PCT
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(51) International Patent Classification 6 =
`(11) International Publication Number:
`WO 97/41502
`gggf‘ésgeé 31/931381 (5331:; gllglzf’lfoa?
`(43) International Publication Date:
`6 November 1997 (06.1 1.97)
`
`7/18, G038 21/132
`
`(81) Designated States: JP, KR, European patent (AT, BE, CH, DE,
`DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE).
`
`Published
`With international search report.
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of the receipt of
`amendments.
`
`(22) International Filing Date:
`
`24 April 1997 (24.04.97)
`
`PCT/IB97/00438
`
`(30) Priority Data:
`96087705
`
`27 April 1996 (27.04.96)
`
`GB
`
`(71) Applicant: PHILIPS ELECTRONICS NV. [NL/NL]; Groc-
`ncwoudseweg I, NL-562l BA Eindhoven (NL).
`
`(71) Applicant (for SE only): PHILIPS NORDEN AB [SE/SE];
`Kottbygatan 7, Kista. 8-164 85 Stockholm (SE).
`
`(72) Inventors: STOVE, Andrew, Gerald; Prof. Holstlaan 6, NL-
`5656 AA Eindhoven (NL). GREWER, Ruediger, Prof. Hol-
`stlaan 6, NL-5656 AA Eindhoven (NL). CARLSEN, In-
`gwer; Prof. Holstlaan 6, NL-5656 AA Eindhoven (NL).
`SVENSSON, Heino; Prof. Holstlaan 6, NL-5656 AA Eind-
`hoven (NL). MOENNICH. Karl-Jfirgen; Prof. Holstlaan 6,
`NL-5656 AA Eindhoven (NL). SCHMIDT, Joachim; Prof.
`Holstlaan 6, NL-5656 AA Eindhoven (NL). WENDLER,
`Thomas; Prof. Holstlaan 6, NL-5656 AA Eindhoven (NL).
`
`(74) Agent: ANDREWS, Arthur, S.; Intemationaal Octrooibureau
`B.V., PO. Box 220, NL-5600 AE Eindhoven (NL).
`
` (21) International Application Number:
`
`(54) Title: POSITION DETERMINATION OF A LASER POINTER IN A PROJECTION DISPLAY SYSTEM
`
`(57) Abstract
`
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`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international applications under the PCT.
`
`Albania
`Armenia
`Austria
`Australia
`Azerbaijan
`Bosnia and Henegovina
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`Cbte d‘lvoire
`Cameroon
`China
`Cuba
`Czech Republic
`Germany
`Denmark
`Estonia
`
`ES
`FI
`FR
`GA
`GB
`GE
`GH
`GN
`GR
`HU
`IE
`[L
`IS
`IT
`JP
`KE
`KG
`KP
`
`KR
`KZ
`LC
`Ll
`LK
`LR
`
`Spain
`Finland
`France
`Gabon
`United Kingdom
`Georgia
`Ghana
`Guinea
`Greece
`Hungary
`Ireland
`Israel
`Iceland
`Italy
`Japan
`Kenya
`Kyrgyzstan
`Democratic People's
`Republic of Korea
`Republic of Korea
`Kazakstan
`Saint Lucia
`Liechtenstein
`Sri Lanka
`Liberia
`
`LS
`LT
`LU
`LV
`MC
`MD
`MG
`MK
`
`ML
`MN
`MR
`MW
`MX
`NE
`NL
`NO
`NZ
`PL
`PT
`R0
`RU
`SD
`SE
`SG
`
`Lesotho
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`The former Yugoslav
`Republic of Macedonia
`Mali
`Mongolia
`Mauritania
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`
`Zimbabwe
`
`SI
`SK
`SN
`82
`TD
`TG
`TJ
`TM
`TR
`TT
`UA
`UG
`US
`UZ
`VN
`YU
`ZW
`
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Turkmenistan
`Turkey
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`Viet Nam
`Yugoslavia
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`WO 97/41502
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`PCT/1397/00438
`
`DESCRIPTION
`
`POSITION DETERMINATION OF A LASER POINTER IN A PROJECTION DISPLAY SYSTEM
`
`The invention relates to a projection display system comprising a
`projector for projecting a computer generated display on to a screen.
`
`Slide and overhead projections have for many years been an effective
`
`technique for making information available to a wide audience, for example in
`
`a conference. The availability of high quality video projectors allows for direct
`
`visualisation of computer display contents such as text, graphics, images etc.
`
`instead of the production of photographic slides or overhead transparencies.
`
`This technique can also handle multimedia information more conveniently than
`
`is likely to play an increasingly
`traditional approaches and consequently it
`important role in future presentations at conferences and the like.
`
`During the presentation of a paper at a conference two major types of
`interaction have been identified. The first may be called a referring interaction
`
`such as pointing at projected objects and the second a managing interaction,
`that is accessing new images or going back to previously shown images.
`Traditionally referring to objects on a screen is done with a pointer. the pointer
`may either be a stick or more elegantly a laser pointer. The latter allows the
`
`speaker to point at the image projected from almost any place in the room and
`
`For the managing
`gives maximum flexibility for the task of referencing.
`interaction a turntable on a slide projector may be controlled or with overhead
`
`transparencies the presenter has to manually remove and replace the
`transparencies on the projector.
`
`When working with a projection display system which projects computer
`generated images directly the same types of interaction are required. The first
`
`can again be achieved with a stick or laser pointer while the second requires
`access to the computer. Clearly the presenter could turn away to a small
`
`computer monitor and use its mouse during a presentation. This, however,
`gives reduced flexibility for the presenter as he has to look away from the
`projected image and go to a particular location to use the computer, thus taking
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`2
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`his attention away from the audience and interrupting the presentation
`
`It is an object of the invention to enable the provision of a projection
`
`display system in which the presenter can with greater flexibility perform both
`
`the referring function and the managing function.
`
`The invention provides a projection display system comprising a
`
`projector for projecting a computer generated display on to a screen, a pointer
`
`producing a narrow beam of radiation of higher intensity than the projected
`
`image, a video camera located in a fixed position relative to the projector and
`
`arranged to view the screen, and means for analysing the video signal
`
`produced by the camera to determine the point on the screen illuminated by the
`
`pointer.
`
`By these means the computer is provided with information which enables
`
`it to determine where the pointer is pointed at on the screen. Since the
`
`computer can detect that the pointer is pointed at a particular object on the
`
`screen both the presentational interaction and the managing interaction may
`
`be achieved without the presenter having to turn away from the audience.
`
`In
`
`this specification higher intensity means the intensity as perceived by the video
`
`camera after any filtering of the image,
`
`if provided, and not as seen by an
`
`observer.
`
`The pointer may be a laser pointer, which is a convenient source of high
`
`intensity radiation having a narrow beam width so that a small area of the
`
`screeen may be indicated.
`
`The managing interaction.
`
`that
`
`is the control of the images to be
`
`displayed, may be achieved in a number of different ways.
`
`It may be arranged,
`
`for example. that the computer is arranged to produced soft buttons on the
`
`screen and by pointing the laser beam at the position of the button on the
`
`screen and maintaining it there for a given period of time may cause the button
`
`to be operated.
`
`The computer then performs the appropriate operation in
`
`response to the simulated button pressing.
`
`Such operations may be for
`
`example to cause a preceding or succeeding image to be displayed or to
`
`enlarge a particular portion of the image currently being displayed. Further
`
`operations which may be carried out are for example to bring up a menu on the
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`screen and to select items from that menu.
`
`3
`
`The computer may be arranged to display a cursor at the determined
`
`point on the screen.
`
`By this means the computer provides a feedback signal to the presenter
`
`which reassures the presenter that the pointer is pointed at the desired point
`
`on the screen. This also allows the use of a laser or other radiation source
`
`which produces radiation in the non—visible region of the spectrum, for example
`
`in the infra red region, where the presenter cannot actually see the position on
`
`the screen that the radiation beam is striking but when the cursor appears then
`
`the presenter knows where the laser beam is positioned.
`
`The pointer may have one or more button(s), one button may be used
`to switch the radiation beam on and off while further buttons may be provided
`
`to enable similar facilities to that of a conventional computer mouse.
`
`A wireless link may be provided between the pointer and the computer.
`
`This link, which may be an infra red link, enables the function of the "mouse
`
`buttons" to be transmitted to the computer. Of course a wired link may be
`
`provided between the pointer and the computer, but a wireless link allows the
`
`presenter greater freedom by not requiring a physical connection between the
`
`pointer and the computer. Thus the presenter may move around more freely
`
`in the lecture theatre when presenting the lecture. The wireless link may take
`
`many forms. An infra link is convenient as infra red transmitters and receivers
`
`are readily available as used in conventional television remote control devices.
`
`Examples of alternatives are radio or ultrasonics which may have advantages
`
`in given situations,
`
`for example in terms of radiation pattern emitted or
`
`absorption of the signals by intervening objects.
`
`The projection display system may include geometrical distortion
`
`correction means to correct distortion caused by the projector screen and video
`
`camera. There will be some distortion caused by the optics of the projector
`
`which means that the projected image will not be precisely the same as that
`
`which would have appeared on a computer monitor screen.
`
`In addition if the
`
`projection screen is not perfectly aligned there will be further distortion and the
`
`video camera will normally be viewing the screen from a different position from
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`4
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`that of the projector. Whilst the video camera and projector may be built into
`
`one unit so that the physical locations are fixed this does not overcome the
`
`problem of possible screen misalignment.
`
`Consequently,
`
`unless such
`
`geometrical distortion correction means is included,
`
`the setting up of the
`
`projection display system has to be very precise in order that the position of the
`
`laser spot on the screen corresponds with that
`
`that
`
`the computer has
`
`generated.
`
`If such correspondence is not maintained then clearly, depending
`
`on the degree of misalignment the operation of the projection system may be
`
`completely erroneous. For example the operation of a soft button may, when
`
`there are several soft buttons in relatively close proximity, entail the detection
`
`by the computer of a different button from that which the presenter thinks the
`
`laser beam is pointing at.
`
`The geometrical correction means may comprise means for generating
`
`a calibration pattern and feeding it to the projector, means for comparing the
`
`pattern produced by the video camera with the generated calibration pattern,
`
`means for generating a correction to bring the pattern produced by the video
`
`camera into conformity with the generated pattern, and means for applying the
`
`correction to subsequently displayed images.
`
`The generated pattern may be for example a cross hatch pattern, that
`
`is a series of equally spaced vertical and horizontal lines. This is a pattern
`
`which is easy to generate and to compare. Clearly any other convenient
`
`calibration pattern could be generated and used.
`
`If necessary or desired the
`
`calibration procedure could be carried out at intervals during the presentation
`
`to ensure that no changes had taken place. These may be either at set
`
`intervals or on demand. Once the calibration has taken place it is likely to
`
`remain stable for a long period as it is primarily a function of the geometry of
`
`the system.
`
`The projection display system may include a presentation computer for
`
`generating the images to be displayed and presenting them to the projector and
`
`an interaction computer for receiving the signal from the video camera and
`
`generating control signals for the presentation computer.
`
`The presentation computer and interaction computer may be combined
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`5
`
`as a single unit. Whether two separate computers are used or a single
`combined computer will depend on the power and speed of the computer and
`the acceptable reaction times of the system.
`
`The above and other features and advantages of the invention will be
`
`apparent from the following description, by way of example, of embodiments
`
`of a projection display system according to the invention with reference to the
`
`accompanying drawings, in which:
`
`Figure 1 shows in block schematic form a first embodiment of a
`
`projection display system according to the invention, and
`
`Figure 2 shows an arrangement for generating the position of the laser
`
`spot on the screen.
`
`the projection display system comprises a
`As shown in Figure 1
`presentation computer 1 which generates images for display and feeds them
`
`over a line 2 to a projector 3 which projects the image onto a screen 4. A
`
`video camera 5 is arranged to view the screen 4 and produce a signal over a
`line 6 which is fed to an interaction computer 7. A laser pointer 8 is provided,
`which is a portable unit which is hand held by the presenter. There is an infra
`
`red transmission link from the laser pointer 8 to an infra red receiver 9 which
`
`is connected to or formed as part of the interaction computer 7. The laser
`pointer 8 has four buttons, one of which is shown as reference sign 10. One
`of the buttons is used to switch the laser pointer on and off and the other three
`buttons are used to provide a mouse function with their status being relayed to
`the computer 7 via the infra red transmission link and infra red receiver 9. The
`interaction computer 7 includes a frame grabber 11 which captures and stores
`each frame of video information in sucession from the camera 5. The
`
`interaction computer 7 also includes a calibration circuit 12 which receives a
`first input from the frame grabber 11 and a second input from the presentation
`computer 1. The calibration circuit compares the calibration pattern generated
`by the presentation computer 1 with that viewed by the camera 5 and captured
`by the frame grabber 11. This comparison produces an output which is
`representative of the difference between the calibration pattern generated by
`the presentation computer 1 and the pattern detected by the camera 5 and
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`6
`
`which is fed to a geometric distortion correction circuit 13 which also forms part
`
`of the interaction computer 7. During the calibration process the output of the
`
`frame grabber 11 is connected to the calibration circuit 12 but during normal
`
`operation the output of the frame grabber 11 is connected to the input of the
`
`geometric distortion correct circuit 13 which then takes the image detected by
`
`the video camera 5 and corrects the distortion in that image. The output of the
`
`geometric distortion correction circuit 13 is fed to a peak detector 14.
`
`The laser pointer 8 produces a spot of light on the screen which is
`
`brighter than any other part of the image projected by the projector.
`
`In order
`
`to enhance the effective greater brightness
`
`it
`
`is possible and in some
`
`instances desirable to include a filter in front of the video camera 5. Thus if a
`
`red laser is used a red filter can be placed in front of the lens of the video
`
`camera 5. This enhances the brightness of the spot produced by the laser
`
`pointer on the screen relative to that of the projected image. Thus the peak
`
`detector 14 determines the coordinates of the brightest spot on the screen and
`
`transmits this information via an interface 15 to a serial port 16 of the
`
`presentation computer 1. The presentation computer 1 may then use this
`
`information to generate a cursor which is superimposed on
`
`the image
`
`projected on to the screen.
`
`it can also use this information to determine
`
`whether the laser spot is located over a soft button or menu item on the screen
`
`and take appropriate action if that is the case.
`
`In addition information regarding
`
`the operation of buttons on the laser pointer is received by the infra red
`
`receiver 9 and passed via the interface 15 and serial
`
`input 16 to the
`
`presentation computer 1. These buttons can perform the normal mouse
`
`functions of a mouse interface with a computer. Thus the orientation of the
`
`laser pointer corresponds to the movement of a mouse over a surface while the
`
`depressing of the buttons corresponds to pressing the mouse buttons. As a
`
`result the presenter may control the presentation computer, in an analogous
`
`way to which he would control a desk top computer, by means of the laser
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`pointer.
`
`As an alternative instead of providing the infra red transmission link the
`
`buttons 10 could modulate the laser light output and this modulation could be
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`7
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`detected by the interaction computer to give the appropriate mouse button
`
`commands. This alternative however introduces some delay in carrying out the
`
`functions as the time required to detect the modulation may extend over
`
`several seconds, whereas the infra red transmission of the button operations
`
`can be achieved much more quickly. A further alternative is for the computer
`
`to detect that the laser pointer has been pointing at a particular spot on the
`
`screen for greater than a given period of time. That is if the laser spot is held
`
`on a soft button for say greater than 2 seconds it is assumed that this is a
`
`button operation. This again has the disadvantage of requiring a certain time
`
`lapse between the desire to perform an operation and it being achieved.
`
`In
`
`addition the presenter has to ensure that he does not inadvertently cause the
`
`laser to hover over a interaction point for longer than the set period.
`
`It can be seen that
`
`the interaction computer 7 transmits certain
`
`information to the presentation computer 1. This information comprises the
`
`absolute X and Y position values of the laser spot on the screen, the mouse
`
`button status, and request for calibration pattern display. There may be more
`
`than one calibration pattern in which case the interaction computer 7 will not
`
`only request the display of a pattern but will also specify which pattern is to be
`
`displayed. Where two computers are provided for the presentation computer
`
`and the interaction computer it is envisaged that the calibration pattern will be
`
`stored in memory in the interaction computer so that no communication from
`
`the presentation computer to the interaction computer is required for setting up
`the calibration.
`
`At present it is desirable to have separate computers for the presentation
`
`computer and interaction computer since the speed and power required of a
`
`single computer would be not economically available. As an example the
`
`presentation computer may be a Sun workstation whereas the interaction
`
`computer is a personal computer.
`
`If both are combined into a more powerful
`
`computer then the interface becomes simpler to handle and no storage of the
`
`calibration pattern is required apart from in the calibration pattern generator of
`
`the presentation part of the computer.
`
`Various modifications may be made to a system according to the
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`8
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`invention. The peak detection may be carried out within the interaction (or
`
`single) computer using software algorithms and the peak detection may be
`
`carried out either before or after the geometric distortion correction. An
`
`advantage of carrying out the peak detection on the raw input data, i.e. before
`
`the geometric distortion correction is that only the peak position needs to be
`
`corrected, thus simplifying the geometric distortion correction as a full video
`
`frame does not have to be corrected. A hardware analogue peak detector, one
`
`embodiment of which is shown in Figure 2 and is described hereinafter may
`
`be used instead of a digital peak detector within the interaction computer.
`
`In
`
`this case the peak detection again takes place before the geometric distortion
`
`correciton and consequently the peak position only has to be corrected. This
`
`arrangement allows a less expensive frame grabber to be used as only the
`
`calibration frames have to be captured for total scene analysis and this can be
`
`spread over a number of frames received from the video camerea as it will be
`
`a stationary pattern. No videoinput is required to monitor the pointer position,
`
`instead the raw analogue video signal
`
`is fed to the peak detector which
`
`supplies the computer with the co-ordinates of the peak only, there being no
`
`need for the computer to capture the video frames apart from during the
`
`calibration process, if implemented.
`
`Figure 2 shows in block schematic form a hardware arrangement for
`
`detecting the position of the peak brightness in the displayed image.
`
`As
`
`shown in Figure 2 the camera 5 receives synchronising signals from a
`
`synchronisation signal generator 20 over a line 21 and produces an analogue
`
`signal over a line 22 which is presented to a first input 23 of an analogue
`
`comparator 24. The signal on line 22 is also applied to the input of a peak
`
`detector 25.
`
`The output of the peak detector 25 is fed via a line 26 to a second input
`
`27 of the analogue comparatOr 24. A clock generator 30 produces a clock
`
`signal at the pixel rate and this clock signal is counted in a counter 31 which
`
`produces an output on a line 32 at line frequency. This output is fed to a
`
`second counter 33 which produces an output on line 34 at frame frequency and
`
`defines the frame flyback period. A line frequency signal
`
`is fed to the
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`9
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`synchronisation signal generator 20 from the counter 31 over a line 35 while
`
`a field frequency signal is fed to the synchronisation signal generator 20 via a
`
`line 36 from the counter 33. The pixel count is fed from the counter 31 to an
`
`intermediate value store 37 over a line 38, while a line count is fed to the
`
`intermediate value store 37 from the line counter 33 over a line 39. The frame
`
`flyback signal is fed to the peak detector 25 over a line 40 as a reset signal for
`the peak detector 25. The output of the analogue comparator 24 is fed to a
`latch input 41 of the intermediate value store 37 over a line 42. This signal will
`cause the current X and Y co-ordinates to be latched into the intermediate
`
`value store 37 in terms of pixel number and line number. The value from the
`
`intermediate value store 37 is fed to an output value store 43 and is clocked
`
`into that store by means of the frame flyback pulse one line 34. The X and Y
`
`coordinates of the peak value then become available at output 34 and 45 at the
`
`end of each frame period.
`
`In operation the synchronisation signal generator 20 receives signals
`from the counters 31 and 33 to enable it to synchronise the camera 5 to the
`
`system clock. The counters 31 and 33 generate numbers corresponding to the
`
`current position of the pixel being received from the camera. The peak
`detector circuit holds the peak value which has previously been detected in the
`
`video wave form. This is compared to the current value and if the current value
`
`is higher than the previous peak then the current pixel co-ordinates are stored
`
`in the intermediate value store 37 replacing the previously stored values. At
`
`the end of the frame, that is once the whole picture has been examined, the co-
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`ordinates of the peak value are transferred into the output value store 43 from
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`whence they can be used by the computer. The peak detector is then reset to
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`a level corresponding to black level before the next frame is received. The
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`peak detector is arranged so that there is a delay through the peak detector
`such that the current value always reaches the analogue comparator before
`its value is transferred through the peak detector to the second input of the
`comparator. This can be achieved in various ways for example by making the
`peak detector a sample and hold circuit triggered by the comparator or by
`employing analogue to digital convertors and subsequent digital to analogue
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`conversion. Alternatively the peak detection could be implemented entirely in
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`the digital domain whereby a digital to analogue convertor is inserted between
`
`the camera output and both the peak detector 25 and comparator 24.
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`In this
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`case a digital comparator rather than an analogue comparator would be used.
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`In one embodiment a projection display system according to the
`
`invention comprises a red laser pointer with four buttons which is used as a
`
`pointing device on a projection screen. The position information as to where
`
`the laser pointer is pointed is obtained by locating the light spot on the screen
`
`by a camera while three buttons and an infra red transmission link provide full
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`mouse compatibility. The fourth push button switches the laser on. The red
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`light spot is detected by a camera equipped with a red light filter. Since the
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`intensity of the laser light is‘generally greater than the intensity of video
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`projectors a simple threshold can be used to discriminate the signal of interest
`
`in a frame of pixels. This position is transformed into normalised absolute
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`screen co-ordinates which is fed into the computer on which the presentation
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`software is running. The mouse cursor follows the red light laser pointer on the
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`screen and remains at its current position if the laser beam is switched off or
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`is outside the active’ screen area. Besides the push button to control the laser
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`there are three other buttons required in order to provide full three button
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`mouse compatibility. The state of these buttons is transmitted via an infra red
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`link to the interaction computer and passed on to the presentation computer.
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`Where a mouse cursor is presented on the screen it is possible to use a laser
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`which emits radiation outside visible wavelengths, for example an infra red
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`laser, and this may have advantages in that there can be no confusion between
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`the position of the cursor and the position where the bright light from the laser
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`lands on the screen. These two positions may not be coterminous if there is
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`any distortion between the generation of the screen display by the presentation
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`computer and the projection of that display onto the screen.
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`From reading the present disclosure, other modifications will be apparent
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`to persons skilled in the art. Such modifications may involve other features
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`which are already known in the design and use of projection display systems
`
`and component parts thereof and which may be used instead of or in addition
`to features already described herein. Although claims have been formulated
`
`in this application to particular combinations of features,
`
`it should be
`
`understood that the scope of the disclosure of the present application also
`
`includes any novel feature or any novel combination of features disclosed
`herein either explicitly or implicitly or any generalisation of one or more of those
`
`features which would be obvious to persons skilled in the art, whether or not
`
`it relates to the same invention as presently claimed in any claim and whether
`
`or not it mitigates any or all of the same technical problems as does the
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`present invention. The applicants hereby give notice that new claims may be
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`formulated to such features and/or combinations of such features during the
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`prosecution of the present application or of any further application derived
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`therefrom.
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`CLAIMS
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`12
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`PCT/11397/00438
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`A projection display system comprising a projector for projecting
`1.
`a computer generated diSplay onto a screen, a pointer producing a narrow
`beam of radiation of higher intensity than the projected image, a video camera
`
`located in a fixed position relative to the projector and arranged to view the
`
`screen, and means for analysing the video signal produced by the camera to
`
`determine the point on the screen illuminated by the laser pointer.
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`10
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`2.
`
`A projection display system as claimed in Claim 1
`
`in which the
`
`pointer is a laser pointer.
`
`3.
`
`A projection display system as claimed in Claim 1 or Claim 2 in
`
`which the computer is arranged to display a cursor at the determined point on
`the screen.
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`15
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`25
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`4.
`
`A projection display system as claimed in any of Claims 1,2 or 3
`
`Claim 2 in which the pointer has one or more buttons.
`
`5.
`
`A projection display system as claimed in Claim 4 comprising a
`
`wireless link between the pointer and the computer.
`
`6.
`
`A projection display system as claimed in Claim 5 in which the
`
`wireless link is an infra red link.
`
`7.
`
`A projection display system as claimed in any preceding claim
`
`including geometrical distortion correction means to correct distortion caused
`
`by the projector, screen and video camera.
`
`8.
`
`A projection display system as claimed in Claim 7 in which the
`
`geometrical correction means comprises means for generating a calibration
`
`pattern and feeding it
`
`to the projector, means for comparing the pattern
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`produced by the video camera with the generated calibration pattern, means
`
`for generating a correction to bring the pattern produced by the video camera
`
`into a conformity with the generated pattern, and means for applying the
`
`correction to subsequently displayed images.
`
`9.
`
`A system as claimed in any preceding claim including a
`
`presentation computer
`
`for generating the images to be displayed and
`
`presenting them to the projector and an interaction computer for receiving the
`
`signal
`
`from the video camera and generating control
`
`signals
`
`for
`
`the
`
`presentation computer.
`
`10.
`
`A system as claimed in Claim 9 in which the presentation
`
`computer and interaction computer are combined as a single unit.
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`N o
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`:
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`.3
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`LBEEES
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`888%
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`mm
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` 82:8
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`33x8;
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`
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`NM.Emu—c300\
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`1
`
`International application No.
`
`PCT/IB 97/00438
`
`A. CLASSIFICATION OF SUBJECT MATTER
`
`IPC6: GOGF 3/00, GOSF 3/033, G06K 11/18, 6098 5/06, G06K 11/08, 6096 3/02,
`H04N 7/18, 6038 21/132
`According to International Patent Classification (IPC) or to both national classification and IPC
`B. FIELDS SEARCHED
`
`Minimum documentation searched (classification system followed by classification symbols)
`
`IPC6: GOGF, G06K, GOQB, G09G, H04N, 8033
`
`Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched
`
`SE,DK,FI,N0 classes as above
`
`C. DOCUMENTS CONSIDERED TO BE RELEVANT
`
`Category‘ Citation of document, with indication. where appropriate, of the relevant passages
`
`Relevant to claim No.
`
`INTERNATIONAL SEARCH REPORT
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`US 5394183 A (DAVID M. HYSLOP), 28 February 1995
`(28.02.95), column 3,
`line 34 - column 4,
`line 35,
`figure 1
`
`
`
`
`
`
`
`
`(13.10.93), abstract
`EP 0565300 A2 (XEROX CORPORATION), 13 October 1993
`
` EP 0690409 A1 (SHARP KABUSHIKI KAISHA),
`
`
`
` m Further documents are listed in the continuation of Box C. m See patent family annex.
`
`
`
`3 January 1996 (03.01.96)
`
`'
`
`”I"
`
`Special categories of cited documents:
`later document published alter are international filing date or priority
`'A" document defining the general state of the art