Abstract:
A marking carried by a physical object and discernible by an infrared (IR) sensor is at least partially concealed from the human eye. The marking is covered with a coating that is at least partially opaque in the visible spectrum and at least partially transparent in the IR spectrum (or other non-visible spectrum). The marking is thus not apparent to a human eye or to visible light sensors, while remaining discernible in the IR spectrum. Using the present invention to prevent a user from detecting the marking adds intrigue to the detection of the object, since the workings of the IR sensor that enable the sensor to identify the marking are not evident to a user. The present invention is also beneficially employed in games where it is desirable that an opponent be unable to see a marking that is detectable by the IR sensor.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally pertains to a computing system having a detector operable to recognize objects in proximity to an interactive display surface, and more specifically, to a computing system having a detector operable to detect markings that are not apparent to an unaided human eye.  
       BACKGROUND OF THE INVENTION  
       [0002]     Because of the widespread popularity of computers, most people have become comfortable with conventional computer input devices such as keyboards and pointing devices. The keystrokes and movements of mice, trackballs, and joysticks are sufficiently intuitive to provide satisfactory interfaces for most computer-related tasks. Nonetheless, as computers become increasingly more indispensable, limits of a human-machine interface that depends upon pressing buttons and dragging a pointer with a mouse or other device tends to restrict how quickly and naturally computers can be used.  
         [0003]     In seeking to further enhance the human-machine interface, ever-improving hardware capabilities have made possible systems that avoid the need to enter text with a keyboard. Personal digital assistants and tablet PCs can now recognize human handwriting. Speech recognition software enables users to operate computers and enter text by speaking into a microphone. Such systems can thus provide a more efficient and satisfying experience for users who prefer not to type on a keyboard or are less proficient in doing so.  
         [0004]     As computers become more ubiquitous throughout our environment, the desire to make computers and their interfaces even more user-friendly continues to promote development in this area. For example, the MIT Media Lab, as reported by Brygg Ullmer and Hiroshi Ishii in “The metaDESK: Models and Prototypes for Tangible User Interfaces,”  Proceedings of UIST 10/1997:14-17,” has developed another form of “keyboardless” human-machine interface. The metaDESK includes a generally planar graphical surface that not only displays computing system text and graphic output, but also receives user input by responding to an object placed against the graphical surface. The combined object responsive and display capability of the graphical surface of the metaDESK is facilitated using infrared (IR) lamps, an IR camera, a video camera, a video projector, and mirrors disposed beneath the surface of the metaDESK. The mirrors reflect the graphical image projected by the projector onto the underside of the graphical display surface to provide images that are visible to a user from above the graphical display surface. The IR camera can detect IR reflections from the undersurface of an object placed on the graphical surface.  
         [0005]     Others have been developing similar keyboardless interfaces. For example, papers published by Jun Rekimoto of the Sony Computer Science Laboratory, Inc. and associates describe a “HoloWall” and a “HoloTable” that display images on a surface and use IR light to detect objects positioned adjacent to the surface.  
         [0006]     By detecting a specially formed object or by detecting IR-reflected light from an object disposed on a graphical display surface, the metaDESK can respond to the contemporaneous placement and movement of the object on the display surface to carry out a predefined function, such as displaying and moving a map of the MIT campus.  
         [0007]     Thus, computing systems such as the HoloWall and metaDESK may provide a more natural degree of human-machine interaction by providing the means for a computer to respond to specific objects. However, while such systems enable a person to interact with a computer by engaging and moving a physical object instead of a keyboard or mouse, the quality of the experience can be undermined somewhat if the object bears a bar code or other visible code detectable by the detectors used in those systems that is also readily apparent to the user. Further, in the case of a game where it is desirable to keep secret a value or identity of a game piece or playing card, a visible code might give away the value or identity to a savvy, observant competitor.  
         [0008]     In the latter case, the presence of a visible IR code may be masked with a filter that is transparent to IR light but opaque to visible light. With such a filter, the IR detectors might still detect the code on the physical object, but the users would not be able to see it. Thus, hiding the codes with filters can restore some of the mystique of the computing system that appears to recognize each object that is placed on an interactive surface, without any apparent way being provided to enable such recognition.  
         [0009]     Unfortunately, the use of filters does not necessarily lend itself to every desired application. Attaching thick filters to surfaces of objects may be just as apparent, if not more conspicuous, than allowing the codes to remain visible. Further, attaching filters to thin objects may not be practical. For example, if a number of cards are to be encoded for use with such a system, applying filters might make the cards too large or clumsy to handle, to be convenient. Ultimately, it would be desirable to be able to encode objects discreetly, without making the markings visible or using conspicuous filters.  
       SUMMARY OF THE INVENTION  
       [0010]     One of the advantages of the present invention is that it provides a method for concealing an IR-detectable marking from an unaided human eye. An IR sensor may be capable of detecting markings that are visible in the IR, non-visible spectrum, and the visible spectrum. For various reasons, it may be desirable for the marking to be discernible to an IR sensor, but not by the human eye. Using an object that has a marking not apparent to the user adds to the mystique when the IR sensor is able to discern the marking and recognize an object. As another example, the physical object may be a game piece, so that it would be desirable that the marking be discernible by the IR sensor, but not by an opponent, to prevent an identity or value of the game piece from being recognized by the opponent upon seeing the marking.  
         [0011]     Although it is known to fit objects with lenses or filters that might limit the ability to identify a marking in a particular spectrum, the thickness of such lenses or filters would likely add undesirable mass, bulk, or thickness to an object. Thus, for example, if the objects that carry the markings are generally two-dimensional objects, such as tokens, chips, pucks, tiles, or playing cards, attaching a filter to the object to cover the marking may cause the object to be unwieldy. By contrast, embodiments of the present invention use a thin coating applied to the object that does not add significant bulk and does not make the object clumsy to handle.  
         [0012]     One aspect of the present invention is thus directed to a method for concealing a marking discernible by an IR sensor. (While the present invention is clearly usable with markings that are detected by sensors responsive to other non-visible portions of the spectrum, such as the ultraviolet waveband, an initial embodiment is directed to an application that employs an IR sensor.) A portion of an object bearing the marking is identified. A fluid coating having the properties of at least partial opacity to light in the visible spectrum and at least partial transparency to light in the IR spectrum is chosen. The fluid coating is then applied over the marking such that the marking remains discernible in the IR spectrum while becoming at least partially invisible in the visible spectrum.  
         [0013]     In accordance with one embodiment of the present invention, the object includes a game piece having at least one surface bearing content that an opponent should not be able to see during at least a portion of a game in which the game piece is used. The game piece may include, for example, a playing card, a chip, a puck, a tile, or a token.  
         [0014]     The marking may include at least one coding scheme, such as a bar code, a matrix code, a radial code, or a gray scale code, or can be an identifiable differentiable shape. The fluid coating may include at least one of a paint, a lacquer, a varnish, or another fluid coating. For example, the fluid coating may include Liquitex® Acrylic Artistic Color acrylic paint in a Naphthol Crimson color. Alternatively, a plurality of fluid coatings may be applied such that the combination of fluid coatings disposed over the markings enable the markings to remain identifiable in the IR spectrum, while becoming largely invisible in the visible spectrum. For example, the fluid coatings may include Design Master™ Color Tool Spray Paints in the colors Deep Blue #743 and Cranberry #713. The fluid coating can be applied by brushing, spraying, dipping, pouring, or electrostatic deposition.  
         [0015]     An embodiment of the present invention may further comprise choosing a thin substrate that is at least partially transparent in the visible and IR spectra. The fluid coating is applied to the thin substrate, and the thin substrate is attached to the object, over the marking. Thus, the fluid coating may be applied to a sheet of the thin substrate that is larger than the marking on the physical object. A section of the substrate is then cut from the substrate and applied over the marking.  
         [0016]     The fluid coating possesses the properties of at least partial opacity to light in the visible spectrum and at least partial transparency to light in the IR spectrum when the fluid coating is dried and/or cured.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0017]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0018]      FIG. 1  is a functional block diagram of a generally conventional computing device or personal computer (PC) that is suitable for use with an interactive display surface in practicing the present invention;  
         [0019]      FIG. 2  is a cross-sectional view illustrating internal components of an interactive display surface in the form of an interactive table that includes an integral PC;  
         [0020]      FIG. 3  is an isometric view of an embodiment in which the interactive table is connected to an external PC;  
         [0021]      FIGS. 4A-4C  illustrate exemplary optical codes that may be applied to objects so that the objects are detectable by an IR vision system;  
         [0022]      FIG. 5A  illustrates an enlarged cross-sectional view of art encoded item with the marking not concealed and thus, visibly apparent to a human observer;  
         [0023]      FIG. 5B  illustrates an enlarged cross-sectional view of an encoded item with the marking concealed with a coating according to an embodiment of the present invention so that the code is not visibly apparent to a human observer;  
         [0024]      FIG. 6  is a flow diagram illustrating the logical steps for masking IR detectable codes in the visible spectrum according to an embodiment of the present invention; and  
         [0025]      FIGS. 7A-7G ,  8 A- 8 B, and  9  illustrate examples of applications for which visible light-blocking coatings according to embodiments of the present invention enhance the application by thinly covering IR-discernible markings to enable an IR vision system to detect optical codes while preventing human observers from viewing the markings. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0000]     Exemplary Computing System for Implementing Present Invention  
         [0026]     With reference to  FIG. 1 , an exemplary system suitable for making use of embodiments of the present invention is shown. It will be appreciated, however, that visual concealment of IR-discernible markings have uses in a range of environments not limited to the system of  FIG. 1 . The system of  FIG. 1  includes a general purpose computing device in the form of a conventional PC  20 , provided with a processing unit  21 , a system memory  22 , and a system bus  23 . The system bus couples various system components including the system memory to processing unit  21  and may be any of several types of bus strictures, including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. The system memory includes read only memory (ROM)  24  and random access memory (RAM)  25 . A basic input/output system  26  (BIOS), containing the basic routines that help to transfer information between elements within the PC  20 , such as during start up, is stored in ROM  24 . PC  20  further includes a hard disk drive  27  for reading from and writing to a hard disk (not shown), a magnetic disk drive  28  for reading from or writing to a removable magnetic disk  29 , and an optical disk drive  30  for reading from or writing to a removable optical disk  31 , such as a compact disk-read only memory (CD-ROM) or other optical media. Hard disk drive  27 , magnetic disk drive  28 , and optical disk drive  30  are connected to system bus  23  by a hard disk drive interface  32 , a magnetic disk drive interface  33 , and an optical disk drive interface  34 , respectively. The drives and their associated computer readable media provide nonvolatile storage of computer readable machine instructions, data structures, program modules, and other data for PC  20 . Although the exemplary environment described herein employs a hard disk, removable magnetic disk  29 , and removable optical disk  31 , it will be appreciated by those skilled in the art that other types of computer readable media, which can store data and machine instructions that are accessible by a computer, such as magnetic cassettes, flash memory cards, digital video disks (DVDs), Bernoulli cartridges, RAMs, ROMs, and the like, may also be used in the exemplary operating environment.  
         [0027]     A number of program modules may be stored on the hard disk, magnetic disk  29 , optical disk  31 , ROM  24 , or RAM  25 , including an operating system  35 , one or more application programs  36 , other program modules  37 , and program data  38 . A user may enter commands and information in PC  20  and provide control input through input devices, such as a keyboard  40  and a pointing device  42 . Pointing device  42  may include a mouse, stylus, wireless remote control, or other pointer, but in connection with the present invention, such conventional pointing devices may be omitted, since the user can employ the interactive display for input and control. As used hereinafter, the term “mouse” is intended to encompass virtually any pointing device that is useful for controlling the position of a cursor on the screen. Other input devices (not shown) may include a microphone, joystick, haptic joystick, yoke, foot pedals, game pad, satellite dish, scanner, or the like. Also, PC  20  may include a Bluetooth radio or other wireless interface for communication with various types of interface device, such as printers, or the interactive display table of the present invention. These and other input/output (I/O) devices are often connected to processing unit  21  through an I/O interface  46  that is coupled to the system bus  23 . The term I/O interface is intended to encompass each interface specifically used for a serial port, a parallel port, a game port, a keyboard port, and/or a universal serial bus (USB). System bus  23  is also connected to a camera interface  59 , which is coupled to an interactive display  60  to receive signals form a digital video camera that is included therein, as discussed below. The digital video camera may be instead coupled to an appropriate serial I/O port, such as to a USB version 2.0 port. Optionally, a monitor  47  can be connected to system bus  23  via an appropriate interface, such as a video adapter  48 ; however, the interactive display table of the present invention can provide a much richer display and interact with the user for input of information and control of software applications and is therefore preferably coupled to the video adaptor. It will be appreciated that PCs are often coupled to other peripheral output devices (not shown), such as speakers (through a sound card or other audio interface—not shown) and printers.  
         [0028]     The present invention may be practiced on a single machine, although PC  20  can also operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  49 . Remote computer  49  may be another PC, a server (which is typically generally configured much like PC  20 ), a router, a network PC, a peer device, or a satellite or other common network node, and typically includes many or all of the elements described above in connection with PC  20 , although only an external memory storage device  50  has been illustrated in  FIG. 1 . The logical connections depicted in  FIG. 1  include a local area network (LAN)  51  and a wide area network (WAN)  52 . Such networking environments are common in offices, enterprise wide computer networks, intranets, and the Internet.  
         [0029]     When used in a LAN networking environment, PC  20  is connected to LAN  51  through a network interface or adapter  53 . When used in a WAN networking environment, PC  20  typically includes a modem  54 , or other means such as a cable modem, Digital Subscriber Line (DSL) interface, or an Integrated Service Digital Network (ISDN) interface for establishing communications over WAN  52 , such as the Internet. Modem  54 , which may be internal or external, is connected to the system bus  23  or coupled to the bus via I/O device interface  46 , i.e., through a serial port. In a networked environment, program modules, or portions thereof, used by PC  20  may be stored in the remote memory storage device. It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used, such as wireless communication and wide band network links.  
         [0000]     Exemplary Interactive Surface  
         [0030]     In  FIG. 2 , an exemplary interactive display table  60  is shown that includes PC  20  within a frame  62  and which serves as both an optical input and video display device for the computer. In this cut-away figure of the interactive display table  60 , rays of light  82   a - 82   c  used for displaying text and graphic images are generally illustrated using dotted lines, while rays of IR light used for sensing objects on or just above a display surface  64   a  of interactive display table  60  are illustrated using dash lines. Display surface  64   a  is set within an upper surface  64  of interactive display table  60 . The perimeter of the table surface is useful for supporting a user&#39;s arms or other objects, including objects that may be used to interact with the graphic images or virtual environment being displayed on display surface  64   a.    
         [0031]     IR light sources  66  preferably comprise a plurality of IR light emitting diodes (LEDs) and are mounted on the interior side of frame  62 . The IR light that is produced by IR light sources  66  is directed upwardly toward the underside of display surface  64   a , as indicated by dash lines  78   a ,  78   b , and  78   c . The IR light from IR light sources  66  is reflected from any objects that are atop or proximate to the display surface after passing through a translucent layer  64   b  of the table, comprising a sheet of vellum or other suitable translucent material with light diffusing properties. As used herein and in the claims that follow in connection with objects positioned on or proximate to the interactive display surface, the term “adjacent to” is used with the intention that this term encompass both an object that is actually touching the interactive display surface as well as one that is just above the interactive display surface. Although only one IR source  66  is shown, it will be appreciated that a plurality of such IR sources may be mounted at spaced-apart locations around the interior sides of frame  62  to prove an even illumination of display surface  64   a . The IR light produced by the IR sources may: 
        exit through the table surface without illuminating any objects, as indicated by dash line  78   a;       illuminate objects on the table surface, as indicated by dash line  78   b ; or     illuminate objects a short distance above the table surface but not touching the table surface, as indicated by dash line  78   c.          
 
         [0035]     Objects above display surface  64   a  include a “touch” object  76   a  that rests atop the display surface and a “hover” object  76   b  that is close to but not in actual contact with the display surface. Thus, both touch and hover objects are “adjacent to” the display surface, as that term is used herein. As a result of using translucent layer  64   b  under the display surface to diffuse the IR light passing through the display surface, as an object approaches the top of display surface  64   a , the amount of IR light that is reflected by the object increases to a maximum level that is achieved when the object is actually in contact with the display surface.  
         [0036]     A digital video camera  68  is mounted to frame  62  below display surface  64   a  in a position appropriate to receive IR light that is reflected from any touch object or hover object disposed above display surface  64   a . Digital video camera  68  is equipped with an IR pass filter  86   a  that transmits only IR light and blocks ambient visible light traveling through display surface  64   a  along dotted line  84   a . A baffle  79  is disposed between IR source  66  and the digital video camera to prevent IR light that is directly emitted from the IR source from entering the digital video camera, since it is preferable that this digital video camera should produce an output signal that is only responsive to the IR light reflected from objects that are a short distance above or in contact with display surface  64   a  and corresponds to an image of IR light reflected from objects on or above the display surface. It will be apparent that digital video camera  68  will also respond to any IR light included in the ambient light that passes through display surface  64   a  from above and into the interior of the interactive display including ambient IR light that also travels along the path indicated by dotted line  84   a.    
         [0037]     IR light reflected from objects on or above the table surface may be: 
        reflected back through translucent layer  64   b , through IR pass filter  86   a  and into the lens of digital video camera  68 , as indicated by dash lines  80   a  and  80   b ; or     reflected or absorbed by other interior surfaces within the interactive display without entering the lens of digital video camera  68 , as indicated by dash line  80   c.          
 
         [0040]     Translucent layer  64   b  diffuses both incident and reflected IR light. Thus, as explained above, “hover” objects such as hover object  76   b  that are closer to display surface  64   a  will reflect more IR light back to digital video camera  68  than objects of the same reflectivity that are farther away from the display surface. The digital video camera  68  senses the IR light reflected from “touch” and “hover” objects within its imaging field and produces a digital signal corresponding to images of the reflected IR light that is input to the PC  20  for processing to determine a location of each such object, and optionally, the size, orientation, and shape of the object. It should be noted that a portion of an object, such as a user&#39;s forearm, may be above the table while another portion, such as the user&#39;s finger, is in contact with the display surface. In addition, an object may include an IR light reflective pattern or coded identifier, such as a bar code, on its bottom surface that is specific to that object or to a class of related objects of which that object is a member. Accordingly, the imaging signal from the digital video camera  68  can also be used for detecting each such specific object, as well as determining its orientation, based on the IR light reflected from its reflective pattern, in accord with the present invention.  
         [0041]     Embodiments of the present invention thus are operable in connection with recognizing an object and/or its position relative to the interactive display surface  64   a  by detecting its identifying characteristics using the IR light reflected from the object. The logical steps implemented to thus detect and identify an object and its orientation are explained in the commonly-assigned patent applications, including application Ser. No. 10/814,577, entitled “Identification Of Object On Interactive Display Surface By Identifying Coded Pattern,” and application Ser. No. 10/814,761, entitled “Determining Connectedness And Offset Of 3D Objects Relative To An Interactive Surface,” both of which were filed on Mar. 31, 2004. The disclosure and drawings of these two patent applications are hereby specifically incorporated herein by reference.  
         [0042]     PC  20  may be integral to interactive display table  60  as shown in  FIG. 2 , or alternatively, may instead be external to the interactive display table, as shown in the embodiment of  FIG. 3 . In  FIG. 3 , an interactive display table  60 ′ is connected through a data cable  63  to an external PC  20  (which includes optional monitor  47 , as mentioned above). Alternatively, external PC  20  can be connected to interactive display table  60 ′ via a wireless link (i.e., WiFi or other appropriate radio signal link). As also shown in this Figure, a set of orthogonal X and Y axes are associated with display surface  64   a , as well as an origin indicated by “0.” While not discretely shown, it will be appreciated that a plurality of coordinate locations along each orthogonal axis can be employed to specify any location on display surface  64   a.    
         [0043]     If an interactive display table  60 ′ is connected to an external PC  20  (as in  FIG. 3 ) or to some other type of external computing device, such as a set top box, video game, laptop computer, or media computer (not shown), then interactive display table  60 ′ comprises an input/output device. Power for interactive display table  60 ′ is provided through a power lead  61 , which is coupled to a conventional alternating current (AC) source (not shown). Data cable  63 , which connects to interactive display table  60 ′, can be coupled to a USB 2.0 port, an Institute of Electrical and Electronics Engineers (IEEE) 1394 (or Firewire) port, or an Ethernet port on PC  20 . It is also contemplated that as the speed of wireless connections continues to improve, interactive display table  60 ′ might also be connected to a computing device, such as PC  20  via such a high-speed wireless connection, or via some other appropriate wired or wireless data communication link. Whether included internally as an integral part of the interactive display, or externally, PC  20  executes algorithms for processing the digital images from digital video camera  68  and executes software applications that are designed to employ the more intuitive user interface functionality of interactive display table to good advantage, as well as executing other software applications that are not specifically designed to make use of such functionality, but can still make good use of the input and output capability of the interactive display table. As yet a further alternative, the interactive display can be coupled to an external computing device, but include an internal computing device for doing image processing and other tasks that would then not be done by the external PC.  
         [0044]     An important and powerful feature of interactive display table  60  or  60 ′ (i.e., of either of the embodiments of the interactive display table discussed above) is its ability to display graphic images or a virtual environment for games or other software applications and to enable an interaction between the graphic image or virtual environment visible on display surface  64   a  and identify objects that are resting atop the display surface, such as object  76   a , or are hovering just above it, such as object  76   b.    
         [0045]     Again referring to  FIG. 2 , interactive display table  60  includes a video projector  70  that is used to display graphic images, a virtual environment, or text information on display surface  64   a . The video projector is preferably of a liquid crystal display (LCD) or digital light processor (DLP) type, or a liquid crystal on silicon (LCOS) display type, with a resolution of at least 640×480 pixels. An IR cut filter  86   b  is mounted in front of the projector lens of video projector  70  to prevent IR light emitted by the video projector from entering the interior of the interactive display table where the IR light might interfere with the IR light reflected from object(s) on or above display surface  64   a . Video projector  70  projects light along dotted path  82   a  toward a first mirror assembly  72   a . First mirror assembly  72   a  reflects projected light from dotted path  82   a  received from video projector  70  along dotted path  82   b  through a transparent opening  90   a  in frame  62 , so that the reflected projected light is incident on a second mirror assembly  72   b . Second mirror assembly  72   b  reflects light from dotted path  82   b  along dotted path  82   c  onto translucent layer  64   b , which is at the focal point of the projector lens, so that the projected image is visible and in focus on display surface  64   a  for viewing.  
         [0046]     Alignment devices  74   a  and  74   b  are provided and include threaded rods and rotatable adjustment nuts  74   c  for adjusting the angles of the first and second mirror assemblies to ensure that the image projected onto the display surface is aligned with the display surface. In addition to directing the projected image in a desired direction, the use of these two mirror assemblies provides a longer path between projector  70  and translucent layer  64   b  to enable a longer focal length (and lower cost) projector lens to be used with the projector.  
         [0047]     The foregoing and following discussions describe an interactive display device in the form of interactive display table  60  and  60 ′. Nevertheless, it is understood that the interactive display surface need not be in the form of a generally horizontal table top. The principles described in this description of the invention suitably also include and apply to display surfaces of different shapes and curvatures and that are mounted in orientations other than horizontal. Thus, although the following description refers to placing physical objects “on” the interactive display surface, physical objects may be placed adjacent to the interactive display surface by placing the physical objects in contact with the display surface, or otherwise adjacent the display surface.  
         [0000]     Representative Forms of IR-Detectable Markings  
         [0048]     Any type of marking or optical code recognizable by a sensor or camera may be used with embodiments of the present invention to provide input to an application executing on an interactive display system. So long as the marking or code is made with a material that reflects light in the IR spectrum (or optionally, in a ultraviolet (UV) spectrum if an appropriate UV light sensor is used), any optical marking or coding scheme can be used. Exemplary embodiments of a method and system for detection of optical codes are described in the above-referenced, co-pending and commonly assigned U.S. patent application Ser. No. 10/814,577, entitled “Identification Of Object On Interactive Display Surface By Identifying Coded Pattern,” which was filed on Mar. 31, 2004.  
         [0049]      FIGS. 4A-4C  provide three examples of optical codes suitable for use in connection with the present invention, although, it will be understood that many other optical codes can instead be used. As shown in  FIG. 4A , a conventional bar code  410  can be used as the marking for a physical object. The sequence and width of bars  412  in the bar code  410  represent a value that can be detected by the vision sensing system of the interactive display system of  FIG. 2 . The value encoded in bar code  410  may be associated or associable with a function, action, or other entity in an application executing on the interactive display system. Positioning bar code  410  in contact with interactive display surface  64   a  thus invokes the associated function, action, or entity, as described above.  
         [0050]      FIG. 4B  illustrates a radial code  420 . Radial code  420  includes a reflective inner circular area  422  with a darkened start bit  424 . (It will be understood that the inverse of the reflective and the darkened areas noted can alternatively be used in almost any of these optical codes.) Start bit  424  is preferably located at a predefined first radius from the center of the coded region, and can take the shape of a keystone, a pie slice, or any other shape that makes the start bit easy to locate. Start bit  424  within light reflective inner circular area  422  defines a starting reference point from which the code value can be determined. Radial code  420  also comprises an outer, evenly divided first annulus  426 , with a series of light and dark keystone-shaped data bits presenting the value of radial code  420 . The value of radial code  420  is read starting from the location of start bit  424  in a predefined clockwise (or alternatively, in a predefined counterclockwise) direction. An outer area  428  sets off radial code  420  from surrounding portions of the image or other optical codes to facilitate detection and identification.  
         [0051]      FIG. 4C  illustrates a matrix code  430 . Matrix code  430  is an exemplary form of a matrix code in the form of a die matrix code having from one to six data bits  432  or die spots arranged in six predetermined patterns within a 3×3 grid  434 . Data bits  432  are read from grid  434  and compared to each of six allowable die face patterns as well as to one or more versions of the die face patterns rotated by some predefined angle, e.g., 45°, relative to the patterns shown in  FIG. 4C . A matrix code  430  of almost any size and associated die face bit pattern can be read. An outer area  436  sets off matrix code  430  from surrounding portions of the image or other optical codes to facilitate detection and identification.  
         [0052]     Other encoding schemes, including shapes differentiable by size and/or form, and any other form of optical encoding scheme presenting codes that is optically identifiable and distinguishable by an appropriate vision sensing system is usable with the present invention.  
         [0000]     Cross-Sectional View of Coating Masking IR Markings  
         [0053]      FIGS. 5A and 5B  illustrate a physical object  500  bearing a marking  510  with and without, respectively, a visible light-blocking coating  550  according to an embodiment of the present invention. Physical object  500 , as shown in both  FIGS. 5A and 5B , is a thin object such as a tile, chip, playing card, or similar object. Physical object  500  includes a first face  502  and a second face  504 . Marking  510  is disposed on second face  504  of physical object  500 , although marking  510  could appear on both faces  502  and  504  of physical object  500 , or different markings  510  could appear on different faces of physical object  500 . Marking  510  may be a bar code  410  ( FIG. 4A ), a radial code  420  ( FIG. 4B ), a matrix code  430  ( FIG. 4C ) or any other pattern. For purposes of this explanation, it is assumed that marking  510  is detectable both in the IR and visible light spectra.  
         [0054]     In  FIG. 5A , marking  510  is not coated with a visible light-blocking coating. As a result, when marking  510  is exposed to visible light source  520 , visible light beam  522  illuminates marking  510 . Marking  510  reflects visible light beam  522 , resulting in visible light reflection  524  that can be discerned by a human eye  528 . As a result, information encoded in marking  510  is detectable by human eye  528 . At the same time, marking  510  is exposed to an IR light source  530 . An IR light beam  532  also illuminates marking  510 , resulting in an IR light reflection  534 . IR light reflection  534  passes through IR pass filter  86   a  and is detected by digital video camera  68 .  
         [0055]     In  FIG. 5B , however, marking  510  is concealed by application of visible light-blocking coating  550 . As was the case in the example of  FIG. 5A , when marking  510  is exposed to IR light source  530 , IR light reflection  534  passes through IR pass filter  86   a  and is detected by digital video camera  68 . However, unlike the example of  FIG. 5A , when object  500  is illuminated by visible light source  520 , visible light beam  522  is not reflected. Instead, visible light beam  522  is absorbed by visible light-blocking coating  550 . As a result, while the information encoded in marking  510  is still discernible by digital video camera  68 , marking  510  is neither discernible nor readable by human eye  528 . Thus, marking  510  may be formed with materials visible in both the IR and visible light spectra, but marking  510  will be substantially invisible and undetectable to the human eye.  
         [0000]     Logical Steps for Deploying Visible-Light Blocking Coating(s)  
         [0056]      FIG. 6  is a flow diagram  600  illustrating the logical steps for applying visible light-blocking coatings over IR-discernible markings (or over UV-discernible markings, if the vision sensing system is responsive to UV light; if a UV vision sensing system is employed, then the term IR in this discussion can be replaced with the term UV). Flow diagram  600  begins at a step  602 . At a step  604 , IR-discernible markings to be used are chosen. The IR-discernible markings selected may be chosen from among the optical coding types previously described in connection with  FIGS. 4A-4C , or any other type of optically recognizable shapes or forms. The selection may be based on the nature of the digital video camera used, the size and/or shape of surfaces to which the marking is to be applied, the application with which the marking is to be used, and a number of other factors.  
         [0057]     At a step  606 , one or more surfaces on an object that will bear IR-discemible markings are identified. As will described further below, it may be desirable for one or more sides or surfaces of an object to bear IR-discernible markings. The same marking or different markings may appear on multiple surfaces of the same physical object. At a step  608 , the selected IR-discemible markings are disposed on the selected surfaces. The markings may be placed on the surfaces by imprinting, screening, transfers, appliqués, or any other process suitable to allow the marking to adhere to the surface.  
         [0058]     At a step  610 , a suitable visible light-blocking coating is selected to be applied over the IR-discemible markings. According to one embodiment of the present invention, the visible light-blocking coating includes one or more layers of a fluid coating applied to the object over the marking. The fluid coating may include a paint, a lacquer, a varnish, or other fluid coating. The fluid coating should be selected so that one or more fluids combined result in a layer that, while largely transparent to light in the IR spectrum, is generally opaque to light in the visible spectrum. As a result, and as was described above in connection with  FIG. 5B , the layer created by the coating enables a digital video camera to discern the marking while preventing a human eye from being able to detect and/or decode the marking.  
         [0059]     In one embodiment of the present invention, a single layer of a single color of paint results in a layer that is largely transparent to light in the IR spectrum while being generally opaque to visible light. One suitable paint includes Liquitex™ Acrylic Artistic Color acrylic paint in the color Naphthol Crimson; this paint is an artist&#39;s acrylic paint. In another embodiment of the present invention, application of multiple colors of paint result in a layer that is largely transparent to light in the IR spectrum, while being generally opaque to visible light. For example, one suitable composite layer is formed of coatings of Design Master™ Color Tool Spray Paint, in the colors Deep Blue #743 and Cranberry #713, which are commonly used for floral coloring. It should be noted that the coating selected need not have the desired optical properties in a transitional state. In other words, a paint that has the desired optical properties upon being dried or otherwise cured is suitable, even if the same paint lacks those same physical properties while the paint is in a liquid state or while it remains “wet.” 
         [0060]     At a step  612 , the visible light-blocking coating is applied over the marking. The fluid coating suitably may be applied by brushing, spraying, flooring, dipping, electrostatic application, or any other suitable means of application.  
         [0061]     Alternatively, instead of applying the fluid coating directly to the surface of a physical object over the marking, the fluid coating may be applied to an intermediate substrate. One substrate may include a thin sheet of generally transparent plastic, vinyl, or similar material. The fluid coating may be applied to the substrate, and the coated substrate then attached to the surface of the object over the marking. A section of the substrate sufficiently large to cover the marking may be formed and then covered with the fluid coating. As a further alternative, a sheet of the substrate larger than the marking may be covered with the fluid coating, with portions of the substrate subsequently being cut from it and attached to the object over the marking.  
         [0062]     In this embodiment of the invention, the coated layer of substrate acts as a filter. However, unlike conventional filters, the substrate need not be formed with the desired or needed optical properties for the particular application. Instead, commonly available materials that are generally transparent to light in the visible and/or IR spectra may be used. Coating readily available materials instead of having filter material specially fabricated can reduce production costs. The ability to thereby produce quantities of materials with desired visible light-blocking properties makes producing small quantities of the materials cost effective when the same may not be true if specially fabricated materials otherwise would need to be produced.  
         [0063]     At a decision step  614 , it is determined if all desired objects have been encoded and the markings covered. If so, the flow diagram ends at a step  618 . On the other hand, if it is determined at decision step  614  that objects or surfaces have yet to be an encoded and covered, at a step  616 , the flow diagram proceeds to a next object and flow diagram  600  loops to block  606 .  
         [0000]     Applications for which Discrete Invisible Markings are Desirable  
         [0064]     Visible light-blocking coatings have a number of applications for masking IR-discernible markings for which attachment of conventional filters may not be suitable. Attachment of conventional filters may add significant cost, bulk, and or weight to physical objects with which they are used. By contrast, applications for visible light-blocking coatings make a number of applications available and practical.  
         [0065]      FIGS. 7A-7G  illustrate one suitable application for applying a visible light-blocking coating to a thin object. In short, in the application for display surface  64   a  of interactive display table  70  ( FIG. 2 ) depicted, placing cards  700  on display surface  64   a  causes interactive display system to make a noise that is associated with an images on each of the cards. More particularly,  FIG. 7A  shows display surface  64   a  of interactive display system on which a number of cards  700  have been placed. As shown in the examples of  FIG. 7B  and  FIG. 7E , cards  700  each bear different images  712   a  and  712   b  on first sides  710   a  and  710   b , respectively. As shown in  FIGS. 7C and 7F , on second sides  720   a  and  720   b , each of the cards carries an optical marking or code. Different markings  722   a  and  722   b  correspond with different images  712   a  and  712   b . In one application supported by interactive display table  70 , placing cards  710   a  and  710   b  on display surface  64   a  enables the display surface to respond to markings  722   a  and  722   b  by playing sounds associated with each card placed on the display surface.  
         [0066]     However, while the application would be functional, in an era where nearly every store uses Universal Product Code (UPC) bar code markings to determine prices and changes to inventory when a product is sold, permitting markings  722   a  and  722   b  to be visible would make it apparent to anyone inspecting the cards how the interactive display table is able to identify each card. As a result, the product would lack the mystique or enjoyment that is attained by hiding markings  722   a  and  722   b  from the view of the user&#39;s eye. Thus, using embodiments of the present invention, a visible light-blocking coating  732 , as shown in  FIG. 7B , is applied to back faces  720   a  and  720   b  of each of cards  710   a  and  710   b . As shown in  FIGS. 7D and 7G , with visible light-blocking coating  732  applied to cards  710   a  and  710   b , finished back faces  730   a  and  730   b  appear identical to an unaided eye because the coating hides the marking that identifies the cards to the vision sensing system of the interactive display system. The interactive display system thus can generate different and appropriate sounds matching images on first sides  710   a  and  710   b  of cards  700  placed on display surface  64   a  even when back faces such as  730   a  and  730   b  appear identical to the unaided eye. Consequently, the interactive display system appears to operate with a certain mystery and mystique, adding to the enjoyment of the application by the user.  
         [0067]     Another application for the interactive display system is depicted in  FIGS. 8A-8B . The application shown involves a word game played on a grid  800 . Grid  800  can be produced on display surface  64   a  by the interactive display system using video projector  70  ( FIG. 2 ). However, while the game board may be virtual, users still can engage the game board using real game pieces. In particular, users can use letter tiles  802  to form words  804  on virtual grid  800 , thereby engaging in a gaming environment that is part real and part virtual.  
         [0068]     In addition to the novelty of a game environment that is both real and virtual, such an environment also affords a number of other advantages. For example, in contrast to an physical version of the game where users manually need to tally their scores, including any bonuses accrued, the combined real and virtual game played on display surface  64   a  can tally and generate scoring totals  810  for the users automatically. Score computation can be facilitated by coding tiles  802  such that display surface  64   a  can identify the values of tiles  802  that are placed on grid  800 . One problem with this, as can be seen in  FIG. 8B , is that opponents should not know the tiles  800  that other players have resting on their tile holders  806 . In other words, each of the users should be able to keep secret the letters and values that are shown on front faces  802   f  of tiles  802  and not have those values betrayed to opponents by visually apparent markings on back faces  802   b  of tiles  802  until each player actually plays tiles  802 .  
         [0069]     To persons familiar with such word games, it will be understood that tiles  802  are small and relatively thin. Outfitting tiles  802  with IR-discernible coatings and then covering those coatings with thick and visible light-blocking filters could make the tiles  802  bulky and cumbersome to handle. Certainly, manufacturing and attaching such filters to many tiles  802 —tiles  802  generally are made of plastic or wood and are otherwise inexpensive to mass-produce—would add significantly to their production costs. However, using embodiments of the present invention, TR-discernible markings can readily be applied to each of the tiles  802  and then covered with visible light-blocking coating, as described above, adding relatively little extra cost. As a result, the strategy and gamesmanship of the game is preserved, while exploiting the functionality inherent in the interactive display system to read values represent codes disposed on back faces  802   b  of tiles  802 .  
         [0070]     In still another useful application of the present invention, embodiments may even be used to conceal IR-discemible markings on playing cards. As a result, using a suitably—but not unfairly—“marked” deck of cards, one or more users can play a card game on the interactive display system. Because embodiments of the present invention employ very thin coatings that are able to block visible light, the card game can be played with cards that are pliable and easily shuffled like conventional playing cards, while providing the advantage that the vision sensing system can identify each of the cards placed on the display surface of the interactive display system.  
         [0071]     As shown in  FIG. 9 , display surface  64   a  presents a grid  900  delineated into a system zone  902 , a face-up zone  904 , and a player zone  906 . Such a grid  900  is suitable for card games such as “Texas Hold &#39;Em” poker, where multiple players (and in this case, one of the players is the interactive display system) attempt to build winning hands using a combination of cards in their own “hands” and in the faceup area  904 . In the “Texas Hold &#39;Em” example of  FIG. 9 , cards  910  are dealt to the interactive display system by placing cards  910  face down in system area  902 . Cards  912  are placed face up in face up area  904  for both players to use. Cards  914  are dealt to a real player by placing them in player area  906  in an unscanned region  908  that is not viewed by the logic of the interactive display system until and unless the cards disposed there are to be shown; alternatively, the user can hold cards  914  in a user&#39;s hand  916 . In this game, only the interactive display system should be able to “see” interactive display system cards  910 , and only the user should be able to see user cards  914 , while both the interactive display system and the user should be able to “see” face up cards  912 .  
         [0072]     Using an embodiment of the present invention, an IR-discemible coding is applied to the backs of all cards in the deck, and the markings are covered using a visible-light blocking coating so that the backs of the cards cannot be read by an unaided human eye. Thus, when cards  912  are placed face up on display surface  64   a , cards  812  can be read by the interactive display system and the user to determine their values. On the other hand, cards  910  dealt to the interactive display system can be read by the interactive display system by their coded values, but cannot be read by the user. The interactive display system can be configured to identify cards from the patterns on the faces of the cards, or a second marking or coding  918  can be placed on the faces of the cards as well. Second markings  918  also are covered by a visible light-blocking coating to add to the mystique of the game, as described above in connection with  FIGS. 7A-7B . Also, cards  914  dealt to a user cannot be read by the interactive display system—or by other human players—as long as cards  914  are left face down in unscanned region  908  of player area  906 , or held in user&#39;s hand  916 . When a user wants to show user&#39;s cards  914 , the user can lay cards  914  on display surface  64   a  of the interactive display system.  
         [0073]     Either the interactive display system or the user can request different cards from a deck (not shown), bet by moving chips  920  (or in the case of the interactive display system, by indicating chips  920  that are to be moved). Chips  920  can be encoded to have different values, such as $1 for chips  922  and $5 for chips  924 , which may be coded on one or both sides to be read by the interactive display system.  
         [0074]     Again, embodiments of the present invention makes coding playing cards and other relatively thin objects practical. By contrast, attempting to apply conventional filters to playing cards or other thin object to hide IR markings would make the object too thick and too cumbersome to be shuffled, dealt, and conveniently held. Embodiments of the present invention enable IR-discernible codes to be concealed without adding unreasonable weight and or thickness to the cards and other types of objects.  
         [0075]     Although the present invention has been described in connection with the preferred form of practicing it and modifications thereto, those of ordinary skill in the art will understand that many other modifications can be made to the present invention within the scope of the claims that follow. Accordingly, it is not intended that the scope of the invention in any way be limited by the above description, but instead be determined entirely by reference to the claims that follow.