Apparatus for aerial and virtual projection of autostereoscopic images or autostereoscopic image sequences, particularly for use in motor vehicles

Abstract

The invention relates to a system for the aerial and virtual projection of autostereoscopic images intended for an observer, said system comprising a housing (30) with an opaque upper wall (20) extending parallel to a plane called the horizontal plane and provided with an opening, a front surface mirror (10) having a reflective surface inclined, for example at an angle of 45° with respect to the horizontal plane passing through said opening, and directed towards said observer, a concave mirror (14) arranged at the base of the front surface mirror, facing said opening and oriented so that its concave reflective surface is directed towards said inclined mirror, and a display screen (16) for displaying an autostereoscopic image extending substantially perpendicular to said horizontal plane, said display screen (16) being arranged below the opaque upper wall at a distance from the centre of the concave mirror image formed by the inclined mirror equal to the radius of curvature of said concave mirror, said display screen having a lenticular array attached to it, the pitch of which is determined so as to be able to compensate for its apparent modification after reflection by the concave mirror.

Description

[Technical Field]

[0001] Technical Field The present invention relates to a device for the aerial and virtual projection of autostereoscopic images or autostereoscopic image sequences, the invention being intended in particular, but not exclusively, for use in the automotive field. [Background technology]

[0002] Technical background The device for aerial and virtual projection of an object projects an image of the object in front of a window formed in a housing, giving the viewer the illusion that the three-dimensional object is floating in space. Such devices are known as devices for projecting real objects, and typically comprise a housing (which may or may not be opaque) with an opening intended to form a viewing window for a virtual image, an optical system (typically a lens, a Fresnel lens, a combination of lenses or a concave mirror), and an object located at a distance from the optical system configured to direct an image of the object towards the viewing window.

[0003] For example, US Pat. No. 6,817,716 discloses an apparatus comprising a lower section in which a real object is illuminated by a light source, an upper section having an observation window disposed in front of it, a concave mirror, and a semi-transparent plane mirror inclined at 45 degrees with respect to the optical axis of the concave mirror, the observation window being located at its center. The semi-transparent plane mirror is disposed between the observation window and the concave mirror in alignment with the real object. Thus, the illuminated object is partially reflected by the semi-transparent mirror inclined at 45 degrees, and the reflected light is reflected by the concave mirror back toward the observation window via the semi-transparent mirror. This gives the observer the visual impression that the real object is floating in front of the observation window. The Applicant has already proposed an apparatus for projecting autostereoscopic images in document WO2018 / 167410. The device has a housing with a front wall, a rear wall, and an upper wall and a lower wall connecting the front wall, the front wall having an opening that forms a viewing window for the aerial and virtual images of the digital autostereoscopic image. The device also includes an optical system consisting of at least one concave spherical mirror having an optical axis, a focal length F, and a center of curvature radius C located on the optical axis, the optical system being arranged within the housing so as to direct at least a portion of the received incident light toward an observation window to form aerial and virtual images of the digital autostereoscopic image.

[0004] The autostereoscopic image is projected by an autostereoscopic image display screen having N viewpoints overlaid by an array of cylindrical lenticules that form viewpoint-selecting optics for the projected digital autostereoscopic image. The autostereoscopic image display screen is housed in a housing opposite a spherical mirror at a distance substantially equal to twice the focal length F, and is spaced vertically from the optical axis of the spherical mirror by a distance equal to or greater than half the height of the display screen (as defined along an axis perpendicular to the optical axis). This device advantageously allows for the observation of autostereoscopic images that appear to be floating in space. Summary of the Invention [Problem to be solved by the invention]

[0005] However, the present inventors have sought to improve upon this device, particularly in automotive applications where space requirements and cost constraints are imposed. Additionally, the inventors have also attempted to improve the quality of the autostereoscopic image as perceived by the observer.

[0006] Object of the invention It is an object of the present invention to provide a system for the aerial and virtual projection of autostereoscopic images that overcomes at least some of the drawbacks of known solutions. It is also an object of the present invention, in at least one embodiment, to provide a projection system that hides components of the system from the viewer. It is a further object of the present invention, in at least one embodiment, to provide a projection system whose components are positioned below the viewer's line of sight towards the viewing area of ​​the air and virtual image. It is also an object of the present invention, in at least one embodiment, to provide a system that can be seamlessly integrated into a vehicle to project driving information for the driver. It is a further object of the present invention, in at least one embodiment, to provide a projection system that is compact and has a limited number of components. It is also an object of the present invention, in at least one embodiment, to provide a projection system that offers a variety of configurations that can accommodate different integration and usage constraints. Finally, the present invention aims to provide an apparatus for displaying driving information to a driver of a motor vehicle, comprising a projection system according to the present invention. [Means for solving the problem]

[0007] Disclosure of the Invention To this end, the invention relates to a system for the aerial and virtual projection of autostereoscopic images aimed at an observer whose eyes are located within a predetermined three-dimensional space called the eyebox. The system according to the invention is characterized in that it comprises: an optical device comprising at least one converging optical element acting like a concave mirror having a radius of curvature R and a focal length F, said optical device being positioned relative to said eyebox so as to be able to direct the light rays it receives towards an observation window observable from said eyebox; an autostereoscopic display screen positioned relative to said optical device such that an emitting light beam can reach said observation window after reflecting off said converging optics and traveling a distance d equal to twice the focal length F, wherein said screen comprises: a pixel matrix with N rows and M columns, where each pixel is composed of multiple sub-pixels of different colors; a lenticular array superimposed on the pixel matrix, the lenticular array having a pitch P determined from a pitch P', called the nominal pitch, of an autostereoscopic screen, called the nominal screen, having the same use characteristics as the screen of the system and intended to be observed by direct viewing at a distance corresponding to the use distance of the screen of the system, the pitch P being determined using the formula P=P'.(1-C / (SM)), where C is the number of viewpoints simultaneously observable in the eyebox from the use distance when a nominal screen with pitch P' is placed in the projection system instead of the screen, and S is the number of different viewpoints addressed by each pixel of the matrix.

[0008] Therefore, the system according to the present invention implements a dedicated autostereoscopic screen designed exclusively for this purpose, in order to enable viewing of a virtual reflection of an autostereoscopic image reflected by a converging optical element. Such converging optical elements include, for example, a concave mirror and a holographic optical element. Such converging optical elements have a similar effect to a concave mirror. In the remainder of this specification, the term "concave mirror" will be mainly used for ease of reading, but it will be understood that this concave mirror can be replaced by a holographic optical element without changing the technical effect of the present invention. In particular, autostereoscopic screens designed for direct viewing are not suitable for use in devices that use reflection of the screen by a concave mirror to virtualize the screen.

[0009] Indeed, in such a screen virtualization device, all the desired characteristics must be ensured in the main lobe of the screen (which specifies the space in front of the screen where the different viewpoints of the autostereoscopic image follow each other at the preferred viewing distance of the screen, called the flat-tint distance, corresponding to the distance at which each of the observer's eyes perceives only one viewpoint of the image across the entire surface of the screen), namely the number of viewpoints, the flat-tint distance, and the distribution of viewpoints on the pixel matrix. However, experience has shown that a concave mirror alters all these characteristics, so that autostereoscopic screens designed for direct viewing are of little or no suitability in devices using concave mirrors.

[0010] If a screen is placed at twice the focal length of the concave mirror, or in front of another optical system with a similar effect (for example, a holographic optical element whose active surface is at least as large as the screen), a reflected image of the screen of the same size but inverted (magnification -1) is obtained. The deformations caused by the concave mirror require the introduction of new rules for defining the parameters of the lenticular array, which differ from those of a direct-view array. In order for the virtual replica obtained by reflection from the screen to have the desired autostereoscopic properties, the characteristics of the lenticular array of the screen must be modified. The presence of the concave mirror alters all the parameters described so far. To maintain the desired characteristics, the pitch of the array must be reduced to a ratio such that the screen is no longer observable by direct viewing. The inventors have succeeded in identifying the amount of pitch correction that must be applied to enable reflective viewing through a concave mirror.

[0011] According to the invention, this pitch reduction is obtained based on the pitch P' of an autostereoscopic screen, called the nominal screen, which has the same usage characteristics as the screen of the system but is intended to be observed by direct viewing at a distance corresponding to the usage distance of said screen of the system, using the formula P=P'.(1-C / SM), where C is the number of viewpoints that can be simultaneously observed in the eyebox from said usage distance if said nominal screen with pitch P' were placed in the projection system instead of said screen, S is the number of different viewpoints of the image addressed by each pixel of the pixel matrix, and M is the number of pixels per row of the pixel matrix. For example, if subpixel addressing is based on a pixel matrix where each pixel contains three subpixels of different colors, S is equal to 3. The pitch P is then obtained using the formula P=P'.(1-C / (3.M)). If the same matrix is ​​addressed in integer pixels, S is equal to 1 and the pitch P is obtained using the formula P=P'.(1-C / M).

[0012] For ease of reading, the remainder of this specification will assume sub-pixel addressing and a matrix in which each pixel is composed of three sub-pixels, although it will be understood that the technical teachings disclosed herein are equally applicable, mutatis mutandis, to integer pixel addressing and / or matrices containing other than three sub-pixels. For example, if a color chart displayed on a nominal autostereoscopic screen is reflected by a concave mirror, the image reflected from the color chart will show a number of color bars corresponding to the projection pitches reaching at least two or three lenses across the array relative to the screen at the initially selected flat tint. For example, in the case of a screen with five viewpoints, if the observer perceives five color bars on the screen, regardless of their distance from the screen, this means that the observer deviates from the flat tint distance by an increase or decrease of the projection pitch by five subpixels, or one lens pitch. If the observer perceives ten color bars, this means that the projection pitch has increased or decreased by ten subpixels, or two lenses. If the screen is displaying a single color, this means that the observer is at the flat tint distance.

[0013] As long as the pitch of the lenticular array of the nominal screen can be known very accurately, for example to the nearest hundredth of a micron, it is possible to correct for the effect of the concave mirror on the optical path from the surface of the actual screen, through the actual virtual conjugate image, to the user's eye by fabricating a new lenticular array with the corrected pitch. This corresponds to producing a flat tint that can be viewed directly outside the projection device at a very short distance from the screen, and therefore corresponds to a significantly reduced pitch of the lenticular array compared to direct viewing applications. For example, if a nominal screen with five viewpoints placed in a projection device allows 12 color bars to be observed at a desired flat tint distance of 1 m (assuming the screen displays five different colors, one for each viewpoint), then the 12 color bars reflected by the concave mirror will represent 12 / 5 of the lens pitch, since the pitch of one lens corresponds to the five direct-view colors. Based on this value, the pitch of the lenticular array must be reduced to fit the device according to the present invention and divided by the total number of lenses to calculate the correct pitch to apply when machining the lenticular array of a screen intended to be placed in a projection device. This results in a system with a virtualized autostereoscopic image reflected by a mirror, making it possible to preserve all the features defined in the central lobe.

[0014] When the screen is housed in a device according to the invention, by knowing the nominal screen pitch and determining the number of viewpoints within the eyebox that are simultaneously observable from the used distance, it is now possible for the first time to simply determine the pitch correction to be applied to a nominal autostereoscopic screen for incorporation into a device implementing a concave mirror. As mentioned above, the number of simultaneously observable viewpoints can be easily determined by displaying a color chart on the screen and simultaneously counting the number of color bands that are visible from the eyebox corresponding to the screen usage distance. Advantageously, according to the invention, the system comprises: - a housing comprising an opaque front wall extending opposite the viewer and an opaque top wall connected to the front wall and extending parallel to a plane referred to as the horizontal plane, the top wall being provided with an upper opening; a front surface mirror inclined at an angle α with respect to the horizontal and extending at least partially above the upper opening, the front surface mirror having a reflective surface directed toward the observer; - the converging optic is disposed at the base of the front surface mirror, facing the opening, and oriented so that its reflective surface is directed towards the tilted mirror extending above the upper opening, the converging optic having an optical axis that forms an angle δ' with the horizontal; - the autostereoscopic display screen is tilted at an angle θ with respect to the vertical and is positioned below an opaque top wall at a distance from the center of the image of the converging optic formed by the tilted mirror equal to the radius of curvature of the converging optic; the angles α, δ′ and θ are related by the following relationship: δ'=2.δ, where δ=45°-α, θ=β, where β is the angle formed with the horizontal by the direction of the observer's gaze directed from the eyebox towards the observation window towards the centre of reflection of the concave mirror.

[0015] Therefore, according to this advantageous variant, the system comprises an inclined plane front surface mirror extending at least partially above an opening in the wall through which the light rays reflected by the converging optical element can pass, and the light rays reflected by the plane front surface mirror form a virtual image of the image from which the light rays originate in the vicinity of the predetermined observation area. Furthermore, the volume occupied by this system is divided into two parts on either side of a median plane called the horizontal plane. The horizontal plane is defined by a top wall of the system, preferably made of an opaque material, which has an opening drilled therein, and the mirror is inclined at an angle α to the horizontal plane so as to extend at least partially above the opening.

[0016] According to one embodiment of the present invention, the front surface mirror defines a mirror portion that passes through the top opening and extends above the horizontal plane visible to the observer, and a mirror portion that extends below the horizontal plane hidden by the opaque wall of the housing. In accordance with the present invention, the top edge of this mirror is positioned closer to the viewer and the bottom edge is positioned further away from the viewer. Other tilt angles are possible depending on the application and integration constraints. The exposed portion of the mirror is, for example, as large as the portion hidden below the horizontal plane. A concave mirror (also referred to using the term converging optic) is positioned at the base of the tilting mirror and oriented so that its concave reflective surface faces upward and faces an upper opening made in the top wall. The concave mirror therefore reflects off the portion of the tilted flat front surface mirror that extends above the upper opening, forming a vertical image therein as if the concave mirror were positioned vertically behind the flat front surface mirror.

[0017] The autostereoscopic screen is positioned below the top wall, with its back surface facing the observer, at a distance equal to the radius of curvature of the concave mirror, starting from the center of the image formed by the tilted front mirror. The top edge of the screen is immediately below and adjacent to the top wall, and is not visible to the observer. The screen is tilted at an angle θ to the vertical. The image displayed by this screen can be viewed identically on the other side of the horizontal plane in the form of a conjugate image at a scale of -1. In fact, all light rays emanating from the screen and reaching the image of the concave mirror are refocused at an equal distance above the horizontal plane, forming a virtual conjugate image of the optically real screen as seen by an observer positioned in front of the device. Light rays emanating from the screen are reflected downward by the portion of the inclined flat front surface mirror that extends below the horizontal plane, then reflected upward by the concave mirror, and then reflected a second time by the visible portion of the inclined flat front surface mirror, before being directed toward the observer's eye. The concave curvature of the mirror directs light rays emanating from a particular point on the screen to intersect at a corresponding location on the screen's conjugate image above the horizontal plane, creating the illusion that the light rays actually emanate from that location. To an observer whose eye is located along the path of the light rays, these light rays combine to form an image similar to the image of the screen itself and what it displays, which remains below the horizontal plane and cannot be directly observed.

[0018] As described above, an autostereoscopic screen has a specific lenticular array so that the image viewed by the observer retains the desired autostereoscopic parameters even after reflection by a concave mirror. The pitch of the lenticular array is adjusted relative to the pitch of a screen viewed directly without reflection by a concave mirror to compensate for the apparent pitch change that occurs after reflection by a concave mirror or transmission through a converging optic, which may be a lens with the same radius of curvature and focal length or a holographic optic. More specifically, the conical perspective effect caused by reflection or transmission by a converging optic changes the perceived pitch. By pre-correcting the pitch, the device can display a three-dimensional image above a horizontal plane, similar to a directly viewed autostereoscopic screen. From the eyebox and in the vicinity of the viewing window, the observer perceives a virtual relief image in the air without viewing any converging optics or screen located below the horizontal plane. Advantageously, according to the invention, said angle α is 36°, said angle β is 20°, said angle δ' is 18° and said angle θ is 20°.

[0019] According to this advantageous variant, the angles are set so that if the axis of the viewer's line of sight towards the projection area makes an angle of 20° with the horizontal, the autostereoscopic image can be perceived through a mirror inclined at 36° with respect to the horizontal, which corresponds to the standard inclination of a car windshield. A device according to this variant can therefore be integrated into a motor vehicle to ensure aerial and virtual projection of autostereoscopic images for the driver. Optionally, the tilting mirror is formed by the windscreen of the motor vehicle and the opaque upper wall of the housing is formed by part of the front of the vehicle. Of course, the system according to the invention can be applied to other applications, and the angle values ​​are not fixed but can be changed according to the conditions and applications, with the aim of maintaining the same results.

[0020] The present invention also relates to a device for displaying driving information for a motor vehicle comprising a windshield, a steering wheel and a front dashboard extending between the windshield and the steering wheel, characterized in that the display device comprises a projection system according to the present invention, wherein the tilting mirror is formed by the windshield, the opaque wall is formed by the front dashboard including an opening for forming the upper projection opening of the autostereoscopic image, the converging optics and the autostereoscopic screen are housed under the front dashboard, and a vehicle driver sitting in front of the windshield can see driving information by aerial and virtual projection of the autostereoscopic image displayed on the display screen in a predetermined projection area extending above the front dashboard.

[0021] Thus, according to the present invention, the front area of ​​the vehicle functions as the upper wall and extends along a horizontal plane, while the windshield (under certain conditions, such as the angle relative to the vertical, the shape, and any surface treatment) functions as an inclined front-view mirror. The front area of ​​the vehicle is the substantially flat space located between the dashboard and the windshield of the vehicle. This space can therefore effectively function as an opaque superstructure extending along a horizontal plane in the system according to the present invention. If the curvature of the windshield is sufficiently uniform and homogeneous, it can be used to complement the concave curvature of the main mirror, which should be adjusted as needed.

[0022] Light rays emitted from the autostereoscopic screen are reflected by the portion of the windshield located below the opening in the dashboard. The screen must be slightly tilted so that its conjugate image is perpendicular to the observer's line of sight and trapezoidal distortion is avoided. The light rays are then reflected downwards onto a concave mirror, which reflects them further onto the portion of the windshield located above the opening in the dashboard, from where they are directed into the eyebox.

[0023] According to an advantageous variant, the windshield is inclined at 36° to the horizontal and the concave mirror at 20° to the vertical, thereby providing a vertical image of the concave mirror as a reflection on the windshield to an observer whose line of sight forms an angle of approximately 20° with the air and with the desired projection area of ​​the virtual image. The important parameter is that the image of the concave mirror is substantially vertical at the reflection on the windshield. Even with slight changes in the position and angle of all components, the virtual image on the screen will reproduce its position, size and inclination directly above the horizontal plane. Thus, according to this alternative embodiment, the projection system can project information from the dashboard (e.g., speedometer, navigation information, GPS, etc.) onto the autostereoscopic screen and project it towards the viewer's eyes. This information is then projected towards the driver's eyes by the windshield and concave mirror. This variant of the system takes advantage of the presence of the windshield, allowing its lower, normally opaque portion to act as a front-view mirror. Note that the windshield may need to be treated to impart this reflective function.

[0024] Advantageously, according to the invention, the concave mirror has a radius of curvature of 300 mm and a focal length of 150 mm. Of course, other mirrors may be used without violating the principles of the present invention. The invention also relates to a method for producing a system for the aerial and virtual projection of autostereoscopic images intended for an observer whose eyes are located within a predetermined three-dimensional space called the eyebox, said method comprising the following steps: - selecting an autostereoscopic screen, called nominal screen, with predetermined usage characteristics and formed by a pixel matrix of N rows and M columns, and superimposed by a lenticular array with a predetermined pitch P'; - placing the nominal screen in a projection system comprising a converging optic acting as a concave mirror of radius R and focal length F, wherein the converging optic is positioned relative to the eyebox such that it can direct incoming light rays towards an observation window observable from the eyebox, and the nominal screen is positioned relative to the converging optic such that outgoing light rays can reflect off the converging optic and reach the observation window after traveling a distance d equal to twice the focal length F; - displaying a color chart on said nominal autostereoscopic screen; - calculating the number C of colors simultaneously observed from said use distance within said eyebox; - manufacturing an autostereoscopic screen, called a dedicated screen, having the same predetermined usage characteristics as said nominal screen and a lenticular array with a pitch P calculated by the formula P=P'.(1-C / (SM)), where S is the number of different viewpoints addressed by each pixel of said matrix; - replacing said nominal screen with said dedicated screen. The advantages and technical effects of the projection apparatus according to the present invention apply equally, mutatis mutandis, to the method of developing the aerial and virtual projection system according to the present invention. The invention also relates to a system for the aerial and virtual projection of autostereoscopic images, as well as to a device for displaying driving information for motor vehicles, characterized by all or some of the features mentioned above or below in combination. [Brief explanation of the drawings]

[0025] Drawing List Further objects, features and advantages of the present invention will appear on reading the description which follows, which description is given by way of non-limiting example only and which makes reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic diagram of a projection system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram of an apparatus for displaying driving information of a motor vehicle according to one embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram of an autostereoscopic screen of a projection system according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] Detailed Description of Embodiments of the Invention Throughout the drawings, for purposes of illustration and clarity, scale and proportions are not strictly reflected. Identical, similar or corresponding elements are designated using the same reference numerals throughout the figures. The embodiment described with reference to the figures relates to the display of autostereoscopic images. FIG. 1 shows a schematic representation of a system according to one embodiment of the present invention, which system is intended to be installed in a motor vehicle and is shown diagrammatically in FIG. In FIG. 1, the dashed lines represent the path of the light rays and the conjugate image of the image and the concave mirror.

[0027] The system comprises an opaque housing 30 including a top wall 20 with an opening 22 through which an angled front surface mirror 10 extends. The front surface mirror 10 is inclined at an angle α to the horizontal, with its reflective surface facing the observer, who is positioned to the right of the device and looks towards the predetermined projection area 18. The front surface mirror 10 defines a mirror portion extending above a horizontal plane observable by an observer, and a mirror portion extending below the horizontal plane obscured by the housing 30 . The system further includes a concave mirror 14 positioned at the base of the front surface mirror 10, facing the opening 22 and oriented with its concave reflective surface facing the tilted front surface mirror 10. This concave mirror has, for example, a radius of 300 mm, a focal length of 150 mm for an effective area of ​​150 mm, i.e. F / 1. The mirror has an optical axis that forms an angle δ' with the horizontal.

[0028] The system also includes a display screen 16 for displaying the autostereoscopic image, the screen being inclined at an angle θ to the vertical. The screen is positioned below the opaque top wall at a distance from the center of the image of the concave mirror formed by the tilted mirror equal to the radius of curvature of the concave mirror 14. The tilt of the screen 16 must be set so that the emitted light rays reach the tilted plane mirror 10 and are reflected downwards towards the concave mirror 14 . The screen has a lenticular array whose pitch is set to compensate for the apparent change that occurs after reflection from a concave mirror.

[0029] 3 shows a schematic representation of an autostereoscopic screen 16 comprising a pixel matrix 16a arranged in rows and columns, each pixel consisting of a number of sub-pixels with different colors assigned to each viewpoint of the autostereoscopic image to be displayed. The screen also comprises a lenticular array 16b superimposed on the matrix 16a. Each lenticular element is tilted at a non-zero angle (e.g., 18°) relative to the column direction of the matrix. According to other embodiments, a vertical array can also be used. As mentioned above, it is not excluded to use pixel addressing for each viewpoint of the image. In the following description, we consider sub-pixel addressing of a pixel formed by three sub-pixels (i.e., S is equal to 3), each sub-pixel having a different color.

[0030] The pitch P of the array 16b of screen 16 is determined from the pitch P', called the nominal pitch, of an autostereoscopic screen, called the nominal screen, having the same use characteristics as the system's screen and intended to be observed by direct viewing at a distance corresponding to the use distance of the system's screen, said pitch P being determined using the formula P=P'.(1-C / 3.M), where C is the number of viewpoints simultaneously observable within the eyebox from the use distance if a nominal screen with pitch P' were placed in the projection system instead of said screen, and M is the horizontal resolution of the pixel matrix.

[0031] For example, consider a 5-inch screen with five viewpoints and a resolution of 800x480. The screen is placed 300 mm from the concave mirror, is a 150 mm square, has a focal length of 150 mm, and a radius of curvature of 300 mm. When installed in a system, an observer can see 12 color bars from the eyebox (assuming one color is displayed on the screen for each viewpoint). If the lens pitch corresponds to the five direct viewing colors, the 12 color bars reflected by the concave mirror correspond to 12 / 5 of the lens pitch. If one image viewpoint is displayed per subpixel, the number of lenses in the screen's array is equal to (800 pixels x 3) / 5, or 480 lenses. Therefore, the total pitch correction is equal to 12 / 5=2.4 lenses. This corresponds to a lens correction equal to 2.4 / 480=0.005. In other words, the lens pitch must therefore be reduced by 0.5%. If the known lens pitch P' is 0.270 mm, then the required pitch correction would remove 0.00135 mm per lens. Although this value of 1.35 microns may seem small at first glance, its impact on optimal viewing of autostereoscopic images reflected by a concave mirror is enormous. This correction is a determining factor for the effective use of autostereoscopic screens reflected by a concave mirror.

[0032] In the embodiment of FIG. 1, angle α is 36°, angle β is 20°, angle δ′ is 18°, angle δ is 9°, and angle θ is 20°. FIG. 2 shows a schematic diagram of how the system of FIG. 1 is incorporated into a vehicle to form an apparatus for displaying driving information for the vehicle, the vehicle having a windshield 100, a steering wheel 110, and a front dashboard 200 extending between the windshield 100 and the steering wheel 110. The windshield 100 forms the tilted mirror of the projection system, and the front dashboard 200 forms the upper opaque wall of the projection system. The front dashboard 200 includes an opening 220 through which light rays projected from a concave mirror (not shown in FIG. 2) are reflected by the windshield 100 . A windshield 100 extends above the opening to receive the light rays projected from the concave mirror. Furthermore, the autostereoscopic screen (not shown) must be tilted so that the light rays emitted from it can be reflected by the windshield.

[0033] As an example, the windshield has an inclination of 36° with respect to the horizontal (α=36°), the concave mirror has an optical axis inclined at 18° with respect to the horizontal, and the autostereoscopic screen has an inclination of 20° with respect to the vertical (θ=20°). As a result, a driver whose line of sight is at an angle of 20° with respect to the horizontal (β=20°) can see the image on the screen in the vicinity of a predetermined observation area extending forward and above the vehicle. Those skilled in the art will readily appreciate that, according to the configuration described with reference to FIG. 1, the autostereoscopic screen and concave mirror of the projection system are housed in a housing located below the front dashboard 200. Thus, the driver of the vehicle can view driving information projected from the autostereoscopic screen toward a predetermined projection area located between the windshield 100 and the driver and extending above the front dashboard 200.

[0034] The system according to the invention can be modified to suit the constraints of a particular use, for example by deviating from the theoretical angles described herein, or by placing the screen at a distance different from the theoretical distance of the concave mirror. For example, if the distance from the screen to the reflective center of the concave mirror is shorter or longer than twice the focal length of the concave mirror, the system can still display an autostereoscopic image, but the actual virtual image will be enlarged (or reduced) so that it is located closer (or farther) to the observer. It is also possible to intentionally change the value of the angle θ, allowing for a small trapezoidal distortion in the image to correct the vertical appearance of the image on the screen, for example to display objects in an orientation that is consistent with the surface of a dashboard. Thus, in some applications, the angle θ can be 12° instead of the theoretical angle of 20°.

Claims

1. 1. A system for the aerial and virtual projection of autostereoscopic images intended for an observer whose eyes are located within a predetermined three-dimensional space called the eyebox, characterized in that the system comprises: an optical device comprising at least one converging optical element (14) acting like a concave mirror with a radius of curvature R and a focal length F, said optical device being positioned relative to said eyebox so as to be able to direct the light rays it receives towards an observation window observable from said eyebox; an autostereoscopic display screen (16) positioned relative to the optical device in such a way that the emitting light rays can reach the observation window after reflecting off the converging optics (14) and traveling a distance d equal to twice the focal length F, wherein the screen comprises: a pixel matrix with N rows and M columns, where each pixel is composed of multiple sub-pixels of different colors; a lenticular array superimposed on the pixel matrix, said lenticular array having a pitch P determined from a pitch P', called the nominal pitch, of an autostereoscopic screen, called the nominal screen, having the same use characteristics as the screen of the system and intended to be observed by direct viewing at a distance corresponding to the use distance of said screen of the system, said pitch P being determined using the formula P=P'.(1-C / (S.M)), where C is the number of viewpoints simultaneously observable in the eyebox from said use distance when a nominal screen of pitch P' is placed in the projection system instead of said screen, and S is the number of different viewpoints addressed by each pixel of the matrix.

2. 10. The system of claim 1, comprising: a housing (30) comprising an opaque front wall (20) extending opposite the observer and an opaque top wall connected to said front wall and extending parallel to a plane called the horizontal plane, said top wall being provided with an upper opening (22); a front surface mirror (10) inclined at an angle α to the horizontal and extending at least partially above said upper opening (22), said front surface mirror (10) having a reflective surface directed towards said observer; It also features: the converging optic (14) is located at the base of the front surface mirror, facing the opening (22) and oriented so that its reflective surface is directed towards the tilted front surface mirror (10) extending above the upper opening, the converging optic having an optical axis that forms an angle δ' with the horizontal; - said autostereoscopic display screen (16) is inclined at an angle θ to the vertical and is positioned below an opaque top wall (20) at a distance from the center of the image of the converging optic formed by the inclined front surface mirror equal to the radius of curvature of said concave mirror; The angles α, δ′ and θ are linked by the following relationship: δ' = 2.δ, where δ = 45° - α, o θ=β, where β is the angle formed with the horizontal by the direction of the observer's gaze directed from the eyebox towards the observation window towards the centre of reflection of the converging optic.

3. 3. The system of claim 2, wherein the front surface mirror (10), inclined at an angle α to the horizontal, passes through the upper opening (22) and defines a mirror portion extending above a horizontal plane visible to an observer and a mirror portion extending below the horizontal plane hidden by the opaque wall of the housing.

4. The angle α is 36°, the angle β is 20°, and the angle δ′ is 18°.

4. A projection system according to claim 2, wherein the angle θ is 20°.

5. 5. The projection system according to claim 1, wherein the converging optic is a concave mirror or a holographic optical element.

6. 6. Projection system according to claim 5, characterized in that the converging optic is a concave mirror (14) with a radius of curvature of 300 mm and a focal length of 150 mm.

7. 1. A device for displaying driving information for a motor vehicle comprising a windshield (100), a steering wheel (110) and a front dashboard (200) extending between the windshield (100) and the steering wheel (110), the display device comprising a projection system according to any one of claims 2 to 4, characterized in that the tilting front mirror is formed by the windshield, the opaque wall is formed by the front dashboard including an opening (220) for forming the upper projection opening of the autostereoscopic image, the converging optics and the autostereoscopic screen are housed below the front dashboard, and a vehicle driver sitting in front of the windshield can view driving information by aerial and virtual projection of the autostereoscopic image displayed on the display screen in a predetermined projection area extending above the front dashboard.

8. 1. A method for manufacturing a system for the aerial and virtual projection of autostereoscopic images intended for an observer whose eyes are located within a predetermined three-dimensional space called the eyebox, said method comprising the steps of: - selecting an autostereoscopic screen, called nominal screen, with predetermined usage characteristics and formed by a pixel matrix of N rows and M columns, and superimposed by a lenticular array with a predetermined pitch P'; - placing said nominal screen in a projection system comprising a converging optic acting like a concave mirror of radius R and focal length F, said converging optic being positioned relative to said eyebox so as to be able to direct the light rays it receives towards an observation window observable from said eyebox, and said nominal screen being positioned relative to said converging optic so that the light rays it emits can reach said observation window after reflecting off said converging optic and having travelled a distance d equal to twice the focal length F; - displaying a color chart on said nominal autostereoscopic screen, - calculating the number C of colors simultaneously observed from said use distance within said eyebox, - manufacturing an autostereoscopic screen, called a dedicated screen, having the same predetermined use characteristics as said nominal screen, and a lenticular array with a pitch P calculated by the formula P=P'.(1-C / (S.M)), where S is the number of different viewpoints addressed by each pixel of said matrix; - replacing said nominal screen with said dedicated screen;

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