EP3350656A1 - Procédé de traitement d'une image holographique - Google Patents
Procédé de traitement d'une image holographiqueInfo
- Publication number
- EP3350656A1 EP3350656A1 EP16775788.9A EP16775788A EP3350656A1 EP 3350656 A1 EP3350656 A1 EP 3350656A1 EP 16775788 A EP16775788 A EP 16775788A EP 3350656 A1 EP3350656 A1 EP 3350656A1
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- Prior art keywords
- hologram
- wavelet
- holographic
- sub
- observer
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Classifications
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- 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
- G03H1/0808—Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific
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- 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
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- 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
- G03H1/0808—Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific
- G03H2001/0825—Numerical processing in hologram space, e.g. combination of the CGH [computer generated hologram] with a numerical optical element
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- 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
- G03H1/0808—Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific
- G03H2001/0833—Look up table
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H2226/00—Electro-optic or electronic components relating to digital holography
- G03H2226/04—Transmission or communication means, e.g. internet protocol
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H2226/00—Electro-optic or electronic components relating to digital holography
- G03H2226/05—Means for tracking the observer
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
- H04N19/63—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using sub-band based transform, e.g. wavelets
- H04N19/64—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using sub-band based transform, e.g. wavelets characterised by ordering of coefficients or of bits for transmission
- H04N19/647—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding using sub-band based transform, e.g. wavelets characterised by ordering of coefficients or of bits for transmission using significance based coding, e.g. Embedded Zerotrees of Wavelets [EZW] or Set Partitioning in Hierarchical Trees [SPIHT]
Definitions
- the present invention relates generally to the field of image processing, and more specifically to the coding of three-dimensional (3D) images and three-dimensional image sequences.
- the present invention relates to the coding of at least one holographic pattern on which is recorded a light signal representative of the light received by at least one object in perspective in a scene.
- the invention may especially, but not exclusively, apply to the video coding implemented in current video encoders and their amendments (MPEG, H.264, H.264 SVC, H.264 MVC, etc.) or to come (ITU-T / VCEG (H.265) or ISO / MPEG (HEVC)), and the corresponding decoding.
- Three-dimensional multi-view or stereoscopic video techniques sometimes cause discomfort to the viewer. These techniques seek to deceive our vision system by displaying a different image dedicated to each eye so as to obtain a depth effect.
- the human eye is adapted to follow moving objects and focus on them as they get closer.
- the images displayed with the classic 3D techniques are displayed on a fixed plane. The viewer is therefore constantly forced to repress this focusing reflex on objects, which frequently causes headaches or other nausea.
- Holograms are known to contain all the intermediate planes of a 3-dimensional scene. The presence of these intermediate planes allows the human eye to focus normally on close objects, thus greatly reducing the feelings of discomfort felt by the spectators.
- the holograms are particularly large and difficult to compress because they include the data necessary for the reconstruction of a holographic image under different viewing points, these data comprising very few redundancies exploitable by a conventional encoder.
- Compression techniques commonly used to encode sequences of images can be extended and generalized to encode holographic sequences, but the The very nature of such images prevents the achievement of satisfactory results. Indeed, these techniques are generally based on a block division of the images and predictions of movements, whereas the holographic images are in the form of diffraction patterns whose variations are very little correlated with the 3D scene. 'they represent.
- sub-hologram is meant a set of patterns of a hologram producing a diffraction towards a particular observation point.
- it is also a set of wavelet coefficients for reconstructing a visible hologram from one or more particular observation points.
- Figure 2a illustrates the frequency spectrum of a Gabor wavelet, such as that used in the prior art. It can be seen that the frequency spectrum is tightened around its spatial frequency fc. A light beam diffracted by such a wavelet produces a cone of narrow light, concentrated around its direction of incidence. The information allowing a correct reconstruction of the hologram is thus very localized in the center of this cone and degrades very quickly while moving away from it. Thus, because the information enabling a good reconstruction of a hologram is very localized, the use of Gabor's wavelet renders the reconstruction extremely sensitive to the position of the user. New Gabor wavelets must be computed at the slightest observer movement and the required calculation time and memory increase significantly with the number of observers. For example, simple movements of the head of an observer require the selection of a new set of wavelets adapted to the new position. Another disadvantage of the prior art is related to the great complexity of the processing and the amount of memory necessary to obtain a sub-hologram.
- the invention responds to this need by proposing a method of processing a sequence of holographic images for rendering on a holographic display device to at least one observer, a subset of wavelet coefficients relevant for reconstructing a visible sub-hologram for the at least one observer from at least one observation point being selected from a decomposition of at least one holographic image on a wavelet basis and information representative of a location of the at least one observer in a repository of the display device, the method being remarkable in that the decomposition of the at least one holographic image is performed on a Shannon wavelet basis.
- the invention is based on a novel and inventive approach to the decomposition of a wavelet holographic image.
- the inventors have sought to optimize computing times and have discovered that a decomposition of Shannon's wavelet holographic image (Cattani, C. "Shannon Wavelets Theory", Mathematical Problems in Engineering) makes it possible to significantly improve performance by compared to the prior art.
- the invention thus consists in exploiting the rectangular character of the Fourier transform of a Shannon wavelet, the directional character of the spectrum associated with a Shannon wavelet and the relation between the frequency localization of a Shannon wavelet and the direction of the Shannon wavelet. the light after diffraction through this wavelet at a point in the holographic image.
- Figure 2b illustrates the frequency spectrum of a Shannon wavelet. It is noted that the frequency spectrum has the same energy across the frequency band [f c - a, f c + a], unlike a Gabor wavelet whose spectrum is shown in Figure 2a. Indeed, the Fourier transform of a Shannon wavelet is a rectangular function (or gate function). A light beam diffracted by such a wavelet produces a cone of narrow light, concentrated around its direction of incidence. Information for reconstruction Correct holograms are available throughout the intersection between the light cone and the viewing plane. Conversely, when Gabor wavelets are used according to the prior art, the information enabling a correct reconstruction of the hologram degrades rapidly when the observer deviates from the center of the intersection between the cone of light and the observation plan.
- the invention makes it possible to solve the technical problem of the robustness of a reconstruction of a holographic image with slight movements of an observer without increasing the complexity of the treatments.
- the use of Shannon wavelets makes the reconstruction much less sensitive to the position of the user and a small movement of the observer does not necessarily require to recalculate a new set of wavelets adapted to the new position.
- the particular shape of the Fourier transform of a Shannon wavelet allows a significant optimization of the computation times and the memory necessary for calculating the sub-holograms.
- the method is such that the calculation of the sub-hologram visible by the at least one observer from the at least one observation point comprises the following steps:
- the method makes it possible, compared with the prior art, to calculate a visible sub-hologram from the observation point in a very efficient manner in terms of calculation time and memory used.
- the calculation of a sub-hologram adapted to a visualization from a particular position is performed by a scalar product between a set of wavelets selected for the point of view, and the hologram.
- the computation of a sub-hologram H v visible from a point V comprises L 2 xnxmx N x M complex multiplications and L 2 xnxmx N x M complex additions, L being the number of points of the wavelet of Shannon, n and m being the dimensions in points of the hologram and N and M corresponding to the dimensions of the hologram visibility area.
- the memory needed for such a calculation is L 2 xnxmx N x M complex values.
- Such complexity requires memorizing the computed sub-holograms for reuse because a real-time computation is excluded.
- the method makes it possible to calculate the sub-holograms corresponding to the position of an observer in the frequency domain, from a simple convolution operation. In this way, it is no longer necessary to calculate a scalar product between the hologram and the selected wavelets, the method allowing a considerable reduction in the calculation time and the memory necessary for computing a sub-hologram with respect to the prior art.
- this new method of calculating a sub-hologram allows the computation of a sub-hologram in real time and makes it possible to avoid the backup of the calculated sub-holograms.
- the invention thus provides a substantial gain in both the calculation time and the memory occupancy level.
- the method is such that the convolution operation is carried out in the frequency domain between the Fourier transform of the hologram and the Fourier transform of the determined Shannon wavelet.
- the rectangular nature of the Fourier transform of a Shannon wavelet makes it possible to carry out the convolution operation in the frequency domain, this operation then corresponding to a simple multiplication.
- the method according to the invention thus makes it possible to further reduce the calculation time required to obtain a sub-hologram.
- the method of processing a holographic image sequence can be implemented by a device for processing a sequence of holographic images with a view to its rendering on a device.
- holographic display to at least one observer.
- the invention relates to a device for processing a sequence of holographic images with a view to restoring it on a holographic display device to at least one observer, a subset of wavelet coefficients relevant for the reconstruction of the visible sub-hologram for the at least one observer from at least one observation point being selected from a decomposition of at least one holographic image on a wavelet basis and information representative of a locating the at least one observer in a repository of the display device, the device being characterized in that it comprises a decomposition unit of the at least one holographic image on a Shannon wavelet basis.
- the device further comprises units configured to: determine maximum and minimum diffraction angles of an incident ray on the hologram, subtended by
- the invention also relates to a server equipment comprising a device for processing a sequence of holographic images.
- the invention also relates to a holographic restitution terminal comprising a device for processing a sequence of holographic images and a display device.
- the invention also relates to a computer program comprising instructions for implementing the steps of a method of processing a holographic image sequence as described above, when this program is executed by a processor.
- Such a program can use any programming language. It can be downloaded from a communication network and / or saved on a computer-readable medium.
- the invention finally relates to a storage medium, readable by a processor, integrated or not to the processing device, possibly removable, storing a computer program implementing a method of treatment as described above.
- the recording media mentioned above can be any entity or device capable of storing the program and readable by a device.
- the media may comprise storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a floppy disk or a disk. hard, or a flash memory.
- the recording media may correspond to a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means.
- the programs according to the invention may in particular be downloaded on an Internet-type network.
- the servers, terminals, devices, programs and information media have at least advantages similar to those conferred by the processing method described above.
- FIG. 1 illustrates a suitable architecture for the implementation of the treatment method, according to a particular embodiment.
- FIG. 2a illustrates the frequency spectrum of a Gabor wavelet, as described previously
- Figure 2b illustrates the frequency spectrum of a Shannon wavelet
- FIG. 3a shows a one-dimensional hologram and radii diffracted towards a point of observation
- FIG. 3b represents the minimum and maximum diffraction angles subtended by a point of observation
- FIG. 3b represents the minimum and maximum diffraction angles subtended by an observation window
- FIG. 4a shows a frequency display of a one-dimensional hologram.
- FIG. 4b illustrates a rectangular function whose frequency band and center frequency are determined according to a particular embodiment of the invention.
- FIG. 5 illustrates the characteristic angles making it possible to obtain a diffraction from a point of a two-dimensional hologram towards a particular observation point
- FIG. 6 illustrates in diagrammatic form the main steps of the treatment method according to one particular embodiment of the invention.
- FIG. 7 represents the architecture of a processing device according to a particular embodiment of the invention.
- a display device 100 comprising a spatial light modulator SLM (for "Spatial Light Modulator"), for example an LCD (Liquid Crystal Display) ).
- the SLM is composed of pixels.
- the set of pixels of the SLM needed to display a wavelet is a pixel of the hologram, which will be considered punctual and will be called "point" thereafter.
- the method is implemented on a server equipment 101 adapted to receive positioning information of an observer 102 relative to the SLM.
- the positioning information can be captured by a motion detection device 105 and transmitted by a connection 104 to the server 101.
- the server 101 communicates with the display device 100 via a communication network 103.
- Calculated holograms are transmitted as wavelet coefficients to the SLM.
- the method can be implemented in a rendering device 100 or in the server 101.
- the general principle of the invention is based on the decomposition of a holographic image from a base of Shannon wavelets.
- the inventors have found that the decomposition of a Shannon wavelet holographic image has advantages related to the properties of these wavelets. These advantages make it possible to significantly reduce the complexity of the processing operations and the memory necessary for implementing a method of compressing a holographic image sequence, allowing a real-time execution of the method.
- the properties of the Shannon wavelets are for example described in an article by Carlo Cattani entitled “Shannon Wavelets Theory", and published in 2008.
- the mother function of a Shannon wavelet is a cardinal sine whose Fourier transform is a rectangular function as illustrated in FIG. 2b showing the frequency spectrum of a Shannon wavelet.
- a Shannon wavelet is obtained by multiplying a sinusoidal function of determined frequency with this mother function defined for a given interval.
- the direction of diffraction of a light beam by a Shannon wavelet is determined by the frequency of the sinusoid, the temporal and spatial dimensions of the mother function, and the orientation of the wavelet.
- a holographic image is decomposed on a Shannon wavelet basis to which particular rotation, translation and expansion parameters are applied. These parameters are calculated for each of the points of the hologram so that an incident ray traversing the wavelet thus parameterized is diffracted towards at least one determined observation point.
- each image of the sequence of holographic images is decomposed on a base of N Shannon wavelets, which leads to obtaining a representation of each image of the sequence in the form of a set of N Shannon wavelet coefficients, with N the number of points of the hologram.
- FIG. 3a In relation to FIG. 3a, consider a two-dimensional space S containing a hologram H, the hologram having n points, the points being indexed by k.
- the hologram shown in Figure 3a has 1 dimension and is composed of 7 points.
- the hologram can be defined as follows: An observation point V belonging to S. is also considered.
- the invention also applies when the space S has 3 dimensions and / or a plurality of observation points. For example, when several observers are looking at a hologram, the invention allows an optimized selection of sub-holograms visible by the different observers.
- the method according to the invention proposes to determine a frequency for each index point k of the hologram H, this frequency being such that an incident ray on this point is diffracted towards the observation point V
- the method uses the properties of the diffraction gratings.
- R ⁇ R 2 be a function that maps any point from 5 to a position in two dimensions (in this example, both dimensions correspond to the position of the index point k in the hologram and at its distance from at observation point V).
- the position of the index point k belonging to H is given by X (k).
- the position of point V in this same system is given by X (V).
- the example used here as a support for the description corresponds to a one-dimensional hologram. Since the hologram is in the same plane as the point of observation, the diffraction direction is determined solely by the angle subtended by the point V. In the case of a two-dimensional hologram in a 3-dimensional space it should also take into account the orientation to cause a diffraction towards the point V.
- the method according to the invention comprises a step of determining a sub-hologram that can generate a diffraction towards at least one observation point. For this, the method proposes to determine, for each index point k of the hologram, a Shannon wavelet ⁇ obtained by multiplying a sinusoidal function whose frequency is adapted to cause a diffraction at the index point k to at least one observation point, and a mother function of cardinal sinus type defined on a particular interval. The sinusoidal function determines the center frequency of the wavelet and the mother function its frequency band.
- the skew coefficient decomposition of Shannon C v corresponds to a set of scalar products of a function representing the holographic image H by the basic function ⁇ ⁇ .
- the scalar product of ⁇ ⁇ with the hologram H is given by:
- a Shannon wavelet in its complex and continuous form, centered on the frequency F c whose frequency band is F b is characterized by the following equation:
- the Fourier transform of this wavelet is given by:
- the hologram H being composed of N discrete points, it is advisable to calculate a discrete Fourier transform (DFT) of the hologram and to take into account the spacing of these points (pitch in English, noted P) to discretize the Shannon wavelet.
- DFT discrete Fourier transform
- the size of the wavelet should be at least sufficient to cover a half-period of the base sine wave.
- the number of discrete points necessary for a wavelet that is to say its length in the spatial domain, is given by:
- FIG 4a schematically illustrates a representation in the frequency domain of a sub-hologram H v obtained by equation (4b).
- Each rectangular function ifj v (k) corresponds to a localized scalar product whose frequency band is denoted f b (k) and the central frequency f v (k).
- Figure 5 illustrates a two-dimensional holographic image 500 and a plane 501 including an observation point V (502) in a 3-dimensional space.
- An incident ray 503 is distinguished. It can be seen that the Shannon wavelet traversed by this incident ray generates a light ray diffracted toward the observation point V according to an azimuth angle ⁇ (V) and a zenith angle ⁇ ( ⁇ ). . Since the Shannon wavelet is discretized, continuous changes in the values ( ⁇ , ⁇ ) do not generate continuous changes in the pair (0, 5). Consequently, a range ⁇ is defined so that each pair (0, 5) corresponds to [ ⁇ - ⁇ , ⁇ + ⁇ ] ⁇ [ ⁇ - ⁇ , ⁇ + ⁇ ].
- the parameter ⁇ corresponds to an approximation of the ideal diffraction direction and makes it possible to anticipate the movements of the observer.
- This parameter corresponds to the bandwidth f b of the Shannon wavelet.
- FIG. 2b it can be seen that the Fourier transform of a Shannon wavelet is a rectangular function. The wavelet thus has the same energy over its entire frequency band.
- FIG. 2a which represents a Fourier transform of a Gabor wavelet, the energy of a Gabor wavelet is concentrated around its central frequency and decreases rapidly by deviating from this frequency. .
- a new sub-hologram must be calculated as soon as the user deviates from the observation point for which a first sub-hologram has been calculated, the fact that a Shannon wavelet retains the same energy over the entire range defined by ⁇ , allows the user to deviate from the observation point to a certain extent determined by ⁇ , without the need to recalculate a sub-hologram.
- the method according to the invention allows a reduction in the number of sub-holograms to be pre-calculated, this reduction to reduce the complexity of processing and the memory required to store these sub-holograms. The method thus has a certain advantage over the prior art.
- a sub-hologram H v is obtained from the minimum number of wavelet coefficients which is necessary to create a diffraction at point V.
- the sub-hologram can be calculated by a scalar product between the set of parameterized wavelets and the set of points of the holographic image. This computation requires L xn complex multiplications and L xn complex additions, L being the number of discrete points in the wavelet ifj v (k) and n the number of points in the holographic image. It can be seen that the calculation of a diffraction sub-hologram at the point V is particularly expensive in computing time according to this method.
- this approach also requires a large amount of memory to store the vectors ⁇ ⁇ for each L xn points of the hologram.
- the required memory will be L xnx N complex values.
- the complexity of the computation will be of the order of L xnx N complex multiplications and L xnx N complex additions. This complexity corresponds to the calculation of a sub-hologram in one dimension.
- the complexity of the computation for a hologram comprising nxm points visible from a display zone comprising N x M positions will be of the order of L 2 xnxmx N x M complex multiplications and L 2 xnxmx N x M complex additions, with a memory occupancy of L 2 xnxmx N x complex values.
- Such complexity prohibits real-time computing.
- the invention proposes, in a particular embodiment, a method adapted to calculate the sub-holograms in the frequency domain so as to reduce the complexity of the processing and the memory required.
- the invention takes advantage of a property of Shannon wavelets according to which the Fourier transform of such a wavelet is a rectangular function.
- the invention proposes to determine a rectangular function adapted to cover the frequencies causing diffraction of light at point V.
- Figure 6 illustrates the main steps of the method of treatment, according to a particular embodiment.
- the calculation of a visible sub-hologram from the observation point comprises a first step denoted 600 in FIG. 6 for determining the maximum and minimum diffraction angles of an incident ray subtended by the point observation.
- the FIG. 3b represents a hologram H and a point of observation V.
- the minimum incident diffraction angle at the observation point V is noted as 9 min .
- the maximum incident diffraction angle at the observation point V is denoted 9 max .
- These angles can be determined from the position of the observer with respect to the holographic rendering device. The position of the observer can be known through a device for monitoring the gaze or motion detection.
- a step 601 the method proposes to determine a frequency for causing diffraction of an incident ray according to the determined minimum angle and a frequency for causing diffraction of an incident ray according to the determined maximum angle.
- the frequency corresponding to a diffraction angle is given by equation (2b).
- a Shannon wavelet is determined, the wavelet being such that its frequency range is equal to the difference between the determined minimum and maximum frequencies, and that its center frequency is equal to half the sum of the determined frequencies.
- the central frequency by the equation: f t _ max (i,) + min (/ i,). .
- the sub-hologram corresponding to the observation point can be obtained by a scalar product between the hologram and the wavelet obtained in step 602.
- one advantage of the invention over the prior art is to allow obtaining the sub-hologram by a simple convolution operation performed in step 603. In the frequency domain, this convolution operation corresponds to a simple multiplication and makes it possible to very significantly reduce the number of complex multiplications to be performed for calculate the sub-hologram. It is observed in FIG. 4b that the sub-hologram H ' v obtained is a superset of the sub-hologram H v obtained by the method represented in FIG. 4a.
- the sub-hologram H ' v contains all the frequencies necessary for diffraction at the point V but also additional frequencies, because all the (discrete) frequencies between min ⁇ ) and max (f v ) are selected. This has the effect of slightly lowering the efficiency of the compression, but the gain in terms of complexity of processing and memory need is particularly advantageous.
- the sub-hologram being completely calculated in the frequency domain, the method according to the invention also has advantages during the reconstruction of the sub-hologram, because it avoids having to recalculate Fourier transforms.
- a single sub-hologram that diffracts to a single point of observation is unsatisfactory. Indeed, the hologram is no longer visible when the observer moves slightly. It is then necessary to calculate several sub-holograms corresponding to each of the points of a viewing window, such as for example the viewing window 504 shown in FIG. 5, a window from which the hologram must be visible. In this way, the observer can move in the limit of the viewing window and continue to see the hologram. According to the prior art, the complexity of the processing is then multiplied by the number of points of the viewing window.
- the method proposes to calculate the maximum diffraction angles 6 ' max and minimum ⁇ ' min incident on the viewing window and to determine the frequencies causing such diffractions.
- a ray incident on any point of the viewing window will have an angle of incidence of between 9 ' min and 6' max .
- FIG. 3c represents a hologram H comprising a dimension and an observation window V whose end points are denoted by P1 and P1.
- the maximum and minimum angles subtended by the point P1 are denoted by 9 ' minl and 9' maxl .
- the maximum and minimum angles subtended by the point P2 are denoted ⁇ 'mira and ⁇ ' max2- had O n P t deduct the minimum and maximum angles incident on the observation plane V, the minimum angle 9 'min being equal to RNIN (0 'MinL, 0' min2) and the maximum angle 9 'max being equal to vnax. (6' maxl, 6 'max2). It is thus possible to determine, from the equations specific to the diffraction gratings, the minimum and maximum frequencies causing an incident diffraction on the viewing window. From these minimum and maximum frequencies, steps 602 and 603 of the method make it possible to calculate a visible sub-hologram over the entire viewing window by a simple multiplication of the Fourier transform of the hologram with the Fourier transform of the Shannon wavelet obtained.
- FIG. 7 represents the architecture of a device for processing a holographic image.
- the device comprises a storage space 701, for example a memory MEM, a processing unit 702 equipped for example with a processor PROC.
- the processing unit may be driven by a program 703, for example a PGR computer program, implementing the processing method as described in the invention with reference to FIG.
- the instructions of the computer program 703 are for example loaded into a RAM (Random Access Memory in English) before being executed by the processor of the processing unit 702.
- the processor of the unit 702 implements the steps of the processing method according to the instructions of the computer program 703.
- the device comprises, in addition to the memory 701, a unit configured to determine maximum and minimum diffraction angles of a radius incident on the hologram subtended by the at least one observation point.
- the device may use data obtained from an observer's motion detection device, which device may be directly connected to the treatment device or may communicate with the treatment device through a network of communication devices. communication.
- the processing device may comprise a communication unit, such as for example a network card, adapted to transmit and receive data, such as, for example, positioning data of an observer relative to a holographic rendering device. .
- the communication device 708 can also be used to transmit a sub-hologram calculated according to the invention to a holographic rendering device, such as for example an SLM.
- the processing device also comprises a module 705 (FREQ) configured to determine minimum and maximum frequencies for creating a diffraction of an incident ray at the determined angles.
- the unit 705 can implement an algorithm adapted to calculate diffractions in a diffraction grating and in particular to implement equation (2b).
- the device also comprises a unit 706 (SHAN) configured to obtain a Shannon wavelet whose frequency range is equal to the difference between the determined frequencies, and whose central frequency is equal to half the sum of the determined frequencies.
- the module 706 can implement equations (12) and (13) in the form of an algorithm for obtaining equation (14).
- the processing device comprises a unit 707 (CONV) for calculating a sub-hologram by a convolution operation performed from a Fourier transform of a hologram and a Fourier transform of the wavelet of Shannon determined by the module 706.
- the communication unit 708 can be used to transmit the resulting coefficients of the convolution operation to a holographic rendering device.
- the device can be integrated into a server equipment adapted to communicate with a holographic reproduction device, or integrated directly into a holographic reproduction equipment.
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FR1558727A FR3041440A1 (fr) | 2015-09-17 | 2015-09-17 | Procede de traitement d'une image holographique |
PCT/FR2016/052207 WO2017046478A1 (fr) | 2015-09-17 | 2016-09-06 | Procédé de traitement d'une image holographique |
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EP (1) | EP3350656A1 (fr) |
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FR3098367B1 (fr) * | 2019-07-05 | 2023-01-27 | Fond B Com | Procédé et dispositif de codage d’une séquence d’hologrammes numériques |
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FR3015743A1 (fr) * | 2013-12-23 | 2015-06-26 | Orange | Procede de traitement d'une sequence d'images holographiques, dispositifs, signaux, dispositifs et programme d'ordinateur associes |
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WO2017046478A1 (fr) | 2017-03-23 |
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