APPARATUS FOR VIEWING STEREOSCOPIC IMAGES

Abstract: An apparatus for forming an autostereoscopic image in which the stereoscopic image of a picture on an image plate, such as a Vectograph or the like, can be viewed without the need for polarizing glasses. The apparatus includes a polarizing system, such as a pair of polarizers or a polarizing prism, for forming two distinctively polarized rays of light. A light source is provided for projecting light through the polarizing system to form a first set of rays of polarized light and a second set of rays of polarized light. The light source is oriented relative to the image plate such that the first and second rays of polarized light pass through the picture on the image plate. The apparatus also includes a lens for directing the first and second set of rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. In this manner, the stereoscopic image of the picture on the image plate can be observed by a viewer positioned within a defined spatial volume without need for the viewer to wear polarizing glasses.

Description: APPARATUS FOR VIEWING STEREOSCOPIC IMAGES Background of the Invention The present invention relates generally to the formation of stereoscopic images from two-dimensional scenes. More particularly, the invention relates to the creation of autostereoscopic images. Conventional stereoscopic imaging systems rely on polarized light to form stereoscopic images. Polarized light has a particular value in stereoscopic imaging because orthogonally polarized light beams do not interfere with one another. This allows the stereoscopic image to be formed from a pair of stereoscopic images, each of which represents a light-polarizing design or image that selectively transmits light of predetermined vector of polarization. The stereoscopic image pairs typically have a left- eye light-polarizing image superimposed on a right-eye light-polarizing image. This enables the perception of a three-dimensional image when the image pair is viewed through a pair of polarizing filters, or analyzers, oriented to allow the left-eye polarized image to reach the left-eye and the right-eye polarized image to reach the right eye. Typically, the analyzers are incorporated into viewing spectacles or glasses for wear by the observer. The wearing of polarizing glasses is undesirable from the point of view of the observer and expensive for the manufacturer of the stereoscopic imaging system, particularly if the system is designed for multiple observers. Stereoscopic imaging systems that do not require polarizing glasses have been proposed. Such systems are limited in application, however, because the left-eye image and the right-eye image can only be viewed from specific, limited locations. Furthermore, such systems require the observer to remain substantially stationary to view the stereoscopic image. Also, such systems are not suitable for use with multiple observers. Accordingly, there is a need for an apparatus for producing autostereoscopic images which allows an observer to view a stereoscopic image without the need for polarizing glasses and which gives the observer a wide range of locations from which to view the stereoscopic image. Alternative stereoscopic imaging systems have also been proposed in which the two images of the stereoscopic image pair are arranged in contiguous positions rather than superimposed. Such spatial multiplexing systems suffer from a loss of image resolution because each eye of the observer receives only a partial image. Other stereoscopic imaging systems rely upon temporally separating the images of the stereoscopic image pairs. Temporal multiplexing systems use electro-optical devices, such as light shutters, to provide alternating polarization that is synchronous with the interlaced left-eye and right-images. Temporal multiplexing systems, however, can suffer from image flicker in addition to being expensive and complex to manufacture. It is an object of the present invention to provide an apparatus for forming an autostereoscopic image in which the stereoscopic image of a picture on an image plate, such as a Vectograph or the like, can be viewed without the need for polarizing glasses. Another object of the present invention is to provide an apparatus for viewing stereoscopic images which can accommodate multiple observers. A further object of the present invention is to provide an apparatus for forming an autostereoscopic image which permits an observer an increased range of motion from which to view a stereoscopic image. Still another object of the invention is to provide an apparatus for forming an autostereoscopic image which does not suffer from a loss of image resolution. Other general and more specific objects of this invention will in part be obvious and will in part be evident from the drawings and the description which follow. Summary of the Invention These and other aspects of the invention are obtained through an apparatus for forming an autostereoscopic image in which the stereoscopic image of a picture on an image plate, such as a Vectograph or the like, can be viewed without the need for polarizing glasses. In one aspect of the present invention, the apparatus includes a polarizing element for forming two distinctively polarized rays of light and a light source for projecting light through the polarizing element to form a first set of rays of polarized light and a second set of rays of polarized light. The light source is oriented relative to the image plate such that the first and second rays of polarized light pass through the picture on the image plate. The apparatus also includes a lens for directing the first and second set of rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. In this manner, a viewer positioned within the defined spatial volume perceives a stereoscopic image of the picture on the image plate, without needing to wear polarizing glasses. Moreover, the stereoscopic image formed does not suffer from the loss of resolution typically exhibited by those autostereoscopic systems that rely on spatial multiplexing. In another aspect of the present invention, the lens can be a Fresnel lens. The lens can be positioned between the image plate and the light source. In the alternative, the lens can be positioned in front of the image plate such that the image plate is positioned between the light source and the lens. Other features of the invention pertain to the focal length of the lens in the autostereoscopic apparatus. For instance, the lens can be positioned such that the distance separating the light source and the image plate approximately equals two times the focal length of the lens. In other arrangements, the lens and the light source can be positioned such that the stereoscopic image of the picture is formed at a distance from the image plate that is approximately greater than or equal to two times the focal length of the lens. In still another aspect of the present invention, the polarizing element can be two polarizers. In addition, the light source and the image plate can be substantially aligned along the optical axis of the lens and the optical axis can separate the first and second polarizers of the polarizing element. The length of the first polarizer, along a plane substantially transverse to the optical axis, is preferably greater than or equal to the interocular distance of a viewer located within the spatial volume. Likewise, the length of the second polarizer, along a plane substantially transverse to the optical axis, is preferably greater than or equal to the interocular distance of a viewer located within the spatial volume thereby allowing the viewer to observe the stereoscopic image while moving in a plane perpendicular to the optical axis. Preferably, the polarizing axis of the first polarizer is orthogonal to the polarizing axis of the second polarizer. Additionally, the autostereoscopic apparatus can include a third polarizer and a fourth polarizer oriented substantially coplanar with the first polarizer. The third and fourth polarizers, analogous to the first and second polarizers, form a stereoscopic image of the picture at a second spatial volume. The autostereoscopic apparatus can also include a positioning system for moving the polarizing element in a manner that forms a stereoscopic image in a different spatial volume. Preferably, the apparatus includes a tracking system for tracking the position of a viewer. The tracking system can be operably coupled with the positional system such that the polarizing system is moved as a function of the position of the viewer. In accordance with a second embodiment of the invention, an apparatus for forming an autostereoscopic image comprises a polarizing system having a pair of polarizers and a light source for projecting light through the first polarizer to form a first set of rays of polarized light and for projecting light through the second polarizer to form a second set of rays of polarized light. The light source is oriented relative to an image plate, such that the first and second set of rays of polarized light pass through a picture on the image plate. The apparatus also includes a first lens positioned intermediate the polarizing system and the image plate, and a second lens for directing the first and second rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. In accordance with the second embodiment of the invention, the second lens and the light source allow a stereoscopic image of the picture to be formed at a distance as short as one focal length from the second lens. The reduction in the distance required to form an image provides a more compact illumination and polarization system. In accordance with a further aspect of the invention, the polarizing system can include a second pair of polarizers oriented substantially coplanar with the first pair of polarizers. The second pair of polarizers can form an image at a second spatial volume. In addition, the first lens can include a plurality of microlenticles, each one of which is optically aligned with one of a pair of polarizers. Preferably, each one of the microlenticles is positioned at a distance from a corresponding pair polarizers equal to the focal length of the microlenticles. In accordance with a third embodiment, the present invention includes a polarizing prism; a light source that projects light through the polarizing prism to form a first set of rays of polarized light and a second set of rays of polarized light; and a lens. The light source is oriented relative to an image plate such that the first and second set of rays of polarized light pass through a picture on the image plate. The lens in turn directs the first and second rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. The polarizing prism can be constructed of birefringent material, such as calcite. The birefringent material causes light rays projected from the light source through the polarizing prism to split into the first and second sets of rays of polarized light. The polarizing prism can be formed of one or more prisms. For instance, the polarizing prism can include a first prism constructed of a birefringent material having a first polarizing axis, and a second prism constructed of a birefringent material having a polarizing axis oriented orthogonal to the first polarizing axis. In this dual prism arrangement, the polarizing prism transmits first and second sets of polarized rays that diverge from each other. One example of a dual prism arrangement is a Wollaston prism. The polarizing prism can also be constructed of a liquid crystal material overlying a plastic prismatic material. The polarizing prism transmits the first set of rays polarized in a first orientation and the second set of rays polarized orthogonal to the first set of rays. The prism can also include a transparent plate overlying the liquid crystal material. In accordance with a fourth embodiment of the invention, an autostereoscopic apparatus includes a polarizing system having a first diffraction grating and a second diffraction grating overlying the first diffraction grating. A light source projects light through the first and second diffraction gratings to form a first set of rays of polarized light and a second set of rays of polarized light. The light source can be oriented relative to an image plate such that the first and second set of rays of polarized light pass through a picture on the image plate. A lens is provided for directing the first and second set of rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. In accordance with another aspect of the invention, the first diffraction grating includes a first substrate formed of a molecularly oriented sheet aligned along a first axis. A dichroic dye is applied to portions of the first substrate such that the portions absorb light polarized in the direction of the first axis. Likewise, the second diffraction grating can include a second substrate formed of a molecularly oriented sheet aligned along a second axis orthogonal to the first axis. A dichroic dye is also applied to portions of the second substrate such that the portions absorb light polarized in the direction of the second axis. In this manner, the first diffraction grating polarizes the first set of rays of polarized light to a first polarization orientation and the second diffraction grating polarizes the second set of rays of polarized light to a second polarization orientation orthogonal to the first polarization orientation. In accordance with a fifth embodiment of the invention an apparatus for viewing autostereoscopic images includes a light source for projecting light through a picture on an image plate and a polarizing system, such as a pair of polarizers, for polarizing the light projected through the picture on the image plate. The pair of polarizers can include a first polarizer for forming a first set of rays of polarized light and a second polarizer for forming a second set of rays of polarized light. A lens is optically aligned with the pair of polarizers to direct the first and the second rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. In accordance with one aspect of the invention, the polarizing system can include a plurality of pairs of polarizers each one of which is oriented substantially coplanar with the other. Preferably, the lens includes a plurality of microlenticles each one of which is optically aligned with one of the pairs of polarizers. Brief Description of the Drawings These and other features and advantages of the present invention will be more fully understood by reference to the following detailed description in conjunction with the attached drawings in which like reference numerals refer to like elements through the different views. The drawings illustrate principals of the invention and, although not to scale, show relative dimensions. FIG. 1 is a diagram of an apparatus for forming an autostereoscopic image according to a first embodiment of the present invention; FIG. 2 is a diagram of an apparatus for forming an autostereoscopic image according to a second embodiment of the present invention; FIG. 3 is a diagram of an apparatus for forming an autostereoscopic image according to a third embodiment of the present invention; FIG. 4 is a diagram of an apparatus for forming an autostereoscopic image according to a fourth embodiment of the present invention; FIG. 5 A is a side-elevational view of a first array of polarizing prisms of the polarizing system of the apparatus of FIGS. 1-4; FIG. 5B is a side-elevational view of a second array of polarizing prisms of the polarizing system of the apparatus of FIGS. 1-4; FIG. 5C is a side-elevational view of a portion of the array of polarizing prisms of FIGS. 5A and 5B; FIG. 5D is a side-elevational view of the array of polarizing prisms of FIGS. 5A- 5B; FIG. 6 is a diagram of the light source and polarizing filters of the apparatus of FIG. 1; FIG. 7 is a diagram of the polarizing system and the image plate of the apparatus of FIG. 3; FIG. 8 is a diagram of the image plate of the apparatus of FIG. 1; FIG. 9 is a diagram of the lens of the apparatus of FIG. 1 illustrating the dimensions of the spatial volume in which the autostereoscopic image is formed; FIG. 10 is a diagram of the positioning system and the head tracking system for use with the apparatus of FIGS. 1-4; FIG. 11 is a diagram of the polarizing system of the apparatus of FIG. 4; FIG. 12 is a diagram of a diffraction grating system of the polarizing system of the apparatus of FIG. 1-4; FIG. 13 is a top view of a diffraction grating of the diffraction grating system of FIG. 12. Description of the Illustrated Embodiments An apparatus 10 for forming an autostereoscopic image in which the stereoscopic image of a picture on an image plate 20 can be viewed without the need for polarizing glasses is shown in FIG. 1. The apparatus 10 includes a light source or illuminator 12 and a polarizing system 14, such as a first polarizing filter 16 and a second polarizing filter 18, for forming two distinctively polarized rays of light. The light source 12 projects unpolarized light through the polarizing system to form a first set of rays of polarized light and a second set of rays of polarized light. The first and second set of rays of polarized light pass through each point or pixel of a stereoscopic image formed on the image plate 20. The apparatus 10 further includes a lens 22, such as a Fresnel lens, which directs the first and second set of rays of polarized light towards a spatial volume, as discussed below, at which a stereoscopic image of the picture is formed. In this manner, the stereoscopic image of the picture on the image plate 20 can be observed by a viewer positioned within the defined spatial volume without needing to wear polarizing glasses. As illustrated in FIG. 1 and FIG. 6, the light source 12 produces scattered, unpolarized light 24 that is incident upon the first polarizing filter 16 and the second polarizing filter 18 of the polarizing system 14. The first polarizing filter 16 has a polarizing axis 26 that is oriented perpendicular to the plane of the page of FIG. 6. The second polarizing filter 18 includes a polarizing axis 28 that lies within the plane of the page of FIG. 6 and is orthogonal to the polarizing axis of the first polarizing filter 16. Unpolarized light from the light source 12 incident upon the first polarizing filter 16 is polarized to a first orientation as indicated by arrows PI in FIG. 6. Conversely, unpolarized light incident upon the second polarizing filter is polarized to a second orientation, orthogonal to the first orientation, as indicated by arrow P2 in FIG. 6. The orientation of the polarizing axes of the first and second polarizing filters 16, 18 is not limited to those shown in FIG. 1 or FIG. 6. One skilled in the art will recognize that the polarizing axes of the two polarizing filters can be oriented in any direction. The most effective arrangement occurs when the two polarizing axes are at right angles to one each other. Additionally, the polarizing system is not limited to a linear polarizing system but can also include a circular or elliptical polarizing system. A stereoscopic image based upon the polarization of light is generally formed of a pair of polarizing images, each of which presents a light-polarizing design that selectively transmits a predetermined vector of polarization. Such a stereoscopic polarized image or picture is formed on the image plate 20. The stereoscopic polarized image comprises a stereoscopic image pair having a left-eye light-polarized image superimposed on a right-eye light-polarizing image. This enables the perception of a three-dimensional image when the stereoscopic pair is viewed with light polarized by the pair of polarizing filters 16, 18, oriented such that the left-polarized image reaches the left-eye and the right-polarized image reaches the right eye. The polarizing image on image plate 20 can be made by a sheet that polarizes light to different percentages, depending upon the density of the image at each point or pixel of the image. In particular, the percentage of polarization is directly related to the image's density, nearly all the light being polarized in high density areas and only a small amount of light being polarized in low-density areas. As shown in FIG. 1 and FIG. 8, the image plate 20 includes a first polarizing substrate 30 having a polarization axis 34 parallel to the polarizing axis 26 of the first polarizer 16 and a second polarizing substrate 32 having a polarization axis 36 parallel to the polarization axis 28 of the second polarizer 18. A dichroic material, such as a dichroic stain or dye, is applied to the first polarization substrate 30 to form the left-eye polarized image. Likewise, a dichroic material is applied to the second polarization substrate 32 to form the right-eye polarized image. The first and second polarizing substrates 30, 32 are optically aligned such that the left-eye image and the right-eye image are stereoscopically registered. When forming the stereoscopic image on the image plate 20, the most effective arrangement occurs when the polarization axis of the left-eye image is at a right angle to the polarization angle of the right-eye image, and when the two images are superimposed in such a position with respect to each other the images carried thereby are stereoscopically registered. The first and second polarizing substrates 30, 32 are preferably polyvinyl alcohol (hereinafter "PVA"), a long chain polymer that readily assumes a linear configuration upon heating and stretching and also absorbs dichroic stains or dyes. Sheets of PVA can be stretched and oriented according to various methods known in the art. Once stretched and oriented and dyed, the sheets of PVA exhibit dichroism. The term dichroism as used herein refers to the property of differential absorption of the components of polarization of an incident beam of light, depending on the vibration direction of the components. Dichroic die or stain as used herein refers to a die or stain whose molecules process the properties of becoming linearly disposed within the oriented sheet material. For example, when a molecularly-oriented polymeric sheet, such as a sheet of PVA, is died with a dichroic dye, the sheet will appear dichroic, i.e., it will absorb differently the vectoral components of polarization of an incident beam of light. The dichroic dye or stain can be applied to the substrates 30, 32 according to various methods known in the art, including, for example, by masking as disclosed by Land in U.S. Patent No. 2,281,101, incorporated herein by reference, or by ink jet printing techniques, as disclosed by Scarpetti in U.S. Patent No. 5,591,508, also incorporated herein by reference. While the two polarizing substrates 30, 32 have been described as carrying respectively a left-eye image and a right-eye-image, it is understood that alternative arrangements fall within the scope of the present invention. For example, the image plate 20 can comprise a single substrate carrying two of such images. In the alternative, the image plate 20 can comprise a continuous film carrying a succession of pair of images. The apparatus 10 of the present invention contemplates the use of all such arrangements, whether the two stereoscopic images are superimposed by the superpositioning of separate elements carrying the images, or whether the images are superimposed by the formation of one image on each face of a substrate, or both images on the same face of a single substrate. Also, it is to be understood that the images need not be so superimposed as to lie in closely adjacent planes. Alternatively, the stereoscopic image on image plate 20 can be formed by electronic means. Such an image plate is described by DuBois in copending U.S. Patent Application No. , filed and incorporated herein by reference. With further reference to FIG. 1, a first set of polarized light rays PI defined by the angle θ i and polarized by the first polarizing filter 16 to the first polarization orientation passes through a point or pixel X of the stereoscopic image formed on the image plate 20. Adjacent the first set of rays, a second set of polarized light rays P2 defined by the angle Θ2 and polarized by the second polarizing filter 18 to the second polarization orientation also passes through pixel X of the stereoscopic image. As discussed above, each pixel X of the stereoscopic image includes a left-eye polarized image superimposed over a right-eye polarized image. Each pixel X receives orthogonally polarized light rays from the first and second polarizing filters 16, 18. In this manner, the left-eye polarized image at each pixel is illuminated and brought to full contrast with polarized light P2 from the second polarizing filter 18 and the right-eye image is illuminated and brought to full contrast with polarized light PI from the first polarizing filter PI. The lens 22 is positioned immediately in front of the image plate 20 to refract the two cones of light toward the optical axis OA of the lens 22. The common ray dividing the two cones of rays passes through the point F along the optical axis OA. This is true for each pixel of the stereoscopic image formed on the image plate 20. For an observer positioned at the point F or distal to the point F in relation to the lens 22, the left eye LE of the observer will see only the set of polarized light rays P2 corresponding to the left- eye image, if the observer's left eye LE is above the optical axis OA. Likewise, if the observer's right eye RE is below the optical axis OA, the observer's right eye RE will see only the set of polarized light rays PI corresponding to the right-eye image. Accordingly, an autostereoscopic image of the stereoscopic image on the image plate 20 is formed and is observable within a spatial volume SV that originates at the point F. As best illustrated in FIG. 9, the lateral limits or diameter D of the spatial volume SV, i.e., the dimension perpendicular to the optical axis OA of the lens 22, within which an observer can view the stereoscopic image is limited by the interocular distance of the particular observer. For an observer positioned within the spatial volume SV to view the stereoscopic image, the observer's left eye must remain above the optical axis OA, while the observer's right eye concomitantly remains below the optical axis OA. Specifically, the diameter D of the spatial volume SV is given by D = 2 * IO, where IO is the interocular distance of a particular observer. Preferably, the light source 12 and the lens are oriented relative to one another along the optical axis OA such that Dl= D2 = 2 * f, where DI is the distance of the point F from the image plate 20, D2 is the distance between the image plate 20 and the light source 12, and f is the focal length of the lens 22. If the light source 12 is positioned closer to the image plate 20, i.e. if the value of D2 is reduced, the value of DI will correspondingly increase and the point F will move to a location on the optical axis OA further away from the image plate 20. Continuing to refer to FIG. 9, to provide the maximum amount of lateral movement for the observer to view the stereoscopic image within the spatial volume SV, - l i ¬ the value of the angle 02 should be large enough that the second cone of rays of polarized light subtends at the point F such that h ≥ IO, wherein h is the subtending height of the second cone of rays and IO is the interocular distance of the observer. To accomplish this, the length D4 of the second polarizing filter 18 should be greater than or equal to the interocular distance of the observer. Likewise, the length D3 of the first polarizing filter 16 should also be greater than or equal to the interocular distance of the observer. In this manner, polarized light from the first and second cones of rays impinges upon the entire diameter D of the spatial volume SV. This permits the observer to view the stereoscopic image while moving within the spatial volume SV along a plane perpendicular to the optical axis OA. The lens 22 for refracting the polarized rays of light PI and P2 toward the OA and point F is preferably a Fresnel lens. The location of the lens 22 is not limited to that illustrated in FIGS. 1 and 9. The lens can alternatively be positioned between the image plate 20 and the light source 12. In this arrangement, the polarized rays of light PI and P2 will be refracted towards the OA of the lens 22 prior to passing through image plate 20. A second embodiment of an apparatus for forming autostereoscopic images according to the present invention is illustrated in FIG. 2. In the second embodiment, the polarizing system 14 comprises a plurality of pairs of polarizing filters. Each pair of polarizing filters includes a first polarizing filter 16 and a second polarizing filter 18. The polarization axis of the first polarizing filter 16 is preferably orthogonal to the polarizing filter of the second polarizing filter 18. The plurality of pairs of polarizing filters permits an observer to view the stereoscopic image on image plate 20 from multiple observation points or spatial volumes. In a manner analogous to that illustrated in FIG. 1 , each pair of polarizing filters in conjunction with the lens 22 forms a first set of rays that direct a first image to the left eye of the observer and a second set of rays that direct a second image to the right eye of the observer. Referring to FIG. 2, for example, an autostereoscopic image is formed at a first spatial volume FI by a first pair of polarizing filters 38. A second autostereoscopic image is formed at a second spatial F2 by a second pair of polarizing filters 39. Accordingly, an autostereoscopic image is formed at a separate, independent spatial volume for each pair of polarizing filters. FIG. 10 illustrate the use of a positioning system 50 for moving the polarizing filters 16 and 18 in a plane perpendicular to the optical axis OA of the lens 22. In this manner, the polarizing filters can be moved relative to the lens 22 such that the lens 22 directs the first and second cones of polarized light rays to different spatial volumes or observation points. The positioning system 50 can include devices known in the art for moving optical elements, such as a motorized endless belt to which each of the polarizing filters 16 and 18 are connected. The positioning system 50 can also include positioning sensors, such as interferometers or the like, to determine the position of the optical elements and provide a feedback control system. If the polarizing system 14 comprises multiple pairs of polarizing filters as illustrated in Figure 2, each pair can be connected to a separate positioning means to permit each pair to move independently of the other pairs of polarizing filters. A head tracking system 52, including an optical sensor 54 such as a charged- coupled device or an infrared sensor, can be used to track the position of the observer. Such a head tacking system is available from Intersense Corporation of Cambridge, MA. The head tracking system is operably coupled with the positioning system 50 such that the polarizing filters 16 and 18 of the polarizing system 14 can be moved as a function of the position of the observer. The optical sensor 54 determines the position of the observer and transmits positioning information to the head tracking system 52. Based on the positioning information, the head tracking system 52 calculates the position and orientation of the observer's head and sends positioning control signals to the positioning system. The positioning systems correspondingly moves the polarizing filters 16 and 18 in response to the positioning control signal. Accordingly, the observer is free to move relative to the apparatus 10 and still view the stereoscopic image on the image plate 20. A third embodiment of an apparatus for forming an autostereoscopic image according to the present invention is shown in FIG. 3. The polarizing system 14 according to this embodiment comprises a plurality of pairs of polarizing filters 16 and 18 and a microlenticular system 60 interposed between the polarizing filters and the image plate 20. The microlenticular system 60 includes a series of cylindrical microlenticles 62 each of which is optically aligned with one of the pairs of polarizers. The polarizing filters 16 and 18 include polarization axises 26 and 28, respectively, orthogonally aligned to one another. In a manner analogous to that illustrated in FIGS. 1 and 2, scattered, unpolarized light from light source 12 is incident upon the polarizing system 14. Two orthogonally polarized light means PI and P2 emerge from the polarization system 14. As illustrated in FIG. 3 and FIG. 7, the first set of polarized light rays PI, defined by the angle θι , and the second set of polarized rays P2, defined by the angle Θ2, each pass through pixel X to illuminate both right-eye polarized image and the left-eye polarized image, respectively, at pixel X. The values of angles θi and Θ2 are approximately given by Θ1 = θ « (W/2)/Φ, where Φ is the focal length and W the width of each cylindrical microlenticle 62. As discussed above, the lens 22 refracts the first and second cones of polarized light rays PI and P2 such that the common ray dividing the cone passes through the point F on the optical axis OA of the lens 22. Thus, the autostereoscopic image of the stereoscopic image on the image plate 20 is formed and is observable within a spatial volume originating a point F. Continuing to refer to FIG. 3, the use of the polarizing system 14 comprising a plurality of pairs of polarizing filters 16 and 18 and a microlenticular system 60 causes the point F to be located a distance D5 from the lens 22, where the value of D5 is D5 = f= (Dl)/2, where f is the focal length of the lens 22 and DI is the distance of the point F from lens 22 in the embodiment illustrated in FIG. 1 and described above. Accordingly, a more compact and convenient apparatus for viewing an autostereoscopic image can be provided. The apparatus can be made further compact by using a flat plate illumination panel for light source 12. A fourth embodiment of an apparatus for viewing autostereoscopic images according to the present invention is shown in FIG. 4 and FIG. 11. The polarizing system 14 is positioned in front of the image plate 20 and includes a plurality of pairs of polarizing filters 16 and 18 and a microlenticular system 70 comprising a series of microlenticles 72. According to this embodiment, the light source 12 illuminates the pixels of the stereoscopic image on the image plate 20 with unpolarized light. Two orthogonally polarized light rays PI and P2 emerge from each pixel, one corresponding to the right- eye polarized image and the other the left-eye polarized image, respectively. In turn, the first polarizing filter 16 of each polarizing pair transmits the right-eye polarized image PI of each pixel, while concurrently blocking the left-eye polarized image P2 of each pixel. Conversely, the second polarizing filter 18 transmits the left-eye polarized image P2 and blocks the right-eye polarized image PI . Each microlenticle 72 of the microlenticular system 70 is optically aligned with one of the pairs of polarizing filters 16 and 18. As best illustrated in FIG. 11, the microlenticles 72 direct the right-eye polarized image PI from the first polarizing filter 16 to the right-eye RE of the observer. Likewise, the microlenticles direct the left-eye image P2 from the second polarizing element 18 to the left-eye LE of the observer. Accordingly, the observer does not receive a complete image for each eye because of the alternating arrangement of the polarizing filters 16 and 18, resulting in a slight loss of resolution. Preferably, the microlenticular system 70 comprises very fine, narrow microlenticles, e.g. 100 microlenticles/inch, so that a great many microlenticles extend in a side-by-side relationship across the polarizing system. This diminishes the effects of any loss of resolution in the system. The apparatus of the present invention contemplates the use of various polarizing elements in the polarizing system 14. For example, the polarizing filters 16 and 18 of the polarizing systems 14 can comprise synthetic sheet polarizing filters, such as the Polaroid H-sheet polarizer, or the like, available from the Polaroid Corporation. Alternatively, the polarizing system 14 can comprises an array of birefringent polarizing prisms, such as an array 80 of micro- Wollaston prisms shown in FIG. 5 A. The terms "birefringence" or "birefringent" used herein refers to the splitting of a light beam into two components which travel at different velocities. The Wollaston prism is constructed of two prisms of a birefringent material, such as calcite. The first prism 82 has an optic axis 84 that lies in the plane of page and the second prism 86 has an optic axis 88 perpendicular to the optic axis 84. The component of the incident light 90 that lie in the plane of the page (i.e., parallel to the optic axis having a polarization vector oriented to 84) travels faster in the first prism 82 than in the second prism 86. Therefore, that component P2 is refracted towards the perpendicular 92 at the prism interface 91 as it passes from the first prism 82 to the second prism 86 at point A. On the other hand, the component PI of the incident light 90 having a direction of polarization perpendicular to the plane of the page (i.e., perpendicular to optical axis 84) travels more slowly in the first prism 82 than in the second prism 86. Thus, the component PI is refracted away from the perpendicular 92 as it passes from the first prism 82 into the second prism 86 at point A. Thus, the Wollaston prism converts an incident unpolarized light beam 90 into two divergent, orthogonally polarized beams PI, P2. Although a single Wollaston prism can be substituted for the array 80 of micro- Wollaston prisms shown in FIG. 5 A, an array 80 is preferable because a single Wollaston prism of sufficient length for the apparatus would be undesirably bulky. The array 80 of micro- Wollaston prisms comprises multiple micro- Wollaston prisms and can be similar to a Fresnel lens in construction. An alternative polarizing element to the Wollaston prism is the polarizing prism 100 shown in FIG 5B. The polarizing prism 100 includes an array 102 of plastic prisms and a transparent cover plate 104 which overlies the array 102. A liquid crystal material 106 fills the intervening space between the cover 104 and the array 102 of plastic prisms. The molecules of the liquid crystal material are preferably oriented parallel to the optic axis 108 of the plastic prisms. The liquid crystal molecules can be oriented according various known methods in the art such as by buffing or rubbing the adjacent surfaces of the cover 104 and the array 102 in the preferred direction of orientation. The liquid crystal material functions as a birefringent material having two indexes of refraction, n 0 and n e . The plastic material comprising the plastic prism 102 can be birefringent, however, this is not necessary. The index of refraction of the plastic material should fall between the two indexes of refraction of the liquid crystal material. Preferably, the index of refraction of the plastic, n p , is given by n p = ( n o + n e) 2 - This results in the polarizing prism 100 functioning in the same manner as the Wollaston prism 80 in which unpolarized light 90 is split into two diverging orthogonally polarized rays, PI and P2. The advantage of the polarizing prism 100 over prior art prisms is that costly birefringent materials, such as calcite, are unnecessary. With the polarizing prism 100, a birefringence can be obtained in which the two indexes of refraction, n 0 and n e , of the liquid crystal material differ by .2, a value similar to that of calcite. As shown in FIG. 5D, the polarizing prism 100 or the array of micro-Wollaston prisms 80 can be illuminated with two cones of rays of unpolarized light from the light source 12. The first cone of unpolarized light is defined by the angle θj and the two rays 110 and 112. The second cone of unpolarized light is defined by the angle Θ2 and the two rays 112 and 114. The shape of the array 102 is defined by the surface angle α, relative to surface 109. Two cones are orthogonally polarized light are generated by the array 102 as a function of the angle Θ1 , the angle Θ2, and the angle . The first cone of emerging polarized light PI is defined by the rays 116, 118, and 120. The second cone of emerging polarized light P2 is defined by the rays 116, 122, and 124. As illustrated in FIG. 5D, each cone of polarized light shares a common ray 116 that includes both PI polarized and P2 polarized light. For example, for angle α = 60 degees and for n 0 = 1.4, n e =1.6, and np = 1.5, two cones of orthogonally polarized light are generated by the array 102 for the following values of θj and Θ2: Θ1 « Θ2 ≤ 3 degrees. FIG. 5C shows two polarizing prisms 130 and 132, such as the micro- Wollaston prisms 80 or the polarizing prisms 100. Unwanted scattering or internal reflection can occur at the sides 134 of the prisms. For example, light rays 135 passing through the interface surface 136 between points E and F in prism 130 are reflected by the side 134 of the prism 130. By applying a mask 140 to the interface between the points E and F in prism 132, the unwanted reflection can be eliminated. Although masking can lead to a reduction in overall illumination by creating "blank" spots, this effect can be reduced by increasing the number of prisms per unit length. The reduction of illumination is unnoticeable for polarizing systems having approximately 50 to 200 prisms per inch. A further alternative for producing the desired polarization for the apparatus of the present invention is to use diffraction gratings in the polarizing system 14. Referring to FIG. 12 and FIG. 13, unpolarized light 150 is incident, at an angle of incidence i, upon two diffraction gratings positioned along the line GH. The diffraction gratings at line GH diffract the perpendicularly polarized light PI through an angle of refraction r _ and the parallel polarized light P2 through an angle of refraction rjj. In this manner, two diverging orthogonally polarized light rays PI and P2 emerge from the diffraction gratings. Diffraction can be accomplished by two diffraction gratings, one for perpendicularly polarized light PI and one for parallel polarized light P2, that are superimposed on top of one another. A diffraction grating 200 for forming perpendicularly polarized light P2 is shown in FIG. 13. Diffraction grating 200 has a spacing of dj_ and can be made by using a molecularly oriented sheet such as stretched PVA, or the like, having an axis 202 perpendicular to the page. A dichroic dye is then applied to the alternate (shaded) regions 204 so that these regions become polarized and absorb light that is polarized in the direction of the axis. The polarized regions 204 will transmit light that is polarized in the direction perpendicularly to the axis 202, as indicated by the arrows 206. Therefore, light polarized in the direction of arrows 206, i.e., parallel polarized light P2, will not be diffracted by the polarized regions 204 of the grating 200. On the other hand, perpendicularly polarized light PI will be totally absorbed by the polarized regions 204 and will, thus, be diffracted. A second diffraction grating (not shown) for the parallel polarized light P2 can also be constructed out of a molecularly oriented sheet such as stretched PVA, or the like, having an axis that is perpendicular to that of the first diffraction grating 200. The spacing d[[ of the second diffraction grating is preferably less than the spacing d j _ of the first grating, such that the diffraction angel, rjj, will be greater than the diffraction angle r_L_ This allows the two diffraction gratings to be superimposed to produce two orthogonally polarized diverging light beams, as shown in FIG. 12. It will thus be seen that the invention efficiently attains the objects set forth above, among those made apparent from the preceding description. Since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are to cover all generic and specific features of the invention described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. Having described the invention, what is claimed as new and desired to be secured by Letters Patent is:

Claims: Claims: 1. An apparatus for forming an autostereoscopic image, the apparatus comprising: a first polarizer; a second polarizer; a light source for projecting light through the first polarizer to form a first set of rays of polarized light and for projecting light through the second polarizer to form a second set of rays of polarized light, the light source being oriented relative to an image plate such that the first and second set of rays of polarized light pass through a picture on the image plate, and a lens for directing the first and second set of rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. 2. The apparatus according to claim 1 , wherein the lens is a fresnel lens. 3. The apparatus according to claim 1, wherein the lens is positioned between the image plate and the light source. 4. The apparatus according to claim 1, wherein the image plate is positioned between the lens and the light source. 5. The apparatus according to claim 1, wherein the distance separating the light source and the image plate approximately equals two times the focal length of the lens. 6. The apparatus according to claim 1 , wherein the lens and the light source are positioned relative to the image plate such that the stereoscopic image of the picture is formed at a distance from the image plate that is approximately greater than or equal to two times the focal length of the lens. 7. The apparatus according to claim 1, wherein the light source and the image plate are substantially aligned along the optical axis of the lens and wherein the optical axis separates the first and second polarizers. 8. The apparatus according to claim 7, wherein the length of the first polarizer, along a plane substantially transverse to the optical axis, is greater than or equal to the interocular distance of a viewer located within the spatial volume thereby allowing the viewer to observe the stereoscopic image while moving in a plane perpendicular to the optical axis. 9. The apparatus according to claim 8, wherein the length of the second polarizer, along a plane substantially transverse to the optical axis, is greater than or equal to the interocular distance of a viewer located within the spatial volume thereby allowing the viewer to observe the stereoscopic image while moving in a plane perpendicular to the optical axis. 10. The apparatus according to claim 1, wherein the polarizing axis of the first polarizer is oriented orthogonal to the polarizing axis of the second polarizer. 11. The apparatus according to claim 10, further comprising a third polarizer and a fourth polarizer oriented substantially coplanar with the first polarizer, the third and fourth polarizers forming polarized light that passes through the image plate and the lens such that a stereoscopic image of the picture is formed at a second spatial volume. 12. The apparatus according to claim 11 , wherein the polarizing axis of the third polarizer is oriented orthogonal to the polarizing axis of the fourth polarizer. 13. The apparatus according to claim 1 , further comprising positional means for moving the first and second polarizers in a plane perpendicular to an optical axis of the lens such that the lens directs the first and second rays of polarized light towards a different spatial volume. 14. The apparatus according to claim 13, further comprising a tracking system for tracking the position of a viewer, the tracking system being operably coupled with the positional means such that the first and second polarizers are moved as a function of the position of the viewer. 15. The apparatus according to claim 1 , wherein the image plate comprises a Vectograph. 16. The apparatus according to claim 1, wherein the image plate comprises a first layer having a first polarization axis, a second layer overlying the first layer and having a second polarization axis oriented orthogonal to the first polarization axis, and a dichroic material applied to the first layer to form a first portion of the picture on the first layer and to the second layer to form a second portion of the picture on the second layer, whereby the first and second layers are optically aligned to combine the first and second portions to form the picture. 17. An apparatus for forming an autostereoscopic image, the apparatus comprising: a pair of polarizers including a first polarizer and a second polarizer; a light source for projecting light through the first polarizer to form a first set of rays of polarized light and for projecting light through the second polarizer to form a second set of rays of polarized light, the light source being oriented relative to an image plate such that the first and second set of rays of polarized light pass through a picture on the image plate, a first lens positioned intermediate the pair of polarizers and the image plate; and a second lens for directing the first and second rays of polarized light towards a spatial volume at which a stereoscopic image of the pictures is formed. 18. The apparatus according to claim 17, wherein the second lens is a fresnel lens. 19. The apparatus according to claim 17, wherein the second lens is positioned between the image plate and the light source. 20. The apparatus according to claim 17, wherein the image plate is positioned between the second lens and the light source. 21. The apparatus according to claim 17, wherein the second lens and the light source are positioned relative to the image plate such that the stereoscopic image of the picture is formed at a distance from the image plate that is greater than or equal to the focal length of the second lens. 22. The apparatus according to claim 17, wherein the length of the first polarizer, along a plane substantially transverse to the optical axis, is greater than or equal to the interocular distance of a viewer located within the spatial volume thereby allowing the viewer to observe the stereoscopic image while moving in a plane perpendicular to the optical axis. 23. The apparatus according to claim 22, wherein the length of the second polarizer, along a plane substantially transverse to the optical axis, is greater than or equal to the interocular distance of a viewer located within the spatial volume thereby allowing the viewer to observe the stereoscopic image while moving in a plane perpendicular to the optical axis. 24. The apparatus according to claim 17, further comprising a second pair of polarizers oriented in the same plane as the pair of polarizers. 25. The apparatus according to claim 24, wherein the first lens comprises a plurality of microlenticles each one of which is optically aligned with one of the pairs of polarizers. 26. The apparatus according to claim 25, wherein each one of the plurality of microlenticles is positioned at a distance from a corresponding pair of polarizers approximately equal to the focal length of the microlenticles. 27. The apparatus according to claim 17, wherein the light source comprises a flat plate illuminator. 28. The apparatus according to claim 17, wherein the polarizing axis of the first polarizer is oriented orthogonal to the polarizing axis of the second polarizer. 29. An apparatus for forming an autostereoscopic image, the apparatus comprising: a polarizing prism; a light source for projecting light through the polarizing prism to form a first set of rays of polarized light and a second set of rays of polarized light, the light source being oriented relative to an image plate such that the first and second set of rays of polarized light pass through a picture on the image plate, and a lens for directing the first and second rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. 30. The apparatus according to claim 29, wherein the polarizing prism is a Wollaston prism. 31. The apparatus according to claim 29, wherein the polarizing prism comprises an array of micro-polarizing prisms. 32. The apparatus according to claim 29, wherein the polarizing prism is constructed of a birefringent material, whereby the plurality of light rays projected from the light source through the polarizing prism are split into the first set of rays of polarized light and the second set of rays of polarized light. 33. The apparatus according to claim 32, wherein the birefringent material is calcite. 34. The apparatus according to claim 29, wherein the polarizing prism comprises a first prism constructed of a birefringent material having a first polarizing axis, and a second prism constructed of a birefringent material having a second polarizing axis oriented orthogonal to the first polarizing axis, whereby the polarizing prism transmits the first set of rays of light polarized parallel to the first polarizing axis and a second set of rays of light polarized parallel to the second polarizing axis. 35. The apparatus according to claim 34, wherein the first set of rays of polarized light diverges from the second set of rays of polarized light. 36. The apparatus according to claim 29, wherein the polarizing prism comprises a prism constructed of a plastic material, and a liquid crystal material overlying the prism, whereby the polarizing prism transmits the first set of rays of light polarized in a first orientation and the second set of rays of light polarized orthogonally to the first set of rays. 37. The apparatus according to claim 36, further comprising a transparent plate overlying the liquid crystal material. 38. An apparatus for forming an autostereoscopic image, the apparatus comprising:: a first diffraction grating; a second diffraction grating overlying the first diffraction grating; a light source for projecting light through the first and second diffraction gratings to form a first set of rays of polarized light and a second set of rays of polarized light, the light source being oriented relative to an image plate such that the first and second set of rays of polarized light pass through a picture on the image plate, and a lens for directing the first and second set of rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. 39. The apparatus according to claim 38, wherein the first diffraction grating polarizes the first set of rays of polarized light to a first polarization orientation and the second diffraction grating polarizes the second set of rays of polarized light to a second polarization orientation orthogonal to the first polarization orientation. 40. The apparatus according to claim 38, wherein the first diffraction grating comprises a first substrate formed of a first molecularly oriented sheet aligned along a first axis, and a dichroic dye applied to portions of the first substrate such that the portions absorb light polarized in the direction of the first axis. 41. The apparatus according to claim 40, wherein the second diffraction grating comprises a second substrate formed of a second molecularly oriented sheet aligned along a second axis orthogonal to the first axis, and a dichroic dye applied to portions of the second substrate such that the portions absorb light polarized in the direction of the second axis. 42. An apparatus for forming an autostereoscopic image, the apparatus comprising: a light source for projecting light through a picture on an image plate; a pair of polarizers for polarizing the light projected through the picture on the image plate, the pair of polarizers including a first polarizer and a second polarizer, the first polarizer forming a first set of rays of polarized light and the second polarizer forming a second set of rays of polarized light; and a lens optically aligned with the pair of polarizers for directing the first and the second rays of polarized light towards a spatial volume at which a stereoscopic image of the picture is formed. 43. The apparatus according to claim 42, wherein the image plate is positioned between the light source and the pair of polarizers. 44. The apparatus according to claim 42, further comprising a plurality of pairs of polarizers each one of which is oriented substantially coplanar with the pair of polarizers. 45. The apparatus according to claim 44, wherein the lens comprises a plurality of microlenticles each one of which is optically aligned with one of the pairs of polarizers. 46. The apparatus according to claim 42, wherein the polarizing axis of the first polarizer is orthogonal to the polarizing axis of the second polarizer. 47. An apparatus for forming an autostereoscopic pixel image, the apparatus comprising: a first polarizer; a second polarizer; a light source for projecting light through the first polarizer to form a first ray of polarized light and for projecting light through the second polarizer to form a second ray of polarized light, the light source being oriented relative to an image plate such that the first and second rays of polarized light pass through a pixel on the image plate, and a lens for directing the first and second rays of polarized light towards a spatial volume at which a stereoscopic image of the pixel is formed.

Inventors: DUBOIS PHILIP M, DUBOIS, PHILIP, M.
Applicants: ROWLAND INST FOR SCIENCE, THE ROWLAND INSTITUTE FOR SCIENCE
Application year: 1997
Main classification: G02B27
IPC codes: G02B27, H04N13