AERIAL AND DEMATERIAL PROJECTION DEVICE FOR AN AUTOSTEREOSCOPIC IMAGE INTENDED FOR MULTIPLE DISTINCT OBSERVERS

Abstract

AERIAL AND DEMATERIALIZED PROJECTION DEVICE OF AN AUTOSTEREOSCOPIC IMAGE FOR SEVERAL DISTINCT OBSERVERS The invention relates to an aerial and dematerialized projection device of a digital image (31) comprising: a housing (10) in which an opening (15) is provided, forming an observation window of a real aerial image and a dematerialized version of said digital image (31); an optical system comprising at least one optical component of the converging spherical mirror type (24), said optical system being arranged in said housing (10) so that it can direct at least part of the incident light received towards said observation window (15); a display screen (23) for the said digital image (31) to be projected housed in said casing (10) opposite said spherical mirror (24) at a distance equal to twice the focal length of the spherical mirror;a prismatic grating with 2 or 3 facets, oriented towards said converging mirror (24) and arranged in the vicinity of the conjugate plane of said autostereoscopic screen, so as to be able to deflect the light rays which it receives from the converging mirror (24) in several distinct directions along which distinct observers can be positioned to perceive the projected autostereoscopic image. Figure for the abbreviation: figure 1;

Description

Title of the invention: DEVICE FOR AERIAL AND DEMATERIALIZED IMAGE PROJECTION AUTOSTEREOSCOPIC FOR MULTIPLE DISTINCT OBSERVERS 1. Technical field of the invention

[0001] The invention relates to an aerial and dematerialized projection device of an autostereoscopic image or a sequence of autostereoscopic images intended for a plurality of distinct observers. 2. Technological background

[0002] An aerial and dematerialized projection device for an object is a device that allows an image of the object to be projected in front of a window made in a box and that gives the observer the illusion of a three-dimensional object floating in space.

[0003] Such a device is known for the projection of real objects. Such a device typically comprises a case (opaque or not) in which an opening is provided to form a window for observing the dematerialized image, an optical system, generally a Fresnel lens or a lens or set of lenses or a converging mirror, and an object arranged at a distance from the optical system which is configured to orient the image of the object towards the window for observation.

[0004] Such a device is also known for projecting an autostereoscopic image. This device was described by the applicant in document WO2018 / 167410. An autostereoscopic image consists of a plurality of nested elementary images, each corresponding to a different viewpoint of an object or scene. Viewing an autostereoscopic image involves the use of a selective optical device, such as a cylindrical lenticle array, arranged in front of the autostereoscopic display screen. This selective optical device ensures that the observer's eyes perceive only two respective elementary images corresponding to two different viewpoints, thus creating a pop-out and depth-progressing 3D stereoscopic volume illusion.

[0005] The device already proposed by the applicant generally only allows one user to observe the projected autostereoscopic image. If the device is large enough, two observers close to each other may be able to observe the same image.

[0006] The inventors sought to improve this device to allow its simultaneous use by several distinct observers and without requiring the observers to be close to each other.

[0007] One of the applications targeted by this new device is in particular an installation in a dashboard of a motor vehicle to allow the driver, the front seat passenger and a passenger located in the centre, for example in the rear of the vehicle or in the centre of a front bench seat, to simultaneously perceive the same autostereoscopic image, while using only one autostereoscopic screen and one converging mirror. 3. Objectives of the invention

[0008] The invention aims to provide an aerial and dematerialized projection device for a digital image which overcomes at least some of the drawbacks of known solutions.

[0009] The invention also aims to provide such a device which is adapted to an autostereoscopic image or to a sequence of autostereoscopic images.

[0010] The invention aims to provide such an aerial projection device for an autostereoscopic image which allows observation of the projected image simultaneously by 2 or 3 distinct observers.

[0011] The invention also aims to provide, in at least one embodiment, such a device adapted to 2 or 3 distinct observers spaced laterally from each other in front of the projection device.

[0012] The invention also aims to provide, in at least one embodiment, such a device adapted to 2 or 3 distinct observers of different sizes.

[0013] The invention also aims to provide, in at least one embodiment, a device that is compact and requires the use of only one autostereoscopic screen and only one converging mirror.

[0014] The invention also aims to provide, in at least one embodiment, such a projection device adapted for integration within a motor vehicle. 4. Description of the invention

[0015] To this end, the invention relates to an aerial and dematerialized projection device of an autostereoscopic digital image intended for P distinct observers, P being equal to 2 or 3.

[0016] Such a device comprises: - a casing comprising a front wall, a rear wall, connected to each other at least by an upper wall and a lower wall, said front wall comprising an opening forming a viewing window for said autostereoscopic image, - an optical system comprising at least one converging spherical mirror (or any converging optical component such as a holographic optical element exhibiting the properties of a converging spherical mirror) having an optical axis, a focal length F, a center of radius of curvature C located on said optical axis, said optical system being arranged in said housing so that it can direct at least a portion of the incident light received towards said observation window, - an autostereoscopic image display screen equipped with a network of cylindrical lenticles forming an optical component that selects the viewpoints of said autostereoscopic digital image to be projected, housed in said casing opposite said spherical mirror at a distance substantially equal to twice the focal length F.

[0017] The device according to the invention is characterized in that it further comprises an optical component of prismatic lenticles with P facets, called a prismatic array, arranged in the vicinity of the conjugate image plane of said autostereoscopic screen and oriented towards said optical system, so as to be able to deflect the light rays which it receives from the optical system in P distinct directions along which distinct observers can be positioned to perceive the projected autostereoscopic image, said directions being dependent on the physical characteristics of the prismatic array.

[0018] A device according to the invention thus allows the dematerialized projection of a digital image to P distinct observers. The prismatic grating facing the converging mirror (in the case where the optical system consists solely of the converging mirror) allows the direction of a portion of the light rays emanating from the converging mirror to be modified. Thus, whereas a prior art device only allowed observation of the projected autostereoscopic image by a single observer positioned opposite the viewing window, the device according to the invention allows simultaneous observation by P distinct observers. The number of distinct observers depends on the number of facets of the prismatic grating used.

[0019] The deviation of light rays by the prismatic network depends on the prismatic network and the rules of geometric optics.

[0020] Throughout the text, the notion of "conjugate screen plane" or "conjugate image plane" of the screen refers to the plane in which the image of the autostereoscopic screen extends after reflection on the converging mirror.

[0021] Throughout the text, the invention is described using a converging spherical mirror, but the invention extends to a device using a converging optical component, such as a concave spherical mirror or holographic optics. In other words, throughout the following, the terminology "spherical mirror" is primarily used. "converging" to facilitate reading, but it is understood that this converging mirror can be replaced by any converging optical component such as holographic optics without altering the technical effects of the invention.

[0022] The inventors have determined that the loss of brightness of each of the images formed by the prismatic network is between 15% and 30% whereas one could have expected to collect only a third (in the case where P is equal to 3) or less of the initial brightness.

[0023] This is explained by the fact that for a device with an aperture of F / l, there are many light rays with unused angles of incidence. When a prismatic grating is interposed in the path of these rays, it becomes possible to recover some of the light rays not used in direct vision to form the images projected by the prismatic grating.

[0024] The autostereoscopic image reflected by the spherical mirror can either be directly viewed by observers after deflection by the prismatic grating by providing the observation window opposite the image returned from the converging mirror, or undergo one or more additional reflections by one or more mirrors, such as front-facing mirrors, and by providing the observation window opposite the image reflected by the last optical component on the optical path thus formed by the front-facing mirrors.

[0025] Since the display screen is housed in the casing at a distance approximately equal to twice the focal length F of the spherical mirror, at the same level as the center of the converging mirror, the projected images are reversed at a scale of 1. As the projected images are at a scale of -1, they retain the quality of the source image, without any magnification, which minimizes the geometric distortions of the conical perspective introduced by the projection optics.

[0026] Advantageously and according to the invention, said prismatic network is formed of microlenses comprising three facets of identical useful surfaces so as to be able to deflect the auto stereoscopic image which it receives towards three distinct observers.

[0027] Thus, a prismatic network in which each microprism comprises three distinct facets makes it possible to form 3 identical relief images for three distinct observers.

[0028] Thus, in the case of an installation in a motor vehicle, the invention makes it possible to project an image for the driver (image deviated to the left), an image for the front passenger (image deviated to the right) and an image for the passenger in the center (center image), for example a rear passenger.

[0029] In the case where the prismatic grid is oriented in the horizontal direction, the device allows two images to be projected in two distinct directions, one above and the other below the position of the one that would be visible without a prismatic grid.

[0030] Advantageously and according to the invention, the prismatic network has a pitch greater than the pitch of the cylindrical lenticule network of said autostereoscopic display screen so as to limit the appearance of moiré patterns in the autostereoscopic images projected to observers.

[0031] Indeed, the actual image projected from the autostereoscopic screen at a scale of -1 behaves like a physical optical component placed in the same location. The prismatic grating is a physical component with a periodic structure, just like the lenticular grating. These two transparent periodic structures are therefore capable of forming a moiré image together.

[0032] Moiré patterns result from the superposition of two gratings and the spatial interference between these two gratings. Therefore, to compensate for this phenomenon, the device according to this advantageous variant uses distinct pitches for the two microlens gratings used in the device (the cylindrical lenticular grating of the autostereoscopic screen and the prismatic grating in the conjugate image plane). It is preferable to use a pitch for the prismatic grating that is larger than the pitch for the lenticular grating.

[0033] Advantageously and according to the invention, said prismatic network is arranged so as to extend in a plane corresponding to the projection by said concave mirror of the plane in which the autostereoscopic screen extends, said conjugate plane of the screen.

[0034] According to this advantageous embodiment, the prismatic grating is arranged at the conjugate plane of the autostereoscopic screen. This limits any light scattering due to the presence of an optical component. It should be noted, however, that this arrangement of the prismatic grating at the conjugate plane of the screen is the one most likely to generate moiré patterns if the pitches of the prismatic grating and the lenticular grating of the autostereoscopic screen are too close.

[0035] However, nothing prevents other embodiments from arranging the prismatic grating in front of the conjugate plane towards the converging mirror or behind the conjugate plane towards the observers (i.e., in the vicinity of the conjugate image plane). In particular, the light rays reflected by the converging mirror continue their propagation in a straight line. Therefore, they are deflected in the same way by the prismatic grating regardless of its arrangement between the converging mirror and the conjugate plane. Arranging the prismatic grating outside the housing enhances the surprising effect of the device by giving observers the impression that the three-dimensional images are floating within the prismatic grating outside the housing.

[0036] Advantageously and according to the invention, the autostereoscopic image display screen is housed in the casing opposite said spherical mirror at a distance substantially equal to twice the focal length F, and offset from said optical axis of said spherical mirror, perpendicular to this optical axis by a distance at least equal to half the height of the display screen, said height being defined along the axis perpendicular to said optical axis.

[0037] According to this variant, the display screen is offset from the optical axis of the spherical mirror by a distance at least equal to half the height of the display screen, to prevent the image reflected by the converging mirror from interfering with the original image displayed on the display screen.

[0038] Advantageously and according to the invention, said converging mirror is arranged at the level of said lower wall of said housing, said optical system further comprises a front-facing mirror inclined at an angle of approximately 45° to the vertical and extending above said converging mirror and oriented towards said opening forming said observation window, and said auto stereoscopic screen is oriented towards said front-facing mirror so that the rays projected by said auto stereoscopic screen reach said prismatic grid, after a first reflection by the front-facing mirror towards said converging mirror, a reflection on the converging mirror towards said front-facing mirror and a second reflection by said front-facing mirror towards said prismatic grid.

[0039] A device according to this variant allows all the elements to be housed in a compact casing and the converging spherical mirror to be completely hidden from observers.

[0040] Advantageously and according to the invention, said prismatic network is oriented in the vertical direction so that said distinct directions along which said prismatic network deflects the light rays which it receives extend in the same horizontal plane.

[0041] Thus, according to this embodiment, the device allows the same autostereoscopic image to be projected to observers located at distinct lateral positions facing the device. This embodiment is, for example, suitable for use in a vehicle for projecting the image to the driver, the front passenger, and a middle passenger, such as, for example, a rear passenger sitting in the middle seat.

[0042] According to another embodiment, said prismatic network is oriented in the horizontal direction so that said P distinct directions along which said prismatic network deflects the light rays it receives extend in the same vertical plane.

[0043] This variant allows the image to be projected to observers of different heights positioned in front of the device according to the invention. Such a device can, for example, be used in a shop window to project an image visible to both an adult and a child.

[0044] The invention also relates to a projection device characterized in combination by all or part of the technical characteristics mentioned above or below. 5. List of figures

[0045] Other objects, features and advantages of the invention will become apparent from the following description, given by way of non-limiting example only, and which refers to the accompanying figures in which: - [Fig. 1] is a schematic view of a device according to a first embodiment of the invention, - [Fig.2] is a schematic view of a device according to a second mode of realization of the invention, - [Fig.3] is a schematic view of the light rays deflected by a prismatic grating of a device according to an embodiment of the invention.

[0046] 6. Detailed description of embodiments of the invention

[0047] In the figures, the scales and proportions are not strictly respected, and this, for illustrative and clarity purposes.

[0048] Identical, similar or analogous elements are designated by the same references in all figures.

[0049] The embodiments described in connection with the figures relate to the display of an autostereoscopic image to a plurality of distinct observers, it being understood that they can also be implemented for the display of a sequence of autostereoscopic images.

[0050] As shown in [Fig.1], the device comprises a housing 10, for example an opaque housing comprising a front wall 11, a rear wall 12, connected to each other by an upper wall 13 and a lower wall 14, as well as side walls not visible in the cross-sectional view of [Fig.1].

[0051] Throughout, the device is described as it is when the lower wall 14 extends in a horizontal plane. Also, in [Fig. 1], the rear wall 12 extends vertically, given by the direction of gravity.

[0052] The front wall 11 includes an opening 15 through which the autostereoscopic image emerges from the box 10. This opening 15 is preferably formed of an inclined anti-reflective glass (of the order of 80° with respect to the horizontal).

[0053] The device according to the invention also includes a screen 23 for displaying an autostereoscopic image to be projected. This screen 23 is a multi-viewpoint autostereoscopic image display screen surmounted by an array of cylindrical lenticules forming an optical component that selects the viewpoints of the image. This screen is, for example, an ALIOSCOPY® screen as described in the patent FR2995713 in the name of the applicant. This screen can be mounted in the case by any type of means, gluing, screwing, mechanical locking, etc.

[0054] The device also includes an optical system comprising a converging spherical mirror 24 with optical axis 20, focal length F, and center of radius of curvature C located on said optical axis 20. The spherical mirror can be mounted in the housing by all types of means, gluing, mechanical locking, etc.

[0055] According to the invention, the screen 23 is arranged opposite the spherical mirror 24 at a distance substantially equal to twice the focal length F of the spherical mirror 24, that is to say at a distance of the order of twice the focal length F.

[0056] In addition, the screen 23 is preferably offset from the optical axis 20, perpendicular to this optical axis 20 by a distance at least equal to half the height H / 2 of the display screen, said height H being defined along the axis perpendicular to said optical axis.

[0057] Preferably, the cylindrical lenticular array of the screen 23 has a reduced pitch compared to the optimal pitch allowing observation at a predetermined nominal distance of autostereoscopic images in the absence of the converging mirror 24. For example, if we consider a screen for use at 80 cm, and a mirror with a focal length of 30 cm, the lenticular array should ideally correspond to the lenticular array that would have been necessary for observation at 20 cm. This reduction in pitch can, for example, be achieved by implementing the technical teachings disclosed in applications FR2314796 and FR2314798 on behalf of the applicant.

[0058] The converging mirror 24 is arranged at the rear wall of the housing, and the screen is arranged at the front wall of the housing, in symmetry with respect to the optical axis of said spherical mirror.

[0059] The device according to the invention also includes a prismatic grating 40 arranged, according to the embodiment shown in Figures 1 and 2, at the level of the conjugate plane of the screen 23, that is to say, the image plane of the screen after reflection by the optical system. Furthermore, and for illustrative purposes, the prismatic grating 40 and the observers 01, 02, 03 are shown in perspective, while the housing 10 is shown in cross-section.

[0060] The prismatic grating 40 can be arranged at the level of the conjugate plane of the screen, that is to say, directly above the autostereoscopic screen 23 as shown in Figures 1 and 2, or behind the conjugate plane, or in front of the conjugate plane, in the housing 10. The only requirement is that the prismatic grating 40 be arranged in the vicinity of the conjugate plane. An arrangement of the prismatic grating at the level of the conjugate plane, as illustrated by Figures 1 and 2, makes it possible to obtain sharp images.

[0061] The prismatic grating 40 is an optical component of prismatic lenticles with P facets, for example with 3 facets of identical surface area. Such a prism is schematically represented in cross-section in [Fig. 3]. The bases of this prism are trapezoids. whose wall 40b is oriented towards the converging mirror and the parallel wall 40d is oriented towards observers 01, 02, 03. The bases of this prism further include inclined walls 40a, 40c. Preferably, the walls 40a, 40b, and 40c have identical surface areas. In one embodiment, the surfaces 40a, 40b, and 40c have angles of 130° with each other. The prismatic grating has dimensions at least equal to the dimensions of the screen so that the image projected by the screen at a scale of -1 can be received by the prismatic grating.

[0062] This figure schematically illustrates the path of light rays originating from the optical system (from the converging mirror 24 for the embodiment of [Fig.1] and from the front-facing mirror 26 for the embodiment of [Fig.2]) and deflected by the prismatic grating 40 towards the observers 01, 02 and 03. The prismatic grating 40 allows a portion of the light rays not used in direct vision to be recovered (rays schematically represented by dotted lines and thick lines) to form the images projected towards the observers 01 and 03, arranged on either side of the central observer 02.

[0063] Such a device is therefore particularly well suited for installation in a motor vehicle and allows, with a single device, the projection of autostereoscopic images to 3 distinct observers installed at distinct locations in the vehicle relative to the device housing.

[0064] Figure 2 illustrates another embodiment of the invention in which the optical system comprises, in addition to the converging spherical mirror 24, a front-facing mirror 26. This front-facing mirror 26 is inclined at an angle of approximately 45° to the vertical and extends above the converging mirror 24, which is arranged horizontally at the level of the lower wall 14 of the housing 10. The front-facing mirror 26 is oriented towards the opening of the housing forming the observation window so as to be able to project the rays it receives towards the prismatic grating 40. The front-facing mirror can form the rear wall of the housing.

[0065] Of course, the shape of the casing in the figures is schematic and this shape has no bearing on the technical effects of the invention. Other variants can be considered without impacting the technical effects of the invention.

[0066] It should also be noted that the invention has been described with a prismatic grating. However, the invention can also be implemented with holographic optics exhibiting behavior identical to a prismatic grating. In other words, throughout this text, the terminology "prismatic grating" covers not only an optical component of prismatic lenticles with P facets, but also holographic optics exhibiting behavior identical to such an optical component.

Claims

Demands

1. Aerial and dematerialized projection device of an autostereoscopic digital image intended for P distinct observers, P being equal to 2 or 3, comprising: - a housing (10) comprising a front wall (11), a rear wall (12), connected to each other at least by an upper wall (13) and a lower wall (14), said front wall (11) comprising an opening forming an observation window (15) of said autostereoscopic image, - an optical system comprising at least one optical component of the type of converging spherical mirror (24) having an optical axis (20), a focal length F, a center of radius of curvature C located on said optical axis, said optical system being arranged in said housing (10) so that it can direct at least a part of the incident light received towards said observation window (15),- a screen (23) for displaying autostereoscopic images equipped with a network of cylindrical lenticles forming an optical component that selects the viewpoints of said autostereoscopic digital image (31) to be projected, housed in said casing (10) opposite said spherical mirror (24) converging at a distance substantially equal to twice the focal length F, characterized in that it further comprises an optical component of prismatic lenticles with P facets, said prismatic network (40), arranged in the vicinity of the conjugate plane of said autostereoscopic screen and oriented towards said optical system, so as to be able to deflect the light rays it receives from the optical system along P distinct directions along which distinct observers can be positioned to perceive the projected autostereoscopic image, said directions being dependent on the physical characteristics of the prismatic network.

2. Projection device according to claim 1, characterized in that said prismatic network is formed of microlenses comprising three facets of identical surfaces so as to be able to deflect the auto stereoscopic image which it receives towards three distinct observers.

3. Projection device according to any one of claims 1 to 2, characterized in that said prismatic grid has a pitch greater than the pitch of the cylindrical lenticule array of said auto stereoscopic display screen so as to limit the appearance of moiré patterns in the autostereoscopic images projected to observers.

4. Device according to any one of claims 1 to 3, characterized in that said prismatic network is arranged so as to extend in a plane corresponding to the projection by said converging mirror of the plane in which the autostereoscopic screen extends, said conjugate plane of the screen.

5. Device according to any one of claims 1 to 4, characterized in that said autostereoscopic image display screen (23) is housed in said casing (10) opposite said spherical mirror (24) at a distance substantially equal to twice the focal length F, and away from said optical axis (20) of said spherical mirror (24), perpendicular to said optical axis (20) by a distance at least equal to half the height of the display screen (23), said height (H) being defined along the axis perpendicular to said optical axis (20) and said spherical mirror (24) is arranged opposite said opening (15) forming said observation window.

6. Device according to any one of claims 1 to 4, characterized in that said converging mirror (24) is arranged at the level of said lower wall (14) of said housing, said optical system further comprises a front-facing mirror (26) inclined at an angle of approximately 45° with respect to the vertical and extending above said converging mirror (24) and oriented towards said opening forming said observation window, and said autostereoscopic screen is oriented towards said front-facing mirror (26) so that the rays projected by said autostereoscopic screen reach said prismatic grid, after a first reflection by the front-facing mirror (26) towards said converging mirror (24), a reflection on the converging mirror (24) towards said front-facing mirror (26) and a second reflection by said front-facing mirror (26) towards said prismatic grid (40).

7. Device according to any one of claims 1 to 6, characterized in that said prismatic grid is oriented in the vertical direction such that said distinct directions along which said prismatic grid deflects the light rays it receives extend in the same horizontal plane. 12

8. Device according to any one of claims 1 to 6, characterized in that said prismatic grid is oriented in the horizontal direction such that said distinct directions along which said prismatic grid deflects the light rays it receives extend in the same vertical plane.

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