GB2641391A

GB2641391A - Hologram interlacing with pixel binning

Info

Publication number: GB2641391A
Application number: GB2407680.4A
Authority: GB
Inventors: Lin Ruisheng; Smeeton Timothy
Original assignee: Envisics Ltd
Current assignee: Envisics Ltd
Priority date: 2024-05-30
Filing date: 2024-05-30
Publication date: 2025-12-03
Also published as: WO2025247889A1; GB202407680D0

Abstract

Determining, or illuminating, a hologram (first) hologram (450, 650), comprising: first (412, 612) and second (414, 614) sub-holograms of a first (402, 602) and second (404, 604) picture content (of a first picture (400)), respectively, wherein the first and second sub-holograms comprise a plurality of first (412 & 612: 1 – 16) and second (414 & 614: 1 – 16) sub-hologram pixels, respectively, wherein the (first) hologram (450, 650) is formed by spatially interlacing first and second sub-holograms, such that each (first) hologram pixel (452, 652) comprises and first (412 & 612: 1 – 16) and second (414 & 614: 1 – 16) sub-hologram pixel. Determining a second hologram (650), comprising: third (616) and fourth (618) sub-holograms of a third (606) and fourth (608) picture content (of a second picture), respectively, wherein the third and fourth sub-holograms comprise a plurality of third (616: 1 – 16) and fourth (618: 1 – 16) sub-hologram pixels, respectively, wherein the second hologram (650) is formed by spatially interlacing third and fourth sub-holograms, such that each second hologram pixel (652) comprises and third (616: 1 – 16) and fourth (618: 1 – 16) sub-hologram pixel. Re-directing first and second sub-holographic wavefronts in two different directions.

Description

HOLOGRAM INTERLACING WITH PIXEL BINNING

FIELD

The present disclosure relates to a method of holographic projection of a picture and a holographic projector arranged to display a picture. More particularly, the present disclosure relates to a method of spatially interlacing multiple holograms for display on a display device, wherein each hologram corresponds to respective picture content of the picture.

BACKGROUND AND INTRODUCTION

Light scattered from an object contains both amplitude and phase information. This amplitude and phase information can be captured on, for example, a photosensitive plate by well-known interference techniques to form a holographic recording, or "hologram", comprising interference fringes. The hologram may be reconstructed by illumination with suitable light to form a two-dimensional or three-dimensional holographic reconstruction, or replay image, representative of the original object.

Computer-generated holography may numerically simulate the interference process. A computer-generated hologram may be calculated by a technique based on a mathematical transformation such as a Fresnel or Fourier transform. These types of holograms may be referred to as Fresnel/Fourier transform holograms or simply Fresnel/Fourier holograms. A Fourier hologram may be considered a Fourier domain/plane representation of the object or a frequency domain/plane representation of the object. A computer-generated hologram may also be calculated by coherent ray tracing or a point cloud technique, for example.

A computer-generated hologram may be encoded on a spatial light modulator arranged to modulate the amplitude and/or phase of incident light. Light modulation may be achieved using electrically-addressable liquid crystals, optically-addressable liquid crystals or micro-mirrors, for example.

A spatial light modulator typically comprises a plurality of individually-addressable pixels which may also be referred to as cells or elements. The light modulation scheme may be binary, multilevel or continuous. Alternatively, the device may be continuous (i.e. is not comprised of pixels) and light modulation may therefore be continuous across the device.

The spatial light modulator may be reflective meaning that modulated light is output in reflection. The spatial light modulator may equally be transmissive meaning that modulated light is output in transmission.

A holographic projector may be provided using the system described herein. Such projectors have found application in head-up displays, "HUD".

SUMMARY

Aspects of the present disclosure are defined in the appended independent claims.

There is disclosed herein a method of determining a hologram of a picture for display. The picture comprises first picture content and second picture content. The second picture content is at least partially spatially separate from the first picture content. It may be said that the first picture content comprises a first picture area of the picture and the second picture content comprises a second picture area of the picture, wherein the second picture area is at least partially spatially separate from the first picture area. The first and second picture content may be formed by dividing the picture into first and second picture areas. The method comprises determining a first sub-hologram of the first picture content and determining a second sub-hologram of the second picture content. The first sub-hologram comprises a plurality of first sub-hologram pixels having respective first sub-hologram pixel values and the second sub-hologram comprises a plurality of second sub-hologram pixels having respective second sub-hologram pixel values. The number of the plurality of first sub-hologram pixels may be substantially equal to the number of the plurality of second sub-hologram pixels. The method further comprises determining a hologram of the picture for display by spatially interlacing the first and second sub-holograms. The hologram comprises a plurality of hologram pixels. Each hologram pixel comprises first and second sub-pixels. The first and second sub-pixels of each hologram pixel are contiguous (e.g., arranged in an array). A first sub-pixel of a hologram pixel corresponds to one of the plurality of first sub-hologram pixels of the first sub-hologram, and a second sub-pixel of the hologram pixel corresponds to a corresponding or equivalent one of the plurality of second sub-hologram pixels of the second sub-hologram. It may be said that each of the first and second sub-holograms contributes a sub-pixel (or pixel value) to each of the hologram pixels of the hologram.

The total number of hologram pixels is less that the sum of the number of first and second sub-hologram pixels. Thus, the hologram for display may be considered to have a reduced effective resolution (i.e., reduced number of hologram pixels). However, the hologram comprises all of the pixels (or pixel values) of the interlaced first and second sub-holograms. Thus, there is no loss in picture content. The inventors have found that, since there is no loss of picture content in the hologram for display, there is no reduction in picture quality despite the reduced effective resolution of the hologram.

The size of each hologram pixel is greater that the size of each of first and/or second sub-hologram pixels. This is because each hologram pixel comprises a plurality of sub-pixels, wherein each sub-pixel has a pixel value corresponding to an equivalent one of the plurality of first and second sub-hologram pixels of the respective first and second sub-holograms. The diffraction angle, which determines the field of view (the angular extent or the size of the holographic reconstruction / holographic replay field at a viewing window of a holographic projector), is dependent on the effective size of the pixels of a hologram. In particular, the diffraction angle is inversely proportional to the size of the pixels. Since, the size of the hologram pixels of the interlaced first and second sub-holograms is increased relative to the size of the sub-hologram pixels of the individual first and second sub-holograms in at least one dimension, the diffraction angle, and thus the size of the field of view (or holographic replay field), is reduced in the at least one dimension. It may be said that the field of view is compressed in at least one dimension.

A display device, such as spatial light modulator, comprises a finite number of active light modulating pixels. Since each light modulating pixel can only be encoded with one hologram pixel value at a time, the number of pixels/sub-pixels of a hologram for a display is limited to the number of active light modulating pixels. Accordingly, when seeking to display a plurality of sub-holograms of respective picture content on a display device at the same time, there is a limitation on the size of the sub-holograms (i.e., number of sub-hologram pixels, which may correspond to hologram resolution) and/or how they are combined or interlaced for display on the available light modulating pixels of the display device.

The inventors have found that calculating smaller sub-holograms of respective picture content of a target picture so that the combined number of pixels of the sub-holograms is less than or equal to the number of light modulating pixels of the display device, and spatially interlacing the sub-holograms at sub-pixel level to form larger hologram pixels for display, results in greater picture quality (i.e. quality of the holographic reconstruction of the target picture) than calculating larger sub-holograms, and spatially interlacing the sub-holograms at a high sampling rate (i.e., at 1 or more pixels) so that the hologram pixel size remains the same. In particular, calculating larger sub-holograms of respective picture content, and spatially interlacing the sub-holograms by sampling the pixels (in one or two dimensions) for display, so that the total number of pixels of the hologram is the less than or equal to the number of light modulating pixels of the display device, is found to lead to the replication of the picture content in the holographic reconstruction, which may appear as ghost images and replication of the so-called DC spot at the DC order formed by unmodulated light.

However, the inventors found that calculating smaller, reduced resolution sub-holograms of respective picture content, and spatially interlacing the sub-holograms for display as described herein (i.e., without loss of picture content through sampling) resulted in good image quality despite the reduced size (or resolution) of the sub-holograms.

The first picture area of the first picture content and the second picture area of the second picture content may be substantially the same. It may be said that the first picture content is the same size as the second picture content. Accordingly, the number of first sub-hologram pixels is substantially equal to the number of second sub-hologram pixels. Thus, when the hologram pixels consist of first and second sub-pixels having respective first and second sub-hologram pixel values, the number of hologram pixels is half the number of first/second sub-hologram pixels and the hologram pixel size is twice the size of the pixels of the first/second sub-holograms. In consequence, the two sub-holograms may be displayed on a display device for reconstruction of the target picture. As noted above, the inventors have found that the display of spatially interlaced sub-holograms in accordance with the present disclosure does not lead to a loss of picture quality.

In some embodiments, each pixel of the hologram comprises a one-dimensional (e.g., 2x1) array of sub-pixels extending in a first direction such that a holographic reconstruction (or field of view) of each picture area (or replay field) of the first or second picture content (or holographic replay field) is reduced in one dimension, which may lead to a rectangular aspect ratio (e.g., 2:1).

Thus, pairs of adjacent sub-pixels corresponding to the first sub-hologram are spatially separated by a sub-pixel corresponding to the second sub-hologram in the first direction.

Similarly, pairs of adjacent sub-pixels corresponding to the second sub-hologram are spatially separated by a sub-pixel corresponding to the first sub-hologram in the first direction. It may be said that the spatial frequencies of the first and second sub-holograms are increased in the first direction. However, pairs of adjacent sub-pixels corresponding to the first and second sub-holograms are contiguous with each other in a second direction, orthogonal to the first direction. In consequence, the size of the field of view (or holographic replay field) of the reconstruction of each of the first and second sub-holograms is reduced in the first direction but remains the same in the second direction. In addition, due to the reduction in the size of the field of view in the first direction (but not in the second direction) the aspect ratio is changed.

In an implementation, the method further comprises calculating a third sub-hologram of third picture content of the target picture and a fourth sub-hologram of second picture content of the target picture. The third and fourth picture content may be at least partially spatially separate from each other and/or from the first and second picture content. The third sub-hologram comprises a plurality of third sub-hologram pixels and the fourth hologram comprises a plurality of fourth sub-hologram pixels. The method further comprises forming the hologram of the target picture by spatially interlacing the first, second, third and fourth sub-holograms. Each of the plurality of hologram pixels comprising first, second, third and fourth sub-pixels corresponding to (or having pixel values corresponding to) respective equivalent first, second, third and fourth sub-hologram pixels.

In examples of this implementation, each pixel of the hologram comprises a two-dimensional (e.g., 2x2 or 2x3) array of sub-pixels such that a field of view of each of the first, second, third and fourth picture content is reduced in two dimensions, which may lead to a square aspect ratio or a rectangular aspect ratio.

Thus, pairs of adjacent sub-pixels of the first sub-hologram are spatially separated by a sub-pixel in the first and second directions. It may be said that the spatial frequencies of the first and second sub-holograms are increased in the first and second directions. In consequence, the size of the field of view (or holographic replay field) of each of the first and second picture content is reduced in the first and second directions.. However, when the number of rows and columns of the array of sub-pixels are the same (e.g., 2x2 array), the aspect ratio may remain the same.

There is disclosed herein a method of holographic projection. The method comprises the above method of determining a hologram of a target picture for display. The method further comprises displaying the hologram on a display device and illuminating the display device so as to form a holographic wavefront. The holographic wavefront comprises a first portion comprising the first picture content and a second portion comprising the second picture content. The method comprises steering the first portion of the holographic wavefront in a first direction and steering the second portion of the holographic wavefront in a second direction. Accordingly, the first picture content is formed at a different position from the second picture content in the holographic reconstruction of the target picture.

A first aspect of the present disclosure is a holographic projection system or holographic projector arranged to display a target picture. The holographic projection system or holographic projector comprises a hologram engine (e.g., hologram processor or subsystem) and a holographic wavefront redirector positioned adjacent the hologram, or an optically relayed copy of the hologram. The hologram engine is arranged to receive or calculate a first sub-hologram of first picture content of the target picture (e.g. the left half of the target picture) and a second sub-hologram of second picture content of the target picture (e.g. the right half of the target picture). The first picture content is at least partially spatially separate from the second picture content. The first sub-hologram comprises a plurality of first sub-hologram pixels and the second hologram comprises a plurality of second sub-hologram pixels. The hologram engine is arranged to form a (composite or combined) hologram of the (entire) target picture by spatially interlacing (or, simply, "combining") the first and second sub-holograms e.g. for display at the same time. In some respects, it may be said that the present disclosure relates to a method of displaying two holograms on a common display device at the same time. The (composite or combined) hologram comprises a plurality of hologram pixels. Each hologram pixel comprises first and second sub-pixels corresponding to respective equivalent first and second sub-hologram pixels of the first and second sub-holograms. Alternatively, it may simply be said that each pixel of (composite or combined) hologram comprises a first sub-hologram pixel of the first sub-hologram and the equivalent or corresponding (e.g. the pixel in the same row-column position) second sub-hologram pixel of the second sub-hologram. The holographic wavefront redirector is arranged to steer light of the first sub-hologram in a first direction. The light of the first sub-hologram is light received from or encoded with the first sub-hologram. It may be said that the light of the first sub-hologram comprises a first portion of the holographic wavefront formed by the hologram corresponding to the first sub-hologram, and thus comprising the first picture content. The holographic wavefront redirector is arranged to steer light of the second sub-hologram in a second direction. The light of the second sub-hologram is light received from or encoded with the second sub-hologram. It may be said that the light of the second sub-hologram comprises a second portion of the holographic wavefront formed by the hologram corresponding to the second sub-hologram, and thus comprising the second picture content. The second direction is different from the first direction.

There is disclosed herein a method of displaying a first hologram and a second hologram on a (common) display device at the same time, wherein the first hologram corresponds to one region of the field of view and the second hologram corresponds to a second region of the field of view. For example, the first region may be a left half of the field of view and the second region may be the right half of the field of view but the present disclosure is applicable to any two different parts of the field of view preferably adjoining but non-overlapping regions. The method comprises forming the combined hologram by adjoining the corresponding pixels of the first and second hologram into pairs. It may be said that each "pixel" of the combined hologram actually comprises two pixel values -a pixel value of the first hologram and the corresponding pixel value of the second hologram. The two pixel values are effectively "adjoined" meaning they are displayed next to each other on the display device. For example, the two pixel values may be adjoined in the x direction or the y direction, where x and y are the dimensions of the display device used to display the combined hologram. All pairs of corresponding pixel values are adjoined in the same way e.g. direction. The first hologram and second hologram may be the same size (number of pixels) and aspect ratio. The combined hologram may therefore comprise twice as many pixels as the first hologram (or second hologram). The process of combining two hologram by adjoining corresponding pixel values (of the first and second hologram) may be referred to as "pixel binning" (but not to be confused with other typers of pixel binning known in the art) or, simply "pixel grouping".

By virtue of the formation of hologram pixels comprising first and second sub-pixels corresponding to first and second sub-hologram pixels, the size of the reconstructed first and second picture content is reduced. However, as described herein, the inventors have found that there is no detrimental effect on picture quality.

Furthermore, since the first and second directions are different, the first picture content is formed at different position/region of the field of view from the second picture content.

In embodiments, the display device comprises spatial light modulator arranged to display the hologram of a target picture and form a holographic reconstruction of the target picture on a replay plane spatially separated from the spatial light modulator.

In some embodiments, the holographic projector comprises a pixelated display device. For example, the display device may be a pixelated spatial light modulator arranged to display the hologram. Each sub-pixel of the hologram is displayed on a respective pixel of the display device.

In some examples, the holographic wavefront redirector is arranged to steer light of the first and second sub-holograms so that the first picture content is displayed adjacent to, such as contiguous with or partially overlapping, the second picture content. In other examples, the holographic wavefront redirector is arranged to steer light of the first and second sub-holograms so that the first picture content is displayed spatially separated from the second picture content.

In an embodiment, the spatial interlacing comprises changing an (effective) aspect ratio of the first sub-hologram and/or second sub-hologram -when/as displayed. In other words, in an embodiment, the spatial interlacing and displaying comprise changing an (effective) aspect ratio of the first sub-hologram and/or second sub-hologram.

In an embodiment, the spatial interlacing comprises changing the pixel pitch of the first and/or second hologram is one dimension but not the other -when/as displayed. In other words, in an embodiment, the spatial interlacing and displaying comprise changing the pixel pitch of the first and/or second hologram is one dimension but not the other.

In an embodiment, the spatial interlacing comprises interposing second sub-hologram pixels of the second sub-hologram between first sub-hologram pixels of the first sub-hologram in one pixel direction of the spatial light modulator but not the other pixel direction of the spatial light modulator, or vice versa -when/as displayed. In other words, in an embodiment, the spatial interlacing and displaying comprise interposing second sub-hologram pixels of the second sub-hologram between first sub-hologram pixels of the first sub-hologram in one pixel direction of the spatial light modulator but not the other pixel direction of the spatial light modulator, or vice versa.

In an embodiment, the spatial interlacing comprises interposing second sub-hologram pixels of the second sub-hologram between first sub-hologram pixels of the first sub-hologram in both pixel directions of the spatial light modulator, or vice versa -when/as displayed. In other words, in an embodiment, the spatial interlacing and displaying comprise interposing second sub-hologram pixels of the second sub-hologram between first sub-hologram pixels of the first sub-hologram in both pixel directions of the spatial light modulator, or vice versa.

In an embodiment, the spatial interlacing comprises increasing the pixel pitch of the first sub-hologram or second sub-hologram in one or both pixel directions -when/as displayed. In other words, the spatial interlacing and displaying comprise increasing the pixel pitch of the first sub-hologram or second sub-hologram in one or both pixel directions.

In an embodiment, the spatial interlacing is such that a pixel pitch of the first/second sub-hologram pixels of the first/second sub-hologram in a first direction is different to a pixel pitch of the first/second sub-hologram pixels of the first/second sub-hologram in a second direction -when/as displayed. In other words, in an embodiment, the spatial interlacing and displaying are such that a pixel pitch of the first/second sub-hologram pixels of the first/second sub-hologram in a first direction is different to a pixel pitch of the first/second sub-hologram pixels of the first/second sub-hologram in a second direction In an embodiment, the spatial interlacing is such that an aspect ratio of the first/second sub-hologram before spatial interlacing is different to an aspect ratio of a holographic reconstruction of the first/second picture content formed by the hologram -when/ as displayed. In other words, the spatial interlacing and displaying are such that an aspect ratio of the first/second sub-hologram before spatial interlacing is different to an aspect ratio of a holographic reconstruction of the first/second picture content formed by the hologram In an embodiment, the spatial interlacing reduces a size of the replay field / field of view of the holographic reconstruction of the first picture content and/or second picture content in at least one direction -when displayed and illuminated. In other words, in an embodiment, the spatial interlacing and displaying reduce a size of the replay field / field of view of the holographic reconstruction of the first picture content and/or second picture content in at least one direction.

In some embodiments, at least one wavefront replicator is used. In these embodiments, the term "replica" may be used to reflect that spatially modulated light is divided such that a complex light field is directed along a plurality of different optical paths. The word "replica" is used to refer to each occurrence or instance of the complex light field after a replication event -such as a partial reflection-transmission by a pupil expander. Each replica travels along a different optical path. Some embodiments of the present disclosure relate to propagation of light that is encoded with a hologram, not an image -i.e., light that is spatially modulated with a hologram of an image, not the image itself It may therefore be said that a plurality of replicas of the hologram are formed. The person skilled in the art of holography will appreciate that the complex light field associated with propagation of light encoded with a hologram will change with propagation distance. Use herein of the term "replica" is independent of propagation distance and so the two branches or paths of light associated with a replication event are still referred to as "replicas" of each other even if the branches are a different length, such that the complex light field has evolved differently along each path. That is, two complex light fields are still considered "replicas" in accordance with this disclosure even if they are associated with different propagation distances -providing they have arisen from the same replication event or series of replication events.

A "diffracted light field" or "diffractive light field" in accordance with this disclosure is a light field formed by diffraction. A diffracted light field may be formed by illuminating a corresponding diffractive pattern. In accordance with this disclosure, an example of a diffractive pattern is a hologram and an example of a diffracted light field is a holographic light field or a light field forming a holographic reconstruction of an image. The holographic light field forms a (holographic) reconstruction of an image on a replay plane. The holographic light field that propagates from the hologram to the replay plane may be said to comprise light encoded with the hologram or light in the hologram domain. A diffracted light field is characterized by a diffraction angle determined by the smallest feature size of the diffractive structure and the wavelength of the light (of the diffracted light field). In accordance with this disclosure, it may also be said that a "diffracted light field" is a light field that forms a reconstruction on a plane spatially separated from the corresponding diffractive structure. An optical system is disclosed herein for propagating a diffracted light field from a diffractive structure to a viewer. The diffracted light field may form an image.

The term "hologram" is used to refer to the recording which contains amplitude information or phase information, or some combination thereof, regarding the object. The term "holographic reconstruction" is used to refer to the optical reconstruction of the object which is formed by illuminating the hologram. The system disclosed herein is described as a "holographic projector" because the holographic reconstruction is a real image and spatially-separated from the hologram. The term "replay field" is used to refer to the 2D area within which the holographic reconstruction is formed and fully focused. If the hologram is displayed on a spatial light modulator comprising pixels, the replay field will be repeated in the form of a plurality diffracted orders wherein each diffracted order is a replica of the zeroth-order replay field. The zeroth-order replay field generally corresponds to the preferred or primary replay field because it is the brightest replay field. Unless explicitly stated otherwise, the term "replay field" should be taken as referring to the zeroth-order replay field. The term "replay plane" is used to refer to the plane in space containing all the replay fields. The terms "image", "replay image" and "image region" refer to areas of the replay field illuminated by light of the holographic reconstruction. In some embodiments, the "image" may comprise discrete spots which may be referred to as "image spots" or, for convenience only, "image pixels".

The terms "encoding", "writing" or "addressing" are used to describe the process of providing the plurality of pixels of the SLM with a respective plurality of control values which respectively determine the modulation level of each pixel. It may be said that the pixels of the SLM are configured to "display" a light modulation distribution in response to receiving the plurality of control values. Thus, the SLM may be said to "display" a hologram and the hologram may be considered an array of light modulation values or levels.

It has been found that a holographic reconstruction of acceptable quality can be formed from a "hologram" containing only phase information related to the Fourier transform of the original object. Such a holographic recording may be referred to as a phase-only hologram. Embodiments relate to a phase-only hologram but the present disclosure is equally applicable to amplitude-only holography.

The present disclosure is also equally applicable to forming a holographic reconstruction using amplitude and phase information related to the Fourier transform of the original object. In some embodiments, this is achieved by complex modulation using a so-called fully complex hologram which contains both amplitude and phase information related to the original object. Such a hologram may be referred to as a fully-complex hologram because the value (grey level) assigned to each pixel of the hologram has an amplitude and phase component. The value (grey level) assigned to each pixel may be represented as a complex number having both amplitude and phase components. In some embodiments, a fully-complex computer-generated hologram is calculated.

Reference may be made to the phase value, phase component, phase information or, simply, phase of pixels of the computer-generated hologram or the spatial light modulator as shorthand for "phase-delay". That is, any phase value described is, in fact, a number (e.g. in the range 0 to 27) which represents the amount of phase retardation provided by that pixel. For example, a pixel of the spatial light modulator described as having a phase value of 7c/2 will retard the phase of received light by 71/2 radians. In some embodiments, each pixel of the spatial light modulator is operable in one of a plurality of possible modulation values (e.g. phase delay values). The term "grey level" may be used to refer to the plurality of available modulation levels. For example, the term "grey level" may be used for convenience to refer to the plurality of available phase levels in a phase-only modulator even though different phase levels do not provide different shades of grey. The term "grey level" may also be used for convenience to refer to the plurality of available complex modulation levels in a complex modulator.

The hologram therefore comprises an array of grey levels -that is, an array of light modulation values such as an array of phase-delay values or complex modulation values.

The hologram is also considered a diffractive pattern because it is a pattern that causes diffraction when displayed on a spatial light modulator and illuminated with light having a wavelength comparable to, generally less than, the pixel pitch of the spatial light modulator. Reference is made herein to combining the hologram with other diffractive patterns such as diffractive patterns functioning as a lens or grating. For example, a diffractive pattern functioning as a grating may be combined with a hologram to translate the replay field on the replay plane or a diffractive pattern functioning as a lens may be combined with a hologram to focus the holographic reconstruction on a replay plane in the near field.

The term "field of view" refers to the angular extent of the holographic reconstruction that is viewable at a viewing window of a holographic projection system. The field of view is generally determined by the range of angles (e.g. horizontal and vertical angles) over which a viewer can see the full holographic reconstruction. The field of view is usually limited by the diffraction angle of the display device. However, in accordance with the present disclosure, the field of view may be increased in one dimension (e.g. the angular extent of the holographic reconstruction in the horizontal dimension may be increased to provide a "widescreen" aspect ratio), but without increasing the total area of the holographic reconstruction (e.g. the angular extent of the holographic reconstruction in the vertical dimension may be correspondingly reduced).

Although different embodiments and groups of embodiments may be disclosed separately in the detailed description which follows, any feature of any embodiment or group of embodiments may be combined with any other feature or combination of features of any embodiment or group of embodiments. That is, all possible combinations and permutations of features disclosed in the present disclosure are envisaged.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments are described by way of example only with reference to the following figures: Figure 1 is a schematic showing a reflective SLM producing a holographic reconstruction on a screen; Figure 2A shows a schematic view of an example pixellated display device of a holographic projection system; Figure 2B shows the maximum diffraction angle of the pixellated display device of Figure 2A; Figure 3 shows a schematic cross-sectional view of a portion of an example holographic projection system; Figure 4 illustrates a method of forming a hologram for display of a target picture comprising first and second pictures in accordance with an embodiment of the present disclosure; Figure 5A shows the shape of the replay field of the holographic reconstructions of the first and second pictures formed by the hologram of Figure 4; Figure 5B shows an example of how a field of view of the target picture may be shaped from the holographic reconstructions of the first and second pictures of Figure 5A; Figure 6 illustrates a method of forming a hologram for display of a target picture comprising first, second, third and fourth pictures in accordance with another embodiment of the present disclosure; Figure 7 shows the shape of the replay field of the holographic reconstructions of the first, second third and fourth pictures formed by the hologram of Figure 6; Figure 8A-E shows various examples of how the field of view of the target picture may be shaped from the holographic reconstructions of the first, second, third and fourth pictures of Figure 7, and Figure 9 shows an example target picture comprising first, second, third and fourth pictures and a holographic reconstruction of a hologram of the target picture formed using the method of Figure 6.

The same reference numbers will be used throughout the drawings to refer to the same or like parts.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention is not restricted to the embodiments described in the following but extends to the full scope of the appended claims. That is, the present invention may be embodied in different forms and should not be construed as limited to the described embodiments, which are set out for the purpose of illustration.

Terms of a singular form may include plural forms unless specified otherwise.

A structure described as being formed at an upper portion/lower portion of another structure or on/under the other structure should be construed as including a case where the structures contact each other and, moreover, a case where a third structure is disposed there between.

In describing a time relationship -for example, when the temporal order of events is described as "after", "subsequent", "next", "before" or suchlike-the present disclosure should be taken to include continuous and non-continuous events unless otherwise specified. For example, the description should be taken to include a case which is not continuous unless wording such as "just", "immediate" or "direct" is used.

Although the terms "first", "second", etc. may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the appended claims.

Features of different embodiments may be partially or overall coupled to or combined with each other, and may be variously inter-operated with each other. Some embodiments may be carried out independently from each other, or may be carried out together in codependent relationship.

In the present disclosure, the term "substantially" when applied to a structural units of an apparatus may be interpreted as the technical feature of the structural units being produced within the technical tolerance of the method used to manufacture it.

Conventional optical configuration for holographic projection Figure 1 shows an embodiment in which a computer-generated hologram is encoded on a single spatial light modulator. The computer-generated hologram is a Fourier transform of the object for reconstruction. It may therefore be said that the hologram is a Fourier domain or frequency domain or spectral domain representation of the object. In this embodiment, the spatial light modulator is a reflective liquid crystal on silicon, "LCOS", device. The hologram is encoded on the spatial light modulator and a holographic reconstruction is formed at a replay field, for example, a light receiving surface such as a screen or diffuser.

A light source 110, for example a laser or laser diode, is disposed to illuminate the SLM 140 via a collimating lens 111. The collimating lens causes a generally planar wavefront of light to be incident on the SLM. In Figure 1, the direction of the wavefront is off-normal (e.g. two or three degrees away from being truly orthogonal to the plane of the transparent layer). However, in other embodiments, the generally planar wavefront is provided at normal incidence and a beam splitter arrangement is used to separate the input and output optical paths. In the embodiment shown in Figure 1, the arrangement is such that light from the light source is reflected off a mirrored rear surface of the SLM and interacts with a light-modulating layer to form an exit wavefront 112. The exit wavefront 112 is applied to optics including a Fourier transform lens 120, having its focus at a screen 125. More specifically, the Fourier transform lens 120 receives a beam of modulated light from the SLM 140 and performs a frequency-space transformation to produce a holographic reconstruction at the screen 125.

Notably, in this type of holography, each pixel of the hologram contributes to the whole reconstruction. There is not a one-to-one correlation between specific points (or image pixels) on the replay field and specific light-modulating elements (or hologram pixels). In other words, modulated light exiting the light-modulating layer is distributed across the replay

field.

In these embodiments, the position of the holographic reconstruction in space is determined by the dioptric (focusing) power of the Fourier transform lens. In the embodiment shown in Figure 1, the Fourier transform lens is a physical lens. That is, the Fourier transform lens is an optical Fourier transform lens and the Fourier transform is performed optically. Any lens can act as a Fourier transform lens but the performance of the lens will limit the accuracy of the Fourier transform it performs. The skilled person understands how to use a lens to perform an optical Fourier transform In some embodiments of the present disclosure, the lens of the viewer's eye performs the hologram to image transformation.

Hologram calculation In some embodiments, the computer-generated hologram is a Fourier transform hologram, or simply a Fourier hologram or Fourier-based hologram, in which an image is reconstructed in the far field by utilising the Fourier transforming properties of a positive lens. The Fourier hologram is calculated by Fourier transforming the desired light field in the replay plane back to the lens plane. Computer-generated Fourier holograms may be calculated using Fourier transforms. Embodiments relate to Fourier holography and Gerchberg-Saxton type algorithms by way of example only. The present disclosure is equally applicable to Fresnel holography and Fresnel holograms which may be calculated by a similar method. In some embodiments, the hologram is a phase or phase-only hologram. However, the present disclosure is also applicable to holograms calculated by other techniques such as those based on point cloud methods.

In some embodiments, the hologram engine is arranged to exclude from the hologram calculation the contribution of light blocked by a limiting aperture of the display system.

British patent application 2101666.2, filed 5 February 2021 and incorporated herein by reference, discloses a first hologram calculation method in which eye-tracking and ray tracing are used to identify a sub-area of the display device for calculation of a point cloud hologram which eliminates ghost images. The sub-area of the display device corresponds with the aperture, of the present disclosure, and is used exclude light paths from the hologram calculation. British patent application 2112213.0, filed 26 August 2021 and incorporated herein by reference, discloses a second method based on a modified Gerchberg-Saxton type algorithm which includes steps of light field cropping in accordance with pupils of the optical system during hologram calculation. The cropping of the light field corresponds with the determination of a limiting aperture of the present disclosure. British patent application 2118911.3, filed 23 December 2021 and also incorporated herein by reference, discloses a third method of calculating a hologram which includes a step of determining a region of a so-called extended modulator formed by a hologram replicator. The region of the extended modulator is also an aperture in accordance with this disclosure.

In some embodiments, there is provided a real-time engine arranged to receive image data and calculate holograms in real-time using the algorithm. In some embodiments, the image data is a video comprising a sequence of image frames. In other embodiments, the holograms are pre-calculated, stored in computer memory and recalled as needed for display on a SLM. That is, in some embodiments, there is provided a repository of predetermined holograms.

Large field of view using small display device

Broadly, the present disclosure relates to image projection. It relates to a method of image projection and an image projector which comprises a display device. The present disclosure also relates to a projection system comprising the image projector and a viewing system, in which the image projector projects or relays light from the display device to the viewing system. The present disclosure is equally applicable to a monocular and binocular viewing system. The viewing system may comprise a viewer's eye or eyes. The viewing system comprises an optical element having optical power (e.g., lens/es of the human eye) and a viewing plane (e.g., retina of the human eye/s). The projector may be referred to as a 'light engine'. The display device and the image formed (or perceived) using the display device are spatially separated from one another. The image is formed, or perceived by a viewer, on a display plane. In some embodiments, the image is a virtual image and the display plane may be referred to as a virtual image plane. In other examples, the image is a real image formed by holographic reconstruction and the image is projected or relayed to the viewing plane. In these other examples, spatially modulated light of an intermediate holographic reconstruction formed either in free space or on a screen or other light receiving surface between the display device and the viewer, is propagated to the viewer. In both cases, an image is formed by illuminating a diffractive pattern (e.g., hologram or kinoform) displayed on the display device.

The display device comprises pixels. The pixels of the display may display a diffractive pattern or structure that diffracts light. The diffracted light may form an image at a plane spatially separated from the display device. In accordance with well-understood optics, the magnitude of the maximum diffraction angle is determined by the size of the pixels and other factors such as the wavelength of the light.

In embodiments, the display device is a spatial light modulator such as liquid crystal on silicon ("LCOS") spatial light modulator (SLM). Light propagates over a range of diffraction angles (for example, from zero to the maximum diffractive angle) from the LCOS, towards a viewing entity/system such as a camera or an eye. In some embodiments, magnification techniques may be used to increase the range of available diffraction angles beyond the conventional maximum diffraction angle of an LCOS.

In some embodiments, the (light of a) hologram itself is propagated to the eyes. For example, spatially modulated light of the hologram (that has not yet been fully transformed to a holographic reconstruction, i.e. image) -that may be informally said to be "encoded" with/by the hologram -is propagated directly to the viewer's eyes. A real or virtual image may be perceived by the viewer. In these embodiments, there is no intermediate holographic reconstruction / image formed between the display device and the viewer. It is sometimes said that, in these embodiments, the lens of the eye performs a hologram-to-image conversion or transform. The projection system, or light engine, may be configured so that the viewer effectively looks directly at the display device.

Reference is made herein to a "light field" which is a "complex light field". The term light field" merely indicates a pattern of light having a finite size in at least two orthogonal spatial directions, e.g. x and y. The word "complex" is used herein merely to indicate that the light at each point in the light field may be defined by an amplitude value and a phase value, and may therefore be represented by a complex number or a pair of values. For the purpose of hologram calculation, the complex light field may be a two-dimensional array of complex numbers, wherein the complex numbers define the light intensity and phase at a plurality of

discrete locations within the light field.

In accordance with the principles of well-understood optics, the range of angles of light propagating from a display device that can be viewed, by an eye or other viewing entity/system, varies with the distance between the display device and the viewing entity. At a 1 metre viewing distance, for example, only a small range of angles from an LCOS can propagate through an eye's pupil to form an image at the retina for a given eye position. The range of angles of light rays that are propagated from the display device, which can successfully propagate through an eye's pupil to form an image at the retina for a given eye position, determines the portion of the image that is 'visible' to the viewer. In other words, not all parts of the image are visible from any one point on the viewing plane (e.g., any one eye position within a viewing window such as eye-box.) In some embodiments, the image perceived by a viewer is a virtual image that appears upstream of the display device -that is, the viewer perceives the image as being further away from them than the display device. Conceptually, it may therefore be considered that the viewer is looking at a virtual image through an 'display device-sized window', which may be very small, for example 1cm in diameter, at a relatively large distance, e.g., 1 metre. And the user will be viewing the display device-sized window via the pupil(s) of their eye(s), which can also be very small. Accordingly, the field of view becomes small and the specific angular range that can be seen depends heavily on the eye position, at any given time.

A pupil expander addresses the problem of how to increase the range of angles of light rays that are propagated from the display device that can successfully propagate through an eye's pupil to form an image. The display device is generally (in relative terms) small and the projection distance is (in relative terms) large. In some embodiments, the projection distance is at least one -such as, at least two -orders of magnitude greater than the diameter, or width, of the entrance pupil and/or aperture of the display device (i.e., size of the array of pixels).

Use of a pupil expander increases the viewing area (i.e., user's eye-box) laterally, thus enabling some movement of the eye/s to occur, whilst still enabling the user to see the image. As the skilled person will appreciate, in an imaging system, the viewing area (user's eye box) is the area in which a viewer's eyes can perceive the image. The present disclosure encompasses non-infinite virtual image distances -that is, near-field virtual images.

Conventionally, a two-dimensional pupil expander comprises one or more one-dimensional optical waveguides each formed using a pair of opposing reflective surfaces, in which the output light from a surface forms a viewing window or eye-box. Light received from the display device (e.g., spatially modulated light from a LCOS) is replicated by the or each waveguide so as to increase the field of view (or viewing area) in at least one dimension. In particular, the waveguide enlarges the viewing window due to the generation of extra rays or "replicas" by division of amplitude of the incident wavefront.

The display device may have an active or display area having a first dimension that may be less than 10 ems such as less than 5 cms or less than 2 cms. The propagation distance between the display device and viewing system may be greater than 1 m such as greater than 1.5 m or greater than 2 m. The optical propagation distance within the waveguide may be up to 2 m such as up to 1.5 m or up to 1 m. The method may be capable of receiving an image and determining a corresponding hologram of sufficient quality in less than 20 ms such as less than 15 ms or less than 10 ms.

In some embodiments -described only by way of example of a diffracted or holographic light field in accordance with this disclosure -a hologram is configured to route light into a plurality of channels, each channel corresponding to a different part (i.e. sub-area) of an image. The channels formed by the diffractive structure are referred to herein as "hologram channels" merely to reflect that they are channels of light encoded by the hologram with image information. It may be said that the light of each channel is in the hologram domain rather than the image or spatial domain. In some embodiments, the hologram is a Fourier or Fourier transform hologram and the hologram domain is therefore the Fourier or frequency domain. The hologram may equally be a Fresnel or Fresnel transform hologram. The hologram may also be a point cloud hologram. The hologram is described herein as routing light into a plurality of hologram channels to reflect that the image that can be reconstructed from the hologram has a finite size and can be arbitrarily divided into a plurality of image sub-areas, wherein each hologram channel would correspond to each image sub-area. Importantly, the hologram of this example is characterised by how it distributes the image content when illuminated. Specifically and uniquely, the hologram divides the image content by angle. That is, each point on the image is associated with a unique light ray angle in the spatially modulated light formed by the hologram when illuminated -at least, a unique pair of angles because the hologram is two-dimensional. For the avoidance of doubt, this hologram behaviour is not conventional. The spatially modulated light formed by this special type of hologram, when illuminated, may be divided into a plurality of hologram channels, wherein each hologram channel is defined by a range of light ray angles (in two-dimensions). It will be understood from the foregoing that any hologram channel (i.e. sub-range of light ray angles) that may be considered in the spatially modulated light will be associated with a respective part or sub-area of the image. That is, all the information needed to reconstruct that part or sub-area of the image is contained within a sub-range of angles of the spatially modulated light formed from the hologram of the image. When the spatially modulated light is observed as a whole, there is not necessarily any evidence of a plurality of discrete light channels.

Nevertheless, the hologram may still be identified. For example, if only a continuous part or sub-area of the spatially modulated light formed by the hologram is reconstructed, only a sub-area of the image should be visible. If a different, continuous part or sub-area of the spatially modulated light is reconstructed, a different sub-area of the image should be visible.

A further identifying feature of this type of hologram is that the shape of the cross-sectional area of any hologram channel substantially corresponds to (i.e. is substantially the same as) the shape of the entrance pupil although the size may be different -at least, at the correct plane for which the hologram was calculated. Each light / hologram channel propagates from the hologram at a different angle or range of angles. Whilst these are example ways of characterising or identifying this type of hologram, other ways may be used. In summary, the hologram disclosed herein is characterised and identifiable by how the image content is distributed within light encoded by the hologram. Again, for the avoidance of any doubt, reference herein to a hologram configured to direct light or angularly-divide an image into a plurality of hologram channels is made by way of example only and the present disclosure is equally applicable to pupil expansion of any type of holographic light field or even any type of diffractive or diffracted light field.

The system can be provided in a compact and streamlined physical form. This enables the system to be suitable for a broad range of real-world applications, including those for which space is limited and real-estate value is high. For example, it may be implemented in a head-up display (HUD) such as a vehicle or automotive HUD.

In accordance with the present disclosure, pupil expansion is provided for diffracted or diffractive light, which may comprise diverging ray bundles. The diffracted light field may be defined by a "light cone". Thus, the size of the diffracted light field (as defined on a two-dimensional plane) increases with propagation distance from the corresponding diffractive structure (i.e. display device). It can be said that the pupil expander/s replicate the hologram or form at least one replica of the hologram, to convey that the light delivered to the viewer is spatially modulated in accordance with a hologram.

In some embodiments, two one-dimensional waveguide pupil expanders are provided, each one-dimensional waveguide pupil expander being arranged to effectively increase the size of the exit pupil of the system by forming a plurality of replicas or copies of the exit pupil (or light of the exit pupil) of the spatial light modulator. The exit pupil may be understood to be the physical area from which light is output by the system. It may also be said that each waveguide pupil expander is arranged to expand the size of the exit pupil of the system. It may also be said that each waveguide pupil expander is arranged to expand/increase the size of the eye box within which a viewer's eye can be located, in order to see/receive light that is output by the system.

Light channelling The hologram formed in accordance with some embodiments, angularly-divides the image content to provide a plurality of hologram channels which may have a cross-sectional shape defined by an aperture of the optical system -as described in British patent 2,603,518 for example which is incorporated herein in its entirety by reference.

Two-Dimensional Pupil Expansion Embodiments of the present disclosure may be used with an optical system providing two-dimensional pupil expansion using a pair of orthogonal pupil expanders (or wavefront replicators) -as described in British patent 2,614,286 for example which is incorporated herein in its entirety by reference.

Combiner shape compensation An advantage of projecting a hologram to the eye-box is that optical compensation can be encoded in the hologram (see, for example, European patent 2,936,252 incorporated herein by herein). The present disclosure is compatible with holograms that compensate for the complex curvature of an optical combiner used as part of the projection system. In some embodiments, the optical combiner is the windscreen of a vehicle. Full details of this approach are provided in European patent 2,936,252 and are not repeated here because the detailed features of those systems and methods are not essential to the new teaching of this disclosure herein and are merely exemplary of configurations that benefit from the

teachings of the present disclosure.

Control device The present disclosure is also compatible with optical configurations that include a control device (e.g. light shuttering device) to control the delivery of light from a light channelling hologram to the viewer. The holographic projector may further comprise a control device arranged to control the delivery of angular channels to the eye-box position. British patent 2,607,899, incorporated herein in its entirety by reference, discloses the at least one waveguide pupil expander and control device. The reader will understand from at least this prior disclosure that the optical configuration of the control device is fundamentally based upon the eye-box position of the user and is compatible with any hologram calculation method that achieves the light channeling described herein. It may be said that the control device is a light shuttering or aperturing device. The light shuttering device may comprise a 1D array of apertures or windows, wherein each aperture or window independently switchable between a light transmissive and a light non-transmissive state in order to control the delivery of hologram light channels, and their replicas, to the eye-box. Each aperture or window may comprise a plurality of liquid crystal cells or pixels.

Holographic Projector with Angular Steering As described herein, a holographic projector comprises display device (e.g., spatial light modulator) and, optionally, a pupil replicator or expander. The display device is encoded with a hologram of a target picture and is illuminated with light in order to output light that is spatially modulated according to the hologram. The output light comprises a wavefront for forming a holographic reconstruction of the target picture. The pupil replicator relays the wavefront to an eye-box. In some embodiments, the pupil replicator comprises first and second pupil replicators, which replicate the wavefront in two dimensions as described above. In some arrangements, the (replicated) wavefront is relayed to an optical combiner, which reflects at least a portion of the wavefront to the eye-box to form a virtual image. A viewing system (e.g., the pupil of a user) is positioned at the eye-box to receive light of the wavefront. A holographic reconstruction is viewable from the eye-box.

Figure 2A shows a schematic view of an example display device 240 of a holographic projection system. In this example, the display device 240 is a pixelated liquid crystal on silicon (LCoS) spatial light modulator. The display device 240 comprises a display area 242 containing the pixels of the display device in periodic array of rows and columns. A portion 210 of the display device 240 is magnified to more clearly show how individual pixels 212 of the display device 240 are arranged in an array. In this example, each pixel 212 is square. A pixel pitch 220 of the display device 240 is defined as the distance between the respective centres of adjacent pixels 212 in the array. In this example, since the pixels 212 are square, the pixel pitch 220 is equal in a first (x) direction and second (y) direction that is perpendicular to the first (x) direction.

The (maximum) diffraction angle of the display device 240 is dependent on this pixel pitch, according to the following equation:

A

9 = ± () where 0 is the diffraction angle, A is the wavelength of incident light and x is the pixel pitch 10 220.

Figure 2B represents the maximum range of diffraction angles of the display device. The central arrow 250 represents a projection axis of the holographic projection system. In all examples, the size of the field of view, and this the size of the holographic reconstruction or replay field, of a holographic projection system is dependent on the maximum diffraction angle. For example, the field of view of a holographic projection system may be substantially equal to 20.

Figure 3 shows a schematic cross-sectional view of portion of an example holographic projection system 300. The holographic projection system 300 comprises a display device 340 and an optical relay 306 downstream of the display device 340. The optical relay 306 comprises a first lens 308 and a second lens 310 downstream of the first lens 308. In this example, the optical power of the first lens 308 is equal to the optical power of the second lens 310. Furthermore, the focal length of the first and second lenses 308, 310 are the same (and are equal to f, as represented by the arrows in Figure 3). The first lens 308 comprises a front focal plane 312 and a back focal plane 314. The second lens 310 comprises a front focal plane 316 and a back focal plane 318. The back focal plane 314 of the first lens 908 and the front focal plane 316 of the second lens 310 are co-planar. Thus, the optical relay 306 may be referred to as a "4f" system because the distance between the front focal plane 312 of the first lens 308 and the back focal plane 318 of the second lens 310 is equal to four times the focal length, f, of the first and second lens 308, 310. The display device 340 is substantially coplanar with the front focal plane 312 of the first lens 308. The holographic projection system 300 further comprises a holographic wavefront redirector 350. In the illustrated arrangement, the holographic wavefront redirector 350 is substantially coplanar with the back focal plane 318 of the second lens 310. In other arrangements, the holographic wavefront redirector may be positioned at the plane of the display device 340, and thus substantially coplanar with the back focal plane 312 of the first lens 308.

The display device 340 in this example is an LCoS spatial light modulator. The display device 340 is arranged to display a sequence of holograms of a respective sequence of target pictures. The display device 340 is arranged to be illuminated by coherent light from a light source (such as laser light of a laser). The display device 340 is arranged to spatially modulate the light incident thereon in accordance with a respective hologram of a respective target picture. This forms a holographic wavefront. The holographic projection system 300 is arranged such that the holographic wavefront is relayed / propagated to the optical relay 306 to be received by the first lens 308 and the second lens 310 in turn. The first lens 908 of the optical relay is arranged to form a holographic reconstruction 326. This holographic reconstruction 326 may be formed substantially at the back focal plane 312 of the first lens 308. The second lens 310 is arranged to form a relayed hologram 322 at the back focal plane 318. The relayed hologram 322 corresponds to the display device (comprising the displayed hologram of the target picture). In this example, the holographic wavefront redirector 350 (positioned at the back focal plane 312 or 318) is arranged to act on / process the holographic wavefront.

As the skilled person will appreciate, the term "angular steering", "beam steering" or simply "steering" or "turning" means changing the propagation direction/axis of light, and thus may be defined in terms of an angular change in the propagation direction/axis of light in one or two dimensions. Accordingly, steering may be defined by an angle of the propagation direction/axis of output light with respect to the propagation direction/axis of incident light in one or two dimensions.

The holographic projection system 300 may further comprise first and second waveguides (not shown) downstream of the holographic wavefront redirector 350. It should be understood that the processed holographic wavefront is relayed from the holographic wavefront redirector 350 to the first and second waveguides where the holographic wavefront is replicated. After replication, the holographic projection system 300 may be arranged such that the replicated holographic wavefront is relayed to an optical combiner. At least a portion of the intensity of the holographic wavefront is reflected / relayed by the optical combiner to an eye-box.

Holographic Wavefront Redirector According to the present disclosure, the holographic wavefront director 350 of the holographic projection system 300 of Figure 3 comprises spatially separate zones (i.e. regions or areas). Each zone is arranged to steer (or deflect) a corresponding area or region of the holographic wavefront that is incident thereon by a defined angle and direction. For example, it is known to use an optical element (e.g., prism or prism array) or a diffraction element (e.g., diffraction grating or DOE) to steer or redirect a light beam incident thereon, by changing the direction of propagation thereof (e.g., changing the direction of the projection/optical axis). In accordance with embodiments, a plurality of zones of the holographic wavefront director 350 are each arranged to steer portions of the holographic wavefront comprising the same picture content by the same angle and direction. Thus, the holographic wavefront redirector 350 may comprise a first group of zones arranged to steer portions of the holographic wavefront comprising first picture content by a first angle and direction, and a second group of zones of arranged to steer portions of the holographic wavefront comprising second picture content by a second angle and direction, different from the first angle and direction. The second angle may be the same or different from the first angle. The second direction may be the same or different from the first direction. In some arrangements, the second group of zones may be arranged to propagate the portions of the holographic wavefront incident thereon without steering (or deflection), that is without changing the angle or direction thereof. Thus, the holographic wavefront director 350 allows different picture content reconstructed from a single hologram to be formed at spatially separate positions within the field of view.

As the skilled person will appreciate, the arrangement of the zones of the holographic wavefront redirector of a holographic projector, as described above, is selected to match the regions of the holographic wavefront corresponding to different picture content. Thus, each zone directs a respective region of the holographic wavefront so as to form a holographic reconstruction of the corresponding picture content at a desired position within the field of view. Regions of a holographic wavefront corresponding to different picture content may be determined by the method used to form the (combined/composite) hologram for display on the display device based on the different picture content (and desired positioning within the field of view). Embodiments of suitable methods are described below.

Hologram Formation by Sub-Pixel Interlacing in One Dimension Figure 4 illustrates a method of forming a hologram of a target picture 400 for display in accordance with an embodiment of the present disclosure. The target picture comprises a first picture comprising first picture content and a second picture comprising second picture content. The first picture is formed in a first picture area 402 and the second picture is formed in a second picture area 404. The first picture area 402 is spatially separate from the second picture area 404. In the illustrated example, the second picture area 404 adjoins (i.e., is contiguous with) the first picture area 402. In other examples, the first and second picture areas 402, 404 are only partially separate and so may partially overlap.

The first picture comprises the letter "L" and the first picture area 402 corresponds to the left-hand side of the target picture 400. The second picture comprises the letter "R" and the second picture area 404 corresponds to the right hand side of the target picture 400. The first and second pictures may be formed by dividing a target picture 400 into left and right picture areas. Alternatively, the first and second pictures may be separate pictures for sideby-side arrangement in the target picture 400.

The method comprises receiving the first picture (content) and determining a hologram of the first picture (content) as a first sub-hologram 412. The method further comprises receiving the second picture (content) and determining a hologram of the second picture (content) as a second sub-hologram 414. Various techniques and algorithms for determining a hologram from received picture (content) are well known in the art, and so are not described in detail herein. The term "sub-hologram" is used herein to mean a hologram of a picture (or picture content) that forms only a part of a target picture, and thus to differentiate it from a hologram of the complete target picture, and so is not imply any limitation to the method by which it is determined.

The first and second pictures are typically received as image data for first and second images each comprising an array of rows and columns of image pixels having image pixel values. Thus, the method determines first and second sub-holograms 412, 414 each comprising an array of rows and columns of hologram pixels having a hologram pixel values as shown in Figure 4. In the illustrated arrangement, each of the first and second sub-holograms 412, 414 comprises a 4x4 array comprising four rows and four columns of pixels of the sub-holograms numbered from 1 to 16 (from top left to bottom right). The pixels 1 to 16 of the second sub-hologram 414 are shown shaded in Figure 4 to distinguish them from the pixels 1 to 16 of the first sub-hologram 412. As the skilled person will appreciate, in practice, each sub-hologram may typically comprise a larger array of pixels, which may be arranged in a rectilinear array comprising any suitable number of rows and columns. The size of the sub-hologram (i.e., number of rows/columns/pixels) may be chosen according to application requirements. In particular, the size of each of the sub-holograms (i.e., number of rows/columns/pixels) may be determined based on the number of sub-holograms to be interlaced to form the hologram to be displayed and the size (i.e. number and arrangement of light modulating pixels) of the display device.

The method further comprises spatially interlacing the first and second sub-holograms 412, 414 to form a combined (or composite) hologram 450 of the target picture 400 comprising first picture area 402 and second picture area 404. In particular, each pair of corresponding or "equivalent" pixels 1 to 16 (i.e., having the same number or row/column position) of the first and second sub-holograms 412, 414 is arranged in a one dimensional, 2x1 array (i.e., an array comprising two rows and one column) to form a single combined, grouped or "binned" hologram pixel 452. Accordingly, each hologram pixel 452 may be considered to comprise a pair of sub-pixels arranged in a 2x1 array. Thus, it may be said that the effective pixel pitch is increased (i.e., doubled) in the column direction. The (combined) hologram pixels 452 may therefore be numbered (1, 1) to (16, 16). The sub-pixel in the first row of the 2x1 array of each hologram pixel 452 has a pixel value of a pixel at a defined row/column position within the array of pixels of the first sub-hologram 412 and the sub-pixel in the second row of the 2x1 array has a pixel value of a pixel at the equivalent row/column position within the array of pixels of the second sub-hologram 414. Since the pixels of the first and second sub-holograms are combined, grouped or binned as a one dimensional (2x1) array of sub-pixels, the method of this embodiment may be described as one dimensional sub-pixel interlacing of the first and second sub-holograms 412, 414.

As shown in Figure 4, the relative position of each (combined) hologram pixel 452 within the array of hologram pixels 452 of the combined hologram 450 is the same as the relative position of each pixel 1 to 16 within the array of pixels of the first and second sub-holograms 412, 414 (i.e., the (combined) hologram pixels having sub-pixels (1, 1) to (16, 16) from top left to bottom right). Thus, the first sub-hologram 412 and the second sub-hologram 414 each contribute a pixel (or pixel value) as a sub-pixel of the (combined) hologram pixel 452. The positions of the sub-pixels corresponding to each of the first and second sub-holograms 412, 414 are maintained in the combined hologram 450.

The method further comprises displaying the combined hologram 450 of the target picture 400 on a display device. In particular, each (combined) hologram pixel 452 is displayed on a 2x1 array of light modulating pixels of the display device; that is, each light modulating pixel is encoded with the pixel value of a respective sub-pixel of the combined hologram 450. Thus, it may be said that the first and second sub-holograms are spatially interlaced at the sub-pixel level in the combined hologram.

Accordingly, the total number of light modulating pixels of the display device required to display the combined hologram 450 is twice the number of light modulating pixels of the display device required to display only one of the first and second sub-holograms. In addition, the combined hologram 450 is twice the size of the first and second sub-holograms in one dimension, but is the same size in the other dimension. Thus, the method results in a change in aspect ratio, in particular from square first and second sub-holograms to a rectangular combined hologram. A rectangular hologram aspect ratio may be desirable for display on a display device comprising a rectangular array of light modulating pixels.

As noted above, the spatial positions of the 4x4 array of pixels (or pixel values) corresponding to each of the first and second sub-holograms 412, 414 are preserved in the combined hologram 450. As shown in Figure 4, the pixels of each row of the first and second sub-holograms 412, 414 correspond to respective rows of sub-pixels in the combined hologram 450 and so remain adjacent in the row direction. However, the pixels of each column of the first and second sub-holograms 412, 414 are interlaced, so that sub-pixels corresponding to a column of the first sub-hologram 412 are each separated by a respective sub-pixel corresponding to a column of the second sub-hologram 414 in the column direction. It may be said that the spatial frequencies of the first and second sub-holograms are increased (i.e., doubled) in the column direction. This changes the size and shape of the holographic reconstruction of the picture (or picture content) of each of the first and second sub-holograms 412, 414. Figure 5 illustrates the change in size and shape of the holographic reconstructions.

Figure 5 shows the first and second picture areas formed by independently displaying each of the first and second sub-holograms 412, 414 on a display device on the left side of the drawing. Thus, a holographic reconstruction of the first picture is formed in a square picture area 502, consistent with the first picture area 402 shown in Figure 4 and, similarly, a holographic reconstruction of the second picture is formed in a square picture area 504, consistent with the second picture area 404 shown in Figure 4. As the skilled person will appreciate, the square shape of the picture areas 502, 504 of the holographic reconstructions (i.e. the shape of the replay field/field of view) is a consequence of the diffractive effect and the square shape of the pixels of the display device as shown in Figure 2A.

Figure 5 shows the first and second pictures formed by displaying the combined hologram 450 comprising the interlaced first and second sub-holograms 412, 414 on a display device on the right side of the drawing. In particular, since the sub-pixels corresponding to the respective first arid second sub-holograms 412, 414 in the row direction are displayed on light modulating pixels that have the same spacing in the combined hologram 450, the size of the picture area 502' of the holographic reconstruction in a first dimension is the same as the first and second picture areas 502, 504. However, since the sub-pixels corresponding to the respective first and second sub-holograms 412, 414 in the column direction are displayed on light modulating pixels that have an increased spacing in the combined hologram 450, the size of the picture area 502' of the holographic reconstruction is reduced in a second dimension, orthogonal to the first dimension. Thus, as shown in Figure 5, since the spacing is doubled in the column direction, the size of each of the first and second picture areas 502', 504' formed is halved in the vertical dimension thereof compared to the first and second picture areas 502, 504 formed by the first and second sub-holograms 412, 414. In addition, the aspect ratio of the first and second picture areas is changed from a square shape with an aspect ratio of 1:1 to a rectangular shape with an aspect ratio of 2:1.

As the skilled person will appreciate, the aspect ratio of a picture area of a holographic reconstruction (i.e., replay field/field of view) is determined by the aspect ratio of the pixels of the display device on which the hologram is displayed. In particular, the aspect ratio of an picture area of a holographic reconstruction has the same magnitude, but orthogonal orientation, relative to the aspect ratio of the pixels of the display device. Accordingly, the first and second picture areas 502', 504' of the first and second pictures formed by the combined hologram 540 has an aspect ratio with the same magnitude, but orthogonal orientation, relative to the aspect ratio of the one dimensional (2x1) array of sub-pixels forming the combined hologram pixels 452.

Thus, the shape of the combined hologram pixels 452 of a combined hologram comprising sub-holograms of a plurality of pictures determines the shape of the picture area of the holographic reconstruction of each of the plurality of pictures.

Figure 5B shows an example of a field of view 510 (or combined holographic reconstruction) of the target picture comprising first and second pictures (picture content) formed by a holographic projection system comprising a display device displaying the combined hologram 450. For example, the holographic projection system may comprise a holographic wavefront redirector as described above with reference to Figure 3. In particular, a first plurality of zones of the holographic wavefront redirector is arranged to steer the first picture in the first picture area 502' by a first angle and direction to a left side of the field of view.

The first plurality of zones is arranged to receive a portion of the holographic wavefront from (i.e., output by) the sub-pixels of the combined hologram 450 that display the pixel values of the first sub-hologram 412. A second plurality of zones of the holographic wavefront redirector is arranged to steer the second picture in the second picture area 504' by a second angle and direction to a right side of the field of view. The second plurality of zones is arranged to receive a portion of the holographic wavefront from (i.e., output by) the sub-pixels of the combined hologram 450 that display the pixel values of the second sub-hologram 414. In the illustrated example, the first picture area 502' and the second picture area 504' are adjacent or contiguous left and right areas of the field of view. It may be said that the first and second picture areas are stitched together in the horizontal dimension Thus, the first and second plurality of zones of the holographic wavefront redirector are arranged to steer incident light by the same angle but in opposite directions. This may lead to an increased angular extent/field of view in the horizontal dimension, as shown in Figure 5B. However, since the angular extent/ field of view is reduced in the vertical dimension, the overall area of the holographic reconstruction/field of view of the target picture is unchanged.

As the skilled person will appreciate, in other arrangements, the zones of the holographic wavefront redirector associated with (the light modulating pixels displaying) (sub-)pixels (or subpixel values) of each sub-hologram may be arranged to steer incident light by any arbitrary angle and in any arbitrary direction, to form the respective picture content at a desired position within the field of view.

As the skilled person will appreciate, the method illustrated in Figures 4 and 5A and 5B may be extended to include target pictures comprising three or more pictures. For example, sub-holograms may be determined for each of three or more pictures, and the sub-holograms spatially interlaced to form a combined (or composite) hologram. In this case, the combined hologram pixels comprise three or more sub-pixels having pixel values of corresponding pixels from each of the sub-holograms arranged together in a one dimensional array (i.e an array comprising three of more rows and one column). The positions of the pixels of the sub-holograms remain the same in the combined hologram, but the spacing in the pixels is increased in the column direction. As the skilled person will further appreciate, the method illustrated in Figures 4 and 5A and 5B may also be applied to form combine hologram pixels from sub-hologram pixels in a one-dimensional array of sub-pixels in the orthogonal direction (i.e., an array comprising one column and two or more rows of sub-pixels).

Hologram Formation by Sub-Pixel Interlacing in Two Dimensions Figure 6 illustrates a method of forming a hologram of a target picture for display in accordance with another embodiment of the present disclosure. The target picture comprises a first, second, third and fourth pictures respectively comprising first, second third and fourth picture content. The first picture comprises the letter L arid is formed in a first picture area 602, the second picture comprises the letter R in a circle and is formed in a second picture area 604, and the third picture comprise the letter S in a diamond and is formed in a third picture area 606 and the fourth picture comprises the & (ampersand) symbol in a hexagon and is formed in a fourth picture area 608. The first, second, third and fourth picture areas 602, 604, 606, 608 are spatially separate from each other. Examples of the arrangement of the first, second, third and fourth picture areas 602, 604, 606, 608 in the target picture are described below with reference to Figures 8A to 8E.

Similar to the method of Figure 4, the method of Figure 6 comprises receiving each of the first, second, third and fourth picture (content) and determining a respective hologram of each of the first, second, third and fourth picture (content) as a first, second, third and fourth sub-holograms 612, 614, 616, 618.

The first, second, third and fourth pictures are typically received as image data for respective first, second, third and fourth images each comprising an array of rows and columns of image pixels having image pixel values. Thus, the method determines first, second, third and fourth sub-holograms 612, 614, 616, 618 each comprising an array of rows and columns of hologram pixels having a hologram pixel values as shown in Figure 6. In the illustrated arrangement, each of the sub-holograms comprises a 4x4 array comprising four rows and four columns of pixels of the sub-holograms numbered from 1 to 16 (from top left to bottom right). The pixels 1 to 16 of the first, second, third and fourth second sub-hologram 612, 614, 616, 618 are shown with different shading in Figure 6 for ease of illustration.

The method further comprises spatially interlacing the first, second third and fourth sub-holograms to form a combined (or composite) hologram 650 of the target picture. In particular, groups of four corresponding or "equivalent" pixels 1 to 16 (i.e., having the same number or row/column position) of the first, second, third and fourth sub-holograms 612, 614 616, 618 are arranged together in a two dimensional, 2x2 array (i.e., an array comprising two rows and two columns) to form a single combined, grouped or "binned" hologram pixel 652. Accordingly, each hologram pixel 452 may be considered to comprise a group of sub-pixels arranged in a 2x2 array. Thus, it may be said that the effective pixel pitch is increased (i.e., doubled) in the column direction and the row direction. The (combined) hologram pixels 652 may therefore be numbered (1, 1, 1, 1) to (16, 16, 16 16). The sub-pixel at the first row and first column position (1, 1) of the 2x2 array of the hologram pixel 652 has a pixel value of a pixel at a particular row/column position within the array of pixels of the first sub-hologram 612, the sub-pixel in the second row and first column position (2, 1) of the 2x2 array has a pixel value of a pixel at the equivalent row/column position within the array of pixels of the second sub-hologram 614, the sub-pixel in the first row and second column position (1, 2) of the 2x2 array has a pixel value of a pixel at the equivalent row/column position within the array of pixels of the third sub-hologram 616 and the sub-pixel in the second row and second column position (2, 2) of the 2x2 array has pixel value at the equivalent row/column position within the array of pixels of the fourth sub-hologram 618. Since the pixels of the first, second, third and fourth sub-holograms are combined, grouped or binned as a two dimensional (2x2) array of sub-pixels, the method of this embodiment may be described as two dimensional sub-pixel interlacing of the first, second, third and fourth sub-holograms 612, 614, 616, 618.

Accordingly, the total number of light modulating pixels of the display device required to display the combined hologram 650 is four times the number of light modulating pixels of the display device required to display only one of the first to fourth sub-holograms. In addition, the combined hologram 650 is twice the size of the first to fourth sub-holograms in both dimensions thereof. However, the aspect ratio remains unchanged. In particular, since the combined hologram pixels comprises an array of sub-pixels having the same number of rows and columns (i.e., 2x2), the aspect ratio of the combined hologram 650 is square. A square hologram aspect ratio may be desirable for display on a display device comprising a square array of light modulating pixels. In other examples of this embodiment, the combined hologram pixels may comprises an array of sub-pixels having different numbers of rows and columns (e.g., 2x3), and the aspect ratio of the combined hologram 650 may be rectangular.

As noted above, the spatial positions of the 4x4 array of pixels of each of the first to fourth sub-holograms 612, 614, 616, 618 are maintained the same in the combined hologram 650. As shown in Figure 6, the pixels of the rows and columns of the each sub-hologram are interlaced, so that each sub-pixel corresponding to a particular sub-hologram is separated by a sub-pixel corresponding to another sub-hologram in both the column and row directions. It may be said that the spatial frequencies of the first and second sub-holograms are increased (i.e., doubled) in the column direction and the row direction. Thus, for example, the sub-pixel corresponding to pixel 1 of the first sub-hologram is separated from the sub-pixel corresponding to pixel 2 of the first sub-hologram by a sub-pixel corresponding to pixel 1 of the second sub-hologram in the row direction. In addition, the sub-pixel corresponding to pixel 1 of the first sub-hologram is separated from the sub-pixel corresponding to pixel 5 of the first sub-hologram by the sub-pixel corresponding to pixel 1 of the third sub-hologram in the column direction. This changes the size (but not the shape) of the holographic reconstruction of the picture (or picture content) of each of the first to fourth sub-holograms as shown in Figure 7.

Figure 7 shows the first, second, third and fourth pictures formed by independently displaying each of the first, second third and fourth sub-holograms 612, 614, 616, 618 on a display device at the top of the drawing. Thus, a holographic reconstruction of the first picture is formed in a square picture area 702, consistent with the first picture area 602 shown in Figure 6. Similarly, a holographic reconstruction of each of the second, third and fourth pictures is formed in a respective square picture area 704, 706, 708 consistent with the second to fourth picture areas 604, 606, 608 shown in Figure 6. As the skilled person will appreciate, the square shape of the picture areas 602, 604, 606, 608 of the holographic reconstructions (or replay field/field of view) is a consequence of the diffractive effect and the square shape of the pixels of the display device as shown in Figure 2A.

Figure 7 shows the first, second, third and fourth pictures formed by displaying the combined hologram 650 comprising the interlaced first to fourth sub-holograms 612, 614, 616, 618 on a display device at the bottom of the drawing. Since the sub-pixels corresponding to the respective first to fourth sub-holograms 612, 614, 616, 618 in the both the column directions are displayed on light modulating pixels that have an increased spacing in the combined hologram 650, the size of each picture areas 702', 704', 706', 708' of the holographic reconstruction is reduced in both dimensions thereof. Thus, as shown in Figure 7, the first to fourth picture areas 702', 704' 706', 708' of the first to fourth second pictures, respectively, formed by the combined hologram is halved in the horizontal and vertical dimensions thereof compared to the first to fourth picture areas 702, 704, 706, 608 formed by the first to fourth second sub-holograms 612, 614, 616, 618. As noted above, the shape of the hologram pixels of a combined hologram comprising sub-holograms of a plurality of pictures, as disclosed herein, determines the shape of the picture area of the holographic reconstruction of each of the plurality of pictures. Accordingly, since the combined hologram pixels 652 are square, the shape of the picture area of the holographic reconstruction is a square shape with an aspect ratio of 1:1. Thus, in the example of Figures 6 and 7, the shape of the picture area remains the same but its dimensions are halved.

Figures 8A to BE shows an example of the arrangement of a field of view of the target picture comprising first to fourth pictures (picture content) formed by a holographic projection system comprising a display device displaying the combined hologram 650. For example, the holographic projection system may comprise a holographic wavefront redirector as described above with reference to Figure 3.

In particular, a first plurality of zones of the holographic wavefront redirector is arranged to steer the first picture in the first picture area 702' in a first direction to a first position in the field of view. The first plurality of zones is arranged to receive a portion of the holographic wavefront from (i.e., output by) the sub-pixels of the combined hologram 650 that display the pixel values of the first sub-hologram 612. Similarly, second, third and fourth pluralities of zones of the holographic wavefront redirector are arranged to steer each of the second, third and fourth pictures in the second to fourth picture areas 704', 706', 708' in respective second, third and fourth directions to corresponding positions in the field of view. Thus, each of the second to fourth pluralities of zones is arranged to receive a portion of the holographic wavefront from (i.e., output by) the sub-pixels of the combined hologram 650 that display the pixel values of the respective second to fourth sub-holograms 614, 616, 618.

In the example shown in Figure 8A, the first to fourth picture areas 702', 704', 706', 708' are positioned as adjacent or contiguous areas of the field of view (holographic reconstruction of the combined hologram) that are arranged in a line from left to right in the horizontal direction. It may be said that the first to fourth second picture areas are stitched together in the horizontal dimension. This may lead to an increased angular extent/field of view in the horizontal dimension (the field of view is doubled in Figure 8A), and a change in shape or aspect ratio (from square to rectangular). However, since the angular extent/field of view of each of the first to fourth picture areas is reduced (halved) in the horizontal and vertical dimensions, the overall size of the area of the holographic reconstruction/field of view of the target picture is unchanged. In the example shown in Figure 8B, the first of fourth picture areas 702', 704', 706', 708' are positioned as adjacent or contiguous areas of the field of view that are arranged as a 2x2 array. Thus, the first picture area 702' occupies the top left quarter of the field of view, the second picture area 704' occupies the top right quarter of the field of view, the third picture area 706' occupies the bottom left quarter of the field of view and the fourth picture area 708' occupies the bottom right quarter of the field of view. In this arrangement, the size and shape of the field of view is unchanged, since the size of each of the first of fourth picture areas is halved in both dimensions. In the example shown in Figure 8C, the first of fourth picture areas are positioned as adjacent or contiguous areas of the field of view that are arranged in an inverted T shape. In particular, the second, third and fourth picture areas 704', 706', 708' extend in a line from left to right in a horizontal direction and the first picture area 702' is positioned vertically above the second picture area 704'. In this case, the field of view is increased (by half in Figure SC) in the horizontal direction but not the vertical direction. Once again, the overall size of the area of the field of view of the target picture is unchanged. Figures SD and BE show examples of forming the first to fourth picture areas 702', 704', 706', 708' as non-contiguous areas of the field of view. In particular, the first of fourth picture areas 702', 704', 706', 708' are spatially separated from each other within the field of view at (arbitrary) desired positions. As noted above, the zones of a holographic wavefront redirector associated with (the light modulating pixels displaying) (sub-)pixels (or subpixel values) of each sub-hologram may be arranged to steer incident light by any appropriate angle and in any appropriate direction, to form the respective picture content at a desired position within the field of view.

Experimental Example

Figure 9 shows a experimental example of a target picture 900 comprising first, second, third and fourth pictures (picture content) 902, 904, 906, 908 (shown on the left hand side of the drawing) and the resulting holographic reconstruction 902' of a combined (or composite) hologram of the target picture 900 (shown in the right hand side of the drawing). The combined hologram was formed by determining first, second, third and fourth sub-holograms of the respective first, second, third and fourth pictures 902, 904, 906, 908 and spatially interlacing the sub-holograms using two-dimensional sub-pixel interlacing in accordance with the method of Figure 6. Thus, each (combined) hologram pixel comprises a 2x2 array of sub-pixels having pixel values corresponding to respective (equivalent or corresponding) pixels of each of the first to fourth sub-holograms.

The combined hologram was displayed on a display device and illuminated to form the holographic reconstruction 900' of the combined hologram of the target picture 900 as shown in Figure 9. The holographic reconstruction 900' was formed in the absence of a holographic wavefront redirector, so that the picture areas of each of the first to fourth pictures of the reconstruction 900' overlap. The inventors found that the picture quality of each of the first of fourth pictures 902, 904, 906, 908 is not significantly degraded, for example due to image artefacts and ghost image formation, despite the reduction in the size of the picture area of each of the first to fourth pictures.

Accordingly, the method of the present disclosure enables different pictures (picture content) for display to be formed using a single hologram, and to be flexibly and dynamically sized and shaped within the field of view, without detrimentally impacting picture quality. This may be achieved by determining and displaying a single hologram from sub-holograms of each picture according to a selected one or two-dimensional sub-pixel interlacing scheme as described above, whereby the hologram pixels each comprise an array of sub-pixels having pixel values of a corresponding pixel of each of the sub-holograms. The method of combining sub-pixels from respective sub-holograms to form (combined) hologram pixels may be performed in software, hardware or a combination thereof. As described herein, the selected interlacing scheme (i.e., to form the (combined) hologram pixels) may determine the size and shape of the picture area of each picture formed in the field of view, without loss of picture quality from the display of the combined hologram on a display device.

Furthermore, the method of the present disclosure enables different pictures (picture content) for display to be formed using a single hologram, and to be flexibly and dynamically positioned within the field of view, by arranging a holographic wavefront redirector in software and/or hardware.

Additional features The methods and processes described herein may be embodied on a computer-readable medium. The term "computer-readable medium" includes a medium arranged to store data temporarily or permanently such as random-access memory (RAM), read-only memory (ROM), buffer memory, flash memory, and cache memory. The term "computer-readable medium" shall also be taken to include any medium, or combination of multiple media, that is capable of storing instructions for execution by a machine such that the instructions, when executed by one or more processors, cause the machine to perform any one or more of the methodologies described herein, in whole or in part.

The term "computer-readable medium" also encompasses cloud-based storage systems. The term "computer-readable medium" includes, but is not limited to, one or more tangible and non-transitory data repositories (e.g., data volumes) in the example form of a solid-state memory chip, an optical disc, a magnetic disc, or any suitable combination thereof. In some example embodiments, the instructions for execution may be communicated by a carrier medium. Examples of such a carrier medium include a transient medium (e.g., a propagating signal that communicates instructions).

It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope of the appended claims. The present disclosure covers all modifications and variations within the scope of the appended claims and their equivalents.

Claims

CLAIMS1. A holographic projection system arranged to display a picture, the system comprising: a hologram engine arranged to: receive a first sub-hologram of first picture content of the picture and a second sub-hologram of second picture content of the picture, wherein the first sub-hologram comprises a plurality of first sub-hologram pixels and the second hologram comprises a plurality of second sub-hologram pixels, and form a hologram of the picture by spatially interlacing the first and second sub-holograms, wherein the hologram comprises a plurality of hologram pixels each comprising a first sub-pixel and a second sub-pixel, wherein the first sub-pixel corresponds to a first sub-hologram pixel of the first sub-hologram and the second sub-pixel corresponds to an equivalent second sub-hologram pixel of the second sub-hologram; and a holographic wavefront redirector positioned adjacent the hologram, or an optically relayed copy of the hologram, wherein the holographic wavefront redirector is arranged to steer light of the first sub-hologram in a first direction and to steer light of the second sub-hologram in a second direction, wherein the second direction is different from the first direction.
2. A system as claimed in claim 1 further comprising a pixelated spatial light modulator arranged to display the hologram, wherein each sub-pixel of the hologram is displayed on a respective light modulating pixel of the spatial light modulator.
3. A system as claimed in any preceding claim wherein the spatial interlacing comprises changing an aspect ratio of the first sub-hologram and/or second sub-hologram.
4. A system as claimed in any preceding claim wherein the spatial interlacing comprises changing the pixel pitch of the first and/or second hologram is one dimension but not the other.
5. A system as claimed in any preceding claim wherein the spatial interlacing comprises interposing second sub-hologram pixels of the second sub-hologram between first sub-hologram pixels of the first sub-hologram in one pixel direction of the spatial light modulator but not the other pixel direction of the spatial light modulator, or vice versa.
6. A system as claimed in any preceding claim wherein the spatial interlacing comprises interposing second sub-hologram pixels of the second sub-hologram between first sub-hologram pixels of the first sub-hologram in both pixel directions of the spatial light modulator, or vice versa.
7. A system as claimed in any preceding claim wherein the spatial interlacing comprises increasing the pixel pitch of the first sub-hologram or second sub-hologram in one or both pixel directions.
8. A system as claimed in any preceding claim wherein the spatial interlacing is such that a pixel pitch of the first/second sub-hologram pixels of the first/second sub-hologram in a first direction is different to a pixel pitch of the first/second sub-hologram pixels of the first/second sub-hologram in a second direction.
9. A system as claimed in any preceding claim wherein the spatial interlacing is such that an aspect ratio of the first/second sub-hologram before spatial interlacing is different to an aspect ratio of a holographic reconstruction of the first/second picture content formed by the hologram.
10. A system as claimed in any preceding claim wherein the spatial interlacing reduces a size of the replay field / field of view of the holographic reconstruction of the first picture content and/or second picture content in at least one direction.
11. A system as claimed in any preceding claim wherein each pixel of the hologram comprises a one-dimensional array of sub-pixels such that a holographic reconstruction (or field of view) of each picture area (or replay field) of the first or second picture content has a rectangular aspect ratio.
12. A system as claimed in any preceding claim wherein the first picture content comprises a first picture area of the picture and the second picture content comprises a second picture area of the picture, wherein the first and second picture areas are at least partially spatially separate.
13. A system as claimed in claim 12 wherein the hologram engine is further arranged to receive a picture and divide the picture into a first picture area and a second picture area.
14. A system as claimed in any preceding claim wherein the holographic wavefront redirector is arranged to steer light of the first and second sub-holograms so that the first picture content is displayed adjacent to, such as contiguous with or partially overlapping, the second picture content.
15. A system as claimed in any preceding claim wherein the holographic wavefront redirector is arranged to steer light of the first and second sub-holograms so that the first picture content is displayed spatially separated from the second picture content.
16. A system as claimed in any preceding claim wherein the hologram engine is further arranged to: calculate a third sub-hologram of third picture content of the picture and a fourth sub-hologram of the picture, wherein the third sub-hologram comprises a plurality of third sub-hologram pixels and the fourth hologram comprises a plurality of fourth sub-hologram pixels, 15 and form the hologram of the picture by spatially interlacing the first, second, third and fourth sub-holograms such that each of the plurality of hologram pixels comprising first, second, third and fourth sub-pixels corresponding to respective equivalent first, second third and fourth sub-hologram pixels of the first, second third and fourth sub-holograms.
17. A system as claimed in claim 16 wherein each pixel of the hologram comprises a two-dimensional array of sub-pixels.
18. A system as claimed in claim 17 wherein: the two dimensional array of sub-pixels has the same number of rows and columns such that a field of view of each of the first, second, third and fourth picture content has a square aspect ratio; or the two dimensional array of sub-pixels has a different number of rows and columns such that a holographic reconstruction of each of the first, second, third and fourth picture content has a rectangular aspect ratio.
19. A method of determining a hologram of a picture comprising first picture content and second picture content for display on a display device comprising: determining a first sub-hologram of the first picture content of the picture and a second sub-hologram of the second picture content of the picture, wherein the first sub-hologram comprises a plurality of first sub-hologram pixels and the second sub-hologram comprises a plurality of second sub-hologram pixels, and forming a hologram of the picture by spatially interlacing the first and second sub-holograms, wherein the hologram comprises a plurality of hologram pixels each comprising a first sub-pixel and a second sub-pixel, wherein the first sub-pixel corresponds to a first sub-hologram pixel of the first sub-hologram and the second sub-pixel corresponds to an equivalent second sub-hologram pixel of the second sub-hologram.
20. A method as claimed in claim 19 wherein the first picture content comprises a first picture area of the picture and the second picture content comprises a second picture area of the picture, wherein the second picture area is at least partially spatially separate from the first picture area, the method further comprising receiving the picture, and dividing the target picture to form the first and second picture areas.
21. A method as claimed in claim 19 or 20 further comprising: determining a third sub-hologram of third picture content of the picture and a fourth sub-hologram of second picture content of the picture, wherein the third sub-hologram comprises a plurality of third sub-hologram pixels and the fourth hologram comprises a plurality of fourth sub-hologram pixels, wherein forming the hologram of the picture comprises spatially interlacing the first, second, third and fourth sub-holograms such that each of the plurality of hologram pixels comprising first, second, third and fourth sub-pixels corresponding to respective equivalent first, second, third and fourth sub-hologram pixels of the first, second, third and fourth subholog rams.
22. A method as claimed in claim 19, 20 or 21 wherein each pixel of the hologram comprises a one dimensional array of sub-pixels or a two-dimensional array of sub-pixels.
23. A method of determining a first hologram and a second hologram of respective first and second pictures for sequential display, the method comprising: determining first and second sub-holograms of respective first and second picture content of the first picture, wherein the first sub-hologram comprises a plurality of first sub-hologram pixels and the second sub-hologram comprises a plurality of second sub-hologram pixels; forming a first hologram of the first picture by spatially interlacing the first and second sub-holograms in accordance with a first interlacing scheme, wherein the hologram comprises a plurality of first hologram pixels each comprising a first sub-pixel and a second sub-pixel, wherein the first sub-pixel corresponds to a first sub-hologram pixel of the first sub-hologram and the second sub-pixel corresponds to an equivalent second sub-hologram pixel of the second sub-hologram; determining third and fourth sub-holograms of respective third and fourth picture content of the second picture, wherein the third sub-hologram comprises a plurality of third sub-hologram pixels and the fourth sub-hologram comprises a plurality of second sub-hologram pixels; forming a second hologram of the second picture by spatially interlacing the third arid fourth sub-holograms in accordance with a second interlacing scheme different from the first interlacing scheme, wherein the second hologram comprises a plurality of second hologram pixels each comprising a first sub-pixel and a second sub-pixel, wherein the first sub-pixel corresponds to a third sub-hologram pixel of the third sub-hologram and the second sub-pixel corresponds to an equivalent fourth sub-hologram pixel of the fourth sub-hologram, wherein the aspect ratio of the first and second pictures displayed is different.
24. A method of holographic projection comprising: determining a hologram according to a method as claimed in claim 19 to 23; displaying the hologram on a display device; illuminating the display device so as to form a holographic wavefront, wherein the holographic wavefront comprises a first portion comprising the first picture content and a second portion comprising the second picture content, and steering the first portion of the holographic wavefront in a first direction and steering the second portion of the holographic wavefront in a second direction, wherein the first direction is different from the second direction.