# US 6,377,249 B1 · Electronic light pen system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,377,249 B1 - Document ID: US6377249B1 - Status: Granted - Kind: B1 - Application number: 09/188,674 - Filed: 1998-11-09 - Granted: 2002-04-23 - Earliest claimed: 1997-11-12 - Assignees: Excel-Tech Ltd. - Inventors: John R. Mumford - Web page: https://patentgrep.com/patent/US6377249B1 ## CPC - G06F 3/0386: {for light pen} - G06F 3/0321: {by optically sensing the absolute position with respect to a regularly patterned surface forming a passive digitiser, e.g. pen optically detecting position indicative tags printed on a paper sheet (constructional details of pen-shaped pointing devices G06F3/03545, G06F3/03542, G06F3/037)} - G06F 3/03542: {Light pens for emitting or receiving light} - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) ## Abstract An electronic light pen used in conjunction with a video display permits the position of the light pen to be determined with respect to the video display by the particular color or grey scale value of light emitted by the video display and received by the electronic light pen. The light from the video display is separated into three primary colors for a color display, namely red, blue, and green, and separated into grey scale shades for a monochrome display. Positional information of the light pen is calculated based on the relation of the color measured to the color previously programmed and presently displayed on that area of the screen, at any instant in time. The light pen has a focusing system that focuses light from the display to its optical detectors. The optical detectors have red, green, and blue filters to determine the brightness of each color. A grey scale value may be determined if the display is monochrome. An optional telephoto lens attachment allows the light pen to be aimed at displays from a distance, or to be used with projection displays. A display can be written with color information to preprogrammed locations on the screen. The colors at each area of the display can be unique, at any instant in time. When that color is read by the light pen the position may be accurately determined. A colored arrow, or other pointer, similar to a conventional mouse pointer, may be created by using software and may be continuously re-displayed to follow the light pen as it points to different parts of the screen, by determining the color gradient encountered by the light pen and re-positioning the arrow underneath the tip of the pen. ## Claims ### Claim 1 An electronic light pen assembly for use in conjunction with a video display having a plurality of pixels thereon, said assembly comprising: light gathering optical means for receiving light emanating from a video display screen, including at least one photo sensitive detector against which said light from said video display screen is directed; circuit means for receiving signals from said at least one photo sensitive detector, for processing said signals, and for transmitting data signals whose value is determined by the light received from said video display screen by said at least one photo sensitive detector at any instant in time; computer means for receiving said data signals and providing information as to the value thereof; wherein, at any instant in time, said video display screen and said computer means are linked together; and wherein, at any instant in time, when said electronic light pen is directed at any pixel or group of pixels on said video display screen, a data signal providing information as to the light received from said pixel or group of pixels is transmitted to mapping software resident in said computer; whereby, upon successive iterations of a sampling sequence under the control of said mapping software, the position of said pixel or group of pixels on said video display screen can be determined and mapped. ### Claim 2 (depends on 1) The electronic light pen assembly of claim 1, wherein said light gathering optical means includes a lens and at least one photo sensitive detector chosen from the group consisting of visible light photo sensitive detectors and invisible light photo sensitive detectors. ### Claim 3 (depends on 2) The electronic light pen assembly of claim 2, wherein said photo sensitive detector is monochromatic, so as to be able to detect luminance values within the chosen chromatic band. ### Claim 4 (depends on 1) The electronic light pen assembly of claim 1, wherein said light gathering optical means includes a lens and at least two photo sensitive detectors chosen from the group consisting of red photo sensitive detectors, green photo sensitive detectors, blue photo sensitive detectors, and invisible light photo sensitive detectors; and wherein each photo sensitive detector has a respective red, green, blue, or invisible light color filter associated therewith. ### Claim 5 (depends on 2) The electronic light pen assembly of claim 2, wherein said electronic light pen contacts said video display screen, and said light gathering optical means further includes a light pipe which comprises a plurality of optical fibres arranged in at least one bundle thereof so as to deliver a portion of the light received from said video display screen to said at least one photo sensitive detector, respectively. ### Claim 6 (depends on 4) The electronic light pen assembly of claim 4, wherein said electronic light pen contacts said video display screen, and said light gathering optical means further includes a light pipe which comprises a plurality of optical fibres arranged in at least two bundles thereof so as to deliver a portion of the light received from said video display screen to said at least two photo sensitive detectors, respectively. ### Claim 7 (depends on 2) The electronic light pen assembly of claim 2, wherein said computer includes software resident therein to write a distinctive signal to other area of the video display screen where said electronic light pen is located at any instant in time, and to retain prior signals in time sequence, whereby a trace of the locus followed by said electronic light pen as it traverses said video display screen can be displayed thereon, in real time. ### Claim 8 (depends on 1) The electronic light pen assembly of claim 1, wherein said video display screen is chosen from the group consisting of cathode ray tubes, liquid crystal displays, projection type displays, conventional television tubes, plasma displays, electroluminescent displays, light emitting diode driven displays, and multi-color lamp driven displays. ### Claim 9 (depends on 4) The electronic light pen assembly of claim 4, where there are at least red, green, and blue photosensitive detectors and respective associated color filters, and wherein the output from each photo sensitive detector is analog, and each respective analog signal is subsequently fed to an analog-to-digital convertor so as to provide digital values of said data signals whose value is determined by the light received from said video display screen by said red, green, and blue photo sensitive detectors at any instant in time. ### Claim 10 (depends on 2) The electronic light pen assembly of claim 2, wherein a cursor pointer on said video display screen may be generated by resident software in said computer, and wherein at least a specified portion of said cursor pointer has a predetermined optical value; whereby when said cursor pointer is displayed and said electronic light pen is placed over at least said specified portion thereof, and when said screen is temporarily re-written, a locating algorithm of said software will associate said cursor pointer with said electronic light pen, so that if said light pen is moved, said cursor pointer will follow said electronic light pen. ### Claim 11 (depends on 4) The electronic light pen of claim 4, wherein a cursor pointer on said video display screen may be generated by resident software in said computer, and wherein a specified gradient of optical values is assigned to said cursor pointer; whereby, when said cursor pointer is displayed and said electronic light pen is placed thereover, and when said screen is temporarily re-written, a locating algorithm of said software will associate said cursor pointer with said electronic light pen; and wherein, when said light pen is moved so as to be associated with another optical value of said gradient of optical values, said software will cause said cursor to move in such a manner as to mimic the speed at which said electronic light pen is being moved. ### Claim 12 (depends on 4) The electronic light pen assembly of claim 4, wherein said lens is a collimating lens. ### Claim 13 (depends on 12) The electronic light pen assembly of claim 12, wherein said electronic light pen further includes a light emitting diode emitter whose output is directed to said collimating lens, and subsequently towards said video display screen; wherein said video display screen includes photo receptor means to receive and decode light signals emanating from said electronic light pen; and wherein said electronic light pen includes signal generating means to cause specific digital data signals to be transmitted therefrom by means of said light emitting diode emitter. ### Claim 14 (depends on 4) The electronic light pen assembly of claim 4, wherein a prism is interposed between said lens and said red, green, blue, and invisible light photo sensitive detectors, instead of said red, green, blue, and invisible light color filters. ### Claim 15 (depends on 1) The electronic light pen assembly of claim 1, wherein said electronic light pen further includes pressure sensitive means to provide various output signals within a predetermined range of values, the value of which output signals varies with the pressure exerted by said electronic light pen against said video display screen. ### Claim 16 (depends on 1) The electronic light pen assembly of claim 1, wherein said electronic light pen further includes a wireless radio transmitter for transmitting data signals to said computer. ### Claim 17 (depends on 1) The electronic light pen assembly of claim 1, wherein said electronic light pen further includes a variable length focusing mechanism, whereby the area on said video display screen from which the optical values thereof may be determined may be changed in size and focus by adjustment of said variable length focusing mechanism. ### Claim 18 An electronic light pen assembly for use in conjunction with a video display having a plurality of pixels thereon, said assembly comprising: light gathering optical means for receiving light emanating from a video display screen, including at least one photo sensitive detector against which said light from said video display screen is directed; circuit means for receiving signals from said at least one photo sensitive detector for processing said signals, and for transmitting data signals whose value is determined by the light received from said video display screen by said at least one photo sensitive detector at any instant in time; and computer means for receiving said data signals and providing information as to the value thereof; wherein, at any instant in time, said video display screen and said computer means are linked together, and at any instant in time the optical value of each pixel on said video display screen is unique and is known to mapping software resident in said computer; whereby, when said electronic light pen is placed adjacent any pixel or group of pixels on said video display screen, said mapping software can determine the position of said electronic light pen by processing the data signals received from said electronic light pen at that instant in time, the value of said data signals having been determined by the light being received from said video display screen by said at least one photo sensitive detector at that instant in time. ### Claim 19 (depends on 18) The electronic light pen assembly of claim 18, wherein each pixel value of said plurality of pixels on said video display screen at any instant in time has a unique grey scale value. ### Claim 20 (depends on 18) The electronic light pen assembly of claim 18, wherein each pixel value of said plurality of pixels on said video display screen at any instant in time has a unique luminance value. ### Claim 21 (depends on 18) The electronic light pen assembly of claim 18, wherein said electronic light pen contacts said video display screen, and said light gathering optical means includes a lens, red, green, and blue color filters, and red, green, and blue photo sensitive detectors associated with said red, green, and blue filters, respectively; and wherein each pixel value of each pixel on said video display screen has a unique value based on the red, green, and blue components thereof. ### Claim 22 (depends on 21) The electronic light pen assembly of claim 21, wherein said electronic light pen contacts said video display screen, and said light gathering optical means further includes a light pipe which comprises a plurality of optical fibres arranged in three bundles so as to deliver a portion of the light received from said video display screen to each of said red, green, and blue color filters. ### Claim 23 (depends on 21) The electronic light pen assembly of claim 21, wherein said computer includes software resident therein to write a distinctive signal to the area of the video display screen where said electronic light pen is located at any instant in time, and to retain prior signals in time sequence, whereby a trace of the locus follows by said electronic light pen as it traverses said video display screen can be displayed thereon, in real time. ### Claim 24 (depends on 18) The electronic light pen assembly of claim 18, wherein said video display screen is chosen from the group consisting of cathode ray tubes, liquid crystal displays, projection type displays, conventional television tubes, plasma displays, electroluminescent displays, light emitting diode driven displays, and multi-color lamp driven displays. ### Claim 25 (depends on 21) The electronic light pen assembly of claim 21, wherein the output from each photo sensitive detector is analog, and each respective analog signal is subsequently fed to an analog-to-digital convertor so as to provide digital values of said data signals whose value is determined by the light received from said video display screen by said red, green, and blue photo sensitive detectors at any instant in time. ### Claim 26 (depends on 21) The electronic light pen assembly of claim 21, wherein a cursor pointer on said video display screen may be generated by resident software in said computer, and wherein at least a specified portion of said cursor pointer has a predetermined optical value; whereby when said cursor pointer is displayed and said electronic light pen is placed over at least said specified portion thereof, and when said screen is temporarily re-written so as to display unique optical values for each pixel thereon, a locating algorithm of said software will associate said cursor pointer with said electronic light pen, so that if said light pen is moved, said cursor pointer will follow said electronic light pen. ### Claim 27 (depends on 21) The electronic light pen of claim 21, wherein a cursor pointer on said video display screen may be generated by resident software in said computer, and wherein a specified gradient of optical values is assigned to said cursor pointer; whereby, when said cursor pointer is displayed and said electronic light pen is placed thereover, and when said screen is temporarily re-written so as to display unique optical values for each pixel thereon, a locating algorithm of said software will associate said cursor pointer with said electronic light pen; and wherein, when said light pen is moved so as to be associated with another optical value of said gradient of optical values, said software will cause said cursor to move in such a manner as to mimic the speed at which said electronic light pen is being moved. ### Claim 28 (depends on 21) The electronic light pen assembly of claim 21, wherein said lens is a collimating lens. ### Claim 29 (depends on 28) The electronic light pen assembly of claim 28, wherein said electronic light pen further includes a light emitting diode emitter whose output is directed to said collimating lens, and subsequently towards said video display screen; wherein said video display screen includes photo receptor means to receive and decode light signals emanating from said electronic light pen; and wherein said electronic light pen includes signal generating means to cause specific digital data signals to be transmitted therefrom by means of said light emitting diode emitter. ### Claim 30 (depends on 21) The electronic light pen assembly of claim 21, wherein a prism is interposed between said lens and said red, green, and blue photo sensitive detectors instead of said red, green, and blue color filters. ### Claim 31 (depends on 21) The electronic light pen assembly of claim 21, wherein said electronic light pen further includes pressure sensitive means to provide various output signals within a predetermined range of values, the value of which output signals varies with the pressure exerted by said electronic light pen against said video display screen. ### Claim 32 (depends on 21) The electronic light pen assembly of claim 21, wherein said electronic light pen further includes a wireless radio transmitter for transmitting data signals to said computer. ### Claim 33 (depends on 18) The electronic light pen assembly of claim 18, wherein said electronic light pen further includes a variable length focusing mechanism, whereby the area on said video display screen from which the optical values thereof may be determined may be changed in size and focus by adjustment of said variable length focusing mechanism. ### Claim 34 A method of locating the position on a video display screen being touched by an electronic light pen; wherein said electronic light pen comprises light gathering optical means for receiving light emanating from said video display screen, including at least one photo sensitive detector against which said light from said video screen is directed; and circuit means for receiving signals from said at least one photo sensitive detector, for processing said signals, and for transmitting data signals whose value is determined by the light received from said video display screen by said at least one photo sensitive detector at any instant in time; wherein a computer receives said data signals, and provides information as to the value thereof; wherein, at any instant in time, said computer and said video display screen are linked together, and said computer includes driver means for writing specific color and/or luminance values to any designated portion of said video display screen; and wherein, at any instant in time, when said electronic light pen is at said position which is adjacent any pixel or group of pixels on said video display screen, a data signal providing information as to the light being received from said pixel or group of pixels is transmitted to mapping software resident in said computer; said method comprising the steps of: (a) momentarily dividing the video display screen into n equal portions, and displaying n mutually exclusive colors or luminance values, one in each of said n equal portions, for at least one screen refresh of said video display screen; (b) during said display of n mutually exclusive colors or luminance values, determining the value of said data signal from said electronic light pen, and matching that value to the driver values for said n equal portions on said video display screen so as to determine in which of said n equal portions said position being touched by said electronic light pen is located; (c) dividing the matched portion in which said position is being touched by said electronic light pen into n equal portions for at least one screen refresh of said video display screen, and permitting the remaining n−1 original equal portions to revert to any previous or current video image intended to be displayed therein; (d) during said display of n mutually exclusive colors or luminance values on said matched portion of said video screen display, once again determining the value of said data signal from said electronic light pen and matching that value to the driver values for said n equal portions of said matched portion of said video screen display, so as to determine in which of said n equal portions of said matched portion said position being touched by said electronic light pen continues to be located; (e) repeating steps (c) and (d) sufficient information as to the pixel or group of pixels being touched by said electronic light pen has been determined, so as to require no further division of the continually smaller matched portion; and (f) determining from said mapping software the exact location of said position on said video display screen as a consequence of the value of the data signal from said electronic light pen as it was at the last iteration of step (e). ### Claim 35 (depends on 34) The method of claim 34, wherein there is at least one photo sensitive detector in said electronic light pen, which at least one photo sensitive detector is capable of distinguishing between two mutually exclusive colors or two mutually exclusive luminance values; and wherein n is equal to 2. ### Claim 36 (depends on 34) The method claim 34, wherein there is at least a monochromatic photo sensitive detector in said electronic light pen, which monochromatic photo sensitive detector is capable of distinguishing among eight mutually distinctive luminance values; and wherein n is equal to 8. ### Claim 37 (depends on 36) The method of claim 36, wherein the values for the mutually exclusive luminance value being displayed on said n equal portions of said video display screen, or said n equal portions of a matched portion thereof, at any instant in time, are 31, 63, 95, 127, 159, 191, 223, and 255, respectively; wherein said values are determined from a table of 0 to 255, where 0 is equal to fully off and 255 is equal to fully on for the driver values for the luminance values on said video display screen being detected by said monochromatic photo sensitive detector. ### Claim 38 (depends on 34) The method of claim 34, wherein there are at least three photo sensitive detectors in said electronic light pen, and each of said three photo sensitive detectors is chosen from the group of photo sensitive detectors comprising red photo sensitive detectors, green photo sensitive detectors, blue photo sensitive detectors, and invisible light photo sensitive detectors; wherein each photo sensitive detector has a respective red, green, blue, or invisible light color filter associated therewith; and wherein said n mutually exclusive colors being displayed on said n equal portions of said video display screen, or said n equal portions of a matched portion thereof, at any instant in time, are in keeping with the follow table: FIRST SECOND THIRD DETECTOR DETECTOR DETECTOR COLOR 1 255 255 255 COLOR 2 255 255 0 COLOR 3 255 0 255 COLOR 4 0 255 255 COLOR 5 255 0 0 COLOR 6 0 255 0 COLOR 7 0 0 255 COLOR 8 0 0 0 where, on a table of 0 to 255, 0 is equal to fully off and 255 is equally to fully on, for the driver values for each of the chosen colors on said video display screen being detected by three of said at least three photo sensitive detectors, respectively. ### Claim 39 (depends on 38) The method of claim 38, wherein there are three photo sensitive detectors in said electronic light pen, which are a red photo sensitive detector, a green photo sensitive detector, and a blue photo sensitive detector, respectively, and each photo sensitive detector has a respective red, green, or blue color filter associated therewith; and wherein said table becomes as follows: RED GREEN BLUE DETECTOR DETECTOR DETECTOR COLOR 1 - WHITE 255 255 255 COLOR 2 - CYAN 255 255 0 COLOR 3 - MAGENTA 255 0 255 COLOR 4 - YELLOW 0 255 255 COLOR 5 - RED 255 0 0 COLOR 6 - GREEN 0 255 0 COLOR 7 - BLUE 0 0 255 COLOR 8 - BLACK 0 0 0