digital Micromirror Devices (DMD) spatial light modulation technologies as these provide the necessary framerates. However, the invention is not constrained to the use of FLCoS, LCoS, or DMDs in the light modulator 7.

The configuration of the focussing optics 8 determines the distance at which the image is formed and the angular spread of the rays on the diffusion screen 5. The focussing optics 8 may be fixed or dynamically variable. In embodiments having dynamically variable focussing optics 8, the focussing optics 8 may be controllable by the controller 2. In this embodiment, to take account of the differences in optical path between the projector 3 and the diffusion screen 5 for the different deflection angles of the angular modulator 4, the focussing optics 8 are controllable by the controller 2 and in a calibration procedure a setting for the focussing optics is determined for each deflection angle such as to focus each virtual projector 22 onto the diffusion screen. In operation, as the angular modulator 4 cycles through deflection angles, the controller 2 synchronously sends control signals to the focussing optics 8 so that, in effect, each virtual projector 22 is in turn focussed onto the diffusion screen 5. In other embodiments, for example embodiments utilising collimated optics or a laser projector, such dynamic control of the focussing optics 8 may not be necessary.

The angular modulator 4 may use reflective optical devices such as: galvanometer mirrors, resonant mirrors, polygonal mirrors, prisms, MEMS mirrors, spatial light modulators (SLMs), acousto-optical modulators or other optical devices suitable for the function described. In configurations where the angular modulator 4 is an optical device mounted on a rotating element, it must have a control subsystem with accurate positioning of the element, so as to achieve precise synchronisation with the projector 3. The angular modulator 4 may rotate in discrete steps or continuously, in a full circle or oscillating between two angular positions, where the angle between the two positions is associated with the field of view of the light field display 1. Careful consideration must be given to the choice of angular modulator 4 and different devices have different benefits. For example, a resonant scanning mirror would give higher speeds than a fast-scanning mirror such as a galvanometer mirror. However, the reduced design flexibility could cause issues such as flicker or give general incompatibility with the projector framerate. A rotating polygonal mirror could be used to provide a stable sawtooth deflection profile without the need for the rotating subsystem to move quickly back to the first virtual projector position between frames. It is important in all these possible implementations that the modulator 4 is large enough to accommodate the full projection beam over the full range of deflection angles.

As discussed above, to synchronise the time varying angular deflection and the changing image from the light modulator 7, the controller 2 is connected to both the angular modulator 4 and the projector 3. The controller 2 may take the 3D image data from an object or scene 31 and perform appropriate rendering computations for the light rays 9 as well as any necessary transformations or mapping onto the virtual projectors 22, or may receive 3D image data already processed into a plurality of light field components. The controller 2 causes the projector 3 to project the light rays 9 corresponding to a virtual projector in synchronisation with the angle of deflection associated with position of said virtual projector. All or part of the function of the controller 2 described here may be incorporated into the projector 3 or the angular modulator 4.

Before 3D image data is received by the image modulator 7 it may be corrected to account for image distortion and aberrations within the optical path for each virtual projector 22, and for keystone correction of distortion of the image that would be introduced by tilting of the angular modulator 4. It is useful for the controller 2 to perform these corrections as the necessary corrections depend on the arrangement of the angular modulator 4, the projector 3, and focussing optics 8 and these components may not be statically fixed.

The necessary framerate for emulating an array 21 of virtual projectors 22 with a single projector 3 is dependent on the number of virtual projectors 22 and the desired framerate from each virtual projector 22. For example, if the single projector 3 was to emulate an array 21 of thirty projectors 22 each to run at a standard framerate of twenty- five frames per second (fps), then the single projector needs to have a framerate of at least twenty- five multiplied by thirty, which is equal to 750fps. The angular modulator 4 must match the framerate of the single projector 3 because it must angularly deflect the light rays from the projector 3 at each of the angles corresponding to a single virtual projector 22 at a rate of 25 times per second. The numbers given here are an example and the invention is not constrained to this arrangement.

The array 21 must have at least two virtual projectors 22 in order to create a 3D image at the diffusion screen 5, and the framerates of each projector may be higher or lower than the framerate given. However, having only two virtual projectors would provide only a stereoscopic 3D effect. In embodiments where the angular modulator 4 is a moving mirror, to achieve one-degree change in deflection the mirror must rotate by half of a degree. An example of how this is used to create a virtual projector array 21 is that a rotation of ±7.5 degrees in 0.5-degree steps corresponds to an array of 30 virtual projectors placed in an arc of ±15 degrees at intervals of 1 degree.

In other embodiments, the projector 3 may form separate red, green and blue images using three separate light modulators, the images from all three light modulators being combined into a single beam via a combining element. Alternatively, the three separate light modulators may be implemented in three separate projectors, each projector having a light source for one of the red light, green light, or blue light. In such embodiments, the 3D image data is processed to generate separate red, green and blue light components.

The light field display 1 may incorporate optical elements in addition to the angular modulator 4 in the path of the light rays between the projector 3 and the diffusion screen 5. For example, the additional optical elements could fold the light path into a smaller volume or magnify of the projected image components. An example is shown in Figure 5 in which a projector 3 illuminates a reflective angular modulator 4 which deflects the light rays onto a large concave mirror 71 before they reach the diffusion screen 5. Folding the light path into a smaller volume can reduce the size of the projection array light field display 1. The magnification allows a larger diffusion screen 5 to be illuminated by a projector 3 normally used to project a smaller diffusion screen 5. The controller 2 or other suitable equipment may correct the image data to compensate for the distortion of the images introduced by the optical elements such as the concave mirror 71 for example, keystone correction may be applied to the image data.

In examples shown in Figure 1 and 2 the angular modulator 4 is a reflective element and the projector 3 is directed substantially away from the diffusion screen 5 and towards the angular modulator 4. However, the invention is not limited to this configuration. In other embodiments, such as in Figure 6, the angular modulator 81 may be a transmissive element capable of deflecting the light rays. Using technology such as prisms, SLMs, diffractive optical elements (DOEs), or HOEs. In embodiments where the angular modulator 81 is a transmissive angular modulator 81 the projector 3 may be positioned substantially behind the diffusion screen 5 from the perspective of a viewer and directed towards the diffusion screen 5. This may allow for simpler arrangements potentially requiring less complex optics and less intensive correction of the images by the controller 2. However, in arrangements where the projector 3 is directed towards the diffusion screen 5 the size of the system may increase as the optical path is not folded. The angular modulator 81 may be a transmissive optical element and reflective optical elements such as mirrors may be employed to fold the light path allowing the projector 3 to be directed away from the diffusion screen 5.

In embodiments having rotatable angular modulators 4 where the angle of deflection changes in a continuous manner, the angular modulator 4 will be moving while each frame of a projected image is deflected by the angular modulator. Accordingly, each frame will experience smearing of the image, where the amount of frame smearing is proportional to the speed of rotation of the angular modulator. Above a certain level the frame smearing becomes noticeable to a viewer and so it is important to configure the system such that the frame smearing is not perceptible to a viewer. Frame smearing may be reduced by decreasing the time over which each frame illuminates the angular modulator 4. This can be done by increasing the framerate of the projector 3 such that there is a smaller angular shift during each frame. Frame smearing can also be reduced by the inclusion of an optical chopper in the optical path or otherwise rapidly modulating the light source 6 such that each frame sees a smaller angular variation over its illumination time. A different solution is to have a second angular modulator in the optical path which is configured to compensate for the angular shift occurring during each frame. The second modulator must switch between angles at least as fast as the first angular modulator 4.

In some examples the angular modulation of the light rays 9 may be achieved by having a moveable projector 3. The projector 3 can be rotated or moved on a rail to change the angle at which the light rays 9 from the projector 3 are incident on the diffusion screen 5. Figure 7 shows an example of a projector 3 mounted to a mechanical assembly that moves the projector 3 along a rail to generate an array of virtual projectors. At each discrete position in its rotation or movement along the rail the projector 3 represents a virtual projector 22.

In some embodiments the angular modulator 4 is not a moveable optical element which varies the angular deflection with time but instead the angular modulator 4 may be a static HOE. In embodiments where the angular modulator 4 is a static HOE the time multiplexing may be provided by a coupled intensity modulator. Figure 8 shows a macropixel of an HOE 101 used as the angular modulator 4 having a sub-pixelated structure where a Y by Y array of subpixels 102 forms a macropixel 101. Each subpixel 102 in the Y by Y array of an HOE macropixel 101 is configured to deflect the incoming light at a different angle meaning that from the Y by Y array 101 there are Y x Y output angles. In Figure 8, the array is a 4x4 array but the subpixels 102 are not constrained to a 4x4 array. This variety in angular selection can be further enhanced by configuring the HOE 101 to be dependent on other orthogonal parameters such as incident angle or polarisation. The intensity modulator is configured into macropixels 103 having a sub- pixelated structure where the macropixel and sub-pixel size match the corresponding HOE used as the angular modulator 4. The intensity modulator is configured to transmit light from only one subpixel per macropixel at a time, this may be done by using a liquid crystal layer on the HOE to select a subpixel. The projected image pixels 104 are the size of the HOE macropixels 101. The angular modulator 101 and the intensity modulator 103 are formed of an array of macropixels but Figure 8 shows only one as an example. The projector 3 projects light rays 9 onto the intensity modulator 103 which only allows one subpixel per macropixel to transmit the light rays 9. The light rays 9 leaving the subpixels in the intensity modulator 103 illuminate respective subpixels 102 on the HOE 101 used as an angular modulator 4. Each illuminated subpixel 102 transmits the light rays 9 at the required angle such that when the light rays 9 are incident on the diffusion screen 5 they pass through the diffusion screen 5 with an associated position and angle corresponding to the light field of the 3D object or scene 31 which the light rays represent. The projector 3 having a similar framerate as the previous embodiments and the coupled intensity modulator 103 having substantially the same or a greater refresh rate as this framerate, allows the angular modulator 101 to emulate an array of angularly separated projectors. It may be possible to combine the function of the angular modulator and diffusion screen 5 into a single apparatus. Having a static HOE for the angular modulator in the projection array light field display 1 allows the system to be less mechanically complex because a precise rotating element and a control subsystem for controlling the rotating element is not needed.

In other embodiments a static HOE may be used as the angular modulator without the use of an intensity modulator; the static HOE having a sub-pixelated structure organised into arrays forming macropixels 101 as in previous embodiments. In an example, each projector pixel is subpixel sized and the projector pixels are each incident on one subpixel 102 of the HOE simultaneously. In this example, the virtual projectors 22 are spatially multiplexed as opposed to time multiplexed as in previous examples and so the projector 3 does not need to have a high frame-rate to emulate an array of projectors running sequentially but instead the projector 3 needs to have a high- resolution. Using a single projector 3 in this arrangement requires said projector 3 to have a resolution sufficient to generate the images of all the virtual projectors 22 in the array 21 simultaneously. However, a tiled array of multiple projectors may also be used, each projector having the resolution of one or more virtual projectors 22.

It will be appreciated that it is possible to combine both spatial and temporal multiplexing in the same display, having the benefit of decreasing the requirements for both schemes. In some embodiments the projector does not comprise focussing optics 8. The focussing optics 8 may be positioned elsewhere along the path of the light rays 9 between the light modulator 7 and the diffusion screen 5.

In some embodiments, the invention may relate to a full-parallax light field display. This may be done using an angular modulator 4 which is capable of varying the deflection angle in both the horizontal and vertical direction. To maintain the same angular resolution and framerate of the viewable image the framerate of the light modulator 7 and the rate at which the angular modulator 4 changes the angle of deflection must be higher than in a horizontal only parallax system. Alternatively, more projectors 3 may be used and these may illuminate multiple or a single angular modulator 4. An angular modulator 4 which is illuminated by two projectors 3 must change deflection angle at a rate greater than the framerate of any one of the two projectors. Introducing vertical parallax in this way increases the number of virtual projectors 22 which must be generated to maintain the same image quality. Using more than one projector 3 allows the system to use projectors which are cheaper and also may increase the field of view at the expense of size and power consumption.

In other embodiments, vertical parallax may be emulated by having one or more tracking cameras 111 which are capable of tracking one or more user’s eyes or head 112. The inclusion of tracking cameras 111 is shown in Figure 9. The information generated by the tracking cameras 111 is used to calculate a desired rotation of the projected image based on the height of the users. This enables the light field display 1 to be a quasi-full parallax projection array light field display.

In some embodiments, the addition of one or more tracking cameras 111 for tracking one or more viewer’s eyes or heads 112 may be used to optimise the operation of the light field display 1. Knowing the position of a viewer’s eyes or head 112 allows the light field display 1 to only project the light field which the viewer is capable of seeing. Reducing the light field’s size allows the display 1 to save power by not projecting unseen light rays. The resources in the light field display 1 may be reallocated to improve the quality of the image seen by the viewer, for example the light field display 1 may be able to increase angular resolution by using more projectors 3 to display a given section of the image than would otherwise be used. Multiple modifications used in known light field displays can be made to the above embodiments. For example, mirrors can be included at the periphery of the diffusion screen 5 to reflect the light rays 9 from the virtual projectors 22 positioned at the outer section of the array 21 onto the diffusion screen 5. The projection array light field display 1 can be used for rear or front projection; in front projection systems the HOE diffusion screen 5 has reflective rather than transmissive properties such that a viewer is positioned facing the same direction as the projector 3, towards the diffusion screen 5.

Any of the discussed embodiments can use a plurality of projectors 3 and angular modulators 4 which may be advantageous where a larger display is desired. An angular modulator 4 can be used to deflect the light rays 9 from multiple projectors 3. Projectors 3 and angular modulators 4 can be configured to illuminate sections of the diffusion screen 5 and these sections may be disjointed or overlapping. Multiple diffusion screens 5 can be joined together to form a larger display.

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.