PATENT ABSTRACT
A data input device and method including an illuminator operative to illuminate at least one engagement plane by directing light along the at least one engagement plane, a two-dimensional imaging sensor viewing the at least one engagement plane from a location outside the at least one engagement plane for sensing light from the illuminator scattered by engagement of a data entry object with the at least one engagement plane and data entry processor receiving an output from the two-dimensional imaging sensor and providing a data entry input to utilization circuitry.

PATENT DESCRIPTION
REFERENCE TO CO-PENDING APPLICATIONS  
       [0001]     This application claims priority from the following co-pending U.S. Patent Applications:  
         [0002]     U.S. provisional application Ser. No.: 60/260,436, entitled “Improved virtual keyboard”, filed Jan. 8, 2001; U.S. provisional application Ser. No.: 60/263,115, entitled “Differential CMOS detector for virtual keyboard”, filed Jan. 19, 2001, U.S. provisional application Ser. No.: 60/303,922, entitled “Algorithms for implementing virtual keyboard detection”, filed Jul. 6, 2001; and U.S. provisional application entitled “Large angle of incidence, narrow band interference filter”, filed Nov. 2, 2001 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     The following patents and publications are believed to represent the current state of the art:  
         [0004]     Published PCT Application WO 01/59975A2; U.S. Pat. No. 6,266,048; Published European application EP 0 982 676 A1; Published European application EP 1 039 365 Aw; U.S. Pat. No. 4,468,694; U.S. Pat. No. 5,969,698; Published Japan application 2000029605; Published PCT application WO 00/39663; Published PCT application WO 01/54110 A1; U.S. Pat. No. 6,175,679; Published PCT application WO 99/13395 A1; U.S. Pat. No. 5,767,842; U.S. Pat. No. 6,043,805; U.S. Pat. No. 5,909,210; U.S. Pat. No. 5,786,810; U.S. Pat. No. 5,821,922; U.S. Pat. No. 5,864,334; Published PCT application WO 00/21024; U.S. Pat. No. 6,037,882; U.S. Pat. No. 6,121,960; U.S. Pat. No. 5,789,739; U.S. Pat. No. 6,031,519; U.S. Pat. No. 5,736,976.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention relates to data input methods and apparatus generally.  
         [0006]     There is thus provided in accordance with a preferred embodiment of the present invention a data input device including an illuminator operative to illuminate at least one engagement plane by directing light along the engagement plane, a two-dimensional imaging sensor viewing the engagement plane from a location outside the engagement plane for sensing light from the illuminator scattered by engagement of a data entry object with the engagement plane and a data entry processor receiving an output from the two-dimensional imaging sensor and providing a data entry input to utilization circuitry.  
         [0007]     There is also provided in accordance with a preferred embodiment of the present invention a data input method, which included illuminating at least one engagement plane by directing light along the engagement plane, employing a two-dimensional imaging sensor for viewing the engagement plane from a location outside the engagement plane for sensing light from the illumination scattered by engagement of a data entry object with the engagement plane and receiving and processing an output from the two-dimensional imaging sensor and providing a data entry input to utilization circuitry.  
         [0008]     Further in accordance with a preferred embodiment of the present invention the data input device also included a data entry matrix projector operative to project at least one visually sensible data entry matrix onto a projection surface underlying the engagement plane.  
         [0009]     Preferably, the visually sensible data entry matrix defines a keyboard.  
         [0010]     Still further in accordance with a preferred embodiment of the present invention the illuminator includes an illuminator light source and a spatial light modulation element operative to receive light from the illuminator light source and to direct light along the engagement plane.  
         [0011]     Additionally in accordance with a preferred embodiment of the present invention the projector includes a projector light source and a spatial light modulation element which operates to receive light from the projector light source and to project at least one visually sensible data entry matrix onto a surface underlying the engagement plane.  
         [0012]     Preferably, the spatial light modulation element includes a diffractive optical element.  
         [0013]     Further in accordance with a preferred embodiment of the present invention the spatial light modulation element includes an aspheric optical element. Additionally or alternatively, the spatial light modulation element includes a joined double side truncated rod lens optical element.  
         [0014]     Typically the spatial light modulation element includes a transparency.  
         [0015]     Further in accordance with a preferred embodiment of the present invention the two-dimensional imaging sensor includes a solid state imaging sensor.  
         [0016]     Still further in accordance with a preferred embodiment of the present invention the data entry processor correlates the output from the two-dimensional imaging sensor with the visually sensible data entry matrix.  
         [0017]     Additionally in accordance with a preferred embodiment of the present invention the data entry matrix projector includes a diffractive optical element which receives light from a diode laser via a collimating lens.  
         [0018]     Typically the light passing through the diffractive optical element is reflected by a curved mirror having optical power via a lens onto the projection surface.  
         [0019]     Preferably, the diffractive optical element, the mirror and the lens are all integrally formed in a prism.  
         [0020]     Further in accordance with a preferred embodiment of the present invention the data entry matrix projector includes an integrally formed beam splitter an diffractive optical elements.  
         [0021]     Preferably, in the data entry matrix projector, a beam of light from a diode laser passes through a collimating lens and impinges on two mutually angles surfaces of the beam splitter, which breaks the beam of light into two beams, each of which passes through a separate diffractive optical element and impinges on the projection surface.  
         [0022]     Typically the diffractive optical elements are integrally formed with the beam splitter in a prism.  
         [0023]     Further in accordance with a preferred embodiment of the present invention the data entry matrix projector includes a plurality of different diffractive optical elements, each of which typically corresponds to a different matrix configuration, which are selectably positionable along a projection light path.  
         [0024]     Still further in accordance with a preferred embodiment of the present invention the data entry matrix projector includes a diffractive optical element having a multiplicity of diffraction orders selected to provide a matrix configuration which has a relatively low maximum diffraction angle.  
         [0025]     Additionally or alternatively, the data entry matrix projector includes a diffractive optical element having a multiplicity of diffraction orders selected to provide a keyboard configuration, which has a generally trapezoidal configuration.  
         [0026]     Further in accordance with a preferred embodiment of the present invention the data entry matrix projector includes a diffractive optical element having a multiplicity of diffraction orders selected to compensate for geometrical distortions inherent in the operation of the diffractive optical element, particularly at high diffraction angles.  
         [0027]     Still further in accordance with a preferred embodiment of the present invention the data entry matrix projector includes a diffractive optical element having a multiplicity of diffraction orders selected to compensate for geometrical distortions occasioned by a highly oblique angle of projection.  
         [0028]     Additionally in accordance with a preferred embodiment of the present invention in the data entry matrix projector, light from a pair of point light sources is combined by a beam combiner, such that tow light beams emerge from the beam combiner and appear to originate in a single virtual light source positioned behind the beam combiner.  
         [0029]     Preferably, the light beams pass through a shadow mask onto the projection surface.  
         [0030]     Further in accordance with a preferred embodiment of the present invention the data entry matrix projector includes an array of light emitting elements and microlenses.  
         [0031]     Typically, the light emitting elements are individually controllable.  
         [0032]     Still further in accordance with a preferred embodiment of the present invention the data entry matrix project includes a monolithic pattern of LEDs formed on a unitary substrate.  
         [0033]     Further in accordance with a preferred embodiment of the present invention the two-dimensional imaging sensor is located on the opposite side of a transparent engagement surface from the engagement plane, whereby the presence of the data entry object at the engagement plane causes light from the illuminator to be scattered and to pass through the transparent engagement surface so as to be detected by the two-dimensional imaging sensor.  
         [0034]     Still further in accordance with a preferred embodiment of the present invention the data input device includes a transparent engagement surface is coextensive with the engagement plane, whereby touching engagement of the data entry object with the transparent engagement surface causes light from the illuminator to be scattered and to pass through the transparent engagement surface so as to be detected by the two-dimensional imaging sensor.  
         [0035]     Preferably, the transparent engagement surface exhibits total internal reflection of a planar beam of light emitted by an illuminator and coupled to an edge of the transparent engagement surface, whereby touching engagement of the data entry object with the transparent engagement surface causes light from the illuminator to be scattered due to frustrated total internal reflection.  
         [0036]     Additionally in accordance with a preferred embodiment of the present invention the illuminator provides illumination generally through 360 degrees and the two-dimensional imaging sensor views generally through 360 degrees.  
         [0037]     Preferably, the illuminator provides a non-uniform intensity distribution.  
         [0038]     Further in accordance with a preferred embodiment of the present invention at least a portion of the non-uniform intensity distribution provides greater intensity at greater illumination angles.  
         [0039]     Still further in accordance with a preferred embodiment of the present invention the data input device also includes a data entry object speed sensor operative to sense the speed with which the data entry object approaches the engagement plane.  
         [0040]     Preferably, the illuminator includes at least first and second wavelength specific illuminators operative at at least first and second different wavelengths and directing light along at least first and second mutually spaces, overlying engagement planes and the two-dimensional imaging sensor senses light at the first and second different wavelengths, differentiates therebetween and provides an output to the data entry object speed sensor.  
         [0041]     Further in accordance with a preferred embodiment of the present invention the illuminator includes at least first and second illuminators operative at the same wavelength and directing light along at least first and second mutually spaced, overlying engagement planes and the data entry object speed sensor is responsive to changes in the intensity of light senses by the two-dimensional imaging sensor for providing an output indication of the speed.  
         [0042]     Preferably, the illuminator directs light, which is emitted from a point source through a large solid angle, into a flat radially directed beam extending along the engagement plane, the beam having a relatively narrow spread in a direction perpendicular to the engagement plane.  
         [0043]     Still further in accordance with a preferred embodiment of the present invention the illuminator includes a point light source which emits light through a generally semi-hemispherical volume centered about a propagation axis, an spheric reflector which reflects the light emitted by the point light source along a line lying in the engagement plane and extending perpendicular to the propagation axis, the aspheric reflector reflecting light from different elevations so that the reflected light passes through the line at differing locations therealong and a twisted elongate mirror, arranged along the line which reflects the light passing through the line a various elevation angles as a planar flat beam which lies in a plane, which plane extends through the line and traverses a slit in the aspheric reflector.  
         [0044]     Preferably, the aspherical reflector includes strips of a spherical mirror whose centers are offset from each other along an axis lying in the engagement plane and extending perpendicular to the propagation axis.  
         [0045]     Preferably, the two-dimensional imaging sensor includes an angle-compensated interference filter.  
         [0046]     Further in accordance with a preferred embodiment of the present invention the angle-compensated interference filter includes a plurality of thin films, each being of non-uniform thickness, formed onto a dome shaped transparent substrate having an axis of symmetry.  
         [0047]     Preferably, the plurality of thin films have a thickness which is selected to vary such that the thickness of the plurality of thin films traversed by light beams impinging onto a given point located along the axis of symmetry is generally identical irrespective of the angular relationship between the light beam and the axis of symmetry.  
         [0048]     Additionally in accordance with a preferred embodiment of the present invention the data input device also includes an imaging lens located at the given point, which directs the light to the two-dimensional imaging sensor.  
         [0049]     Typically, the dome shaped transparent substrate is configured such that uniform evaporation of film material thereonto from a location spaced therefrom produces the plurality of thin films each being of non-uniform thickness which is selected to vary such that the thickness of the plurality of thin films traversed by light beams impinging onto a given point located along the axis of symmetry is generally identical irrespective of the angular relationship between the light beam and the axis of symmetry.  
         [0050]     Further in accordance with a preferred embodiment of the present invention the data entry processor is operative to map locations on the two-dimensional image sensor to data entry functions.  
         [0051]     Preferably, the data entry processor is operative to map received light intensity at the locations on the two-dimensional image sensor to the data entry functions.  
         [0052]     Further in accordance with a preferred embodiment of the present invention the data entry processor includes the following functionality: as each pixel value is acquired, determining, using the pixel coordinates, whether that pixel lies within a predefined keystroke region, acquiring pixel values for various pixel coordinates, adding or subtracting each pixel value to or from a pixel total maintained for each the keystroke region based on determining a pixel function of each pixel and comparing the pixel total for each the keystroke region with a current key actuation threshold. If the pixel total exceeds the key actuation threshold for a given keystroke region in a given frame and in the previous frame the pixel total did not exceed the key actuation threshold for that keystroke region, provide a key actuation output. Additionally or alternatively, if the pixel total does not exceed the key actuation threshold for a given keystroke region in a given frame and in the previous frame the pixel total did exceed the key actuation threshold for that keystroke region, provide a key deactuation output.  
         [0053]     Preferably, the data input device determines whether that pixel lies within a predefined keystroke region is made by employing a pixel index table which indicates for each pixel, whether that pixel lies within a predetermined keystroke region and, if so, within which keystroke region it lies.  
         [0054]     Further in accordance with a preferred embodiment of the present invention both determining steps employ the pixel index table.  
         [0055]     Preferably, the pixel total is maintained for each keystroke region in a keystroke region accumulator table.  
         [0056]     Preferably, the comparing step employs a keystroke region threshold table.  
         [0057]     Still further in accordance with a preferred embodiment of the present invention the data input device also includes the following functionality: once all of the pixels in a frame have been processed, determining an updated background level for a frame and determining a key actuation threshold for the keystroke region threshold table by subtracting the updated background level from a predetermined threshold level which is established for each keystroke region.  
         [0058]     Further in accordance with a preferred embodiment of the present invention the pixel function includes adding the pixel values of a plurality of pixels in the keystroke region.  
         [0059]     Additionally or alternatively, the pixel function includes adding the pixel values of the plurality of pixels in the keystroke region and subtracting therefrom pixel values of a plurality of pixels in a keystroke region border outside the keystroke region.  
         [0060]     Additionally or alternatively, the pixel function includes adding the pixel values of the plurality of pixels in the keystroke region, ignoring the pixel values of a plurality of pixels in a first keystroke region border outside the keystroke region and subtracting pixel values of a plurality of pixels in a second keystroke region border, outside the first keystroke region border.  
         [0061]     Further in accordance with a preferred embodiment of the present invention the data entry processor is operative to determine the “center of gravity” of pixel values of pixels in the two-dimensional image sensor.  
         [0062]     Still further in accordance with a preferred embodiment of the present invention the data entry processor includes the following functionality: as each pixel value is acquired, determining, using the pixel coordinates, whether that pixel lies within a predefined active region, acquiring pixel values for various pixel coordinates and determining the “center of gravity” of the pixel values.  
         [0063]     Preferably, the step of determining the “center of gravity” is achieved by: multiplying the pixel values by X and Y values representing the geographic position of each pixel, summing the results along mutually perpendicular axes X and Y, summing the total of the pixel values for all relevant pixels for the active region and dividing the summed results by the total of the pixel values to determine the X and Y coordinates of the “center of gravity”, which represents a desired engagement location.  
         [0064]     Typically, the pixel values are thresholded prior to summing thereof.  
         [0065]     Further in accordance with a preferred embodiment of the present invention the non-uniform intensity distribution varies over time.  
         [0066]     Preferably, the two-dimensional sensor operates to view different imaging fields at different times and wherein the operation of the illuminator is correlated with the operation of the two-dimensional image sensor, whereby the intensity of light produced by the illuminator varies in synchronization with an imaging field location of the two-dimensional image sensor.  
         [0067]     Preferably, the distance between the two-dimensional sensor and its the imaging field location increases, the intensity of light provided by the illuminator increases.  
         [0068]     Typically, the data input device also includes variable intensity drive electronics which is coupled to the illuminator and to the two-dimensional detector and which causes the intensity of light produced by the illuminator to vary in synchronization to the imaging field location of the two-dimensional detector.  
         [0069]     Still further in accordance with a preferred embodiment of the present invention the data input device also includes a digital signature generator receiving an input from the data entry processor including intensity, position and timing outputs and employs the outputs to provide a digital signature.  
         [0070]     There is also provided in accordance with a preferred embodiment of the present invention a data input device, which includes an illuminator operative to illuminate at least one engagement surface, a two-dimensional imaging sensor viewing the engagement surface from a location outside the engagement surface for sensing engagement of a data entry object with the engagement surface and a data entry processor receiving an output from the two-dimensional imaging sensor and providing a data entry input to utilization circuitry, the data entry processor employing shadow analysis.  
         [0071]     There is further provided in accordance with a preferred embodiment of the present invention a data input method, which includes illuminating at least one engagement surface, viewing the engagement surface with a two-dimensional image sensor from a location outside the engagement surface for sensing engagement of a data entry object with the engagement surface and processing an output from the two-dimensional imaging sensor and providing a data entry input to utilization circuitry, the data entry processor employing shadow analysis.  
         [0072]     Further in accordance with a preferred embodiment of the present invention the illuminator includes a non-point light source and the data entry processor employs a shadow density analyzer to determine the sharpness of edges of a shadow defined by the non-point light source and the data entry object on the engagement surface, which indicates the propinquity of the data entry object to the projection surface.  
         [0073]     Additionally or alternatively, the illuminator includes a plurality of light sources and the data entry processor employs a shadow coalescence analyzer to determine the extent of coalescence of shadows defined by the plurality of light sources and data entry object on the engagement surface, which indicates the propinquity of the data entry object to the projection surface.  
         [0074]     Preferably, the data entry processor includes the following functionality: as each pixel value is acquired, determining, using the pixel coordinates, whether that pixel lies within a predefined keystroke region and within predefined left and right keystroke subregions therewithin, acquiring pixel values for various pixel coordinates, obtaining the derivative of each pixel value along an X axis, summing the derivatives for each the subregion, one from the other to provide a difference and comparing the difference with a current key actuation threshold. If the difference exceeds the key actuation threshold for a given keystroke region in a given frame and in the previous frame the pixel total did not exceed the key actuation threshold for that keystroke region, provide a key actuation output. Additionally or alternatively, if the difference does not exceed the key actuation threshold for a given keystroke region in a given frame and in the previous frame the pixel total did exceed the key actuation threshold for that keystroke region, provide a key deactuation output.  
         [0075]     Preferably, the step of determining employs a pixel index table, which indicates for each pixel, whether that pixel lies within a predetermined keystroke region and, if so, within which keystroke region as well as within which keystroke subregion it lies.  
         [0076]     Typically, the pixel total is maintained for each keystroke subregion in a keystroke subregion accumulator table.  
         [0077]     Still further in accordance with a preferred embodiment of the present invention the step of comparing employs a keystroke region threshold table.  
         [0078]     Additionally in accordance with a preferred embodiment of the present invention the engagement plane is associated with a pull-down tray in a vehicle wherein the pull-down tray defines an engagement surface which is configured by projection.  
         [0079]     Further in accordance with a preferred embodiment of the present invention the two-dimensional detector and illuminator are associated with a camera.  
         [0080]     Still further in accordance with a preferred embodiment of the present invention the two-dimensional detector and illuminator are associated with a home entertainment system.  
         [0081]     Additionally in accordance with a preferred embodiment of the present invention the engagement plane overlies a television screen forming part of the home entertainment system.  
         [0082]     Further in accordance with a preferred embodiment of the present invention the engagement plane is associated with a table.  
         [0083]     Still further in accordance with a preferred embodiment of the present invention the engagement plane is associated with a remote control device.  
         [0084]     Additionally in accordance with a preferred embodiment of the present invention the engagement plane is located within a restricted particulate manner environment.  
         [0085]     Further in accordance with a preferred embodiment of the present invention the engagement plane is located within an industrial environment unsuitable for a conventional keyboard.  
         [0086]     Preferably, the two-dimensional detector and illuminator are associated with a video projector.  
         [0087]     Still further in accordance with a preferred embodiment of the present invention the two-dimensional detector and illuminator are associated with a restaurant patron interface system.  
         [0088]     Additionally in accordance with a preferred embodiment of the present invention the two-dimensional detector and illuminator are associated with a mobile audio player.  
         [0089]     Further in accordance with a preferred embodiment of the present invention the two-dimensional detector and illuminator provide touch screen functionality.  
         [0090]     Preferably, the touch screen functionality employs a video display screen.  
         [0091]     Still further in accordance with a preferred embodiment of the present invention the two-dimensional detector and illuminator provide access control functionality.  
         [0092]     Preferably, the engagement plane is associated with a game board and wherein the game board defines an engagement surface, which is configured by projection.  
         [0093]     Additionally in accordance with a preferred embodiment of the present invention the engagement plane is associated with a musical instrument and wherein the musical instrument defines an engagement surface, which is configured by projection.  
         [0094]     Further in accordance with a preferred embodiment of the present invention the two-dimensional detector and illuminator provide vehicle telematics functionality. Preferably, the vehicle defines an engagement surface, which is configured by projection.  
         [0095]     Still further in accordance with a preferred embodiment of the present invention the two-dimensional detector and illuminator provide automatic vending user interface functionality.  
         [0096]     There is further provided in accordance with another preferred embodiment of the present invention an angle-compensated interference filter which includes a plurality of thin films, each being of non-uniform thickness, formed onto a dome shaped transparent substrate having an axis of symmetry. The plurality of thin films have a thickness, which is selected to vary, such that the thickness of the plurality of thin films traversed by light beams impinging onto a given point located along the axis of symmetry is generally identical irrespective of the angular relationship between the light beam and the axis of symmetry.  
         [0097]     There is also provided in accordance with a further preferred embodiment of the present invention a method for filtering light employing an angle-compensated interference filter, which includes a plurality of thin films, each being of non-uniform thickness, formed onto a dome shaped transparent substrate having an axis of symmetry. The plurality of thin films have a thickness which is selected to vary such that the thickness of the plurality of thin films traversed by light beams impinging onto a given point located along the axis of symmetry is generally identical irrespective of the angular relationship between the light beam and the axis of symmetry.  
         [0098]     Further in accordance with a preferred embodiment of the present invention the dome shaped transparent substrate is configured such that evaporation of film material thereonto from a location spaced therefrom produces the plurality of thin films each being of non-uniform thickness. The non-uniform thickness is selected to vary such that the thickness of the plurality of thin films traversed by light beams impinging onto a given point located along the axis of symmetry is generally identical irrespective of the angular relationship between the light beam and the axis of symmetry.  
         [0099]     Preferably, the step of evaporation is performed in a uniform matter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0100]     The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:  
         [0101]      FIG. 1  is a simplified and generalized illustration of a projection keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0102]      FIG. 2  is a simplified illustration of a keyboard projection subsystem employing a diffractive optical element and having optical power, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0103]      FIGS. 3A and 3B  are respective simplified pictorial and top view illustrations of a keyboard projection subsystem employing an integrally formed beam splitter and diffractive optical elements, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0104]      FIG. 4  is a simplified illustration of a multiple format keyboard projection subsystem employing a plurality of different diffractive optical elements which are selectably positionable along a keyboard projection light path, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0105]      FIGS. 5A and 5B  are respective simplified pictorial and side view illustrations of a keyboard projection subsystem employing a diffractive optical element having diffraction orders selected to provide a keyboard configuration which has a relatively low maximum diffraction angle, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0106]      FIGS. 6A and 6B  are respective simplified pictorial and top view illustrations of a keyboard projection subsystem employing a beam combiner, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0107]      FIG. 7  is a simplified illustration of a keyboard projection subsystem employing an array of light emitting elements and microlenses, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0108]      FIG. 8  is a simplified illustration of a keyboard projection subsystem employing specially configured light emitting elements, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0109]      FIGS. 9A and 9B  are respective pictorial and side view illustrations of a data entry object engagement location sensing subsystem employing a camera located on the opposite side of a transparent data entry object engagement surface from a data entry object engagement location sensing illuminator, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0110]      FIGS. 10A and 10B  are respective pictorial and side view simplified illustrations of a data entry object engagement location sensing subsystem employing a transparent data entry object engagement surface exhibiting total internal reflection, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0111]      FIGS. 11A and 11B  are simplified illustrations of a data entry object engagement location sensing subsystem employing shadow sharpness analysis, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0112]      FIGS. 12A and 12B  are simplified illustrations of a data entry object engagement locations sensing subsystem employing shadow coalescence sensing, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0113]      FIGS. 13A and 13B  are simplified illustrations of a data entry object engagement location sensing subsystem having a 360 degree detection range, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0114]      FIG. 14A  is a simplified illustration of an illumination subsystem including an illuminator which provides desired non-uniform illumination intensity and employing an aspheric element, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0115]      FIG. 14B  is a simplified illustration of an illumination subsystem including an illuminator which provides desired non-uniform illumination intensity and employing a diffractive element, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0116]      FIG. 14C  is a simplified illustration of an illumination subsystem including an illuminator which provides desired non-uniform illumination intensity and employing a combination of cylindrical lenses, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0117]      FIGS. 15A and 15B  are respective simplified pictorial and side view illustrations of a data entry object engagement location sensing subsystem including a data entry object engagement speed sensor having plural illumination and detection planes and employing plural illuminators and sensors, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0118]      FIGS. 16A and 16B  are respective simplified pictorial and sectional illustrations of a data entry object engagement location sensing subsystem including a data entry object engagement speed sensor having plural illumination and detection planes and employing plural illuminators and sensors, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0119]      FIGS. 17A and 17B  are respective simplified pictorial and sectional illustrations of a data entry object engagement location sensing subsystem including a data entry object engagement speed sensor having plural illumination and detection planes and employing a single illuminator and a single sensor, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0120]      FIG. 18  is a simplified illustration of an illuminator useful in a data entry object engagement location sensing subsystem and employing aspheric reflectors, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0121]      FIG. 19  is a simplified illustration of a angle-compensated interference filter employed in data entry object engagement location sensing subsystem, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0122]      FIG. 20  is a simplified flow chart illustrating operation of a data entry object engagement location sensing subsystem employed in the projection keyboard system and methodology of  FIG. 1  in accordance with a preferred embodiment of the present invention;  
         [0123]      FIG. 21  is a simplified illustration of a preferred data structure employed in the operation of the data entry object engagement location sensing subsystem shown in  FIG. 20 ;  
         [0124]      FIG. 22  is a simplified pictorial illustration of outlines of typical keystroke regions as senses by a two-dimensional image sensor viewing a keyboard, such as the keyboard seen in  FIG. 5A ;  
         [0125]      FIG. 23  is a simplified pictorial illustration of outlines of typical footprints of a typical light pattern occasioned by data entry object engagement with several keystroke regions, such as those shown in  FIG. 22 ;  
         [0126]      FIGS. 24A, 24B  and  24 C are simplified illustrations of three alternative methodologies for determining the function of the pixel within the keystroke region in which it lies as shown in  FIG. 21 ;  
         [0127]      FIGS. 25A, 25B  and  25 C are simplified illustrations of traces which are useful in understanding  FIGS. 24A, 24B  and  24 C;  
         [0128]      FIG. 26  is a simplified flow chart illustrating operation of a data entry object engagement location sensing subsystem employed in a tracking system and methodology constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0129]      FIG. 27  is a simplified flowchart illustrating operation of functionality providing shadow sharpness analysis in accordance with a preferred embodiment of the present invention;  
         [0130]      FIG. 28  is a simplified illustration of a preferred data structure employed in the operation of the data entry object engagement location sensing subsystem shown in  FIG. 27 ;  
         [0131]      FIG. 29  is an illustration which is useful in understanding the flowchart of  FIG. 27 ;  
         [0132]      FIG. 30  is a simplified illustration showing synchronized illumination power variation functionality useful in accordance with a preferred embodiment of the present invention;  
         [0133]      FIG. 31  is a simplified illustration of a system and functionality for providing a digital signature in accordance with a preferred embodiment of the present invention;  
         [0134]      FIG. 32  is a simplified illustration of a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention and employing sensing of a data entry object interaction with an inert keyboard defined on a pull-down tray;  
         [0135]      FIG. 33  is a simplified illustration of a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention and providing alphanumeric annotation of photographs using a suitably equipped camera;  
         [0136]      FIGS. 34A, 34B ,  34 C and  34 D are simplified illustrations of four alternative embodiments of a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention and providing control, by data entry object interaction, of a home entertainment system;  
         [0137]      FIG. 35  is a simplified illustration of a restricted particulate matter environment keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0138]      FIG. 36  is a simplified illustration of a industrial environment keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0139]      FIG. 37  is a simplified illustration of a video projector having integrally formed or associated therewith a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0140]      FIG. 38  is a simplified illustration of a restaurant patron interface system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0141]      FIG. 39  is a simplified illustration of a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0142]      FIGS. 40A and 40B  are simplified illustrations of a data entry object engagement sensing screen system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0143]      FIG. 41  is a simplified illustration of a security and access control system employing data entry object engagement sensing methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0144]      FIG. 42  is a simplified illustration of a object engagement sensing game system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0145]      FIGS. 43A, 43B  and  43 C are simplified illustrations of a data entry object engagement sensing musical instrument and methodology, constructed and operative in accordance with a preferred embodiment of the present invention;  
         [0146]      FIG. 44  is a simplified illustration of a vehicle mounted user interface system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention; and  
         [0147]      FIG. 45  is a simplified illustration of a vending machine incorporating a data entry object engagement detection system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0148]     Reference is now made in  FIG. 1 , which is a simplified and generalized illustration of a projection keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention. A projection subsystem  100 , preferably including a solid state light source (not shown) which illuminates a spatial light modulation element (not shown), defines an image  102  of a keyboard on a projection surface  104 , preferably an inert surface, such as a desktop.  
         [0149]     An illumination subsystem  106 , preferably including a solid state light source (not shown), direct light in a radially directed illumination pattern  108 , which preferably extends in a plane generally parallel to the projection-surface  104 . It is appreciated that the radially directed illumination pattern  108  has a very narrow spread in the direction generally perpendicular to the projection surface  104 . It is further appreciated that the radially directed illumination pattern  108  is preferably located very close to the projection surface  104 .  
         [0150]     Impingement of light in the radially directed illumination pattern  108  on a data entry object  110 , such as a user&#39;s finger, a stylus or other use implement, causes light to be scattered or reflected therefrom. It is appreciated that the light is only scattered or reflected when the data entry object  110  is in close contact with the keyboard  102  defined on projections surface  104 .  
         [0151]     A detection subsystem  112 , preferably employing a solid state imaging sensor (not shown), receives light reflected or scattered from data entry object  110 . The received light is mapped onto the imaging sensor with respect to a representation of the keyboard for associating the location of the data entry object  110  sensed by detection subsystem  112  with a key location  113  on the keyboard  102 . Thus the sensed location of data entry object  110  indicates which key of the keyboard  102  is being engaged.  
         [0152]     Reference is now made to  FIG. 2 , which is a simplified illustration of a preferred embodiment of a keyboard projection subsystem  100  ( FIG. 1 ) employing a diffractive optical element  120  which receives light from a light source  122 , such as a diode laser, via a collimating lens  124 . Light passing through the diffractive optical element  120  preferably is reflected by a curved mirror  126  having optical power, optionally via a lens  128  onto projection surface  104  ( FIG. 1 ), preferably defining a keyboard  102  ( FIG. 1 ).  
         [0153]     In accordance with a preferred embodiment of the present invention, the diffractive optical element  120 , the mirror  126  and optionally the lens  128  are all integrally formed in a suitably configured prism  130 , as by embossing.  
         [0154]     The configuration of  FIG. 2  is preferred in order to enable a diffractive optical element having a relatively small maximum diffraction angle to be used. The mirror  126 , having optical power spreads the light passing through the diffractive optical element  120  to a sufficient degree to enable projection of a full sized keyboard  102  on projection surface  104 , even when projection surface  104  is relatively close to the diffractive optical element  120 . Alternatively, the prism  103  and the mirror  126  may be replaced by one or more lenses.  
         [0155]     Reference is now made to  FIGS. 3A and 3B , which are respective simplified pictorial and top view illustrations of the keyboard projection subsystem  100  ( FIG. 1 ) employing an integrally formed beam splitter and diffractive optical elements, constructed and operative in accordance with a preferred embodiment. This embodiment employs a beam splitter  140  preferably integrally formed with plural diffractive optical elements  142 . A beam of light from a light source  144 , such as a diode laser, preferably passes through a collimating lens  146  and impinges on two mutually angles surfaces  148  of beam splitter  140 . The beam splitter  140  breaks the beam of light into two beams, each of which passes through a separate diffractive optical element  142 . Light passing through both diffractive optical elements  142  impinges on projection surface  104  ( FIG. 1 ), preferably defining a keyboard  102  ( FIG. 1 ).  
         [0156]     In accordance with a preferred embodiment of the present invention, the diffractive optical elements  142  are integrally formed with the beam splitter  140  in a suitably configured prism, as by embossing.  
         [0157]     The configuration of  FIGS. 3A and 3B  is preferred in order to enable a pair of diffractive optical elements, each having a relatively small maximum diffraction angle, to be used in combination together to define a full sized keyboard  102  on projection surface  104 , even when projection surface  104  is relatively close to the diffractive optical element  120 . An added advantage of using plural diffractive optical elements is an increase in resolution, inasmuch as each diffractive optical element defines only part of the image projected onto projection surface  104 . Preferably, the beam splitter  140  is configured such that the tow beams each impinge perpendicularly onto a corresponding diffractive optical element  142 .  
         [0158]     Reference is now made to  FIG. 4 , which is a simplified illustration of a preferred multiple format embodiment of keyboard projection subsystem  100  ( FIG. 1 ). This embodiment employs a plurality of different diffractive optical elements  160 , each of which typically corresponds to a different keyboard configuration. The optical elements  160  are preferably mounted onto a rotatable support  162  in order to be selectably positionable along a keyboard projection light path  164  extending from a light source  166 , such as a diode laser, preferably through a collimating lens  168  and preferably impinging on a mirror  170 , which directs light passing therealong onto projection surface  104  ( FIG. 1 ), preferably defining a keyboard  102  ( FIG. 1 ).  
         [0159]     Reference is now made to  FIGS. 5A and 5B , which are simplified illustrations of a keyboard projection subsystem employing a diffractive optical element  180  having a multiplicity of diffraction orders  182  selected to provide a keyboard configuration which has a relatively low maximum diffraction angle  184 . Angle  184  is preferably in excess of 90 degrees and is typically between 60 degrees and 120 degrees.  
         [0160]     As seen in  FIG. 5A , light from a light source  186  passing through a collimating lens  188  and thence through the diffractive optical element  180  preferably falls onto a projection surface  104  ( FIG. 1 ), preferably defining a generally trapezoidal shaped keyboard  190 , which is configured in accordance with a preferred embodiment of the present invention.  
         [0161]     The diffraction orders  182  of the diffractive optical element  180  are calculated and selected to compensate for geometrical distortions inherent in the operation of a diffractive optical element, such as element  180 , particularly at high diffraction angles, such as angle  184 . To this end, the individual diffraction orders  182  are preferably arranged in rows  194  which extend obliquely with respect to lines  196  defined thereby.  
         [0162]     Additionally, the diffraction orders  182  are calculated and selected in order to compensate for geometric distortions occasioned by a highly oblique angle of projection, such as angle  192 , seen in  FIG. 5B . To this end the diffraction orders are arranged as shown in  FIG. 5A , to have a barrel-like distortion and to have a non-uniform outwardly increasing spacing between lines which are sought to appear parallel on keyboard  190 . Angle  192  is preferably less than less than 30 degrees and is typically between 20 degrees and 90 degrees.  
         [0163]     Reference is now made to  FIGS. 6A and 6B , which are simplified illustrations of a keyboard projection subsystem employing a beam combiner  200 . As seen in  FIGS. 6A and 6B , light from a pair of point light sources  202  and  204  is combined by beam combiner  200 , such that two light beams  206  and  208  emerge from the beam combiner  200  and appear to originate in a single virtual light source  210  positioned behind beam combiner  200 . In actuality the two light beams  206  and  208  nearly overlap, but may define a no-light beam region  212  therebetween.  
         [0164]     The light beams  206  and  208  pass through a shadow mask  214  onto projection surface  104  ( FIG. 1 ), preferably defining a keyboard  102  ( FIG. 1 ).  
         [0165]     The embodiment of  FIGS. 6A and 6B  has an advantage in that it may employ multiple relatively low power and low cost laser diodes to provide the same power as would be provided by a single much more expensive laser diode.  
         [0166]     Reference is now made to  FIG. 7 , which is a simplified illustration of a keyboard projection subsystem employing an array  230  of light emitting elements  232  and microlenses  234 . As seen in  FIG. 7 , light from multiple point light emitting elements  232 , such as LEDs, is imaged by corresponding multiple microlenses  234  onto projection surface  104  ( FIG. 1 ), preferably defining a portion of keyboard  102  ( FIG. 1 ), such as the letter “E”. It is appreciated that each of light emitting elements  232  is individually controllable in order to provide a correspondingly individual light spot  236  on projection surface  104 . The collection of light spots  236  makes up the keyboard  102  ( FIG. 1 ). The embodiment of  FIG. 7  provides a selectable and changeable keyboard.  
         [0167]     Reference is now made to  FIG. 8 , which is a simplified illustration of a keyboard projection subsystem employing specially configured light emitting elements, preferably a monolithic pattern  250  of LEDs formed on a unitary substrate  252 .  
         [0168]     As seen in  FIG. 8 , light from the pattern  250  is imaged by a lens  254  onto projection surface  104  ( FIG. 1 ), preferably defining keyboard  102  ( FIG. 1 ). This arrangement has the advantage of electrical efficiency and low unit cost but does not provide a variable keyboard configuration.  
         [0169]     Reference is now made to  FIGS. 9A and 9B , which are respective pictorial and side view illustrations of a data entry object engagement location sensing subsystem employing a camera  270  located on the opposite side of a transparent data entry object engagement surface  272  from a data entry object engagement location sensing illuminator  274 . A generally flat planar beam of light, designated by reference numeral  276 , is preferably emitted by illuminator  274  generally parallel to and spaced from data entry object engagement surface  272 . As seen particularly in  FIG. 9B , the presence of an object, such as a data entry object  278  in beam  276 , causes light from beam  276  to be scattered into a scattered beam  280  and inter alia to pass through transparent data entry object engagement surface  272  so as to be detected by camera  270 , which preferably forms part of detection subsystem  112  ( FIG. 1 ).  
         [0170]     Reference is now made to  FIGS. 10A and 10B , which are respective pictorial and side view simplified illustrations of a data entry object engagement location sensing subsystem employing a transparent data entry object engagement surface  290 , exhibiting total internal reflection. A planar beam of light, designated by reference numeral  292 , is emitted by an illuminator  294  and coupled to an edge  295  of surface  290  through which beam  292  passes by total internal reflection. As seen particularly in  FIG. 10B , the presence of an object, such as a data entry object  296  in contact with surface  290 , causes light from bean  292  to be scattered into a scattered beam  297  due to frustrated total internal reflection and inter alia to pass through transparent data entry object engagement surface  290  so as to be detected by a camera  298 , which preferably forms part of detection subsystem  112  ( FIG. 1 ).  
         [0171]     Reference is now made to  FIGS. 11A and 11B , which are a simplified illustration of a data entry object engagement location sensing subsystem, forming part of detection subsystem  112  ( FIG. 1 ) and employing shadow sharpness analysis, constructed and operative in accordance with a preferred embodiment of the present invention. An object, such as a data entry object  300 , casts a shadow  302  on a projection surface  104  ( FIG. 1 ) when illuminated by a light source  304 . A camera  306  senses the shadow and a shadow density analyzer  308 , determines the optical density of the shadow, which indicates the propinquity of the data entry object  300  to projection surface  104 .  
         [0172]     Reference is now made to  FIGS. 12A and 12B , which are simplified illustrations of a data entry object engagement location sensing subsystem forming part of detection subsystem  112  ( FIG. 1 ) and employing shadow coalescence sensing. An object, such as a data entry object  320 , casts shadows  322  and  324  on a projection surface  104  ( FIG. 1 ) when illuminated by a pair of infrared point light sources  326  and  328 , such as LEDs. A camera  330  senses the shadows  322  and  324  and a shadow coalescence sensor  332  determines the extent of overlap or the separation between the shadows  322  and  324 , which indicates the propinquity of the data entry object  320  to projection surface  104 .  
         [0173]     Reference is now made to  FIGS. 13A and 13B , which are simplified illustrations of a data entry object engagement location sensing subsystem  340  having a 360 degree annular detection range  342 . The data entry object engagement location sensing subsystem  340  of  FIG. 13  preferably includes an illuminator  344 , such as a diode laser, providing an generally conical output beam  346  which impinges on a generally conical mirror  348 , which provides via an annular window  350 , a generally planar, radially directed illumination beam  351 , generally parallel to the projection surface  104  ( FIG. 1 ), such as a table top  352 . A camera  354  views a generally annular range  342  defined between virtual circles  356  and  358  on table top  352  and senses light scattered by objects, such as data entry object tips  360 . Preferably, the scattered light is received by camera  354  via a conical mirror  362  and via an annular window  364 .  
         [0174]     Reference is now made to  FIG. 14A , which is a simplified illustration of an illumination subsystem  106  ( FIG. 1 ) including an illuminator  370 , preferably including a diode laser light source  372 , a collimating lens  374  and an aspheric element  376 , such as an aspheric cylindrical lens, receiving light from the light source  372  via the collimating lens  374 . The aspheric element  376  preferably directs light in a radially directed illumination pattern  378 , which preferably extends in a plane generally parallel to the projection surface  104  ( FIG. 1 ). It is appreciated that the radially directed illumination pattern  378  has a very narrow spread in the direction generally perpendicular to the projection surface  104 . It is further appreciated that the radially directed illumination pattern  378  is preferably located very close to the projection surface  104 .  
         [0175]     The illumination subsystem of  FIG. 14A  provides the desired spatially non-uniform illumination intensity pattern  378 , wherein the intensity varies as a function of the illumination angle  379 , as seen for example, at graph  380 . It is noted that greater illumination intensity is provided at large illumination angles in order to compensate for the non-uniform detection effects at the large viewing angles. These non-uniform detection effects include the reduction of the effective angular cross-section of the data entry object  110  ( FIG. 1 ) and the reduced light collection efficiency of the lens on the camera in the detection subsystem  112  ( FIG. 1 ).  
         [0176]     Reference is now made to  FIG. 14B , which is a simplified illustration of the illumination subsystem  106  ( FIG. 1 ) including an illuminator  390 , preferably including a diode laser light source  392 , a collimating lens  394  and an diffractive optical element  396 , receiving light from the light source  392  via the collimating lens  394 . The diffractive optical element  396  preferably directs light in a radially directed illumination pattern  398 , which preferably extends in a plane generally parallel to the projection surface  104  ( FIG. 1 ). It is appreciated that the radially directed illumination pattern  398  has a very narrow spread in the direction generally perpendicular to the projection surface  104 . It is further appreciated that the radially directed illumination pattern  398  is preferably located very close to the projection surface  104 .  
         [0177]     The illumination subsystem of  FIG. 14B  provides the desired spatially non-uniform illumination intensity pattern  398 , wherein the intensity varies as a function of the illumination angle  399 , as seen for example, at graph  400 . It is noted that greater illumination intensity is provided at large illumination angles in order to compensate for the non-uniform detection effects at the large viewing angles. These non-uniform detection effects include the reduction of the effective angular cross-section of the data entry object  110  ( FIG. 1 ) and the reduced light collection efficiency of the lens on the camera in the detection subsystem  112  ( FIG. 1 ).  
         [0178]     Reference is now made to  FIG. 14C , which is a simplified illustration of the illumination subsystem  106  ( FIG. 1 ) including an illuminator  410 , preferably including a diode laser light source  412 , a collimating lens  414  and a joined double side-truncated rod lens optical element  416 , receiving light from the light source  412  via the collimated lens  414 . The optical element  416  preferably directs light in a radially directed illumination pattern  418 , which preferably extends in a plane generally parallel to the projection surface  104  ( FIG. 1 ). It is appreciated that the radially directed illumination patter  418  has a very narrow spread in the direction generally perpendicular to the projection surface  104 . It is further appreciated that the radially directed illumination pattern  418  is preferably located very close to the projection surface  104 .  
         [0179]     The illumination subsystem of  FIG. 14C  provides the desired spatially non-uniform illumination intensity pattern  418 , wherein the intensity varies as a function of the illumination angle  419 , as seen for example, at graph  420 . It is noted that greater illumination intensity is provided at large illumination angles in order to compensate for the non-uniform detection effects at the large viewing angles. These non-uniform detection effects include the reduction of the effective angular cross-section of the data entry object  110  ( FIG. 1 ) and the reduced light collection efficiency of the lens on the camera in the detection subsystem  112  ( FIG. 1 ).  
         [0180]     The precise illumination distribution may be selected by suitable variation of the radii R of the side-truncated rod lenses  422  and  424  and the extent X of their mutual side truncation.  
         [0181]     Reference is now made to  FIGS. 15A and 15B , which are respective simplified pictorial and sectional illustrations of a data entry object engagement location sensing subsystem including a data entry object engagement speed sensor having plural illumination and detection planes and employing plural illuminators and sensors, constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0182]     As seen in  FIGS. 15A and 15B , first and second generally flat mutually spaced and overlying planar beams of light of differing wavelengths, designated respectively by reference numeral  430  and  432 , are preferably emitted by respective illuminators  434  and  436  generally parallel to and spaced from a data entry object engagement surface  438 . As seen particularly in  FIG. 15B , the presence of an object, such as a data entry object  440  in beams  430  and  432 , causes light from the respective beams to be scattered into scattered beams  439  and  441  and to be detected by respective cameras  442  and  444 , which have detection wavelengths corresponding to those of beams  430  and  432  respectively. The cameras may be equipped with suitable filters  446  and  448  for this purpose. Illuminators  434  and  436  form part of illumination subsystem  106  ( FIG. 1 ) while cameras  442  and  444  form part of detection subsystem  112  ( FIG. 1 ).  
         [0183]     The data entry object engagement location sensing subsystem of  FIGS. 15A and 15B  also includes a timing analyzer  450 , which receives outputs from cameras  442  and  444  and determines from the timing thereof, the speed of engagement of the data entry object with data entry object engagement surface  438 . The speed of engagement of the data entry object with data entry object engagement surface  438  may be employed in various applications, such as musical instruments and games.  
         [0184]     Reference is now made to  FIGS. 16A and 16B , which are respective simplified pictorial and sectional illustrations of a data entry object engagement location sensing subsystem including a data entry object engagement speed sensor having plural illumination and detection planes and employing plural illuminators and a single sensor, constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0185]     As seen in  FIGS. 16A and 16B , first and second generally flat planar mutually spaced and overlying beams of light of differing wavelengths, designated respectively by reference numeral  460  and  462 , are preferably emitted by respective illuminators  464  and  466  generally parallel to and spaced from a data entry object engagement surface  468 . As seen particularly in  FIG. 16B , the presence of an object, such as a data entry object  470  in beams  460  and  462 , causes light from the respective beams to be scattered and to be detected by a camera  472 , having first and second detection regions  474  and  476 , which have detection wavelengths corresponding to those of beams  460  and  462  respectively. The detection regions of camera  472  are preferably defined by suitable filters to provide desired wavelength differentiation. Illuminators  464  and  466  form part of illumination subsystem  106  ( FIG. 1 ) while, camera  472  forms part of detection subsystem  112  ( FIG. 1 ).  
         [0186]     Light scattered by data entry object  470  from beams  460  and  462  is preferably refracted by a prism  478  and split into two beams  480  and  482  which are imaged by a lens  484  onto the two detection regions  474  and  476 .  
         [0187]     The data entry object engagement location sensing subsystem of  FIGS. 16A and 16B  also includes a timing analyzer  486 , which receives outputs from camera  472  and determines from the timing thereof, the speed of engagement of the data entry object  470  with data entry object engagement surface  468 . The speed of engagement of the data entry object with data entry object engagement surface  468  may be employed in various applications, such as musical instruments and games.  
         [0188]     Reference is now made to  FIGS. 17A and 17B , which are respective simplified pictorial and sectional illustrations of a data entry object engagement location sensing subsystem including a data entry object engagement speed sensor having plural illumination and detection planes and employing a single illuminator and a single sensor, constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0189]     As seen in  FIGS. 17A and 17B , first and second generally flat mutually spaced and overlying planar beams of light, designated respectively by reference numeral  500  and  502 , are preferably emitted by an illuminator  504  which outputs via a beam splitter  506  and a mirror  508 . Beams  500  and  502  are generally parallel to and spaced from a data entry object engagement surface  510 . As seen particularly in  FIG. 17B , the presence of an object, such as a data entry object  512  in beams  500  and  502 , causes light from the respective beams to be scattered and to be imaged by a lens  514  into a camera  516 . Illuminator  504  forms part of illumination subsystem  106  ( FIG. 1 ) while camera  516  forms part of detection subsystem  112  ( FIG. 1 ).  
         [0190]     The data entry object engagement location sensing subsystem of  FIGS. 17A and 17B  also includes an intensity timing analyzer  518 , which receives an output from cameras  516  and determines from the timing of a stepwise increase in detected light intensity thereat, the speed of engagement of the data entry object with data entry object engagement surface  510 . The speed of engagement of the data entry object with data entry object engagement surface  510  may be employed in various applications, such as musical instruments and games.  
         [0191]     Reference is now made to  FIG. 18 , which is a simplified illustration of an illuminator useful in a data entry object engagement location sensing subsystem and employing aspheric reflectors, constructed and operative in accordance with a preferred embodiment of the present invention. It is appreciated that the illuminator of  FIG. 18  of the present invention directs light, which is emitted from a point source through a large solid angle, into a flat radially directed beam extending along an engagement plane. The beam has a very narrow spread in a direction perpendicular to the projection surface  104  ( FIG. 1 ).  
         [0192]     As seen in  FIG. 18 , a point light source  550 , such as an LED, emits light through a generally semi-hemispherical volume denoted by reference numeral  552 . An aspheric reflector, strips of which are designated by reference numerals  554 ,  556  and  558 , reflects the light emitted by the point light source  550  along a line  560 , which typically passes through the light source  550 . In a preferred embodiment of the present invention, the aspherical reflector may be constructed from strips of a spherical mirror whose centers have been offset from each other along the line  560 . The aspheric reflector thus reflects light from different elevations so that the reflected light passes through line  560  at differing locations therealong.  
         [0193]     A twisted elongate mirror  562 , preferably arranged along line  560 , reflects the light passing through line  560  at various elevation angles as a planar flat beam, denoted by reference numeral  564 . Beam  564  typically lies in a plane, which extends through line  560  and traverses a slit, not shown, appropriately positioned in the aspheric reflector.  
         [0194]     Reference is now mad to  FIG. 19 , which is a simplified illustration of an angle-compensated interference filter employed in a data entry object engagement location sensing subsystem, constructed and operative in accordance with a preferred embodiment of the present invention. The filter of  FIG. 19  is useful in the present invention, for example as filter  446  and  448  in  FIGS. 15A and 15B  and filters  474  and  476  in  FIGS. 16A and 16B .  
         [0195]     As seen in  FIG. 19 , in an exaggerated form which is not drawn to scale for the purposes of clarity, a plurality of thin films, collectively designated by reference numeral  580 , each being of non-uniform thickness are formed onto a dome shaped curved transparent substrate  582 , which need not be spherical, to define an interference filter. The thickness of the thin films  580  is selected to vary over the substrate  582  such that the thickness of the thin films  580  traversed by every light beam impinging onto a given point  584  located along an axis of symmetry  586  of substrate  582  is identical irrespective of the angular relationship between the light beam and the axis of symmetry  586  (OA in  FIG. 19 ). The imaging lens of a camera, such as camera  516  ( FIG. 17A ), is located at point  584 .  
         [0196]     Therefore, the intensity of the light beam reaching the camera  516  is independent of the location of the keystroke, which is being engaged by data entry object  512 .  
         [0197]     A preferred technique for the construction of the interference filter of  FIG. 19 , by using methods, such as film evaporation, is set forth hereinbelow with reference to  FIG. 19 .  
         [0198]     According to Snell&#39;s Law:
 
Sin (α)= n ·Sin (α 1 )  (1)
 
 where α is the local incidence angle at the filter&#39;s surface of a ray that will eventually reach point O, α 1  is the local effective refraction angle at the filter&#39;s surface and n is the effective refractive index of the filter coating 
 
         [0199]     Typically, in a first approximation, the optical axis of the dome shaped substrate  582  is in the direction of the evaporated material, which is preferably used for manufacturing the interference filter. Additionally, in a first approximation, the flow of evaporated material on the dome is in a direction, which is typically perpendicular to the small region of the dome to which the material is being applied.  
         [0200]     Thus, from mass conservation of the coating process, the thickness of the filter material in a direction θ, is given by:
 
 t (θ)= t ·cos (θ)  (2)
 
 Thus, the length of a refracted ray, through the filter  582 , is given by:
 
 d (θ)= t (74)/Cos (α 1 ),
 
 where θ is the deflection angle between the normal to the filter at the point of incidence and the axis of symmetry  586  and t(θ) is the local thickness of the filter. 
 
         [0201]     If the thickness of the filter is equal in all directions (eqi-filtering), then
 
 d (θ)= t 
 
 and
 
Cos (θ)=Cos (α 1 ) or θ=α 1   (3)
 
 where d(θ) is the local path distance in the filter along the refracted ray. 
 
         [0202]     Therefore, equation (1) becomes:
 
Sin (α)= n ·Sin (θ)  (4)
 
 Using know trignometrical relationships, equation (1) may be written as:
 
Cos (α)=√{square root over (1−π·Sin 2 (θ))}  (5)
 
 As is known in the art, there are typically an infinite number of solutions, to equation (5), for the geometry of the dome  582 . Preferably, one solution may be for the case for a typical light ray hitting the dome at angle α and defining a certain point P. The distance along the optical axis from point P to the dome is given by R(θ). 
 
         [0203]     According to the Sine Rule:  
                     R   ⁡     (   θ   )       -   X       R   ⁡     (   θ   )         =       Sin   ⁢           ⁢     (   α   )         Sin   ⁢           ⁢     (     α   +   θ     )           ⁢     
     ⁢   and           (   6   )                   r   ⁡     (   θ   )         Sin   ⁢           ⁢     (   θ   )         =       R   ⁡     (   θ   )         Sin   ⁢           ⁢     (     α   +   θ     )                 (   7   )             
 
 where R(θ) is the distance along the local normal to the filter between the filter and point P; 
    φ(θ) is the local deflection angle, such that φ=α+θ;     X is a distance between the point  584  and the filter  582  in the direction of OA;     r(θ) is the distance between point  584  and the local incidence point on the filter  582 ;    
 
         [0207]     After substituting: equations (4) and (5) into equations (6) and (7), the following relationship may be obtained:  
                     R   ⁡     (   θ   )       -   X       R   ⁡     (   θ   )         =       1       Cos   ⁡     (   θ   )       +       (       1   -       n   2     ·       Sin   2     ⁡     (   θ   )             n   2       )       1   /   2           =     f   ⁡     (   θ   )           ⁢     
     ⁢   and           (   8   )                 r   ⁢     (   θ   )       =         f   ⁢     (   θ   )         1   ⁢           -           ⁢     f   ⁢     (   θ   )           ·     X             ⁢   n                 (   9   )             
 
         [0208]     For small values of θ, f(θ)≅n/(n+1).  
         [0209]     Thus, the length X may be selected so that
 
 X=R   eq /( n =1)
 
 where R eq  is some equivalent radius that is approximately equal to the radius of the dome. 
 
         [0210]     For specific deflection angle φ, the following equation may be solved:
 
φ=θ+α=θ+Sin −1 ( n  Sin (θ))
 
 θ=θ[φ] may be determined. 
 
         [0211]     Therefore, the aspheric dome can be described by:
 
ρ(φ)=Sin (φ)· r (θ[φ]) and  (10)
 
 Y (φ)= X −Cos (φ)· r (θ[φ])  (11)
 
 where ρ(φ) is the distance from the optical axis OA to a point on the dome  582  (as shown in  FIG. 19 ) and Y(φ) is the distance along the optical axis OA ordinate from the vertex of the dome to a point on the dome  582 , as shown in  FIG. 19 . 
 
         [0212]     Thus, a dome  582  may be constructed with a spherical surface of a single radius that closely corresponds to the ideal structure derived above at every point on the surface of the dome  582 . It is appreciated that the incidence angle of a ray of light would then deviate slightly from the central wavelength of the interference filter but would remain significantly less than the variation resulting from a conventional interference filter. It also appreciated that if the dome has a low optical power, then the coating could be place either side of the dome, without significantly changing the optical paths of the light passing through the coatings, which comprise the optical filter.  
         [0213]     Reference is now made to  FIG. 20 , a simplified flow chart illustrating operation of a data entry object engagement location sensing subsystem employed in the projection keyboard system and methodology of  FIG. 1  in accordance with a preferred embodiment of the present invention and to  FIG. 21 , which is a simplified illustration of a preferred data structure employed in the operation of the data entry object engagement location sensing subsystem shown in  FIG. 20 .  
         [0214]      FIG. 20  shows a simplified illustration of a preferred data structure employed in the operation of the data entry object engagement location sensing method described hereinbelow with respect to  FIG. 21 . It is appreciated that the imaging sensor of a camera, such as camera  516  ( FIG. 17A ), is typically comprised of a set of M×N pixels, wherein a particular group of pixels views a defined region of the engagement plane which preferably overlies the projection surface  104  ( FIG. 1 ). Thus, it is possible that a particular pixel group, located in the image plane of the camera  516  may receive scattered light from a data entry object  512  engaging the key location  113 .  
         [0215]     Thus, as the camera  516  views the projection surface  104 , each of the M×N pixels in the image plane of the camera  516  may receive light from a corresponding region in the engagement plane in respect of a data entry object engagement therewith.  
         [0216]     Thus, as each pixel value is acquired, a determination is made, using the pixel coordinates, as to whether that pixel lies within a predefined keystroke region, such as keystroke regions  600  shown in  FIG. 22 . This determination is preferably made by employing a pixel index table  601  which indicates for each pixel, whether that pixel lies within a predetermined keystroke region, such as keystroke regions  625 ,  626 ,  627  and  628  ( FIG. 22 ), and, if so, within which keystroke region it lies.  
         [0217]     As seen in  FIGS. 20 and 21 , pixel values, such as gray level values, are acquired for various pixel coordinates. As each pixel value is acquired, a determination is made, using the pixel coordinates, as to whether that pixel lies within a predefined keystroke region ( FIG. 22 ). This determination is preferably made by employing a pixel index table  601  which indicates for each pixel, whether that pixel lies within a predetermined keystroke region and, if so, within which keystroke region it lies.  
         [0218]     The function of the pixel within the keystroke region in which it lies is then determined, preferably by employing table  601 . This function is typically additive or subtractive, but may alternatively have another function. Typically, depending on the function, the pixel value is added to or subtracted from a pixel total maintained for each keystroke region in a keystroke region accumulator table  602 .  
         [0219]     Once all of the pixels in a frame have been processed as aforesaid, an updated background level is determined for the frame and a key actuation threshold is determined typically by subtracting the updated background level from a predetermined threshold level which is established for each keystroke region. This is preferably carried out by employing a keystroke region threshold table  604 .  
         [0220]     The contents of the keystroke region accumulator table  602  for each keystroke region preferably are then compared with the current key actuation threshold. If the contents of the accumulator table  602  exceed the key actuation threshold for a given key actuation region in a given frame and in the previous frame the contents of the accumulator table  602  did not exceed the key actuation threshold, a key actuation output is provided.  
         [0221]     Similarly, if the contents of the accumulator table  602  does not exceed the key actuation threshold for a given key actuation region in a given frame and in the previous frame the contents of the accumulator table  602  did exceed the key actuation threshold, a key deactuation output is provided. In all other cases, no output need be generated.  
         [0222]     Reference is now made to  FIG. 22 , which is a simplified pictorial illustration of outlines of typical keystroke regions  625 , 626 , 627  and  628  as sensed by a two-dimensional image sensor ( FIG. 1 ) viewing a keyboard, such as the keyboard  190 , seen in  FIG. 5A .  
         [0223]     Reference is now made to  FIG. 23 , which is a simplified pictorial illustration of outlines of typical footprints  629 ,  630 ,  631  and  632  of a typical light pattern occasioned by data entry object engagement corresponding to the keystroke regions  625 , 626 , 627  and  628  ( FIG. 22 ).  
         [0224]     Reference is now made to  FIGS. 24A, 24B  and  24 C, which are simplified illustrations of three alternative methodologies for determining the function of the pixel within the keystroke region in which it lies as shown in  FIG. 21  and to  FIGS. 23A, 23B  and  23 C, which are simplified illustrations of traces which are useful in understanding  FIGS. 22A, 22B  and  22 C.  
         [0225]     Turning now to  FIG. 24A , there is shown arranged along a common arbitrary axis  610  a simplified keystroke region  620  corresponding to a given key and containing a plurality of pixels  622 . A typical simplified footprint of a typical light pattern occasioned by data entry object engagement with the given key is indicated by reference numeral  624 .  FIG. 23  shows outlines of typical footprints  625 ,  626 ,  627  and  628 , corresponding to keystroke regions designated  629 ,  630 ,  631  and  632  in  FIG. 22 .  
         [0226]     A typical background signal pattern is indicated by reference numeral  634 . Superimposition of the footprint  624  over the background signal pattern  626  is indicated at reference number  635 . A one dimensionally selectable overlap of footprint  624  over keystroke region  620  is indicated at reference numeral  636 . A one dimensionally selectable overlap of background signal pattern  634  over keystroke region  620  is indicated at reference numeral  637 . A one dimensionally selectable overlap of superimposition  638  over keystroke region  620  is indicated at reference numeral  638 .  
         [0227]      FIG. 25A  illustrates a bias function  640  corresponding to a cross section of the keystroke region  620  taken along axis  610 , which bias function defines keystroke region  620  along axis  610 . There is also seen a signal function  644  corresponding to a cross section of the footprint  624  along axis  610 ; a background signal function  646  corresponding to a cross section of the background signal pattern  634  along axis  610  and a combination signal  648  corresponding to a cross section of the superimposition  635 .  
         [0228]     There is also shown in  FIG. 25A  a one dimensional convolution  650  corresponding to one dimensionally selectable overlap  636 ; a one dimensional convolution  652  corresponding to one dimensionally selectable overlap  637  and a one dimensional convolution  654  corresponding to one dimensionally selectable overlap  638 . Convolution  650  is shown with a threshold  660 ; convolution  652  is shown with a threshold  662  and convolution  654  is shown with a threshold  664 .  
         [0229]     Turning now to  FIG. 24B , there is shown arranged along a common arbitrary axis  670  a simplified keystroke region  680  corresponding to a given key and containing a plurality of pixels  682 . The simplified keystroke region  680  is here shown surrounded by a simplified keystroke region border  683 . A typical simplified footprint of a typical light pattern occasioned by data entry object engagement with the given key is indicated by reference numeral  684 . A typical background signal pattern is indicated by reference numeral  686 . Superimposition of the footprint  684  over the background signal pattern  686  is indicated at reference numeral  688 . A one dimensionally selectable overlap of footprint  684  over keystroke region  680  and border  683  is indicated at reference numeral  690 . A one dimensionally selectable overlap of background signal pattern  686  over keystroke region  680  and border  683  is indicated at reference numeral  692 . A one dimensionally selectable overlap of superimposition  688  over keystroke region  680  and border  683  is indicated at reference numeral  
         [0230]      FIG. 25B  illustrates a bias function  700  corresponding to a cross section of the keystroke region  680  and of the border  683  taken along axis  670 , which bias function defines keystroke region  680  along axis  670 . It is seen that border  683  is assigned a negative value relative to the value of the keystroke region  680 . This value assignment is appreciated to enhance the value of data entry object engagements to the extent that they lie within the keystroke region  680  and to decrease the value of such data entry object engagements to the extent that they extend over the border  683 . There is also seen a signal function  704  corresponding to a cross section of the footprint  684  along axis  670 ; a background signal function  706  corresponding to a cross section of the background signal pattern  686  along axis  670  and a combination signal  708  corresponding to a cross section of the superimposition  688 .  
         [0231]     There is also shown in  FIG. 25B  a one dimensional convolution  720 , corresponding to one dimensionally selectable overlap  690 ; a one dimensional convolution  722 , corresponding to one dimensionally selectable overlap  692  and a one dimensional convolution  724  corresponding to one dimensionally selectable overlap  694 . Convolution  720  is shown with a threshold  726 ; convolution  722  is shown with a threshold  727  and convolution  724  is shown with a threshold  728 .  
         [0232]     Turning now to  FIG. 24C , there is shown arranged along a common arbitrary axis  730  a simplified keystroke region  740  corresponding to a given key and containing a plurality of pixels  741 . The simplified keystroke region  740  is here shown surrounded by a simplified keystroke region inner border  742  and by a simplified keystroke region outer border  743 . A typical simplified footprint of a typical light pattern occasioned by data entry object engagement with the given key is indicated by reference numeral  744 . A typical background signal pattern is indicated by reference numeral  746 . Superimposition of the footprint  744  over the background signal pattern  746  is indicated at reference numeral  748 . A one dimensionally selectable overlap of footprint  744  over keystroke region  740  and borders  742  and  743  is indicated at reference numeral  750 . A one dimensionally selectable overlap of background signal pattern  746  over keystroke region  740  and borders  742  and  743  is indicated at reference numeral  752 . A one dimensionally selectable overlap of superimposition  748  over keystroke region  740  and borders  742  and  743  is indicated at reference numeral  754 .  
         [0233]      FIG. 25C  illustrates a bias function  760  corresponding to a cross section of the keystroke region  740  and of the borders  742  and  743  taken along axis  730 , which bias function defines keystroke region  740  along axis  730 . It is seen that border  742  is assigned a zero value and border  743  is assigned a negative value relative to the value of the keystroke region  740 . It is appreciated that these value assignments enhance the value of data entry object engagements that to the extent that they lie within the keystroke region  740  and to decrease the value of such data entry object engagements to the extent that they extend across the border  742  and at least into border  743 . There is also seen a signal function  764  corresponding to a cross section of the footprint  744  along axis  730 ; a background signal function  766  corresponding to a cross section of the background signal pattern  746  along axis  730  and a combination signal  768  corresponding to a cross section of the superimposition  748 .  
         [0234]     There is also shown in  FIG. 25C  a one dimensional convolution  780 , corresponding to one dimensionally selectable overlap  750 ; a one dimensional convolution  782 , corresponding to one dimensionally selectable overlap  752  and a one dimensional convolution  784  corresponding to one dimensionally selectable overlap  754 . Convolution  780  is shown with a threshold  786 ; convolution  782  is shown with a threshold  787  and convolution  784  is shown with a threshold  788 .  
         [0235]     It may be appreciated from a consideration of convolutions  638 ,  694  and  754  that the dual border arrangement of  FIGS. 24C and 25C  provides the best detection of data entry object keystroke engagement, while minimizing background effects.  
         [0236]     Reference is now made to  FIG. 26 , which is a simplified flow chart illustrating operation of a data entry object engagement location sensing subsystem employed in a tracking system and methodology constructed and operative in accordance with a preferred embodiment of the present invention.  
         [0237]     As seen in  FIG. 26 , pixel values, such as gray level values, are acquired for various pixel coordinates. As each pixel value is acquired, a determination may be made, using the pixel coordinates, as to whether that pixel lies within a predefined active region. Typically, if the pixel does not lie within a predetermined active region, its value is ignored.  
         [0238]     The pixel value for each pixel is preferably thresholded and typically all pixel values falling below a given threshold are ignored. The remaining pixel values may be weighted by a selected weighting parameter. In order to determine the “center of gravity” of the thresholded and weighted pixel values, the thresholded and weighted pixel values are multiplied respectively by X and Y values representing the coordinate position of each pixel and the results are summed along mutually perpendicular axes X and Y and stored in X and Y accumulators. The total of the thresholded and weighted pixel values for all relevant pixels are also summed and stored in a data accumulator, for the entire active region.  
         [0239]     Once all of the pixels in a frame have been processed as aforesaid, the summed thresholded and weighted pixel values along the X and Y axes respectively are divided by the total of the thresholded and weighted pixel values for the entire active region to determine the X and Y coordinates of the “center of gravity”, which represents a desired engagement location.  
         [0240]     Reference is now made to  FIG. 27 , which is a simplified flowchart illustrating operation of functionality providing shadow sharpness analysis in accordance with a preferred embodiment of the present invention, to  FIG. 28 , which is a simplified illustration of a preferred data structure employed in the operation of the data entry object engagement location sensing subsystem shown in  FIG. 27  and to  FIG. 29 , which is an illustration which is useful in understanding the flowchart of  FIG. 27 .  
         [0241]     As seen in  FIGS. 27-29 , pixel values, such as gray level values, are acquired for various pixel coordinates. As each pixel value is acquired, a determination is made, using the pixel coordinates, as to whether that pixel lies within a predefined keystroke region  800  ( FIG. 29 ) and whether it lies within left or right subregions  802  and  804  respectively. This determination is preferably made by employing a pixel index table  806  which indicates for each pixel, whether that pixel lies within a predetermined keystroke region and, if so, within which keystroke region as well as within which keystroke subregion it lies.  
         [0242]     The derivative of the pixel values along the X axis  808  ( FIG. 29 ) is calculated and thresholded. X axis derivative values, the absolute values of which exceed a predetermined threshold, are summed for each subregion of each keystroke region and stored in a keystroke region accumulator table  810 . The variation of pixel values along the X axis  808  for a situation, such as that illustrated in  FIG. 11A , is shown at reference numeral  812 . The X-axis derivative thereof is shown at reference numeral  814 . The variation of pixel values along the X axis  808  for a situation, such as that illustrated in  FIG. 11B , is shown at reference numeral  816 . The X-axis derivative thereof is shown at reference numeral  818 . The threshold applied to derivatives  814  and  818  is indicated by reference numeral  820 .  
         [0243]     It is clearly seen that the closer that the data entry object is to the engagement surface  104  ( FIGS. 11A &amp; 11B ), the sharper is the detected edge and the greater is the derivative.  
         [0244]     Once all of the pixels in a frame have been processed as aforesaid a key actuation threshold is determined typically from a predetermined threshold level which is established for each keystroke region. This is preferably carried out by employing a keystroke region threshold table  822 .  
         [0245]     The contents of the keystroke region accumulator table  810  for the two subregions in each keystroke region preferably are then subtracted one from the other. The difference is compared with the current key actuation threshold. If the difference exceeds a key actuation threshold for a given key actuation region in a given frame and in the previous frame the difference did not exceed the key actuation threshold, a key actuation output is provided.  
         [0246]     Similarly, if the difference does not exceed the key actuation threshold for a give key actuation region in a give frame and in the previous frame the difference did exceed the key actuation threshold, a key deactuation output is provided. In all other cases, no output need be generated.  
         [0247]     Reference is now made to  FIG. 30 , which is a simplified illustration showing synchronized illumination power variation functionality useful in accordance with a preferred embodiment of the present invention. The functionality illustrated in  FIG. 30  is directed to modulating the amount of illumination provided for data entry object engagement detection. This modulation is desirable because the intensity of light impinging on a data entry object and is thus scattered thereby, decreases with the distance between an illuminator  830  and a data entry object. Thus it may be appreciated that the amount of light impinging on a data entry  832  is substantially greater than the amount of light impinging on a data entry object  834 . Furthermore the amount of scattered light impinging on a detector  836  decreases with the distance between the data entry object and the detector. These two distance dependencies make detection of data entry object engagement difficult.  
         [0248]     In order to overcome this difficulty, there is provided in accordance with a preferred embodiment of the present invention variable intensity drive electronics  840  which is coupled to both illuminator  830  and detector  836  and which causes the intensity of light produced by the illuminator  830  to vary, typically in a ramp fashion, in synchronization to the imaging field location of detector  836 .  
         [0249]     Thus, it may be seen that when a near portion (A) of the engagement surface  104  ( FIG. 1 ) is being imaged, typically at the top portion A of detector  836 , the intensity is at a minimum. When an intermediate portion (B) of the engagement surface  104  is being imaged, typically at the middle of detector  836 , the intensity is at an intermediate level and when a far portion (C) of the engagement surface  104  is being imaged, typically at the bottom portion (C) of the detector  836 , the intensity is at a maximum.  
         [0250]     Variable intensity drive electronics  840  operates preferably by providing a synchronization output  842  to detector  836  and a corresponding synchronization output  844  to illuminator  830 , causing the intensity level to increase in time in synchronization with the location of a scanned image region in detector  836 .  
         [0251]     Reference is now made to  FIG. 31 , which is a simplified illustration of a system and functionality for providing a digital signature in accordance with a preferred embodiment of the present invention. As seen in  FIG. 29 , an output from a data entry object engagement detection subsystem  850 , such as detector subsystem  112  ( FIG. 1 ), provides intensity, position and timing outputs which are combined in a digital signature generator  852 . Digital signature generator  852  preferable provides a unique digital signature based on these outputs. The intensity and timing outputs may be generated by the functionality described hereinabove with reference to  FIGS. 20 and 21 . The position output may be generated by the functionality described hereinabove with reference to  FIG. 26 .  
         [0252]     Reference is now made to  FIG. 32 , which is a simplified illustration of a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention and employing sensing of data entry object interaction with an inert keyboard defined on a surface, such as a pull-down tray  900 . Such a pull-down tray may be located in a vehicle, such as an airplane, and may have multiple uses, such as a dining tray. The keyboard may be defined by printing on the tray or on a sheet which can be placed on the tray or alternatively by suitable illumination thereof. Data entry object engagement detection may be provided by apparatus  902  incorporated in the vehicle or alternatively by portable apparatus, such as that carried by a passenger. Computer functionality may be provided by apparatus incorporated in the vehicle or alternatively by portable apparatus carried by a passenger. Computer memory, such as a memory element  904 , may be carried by a passenger and may be inserted into a suitable socket  906  in the vehicle.  
         [0253]     Reference is now made to  FIG. 33 , which is a simplified illustration of a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention and providing alphanumeric annotation of photographs using a suitable equipped camera, such as a video camera  910 . A keyboard  912  may be projected by a projection subsystem  914  integrally formed or otherwise associated with camera  910  and data entry object engagement detection may be provided by detection apparatus  916 , also integrally formed or otherwise associated with camera  910 . The keyboard may advantageously be employed for annotating pictures taken with the camera.  
         [0254]     Reference is now made to  FIGS. 34A, 34B ,  34 C and  34 D, which are simplified illustration of four alternative embodiments of a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention and providing control, by data entry object interaction, of a home entertainment system.  FIG. 34A  shows a keyboard  920  defined on a television screen, typically either by operation of the television or by projection on the screen. Data entry object engagement detection is provided by apparatus  922  which may be portable or fixedly attached to the television.  
         [0255]      FIG. 34B  shows a keyboard  930  defined alongside a home entertainment system. The keyboard  930  may be provided by projection or may be printed onto any suitable surface. Data entry object engagement detection is provided by apparatus  932  which may be portable or fixedly attached to the home entertainment system.  
         [0256]      FIG. 34C  shows a user interface board  934  defined on a table alongside a home entertainment system. The user interface board  934  may be provided by projection or may be printed onto any suitable surface. Data entry object engagement detection is provided by apparatus  936  which may be portable or fixedly attached to the home entertainment system.  
         [0257]      FIG. 34D  shows a user interface board  938  defined on a remote control unit alongside a home entertainment system. The user interface board  938  may be provided by projection or may be printed onto any suitable surface. Data entry object engagement detection is provided by apparatus  939  which may be integralled formed of fixedly attached to the remote control unit.  
         [0258]     In all of the above embodiments, the keyboard can be used for any suitable function, such as interactive entertainment and infotainment.  
         [0259]     Reference is now made to  FIG. 35 , which is simplified illustration of a restricted particulate matter environment keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention. A keyboard  940  may be provided by projection or may be printed onto any suitable surface. Data entry object engagement detection is provided by apparatus  942  which may be portable or fixedly attached to equipment. The keyboard  940  may be employed for controlling the equipment.  
         [0260]     Reference is now made to  FIG. 36 , which is a simplified illustration of a industrial environment keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention. A keyboard  950  may be provided by projection or may be printed onto any suitable surface. Data entry object engagement detection is provided by apparatus  952  which may be portable or fixedly attached to industrial equipment. The keyboard  950  may be employed for controlling the industrial equipment.  
         [0261]     Reference is now made to  FIG. 37  which illustrate a video projector  960  having integrally formed or associated therewith a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention. A keyboard  962  is preferably provided by projection or may be printed onto any suitable surface. Data entry object engagement detection is provided by apparatus  964  which may be portable or fixedly attached to the projector  960 .  
         [0262]     Reference is now made to  FIG. 38 , which is a simplified illustration of a restaurant patron interface system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention. As seen in  FIG. 38 , a menu selection board  970  may be provided by projection or may be printed onto any suitable surface. Data entry object engagement detection is provided by apparatus  972  which may be portable or fixedly attached to a table. A virtual credit card signature pad  974  may also be provided by projection or otherwise. Detection of a signature may also be provided by engagement detection apparatus  972 .  
         [0263]     Reference is now made to  FIG. 39 , which is a simplified illustration of a keyboard system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention and providing alphanumeric annotation or photographs using a suitably equipped audio player  980 . A keyboard  982  may be projected by a projection subsystem  984  integrally formed or otherwise associated with player  980  and data entry object engagement detection may be provided by detection apparatus  986 , also integrally formed or otherwise associated with player  980 . The keyboard  982  may advantageously be employed for annotating or selecting music to be played by the player.  
         [0264]     Reference is now made to  FIGS. 40A and 40B , which are simplified illustrations of a data entry object engagement sensing screen system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention and which provides “touch screen” functionality using data entry object engagement detection functionality of the type described hereinabove. Data entry object engagement with a screen  1000 , a conventional CRT screen, a flat panel screen, or a screen projected, in a manner similar to that of the various keyboards described hereinabove, may be detected by detection apparatus  1002 , integrally formed or otherwise associated with screen  1000 . The screen  1000  may be employed for any suitable application, such as in an interactive information kiosk, one example of which is an automatic teller machine.  
         [0265]     Reference is now made to  FIG. 41 , which is a simplified illustration of a security and access control system employing data entry object engagement sensing methodology, constructed and operative in accordance with a preferred embodiment of the present invention. Data entry object engagement with a screen  1010 , such as a conventional CRT screen, a flat panel screen, or a screen, projected in a manner similar to that of the various keyboards described hereinabove, may be detected by detection apparatus  1012 , integrally formed or otherwise associated with screen  1010 . The screen  1010  may be located at any suitable location and employed for entry of access information by a user.  
         [0266]     Reference is now made to  FIG. 42 , which is a simplified illustration of a object engagement sensing game system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention using data entry object engagement detection functionality of the type described hereinabove. Object engagement with a game board  1020 , which may be defined, for example by a conventional CRT screen, a flat panel screen, or a screen projected in a manner similar to that of the various keyboards described hereinabove, may be detected by detection apparatus  1022 , integrally formed or otherwise associated with game board  1020 . The game board  1020  and associated functionality may be employed for any suitable game application, such as chess or checkers.  
         [0267]     Reference is now made to  FIGS. 43A, 43B  and  43 C, which are simplified illustrations of a data entry engagement sensing musical instrument and methodology, constructed and operative in accordance with a preferred embodiment of the present invention using data entry object engagement detection functionality of the type described hereinabove. Data entry object engagement with piano keys  1030 , drum surfaces  1032  and guitar frettes  1034 , which may be projected in a manner similar to that of the various keyboards described hereinabove, or otherwise defined, as by drawing, may be detected by detection apparatus  1036 . This embodiment of the present invention may be employed for any suitable hand operated musical instrument.  
         [0268]     Reference is now made to  FIG. 44 , which is a simplified illustration of a vehicle mounted user interface system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention. The system of  FIG. 44  preferably projects a keyboard  1040  onto a vehicle surface, preferably a vehicle windscreen. This keyboard may be used for inputting information for any purpose, preferably for entering a desired destination into a navigation system. Data entry object engagement with keyboard  1040 , such as a conventional CRT screen, a flat panel screen, or a screen projected in a manner similar to that of the various keyboards described hereinabove, may be detected by detection apparatus  1042 , integrally formed or otherwise associated with the vehicle. The keyboard  1040  may be located at any suitable location.  
         [0269]     Reference is now made to  FIG. 45  which is a simplified illustration of a vending machine incorporating a data entry object engagement detection system and methodology, constructed and operative in accordance with a preferred embodiment of the present invention. Data entry object engagement with selection board  1050 , such as a conventional CRT screen, a flat panel screen, or a screen projected in a manner similar to that of the various keyboards described hereinabove, may be detected by detection apparatus  1052 , integrally formed or otherwise associated with the vending machine. The selection board  1050  may be employed for any suitable user interaction with the vending machine, including not only selection of products, but also entry of payment information.  
         [0270]     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereof which do not form part of the prior art.