# US 2021/0240135 A1 · Method for processing a hologram, and associated device, holographic display system and computer program > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0240135 A1 - Document ID: US20210240135A1 - Status: Published application - Kind: A1 - Application number: 17/050,214 - Filed: 2019-03-20 - Published: 2021-08-05 - Earliest claimed: 2018-04-23 - Assignees: Fondation B-Com - Applicants: Fondation B-Com - Inventors: Patrick GIOIA; Antonin GILLES - Web page: https://patentgrep.com/patent/US20210240135A1 ## CPC - G03H 1/2294: {Addressing the hologram to an active spatial light modulator} - G03H 1/0808: {Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific} - G06F 3/011: {Arrangements for interaction with the human body, e.g. for user immersion in virtual reality (blind teaching G09B21/00)} - G03H 2001/0825: {Numerical processing in hologram space, e.g. combination of the CGH [computer generated hologram] with a numerical optical element} - G03H 2001/2207: {Spatial filter, e.g. for suppressing higher diffraction orders} - G03H 2001/221: {Element having optical power, e.g. field lens} - G03H 2001/2284: {Superimposing the holobject with other visual information} - G03H: HOLOGRAPHIC PROCESSES OR APPARATUS (holograms, e.g. point holograms, used as ordinary optical elements G02B5/32; producing stereoscopic or other three-dimensional effects G02B30/00; diffraction-grating systems G02B27/44; systems using moiré fringes G02B27/60; optical logic elements G02F3/00; stereo-photography G03B35/00; photosensitive materials or processes for photographic purposes G03C; {stereo-photographic or similar processes G03C9/00}; apparatus for processing exposed photographic materials G03D; analogue computers performing mathematical operations with the aid of optical elements G06E3/00; authentication by radiation, of concealed information carried by holograms or diffraction gratings G06K19/16; holographic storage G11B7/0065, G11C13/04; {stereoscopic or other three dimensional effects in television systems H04N13/00}) - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract Disclosed is a method for processing an input hologram HE associated with an input plane, to obtain an output hologram displayable on a holographic screen placed in a plane called the output plane of a display system, viewable from a viewing plane of the system. The method includes: receiving the input hologram and a position of the input plane; obtaining a first transfer matrix representative of a propagation between the input plane and the viewing plane; obtaining a second transfer matrix representative of a propagation between the viewing plane and the output plane; calculating an overall matrix of transfer of a light field emitted by the input hologram, between the input plane and the output plane, by taking the product of the two matrices; and converting the input hologram into the output hologram by applying an operator dependent of the input hologram and on the screen. ## Claims ### Claim 1 A method for processing at least one input hologram associated with at least one input plane in a World reference frame, in order to obtain an output hologram that is capable of being displayed on a holographic screen placed in a so-called output plane of a reproduction system and viewable by an observer from a viewing plane of said system, said system comprising at least one optical element arranged between the viewing plane and the output plane, wherein the method comprises the following steps: obtaining the input hologram and a pose of the associated input plane in the World reference frame; obtaining at least one first ray transfer matrix, called extrinsic matrix, depending on the position and the direction of the observer and representative of a propagation in free space between the input plane and the viewing plane of the reproduction system; obtaining at least one second ray transfer matrix, called intrinsic matrix, representative of a propagation between the viewing plane and the output plane of the reproduction system through said at least one optical element; calculating at least one overall ray transfer matrix of a light field emitted by the input hologram between the input plane and the output plane of the reproduction system, by a product of at least two of said extrinsic and intrinsic matrices; and transforming a light field of the input hologram into a light field of the output hologram by application of at least one linear integral operator determined from the at least one calculated overall ray transfer matrix, as a function of input sizes and input resolutions of the input hologram and of output sizes and output resolutions of the holographic screen. ### Claim 2 (depends on 1) The method according to claim 1, wherein, when the holographic reproduction system comprises a module for non-linear processing of the light field of the input hologram, the step of obtaining at least one intrinsic matrix comprises obtaining a first intrinsic matrix representative of a propagation of the light field through at least one linear optical element located upstream from the non-linear processing module and obtaining a second intrinsic matrix representative of a propagation of the processed light field through at least one other linear optical element located downstream from the non-linear processing module, the step of calculating at least one overall ray transfer matrix comprises calculating a first overall matrix by a product of the at least one extrinsic matrix and the first intrinsic matrix and a second overall matrix from the second intrinsic matrix, the step of transforming the light field of the input hologram comprises the successive application of a first linear integral operator determined from the first overall matrix, an operator of the non-linear processing and a second linear integral operator determined from the second overall matrix. ### Claim 3 (depends on 2) The method for processing at least one input hologram according to claim 2, further comprising: a step of obtaining a pose of the observer in the World reference frame, and a step of evaluating a visibility of at least one input hologram by the observer, wherein the steps of obtaining a first ray transfer matrix, obtaining a second ray transfer matrix and transforming the input hologram are implemented when the at least one input hologram is evaluated as visible by the observer. ### Claim 4 (depends on 3) The method for processing at least one input hologram according to claim 3, further comprising: after detection of a change of the observer's pose in the World reference frame, updating at least one extrinsic matrix and the at least one overall ray transfer matrix as a function of said change, and transforming the input hologram by application of at least one updated linear integral operator determined from the at least one updated overall ray transfer matrix. ### Claim 5 (depends on 3) The processing method according to claim 3, wherein, if the output plane of the reproduction system is not parallel to the input plane of the input hologram, the method further comprises: obtaining a rotation matrix representing rotation of the light field between the input plane and a corrected plane, parallel to the viewing plane, and determining a non-linear operator of transformation of the light field by composition of a Fourier transform, a rotation frequency operator determined from said rotation matrix and an inverse Fourier transform, wherein the transforming step further comprises the application of said non-linear operator previously to said at least one linear integral operator. ### Claim 6 (depends on 5) The processing method according to claim 5, wherein the step of calculating a first overall matrix implements the product of the inverse Fourier transform, the extrinsic matrix and the first intrinsic matrix. ### Claim 7 (depends on 1) The processing method according to claim 1, wherein the light field of the input hologram comprises a plurality of samples depending on the input sizes and input resolutions, and wherein the step of transforming the light field of the input hologram by application of at least one linear integral operator comprises the application to said samples of a discrete Fourier transform and a sampling of the light field transformed as a function of the output resolutions and output sizes of the output hologram. ### Claim 8 (depends on 1) The method for processing at least one input hologram according to claim 1, wherein, when a plurality of input holograms is associated with a plurality of input planes forming the faces of a geometric solid, the method further comprises: selecting input planes corresponding to faces visible from the output plane, wherein obtaining at least one extrinsic matrix, and calculating at least one overall ray transfer matrix are repeated for each of the selected input planes, and the transforming transforms the fields of the selected input planes and sums the transformed fields to obtain the output hologram. ### Claim 9 (depends on 1) The processing method according to claim 1, wherein the at least one obtained extrinsic matrix and the at least one obtained intrinsic matrix are stored into a memory. ### Claim 10 A device for processing an input hologram associated with an input plane in a World reference frame, in order to obtain an output hologram that is capable of being displayed on a holographic screen placed in a plane, called output plane, of a reproduction system and viewable by an observer from a viewing plane of said system, said system comprising at least one optical element placed between the viewing plane and the output plane, wherein the device comprises a processor configured to: obtain the input hologram and a pose of the associated input plane in the World reference frame; obtain at least one first ray transfer matrix, called extrinsic matrix, depending on the position and the direction of the observer and representative of a propagation in free space between the input plane and the viewing plane of said system; obtain at least one second ray transfer matrix, called intrinsic matrix, representative of a propagation between the viewing plane and the output plane of the reproduction system through said at least one optical element; calculate at least one overall ray transfer matrix of a light field emitted by the input hologram between the input plane and the output plane of the reproduction system, by a product of at least two of said extrinsic and intrinsic matrices; transform a light field of the input hologram into a light field of the output hologram by application of at least one linear integral operator determined from the at least one calculated overall ray transfer matrix, discretized as a function of input sizes and input resolutions of the input hologram and resampled as a function of output sizes and output resolutions of the holographic screen. ### Claim 11 (depends on 10) A holographic reproduction system comprising a module for obtaining an input hologram associated with an input plane in a World reference frame, an output plane in which is placed a holographic screen intended to reproduce a hologram, called the output hologram, a viewing plane in which the output hologram is intended to be viewed by an observer, and at least one optical element, arranged between the viewing plane and the output plane, further comprising a device for processing the input hologram into the output hologram according to claim 10. ### Claim 12 (depends on 11) The holographic reproduction system according to claim 11, the holographic reproduction system being a head-mounted device type, capable of being worn on the head of the observer, wherein the viewing plane is placed in front of the observer's eyes, the output plane is placed out of a vision cone of the observer, the holographic reproduction system comprising: a module capable of receiving an input hologram having input sizes and input resolutions; a module capable of obtaining a pose of the observer in the World reference frame; the holographic screen in the output plane, having said output sizes and said output resolutions; an optical filtering system, of the 4F type, comprising a non-linear filtering module and two thin lenses; a field lens capable of enlarging a viewing field of the light field perceived by the observer on the viewing plane; and a beam splitter capable of redirecting the light field of the hologram in the direction of the viewing plane. ### Claim 13 (canceled) ### Claim 14 (depends on 1) A non-transitory recording medium, readable by a computer, on which is recorded a computer program comprising program code instruction that, when executed by the computer, perform the method according to claim 1. ### Claim 15 (depends on 1) The method for processing at least one input hologram according to claim 1, wherein the method comprises a step of obtaining a pose of the observer in the World reference frame, a step of evaluating a visibility of at least one input hologram by the observer, and wherein, the steps of obtaining a first ray transfer matrix, obtaining a second ray transfer matrix and transforming the input hologram are implemented when the at least one input hologram is evaluated as visible by the observer. ### Claim 16 (canceled) ### Claim 17 (canceled) ### Claim 18 (canceled) ### Claim 19 (canceled) ### Claim 20 (canceled) ### Claim 21 (depends on 2) A non-transitory recording medium, readable by a computer, on which is recorded a computer program comprising program code instruction that, when executed by the computer, perform the method according to claim 2.