AUTOSTEREOSCOPIC HEAD-UP DISPLAY TYPE SYSTEM

Abstract

AUTOSTEREOSCOPIC HEAD-UP DISPLAY SYSTEM The invention relates to a system for the dematerialized projection of an autostereoscopic image to an observer whose eyes are positioned within a predetermined three-dimensional space, referred to as the eyebox. The system comprises: an optical device including at least one converging optical component arranged relative to the eyebox so as to direct the light rays it receives towards the eyebox; an autostereoscopic screen arranged relative to the optical device so that the light rays it emits can reach the converging optical component, and comprising: a pixel matrix and a lenticular grating above the pixel matrix. The grating has a pitch P determined from a known pitch P' of a screen intended for direct viewing. Figure 1

Description

Title of the invention: AUTOSTEREOSCOPIC HEAD-UP DISPLAY TYPE SYSTEM Technical field of the invention

[0001] The invention relates to an autostereoscopic system, of the head-up display type, allowing at least one observer positioned in front of the display system to observe an aerial and dematerialized projection of an autostereoscopic image. Technological background

[0002] Autostereoscopy is a technique that allows the display of three-dimensional images without requiring the observer to wear special glasses. This technique is known, in particular from patent documents WO2006 / 024764, WO2014 / 041504, WO2013 / 140363, WO2014 / 016768, WO2019207235 and WO2022175052 in the name of the applicant.

[0003] Generally speaking, an autostereoscopic image consists of a plurality of elementary image strips nested according to a predetermined mixing scheme, corresponding to views of the same object or scene from different viewpoints. A selector device, typically consisting of a cylindrical lenticle array or a parallax barrier, is positioned in front of the display screen so as to allow the projection of a pair of elementary images corresponding to two different viewpoints of the scene, respectively towards the two eyes of the observer, thus creating an impression of depth in the observer's brain.

[0004] Autostereoscopic screens generally result from the addition of a glass optical component to the surface of an LCD panel. The size, thickness, and weight of the glass are proportional to the screen size. In practice, manufacturing and mounting a lenticular lens array on a screen wider than 2 m proves so cumbersome that manufacturers rarely offer solutions for larger screen sizes.

[0005] Moreover, it is very rarely possible to display content whose total depth exceeds the screen diagonal, with clarity and without ghosting. The content must therefore be designed to limit its size. Consequently, multi-camera systems, whether physical equipment for shooting or software cameras, are often associated with geometric parameterization models that correlate the stereoscopic base and the focal length in order to control the distance to the most distant backgrounds of a scene. The largest available autostereoscopic screens can display a scene with a maximum depth of 3 m.

[0006] The inventors sought to overcome the limitations of current autostereoscopic screens to propose a solution enabling the projection of large-dimension images with a very large depth of field. Objectives of the invention

[0007] The invention thus aims to provide an autostereoscopic system which makes it possible to project large-dimension images (for example 4 meters wide) with a very large depth of field (for example 100 meters deep).

[0008] The invention also aims to provide an autostereoscopic system that allows an observer to benefit from a binocular vision close to reality.

[0009] The invention also aims to provide such a system which allows content to be displayed which can maintain orthostereoscopic proportions.

[0010] The invention also aims to provide, in at least one embodiment, such a system which allows a coherence of the proportions of the autostereoscopic image projected by the system with the proportions of the real elements of the environment near the system.

[0011] The invention also aims to provide, in at least one embodiment, such a system which can be used for augmented reality applications.

[0012] The invention also aims to provide, in at least one embodiment, a compact autostereoscopic system, which can for example be used for automotive applications.

[0013] The invention also aims to provide a versatile system that can be used in different configurations for various applications. Description of the invention

[0014] To this end, the invention relates to a dematerialized projection system of an autostereoscopic image intended for an observer whose eyes are positioned within a predetermined three-dimensional space, called an eye box, having a predetermined width L, at least greater than the average interpupillary distance of an observer and preferably greater than the average width of a human head.

[0015] The system according to the invention is characterized in that it comprises: - an optical device comprising at least one converging optical component with behavior identical to a concave mirror of radius of curvature R and focal length F, said optical device being arranged with respect to said eye box so as to be able to direct the light rays it receives towards a viewing window observable from said eye box, - an autostereoscopic screen arranged in relation to said optical device so that the light rays it emits can reach said window of visualization, after reflection on said converging optical component, and having traveled a distance d less than F, said auto stereoscopic screen further comprising: • a pixel matrix of N rows and M columns, each pixel being composed of a plurality of sub-pixels of different colors, • a lenticular array surmounting said matrix and having a pitch P determined from a pitch P', called the nominal pitch, of an autostereoscopic screen, called the nominal screen, having usage characteristics identical to those of the system's screen and intended to be viewed directly at a distance corresponding to the usage distance of said system's screen, by the formula P=P\(\+CI(SM )) where C is the number of viewpoints visible simultaneously from said usage distance inside said eye box, when said nominal screen of pitch P' is arranged in said projection system in place of said screen, and S is the number of different image viewpoints addressed by each pixel of said pixel matrix

[0016] The system according to the invention thus allows an observer placing his eyes within a predetermined three-dimensional space, called an eye box, to perceive a large-dimension image from a smaller-dimension autostereoscopic screen (for example a 5.5-inch (13.97 cm) or 13.3-inch (33.782 cm) screen), and whose image has a large depth of field.

[0017] The observer benefits from a relief amplitude unmatched by the autostereoscopic screens of the prior art and from a large-dimension image, whereas the autostereoscopic screen, which he does not perceive directly, may be of reduced dimension.

[0018] To obtain this result, the invention uses a specific autostereoscopic screen, arranged with respect to the optical device, in such a way that its reflection appears greatly magnified behind the converging optical component, or behind a front-facing or semi-transparent plane mirror allowing for an angle reflection of the screen's reflection.

[0019] The viewing window observable from said eye box and through which the observer observes the scene in relief can be physically delimited by the converging optical component or be formed by the reflection of the converging optical component in a front-facing mirror or a semi-transparent mirror inclined towards the observer and the converging optical component, preferably at an angle close to 45°.

[0020] Furthermore, the autostereoscopic screen is separated from the converging optical component (which behaves identically to a concave mirror of radius R and focal length F) by a distance d less than the focal length F of the optical component. When the distance from the screen to the optical component is strictly less than its focal length (equal to R / 2 where R denotes the radius of the mirror), it thus acts as a magnifying mirror. The screen is then reflected behind the optical component, with the image magnified more or less depending on the distance.

[0021] The system according to the invention thus implements a specific autostereoscopic screen specially designed for this sole purpose, to allow observation of the dematerialized reflection of an autostereoscopic image reflected by a converging optical component. Such a converging optical component is, for example, a concave mirror or a holographic lens. Throughout, the terminology of concave mirror is used primarily for ease of reading, but it is understood that this concave mirror can be replaced by a holographic lens without altering the technical effects of the invention.

[0022] In particular, an autostereoscopic screen designed for direct observation is not suitable for use within a device implementing reflection of the screen on a concave mirror.

[0023] Indeed, such a screen dematerialization device must make it possible to find in the main lobe of the screen all the targeted characteristics: number of viewpoints, flat tint distance and distribution of viewpoints on the pixel matrix of the screen.

[0024] The flat tint distance, which results from moiré theory, designates the distance from the screen from which it is possible to observe only one of the multiple viewpoints of the image on the entire surface of the screen (regardless of the number of viewpoints of the image). This distance is unique for each model of autostereoscopic screen.

[0025] At the flat tint distance, an observer can successively see, with a single eye, the series of viewpoints used, which is repeated across the entire width of the screen. Each of the series thus observed corresponds to a lobe. Care must be taken to ensure that both eyes of the observer are in the same lobe.

[0026] As an example, we want the screen to be observed at the preferred distance of 1 m (in other words, we want the screen to have a flat color distance of 1 m). We consider the average distance between the observer's two eyes to be 6.5 cm. We want a succession of viewpoints every 3.25 cm of displacement parallel to the plane of the screen at the flat color distance. With 10 viewpoints, the lobe is 3.25 cm x 10, or 32.5 cm; this is the central lobe 0. After this, the series of 10 viewpoints reappears in the same order on each side of the main lobe. This forms the two lobes -1 and +1. And so on, moving further and further away from lobe 0 in continuity and right / left symmetry. Lobes -2 and +2 etc.

[0027] Practice shows that a concave mirror alters all of these characteristics so that an autostereoscopic screen designed for direct vision is poorly or not at all suitable for use in a device implementing a concave mirror.

[0028] The distortions induced by the concave mirror necessitate the introduction of new rules for defining the parameters of the lenticular grating, different from those of a grating used in direct vision. For the reflected image of the screen to have the desired autostereoscopic properties, it is necessary to modify the characteristics of the screen's lenticular grating. The presence of a concave mirror transforms all the parameters described above. To maintain the desired characteristics, the grating pitch must be increased compared to the pitch of an equivalent screen that would be viewed directly without reflection by a concave mirror. The inventors have succeeded in determining the level of correction required for the pitch to enable this reflected observation in a concave mirror.

[0029] This increase in the step size is obtained according to the invention from the step size P' of an autostereoscopic screen, called the nominal screen, having identical usage characteristics to that of the system screen (i.e., same flat tint distance, same number of viewpoints, same focal length, etc.) and intended to be observed in direct vision at a distance corresponding to the usage distance of said system screen, by the formula P=P'.(1+C / (SM )) where C is the number of viewpoint parts visible simultaneously from said usage distance (flat tint distance) inside the eye box, when said nominal screen of step size P' is arranged in said projection system in place of said screen, S is the number of different viewpoints of the image addressed by a pixel of the pixel matrix and M the horizontal resolution of the pixel matrix.

[0030] For example, for sub-pixel addressing from a pixel matrix where each pixel comprises 3 sub-pixels of different color, then S is equal to 3. Thus, the step P is obtained by the formula P=P'.(1+C / 3.M).

[0031] If the same matrix is ​​used for addressing the entire pixel, then S is equal to 1 and the step P is obtained by the formula P=P'.(1+C / M).

[0032] Throughout the following, and to facilitate reading, we consider sub-pixel addressing and a matrix in which each pixel is formed of 3 sub-pixels, it being understood that the technical teachings provided apply mutatis mutandis to whole pixel addressing and / or to matrices comprising a number of sub-pixels distinct from 3.

[0033] If a color test pattern displayed on a nominal autostereoscopic screen (whose operating parameters are identical to those of the system) is reflected into a concave mirror, the reflected image of this color test pattern, in return, presents at the flat tint initially chosen a number of color bars corresponding to a projected step having gained several lenses for the entire network compared to the screen.

[0034] For example, for a 10-viewpoint screen, if the observer perceives 10 color bars at any distance from the screen (assuming the screen displays one color per viewpoint), this means they have moved away from the flat color distance to the point where the projected pixel pitch has increased or decreased by 10 sub-pixels, i.e., by the pitch of one lens. If the observer perceives 20 color bars, it means the projected pixel pitch has increased or decreased by 20 sub-pixels, i.e., by two lenses. If the screen displays only one color, it means the observer is precisely at the flat color distance.

[0035] Insofar as it is possible to know (by manufacturing) very precisely the pitch of the lenticular array of a nominal screen, for example to the nearest 100th of a micron, it becomes possible to correct the effect of the concave mirror on the optical path which connects the surface of the real screen to the eyes of the user via the conjugate dematerialized real image, by machining a new lenticular array with the corrected pitch.

[0036] It can be seen that this amounts to creating a flat tint when viewed directly from outside the projection device at a very long distance from the screen. This therefore amounts to increasing the pitch of the lenticular grating compared to direct viewing.

[0037] If a nominal 10-viewpoint screen placed in the projection device allows 12 color bars to be viewed at the desired flat tint distance of 1 m, for example (assuming the screen displays 10 distinct colors, each color corresponding to a viewpoint), and since the pitch of a lens corresponds to 10 colors in direct vision, 12 color bars reflected in the concave mirror represent 12 / 10ths of the lens pitch. It is necessary to increase the pitch of the lenticular array by this value to adapt it to the device according to the invention and to divide it by the total number of lenses to calculate the exact impact on the pitch that will be applied to the machining of the lenticular array of the screen intended to be arranged in the projection device.

[0038] This makes it possible to obtain a system in which the dematerialized autostereoscopic image and reflected by the mirror allows us to recover all the characteristics predicted in the central lobe.

[0039] For the first time, it becomes possible to easily determine the pitch correction to be applied to a nominal autostereoscopic screen, for its integration into a device implementing a converging optical component such as a concave mirror, by knowing the pitch of the nominal screen and determining the number of viewpoints visible simultaneously from said operating distance. inside said eye box, when this screen is housed in the device according to the invention.

[0040] It therefore becomes possible for the first time to use an auto stereoscopic screen in association with a concave mirror.

[0041] As previously seen, this determination of the number of viewpoint parts visible simultaneously can be facilitated by displaying a color target on the screen, which makes it possible to count, from said eye box corresponding to the screen's usage distance, the number of color bands visible simultaneously.

[0042] Advantageously and according to the invention, said lenticular network of said autostereoscopic screen forms a plurality of zones in front of the screen, called lobes, in which all the different viewpoints of the image succeed one another at a privileged distance from the screen, called the flat tint distance, corresponding to the distance at which each eye of the observer perceives only one viewpoint among all the viewpoints of the image on the entire surface of the screen and said network is perfectly focused in the central lobe so as to avoid any overlap of viewpoints only in the central lobe.

[0043] According to this advantageous embodiment, the lenticular grating is perfectly focused in the central lobe. The notion of a grating perfectly focused in the central lobe means that there is no overlap of viewpoints in the central lobe.

[0044] Indeed, it is known that an autostereoscopic screen is characterized in particular by its resolving power, that is to say, by its ability to limit or eliminate the overlap between viewpoints, which generates ghosting and double images. The LCD screens used to design autostereoscopic screens are generally not designed by the original manufacturers with the intention of later accommodating a lenticular lens array on their surface. The structure of their panel, made up of colored pixels and subpixels, can have very varied shapes. Every detail of a pixel—its geometry, its topology, that of its subpixels, as well as the black mask surrounding them—is magnified when it crosses the optical axis of the lenses forming the micro-lenticular array placed on its surface. Contagion can occur and generate mixing between neighboring viewpoints or luminous inhomogeneities.The final optical quality of a screen therefore depends on its resolving power.

[0045] Furthermore, optical components do not have homogeneous optical properties at all angles of incidence from the observer's gaze, due to variations in their front and side focus. Optically speaking, the lobes follow one another but are not exactly alike. In general, designers of autostereoscopic screens favor the two secondary lobes adjacent to the central lobe, so as to optimize two lobes rather than just one. The focal length of the central lobe (No. 0) is slightly shorter, The focal length of the adjacent lobes n°-1 and n°+1 is perfect, while that of lobes n°-2 and n°+2 is slightly longer. The overlap between viewpoints resulting from these local variations in focus prevents the desired ideal focal length from all angles.

[0046] In the case of the present invention, it was decided to optimize only the central lobe and to ensure that its focal length is perfect, to the detriment of the other lobes.

[0047] The system according to the invention introduces a constraint on the placement of the observer's eyes in order to optimize the resolving power of the screen and offer an unparalleled experience of relief and depth.

[0048] When used with a flat tint and viewed from the front, the resolving power of a lenticular grating perfectly focused in the central lobe is optimum and allows for exceptional depths of field without ghosting.

[0049] The virtual image of the autostereoscopic screen of a system according to the invention, more or less enlarged, is visible in the central lobe but not from the side in the secondary lobes.

[0050] The depth of field made possible under these conditions allows us to overturn the rules of composition of relief scenes which are usually imposed in autostereoscopy.

[0051] The virtual image perceived through the "porthole" formed by the concave mirror can even reproduce the proportions of the surrounding real physical space. The orthoscopic relationship between the real and the virtual is of high quality.

[0052] Under these conditions and in an augmented reality configuration with a semi-transparent flat mirror, it becomes possible to project virtual objects into physical space on the scale of the real world, at depths unimaginable until now.

[0053] The relief efficiency of the system is very favorable: a small disparity results in the perception of a very large volume.

[0054] Whereas the same scene in relief with little disparity in the most opposite planes of the image gives a modest sensation of volume on a small screen seen up close, it delivers considerable depth of field and perfectly superimposed on the real world, without effort or fatigue, when the virtual image of this same screen is enlarged and moved back thanks to its reflection in the concave mirror.

[0055] Whether the concave mirror is viewed directly or by reflection in a front-facing plane mirror, a semi-transparent mirror, or even a vehicle's windshield, the size of the window through and beyond which the viewer can observe the scene is limited by the physical size of the concave mirror. Consequently, it is not advisable to use mirrors that are too small. A mirror 30 cm wide placed at approximately 1 m seems to be a minimum size for perceiving a scene in relief by binocular vision, whether in augmented reality in combination with a semi-transparent mirror or in direct vision.

[0056] Preferably, the lenticular grating is further configured so that successive projected viewpoints of the central lobe cover the width L of the eyebox. Thus, no lobe transitions are observable in the eyebox.

[0057] Different configurations are possible to benefit from the advantages of a system according to the invention.

[0058] Thus and according to a first embodiment, said converging optical component and said autostereoscopic screen extend horizontally and are arranged on the same vertical axis, said optical device further comprising a semi-transparent mirror having a reflective surface oriented towards said eye box and towards said converging optical component, said semi-transparent mirror being inclined at an angle of 45° with respect to the optical axis of said converging optical component which extends vertically, and arranged between said screen and said converging optical component.

[0059] Thus, according to this embodiment, the screen and the converging optical component (concave mirror or holographic optic) face each other and are each arranged on the same axis, which corresponds to the optical axis of the converging optical component. A second semi-transparent mirror is arranged at 45° between the converging optical component and the autostereoscopic screen, with its semi-reflective front face oriented towards the converging optical component and facing the eye box.

[0060] Thus, the light emitted by the screen passes through the semi-transparent mirror on the non-reflective side. The light is then reflected by the concave mirror, and this reflection is in turn reflected at 45° by the reflective front face of the semi-transparent mirror.

[0061] It should be noted that some light is lost each time it passes through the semi-transparent mirror. Therefore, it is preferable to have a very bright screen to compensate for these successive line losses of light, which are equivalent to 75% of the original screen light.

[0062] Viewed through the semi-transparent mirror, the virtual images are superimposed on the real world and can produce an illusion of augmented reality.

[0063] If the system is placed in front of a black background, the reflectivity of the mirror is much better, the relief image is much brighter and more contrasted, but augmented reality is no longer possible.

[0064] This configuration has a drawback resulting from the "in-axis" architecture of the system, namely that the reflection of the observer's face can interfere with the stereoscopic image. When the observer is illuminated, the light they reflect follows the same optical path in reverse. It is reflected off the reflective surface of the semi-transparent mirror at a 45° angle to them, partially reflected back towards the concave mirror, then combined with the reflection from the screen, and finally returned to the observer's eyes. The viewer, when positioned closer than the focal length of the concave mirror, perceives a greatly enlarged, distorted reflection of their face in the background. If they stand at the mirror's focal length, the reflection is projected to infinity and is no longer visible. However, if they move back, the inverted, reduced reflection of their face again distorts the three-dimensional scene.

[0065] For certain use cases, and particularly when ambient light is controlled, this system offers significant practical advantages because it allows for easy adjustment of all the parameters of the stereoscopic scene to match the real environment. Furthermore, since the screen and the concave mirror are centered on the axis, this design minimizes the spherical distortions inherent in using an off-axis concave mirror.

[0066] According to a second embodiment, said converging optical component and said autostereoscopic screen extend vertically, facing each other, vertically offset from each other, and arranged with respect to the eyebox such that the eyebox is located behind and above the autostereoscopic screen, said converging optical component whose optical axis extends horizontally being arranged facing the eyebox.

[0067] This second configuration eliminates the unwanted reflections of the observer that are present in the first configuration. Furthermore, this second configuration preserves the initial screen brightness but does not allow for use in augmented reality.

[0068] The screen and the concave mirror are arranged horizontally in a line, one behind the other. The screen is turned away from the viewer and the concave mirror faces him.

[0069] The user positions themselves behind the screen and looks at the concave mirror located behind it, slightly higher than the screen. The "eye box" is located above the screen.

[0070] The system operates "off-axis". The concave mirror is oriented so that its horizontal median axis divides the space into two superimposed volumes. The screen, facing the mirror, occupies the lower volume. It is tilted so that its reflection in the concave mirror is upright, allowing the user to see a perfectly vertical, enlarged virtual image.

[0071] It is possible to offset the system further to enlarge the "eye box". The screen can be lowered slightly more and reoriented relative to the concave mirror. This results in greater distortion of the imaged scene. When using a concave mirror with a longer focal length, these distortions remain acceptable.

[0072] The viewer looks at the enlarged reflection of the screen through the "window" of the concave mirror and he abstracts from the physical screen.

[0073] Thanks to this "off-axis" architecture, unwanted reflections are eliminated. Even when the user is illuminated, the light they reflect takes the reverse optical path and ends up on the screen, which reflects virtually nothing back.

[0074] According to a third embodiment, said optical device further comprises a semi-transparent mirror arranged on the optical axis of said converging optical component, having a reflective surface oriented towards said eye box and towards the converging optical component, said semi-transparent mirror being inclined at an angle of 45° with respect to the optical axis of said converging optical component which extends vertically, said screen being arranged with respect to the eye box such that the eye box is located at the rear of said screen which faces said semi-transparent mirror, and is vertically offset with respect to the reflection of the converging optical component in said semi-transparent mirror.

[0075] This third configuration makes it possible to eliminate unwanted reflections, while offering the possibility of projecting 3D content in augmented reality.

[0076] Thus, and as in the second configuration, the screen is arranged with its back to the eye box and slightly inclined upwards relative to the vertical.

[0077] Instead of facing it, the concave mirror is here placed flat in front of the screen.

[0078] A semi-transparent plane mirror inclined at 45° is arranged above the concave mirror, with its reflective face oriented towards the mirror and towards the screen. By reflection, it forms a virtual image of the concave mirror at the same location where it is physically situated in the second configuration.

[0079] The screen is reflected in the virtual image of the concave mirror under the same conditions as before, but this time in augmented reality.

[0080] The viewer sees the environment through the semi-transparent mirror inclined at 45°, onto which are superimposed the objects on a black background displayed in relief on the screen.

[0081] As in the first configuration, this is done at the expense of the original brightness of the screen, divided here by a factor of 4. Not only is the reflection of the concave mirror in the semi-transparent mirror at 45° attenuated by a factor of 2 but the light emitted by the screen also passes through this same mirror, which absorbs half of it.

[0082] It is therefore preferable to use a screen 4 times brighter to obtain a light intensity comparable to that of a screen seen live.

[0083] According to a fourth embodiment, said converging optical component and said autostereoscopic screen extend opposite each other, horizontally offset from each other, and inclined with respect to the horizontal, said optical device further comprising a semi-transparent mirror having a reflective surface oriented towards said eye box and towards said converging optical component, said semi-transparent mirror being inclined at an angle of 45° with respect to the vertical and arranged in so that the light rays from the screen can reach the converging optical component without passing through the semi-transparent mirror.

[0084] This fourth configuration allows for use in augmented reality while limiting the decrease in brightness.

[0085] This is an "off-axis" variant of the first embodiment. Thus, the semi-transparent flat mirror remains essential to generate an augmented reality experience, but it is no longer aligned with the screen, so as to prevent the light from the screen from passing through the flat mirror before being reflected in the concave mirror.

[0086] The screen is offset from the plane mirror after a slight forward tilt of the concave mirror / plane mirror assembly. The screen is moved forward until it no longer overhangs the plane mirror. It is then tilted backward so as to remain facing and parallel to the concave mirror. The rear of the screen is then substantially aligned with the front of the concave mirror.

[0087] The orthogonal projection of the center of the screen onto the concave mirror is no longer at its center. We are therefore in the conditions of an "off-axis" projection. As in the second and third embodiments, this prevents the reflection of the screen from being contaminated by the unwanted reflection of the viewer's face.

[0088] The light from the screen no longer passes through the flat mirror before being reflected in the concave mirror and is therefore no longer attenuated.

[0089] The enlarged and receding reflection of the screen in the concave mirror is reflected towards the semi-transparent flat mirror, forming an angle close to 45° with respect to the vertical. Facing the flat mirror, the user sees this enlarged reflection through the virtual window formed by the reflection of the concave mirror. Its brightness has indeed been reduced this time, but the total loss is now only 50%, and not 75%.

[0090] The perceived distance and size of the projected screen relative to this virtual window depends on the distance between the screen and the concave mirror. For example, as a 13.3-inch screen is moved further away from the concave mirror, its projection can be considered as a 32-inch screen viewed at 2 m, a 55-inch screen viewed at 3 m, a 65-inch screen viewed at 4 m, or a 5 m wide screen viewed at 12 m.

[0091] The off-axis reflection of the screen in the concave mirror, however, causes a geometric distortion of the content, similar to a slight bean-shaped distortion. It is difficult to identify and not very problematic in most use cases. If necessary, minor corrections could be made to the images to compensate for this distortion.

[0092] Since the light from the screen completely escapes the flat mirror and no longer needs to pass through it, it is no longer necessary to use a semi-transparent mirror to reflect the concave mirror. A 100% front-facing mirror can be used perfectly well if augmented reality is not the desired effect and to maintain full screen brightness. You can also darken the area behind the semi-transparent mirror to enhance contrast and increase its reflectivity.

[0093] According to a variant of this fourth embodiment, the system further comprises a stereoscopic camera arranged behind the semi-transparent mirror facing said eye box so as to be able to film said observer, said semi-transparent mirror having a black rear face so that the camera is not visible to the observer.

[0094] According to this embodiment, a stereoscopic camera is placed behind the semi-transparent flat mirror, facing the user. The rear surface of the mirror around the lens is completely blacked out, so that no light can pass through it. The user therefore does not see the camera filming them from the front.

[0095] The camera angle is adjusted to correspond to the observer's line of sight. It then becomes possible to film in stereoscopy without worrying about "false eye contact," because, unbeknownst to them, the user is always looking directly at the camera. As a result, their interlocutor has the impression of being looked at directly, and vice versa.

[0096] A tracking camera can be placed at the lower edge of the plane mirror, facing the user. Pupil detection allows the content displayed by the autostereoscopic screen to be dynamically adjusted.

[0097] According to a fifth embodiment and for an automotive, railway or aeronautical application, said optical device further comprises a windshield inclined with respect to a vertical axis towards said eye box and a semi-transparent mirror arranged under the windshield and having a reflective surface oriented towards said windshield, and said converging optical component extends vertically under the windshield and said autostereoscopic screen extends horizontally facing the semi-transparent mirror.

[0098] This configuration makes it possible to form an augmented reality device for a vehicle that can overlay information onto the road.

[0099] The proposed configuration is a variant of the third embodiment to obtain an augmented reality effect without parasitic reflection.

[0100] The screen is fixed horizontally, for example under the dashboard, face down.

[0101] The concave mirror is placed vertically in line with the front edge of the screen, with the reflective face facing backwards.

[0102] The flat mirror is inclined at 45°, with the reflective face facing upwards. It starts from the bottom of the concave mirror and goes up towards the rear of the opening in the dashboard.

[0103] The light rays emitted by the screen are reflected a first time by the mirror at 45° towards the concave mirror, which in turn reflects them a second time into the mirror at 45°. Thanks to this angle of reflection, the rays are redirected upwards and pass through the dashboard via a specially designed opening. They then strike the windshield, which reflects them towards the driver's eyes. The driver thus sees a magnified, three-dimensional image in front of the windshield. The driver's driving position determines the position of the eye box, from which the other parameters are determined. List of figures

[0104] 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: • Figure [1] is a schematic view of a projection system according to a first embodiment of the invention, • Figure [Fig. 2] is a schematic view of a projection system according to a second embodiment of the invention, • Figure 3 is a schematic view of a projection system according to a third embodiment of the invention. • Figure 4 is a schematic view of a projection system according to a fourth embodiment of the invention. • Figure 5 is a schematic view of a projection system according to a fifth embodiment of the invention. • [Fig.6] is a schematic view of an autostereoscopic screen of a projection system according to an embodiment of the invention.

[0105] Detailed description of an embodiment of the invention

[0106] In the figures, scales and proportions are not strictly respected for the purposes of illustration and clarity.

[0107] Identical, similar or analogous elements are designated by the same reference numerals in all figures.

[0108] Regardless of the embodiment, the autostereoscopic projection system according to the invention comprises an optical device including at least one concave mirror 30 having a radius of curvature R and a focal length F. This optical device is arranged with respect to a predetermined three-dimensional space (eye box 50) which defines the space within which the observer must place their eyes to perceive the autostereoscopic image projected by the system according to the invention, so as to be able to direct the light rays it receives towards a viewing window observable from the eye box. As previously stated, according to another embodiment, the concave mirror can be replaced by holographic optics which then form the converging optical component.

[0109] According to the embodiment of figures 1, 3, 4 and 5, the optical device further comprises a semi-transparent mirror 20.

[0110] The system according to the invention also includes, regardless of the embodiment, an auto stereoscopic screen 10 arranged in relation to the optical device so that the light rays it emits can reach the concave mirror 30, either directly or after reflection on the semi-transparent mirror 20.

[0111] The auto stereoscopic screen 10 is separated from the concave mirror 30 by a distance d less than F.

[0112] The screen 10 further comprises a matrix 10a of pixels arranged by rows and columns, each pixel being composed of a plurality of sub-pixels of different colors, each assigned to a viewpoint of the image.

[0113] The screen also includes a lenticular grating 10b which surmounts the matrix and each lens of which is inclined at a non-zero angle with respect to the direction of the matrix columns. This aspect of the invention is known and is not shown in the figures. It is also possible to have a vertical grating.

[0114] The lenticular network of the screen 10 also has the particularity of being perfectly focused in the central lobe so as to avoid any overlap of viewpoints only in the central lobe.

[0115] In particular, the autostereoscopic screen comprises a matrix of pixels arranged by rows and columns, each pixel being composed of a plurality of sub-pixels of different colors, each assigned to a viewpoint of the autostereoscopic image to be displayed, and a lenticular grating that sits atop the matrix. Each lens is inclined, in the embodiment shown in the figures, at a non-zero angle with respect to the direction of the columns of the matrix (for example, 18°). As mentioned previously, however, there is nothing preventing the use of a vertical grating. As mentioned previously, there is nothing preventing the use of pixel addressing of the viewpoints of the image. Throughout, S is considered to be equal to 3 for sub-pixel addressing of pixels, each formed of three sub-pixels of different colors.

[0116] Figure 6 schematically illustrates an autostereoscopic screen 10 comprising a pixel matrix 10a arranged in rows and columns, each pixel being composed of a plurality of sub-pixels of different colors, each assigned to a viewpoint of the autostereoscopic image to be displayed. The screen also includes a lenticular grating 10b which is mounted above the matrix 10a.

[0117] The screen grating spacing P is determined from the spacing P', called the nominal spacing, of an autostereoscopic screen, called the nominal screen, having identical usage characteristics to the system screen and intended to be observed in direct vision at a distance corresponding to the usage distance of the system screen, by the formula P=P'.(1+C / (SM)) where C is the number of visible viewpoints simultaneously from the distance of use inside the eye box, when said nominal screen of pitch P' is arranged in said projection system in place of said screen, S is the number of viewpoints addressed by each pixel of the pixel matrix and M the horizontal resolution of the matrix.

[0118] For example, consider a 13.3-inch (33.782 cm) screen with 10 viewpoints and a resolution of 3840 x 2160. This screen is placed at a distance of 700 mm from a concave mirror with a rectangular format of 350 mm by 250 mm, a focal length of 750 mm, and a radius of curvature of 1500 mm. Once placed in the system, the observer sees 12 color bars through the eyepiece (assuming one color is displayed on the screen per viewpoint). Since the pitch of a lens corresponds to 10 colors in direct vision, 12 color bars reflected in the concave mirror represent 12 / 10ths of the lens pitch.

[0119] Insofar as one image viewpoint is displayed per sub-pixel, the number of lenses in the screen array considered is equal to (3840 pixels x 3) / 10, i.e. 1152 lenses.

[0120] The total pitch correction is therefore equal to 12 / 10 = 1.2 lenses.

[0121] This corresponds to a lens correction equal to 1.2 / 1152 = 0.00104.

[0122] In other words, the pitch of the lenses must therefore be increased by 0.1%.

[0123] If the known pitch P' of a lens is 0.240 mm, the necessary pitch correction amounts to adding 0.00024 mm per lens.

[0124] Although this value of 0.24 microns seems relatively small, its impact is actually considerable for optimal observation of the autostereoscopic image reflected by the concave mirror. This correction is crucial for the successful use of an autostereoscopic screen reflecting in a concave mirror.

[0125] According to one embodiment, a 14-point screen with a pitch of 2 is used, resulting in a 45.5 cm lobe, sufficient to occupy the entire width of the "eye box." The exceptional resolving power obtained in the central lobe allows for very comfortable viewing of stereoscopic scenes extending continuously from 1 m to 100 m in depth. Within the limits of a lateral displacement of about 20 cm on either side of the center of the "eye box," the 14 points also offer a horizontal parallax that conforms to reality. When moving away from the flat color distance, they also allow the images to recompose themselves according to physiological expectations. These properties are very useful for giving the user a certain degree of positioning latitude. However, the quality of the sensations is so exceptional at the flat color distance that it is intuitive to position oneself there spontaneously.

[0126] According to one embodiment, the concave mirror has a radius of 1.5 m and a focal length of 0.75 m. The distance d between the screen 10 and the concave mirror 20 is fixed at 0.8 m.

[0127] The various components of the system according to the invention (concave mirror, autostereoscopic screen, and semi-transparent mirror) can be housed in a casing not shown in the figures or arranged relative to each other in a dedicated observation space corresponding to the intended use. The observation area may depend on the intended use. Thus, in the embodiment of [Fig. 5] intended for automotive use, the eye box 50 is determined by the driver's position in the motor vehicle in which the system according to the invention is installed.

[0128] In [Fig. 1], the system comprises a concave mirror 30 and a screen The autostereoscopic 10 extend horizontally and are arranged on the same vertical axis represented by a dashed line. In addition, the system includes a semi-transparent mirror 20 having a reflective surface oriented towards the eye box 50 and towards the concave mirror 30, inclined at an angle of 45° to the optical axis of the concave mirror and arranged between the screen 10 and the concave mirror 30.

[0129] As previously stated, according to this embodiment, the light emitted by the screen 10 passes through the semi-transparent mirror 20 on the non-reflective side. The light is then reflected by the concave mirror 20, and this reflection is in turn reflected at 45° by the reflective front face of the semi-transparent mirror 20. The viewer, whose eyes are placed in the eye box 50, can thus perceive the image reflected by the semi-transparent mirror 20.

[0130] According to one embodiment, the screen is a 13.3-inch 4K screen and the concave mirror is a mirror with a focal length of 75 cm, open at F / 2 and sufficiently wide (37.5 cm for example).

[0131] In [Fig.2], the system comprises a concave mirror 30 and a screen autostereoscopic 10s, each extending vertically, facing each other. They are also vertically offset from each other and arranged relative to the eye box 50 such that the eye box is located behind and above the autostereoscopic screen 10. The concave mirror 30 is arranged opposite the eye box 50.

[0132] The concave mirror is oriented so that its horizontal median axis, represented in [Fig. 2] by a dashed line, divides the space into two superimposed volumes. The screen 10, facing the mirror 30, occupies the lower volume. It can be slightly tilted so that its reflection in the concave mirror 30 is upright, allowing the user to see a perfectly vertical, enlarged virtual image.

[0133] In [Fig.3], the system comprises a semi-transparent mirror 20 arranged on the axis optics of the concave mirror 30 and which has a reflective surface oriented towards the eye box 50 and towards the concave mirror 30.

[0134] This semi-transparent mirror 20 is inclined at an angle of 45° with respect to the optical axis of the concave mirror, represented in the figure by a vertical dashed line. The screen 10 is arranged with respect to the eyebox 50 such that the eyebox located at the rear of the screen facing the semi-transparent mirror 20. In addition, the screen 10 is vertically offset from the reflection of the concave mirror 30 in the semi-transparent mirror 20.

[0135] As previously stated, this embodiment makes it possible to eliminate unwanted reflections while offering the possibility of projecting 3D content in augmented reality.

[0136] In [Fig.4], the system comprises a concave mirror 30 and an autostereoscopic screen 10 which extend opposite each other, horizontally offset from each other, and inclined with respect to the horizontal.

[0137] The system further includes a semi-transparent mirror 20 having a reflective surface oriented towards the eye box 50 and towards the concave mirror 30. The semi-transparent mirror 20 is inclined at an angle of 45° with respect to the vertical and arranged so that the light rays from the screen can reach the concave mirror without passing through the semi-transparent mirror.

[0138] As previously stated, this embodiment allows for use in augmented reality while limiting the decrease in brightness.

[0139] It is also possible, as illustrated in [Fig. 4], to place an opaque mask 60 behind the semi-transparent mirror to enhance contrast and increase reflectivity. Of course, with this variant, augmented reality is not possible.

[0140] The system of [Fig. 5] further comprises a windscreen 40 inclined with respect to a vertical axis, for example at an angle of 37°, towards the eye box 50 and a semi-transparent mirror 20 arranged under the windscreen 40 and having a reflective surface oriented towards the windscreen 40. In addition, the concave mirror 30 extends vertically under the windscreen 40 and the autostereoscopic screen 10 extends horizontally facing the semi-transparent mirror 20.

[0141] When used in a motor vehicle, the screen 10 is fixed horizontally under the dashboard of the vehicle, face downwards.

[0142] The flat mirror is inclined at 45°, with the reflective face facing upwards. It starts from the bottom of the concave mirror and goes up towards the rear of the opening in the dashboard.

[0143] This embodiment thus makes it possible to form an augmented reality device for a vehicle which can superimpose information onto the road.

[0144] The light rays emitted by the screen 10 are reflected first by the 45° mirror towards the concave mirror 30, which in turn reflects them a second time into the 45° mirror. Thanks to this angle reflection, the rays travel upwards and pass through the dashboard via the opening provided there. They then encounter the windshield 40, which finally reflects them towards the driver's eyes arranged in the eye box 50. The driver then sees a magnified three-dimensional image in front of the windshield 40.

Claims

1. Demands A system for projecting a dematerialized image auto stereoscopic for an observer whose eyes are positioned within a predetermined three-dimensional space, called an eye box (50), having a predetermined width L, at least greater than the average interpupillary distance of an observer and preferably greater than the average width of a human head, said system being characterized in that it comprises: an optical device comprising at least one converging optical component (30) with behavior identical to a concave mirror having a radius of curvature R and a focal length F, said optical device being arranged with respect to said eyebox (50) so as to be able to direct the light rays it receives towards a viewing window observable from said eyebox, an autostereoscopic screen (10) arranged with respect to said optical device so that the light rays it emits can reach said viewing window, after reflection on said converging optical component (30), and having traveled a distance d less than F, said autostereoscopic screen (10) further comprising: • a pixel matrix of N rows and M columns, each pixel being composed of a plurality of sub-pixels of different colors, • a lenticular array surmounting said pixel matrix, and having a pitch P determined from a pitch P', called the nominal pitch, of an autostereoscopic screen, called the nominal screen, having usage characteristics identical to those of the system's screen and intended to be viewed directly at a distance corresponding to the usage distance of said system's screen, by the formula P=P'.(1+C / (SM )) where C is the number of viewpoints visible simultaneously from said usage distance inside said eye box, when said nominal screen of pitch P' is arranged in said projection system in place of said screen, and S is the number of different viewpoints addressed by each pixel of said matrix.

2. System according to claim 1, characterized in that said lenticular array of said autostereoscopic screen (10) forms a plurality of areas in front of the screen, called lobes, in which all the different viewpoints of the image succeed one another at a privileged distance from the screen, called the flat tint distance, corresponding to the distance at which each eye of the observer perceives only one viewpoint among all the viewpoints of the image over the entire surface of the screen and in that said array is perfectly focused in the central lobe so as to avoid any overlap of viewpoints only in the central lobe.

3. System according to any one of claims 1 or 2, characterized in that said converging optical component (30) and said auto stereoscopic screen (10) extend horizontally and are arranged on the same vertical axis, said optical device further comprising a semi-transparent mirror (20) having a reflective surface oriented towards said eye box and towards said converging optical component (30), said semi-transparent mirror (20) being inclined at an angle of 45° with respect to the optical axis of said converging optical component which extends vertically, and arranged between said screen and said converging optical component.

4. System according to any one of claims 1 or 2, characterized in that said converging optical component (30) and said autostereoscopic screen (10) extend vertically, facing each other, vertically offset from each other, and arranged with respect to the eyebox such that the eyebox is located behind and above the autostereoscopic screen, said converging optical component whose optical axis extends horizontally being arranged opposite the eyebox.

5. A system according to claim 1 or 2, characterized in that said optical device further comprises a semi-transparent mirror (20) arranged on the optical axis of said converging optical component (30), having a reflective surface oriented towards said eyebox and towards the converging optical component (30), said semi-transparent mirror (20) being inclined at an angle of 45° with respect to the optical axis of said converging optical component (30) which extends vertically, said screen (10) being arranged with respect to the eye box such that the eye box is located at the rear of said screen (10) which faces said semi-transparent mirror, and is vertically offset with respect to the reflection of the converging optical component in said semi-transparent mirror.

6. System according to any one of claims 1 or 2, characterized in that said converging optical component (30) and said auto stereoscopic screen (10) extend opposite each other, horizontally offset from each other, and inclined with respect to the horizontal, said optical device further comprising a semi-transparent mirror (20) having a reflective surface oriented towards said eye box and towards said converging optical component, said semi-transparent mirror being inclined at an angle of 45° with respect to the vertical and arranged so that the light rays from the screen can reach the converging optical component without passing through the semi-transparent mirror.

7. System according to claim 6, characterized in that it further comprises a stereoscopic camera arranged behind the semi-transparent mirror (20) facing said eye box so as to be able to film said observer, said semi-transparent mirror having a black rear face so that the camera is not visible to the observer.

8. System according to any one of claims 1 or 2, characterized in that said optical device further comprises a windscreen (40) inclined with respect to a vertical axis towards said eye box and a semi-transparent mirror (20) arranged under the windscreen and having a reflective surface oriented towards said windscreen, and in that said converging optical component (30) extends vertically under the windscreen and said autostereoscopic screen (10) extends horizontally facing the semi-transparent mirror.

9. System according to any one of the preceding claims, characterized in that said autostereoscopic screen (10) is a 5.5 inch (13.97 cm) or 13.3 inch (33.782 cm) screen.

10. System according to any one of claims 1 to 9, characterized in that said converging optical component (30) is a concave mirror or a holographic optic.

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