Systems for capturing images through a display

[0001] Embodiments of the current invention relate to remote collaboration systems.

[0002] Some of the most productive interactions in the workplace occur when a small group of people get together at a blackboard or a whiteboard and actively participate in presenting and discussing ideas. However it is very hard to support this style of interaction when one or more participants are at a different location, a situation that occurs more and more frequently as organizations become more geographically distributed. To date, conventional video-conferencing systems are not well suited to this scenario. Effective collaboration relies on the ability for the parties to see each other and the shared collaboration surface, and to see where the others are looking and/or gesturing. Conventional video-conferencing systems can use multi-user screen-sharing applications to provide a shared workspace, but there is a disconnect from the images of the remote participants and the cursors moving over the shared application.

[0003] FIGS. 1-3 show schematic representations of systems configured to project images without interfering with images captured by a camera. FIG. 1 shows a communication medium with a half-silvered mirror 102, a camera 104 located above the mirror 102, and a projector 106. The mirror 102 and the projector 106 are positioned so that an image of a person or object located at a remote site is projected by the projector 106 onto the rear surface of the half-silvered mirror 102 and is visible to a viewer 108. The camera 104 captures an image of the viewer 108 via that viewer's reflection in the mirror 102 and transmits the image to another person. The configuration of mirror 102, projector 106, and camera 104 enable the viewer 108 to have a virtual face-to-face interaction with the other person. However, close interaction between the viewer 108 and the other person can be disconcerting because the tilted screen makes for unnatural views of the remote user. FIG. 2 shows a communication medium with a switchable diffusing screen 202, a camera 204, and a projector 206. The screen 202 can be composed of a material that can be cycled rapidly between diffusive and transparent states. The state of the screen 202, projector 206, and camera 204 can be synchronized so that the projector 206 projects images when the screen is diffusive and the camera 204 captures images when the screen in transparent. However, it is difficult to design a screen that can switch fast enough to avoid flicker, and the need to synchronize these fast switching components adds to the complexity of the system and limits the projected and captured light levels. FIG. 3 shows a top view of a communication medium with two cameras 302 and 304 on each side of a display 306. Images of a viewer 308, for example, are captured by the cameras 302 and 304 and processed to create a single image of the viewer 308 which appears to be captured by a single virtual camera 310 for viewing by another person at a different location. However, an image captured in this manner typically suffers from processing artifacts, especially when the captured views are at a very different angle from the intended virtual view, as would be the case with a user close to a large screen. This system also fails to capture hand gestures near, or drawing on, the screen surface.

[0004] It is desirable to have visual-collaborative systems that project images without interfering with and diminishing the quality of the images simultaneously captured by a camera.

[0016] Embodiments of the present invention are directed to visual-collaborative systems enabling geographically distributed groups to engage in face-to-face, interactive collaborative video conferences. The systems include a rear projection display screen that enables a camera to captures images from a direction originating from within the boundaries of the display screen and send the images to a remote site. In addition, the display screen can be used to simultaneously display images from the remote site.

[0017] FIG. 4 shows a schematic representation of a visual-collaborative system 400 configured in accordance with embodiments of the present invention. The system 400 comprises a display screen 402, a camera 404, and a projector 406 and includes a filter A disposed between the camera lens 408 and the screen 402 and a filter B disposed between the projector lens 412 and the screen 402. The camera lens 408 and projector lens 412 are positioned to face the same first surface 410 of the display screen 402. The screen 402 is a rear projection display screen comprising a screen material that diffuses light striking the first surface 410 within a first range of angles. The projector 406 is positioned to project images onto the first surface 410 within the first range of angles. A viewer 414 facing the outer second surface 416 of the screen 402 sees the images projected onto the screen 402 from the projector 406. The screen 402 is also configured to transmit light scattered from objects facing the second surface 416. In other words, the camera lens 408 is positioned to face the first surface 410 so that light scattered off of objects facing the second surface 416 pass through the display screen and is captured as images of the objects by the camera 404.

[0018] In certain embodiments, the display screen 402 comprises a relatively low concentration of diffusing particles embedded within a transparent screen medium. The low concentration of diffusing particles allows a camera 404 to capture an image through the screen (providing the subject is well lit), while diffusing enough of the light from the projector 406 to form an image on the screen. In other embodiments, the display screen 402 can be a holographic film that has been configured to accept light from the projector 406 within a first range of angles and transmit light that is visible to the viewer 414 within a different range of viewing angles. The holographic film is otherwise transparent. In both embodiments, light projected onto the first surface 410 within the first range of angles can be observed by viewing the second surface 416, but light striking the second surface 416 is transmitted through the screen 402 to the camera. However, in both embodiments the camera 404 also captures light from the projector 406 diffused or scattered off the first surface 410.

[0019] In order to prevent ambient light from striking the first surface 410 of the screen 402 and reducing the contrast of the projected and captured images, the system 400 may also include a housing 418 enclosing the camera 404 and projector 406. The housing 418 is configured with an opening enclosing the boundaries of the screen 402 and is configured so that light can only enter and exit the housing 418 through the screen 402.

[0020] As shown in FIG. 4, filters A and B are positioned so that light output from the projector 406 passes through filter B before striking the first surface 410 and light captured by the camera 404 passes through filter A. The filters A and B are configured to prevent light produced by the projector 406 and scattered or diffused from the screen 402 from interfering with light transmitted through the screen 402 and captured by the camera 404. In particular, filter B can be configured to transmit a first set of wavelengths ranges that when combined create the visual sensation of a much broader range of colors in projecting images on the display screen 402, and filter A can be configured to transmit a second set of wavelength ranges that are different from the first set of wavelength ranges. The second set of wavelength ranges can also be used to create the visual sensation of a much broader range of colors. In other words, filter A is configured and positioned to block the wavelength ranges that are used to create images on the display screen 402 from entering the camera lens 408. Even though the wavelength ranges used to produce images viewed by the viewer 414 are different from the wavelengths of light used to capture images by the camera 404, the projector 406 can still use the colors transmitted through filter B to project full color images and light transmitted through filter A and captured by the camera 404 can still be used to record and send full color images. It is the component wavelengths of the light used to project and capture the full color images that are prevented from interfering.

[0021] FIG. 5 shows exemplary plots 502 and 504 of wavelength ranges over which filters A and B, respectively, can be configured to transmit light in accordance with embodiments of the present invention. Horizontal line 506 represents the range of wavelengths comprising the visual spectrum. Vertical axes 508 and 510 represents intensities of light transmitted through filters A and B, respectively. As shown in FIG. 5, the red, green and blue portions of the spectrum are each split into two halves with curves 511-513 representing relatively shorter wavelength rangers of the red, green, and blue portions of visible spectrum transmitted through filter A and curves 515-517 representing relatively longer wavelength ranges of the red, green, and blue portions of visible spectrum transmitted through filter B. As shown in FIG. 5, filters A and B do not transmit the same wavelength ranges of the red, green, and blue portions of the visible spectrum. In particular, filter A is configured to transmit shorter wavelength ranges of the red, green, and blue portions of the visible spectrum, and substantially block the longer wavelength ranges of the red, green, and blue portions of the spectrum. In contrast, filter B is configured to transmit the longer wavelength ranges of the red, green, and blue portions of the visible spectrum and substantially block the short wavelength ranges of the red, green, and blue portions of the visible spectrum. Both sets of red, green, and blue wavelengths can be treated as primary colors that can be combined to produce a full range of colors in projecting images on the display screen 402 and capturing images through the display screen 402. Thus, the combination of filters A and B effectively block the light used to project color images on the display screen 402 form being back scattered and interfering with the color images captured by the camera 404.

[0022] In other embodiments, operation of the filters A and B can be reversed. In other words, filter A can transmit the longer wavelength ranges of the red, green, and blue portions of the visual spectrum while filter B transmits the shorter wavelength ranges of the red, green, and blue portions of the visible spectrum.

[0023] FIG. 6 shows a visual-collaborative system 600 configured in accordance with embodiments of the present invention. The system 600 is nearly identical to the system 400 except filter B and the projector 406 are replaced with a single projector 602 configured to project color images using wavelength ranges that are blocked by filter A. For example, the projector 602 can be a conventional projector using three microdisplays and color splitting optics that send red, green and blue light from the projector bulb to the corresponding display. The microdisplays can be well-known liquid crystal display (“LCD”), liquid crystal on silicon (“LCoS”), or digital-micromirror device (“DMD”) technologies. In such a system, the functionality of filter B can be incorporated into the color splitting optics within the projector 602. Filter A is configured to transmit wavelength ranges other than the wavelengths reflected by the color splitter, as described above with reference to FIG. 5. For example, the internal color splitter can be a series of dichroic mirrors that each reflects one of the primary colors to a separate microdisplay, while passing other wavelengths of light. Each reflected color is modulated by the corresponding microdisplay, and the colors are recombined to produce images that are projected onto the first surface 410. Each microdisplay provides pixelized control of the intensity of one color. The colors not reflected by the color splitter are discarded. For example, in order to produce a red object, the microdisplays corresponding to projecting green and blue light are operated to block green and blue light from passing through the projector 602 lens.

[0024] In other embodiments, the lamp producing white light and the internal color splitter of the projector 602 can be replaced by separate lasers, each laser generating a narrow wavelength range of light that when combined with appropriate intensities produce a full range of colors. For example, the lamp and internal color splitter can be replaced by three lasers, each laser generating one of the three primary colors, red, green, and blue. Each color produced by a different laser passes through a corresponding LCD or is reflected off of a corresponding LCoS and the colors are recombined within the projector 602 to project full color images onto the first surface 410. Note that the use of a relatively narrow set of wavelengths at the projector allows the complementary set of wavelengths passed by filter A to be relatively broader, allowing more light into the captured image.

[0025] In other embodiments the function of filter A could be incorporated into the camera optics. For example the color filter mosaic that forms part of a camera's image sensor could be selected to pass only selected wavelengths.

[0026] FIG. 7A shows a visual-collaborative system 700 configured in accordance with embodiments of the present invention. The system 700 is nearly identical to the system 400 except filter B and the projector 406 are replaced with a sequential color projector 702. An example of such a projector is a “DMD projector” that includes a single digital micromirror device and a color wheel filter B comprising red, green, and blue segments. The color wheel filter B spins between a lamp and the DMD, sequentially adding red, green, and blue light to the image displayed by the projector 702. Also, filter A is replaced by a second color wheel filter A which contains filters that transmit complementary colors to those of filter B. For example, as shown in FIG. 7B, the color wheel filter A can use cyan, yellow, and magenta transparent color panels to sequentially block the color being projected through the color wheel filter A. Color wheel filters A and B can be synchronized so that when the color wheel filter A transmits one color the color wheel filter B transmits a complementary color. For example, when the red panel of the color wheel filter B passes between the lamp and the DMD of the projector 702, the color red is projected onto the screen 402 while the cyan panel of the color wheel filter A covers the lens 408 enabling the camera 404 to capture only green and blue light and ignore the projected red light.

[0027] FIG. 7C shows exemplary plots 704-706 of wavelength ranges over which color wheel filters A and B, respectively, can be operated to transmit light in accordance with embodiments of the present invention. Plot 704 shows that at a first time T₁, filter B passes a different range of wavelengths than filter A. Plot 705 shows that at a later second time T₂, filter B passes a range of wavelengths sandwiched between two different wavelength ranges passed by filter A. Plot 706 shows that at a later time T₃, filter B again passes a different range of wavelengths than filter A. In other words, plots 704-706 reveal that at any given time, filters A and B are operated to pass different wavelength ranges. Plots 704-706 also reveal that filters A and B can be operated to pass wavelengths over the same wavelength ranges, but not at the same time.

[0028] In still other embodiments, the housing 418 can include fully reflective mirrors that reflect projected images onto a display screen within the range of angles for which the screen is diffusive. FIG. 8 shows a visual-collaborative system 800 configured in accordance with embodiments of the present invention. The system 800 is nearly identical to the system 400 except mirrors 802 and 804 are included to reflect images produced by the projector 406 onto a display screen 806 within a range of angle for which the screen 806 is diffusive.

[0029] The visual-collaborative systems described above with reference to FIGS. 4-8 can be used in interactive video conferencing. The camera 404 and projector 406 can be positioned so that the display screen 402 acts as a window to a remote site. This can be accomplished by positioning the camera 404 at approximately eye level to the viewer 414 facing the second surface 416 and at approximately the same distance the viewer 414 would feel comfortable standing away from the screen. FIG. 9 shows the camera 404 positioned at approximately eye level to the viewer 414 in accordance with embodiments of the present invention. As a result, the viewer 414 appears face-to-face with a second viewer represented by dashed-line figure 902 located at a remote site. The second viewer 902 and the viewer 414 can engage in an interactive, virtual, face-to-face conversation with the display screen 402 serving as a window through which the second viewer and the viewer 414 can clearly see each other.

[0030] FIG. 10A shows an isometric view of an interactive video conference between the viewer 414 and a projected image of a second viewer 1002 located at a remote site in accordance with embodiments of the present invention. The second viewer 902 is projected on the display screen 402 by the projector (not shown), as described above with reference to FIGS. 4-8. As shown in FIG. 10A, a visual-collaborative system configured in accordance with embodiments of the present invention enables the second viewer 1002 to visually display and present an object 1004 for the viewer 414 from the remote site.

[0031] In other embodiments, the second surface 416 of the display screen 402 can be configured or coated with a transparent and erasable material enabling the viewer 414 to write and erase on the second surface 416 during an interactive video conference. In other embodiments a transparent, electronic, interactive surface (e.g., a touch screen) may be disposed on the second surface 416 of display screen 402, enabling the viewer 414 to draw, or otherwise interact with computer generated imagery overlaid on the video image of the remote user 1002 projected on the screen. In still other embodiments, other optical or ultrasound based tracking techniques may be used to track the viewer's 414 gestures or a pointer in order to interact with the computer generated imagery. In all these embodiments, the video images of the viewers 414 and 1002 are relayed between the local and remote sites and are mirrored horizontally so that the remote viewer 1002's writing appears correctly oriented for the viewer 414. FIG. 10B shows an isometric view of a video conference between the viewer 414 and the second viewer 1002 with the second surface 416 configured as a transparent writing surface in accordance with embodiments of the present invention. As shown in FIG. 10B, the viewer 414 has drawn a graph 1006 on the second surface 416. The camera 404 (not shown) located behind the screen 402 captures an image of the viewer 402 and the graph 1006, which can be observed by the second viewer 1002. The display screen 402 also exhibits a pie chart 1008 drawn by the second viewer 702 on a similar transparent writing surface at the remote site. The projector 406 (not shown) displays the second viewer 1002 and the chart 1008 for observation by the viewer 414.

[0032] FIG. 11 shows a control-flow diagram for a method for video collaborative interaction method in accordance with embodiments of the present invention. Steps 1101-1104 do not have to be completed in any particular order and can be performed at the same time. In step 1101, images captured at a remote site are projected on a rear projection display screen, as described above with reference to FIGS. 4-7. In step 1102, the projected images are filtered, as described above with reference to FIGS. 4-7. In step 1103, the wavelengths of light reflected and emitted from objects pass through the display screen and are filtered so that the wavelengths of light used to project images on the display screen are different from the wavelengths of light passing through the screen, as described above with reference to FIG. 5. In step 1104, the wavelengths of light passing through the screen are captured, as described above with reference to FIGS. 4-7.

[0033] Embodiments of the present invention have been demonstrated using a dnp Holo Screen™ from DNP, a Canon Vixia HF 100 HD camcorder, and a Mitsubishi HC600HD projector. Images were projected onto the holographic screen at an angle of approximately 35° from a distance of approximately 8 ft. The optical path length was folded using a visual-collaborative system similar to the system 800, described above with reference to FIG. 8. The camera was positioned to a have a view of the back of the holographic screen from an average eye height and a distance of approximately 2 ft, which is roughly the distance a viewer stands from the screen.

[0034] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. The foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive of or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations are possible in view of the above teachings. The embodiments are shown and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents: