|Número de publicación||US20050057788 A1|
|Tipo de publicación||Solicitud|
|Número de solicitud||US 10/827,043|
|Fecha de publicación||17 Mar 2005|
|Fecha de presentación||19 Abr 2004|
|Fecha de prioridad||12 Sep 2003|
|También publicado como||EP1664902A1, US6871956, WO2005033777A1|
|Número de publicación||10827043, 827043, US 2005/0057788 A1, US 2005/057788 A1, US 20050057788 A1, US 20050057788A1, US 2005057788 A1, US 2005057788A1, US-A1-20050057788, US-A1-2005057788, US2005/0057788A1, US2005/057788A1, US20050057788 A1, US20050057788A1, US2005057788 A1, US2005057788A1|
|Inventores||Joshua Cobb, David Kessler, James Roddy|
|Cesionario original||Eastman Kodak Company|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citas de patentes (11), Clasificaciones (16), Eventos legales (6)|
|Enlaces externos: USPTO, Cesión de USPTO, Espacenet|
This is a continuation-in-part of application Ser. No. 10/662,208, filed Sep. 12, 2003, entitled AUTOSTEREOSCOPIC OPTICAL APPARATUS, by Cobb et al.
This invention generally relates to display apparatus and more particularly relates to an autostereoscopic display apparatus providing a wide field of view, large viewing pupils, and high brightness.
The potential value of autostereoscopic display systems is well appreciated for a broad range of data visualization uses and for a wide range of applications that include entertainment, engineering, medical, government, security, and simulation fields. Autostereoscopic display systems include “immersion” systems, intended to provide a realistic viewing experience for an observer by visually surrounding the observer with a three-dimensional (3-D) image having a very wide field of view. As differentiated from the larger group of stereoscopic displays that include it, the autostereoscopic display is characterized by the absence of any requirement for a wearable item of any type, such as goggles, headgear, or special polarized or filter glasses, for example. That is, an autostereoscopic display attempts to provide “natural” viewing conditions for an observer.
An article entitled “3-D displays: A review of current technologies” by Siegmund Pastoor and Mathias Wopking in Displays 17 (1997) surveys various approaches that have been applied for obtaining autostereoscopic display images for one or more viewers. Among the many techniques described in the Pastoor et al. article are electro-holography, volumetric display, direction-multiplexed, diffraction-based, refraction-based, and reflection-based methods for autostereoscopic presentation. While each of these approaches may have merit in one or more specific applications, these approaches have a number of characteristic shortcomings that constrain usability and overall performance. As a group, these conventional approaches have been adapted for autostereoscopic displays, but allow only a narrow field of view and provide limited brightness and poor contrast. Imaging systems employing time-based or spatial multiplexing require complex image processing algorithms in order to provide left- and right-eye images in the proper sequence or with the necessary spatial separation. Time-based multiplexing introduces the inherent problem of image flicker. Spatial multiplexing generally produces an image having reduced resolution. Combining these multiplexing techniques, as is disclosed in European Patent Application EP 0 764 869 A2 to Ezra et al., may provide an increased number of views, but does not compensate for these inherent drawbacks. A number of multiplexing technologies also require tracking of view eye position and compensation for changes in head position. As a further disadvantage, each of the imaging technologies described in the Pastoor et al. article present the viewer with a real image, rather than with a virtual image.
In an article entitled “An Autostereoscopic Display Providing Comfortable Viewing Conditions and a High Degree of Telepresence” by Klaus Hopf in IEEE Transactions on Circuits and Systems for Video Technology, Vol. 10, No. 3, April, 2000, a teleconferencing system employing a spherical mirror is disclosed, recommended particularly for its value in reducing chromatic aberration. However, the optical system disclosed in this article is subject to field curvature constraints, limiting its field of view. Notably, the system described in the Hopf article provides a virtual image; however, due to substantial field curvature, the total field of view of such a system is limited to less than about 15 degrees. While such a narrow field of view may be acceptable for videoconferencing applications, this level of performance would not be useful for a desktop display system.
Virtual imaging provides an advantageous alternative to real image projection, as is used in the apparatus described in the Pastoor article and in EP 0 764 869 A2. In contrast to conventional projection methods for forming a real image, a virtual image is not formed on a display surface. That is, if a display surface were positioned at the perceived location of a virtual image, no image would be formed on that surface. Virtual image display has a number of inherent advantages, as is outlined in U.S. Pat. No. 5,625,372 (Hildebrand et al.) As one significant advantage for stereoscopic viewing, the size of a virtual image is not limited by the size or location of a display surface. Additionally, the source object for a virtual image may be small; a magnifying glass, as a simple example, provides a virtual image of its object. Thus, it can be seen that, in comparison with prior art systems that project a real image, a more realistic viewing experience can be provided by forming a virtual image that is disposed to appear some distance away. Providing a virtual image also obviates any need to compensate for screen artifacts, as may be necessary when projecting a real image.
It is generally recognized that, in order to minimize vergence/accommodation effects, a 3-D viewing system should display its pair of stereoscopic images, whether real or virtual, at a relatively large distance from the observer. For real images, this means that a large display screen must be employed, preferably placed a good distance from the observer. For virtual images, however, a relatively small curved mirror can be used as is disclosed in U.S. Pat. No. 5,908,300 (Walker et al.). The curved mirror acts as a collimator, forming a virtual image at a relatively large distance from the observer.
From an optical perspective, it can be seen that there would be advantages to autostereoscopic design using pupil imaging. A system designed for pupil imaging must meet a fairly demanding set of requirements, including the following:
It is recognized in the optical arts that each of these requirements, by itself, can be difficult to achieve. An ideal autostereoscopic imaging system must meet the challenge of each of these requirements to provide a more fully satisfactory and realistic viewing experience. Moreover, additional physical constraints presented by the need for a system to have small footprint, and dimensional constraints for interocular separation must be considered, so that separate images directed to each eye can be advantageously spaced and correctly separated for viewing. It is instructive to note that interocular distance constraints limit the ability to achieve larger pupil diameter at a given ultrawide field by simply scaling the projection lens.
Clearly, the value and realistic quality of the viewing experience provided by an autostereoscopic display system using pupil imaging is enhanced by presenting the stereo 3-D image with a wide field of view and large exit pupil. For fully satisfactory 3-D viewing, such a system should provide separate, high-resolution images to right and left eyes. To create a realistic illusion of depth and width of field, the observer should be presented with a virtual image that requires the viewer to focus at some distance.
It is well known that conflict between depth cues associated with vergence and accommodation can adversely impact the viewing experience. Vergence refers to the degree at which the observer's eyes must be crossed in order to fuse the separate images of an object within the field of view. Vergence decreases, then vanishes as viewed objects become more distant. Accommodation refers to the requirement that the eye lens of the observer change shape to maintain retinal focus for the object of interest. It is known that there can be a temporary degradation of a viewer's depth perception when the viewer is exposed for a period of time to mismatched depth cues for vergence and accommodation. It is also known that this negative effect on depth perception can be mitigated when the accommodation cues correspond to distant image position.
There are also other basic optical limitations for immersion systems that must be addressed with any type of optical projection that provides a wide field of view. An important limitation is imposed by the Lagrange invariant. A product of the size of the emissive device and the numerical aperture, the Lagrange invariant determines output brightness and is an important consideration for matching the output of one optical system with the input of another. Any imaging system conforms to the Lagrange invariant, whereby the product of pupil size and semi-field angle is equal to the product of the image size and the numerical aperture. An invariant that applies throughout the optical system, the Lagrange invariant can be a limitation when using, as an image generator, a relatively small spatial light modulator or similar pixel array which operate over a relatively small numerical aperture, since the Lagrange value associated with the device is small. In practical terms, the larger the size of the image source, the easier it is to form an image having a wide field of view and large pupil.
In response to the need for more realistic autostereoscopic display solutions offering a wide field of view, commonly assigned U.S. Pat. No. 6,416,181 (Kessler et al.), incorporated herein by reference and referred to as the '181 patent, discloses an autostereoscopic imaging system using pupil imaging to display collimated left and right virtual images to a viewer. In the '181 disclosure, a curved mirror is employed in combination with an imaging source, a curved diffusive surface, a ball lens assembly, and a beamsplitter, for providing the virtual image for left and right viewing pupils. Overall, the monocentric optical apparatus of the '181 disclosure provides autostereoscopic imaging with large viewing pupils, a very wide field of view, and minimal aberration.
While the autostereoscopic system of the '181 disclosure provides a high-performance immersive display, there is still room for improved embodiments. For example, while the '181 system provides a large viewing pupil, there would be advantages in even further increases in pupil size. At the same time, however, some amount of correction may be needed, since eye movement within a larger viewing pupil can cause some amount of “swim” effect, in which pixels appear to shift position as the eye moves within the viewing pupil. In addition, as is well known in the imaging arts, some amount of spherical aberration is generally inherent in any optical system that employs a curved mirror for image collimation.
Generating its source image on a small spatial light modulator device, the '181 system overcomes inherent Lagrange invariant conditions by forming an intermediate curved image for projection on a curved diffusive surface. Use of the diffuser with the '181 apparatus is necessary because the image-forming device, typically a reflective LCD or other spatial light modulator, is a relatively small emissive device, measuring typically no more than about 1 inch square. At the same time, however, the use of a diffusive surface effectively reduces overall brightness, introduces some level of graininess to the image, and limits the achievable contrast.
There are other minor drawbacks to autostereoscopic displays that use the design approach of the '181 disclosure. For example, slight “keystoning” aberrations are detectable in a system using the '181 design approach, due to the use of a single curved mirror; moreover, this effect can be compounded by right and left images exhibiting keystoning in opposite orientations with respect to the final image. While spherical lenses such as the ball lenses of the '181 disclosure have overall advantages for maximizing field of view and for minimizing some types of imaging aberration, there are some inherent disadvantages to the use of highly spherical optics, requiring compensation for chromatic effects for example. Curved images can be produced in a number of ways using more conventional optics, which, while not providing some of the advantages of ball lenses, might provide less expensive options for forming intermediate images in an autostereoscopic system.
Thus, it can be seen that there is a need for an improved autostereoscopic imaging apparatus that provides improved brightness, enhanced viewing pupil dimensions, reduced image aberrations, and higher resolution.
It is an object of the present invention to provide an autostereoscopic display device having improved viewing pupil size, brightness, and resolution, with reduced optical aberrations. With this object in mind, the present invention provides an autostereoscopic optical apparatus for viewing a stereoscopic virtual image comprising a left image to be viewed by an observer at a left viewing pupil and a right image to be viewed by the observer at a right viewing pupil, the apparatus comprising:
It is a feature of the present invention that it provides a completely specular autostereoscopic imaging display apparatus, without the need for curved diffusive surfaces. This allows image brightness to be optimized and allows improved contrast over earlier design solutions.
It is an advantage of the present invention that it uses a larger imaging display than previous solutions, relaxing Lagrange invariant constraints on available luminance.
It is a further advantage of the present invention that it provides an improved viewing pupil size when compared with earlier solutions.
It is a further advantage of the present invention that it provides a compact autostereoscopic display system providing a virtual image.
These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the present invention, it is believed that the invention will be better understood from the following description when taken in conjunction with the accompanying drawings, wherein:
The present description is directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
For the purposes of the present application, a curved image is an image for which best focus lies in a shape that is substantially spherical. The optical path is simplest when curved images are themselves spherically curved. By forming and using curved intermediate images, for example, rather than flat, planar images, the optics of the present invention take advantage of various symmetrical arrangements and relationships that are favorable for pupil imaging using virtual images, as is described in this section. Curved intermediate images can be formed using fully spherical lenses or using highly spherical lens segments as well as using more conventional image projection optics.
Similarly, for reasons that become apparent upon reading this detailed description, a curved mirror, as described in this application, is preferably spherical, having a single center of curvature.
In the prior art autostereoscopic projection apparatus 10 described in U.S. Pat. No. 6,416,181 and as shown in
Forming a Curved Intermediate Image
To eliminate the need for diffusing element 32 as was required using the approach of the '181 disclosure, the present invention provides an alternate method for forming a curved intermediate image using a specular optical system. Referring to
Using the overall arrangement of
As described with reference to the Lagrange invariant in the background section above, brightness in an optical system is a product of the emissive area and the solid angle. By allowing image source 94 to have a large emissive area, the method of the present invention allows substantial brightness levels while, at the same time, allowing light angles to be relatively small. Small light angles are advantageous for maximizing image contrast and minimizing color shifting and other related image aberrations.
Separate image sources 94 are used for left and right eyes, respectively. Ideally, image source 94 for left image generation system 70 l and image source 94 for right image generation system 70 r are well-matched for image size and color. CRT displays, however, may be at a disadvantage if used as image sources 94. Color differences between CRTs may degrade stereoscopic imaging performance. Additionally, as a result of display ageing, CRT image areas may vary dimensionally, effectively causing left/right pixel misalignment. In contrast to CRT displays, LCD displays offer dimensional stability with stable pixel locations, ease of alignment, and simpler mounting.
Ideal Ball Lens Operation
In a preferred embodiment, meniscus lenses 42 and 44 are selected to reduce image aberration and to optimize image quality for the projected image projected. It must be noted that ball lens assembly 30 could comprise any number of arrangements of support lenses surrounding central spherical lens 46. Surfaces of these support lenses, however many are employed, would share a common center of curvature with Cball, the center of curvature of central spherical lens 46. Moreover, the refractive materials used for lens components of ball lens assembly 30 could be varied, within the scope of the present invention. For example, in addition to standard glass lenses, central spherical lens 46 could comprise a plastic, an oil or other liquid substance, or any other refractive material chosen for the requirements of the application. Meniscus lenses 42 and 44, and any other additional support lenses in ball lens assembly 30, could be made of glass, plastic, enclosed liquids, or other suitable refractive materials, all within the scope of the present invention. In its simplest embodiment, ball lens assembly 30 could simply comprise a single spherical lens 46, without additional supporting refractive components.
In ideal operation, curved image 50 shares the same center of curvature Cball as ball lens assembly 30. When arranged in this fashion, light from curved image 50 is imaged with low levels of aberration, as is represented in the light rays of
The inherent advantages of a ball lens can be exploited using a modified design, such as using a hemisphere combined with a folding mirror, as is shown in the cross-sectional ray diagram of
For the purposes of this disclosure, the term “ball lens segment” comprises both fully spherical ball lens assembly 30, as shown in
First Embodiment of Image Generation System
It must be emphasized that curved mirror 92 serves as an image generation component that serves image generation system 100 for forming intermediate curved image 110, as shown in
Second Embodiment of Image Generation System
Common to telescopic, microscopic, and similar “tube” optical systems, field lenses are widely employed in the optical arts, placed at the image location of a first lens, where the image formed at that image location becomes the object of a second lens. In this way, field lens 112 improves the overall brightness and field of view of the optical system. Background information on field lens use and theory can be found, for example, in Modern Optical Engineering, the Design of Optical Systems, by Warren J. Smith, McGraw-Hill, N.Y., pp. 212-213 and in other textbooks known in the optics field.
In one embodiment, surface SI of field lens 112 is concentric with mirror center of curvature Cs and therefore does not deviate chief rays towards Cball. In such an embodiment, surface S2, not concentric with mirror center of curvature Cs, operates to bend chief rays toward Cball. Alternately, surface S2 could be concentric with mirror center of curvature Cs, surface S1 performing the operation of bending chief rays toward Cball. Embodiments with either surface S1 or S2 concentric with Cs or Cball represent the most straightforward approaches to the design of field lens 112; other designs could have neither surface S1 nor S2 concentric with mirror center of curvature Cs or Cball, however, these designs could be more complex.
As was noted above with reference to
Providing Advantages of Telecentric Light
Still referring to
Considerations for Beamsplitter 102
As is shown in
Embodiment for Stereoscopic Viewing
Alternate Embodiment for Stereoscopic Viewing, Using Left and Right Mirrors
The embodiment of
Designs using left and right curved mirrors 24 l and 24 r, such as shown in
The same general principles used for forming a virtual image with the prior art configuration of
Alternate Embodiment Using Broad Range of Image Generation Systems 100
While ball lens segments 1301 and 130r shown in
The ideal spatial relationships for pupil placement provided by left and right image generation systems 100 l and 100 r, left and right curved mirrors 24 l and 24 r, and beamsplitter 16, as represented in
With this spatial arrangement of optical components, a real image of the exit pupil of left image generation system 100 l and a virtual image of left curved image 110 l are formed at left viewing pupil 14 l. Correspondingly, a real image of the exit pupil of right image generation system 100 r and a virtual image of right curved image 110 r are formed at right viewing pupil 14 r.
It must be emphasized that the relationships listed in (i)-(vii) above are ideal spatial relationships; optimal pupil imaging is obtained when the requirements of (i)-(vii) are satisfied. In practice, some amount of tolerance error is acceptable, provided that viewing pupils 14 l and 14 r are formed at suitable positions for the observer.
Correcting for Spherical Aberration
As was described with reference to
However, as a result of residual spherical aberration due to higher order aberrations, the size of viewing pupils 14 l, 14 r is still somewhat limited. Due to this residual aberration, movement of the eyes of observer 12 within viewing pupils 14 l, 14 r can cause some amount of image “swim”.
Spherical aberration is a recognized problem in optical systems that employ a concave mirror, such as astronomical telescopes for example. To compensate for this type of aberration, the Schmidt optical system, as described in Modern Optical Engineering, the Design of Optical Systems, by Warren J. Smith (cited above), pp. 393-394, employs an aspheric corrector plate. In the Schmidt system, a thin, aspheric corrector plate is positioned at the center of curvature of the curved mirror.
Comparing aberration curves 150 in
Placing aspheric corrector element 140 near the center of curvature of curved mirror 92 effectively images aspheric corrector element 140 into the pupil of ball lens segment 130; that is, corrector element 104 and the pupil of ball lens segment 130 are optically conjugate. This allows aspheric corrector element 140 to provide effective correction across the full field of view. As a result, pupil size can be increased to 50 mm, with minimal aberration, as shown in aberration curve 150 of
In an alternate embodiment, aspheric corrector element 140 could be a compound lens that corrects chromatic as well as spherical aberration. Such an arrangement would require more complexity than the design of a single-component aspheric corrector element 140, but would simplify the design requirements of ball lens segment 130. For example, where a compound lens is used for aspheric corrector element 140, it may be possible to use only a single element as ball lens segment 130.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention as described above, and as noted in the appended claims, by a person of ordinary skill in the art without departing from the scope of the invention. For example, field lens 112 can be more complex than is shown here, having different curvature, composition, or coatings. Image source 94, a transmissive LCD device in one embodiment, can be any of a number of types of image source, including film, CRT, LCD, and digital imaging devices. Image source 94 could be an emissive array, such as an organic light emitting diode (OLED) array, for example. In order to take advantage of the benefits of monocentric imaging, curved mirror 92 will be substantially spherical in most embodiments; however, some slight shape modifications might be used, with the corresponding changes to supporting optics and to optional aspheric corrector element 140. Either ball lens assembly 30 or hemispheric lens assembly 60 could serve as the ball lens segment for either or both left and right image generation systems. Separate left and right curved mirrors 24 could be used to improve the image quality of each viewing pupil 14 l, 14 r, reducing undesirable “keystoning” effects that can result from off off-axis positioning of left and right ball lens segments 130 l, 130 r. Curved mirror 24 could be fabricated as a highly reflective surface using a number of different materials.
Thus, what is provided is an apparatus and method for autostereoscopic image display having improved brightness, pupil size, and resolution.
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|Clasificación de EE.UU.||359/7, 348/E13.027, 348/E13.058|
|Clasificación internacional||H04N13/00, G02B27/22, G02B17/08|
|Clasificación cooperativa||H04N13/0459, H04N13/0402, G02B17/08, G02B27/225, G02B17/0804|
|Clasificación europea||H04N13/04P, H04N13/04A, G02B17/08A, G02B17/08, G02B27/22S3|
|19 Abr 2004||AS||Assignment|
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