Patent number 8625182 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "We have previously described techniques for displaying an image holographically (see, for example, WO 2005/059660, WO 2006/134398, WO 2006/134404, WO 2007/031797, WO 2007/085874, and WO 2007/110668, all hereby incorporated by reference in their entirety). They have a range of applications including, for example, in hand held battery powered devices such as digital cameras, mobile phones, portable media players, laptop computers and the like.
"Broadly speaking in this technique an image is displayed by displaying a plurality of holograms each of which spatially overlaps in the replay field and each of which, when viewed individually, would appear relatively noisy because noise is added (by phase modulation) prior to a holographic transform of the image data. However when viewed in rapid succession the replay field images average together in the eye of a viewer to give the impression of a reduced (low) noise image. The noise in successive temporal subframes may either be pseudo-random (substantially independent) or the noise in a subframe may be dependent on the noise in one or more earlier subframes with the aim of at least partially cancelling this out, or a combination of both may be employed. More details of such OSPR (One Step Phase Retrieval)-type procedures and the associated ADOSPR (adaptive OSPR) are described later.
"The conventional ADOSPR approach functions by sequentially considering whole colour planes of the input image, which (subsequent to appropriate pre-processing) are embedded in a frame of suitable size (e.g. 1024.times.1024 pixels), from which a number of hologram subframes are produced. Each hologram subframe is the same resolution as the frame, and its computation necessitates a Fourier transform of that size. Due to the nature of the implementation of the fast Fourier transform operation in hardware, a large, fast memory is required to store the fully-complex intermediate data produced. The memory bandwidth required makes an off-chip implementation difficult, while the memory size required would make an on-chip implementation uneconomical.
"Additionally, while holograms produced in this manner may exhibit good performance in simulation, in reality the images produced will exhibit the phenomenon of inter-pixel interference, compromising the uniformity and readability of images. Such a phenomenon results from optical system aberrations resulting from non-flatnesses in the SLM surface and lenses: such aberrations cause the system's point spread function (PSF) to increase in spatial extent, with the result that spots from adjacent pixels now overlap. Because the spots are coherent, they interfere with each other, and because the associated target pixels have random phase, the interference consists of random regions of constructive and destructive interference which appear as blotchiness in the output. (This effect is referred to by some authors as 'speckle'. However, the effect has nothing whatsoever to do with the phenomenon of laser speckle, in the usual sense of the term, which results from interference of coherent light on the eye's retina, subsequent to scattering from a rough surface.) The approach described in the applicant's pending application GB 0706264.9 published as GB 2448132 (incorporated herein by reference) corrects for inter-pixel interference by taking the system's PSF into account, but if the PSF is not known exactly, as is the case when non-systematic non-flatnesses are present in the system, its efficacy is significantly reduced.
"A two-dimensional encoding method for hologram recording is described in JP09197947."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventor's summary information for this patent: "According to a first aspect of the invention there is provided a method of displaying an image holographically, the method comprising displaying a hologram on pixels of a spatial light modulator (SLM) and illuminating said SLM such that said image is displayed in pixels of a replay field (RPF) of said hologram, and wherein the method further comprises subdividing said replay field into a plurality of spatially interlaced regions, and displaying holograms for each of said interlaced regions of said replay field sequentially at different times such that in an observer's eye said interlaced regions integrate to give the impression of said image and such that interference between adjacent pixels of said replay field is reduced.
"Each said interlaced region may comprise a set of pixels of said replay field in which each pixel is surrounded by pixels of substantially zero light intensity. Said set of pixels may be arranged in a regular grid having spaces in between, said grids of different said interlaced regions being spatially displaced with respect to one another such that pixels of one said grid are located in said spaces of another said grid.
"Since multiple interlaced regions are formed to represent each whole input image instead of one replay field, the frame rate to the display needs to be increased by the number of interlaced regions to maintain an equivalent pixel uniformity. Accordingly, the method may further comprise calculating a hologram to display a said interlaced region of said replay field by calculating a subfield hologram to display pixels in said replay field at a reduced resolution and wherein said hologram displaying comprises displaying a plurality of substantial replicas of said subfield hologram simultaneously on said SLM. Said substantial replicas may comprise substantially the same data or inverted data as the subfield hologram. Said reduced resolution may be reduced in proportion to a number of said spatially interlaced regions employed and the plurality of substantial replicas of said subfield hologram may be in proportion to the number of said spatially interlaced regions employed.
"Four said interlaced regions may be employed each having a pixel spacing of twice a spacing of said pixels in said replay field. The interlaced regions may be defined by defining orthogonal axes (e.g. x and y axes) in the replay field and dividing said replay field such that a first interlaced region contains the pixels with even x and even y coordinates with surrounding zeros, a second interlaced region contains the image pixels with odd x and even y coordinates with surrounding zeros, a third interlaced region contains the image pixels with even x and odd y coordinates with surrounding zeros, and a fourth interlaced region contains the image pixels with odd x and odd y coordinates with surrounding zeros. Subfield holograms for said interlaced regions may be calculated by disregarding the zero pixels.
"Holograms for said interlaced regions may be displayed on said SLM with, respectively, phases to provide lateral displacement in said replay field of: substantially zero pixels, one pixel horizontally, one pixel vertically, and one pixel both horizontally and vertically. Said calculating of a said hologram may comprise applying phase shift to provide said lateral displacement.
"Multiple holograms may be used for each spatially interlaced region, for example using an OSPR-type procedure to generate multiple temporal subframes for each interlaced region.
"Optionally an OSPR procedure with feedback may be employed for improved results. However the technique is not restricted to holograms calculated using an OSPR-type procedure and, in general, any type of procedure may be employed to calculate one or more holograms displaying each interlaced region.
"According to another aspect of the invention, there is provided a holographic image display system, the system comprising: a substantially coherent light source; a display SLM to modulate light from said light source with a hologram; display optics to form an image from said hologram, said display optics having an intermediate image position at which an image of a replay field of said hologram is formed; a system for dividing said replay field into a plurality of spatially interlaced regions and for calculating hologram data for each of said spatially interlaced regions, wherein said SLM is configured to display holograms for each of said interlaced regions of said replay field sequentially at different times such that in an observer's eye said interlaced regions integrate to give the impression of said image and such that interference between adjacent pixels of said replay field is reduced.
"If there are four interlaced regions, previously 25 frames/sec video using 24 sub-frames per frame (by implementing the OSPR method), would require a display frame rate of 600 frames/sec, whereas now the required rate quadruples to 2400 frames/sec. Accordingly, the holographic image display system may be configured to calculate a subfield hologram to display pixels in said replay field at a reduced resolution with said hologram to be displayed comprising a plurality of substantial replicas of said subfield hologram. Said system may transmit said subfield holograms to said SLM and said SLM may be configured to construct said hologram to be displayed from said subfield holograms. In this way, the same bandwidth may be retained between the system and the SLM.
"According to another aspect of the invention, there is provided a display spatial light modulator (SLM) to modulate light from a light source with a hologram, said SLM comprising an input to receive a subfield hologram, and a system to construct said hologram from a plurality of substantial replicas of said received subfield holograms. In other words, the display may be configured to internally generate the hologram from the subfield holograms. Thus, although four times the number of sub-frames are used, each sub-frame is represented by data of only a quarter the size.
"The display SLM may comprise a select line to select a tile in said hologram for writing said subfield hologram and an invert pin which is adjustable to write a normal or inverted subfield hologram for each selected tile.
"According to another aspect of the invention, there is provided a data processing system for generating hologram data to be displayed on a holographic image display system, said data processing system comprising an input to receive an image of a replay field of a hologram; a processor configured to divide said replay field into a plurality of spatially interlaced regions and to calculate hologram data for each of said spatially interlaced regions; and an output to transmit said calculated hologram data to a spatial light modulator such that when said hologram data is displayed on said spatial light modulator sequentially at different times said interlaced regions integrate to give the impression of an image from said hologram and interference between adjacent pixels of said replay field is reduced.
"The invention further provides processor control code to implement the above-described systems and 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). As the skilled person will appreciate such code and/or data may be distributed between a plurality of coupled components in communication with one another.
"Embodiments of the above described methods and systems may be incorporated into a consumer electronics device, or into an advertising or signage system, or into a helmet mounted or head-up display or, for example, an aircraft or automobile."
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