METHOD FOR PRODUCING A DIGITAL HOLOGRAM AND ASSOCIATED DIGITAL HOLOGRAPHIC SYSTEM

Description

Technical field of the invention

[0001] The present invention relates generally to the technical field of digital holography.

[0002] In particular, it relates to a method for constructing a digital hologram and an associated digital holography system. State of the art

[0003] Digital holography aims to reconstruct a three-dimensional scene for an observer by displaying a digital hologram using a light modulator.

[0004] The resulting field of vision may, however, be limited and too restricted for the chosen application (the emission angle being directly linked to the pixel density of the light modulator).

[0005] In order to enlarge the field of vision (which is particularly interesting in the case of augmented reality where we want to superimpose the displayed hologram on the observer's real environment), it has already been proposed to display the digital hologram by means of a display system comprising a light modulator producing a light beam and a converging optical device designed to converge the light beam towards a focal point. FTOS (for “Fourier Transform Optical System” ) such a system.

[0006] Thus, by placing the observer's eye between the converging optical device and the focal point (typically close to the focal point), the field of vision seen by the observer is widened. US 2013 / 250049 A1 and "Real-time layer-based computer-generated hologram calculation for the Fourier transform optical system", Antonin Gilles et al. (Applied Optics, vol.57, no.29, 10 October 2018, pp.8508-8517) disclose methods for reconstructing a digital hologram intended to be displayed by means of a display system comprising a light modulator. Presentation of the invention

[0007] In this context, the invention proposes a method for constructing a digital hologram representing a scene and intended to be displayed by means of a display system comprising a light modulator producing a light beam and a converging optical device designed to converge the light beam towards a focal point, the scene being defined by a set of light elements, characterized in that it comprises a step of determining values ​​respectively associated with pixels of the digital hologram by summing light contributions respectively produced by light elements with weighting, for each of the light contributions, by a correction coefficient depending on the area of ​​the intersection of a surface located between the converging optical device and the focal point,and a light beam having a predetermined angular aperture and transmitted through the converging optical device from the light element producing the relevant light contribution.,

[0008] The use of the correction coefficient makes it possible to take into account in advance (when constructing the digital hologram) the fact that certain light rays produced by the light modulator are only partially received by the observer's pupil (a phenomenon which is amplified due to the convergence of these rays produced by the converging optical device). The reproduction of the three-dimensional scene by the display system is thus improved.

[0009] Other non-limiting and advantageous characteristics of the product / process according to the invention, taken individually or in all technically possible combinations, are as follows: the light elements are respectively located on a plurality of points of the scene; the method comprises, for each point of said plurality, a step of calculating, as a function of the position of the point concerned, the correction coefficient weighting the light contributions produced by the light element located at the point concerned; the step of determining values ​​comprises, for each pixel of the digital hologram, a step of determining the field generated, at the pixel concerned, by a light element located at a given point and a step of weighting the field determined by the correction coefficient calculated for the given point; the light elements are located in at least one plane;the step of determining values ​​comprises a step of propagating the light field from a first plane to a second plane adjacent to the first plane, with application of a matrix mask (or compensation mask) whose elements are respectively associated with the different points of the first plane and have a value depending on the area of ​​the intersection of said surface and a light beam having the predetermined angular aperture and transmitted through the converging optical device from the point associated with the element concerned; the method comprises a step of displaying, by means of the display system, the constructed digital hologram; the display system comprises a shutter interposed between two lenses; the orientation of the shutter is determined as a function of the distribution of the light elements in angular sectors defined around the axis of the display system;the determined field is zero if the light beam emitted by the light element located at the given point with said predetermined angular aperture is entirely intercepted by the shutter; the two lenses have an identical focal length; the shutter is separated from each of the two lenses by a distance equal to the focal length; said surface is a disk centered on the optical axis of the converging optical device; the predetermined angular aperture is the angular aperture of the light beam generated by the light modulator.

[0010] The invention also proposes a digital holography system comprising a module for constructing a digital hologram representing a scene and intended to be displayed by means of a display system comprising a light modulator producing a light beam and a converging optical device designed to converge the light beam towards a focal point, the scene being defined by a set of light elements, characterized in that the construction module is designed to determine values ​​respectively associated with pixels of the digital hologram by summing light contributions respectively produced by light elements with weighting, for each of the light contributions, by a correction coefficient depending on the area of ​​the intersection of a surface located between the converging optical device and the focal point,and a light beam having a predetermined angular aperture and transmitted through the converging optical device from the light element producing the relevant light contribution.,

[0011] Such a holography system may further comprise the aforementioned display system.

[0012] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Detailed description of the invention

[0013] In addition, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate non-limiting embodiments of the invention and where: there figure 1 represents the main elements of a digital holography system as proposed by the invention; the figure 2 is a schematic representation of a display system of the digital holography system of the figure 1 ; there figure 3 represents a possibility of realizing a part of the display system of the figure 2 ; there figure 4 illustrates the construction of a digital hologram from light elements located at different points in a scene; the Figure 5 illustrates the construction of a digital hologram from a distribution of light elements in a set of planes; the figure 6 illustrates the determination of a correction coefficient taking into account a light beam propagating in the display system of the figure 2 ; and the figure 7 shows the intersection of the light beam and a disc representing the pupil of a user of the display system.

[0014] The digital holography system described in the following and shown in the figure 1comprises a building module 2 of a digital hologram H and a display system 10 of the digital hologram H.

[0015] The construction module 2 here comprises a processor 4 and at least one memory 6 (such as a RAM or a rewritable non-volatile memory; however, it could alternatively be a hard disk). The construction module 2 is, for example, a computer.

[0016] As explained below, memory 6 stores data representative of a scene to be represented. Memory 6 can also store variables manipulated during the construction of the digital hologram. H, as described below.

[0017] The memory 6 further stores computer program instructions designed, when executed by the processor 4, to implement the various operations described below and allowing the construction of the digital hologram H.

[0018] The display system 10 comprises a light source 11 (here monochromatic of wavelength λ), a light modulator 12 producing a light beam (by modulation of the light emitted by the light source 11) and a converging optical device 14 designed to converge this light beam towards a focal point A, as described below with reference to the figure 2 .

[0019] According to a first embodiment, the construction module 2 and the display system 10 can be combined within a single holographic display device. The digital hologram H can then be transmitted from the construction module 2 to the display system 10 by means of an internal bus of this holographic display device.

[0020] According to a second embodiment, the construction module 2 and the display system 10 may be remote from each other; the construction module 2 being for example located in a remote server with which the display system 10 exchanges data via at least one communication network. In this case, the digital hologram H may be transmitted (for example in the form of coded data representing this digital hologram H) via this communication network.

[0021] There figure 2 represents the main elements of the display system 10.

[0022] As already indicated, the display system 10 comprises a light source 11, a light modulator 12 (for example of the SLM type for "Spatial Light Modulator ") and a converging optical device, here a converging lens 14.

[0023] In the remainder of the explanation, an orthonormal reference frame R (O, ux , uy , uz ) will be used, where O is the center of the light modulator 12, the vector uz is orthogonal to the plane of the light modulator 12 and directed in the direction of propagation of the light beam generated by the light modulator 12, and the vectors ux and uy are respectively parallel to the long and short edges of the light modulator 12.

[0024] As visible on the figure 2 , the optical axis Oz of the display system 10 is the axis collinear with the vector uz passing through the point O.

[0025] In the display system 10, the converging lens 14 is placed perpendicular to the optical axis so that the optical axis Oz passes through the center CL of this converging lens 14. In other words, the axis of the converging lens 14 is coincident with (or identical to) the optical axis Oz.

[0026] The extension plane of the light modulator 12 and the extension plane of the converging lens 14 are thus parallel.

[0027] We note d the distance separating the image plane (that is to say, in the embodiment of the figure 2 , the plane of the light modulator 12) and the converging lens 14 (i.e. here d = OC L ).

[0028] A light ray emitted perpendicular to the light modulator 12, and therefore incident on the converging lens 14 along the axis of this converging lens 14, will therefore be transmitted (after passing through the converging lens 14) in the direction of the focal point A (located on the optical axis Oz). We note f the focal length of the converging lens 14: f = AC L .

[0029] As shown in the figure 2 , the light beam generated by the light modulator 12 has an angular aperture ω (variable depending on the type of light modulator 12 used).

[0030] Furthermore, a disk δ represents the pupil of the user who observes the light beam generated by the light modulator 12 after passing through the converging lens 14. As explained below, the disk δ corresponding to the pupil of the user is placed between the converging lens 14 and the focal point A.

[0031] This disk δ (i.e. the user's pupil) is considered to be perpendicular to the optical axis Oz and centered on the optical axis Oz. Here, the disk δ is further considered to be located on the optical axis Oz at the point closest to the center CL of the converging lens 14 which receives light rays from the entire light modulator 12. In other words, as seen in the figure 2, we consider the disk δ placed at the point of the optical axis Oz closest to the converging lens 14 touched by a ray emitted with an angle equal to the angular aperture ω from a peripheral pixel of the light modulator 12.

[0032] This position of the δ disk (i.e. the user's pupil) is optimal in the sense that it allows the user's field of vision to be maximized while allowing the user to see the entire hologram formed by the light beam.

[0033] As visible in figure 2 , we note d 1 the distance between the converging lens 14 and the disk δ representing the user's pupil.

[0034] There figure 3 represents a possible embodiment of the display system 10 according to which a so-called 4F filtering technique is used to suppress a symmetrical ray generated by the light modulator 12.

[0035] According to this technique, downstream of the light modulator 12, an optical assembly is provided comprising a shutter 20 interposed between two lenses 16, 18.

[0036] The two lenses 16, 18 have an identical focal length F and the shutter 20 is separated from each of the two lenses 16, 18 by a distance equal to the focal length F.

[0037] The light modulator 12 is itself placed upstream, at a distance equal to the focal length F, from the first lens 16.

[0038] The display system 10 thus comprises successively, along the optical axis Oz and with a spacing equal to the focal distance F between two successive elements: the light modulator 12, the first lens 16, the shutter 20, the second lens 18 and an image plane I.

[0039] The shutter 20 stops the light rays intersecting a given half-plane and lets through the light rays located in the complementary half-plane so that at the level of the image plane I a light beam is generated corresponding to the beam generated by the light modulator 12, but with suppression of a part of the spatial frequency components.

[0040] We can refer to the article " Band-limited zone plates for single-sideband holography", by Y. Takaki and Y. Tanemoto, in Appl. Opt. 48, H64-H70 (2009) for more details on this filtering technique.

[0041] In this embodiment, the distance d mentioned above is therefore equal to the distance between the image plane I and the converging lens 14, as indicated in the figure 3 .

[0042] The shutter 20 may be fixed (in which case the half-plane for stopping the light rays is constant). Alternatively, a transmissive modulator may be used (as shutter 20) in order to choose for each frame the half-plane in which the rays are stopped.

[0043] In the following, we note θ 0 the angle formed, in the plane of the shutter 20, between an edge of the shutter 20 and the direction Ox so that, for a point M with coordinates (x, y, z) in the frame R and located in the plane of the shutter 20, the cylindrical coordinates (ρ, θ, h) of M are such that ρ = SQRT(x 2< +y 2< ), θ = atan2(y,x), z = h and the point M is located in the half-plane of the shutter 20 if and only if θ 0 < θ < θ 0 + π (where SQRT is the square root function).

[0044] The value of the angle θ 0 is fixed when the shutter 20 is fixed, or variable (from one frame to another) when the position of the shutter is adjustable (by using a transmissive modulator as indicated above).

[0045] We now describe with reference to the figure 4 the construction of a digital hologram H intended to be displayed by means of the display system 10 from light elements located at different points P 1 , P 2 , P 3 , P i , PN (here at N different points) of a scene to be represented. We note A i the light intensity of the light element located at point P i .

[0046] The coordinates (xi, yi, zi) of the points P i and the light intensity A i of the light elements located at the points P i are stored here in memory 6.

[0047] Here we describe the construction of the digital hologram H for one frame. This construction can be repeated for other frames when the scene is changed.

[0048] When the orientation of the shutter 20 is adjustable, the construction module 2 first determines the orientation of the shutter 20 (i.e. the aforementioned angle θ 0) as a function of the distribution of the luminous elements in angular sectors defined around the optical axis Oz of the display system 10.

[0049] In practice, we use a predetermined number k of angular sectors and a function S(n) which indicates the number of points P i in the angular sector of index n (with n between 1 and k): S n = card P i 2 π . n − 1 / k ≤ θ P i < 2 π . n / k , where θ(P i ) is the second cylindrical coordinate of point P i : θ(P i ) = atan2(yi ,xi ).

[0050] By defining X θ as a random variable with probability density S(n) after normalization, construction module 2 can choose a realization m of the random variable Xθ (by simulation using a pseudo-random process, for example by reducing to a uniform probability law) and thus determine the angle θ 0: θ 0 = 2 m + 1 . π / k .

[0051] The construction module 2 then proceeds to construct the digital hologram H. To do this, the following operations are implemented for each pixel pk,l of indices k, l of the light modulator 12.

[0052] In the sequence (xk,l , yk,l , zk,l ) we note the coordinates of the pixel pk,l in the frame R and (ρ k,l , θ k,l , hk,l ) the associated cylindrical coordinates: ρ k,l = SQRT(xk,l 2< +yk,l 2< ), θ = atan2(yk,l ,xk,l ), zk,l = hk,l .

[0053] For each point P i of the scene, the construction module 2 can thus determine the distance di,k,l between the point P i and the pixel pk,l , and the field ci,k,l generated, at the level of the pixel pk,l , by the light element located at the point P i: d i , k , l = SQRT x k , l − x i 2 + y k , l − y i 2 + z k , l − z i 2 c i , k , l = 0 si θ 0 < θ k , l < θ 0 + π c i , k , l = Ai . exp 2 π . j . d i , k , l / λ otherwise, where exp is the exponential function, λ the wavelength of the light used and j the imaginary unit: j 2< = -1.

[0054] Construction module 2 then weights the contribution ci,k,l of the light element located at point P i (contribution ci,k,l to the field as just determined) by a correction coefficient ψ(P i ) calculated as described below with reference to figures 6 and 7 to take into account the fact that only a part of the user's pupil (represented by the disc δ) receives the light beam generated by the light modulator 12 (as explained below with reference to the figure 6 ).

[0055] The weighted contribution c' i,k,l thus obtained is: c ′ i , k , l = ψ P i . c i , k , l .

[0056] Construction module 2 can then determine the field F k,l produced at pixel pk,l by all N points P i by summing the weighted contributions c' i,k,l of the different points P i determined above: F k , l = ∑ 1 ≤ i ≤ N c ′ i , k , l .

[0057] Construction module 2 can therefore determine the value H k,l of the digital hologram H for pixel pk,l: = (F k,l + A) 2< , where A is the complex amplitude of the reference wave.

[0058] By performing the operations below for all pixels pk,l , the construction module 2 thus determines the values ​​H k,l respectively associated with these pixels pk,l by summing (as explained above) the light contributions ci,k,l respectively produced by the light elements located at points P i with weighting, for each of the light contributions ci,k,l , by a correction coefficient ψ(P i ) depending on point P i .

[0059] We now describe with reference to the Figure 5 the construction of a digital hologram H intended to be displayed by means of the display system 10 from a distribution of light elements in a set of N planes each comprising an image I i (for 1 ≤ i ≤ N).

[0060] These N images I i are respectively located in planes of equation z = z i-1 , the light modulator 12 being located in the plane of equation z = z N (with z N = 0).

[0061] The content of the images I i (defined by the light contributions, here the amplitude I i (x,y) of the light wave, at the coordinate points (x,y) of the plane concerned with the equation z = z i-1 ) is here stored in memory 6.

[0062] In the example described, memory 6 also stores binary masks O i defining the occultations respectively in the planes of equation z = zi (for 0 ≤ i ≤ N-1).

[0063] Here we describe the construction of the digital hologram H for one frame. This construction can be repeated for other frames when the scene is changed.

[0064] When the orientation of the shutter 20 is adjustable, the construction module 2 first determines the orientation of the shutter 20 (i.e. the aforementioned angle θ 0) as a function of the distribution of the passing points (points of value 1) of the binary occultation masks O i in angular sectors defined around the optical axis Oz of the display system 10.

[0065] As in the case of the embodiment described above with reference to the figure 4 , we use a predetermined number k of angular sectors. Here we denote by S' the set of points in space associated with a pixel of value 1 in an occultation mask Oi: S' = {P(x,y,z) | there exists i such that z = zi and O i (x,y) = 1}.

[0066] We can then also use a function S(n) which indicates the number of points of the set S' in the angular sector of index n (with n between 1 and k): S n = card P ∈ S ′ 2 π . n − 1 / k ≤ θ P < 2 π . n / k , where θ(P) is the second cylindrical coordinate of the point P(x,y,z): θ(P) = atan2(y,x).

[0067] By defining X θ as a random variable of probability density S(n) after normalization, the construction module 2 can choose a realization m of the random variable X θ (by simulation using a pseudo-random process, for example by reducing to a uniform probability law) and thus determine the angle θ 0: θ 0 = 2 m + 1 . π / k .

[0068] The construction module 2 then successively calculates the different fields C' i present respectively at the level of the planes of equation z = zi (for i between 0 and N) by propagation from a plane to an adjacent plane as described now (and represented schematically by means of an arrow in Figure 5 ).

[0069] To do this, construction module 2 performs the following operations for each plane (starting with the plane furthest from the light modulator 12, with equation z = z 0 , and moving closer to the light modulator 12), i.e. for i ranging from 0 to N-1: the construction module 2 applies to the propagated field C i the binary mask O i defining the occultations in the plane z = zi , adds the contribution of the image I i+1 located in the plane z = zi , and applies a compensation mask ψ i defined below, for example as follows for the points (x,y,zi ) concerned: C ′ i x y z i = I i + 1 x y + O i x y . C i x y z i . ψ i x y ; the construction module 2 propagates the field C' thus obtained to the adjacent plane (of equation z = z i+1 ) by means of a propagation operator T zi : C i + 1 = T zi C ′ i .

[0070] The propagation operator T zi is defined here as follows: T zi C ′ i x ′ , y ′ , z i + 1 = ∑ x ∑ y K θ 0 x , x ′ , y , y ′ , z i , z i + 1 . C ′ i x y z i . Δ x . Δ y where Δx and Δy correspond to the discretization steps of the operator (respectively in the Ox direction and in the Oy direction) and K θo = ξ.Γ θo , the functions ξ and Γ θo being defined as follows: ξ x , x ′ , y , y ′ , z , z ′ = K x , x ′ , y , y ′ , z , z ′ si y ′ < y ξ x , x ′ , y , y ′ , z , z ′ = 0 si y ′ ≥ y Γ θo x , x ′ , y , y ′ , z , z ′ = cos θ 0 . x − sin θ 0 . y , cos θ 0 . x ′ − sin θ 0 . y ′ , sin θ 0 . x + cos θ 0 . y , sin θ 0 . x ′ + cos θ 0 . y ′ , z , z ′ .

[0071] The compensation mask ψ i is a matrix mask whose elements are respectively associated with the different points of the equation plane z = zi . This matrix mask ψ i aims to compensate for the fact that only a part of the user's pupil (represented by the disk δ) receives the light beam generated by the light modulator 12 (as explained below with reference to the figure 6 )

[0072] Each element is therefore a correction coefficient ψ(x,y,zi ) which depends on the point concerned, with coordinates (x,y,zi ) in the plane of equation z = zi, in a manner analogous to what was mentioned above in the context of the embodiment of the figure 4. In other words, we have: ψ i (x,y) = ψ(x,y,zi ) (the calculation of the correction coefficient being described below with reference to figures 6 and 7 ).

[0073] We thus obtain, after propagation within the different planes, the CN field present at the level of the plane of equation z = z N (plane of the light modulator 12).

[0074] Construction module 2 can therefore determine the digital hologram H for the different points of the light modulator as follows: H = C N + A 2 , where A is the complex amplitude of the reference wave.

[0075] We now describe with reference to the figure 6 determining the correction coefficient ψ aimed at compensating for the fact that only part of the user's pupil (represented by the disc δ) receives the light beam generated by the light modulator 12.

[0076] As explained above, we seek to determine the value of the correction coefficient ψ associated with a point P in the coordinate space (x,y,z) (this value being noted ψ(P) in the context of the figure 4 and ψ(x,y,z) in the context of the Figure 5 ).

[0077] We have thus represented on the figure 6 a light beam φ coming from the point P concerned and having an angular aperture ω corresponding to the angular aperture of the light modulator 12. This angular aperture ω is therefore constant here (whatever the pixel concerned of the light modulator 12, and therefore of the digital hologram H).

[0078] The light beam φ is transmitted at the output of the light modulator 12 (with its central ray perpendicular to the plane of the light modulator 12), then through the converging lens 14 (with its central ray directed accordingly towards the focal point A).

[0079] As explained above, the disk δ (corresponding to the user's pupil) is placed so that at least part of the light beam φ crosses the disk δ.

[0080] It has been represented on the figure 7 the disk δ, the light beam φ and their intersection ε in the plane of the disk δ (plane of equation z = d+d 1 ).

[0081] The area α of the intersection ε of the disk δ and the brush φ is: α = R 2 . β − 0 , 5 . sin β + r 2 . σ − 0 , 5 . sin σ with β = arcos R 2 + D 2 − r 2 / 2 . R . D σ = arcos r 2 + D 2 − R 2 / 2 . r . D where (as visible in figure 7 ) r is the radius of the disk δ, R the radius of the intersection of the light beam φ and the plane of the disk δ, and D the distance between the center of the light beam φ and the center of the disk δ (i.e. the distance between the central radius of the light beam φ and the Oz axis at the plane of the disk δ), and we therefore have: D = ρ . f − d 1 / f en considérant le caractère rectiligne du rayon central précité And R = 1 − d − z / f . d 1 + d − z . tan ω , with ρ the distance from point P to the Oz axis (or first polar coordinate of point P): ρ = SQRT(x 2< +y 2< ) and z is the third Cartesian coordinate of point P.

[0082] For example, in practice, for the radius r of the disc δ, we use an average value generally encountered for the radius of the pupil of the human eye, for example a value between 4 mm and 8 mm, here 6 mm.

[0083] It is also recalled that f, d, d 1 and ω are characteristics of the display system 10 presented above with reference to the figure 2 .

[0084] Construction module 2 can thus determine (using the formulas above) the area α of the intersection ε as a function of the coordinates (x,y,z) of the point P concerned.

[0085] Construction module 2 can determine on this basis the value of the correction coefficient ψ associated with point P with coordinates (x,y,z): Ψ P = π . r 2 / α x y z .

[0086] This correction coefficient Ψ(P) is inversely proportional to the proportion of the disk δ (corresponding to the user's pupil) receiving the light beam φ so that by weighting a light contribution received from point P by this correction coefficient Ψ(P) as proposed above, we compensate for the fact that only this proportion of the user's pupil (represented by the disk δ) receives this light beam φ.

[0087] Of course, various other modifications may be made to the invention within the scope of the appended claims.

Claims

1. A method for constructing a digital hologram (H) representing a scene and intended to be displayed by means of a display system (10) comprising a light modulator (12) producing a light beam and a converging optical device (14) designed to make the light beam converge towards a focal point (A), the scene being defined by a set of luminous elements, characterised in that it comprises a step of determining values respectively associated with pixels of the digital hologram (H) by summing light contributions respectively produced by luminous elements with weighting, for each of the light contributions, by a correction coefficient depending on the area of the intersection (ε) of a surface (δ) located between the converging optical device (14) and the focal point (A), and a pencil of light (φ) having a predetermined angular aperture (ω) and transmitted through the converging optical device (14) from the luminous element producing the concerned light contribution.

2. A method according to claim 1, wherein the luminous elements are located on a plurality of points (Pi) of the scene, respectively, and wherein the method comprises, for each point (Pi) of said plurality, a step of calculating, as a function of the position of the concerned point, the correction coefficient weighting the light contributions produced by the luminous element located at the concerned point (Pi).

3. A method according to claim 2, wherein the step of determining values comprises, for each pixel of the digital hologram (H), a step of determining the field generated, at the concerned pixel, by a luminous element located at a given point (Pi) and a step of weighting the determined field by the correction coefficient calculated for the given point (Pi).

4. A method according to claim 1, wherein the luminous elements are located in at least one plane.

5. A method according to claim 4, wherein the step of determining values comprises a step of propagating the light field from a first plane to a second plane adjacent to the first plane, with application of a matrix mask whose elements are respectively associated with the different points of the first plane and have a value depending on the area of the intersection of said surface and a pencil of light having the predetermined angular aperture and transmitted through the converging optical device from the point associated with the concerned element.

6. A method according to one of claims 1 to 5, comprising a step of displaying the constructed digital hologram (H), by means of the display system (10).

7. A method according to one of claims 1 to 6, wherein the display system (10) comprises a shutter (20) interposed between two lenses (16, 18).

8. A method according to claim 7, wherein the orientation of the shutter (20) is determined as a function of the distribution of the luminous elements in angular sectors defined about the axis (Oz) of the display system (10).

9. A method according to claim 8, claim 7 being taken as depending on claim 3, wherein the determined field is zero if the pencil of light (φ) emitted by the luminous element located at the given point (Pi) with said predetermined angular aperture (ω) is entirely intercepted by the shutter (20).

10. A method according to one of claims 7 to 9, wherein the two lenses (16, 18) have a same focal distance and wherein the shutter (20) is separated from each of the two lenses by a distance (F) equal to the focal distance.

11. A method according to one of claims 1 to 10, wherein said surface (δ) is a disk centred on the optical axis (CLz) of the converging optical device (14).

12. A method according to one of claims 1 to 11, wherein the predetermined angular aperture (ω) is the angular aperture of the light beam generated by the light modulator (12).

13. A digital holography system comprising a module (2) for constructing a digital hologram (H) representing a scene and intended to be displayed by means of a display system (10) comprising a light modulator (12) producing a light beam, and a converging optical device (14) designed to make the light beam converge towards a focal point (A), the scene being defined by a set of luminous elements, characterized in that the construction module (2) is designed to determine values respectively associated with pixels of the digital hologram (H) by summing light contributions respectively produced by luminous elements with weighting, for each of the light contributions, by a correction coefficient depending on the area of the intersection (ε) of a surface (δ) located between the converging optical device (14) and the focal point (A), and a pencil of light (φ) having a predetermined angular aperture (ω) and transmitted through the converging optical device (14) from the luminous element producing the concerned light contribution.

14. A holography system according to claim 13, further comprising said display system (10).