Device for aerial and dematerialised projection of an autostereoscopic image to a plurality of distinct observers

Abstract

The invention relates to a device for aerial and dematerialised projection of a digital image (31), comprising: a housing (10) in which an opening (15) is provided, the opening forming a window for observing an actual and dematerialised aerial image of the digital image (31); an optical system comprising at least one optical component of the converging spherical mirror (24) type, the optical system being arranged in the housing (10) such that it can orient at least part of the incident light received towards the observation window (15); a screen (23) for displaying the digital image (31) to be projected, the screen being accommodated in the housing (10) opposite the spherical mirror (24) at a distance equal to twice the focal length of the spherical mirror; a prismatic grating which has 2 or 3 facets, is oriented towards the converging mirror (24) and is arranged in the vicinity of the conjugate plane of the autostereoscopic screen, so as to be able to deflect the light rays it receives from the converging mirror (24) in multiple distinct directions along which distinct observers can be positioned in order to perceive the projected autostereoscopic image.

Description

[0001] TITLE OF THE INVENTION: AERIAL AND DEMATERIALIZED PROJECTION DEVICE FOR AN AUTOSTEREOSCOPIC IMAGE INTENDED FOR SEVERAL DISTINCT OBSERVERS

[0002] 1. Technical field of the invention

[0003] 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.

[0004] 2. Technological background

[0005] 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.

[0006] Such a device is known for the projection of real objects. Such a device typically includes a case (opaque or not) in which an opening is provided to form a window for viewing 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 viewing window.

[0007] Such a device is also known for projecting an autostereoscopic image. This device was described by the applicant in document W02018 / 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.

[0008] 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.

[0009] The inventors sought to improve this device to allow its simultaneous use by several distinct observers without requiring the observers to be close to each other.

[0010] One of the applications targeted by this new device is installation in a dashboard of a motor vehicle to allow the driver, the front seat passenger and a passenger located in the center, for example in the rear of the vehicle or in the center of a front bench seat, to simultaneously perceive the same autostereoscopic image, while using only one autostereoscopic screen and one converging mirror.

[0011] 3. Objectives of the invention

[0012] The invention aims to provide an aerial and dematerialized projection device for a digital image that overcomes at least some of the drawbacks of known solutions.

[0013] The invention also aims to provide such a device which is suitable for an autostereoscopic image or a sequence of autostereoscopic images.

[0014] 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 separate observers.

[0015] 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.

[0016] The invention also aims to provide, in at least one embodiment, such a device adapted to 2 or 3 distinct observers of different sizes.

[0017] 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 one converging mirror.

[0018] The invention also aims to provide, in at least one embodiment, such a projection device adapted for integration within a motor vehicle.

[0019] 4. Description of the invention

[0020] To achieve this, 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.

[0021] Such a device comprises: a housing including a front wall, a rear wall, connected to each other at least by a top wall and a bottom wall, said front wall including an opening forming an observation window for said autostereoscopic image, an optical system including at least one converging spherical mirror (or any converging optical component such as a holographic optical element having 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 part of the incident light received towards said observation window, an autostereoscopic image display screen equipped with an array of cylindrical lenticles forming an optical component for selecting the viewpoints of said autostereoscopic digital image to be projected,housed in said casing opposite said spherical mirror at a distance approximately equal to twice the focal length F.,

[0022] 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.

[0023] 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.

[0024] The deviation of light rays by the prismatic grating depends on the prismatic grating and the rules of geometric optics.

[0025] 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.

[0026] Throughout this 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, the term "converging spherical mirror" is used throughout for ease of 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.

[0027] The inventors determined that the loss of brightness of each of the images formed by the prismatic network is between 15% and 30%, whereas one might have expected to collect only a third (in the case where P is equal to 3) or less of the initial brightness.

[0028] This is explained by the fact that for a device with an aperture of f / 1, there are many light rays with unused angles of incidence. When a prismatic grating is placed 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.

[0029] The autostereoscopic image reflected by the spherical mirror can either be directly viewed by observers after deflection by the prismatic grating by maintaining the viewing 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 maintaining the viewing window opposite the image reflected by the last optical component on the optical path thus formed by the front-facing mirrors.

[0030] 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.

[0031] 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 autostereoscopic image it receives towards three distinct observers.

[0032] 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.

[0033] 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.

[0034] In the case where the prismatic network 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 network.

[0035] Advantageously and according to the invention, the prismatic network has a pitch greater than the pitch of the cylindrical lenticle network of said autostereoscopic display screen so as to limit the appearance of moiré patterns in the autostereoscopic images projected to observers.

[0036] 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 pattern together.

[0037] Moiré patterns result from the superposition of two gratings and the spatial interference between them. Therefore, to compensate for this phenomenon, the device, according to this advantageous variant, uses distinct spacings for the two microlens arrays used in the device (the cylindrical lenticular array of the autostereoscopic screen and the prismatic array in the conjugate image plane). It is preferable to use a larger spacing for the prismatic array than for the lenticular array.

[0038] 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.

[0039] According to this advantageous variant, the prismatic grating is arranged at the conjugate plane of the autostereoscopic screen. This limits any light scattering caused by the presence of an optical component. However, it should be noted 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.

[0040] 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 casing 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 casing.

[0041] 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 away 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.

[0042] 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 interacting with the original image displayed on the display screen.

[0043] Advantageously, and according to the invention, the converging mirror is arranged on the lower wall of the housing. The optical system further comprises a front-facing mirror inclined at an angle of approximately 45° to the vertical, extending above the converging mirror and oriented towards the opening forming the observation window. The autostereoscopic screen is oriented towards the front-facing mirror such that the rays projected by the autostereoscopic screen reach the prismatic grating after a first reflection from the front-facing mirror to the converging mirror, a reflection from the converging mirror back to the front-facing mirror, and a second reflection from the front-facing mirror back to the prismatic grating. A device according to this embodiment allows all the elements to be housed in a compact casing and completely obscures the converging spherical mirror from the observers.

[0044] 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 it receives extend in the same horizontal plane.

[0045] Thus, according to this variant, the device allows the same autostereoscopic image to be projected to observers located at distinct lateral positions in front of the device. This variant 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 a rear passenger sitting in the middle seat.

[0046] According to another embodiment, said prismatic network is oriented in the horizontal direction so that said distinct directions along which said prismatic network deflects the light rays it receives extend in the same vertical plane.

[0047] 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.

[0048] The invention also relates to a projection device characterized in combination by all or part of the technical characteristics mentioned above or below.

[0049] 5. List of figures

[0050] 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:

[0051] [FIG 1] is a schematic view of a device according to a first embodiment of the invention,

[0052] [FIG 2] is a schematic view of a device according to a second embodiment of the invention,

[0053] [FIG 3] is a schematic view of the light rays deflected by a prismatic grating of a device according to one embodiment of the invention.

[0054] 6. Detailed description of embodiments of the invention

[0055] In the figures, the scales and proportions are not strictly respected for the purposes of illustration and clarity.

[0056] Identical, similar or analogous elements are designated by the same references in all figures.

[0057] 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.

[0058] As shown in Figure 1, the device includes 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 Figure 1.

[0059] Throughout, the device is described as it is when the lower wall 14 extends in a horizontal plane. Also, in Figure 1, the rear wall 12 extends vertically, given by the direction of gravity.

[0060] 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).

[0061] 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 lenticles forming an optical component that selects the image viewpoints. This screen is, for example, an ALIOSCOPY® screen as described in patent FR2995713 filed by the applicant. This screen can be mounted in the housing by any type of means, such as gluing, screwing, mechanical fastening, etc.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] Preferably, the cylindrical lenticular array of the screen 23 has a reduced pitch compared to the optimal pitch for observing autostereoscopic images at a predetermined nominal distance 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.

[0066] 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.

[0067] The device according to the invention also includes a prismatic grating 40 arranged, as 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, 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.

[0068] The prismatic grating 40 can be arranged at the level of the conjugate plane of the screen, that is, 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, within the housing 10. The only requirement is that the prismatic grating 40 be arranged in the vicinity of the conjugate plane. Arranging the prismatic grating at the level of the conjugate plane, as illustrated in Figures 1 and 2, produces sharp images.

[0069] 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 Figure 3. The bases of this prism are trapezoids, with wall 40b oriented towards the converging mirror and the parallel wall 40d oriented towards the observers 01, 02, 03. The bases of this prism also include inclined walls 40a, 40c. Preferably, walls 40a, 40b, and 40c have identical surface areas. In one embodiment, surfaces 40a, 40b, and 40c are at angles of 130° to 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.

[0070] This figure schematically illustrates the path of light rays originating from the optical system (from the converging mirror 24 for the embodiment of figure 1 and from the front face mirror 26 for the embodiment of figure 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.

[0071] 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 in distinct locations in the vehicle relative to the device's housing.

[0072] 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.

[0073] 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 variations can be considered without impacting the technical effects of the invention. It should also be noted that the invention has been described using a prismatic array.

[0074] The invention can nevertheless 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. A device for the aerial and dematerialized projection 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 converging spherical mirror type optical component (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 which 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 autostereoscopic 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 network has a pitch greater than the pitch of the cylindrical lenticle network of said autostereoscopic 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 network is oriented in the vertical direction so that said P distinct directions along which said prismatic network deflects the light rays it receives extend in the same horizontal plane.

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

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