[go: up one dir, main page]

WO2008001137A2 - Systèmes d'affichage d'images holographiques - Google Patents

Systèmes d'affichage d'images holographiques Download PDF

Info

Publication number
WO2008001137A2
WO2008001137A2 PCT/GB2007/050364 GB2007050364W WO2008001137A2 WO 2008001137 A2 WO2008001137 A2 WO 2008001137A2 GB 2007050364 W GB2007050364 W GB 2007050364W WO 2008001137 A2 WO2008001137 A2 WO 2008001137A2
Authority
WO
WIPO (PCT)
Prior art keywords
data
hologram
display device
phase mask
image
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB2007/050364
Other languages
English (en)
Other versions
WO2008001137A3 (fr
Inventor
Edward Buckley
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Light Blue Optics Ltd
Original Assignee
Light Blue Optics Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Light Blue Optics Ltd filed Critical Light Blue Optics Ltd
Publication of WO2008001137A2 publication Critical patent/WO2008001137A2/fr
Publication of WO2008001137A3 publication Critical patent/WO2008001137A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
    • G03H1/0841—Encoding method mapping the synthesized field into a restricted set of values representative of the modulator parameters, e.g. detour phase coding
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2294—Addressing the hologram to an active spatial light modulator
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/14—Picture signal circuitry for video frequency region
    • H04N5/21—Circuitry for suppressing or minimising disturbance, e.g. moiré or halo
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/0005—Adaptation of holography to specific applications
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/0005—Adaptation of holography to specific applications
    • G03H2001/0066—Adaptation of holography to specific applications for wavefront matching wherein the hologram is arranged to convert a predetermined wavefront into a comprehensive wave, e.g. associative memory
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/08—Synthesising holograms, i.e. holograms synthesized from objects or objects from holograms
    • G03H1/0841—Encoding method mapping the synthesized field into a restricted set of values representative of the modulator parameters, e.g. detour phase coding
    • G03H2001/085—Kinoform, i.e. phase only encoding wherein the computed field is processed into a distribution of phase differences
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2202—Reconstruction geometries or arrangements
    • G03H1/2205—Reconstruction geometries or arrangements using downstream optical component
    • G03H2001/2213—Diffusing screen revealing the real holobject, e.g. container filed with gel to reveal the 3D holobject
    • G03H2001/2215—Plane screen
    • G03H2001/2218—Plane screen being perpendicular to optical axis
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2202—Reconstruction geometries or arrangements
    • G03H2001/2236—Details of the viewing window
    • G03H2001/2239—Enlarging the viewing window
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/22—Processes or apparatus for obtaining an optical image from holograms
    • G03H1/2294—Addressing the hologram to an active spatial light modulator
    • G03H2001/2297—Addressing the hologram to an active spatial light modulator using frame sequential, e.g. for reducing speckle noise
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G03H2001/2605—Arrangement of the sub-holograms, e.g. partial overlapping
    • G03H2001/261—Arrangement of the sub-holograms, e.g. partial overlapping in optical contact
    • G03H2001/2615—Arrangement of the sub-holograms, e.g. partial overlapping in optical contact in physical contact, i.e. layered holograms
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G03H1/30—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique discrete holograms only
    • G03H2001/303—Interleaved sub-holograms, e.g. three RGB sub-holograms having interleaved pixels for reconstructing coloured holobject
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2223/00—Optical components
    • G03H2223/13—Phase mask
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2225/00—Active addressable light modulator
    • G03H2225/30—Modulation
    • G03H2225/32—Phase only
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2225/00—Active addressable light modulator
    • G03H2225/55—Having optical element registered to each pixel
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H2240/00—Hologram nature or properties
    • G03H2240/20—Details of physical variations exhibited in the hologram
    • G03H2240/40—Dynamic of the variations
    • G03H2240/41—Binary

Definitions

  • This invention relates to method, apparatus and computer program code for improved techniques for holographic image display systems.
  • the techniques may be employed with a spatial light modulator (SLM) on which is display a computer generated hologram which, in a replay field of the hologram, provides a two-dimensional display, for example, projected onto a screen, or a three-dimensional display.
  • SLM spatial light modulator
  • the viewing angle depends upon the diffraction of the light through the computer generated hologram by the pixels of the SLM; we have described how a phase mask may be provided over the SLM in order to increase the viewing angle of the projected display.
  • a similar technique may be employed to increase the resolution of the display in the replay field and/or to suppress the presence of a conjugate image in the replay field.
  • a holographic display comprising a pixellated hologram display device having a predetermined resolution and a pixellated phase mask arranged such that holograms displayed on the SLM are viewed through the phase mask, wherein the phase mask co-operates with the SLM such that the repeating pattern of holographic elements has a higher resolution than the predetermined resolution, hi embodiments the phase mask is pixellated and may have four phase levels, for example taking one as 0, providing respective phase shifts of [ ⁇ , ⁇ /2, at a replay wavelength.
  • phase mask is pseudo-random and the pixels of the hologram have phase values which combine with those of the phase mask in a given relative position of the phase mask with respect to the hologram to define a hologram to replay one of the multiple images. Since the phase mask pattern is pseudo-random the other encoded holograms are effectively scrambled so that only the selected hologram is replayed, and in this way single pixel shifts in the relative position of the hologram and phase mask may define different displayed images, for example "1", "2", "3", and so forth.
  • Figures Ia to Ic illustrate the above-described techniques, each of these figures showing, schematically, a portion of a spatial light modulator or other hologram display device (on the left) and a corresponding portion of a pixellated phase mask (on the right).
  • a spatial light modulator or other hologram display device on the left
  • a pixellated phase mask on the right.
  • phase mask pixels provide phase shifts of 0 and y whereas a conventional SLM is only able
  • phase shift values of ⁇ ⁇ and A enables phase shift values of ⁇ ⁇ and A to be accessed by the SLM by displaying an appropriate phase shift (0 or ⁇ ) under the appropriate phase mask pixel ( ⁇ /C ).
  • This allows a computer generated hologram to be displayed which has values other than just 0 and ⁇ , in particular ⁇ ⁇ y and ⁇ ⁇ A ⁇ , and this allows the display of holograms in which the conjugate image which would otherwise be present is suppressed. This is at the expense of SLM resolution in the hologram plane, and thus results in a 3dB (factor of 2) loss in signal-to-noise (SNR) ratio.
  • Figure Ib shows an arrangement which may be employed to increase resolution in the replay field, or equivalently, increase viewing angle
  • there are four phase mask pixels for each pixel of the SLM leading to a doubling of resolution (in each direction) in the replay field.
  • the (pseudo-random) phase mask allows holograms to be generated and displayed with effectively twice the resolution in the hologram plane.
  • the resolution of the image displayed in the replay field may be substantially the same as that of the phase mask.
  • the size of the pixels in the hologram display plane are effectively those of the phase mask, and because the pixel pitch is smaller (by a factor of 2) the viewing angle which depends upon the inverse of the pixel size in a given dimension, is increased. Doubling the viewing angle (or resolution) again results in a 3dB loss in SNR ( ⁇ 3.8dB total if the conjugate image is also suppressed).
  • Figure Ic illustrates, conceptually, how different relative positions of a random phase mask on a hologram display device can effectively decouple different sets of encoded images.
  • the hologram for each image is calculated taking account of the relative position of the pseudo-random phase mask and then the holograms are added together and displayed on the hologram display device.
  • each separately encoded image we refer to each separately encoded image as a "view”.
  • the resolution of the system depends upon the pixel pitch (which is typically the same for the hologram display device and phase mask in this application), and may be less than 50 ⁇ m, 10 ⁇ m or 1 ⁇ m.
  • the hologram display device may comprise any diffractive optical element, not limited to an SLM, in particular including a diffractive optical element in which the multiple views have been permanently encoded, for example by lithographic, in particular photolithographic, or other techniques.
  • a common thread running through all of the above-described techniques is the loss in SNR associated with the improvement in resolution/viewing angle/suppression of conjugate image/encoding of multiple views.
  • the inventors have observed that although a doubling of viewing angle or resolution results in a 3dB loss of SNR, no matter how much the viewing angle (or resolution) is further increased, the associated loss in SNR is limited to an apparent maximum of approximately 4.IdB. Nonetheless an improvement to the above technique is desirable, and the inventor has recognised how the effects of this loss in SNR may be mitigated or, in embodiments, substantially suppressed at least in a portion of the replay field.
  • a method of generating data for a pixellated hologram display device provided with a phase mask represented by phase mask data, for generating a holographic image comprising: inputting image data for said holographic image; performing a holographic transform on data derived from said image data to generate hologram data (m) for said hologram display device, using said phase mask data to adjust said hologram data for corresponding regions of said hologram display device and said phase mask; and quantising said hologram data (m) to generate quantised pixel data for display on said hologram display device with said phase mask to generate said holographic image; wherein said quantising is performed successively for pixels of said hologram display device; and wherein the method further comprises: determining an error in said data for a pixel of said hologram display device resulting from said quantising and using said error data to compensate said hologram data (m c ) prior to quantising said hologram data to generate quantised pixel data
  • Embodiments of the method may be used either to generate a two-dimensional replay image, for example for projection onto a screen, or to generate a three-dimensional holographic image.
  • Embodiments of the method compensate the hologram data for one or both of the effect of the phase mask and noise introduced by the quantising.
  • continuous data would be displayed on a spatial light modulator (SLM) but because of the demands of currently available SLMs the hologram data is quantised, as described above.
  • SLM spatial light modulator
  • the inventors have, however recognised that by, in effect, keeping track of the errors introduced by this quantisation, which in embodiments also include the effects of the phase mask, the error in one or more quantised pixels can be taken into account when quantising one or more other pixels of the display.
  • a real and an imaginary component of the complex hologram data may be selected for quantisation, although a linear combination of the real and imaginary components of this data may also be used.
  • the quantising is performed successively for pixels of the hologram display device (SLM). That is, in embodiments, one pixel is processed, and an error is determined, and this error is used in quantising the next pixel generally, although not necessarily, incrementally indexing rows and columns of the hologram display device.
  • SLM hologram display device
  • the method takes account of the error in quantising a pixel by compensating the hologram data using the error and then quantising.
  • the error for an individual pixel of the SLM may be determined by taking the difference between the hologram data (either before or after compensation) and the quantised data for the pixel.
  • the hologram data for a pixel is compensated based upon errors of a plurality of other pixels of the hologram display device which have previously been calculated.
  • a window is defined in the replay field, this defining, in effect, a window in the hologram field and previously determined errors over this window (in the later description indexed by r,s) are used for compensating the hologram data for an SLM pixel.
  • More particularly embodiments of the method employ error weighting data defining a window in the generated holographic image, and this is used to weight the error data previously calculated for one or more of the SLM pixels, as well as phase mask phase data for regions of the phase mask corresponding to the regions of the SLM for which previously calculated error data is available.
  • the error weighting data comprises data representing a space-frequency transform of the window, more particularly a Fourier transform of the window, that is, in embodiments, the weighting, which may be considered as an error diffusion kernel, in the hologram plane transforms to approximate the window in the replay field.
  • the Fourier or other space- frequency transform may be truncated to reduce the region of the hologram display device over which errors are summed.
  • the window may have a "soft" edge.
  • the window in the replay field may be made large, for example even close to the full size of the replay field. In this case, the noise is effectively moved to the small remaining portion of the replay field, resulting in a noisier remaining portion of the replay field. However in an equivalent signal-to-noise ratio within the window more processing power is needed to implement this. In many applications a relatively small window with relatively little or no SNR degradation may be employed, nonetheless obtaining a useful system since points within the window are still at high resolution/increased viewing angle, which is generally what an observer desires.
  • the phase mask is pixellated.
  • the hologram display device may comprise an SLM, for example a ferroelectric liquid crystal-based SLM.
  • SLM for example a ferroelectric liquid crystal-based SLM.
  • any type of pixellated microdisplay which is able to phase modulate light may be employed for the SLM, optionally in association with an appropriate driver chip if needed.
  • Preferred embodiments use an electrically addressable SLM.
  • Suitable SLMs include, but are not limited to, liquid crystal SLMs including LCOS (liquid crystal on silicon) and DLP (registered TM) (digital light processing) SLMs.
  • the phase mask may have different respective numbers of pixels, hi such a case one error value may be determined for each of the phase mask pixels (that is, there may be more than one error value for each pixel of the SLM), since the hologram data will generally have a resolution which corresponds to that of the replay field.
  • the regions of the phase mask selected by the window may comprise a sum of regions of the phase mask over the different views encoded in the hologram, more particularly over the different positions of the phase mask corresponding to each of the encoded views. It is convenient, in embodiments, to maintain an error matrix comprising pixel error data for each of the pixels in the hologram plane, for example one entry per phase mask pixel (in embodiments an integral multiple of entries for each pixel of the hologram display device).
  • the holographic transform comprises a Fourier transform, but a Fresnel transform may also be employed if a Fresnel phase component is included.
  • the hologram display device may comprise an SLM, however in metrology applications in particular the hologram display device may comprise a permanently encoded hologram, for example a diffractive optical element in which multiple (replay field) views are stored.
  • the holographic transform may be performed for each of the views to generate hologram data representing each of the stored images, and the error determining and compensating of the hologram data may use the hologram data representing this plurality of images (views), for example summing overviews as mentioned above.
  • embodiments of the above-described method may be incorporated into a technique in which an image is displayed using a plurality of spatially overlapping (and preferably substantially coincident) temporal subframes which integrate in an observer's eye to give the impression of a reduced noise image.
  • the invention provides a method of displaying a holographic image using a hologram display device provided with a phase mask, the method comprising: inputting image data for display in a replay field of phase holograms modulating said hologram display device; and calculating hologram data for display on said hologram display device to generate said holographic image in said replay field; and wherein said calculating of said hologram data further comprises compensating for a degradation of signal-to-noise ratio of said holographic image resulting from said phase mask by controlling a spatial distribution of errors in said replay field defined by said hologram data to move a proportion of said errors outside a window in said replay field to thereby increase a signal-to-noise ratio (SNR) a region of said displayed image inside said window as compared with an SNR of a region of said displayed image outside said window.
  • SNR signal-to-noise ratio
  • the controlling of the spatial distribution of errors uses an error diffusion technique, examples of which are described later.
  • a technique previously determined errors in a plurality of pixels over a region in the hologram plane, generally this region including a current pixel, provide error values which are taken into account when compensating the hologram data for the current pixel.
  • a diffusion kernel may define a weighting for the errors of the pixels over this region.
  • the error in a pixel in the hologram plane (which may be a pixel of the phase mask) may be considered to be spread out over the eiTor diffusion window.
  • the invention provides A method of displaying a holographic image using a hologram display device provided with a phase mask, the method comprising: inputting image data for display in a replay field of a phase hologram modulating said hologram display device; and calculating hologram data for display on said hologram display device to generate said holographic image in said replay field; wherein said phase mask is pixellated and has pixels of two different phases, one of said phases having a relative phase shift with respect to the other, at a replay wavelength of said holographic image, comprising an odd integer multiple of ⁇ / ⁇ ; and wherein said calculating is configured to suppress a conjugate image in said replay field whilst substantially maintaining the signal-to-noise ratio in a window of said replay field.
  • the invention also provides a hologram for use in conjunction with a phase mask, the hologram encoding a plurality of images selectable for replay by a relative spatial position of said hologram and said phase mask, and wherein a said replayed image has first and second spatial regions, a signal-to-noise ratio (SNR) of one of said first and second spatial regions being greater than an SNR of the other region.
  • SNR signal-to-noise ratio
  • the invention further provides apparatus comprising means to implement each of the methods according to aspects of the invention described above, and means to implement embodiments of these methods as described above.
  • the invention further provides a system for generating data for a pixellated hologram display device provided with a phase mask represented by phase mask data, for generating a holographic image
  • the system comprising: an input to input image data for said holographic image; means for performing a holographic transform on data derived from said image data to generate hologram data (m) for said hologram display device, using said phase mask data to adjust said hologram data for corresponding regions of said hologram display device and said phase mask; and means for quantising said hologram data (m) to generate quantised pixel data for display on said hologram display device with said phase mask to generate said holographic image, wherein said quantising is performed successively for pixels of said hologram display device; and wherein the system further comprises means for determining an error in said data for a pixel of said hologram display device resulting from said quantising and means for using said error data to compensate said hologram data (m c ) prior to quantising said hologram data to generate quantised
  • the invention further provides a system for displaying a holographic image using a hologram display device provided with a phase mask, the system comprising: an input to input image data for display in a replay field of phase holograms modulating said hologram display device; and means for calculating hologram data for display on said hologram display device to generate said holographic image in said replay field; and wherein said means for calculating hologram data further comprises means for compensating for a degradation of signal-to-noise ratio of said holographic image resulting from said phase mask by controlling a spatial distribution of errors in said replay field defined by said hologram data to move a proportion of said errors outside a window in said replay field to thereby increase a signal-to-noise ratio (SNR) a region of said displayed image inside said window as compared with an SNR of a region of said displayed image outside said window.
  • SNR signal-to-noise ratio
  • the invention further provides a system for displaying a holographic image using a hologram display device provided with a phase mask, the system comprising: an input to input image data for display in a replay field of phase holograms modulating said hologram display device; and means for calculating hologram data for display on said hologram display device to generate said holographic image in said replay field; and wherein said phase mask is pixellated and has pixels of two different phases, one of said phases having a relative phase shift with respect to the other, at a replay wavelength of said holographic image, comprising an odd integer multiple of ⁇ ⁇ . ; wherein said calculating means is configured to suppress a conjugate image in said replay field whilst substantially maintaining the signal-to-noise ratio in a window of said replay field.
  • the invention further provides a holographic image projection system, for example embodied in a helmet-mounted or head-up display, or in measuring apparatus, or in a consumer electronic device.
  • the invention further provides processor control code, for example for a Digital Signal Processor (DSP) to implement the above-described methods, in particular on a data carrier such as a disk, CD- or DVD-ROM, programmed memory such as read-only memory (Firmware), or on a data carrier such as an optical or electrical signal carrier.
  • Code (and/or data) to implement embodiments of the invention may comprise source, object or executable code in a conventional programming language (interpreted or compiled) such as C, or assembly code, code for setting up or controlling an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), or code for a hardware description language such as Verilog (Trade Mark) or VHDL (Very high speed integrated circuit Hardware Description Language).
  • DSP Digital Signal Processor
  • system may be implemented using dedicated hardware, or using a combination of software with dedicated hardware acceleration.
  • suitable hardware in PCT/GB2006/050152 filed on 13 June 2006, hereby incorporated by reference.
  • Figures Ia to Ic show examples of hologram-phase mask combinations
  • Figure 2 shows an example holographic projection system
  • Figure 3 shows a block diagram of a system in which an image frame is used to produce one or more holographic sub-frames
  • Figure 4 shows example energy distributions for an image before and after phase- modulation
  • Figure 5 illustrates a principle of operation of an SLM with a phase mask
  • Figures 7a and 7b show the effect of, respectively, hologram resolution and number of on-pixels, on replay field SNR, with and without a phase mask;
  • Figures 8a and 8b show replay fields produced by 256x256 holograms respectively without, and with, a 512x512 phase mask;
  • Figure 9 shows a graph of SNR variation with resolution of a [0; ⁇ ] phase mask employed in conjunction with 256 x 256-pixel holograms
  • Figures 10a and 10b show, respectively, simulated and measured performance of a 512x512-pixel hologram used with a 1024 x 1024-pixel phase mask to double the viewing angle;
  • Figure 11 shows a bar chart illustrating the effects of different types of phase mask on SNR
  • Figure 12 shows a graph of SNR variation with phase mask resolution for a replay field (RPF) with 500 on pixels and for a range of different hologram resolutions
  • Figure 13 shows an example results of implementation of a procedure according to the invention, showing replay fields of a hologram/phase mask combination with respectively a degraded SNR (SNR ⁇ 16), and an SNR improved over a window by an error diffusion technique (SNR - 43).
  • SNR ⁇ 16 degraded SNR
  • SNR - 43 error diffusion technique
  • Holographic display systems have a number of advantages for display of both 3D and 2D images.
  • a diffractive element such as a binary phase hologram
  • a binary phase hologram which imparts a purely real modulation on an incident wavefront, produces a conjugate image in the replay field thereby reducing the usable display area and optical efficiency by half.
  • it is straightforward to generate quaternary phase holograms which would solve tliis problem, such holograms cannot be displayed on binary ferroelectric SLM devices.
  • a second problem arises from the fact that the viewing angle ⁇ of a holographic display varies inversely with pixel size. We have described techniques to address this in PCT/GB2006/050158, but if small display pixels are used to achieve a wide field of view a large bandwidth may be needed to display a large image.
  • OSPR-type procedure In broad terms as One Step Phase Retrieval (OSPR), strictly speaking in some implementations it could be considered that more than one step is employed (as described for example in GB0518912.1 and GB0601481.5, incorporated by reference, where "noise" in one sub-frame is compensated in a subsequent sub-frame).
  • OSPR One Step Phase Retrieval
  • a method of displaying a holographically generated video image comprising plural video frames, the method comprising providing for each frame period a respective sequential plurality of holograms and displaying the holograms of the plural video frames for viewing the replay field thereof, whereby the noise variance of each frame is perceived as attenuated by averaging across the plurality of holograms.
  • the SLM is modulated with holographic data approximating a hologram of the image to be displayed.
  • this holographic data is chosen in a special way, the displayed image being made up of a plurality of temporal sub-frames, each generated by modulating the SLM with a respective sub-frame hologram.
  • These sub-frames are displayed successively and sufficiently fast that in the eye of a (human) observer the sub-frames (each of which have the spatial extent of the displayed image) are integrated together to create the desired image for display.
  • Each of the sub-frame holograms may itself be relatively noisy, for example as a result of quantising the holographic data into two (binary) or more phases, but temporal averaging amongst the sub-frames reduces the perceived level of noise. Embodiments of such a system can provide visually high quality displays even though each sub-frame, were it to be viewed separately, would appear relatively noisy.
  • a scheme such as this has the advantage of reduced computational requirements compared with schemes which attempt to accurately reproduce a displayed image using a single hologram, and also facilitate the use of a relatively inexpensive SLM.
  • an SLM will, in general, provide phase rather than amplitude modulation, for example a binary device providing relative phase shifts of zero and ⁇ , +1 and -1 for a normalised amplitude of unity).
  • a hardware accelerator for a holographic image display system the image display system being configured to generate a displayed image using a plurality of holographically generated temporal sub- frames, said temporal sub-frames being displayed sequentially in time such that they are perceived as a single reduced-noise image, each said sub-frame being generated holographically by modulation of a spatial light modulator with holographic data such that replay of a hologram defined by said holographic data defines a said sub-frame
  • the hardware accelerator comprising: an input buffer to store image data defining said displayed image; an output buffer to store holographic data for a said sub-frame; at least one hardware data processing module coupled to said input data buffer and to said output data buffer to process said image data to generate said holographic data for a said sub-frame; and a controller coupled to said at least one hardware data processing module to control said at least one data processing module to provide holographic data for a plurality of said sub-frames corresponding
  • the hardware data processing module comprises a phase modulator coupled to the input data buffer and having a phase modulation data input to modulate phases of pixels of the image in response to an input which preferably comprises at least partially random phase data.
  • This data may be generated on the fly or provided from a non-volatile data store.
  • the phase modulator preferably includes at least one multiplier to multiply pixel data from the input data buffer by input phase modulation data. In a simple embodiment the multiplier simply changes a sign of the input data.
  • An output of the phase modulator is provided to a space-frequency transformation module such as a Fourier transform or inverse Fourier transform module.
  • a space-frequency transformation module such as a Fourier transform or inverse Fourier transform module.
  • these two operations are substantially equivalent, effectively differing only by a scale factor.
  • other space-frequency transformations may be employed (generally frequency referring to spatial frequency data derived from spatial position or pixel image data).
  • the space-frequency transformation module comprises a one-dimensional Fourier transformation module with feedback to perform a two-dimensional Fourier transform of the (spatial distribution of the) phase modulated image data to output holographic sub-frame data. This simplifies the hardware and enables processing of, for example, first rows then columns (or vice versa).
  • the hardware also includes a quantiser coupled to the output of the transformation module to quantise the holographic sub-frame data to provide holographic data for a sub-frame for the output buffer.
  • the quantiser may quantise into two, four or more (phase) levels.
  • the quantiser is configured to quantise real and imaginary components of the holographic sub-frame data to generate a pair of sub-frames for the output buffer.
  • the output of the space-frequency transformation module comprises a plurality of data points over the complex plane and this may be thresholded (quantised) at a point on the real axis (say zero) to split the complex plane into two halves and hence generate a first set of binary quantised data, and then quantised at a point on the imaginary axis, say Oj, to divide the complex plane into a further two regions (complex component greater than 0, complex component less than 0). Since the greater the number of sub-frames the less the overall noise this provides further benefits.
  • the input and output buffers comprise dual-ported memory.
  • the holographic image display system comprises a video image display system and the displayed image comprises a video frame.
  • the hardware may implement a version or variant of the algorithm given below.
  • Statistical analysis of the algorithm has shown that such sets of holograms form replay fields that exhibit mutually independent additive noise.
  • Step 1 forms N targets G ⁇ equal to the amplitude of the supplied intensity target I x ⁇ , but with independent identically-distributed (i.i.t.X uniformly-random phase.
  • Step 2 computes the N corresponding full complex Fourier transform holograms g ⁇ " ⁇ ⁇ .
  • Steps 3 and 4 compute the real part and imaginary part of the holograms, respectively. Binarisation of each of the real and imaginary parts of the holograms is then performed in step 5: thresholding around the median of m ⁇ ensures equal numbers of -1 and 1 points are present in the holograms, achieving DC balance (by definition) and also minimal reconstruction error.
  • the quantisation may be performed in a number of ways; in an embodiment, the median value of m ⁇ is assumed to be zero. This assumption can be shown to be valid and the effects of making this assumption are minimal with regard to perceived image quality. Further details can be found in the applicant's earlier application (ibid), to which reference may be made.
  • FIG. 2 shows an example holographic projection system, further details of which may be found in PCT/GB2006/050158 to which reference may be made.
  • a laser diode 20 (for example, at 532nm), provides substantially collimated light 22 to a spatial light modulator 24 such as a pixellated liquid crystal modulator.
  • the SLM 24 phase modulates light 22 with a hologram and the phase modulated light is provided to a demagnifying optical system 26 which projects a 2D (in this example) image onto screen 14.
  • the system includes a phase mask 25, as described further later.
  • the relative positions of the phase mask and hologram (here an SLM) are moveable, as indicated by the arrow.
  • optical system 26 comprises a pair of lenses 28, 30 with respective focal lengths f ⁇ , f 2 , fi ⁇ f 2 , spaced apart at distance fi+f 2 .
  • Optical system 26 (which is not essential) increases the size of the projected holographic image by diverging the light forming the displayed image, as shown.
  • One or more of the lenses may be encoded in the hologram, as described in UK patent application GB 0606123.8 filed on 28 March 2006.
  • a filter may be included to filter out unwanted parts of the displayed image, for example a zero order undiffracted spot.
  • the demagnifying optics may be omitted and the holographic image viewed by eye.
  • lens 30 (L4) and screen 14 may be replaced by, for example, a digital camera.
  • a digital signal processor 100 has an input 102 to receive image data from the consumer electronic device defining the image to be displayed.
  • the DSP 100 implements a procedure, for example along the lines described above, to generate phase hologram data, in an OSPR-based display device data for a plurality of holographic sub-frames. This data is provided from an output 104 of the DSP 100 to the SLM 24, optionally via a driver integrated circuit if needed.
  • the DSP 100 drives SLM 24 to project a plurality of phase hologram sub-frames which combine to give the impression of displayed image 14 in the replay field (RPF).
  • the DSP 100 may comprise dedicated hardware and/or Flash or other read-only memory storing processor control code to implement an OSPR-type hologram generation procedure.
  • Figure 3 shows a block diagram of a system in which an image frame, I xy , is used to produce one or more holographic sub-frames by means of a set of operations comprising one or more of: a phase modulation stage, a space-frequency transformation stage and a quantisation stage.
  • the purpose of the phase-modulation block is to redistribute the energy of the input frame in the spatial-frequency domain, such that improvements in final image quality are obtained after performing later operations; the phase-modulation data may comprise a pseudo-random sequence.
  • the quantisation block of Figure 3 has the purpose of taking complex hologram data, which is produced as the output of the preceding space-frequency transform block, and mapping it to a restricted set of values, which correspond to actual phase modulation levels that can be achieved on a target SLM.
  • the number of quantisation levels may be set at two, for example for an SLM producing phase retardations of 0 or ⁇ at each pixel.
  • Figure 3 shows use of the real part of the holographic sub-frame data for quantisation but alternatively real and imaginary components of the holographic sub-frame data may be quantised to generate a pair of sub-frames, each with two phase-retardation levels (for discretely pixellated fields these are uncorrelated).
  • Figure 4 shows an example of how the energy of a sample image is distributed before and after a phase-modulation stage in which a random phase distribution is used. It can be seen that modulating an image by such a phase distribution has the effect of redistributing the energy more evenly throughout the spatial-frequency domain.
  • the conjugate image manifest in the RPF, caused by the purely real [0; ⁇ ] modulation imparted by a binary phase ferro-electric SLM, can be suppressed by using a spatially random binary pixellated phase mask.
  • the principle of operation is shown in Figure 5, Figure 5a showing a hologram pattern h uv , Figure 5b showing a phase mask pattern P m , and Figure 5 c the effective pattern P m ,h uv .
  • the phase mask P u ⁇ which has a pixellated pattern of the same pitch as the hologram pixels, is placed in close contact and aligned to the hologram pattern h uv displayed on an SLM.
  • phase mask pixels impart phase modulation in the set [0, ⁇ /2] radians
  • SLM pixels retard the incident light by [0, ⁇ ] radians
  • the effective phase pattern of Figure 5(c) results, with the pixels imparting a net modulation in the set [0, ⁇ 12, ⁇ , 3 ⁇ I7 ⁇ . This provides an extra degree of freedom for suppressing the conjugate image, despite the fact that the SLM itself is binary.
  • FIG. 6 An example simulated result is shown in Figure 6.
  • viewing angle ⁇ and pixel size ⁇ means that to achieve a display with a wide field of view, a hologram with small feature size is helpful. More specifically, the viewing angle ⁇ of a hologram illuminated by coherent light of wavelength J varies inversely with pixel size according to the equation
  • FLC ferroelectric liquid crystal
  • phase mask technique is extended to demonstrate that a binary [0; ⁇ ] phase mask P rs of resolution Mx M, identical in physical size to that of the P x P-pixel SLM but of greater resolution, can be used to increase the viewing angle of the overall system by a factor of approximately P/M.
  • This technique increases the number of addressable points in the RPF from P x P to Mx M, at the cost of introducing additional RPF noise, which reduces the RPF SNR by 3 dB.
  • An OSPR-type algorithm exploiting the human perception of statistical image noise parameters encountered in holographically-generated images can generate images of substantially improved quality.
  • An example algorithm begins with the specification of a P x P-pixel target intensity image T xy , returning a set of N individual P x P-pixel holograms H["J .
  • a modified version of the OSPR algorithm can be used to account for the presence of a phase mask, and is detailed below.
  • the algorithm accounts for the presence of the super- resolution Mx M-pixel phase mask P uv to generate 2N distinct P x P-pixel holograms H ⁇ .
  • P is an integer multiple of M.
  • This example algorithm also includes real and imaginary components to generate two holograms per Fourier transform.
  • Step 1 of algorithm 1.1 forms N targets equal to the amplitude of the supplied intensity target Txy, but with i.i.d. uniformly-random phase (the image has x, y resolution of Mx M).
  • Step 2 computes the inverse Fourier transform, taking into account the presence of the phase mask P ⁇ m to produce continuous complex holograms of size Mx M.
  • Step 3 averages the resultant complex hologram over blocks of size F x F to produce s J ⁇ , a set of TV averaged complex hologram fields of the (smaller) required (SLM) size P x P (u,v run over the P x P SLM range).
  • Two independent holograms are then generated in steps 4 and 5 from each single complex hologram field s ["J . Binarisation of these holograms is then performed in step 6, as per previous implementations of the OSPR algorithm. Thresholding around the median of M ( "J helps to ensure equal numbers of
  • FIG. 8 shows the simulated RPFs - which both have the same physical dimensions. From Figure 8(a), it can be seen that viewing angle is limited by the presence of side- orders in the RPF. The area inside the rectangle is the first order diffraction pattern determined by the pixel pitch of the hologram; outside the rectangle are the repeated higher orders, which cannot be controlled by the hologram alone.
  • the phase mask is employed as shown in Figure 8(b), the addressable RPF area, and hence the viewing angle, is doubled in each dimension.
  • phase diffractive optical elements were made to simulate the operation of a SLM and phase mask.
  • the pixel size was 40 ⁇ m, so that the active area was approximately 20 mm.
  • the spatially random phase mask DOE was designed to contain 1024 x 1024 pixels, each of size 20 ⁇ m, resulting in a viewing angle increase of F — 2. Both DOEs were made by e-beam etching of a 1.5 mm-thick fused silica substrate of refractive index 1.46, with a step height of 0:65 ⁇ m to optimise operation at a wavelength of 532 nm. The phase mask and hologram DOEs were placed in close contact, and carefully aligned using custom optical mounts so that the pixels were accurately registered.
  • the elements were illuminated using a 10 mW green laser coupled into a single mode fibre, and since the diffraction angle from the hologram and phase mask combination was small, an objective lens of focal length 100 mm was used to image the resultant RPF onto a CMOS sensor array of active area 25 mm x 25 mm.
  • the simulated and captured RPFs are shown in Figures 10(a) and (b) respectively; the "AJC+EB” image corresponds to the first-order diffraction pattern that would occur from a hologram with pixel size 40 ⁇ m., whilst the "EXTRA" pattern is due to the increased viewing angle provided by the 20 ⁇ m pixels of the phase mask. If a 512 x 512-pixel hologram had been used alone, the space occupied by the "EXTRA" image would have contained the overlapping secondary orders of Figure 8(a).
  • Removal of the conjugate image can be accomplished with a [0; ⁇ /2] random phase mask and the viewing angle can be increased through use of another random super- resolution phase mask, albeit with pixels imparting phase modulation in the set [0; ⁇ ]. Utilization of each mask individually incurs an SNR penalty of approximately 3 dB.
  • a reasonable conjecture is that the use of both a [0; ⁇ /2] mask and a [0; ⁇ ] mask in an optical system would facilitate simultaneous removal of the conjugate image and an increase in viewing angle. Since the optical system is linear, the total phase modulation imparted on the incident wave by both masks together is equal to the sum of the phase shifts imparted by each mask.
  • Figure 11 illustrates that this general result appears to hold independent of resolution or "on" pixel count.
  • the Figure shows SNR degradation caused by use of different types of phase mask: Case 1 - No phase mask, Case 2 - Conjugate image removal using a [0, ⁇ /2] phase mask, Case 3 - [0, ⁇ ] super-resolution phase mask used to double the viewing angle, Case 4 - Conjugate Image removal and viewing angle doubling using a quarternary [0, ⁇ 12, ⁇ , 3 ⁇ /2] phase mask.
  • the [0; ⁇ ] mask further increases in viewing angle can be achieved at very little expense in terms of RPF SNR degradation.
  • This is shown in Figure 12 for a variety of hologram and phase mask resolutions.
  • Manufacturing random pixellated phase masks generally proceeds by first producing a premask as a binary amplitude pattern, either printed on plastic or as a chrome- on-glass structure. UV-sensitive photoresist is then spun onto glass and the required phase pattern is produced photolithographically using the premask, exposing the photoresist for the necessary duration to form the required phase steps.
  • production of four-phase masks using this technique is complicated.
  • Dektak scanning surface profilimeter
  • the techniques we describe are not limited to holographic display systems but may also be used in sensing and metrology systems. It is helpful, therefore, to explain how the multiple holograms are encoded (and replayed) in such a system, resulting in a loss in SNR which can be addressed using our techniques.
  • h xy comprises the (complex) sum of holograms h ⁇ y k for the individual views (which may afterwards be quantised, in particular binarised).
  • the phase mask (like the hologram) has pixels with relative phase retardations of either 0 or ⁇ .
  • p[ y k only one hologram U y k of the composite h x ⁇ will provide a image (view), the others merely contributing noise.
  • Different replayed views may be encoded for different relative displacements of the (composite) hologram and phase mask, either for human or for machine vision or, more simply, for detection by a light sensor (depending upon the image encoded in the view, which may be complex, for example a numeral, or simple, for example a light or dark region or spot).
  • the conjugate image may be suppressed by employing a phase mask with pixels which imparted phase modulation in the set [0; ⁇ /2], aX the expense of a 3 dB drop in RPF SNR.
  • Viewing angle may be increased using a super-resolution fixed pixellated phase mask which imparts [0; ⁇ ] modulation, but whilst doubling the viewing angle incurred a 3dB drop in contrast, the viewing angle can be increased arbitrarily with only a small further decrease in contrast: For example an increase in viewing angle of 12 times results in an SNR decrease of just 4.1 dB. Further these improvements can be combined into one quaternary phase mask, providing increased viewing angle and conjugate image suppression. OSPR-type algorithms may be used to reduce a perceived noise level. However there exists a need for improved techniques.
  • phase mask there are two possible ways in the RPF SNR can be degraded. If a [0, ⁇ /2] phase mask is used in conjunction with a [0, ⁇ ] hologram, then the energy contained in the conjugate image is spread throughout the RPF - which, although enabling conjugate image removal, results in a 3 dB SNR decrease. Alternatively, increasing the number of views encoded in a [0, ⁇ ] hologram employed in combination with a [0, ⁇ ] phase mask combination results in a commensurate RPF SNR degradation. This can be a particular disadvantage for an automatic measurement system needing a large number of views, each of which requires a high probability of detection.
  • the above procedure comprises a modification of the algorithm described above for the generation of a PxP pixel hologram in the presence of a phase mask.
  • the version of the procedure is for a PxP pixel phase mask; we will describe later how this is modified to take account of a phase mask which provides an increased resolution (or viewing angle).
  • Steps 1, 2 and 3 of the procedure correspond to the previously described steps, 1, 2 and 4.
  • ED error diffusion
  • the diffusion kernel is calculated by calculating the Fourier transform (in 2 or more dimensions) of the window function, and then truncating the potentially infinite Fourier series, for example taking a set of components around zero-spatial frequency.
  • the window function may conveniently comprise a function defined over the area of the replay field, with a value of "1" over the window and a value of "0" elsewhere.
  • e uv comprises a matrix which, in embodiments, represents errors introduced by the quantisation (binarisation) process, more particularly the error in binarising one or more previous pixels [u,v].
  • the diffusion kernel d rs represents a weighting of these errors over a window of dimension [r,s], preferably centred on the currently processed pixel [u,v].
  • the error matrix e uv may initially be set to zero and will gradually accumulate error data as more pixels are processed.
  • An error for a currently processed pixel is calculated at step 5 and may be determined in a number of different ways. For example a Minimum Average Error (MAE) calculation may be employed to determine the difference between a binarised pixel value h uv and a real (and/or imaginary) part of the complex hologram data; or in an error diffusion (ED) procedure the difference may be between the binarised pixel value and a changed (c) value determined in error diffusion step 4.
  • the binarisation step 6 of the procedure may be similar to that previously described.
  • the error diffusion step 4 diffuses errors over a window of size [r,s] determining a changed or adjusted value for the real and/or imaginary component of the complex hologram data taking into account these diffused errors, that is taking into account the binarisation which is employed (at a later step) for displaying the hologram on an SLM or, in embodiments, for encoding the hologram into an non-volatile medium, for example for sensing or metrology applications.
  • the error broadly speaking comprises a difference between a quantised (binarised) pixel and the unquantised, continuous value of the pixel. The region over which the error diffusion is applied depends upon the size of the window, a larger window using a larger diffusion kernel.
  • the size of the diffusion kernel determines the "quality" of the diffusion process, but a larger kernel requires greater computation. Similarly a greater improvement in signal-to-noise ratio (SNR) can be achieved by using a larger diffusion kernel (or a less truncated Fourier series).
  • SNR signal-to-noise ratio
  • the size of the window can approach the size of the replay field but it then becomes harder to remove noise from the window; in practice a smaller window can nonetheless provide useful benefits because the points in the (replay field) window are still effectively at higher resolution, albeit the image area is reduced.
  • Step 4 of the procedure as well as summing the product of the error diffusion kernel and error matrix over [r,s], taking account of (multiplying by) the phase mask, there is an additional sum over all views of the phase mask over all views (that is over each of the relative positions of the phase mask and composite hologram defining a view):
  • the version of the procedure described above is for a pixel phase mask having substantially the same resolution as the hologram.
  • the procedure can be modified to address the case where the phase mask has a higher resolution than the hologram, broadly speaking by introducing step 3 of the procedure described above for the generation of holograms in the presence of a higher resolution phase mask (this step effectively averaging over a block having a size equal to a size of an SLM pixel).
  • this additional step is included after the error diffusion step, that is between steps and 4 and 5 of the above procedure.
  • the errors are calculated for the phase mask pixels and thus, at step 5, there will in general be more than one phase mask pixel for each SLM pixel and thus more than one error value for each SLM pixel (and thus u and v run over different ranges for the hologram h (which refers to the SLM) and for m). For example, there may be four phase mask pixels for each SLM pixel.
  • a binary [0, ⁇ ] hologram and [0, ⁇ ] phase mask combination containing several views was designed using the previously described procedure, that is an OSPR algorithm [4.2] that was modified for presence of a phase mask. Reconstruction of one view is shown in Figure 13 a.
  • the resultant SNR was approximately 16, both due to quantisation of the hologram to binary phase and the increased number of views.
  • Figure 136 the SNR has been improved in a local region of the RPF by the use of a combined OSPR/ED procedure as described above.
  • the technique can be used for ameliorating the SNR degradation caused by conjugate image removal and/or an increased number of views in a hologram/phase mask combination.
  • Applications for the above described techniques include, but are not limited to, the following: optical metrology systems; optical sensors; mobile phone; PDA; laptop; digital camera; digital video camera; games console; in-car cinema; personal navigation systems (in-car or wristwatch GPS); head-up/helmet-mounted displays for automobiles or aviation; watch; personal media player (e.g. MP3 player, personal video player); dashboard mounted display; laser light show box; personal video projector (a "video iPod (RTM)"); advertising and signage systems; computer (including desktop); and a remote control unit.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Holo Graphy (AREA)

Abstract

Cette invention concerne un procédé, un appareil et un code de programme informatique s'appliquant à des techniques améliorées de systèmes d'affichage d'images holographiques. L'invention concerne également un procédé de génération de données destinées à un dispositif d'affichage d'hologramme pixellisé pourvu d'un masque de phase représenté par des données de masque de phase, et de génération d'une image holographique. Le procédé consiste à : introduire des données de l'image holographique; effectuer une transformée holographique sur des données extraites des données d'images de façon à générer des données d'hologramme (m) pour le dispositif d'affichage d'hologramme, utiliser ces données de masque de phase pour ajuster les données d'hologramme des régions correspondantes du dispositif d'affichage d'hologramme et du masque de phase, et quantifier les données d'hologramme (m) pour générer des données de pixel quantifiées destinées être affichées sur le dispositif d'affichage d'hologramme avec le masque de phase afin de générer l'image holographique, la quantification étant effectuée successivement pour des pixels du dispositif d'affichage d'hologramme. Le procédé consiste également à déterminer une erreur dans les données d'un pixel du dispositif d'affichage d'hologramme, ces erreurs résultants de la quantification, et utiliser les données d'erreur pour compenser les données d'hologrammes (mc) avant de quantifier les données d'hologramme pour générer des données de pixel quantifiées pour un autre pixel du dispositif d'affichage d'hologramme.
PCT/GB2007/050364 2006-06-29 2007-06-27 Systèmes d'affichage d'images holographiques Ceased WO2008001137A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0612882A GB2438472B (en) 2006-06-29 2006-06-29 Holographic image display systems
GB0612882.1 2006-06-29

Publications (2)

Publication Number Publication Date
WO2008001137A2 true WO2008001137A2 (fr) 2008-01-03
WO2008001137A3 WO2008001137A3 (fr) 2008-02-28

Family

ID=36888277

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2007/050364 Ceased WO2008001137A2 (fr) 2006-06-29 2007-06-27 Systèmes d'affichage d'images holographiques

Country Status (2)

Country Link
GB (1) GB2438472B (fr)
WO (1) WO2008001137A2 (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008000589A1 (de) * 2008-03-11 2009-10-15 Seereal Technologies S.A. Verfahren zur Kodierung von computergenerierten Hologrammen in pixelierten Lichtmodulatoren
WO2010125367A1 (fr) 2009-04-29 2010-11-04 Light Blue Optics Ltd Dispositif d'affichage holographique
CN102323733A (zh) * 2011-07-28 2012-01-18 浙江师范大学 基于分区计算的数字全息图零级斑和共轭像的消除方法
WO2014209268A1 (fr) * 2013-06-24 2014-12-31 Intel Corporation Modèles d'éclairage structurés permettant la détection et la correction d'erreurs
WO2017155730A1 (fr) * 2016-03-07 2017-09-14 Microsoft Technology Licensing, Llc Imagerie à travers des milieux hautement diffusifs avec formation de front d'onde
WO2018050840A1 (fr) * 2016-09-16 2018-03-22 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Système optique permettant de produire des répartitions de champ lumineux et procédé permettant de faire fonctionner un système optique
KR20200078718A (ko) * 2011-04-19 2020-07-01 돌비 레버러토리즈 라이쎈싱 코오포레이션 고휘도 투사형 디스플레이들 및 관련 방법들
CN118644406A (zh) * 2024-08-14 2024-09-13 浙江大学 全息图像多目标自动融合方法、装置、设备、介质及产品

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2461294B (en) * 2008-06-26 2011-04-06 Light Blue Optics Ltd Holographic image display systems
CN106706638B (zh) * 2016-12-14 2023-06-09 北京理工大学 基于暗条纹逻辑判断的相位成像设备及方法
GB2551870B (en) * 2017-04-07 2020-04-01 Dualitas Ltd Holographic projector

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB0329014D0 (en) * 2003-12-15 2004-01-14 Univ Cambridge Tech Hologram viewing device
GB0329012D0 (en) * 2003-12-15 2004-01-14 Univ Cambridge Tech Hologram viewing device
JP2005259221A (ja) * 2004-03-10 2005-09-22 Pioneer Electronic Corp ホログラム再生装置、及び再生方法
GB2434706B (en) * 2006-11-15 2008-12-24 Light Blue Optics Ltd Data processing apparatus

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008000589B4 (de) * 2008-03-11 2018-02-01 Seereal Technologies S.A. Verfahren zur Kodierung von computergenerierten Hologrammen in pixelierten Lichtmodulatoren
DE102008000589A1 (de) * 2008-03-11 2009-10-15 Seereal Technologies S.A. Verfahren zur Kodierung von computergenerierten Hologrammen in pixelierten Lichtmodulatoren
WO2010125367A1 (fr) 2009-04-29 2010-11-04 Light Blue Optics Ltd Dispositif d'affichage holographique
KR20200078718A (ko) * 2011-04-19 2020-07-01 돌비 레버러토리즈 라이쎈싱 코오포레이션 고휘도 투사형 디스플레이들 및 관련 방법들
KR102296377B1 (ko) 2011-04-19 2021-09-02 돌비 레버러토리즈 라이쎈싱 코오포레이션 고휘도 투사형 디스플레이들 및 관련 방법들
CN102323733A (zh) * 2011-07-28 2012-01-18 浙江师范大学 基于分区计算的数字全息图零级斑和共轭像的消除方法
US9270386B2 (en) 2013-06-24 2016-02-23 Intel Corporation Error detecting and correcting structured light patterns
WO2014209268A1 (fr) * 2013-06-24 2014-12-31 Intel Corporation Modèles d'éclairage structurés permettant la détection et la correction d'erreurs
WO2017155730A1 (fr) * 2016-03-07 2017-09-14 Microsoft Technology Licensing, Llc Imagerie à travers des milieux hautement diffusifs avec formation de front d'onde
US10162086B2 (en) 2016-03-07 2018-12-25 Microsoft Technology Licensing, Llc Imaging through highly diffusive media with wavefront shaping
WO2018050840A1 (fr) * 2016-09-16 2018-03-22 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Système optique permettant de produire des répartitions de champ lumineux et procédé permettant de faire fonctionner un système optique
US11668961B2 (en) 2016-09-16 2023-06-06 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Optical arrangement for generating light field distributions and method for operating an optical arrangement
CN118644406A (zh) * 2024-08-14 2024-09-13 浙江大学 全息图像多目标自动融合方法、装置、设备、介质及产品

Also Published As

Publication number Publication date
WO2008001137A3 (fr) 2008-02-28
GB2438472A (en) 2007-11-28
GB0612882D0 (en) 2006-08-09
GB2438472B (en) 2008-07-23

Similar Documents

Publication Publication Date Title
WO2008001137A2 (fr) Systèmes d'affichage d'images holographiques
US20110002019A1 (en) Holographic image display systems
US20090002787A1 (en) Holographic Display Devices
US8432590B2 (en) Holographic image display system
US20090207466A1 (en) Holographic display devices
US20090219591A1 (en) Methods and apparatus for displaying colour images using holograms
US20100165429A1 (en) Optical systems
US20100277566A1 (en) Holographic image display systems
US11231683B2 (en) Pixel mapping onto a display device for holographic projection
WO2008075096A1 (fr) Systèmes d'affichage holographique d'images
CN112415880A (zh) 全息投影
CN112558452A (zh) 全息投影
WO2012069811A2 (fr) Systèmes holographiques
GB2434706A (en) Concurrent hologram image data generation and hologram data quantization
GB2587400A (en) Hologram display using a liquid crystal display device
GB2441447A (en) Holographic display with improved signal-to-noise ratio
GB2485607A (en) Diffractive image display having hexagonal or diamond shaped phase modulating pixels
US20200326464A1 (en) Diffuser Assembly
US12242228B2 (en) Systems and methods for holographic projection
WO2025168807A1 (fr) Circuit de commande numérique pour lcos
HK40023013A (en) Pixel mapping onto a display device for holographic projection
EP4252080A1 (fr) Dispositif et procédé d'affichage

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 07733785

Country of ref document: EP

Kind code of ref document: A2

NENP Non-entry into the national phase

Ref country code: DE

NENP Non-entry into the national phase

Ref country code: RU

122 Ep: pct application non-entry in european phase

Ref document number: 07733785

Country of ref document: EP

Kind code of ref document: A2