3,668,312
`[151
`7
`United States Patent
`
`‘Yamamoto et al. [451 , June 6, 1972 7 A
`
`
`
`
`Stuparetal. .........,..........2so/217 CR
`3,475,612 10/1969
`Bridgett . . . . . . . . .
`. . . . §§340,324A
`3,189,889
`6/1965
`
`3,292,489 12/1966 ' Johnson et al.
`".340/324A
`3,516,062
`6/1970
`Spraker ............................... ..340/152
`
`Primary Examiner——Robert 1... Griffin
`Assistant Examiner—Barry Leibowitz
`Attorney——Sughrue. Rothwell, Mion, Zinn & Macpeak
`'
`ABSTRACT
`
`[57]
`
`A televisiomtelephone system for information transmission in
`a subscriber-subscriber communication mode or subscr'ber-
`computer communicafion mode’ wherein the informgmon
`transmission is effected between an information receiving
`wry. am.’ a."=".m*¥I*"s pm» which may be 2 comm. A
`"°‘"'°“ ‘“d‘°““"g “3““' °""‘ be 5'3"‘ b‘‘‘’'‘ f’°‘“ ‘he ’°°°'""3
`party to the transmitting party by using a light-pen and a signal
`switching network. The position indicating signal is sent to the
`transmitting party to indicate a command of the receiving
`party by displaying the position indicating signal superposed
`on the transmitted picture, or this indication information may
`be further processed and utilized by the transmitting party to
`form a definite digital indication of the position information.
`
`-
`
`10 Claims, 7 Drawing Figures
`
`[54] TELEVISION TELEPHONE SYSTEM
`[72]
`Inventors: Kazuyuki 1
`Yamamoto,
`Tokorozawa;
`Ryoichi Matsuda, Tokyo, both of Japan
`
`[73] Assignee: Nippon Telegraph & Telephone Public
`Corporation, Tokyo, Japan
`'
`
`Apr‘ 2’ 1970
`Filed:
`[22]
`[21] Appl. No.: 25,136
`
`[30]
`
`Foreign Application Priority Data
`Apr. 10, 1969
`Japan...................................44/27239
`
`}’,'.S'§£'.:':':‘:::::""‘"""'"::::::::::::::::::iT?Tf:??.i.‘fl3i‘}o’;§
`{iii
`[58] Field oiS.e.a-rch............... .. 178/615, 6.8; 340/324 A, 152,
`340/154; 280/214, 217; 179/2 TV
`
`[56]
`
`.
`References Cned
`UNITED STATES pA1-EN1-S
`
`7
`
`_ Schoeffler............................. ..178/6.8
`Cuccio.....
`..340/324 A
`
`............ .._.'.340/324 A
`Koster...,..
`
`
`
`6/ 197 1.
`3/1970
`6/1968
`
`3,584,142
`3,500,336
`3,389,404
`
`
`
`Zynga Exhibit 1008
`
`

`
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`1
`TELEVISION TELEPHONE SYSTEM
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`
`3,668,312
`
`2
`
`c. If a selected indication signal is to be sent back from the
`infonnation receiving party to an information center based on
`the recognition of the received picture and on the selection of
`an item in the received two-dimensional picture by means of a
`push button or the like, some additional information must also
`be supplied from the infomiation center indicating by which
`button the selected indication signals are to be sent. Such ad-
`ditional information is supplied by means of a voice signal or
`as a visual signal in the same transmitted picture signal. How-
`ever, the indication by voice takes a lot of time, and the indi-
`cation by picture is limited by the size of the picture and also
`by the frequency bandwidth of the transmitting path.
`d. Since the indication from the receiving party to the infor-
`mation supplying party is either by voice or dial signals, the in-
`dication is indefinite and insufiicient to indicate detailed two-
`dimensional
`information. Therefore, communication of a
`decision may not smoothly be effected.
`SUMMARY OF THE INVENTION
`
`The present invention has for its object to realize a novel
`television-telephone system wherein during the communica-
`tion of a television-telephone subscriber with an information
`supplying party, such as another subscriber or a computer, to
`request transmission of certain picture information from the
`supplying party, the information receiving party can send back
`to the supplying party a position indicating signal by pointing
`out a desired point on the received picture, and at the trans-
`mitting side of the supplying party the sent back signal is either
`utilized by visually displaying it as superposed on the trans-
`mitted picture or is utilized by further converting it into a posi-
`tion indicating digital information which may directly be
`processed as an input to the computer.
`The present invention has for its further object to provide
`an indicating means which may easily be applied to existing
`television-telephone sets by making a quite minor modifica-
`tion of the equipment.
`Another object of the present invention is to provide such a
`television system in which the picture infonnation receiving
`television-telephone subscriber may send back definite posi-
`tion indicating information signal irrespective of the image
`brightness of the indicating point in the received television
`image, and moreover this position indicating information may
`definitely be detected at the transmitting side or information
`supplying party visually or may further be processed to detect
`the very accurate position indicating information.
`The television-telephone system of the present invention is
`characterized in that a light-pen means is provided with the
`receiving television-telephone equipment, which light-pen
`means comprises hook or jack type nonnally off switches
`which operate by the removal of the light-pen from the normal
`position. The television-telephone equipment
`is so con-
`structed that by the operation of these switches the local
`synchronizing
`signal
`oscillating
`circuit
`producing
`a
`synchronizing signal for its own transmitter is switched off,
`and a synchronizing signal is obtained by a separation process
`from the signal of the received picture information. By placing
`the light-pen at a position in the rasterof the received picture,
`the light-pen is energized to produce a position indicating
`signal which is sent back to the transmitting party by superpos-
`ing it on the separated synchronizing signal.
`the thus
`In a further aspect of the present
`invention,
`produced position indicating signal sent back in superposition
`with the synchronizing signal is received at the transmitting
`side and is divided into the position indicating signal and the
`synchronizing signal. The synchronizing signal is further di-
`vided into a horizontal synchronizing signal and a vertical
`synchronizing signal which signals are used to open respective
`gate circuits so as to pass pulses produced from pulse oscilla-
`tors each having oscillating frequencies corresponding to the
`desired accuracy of the detection of the identification of the
`point indicated by the receiving party. These oscillator pulses
`are passed to horizontal and vertical pulse counters, respec-
`
`l0
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`15
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`20
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`25
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`invention relates to a televion-telephone
`The present
`system,-and more particularly to such a system having means
`for sending back an indication signal from an information
`receiving party of a television telephone system to an infonna-
`tion transmitting party_ of the system by using a light-pen
`which detects the light of the raster of the transmitted infor-
`rnation pictureso asito indicate a command of the receiving .
`party to the information transmitting party. This system can be
`applied to existing television-telephone subscribers by a minor
`modification and it greatly improves the utility of the televi-
`sion telephone system for information exchanging.
`2. Description of the Prior Art
`It is known to transmit picture information by means of a
`television-telephone system" in a subscriber-to-subscriber com-
`munication system or in a subscriber-to-computer communi-
`cation system. Such systems, which will be in actual use in the
`near future, have been disclosed, for instance, in Bell Labora-
`tories Record, Vol. 46, No. 6, June 1968, page 206 entitled “-
`Picture Phone Set Puts a Computer on Executive’s Desks," or
`Bell Laboratories Record, Vol. 47, No. 5, May -June 1969,
`pages 137 -14], “Picture Phone,“ by lriwin Daras. In one of
`the proposed system « for
`the utilization of a television
`telephone system for providing communication between two
`parties, one of which is an information requesting party and
`the other one of which is an infomiation supplying party, the
`information supplying party transmits picture information to
`the other party while monitoring his own picture, and the
`parties communicate with each other by means of verbal com-
`munication. In a more developed form of such a system, the
`information supplying party may be a centralized computer
`which sends out memorized and stored information by means
`of picture and voice signals to an information requesting. par-
`ty, and the information requesting party rnayalso send back
`demand information to the information supplying party by
`means of selecting equipment, such as push button selecting
`means in the telephone set.
`V Such a "type of communication may be applied to ,a televi-
`sion-telephone service, wherein a television-telephone sub-
`scriber can request infonnation from ,at central information
`storage center, which may be an electronic computer. Appli-
`cations of this type of service, which_may be termed an infor-
`mation service, may be weather reports, the road weather,
`stock prices and so on. Among such services there is, a seat
`reservation service, for instance, for the reservation of a seat
`in a train, an airplane, theaters, etc. In such a case, the infor-
`mation supplying party supplied visual information showing
`the reserved condition of seats at a certain date or of a certain
`number of a train or a flight. Then a demand from the infor-
`mation requesting party is received by voice or a dial selecting
`signal so as to complete the reservation.
`In such a prior art system, for the above type of service, the
`demand from the information requesting party is sent either
`by voice or by multifrequency audio tone signal produced by
`push buttons to the information supplying party. The televi-
`sion monitoringvportion of a television-telephone set of the
`television-telephone receiving subscriber or party is used to
`display the received infonnation from the information service
`or supplying party, and voice or the dial selecting signal is used
`transmit indication information back to the information sup-
`plying party. Such a_system is not satisfactory, since it in-
`evitably includes substantial disadvantages as listed below.
`a. The camera equipment part of the information receiving
`party is not utilized.
`‘
`b. In the television-telephone exchange equipment, there
`are provided high quality two wideband video transmission
`networks. Nevertheless, in the above type of service, one of
`the wideband transmission networks, i.e., the path from the
`receiving party to the transmitting party is not utilized. There-
`fore, it is uneconomical from the traffic view point.
`
`50
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`55
`
`60
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`65
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`um.-
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`3,668,312
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`3
`tively, which operate to close these gate circuits so as to stop
`the counters and thus to convert the position indicating signal
`into definite digital horizontal and vertical signals representing
`the corresponding horizontal and vertical positions of the in-
`dicated point at the receiving end, and these digital signals are
`treated directly by the computer according to the need.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a detailed block diagram showing a subscriber ap-
`paratus of the television telephone system according to the
`present invention;
`FIG. 2 shows signal wave forms at various parts of the em-
`bodiment shown in FIG. 1;
`FIG. 3 is a schematic diagram illustrating the relation
`between the scanning lines of the raster of the transmitted pic-
`ture and the position of the light-pen;
`FIG. 4 is a simplified block diagram showing an embodi-
`ment of the coupling device of a central computer according
`to the present invention;
`FIG. 5 is a block diagram showing the subscriber apparatus
`of a modified embodiment of the present invention;
`FIG. 6 shows wave forms illustrating the operation of the
`device shown in FIG. 5; and
`FIG. 7 is a diagram illustrating a practical application of the
`system of the present invention.
`
`DESCRIPTION OF THE PREFERRED EMBODIMENTS
`
`FIG. 1 is a block diagram showing a practical embodiment
`of the system of the present invention.
`In FIG. 1, 10 is a telephone set of a television telephone sub-
`scriber B, 11 is a handset and 12 is a selecting signal sending
`equipment, for instance, shown in the form of a push button
`type. Since the telephone set per se is known, the detailed ex-
`planation of the same is not made in this specification, but it
`may suffice to note that the set is connected to a central
`exchange 20 via a telephone line 23 by taking off the handset
`11 from the cradle of the telephone set. The subscriber B can
`effect the desired selection by sending out, for instance, mul-
`tifrequency audio signal m by means of the selecting signal
`sending equipment 12, and he can make necessary communi-
`cation by voice through the handset 11.
`30 is a displaying cathode ray tube of the television
`telephone set and 31 refers generally to the display screen of
`the tube. In order to simplify the explanation ofthe present in-
`vention, only the necessary parts for the understanding of the
`invention are shown in the figures, but it should be understood
`that all the necessary parts for the function of the television
`set. such as various deflecting coils of the cathode ray tube or
`the electric sources, are provided in the equipment.
`In accordance with the system of the present invention a
`light-pen 40 is additionally provided and comprises a photo-
`electric element 41, consisting of photo-diode, photo
`transistor or the like, and a contact switch 42, the details of
`which will more fully be described hereinafter. Adjacent to
`the set, for instance,
`in an appropriate portion near the
`cathode ray tube there is provided a cradle type or jack type
`switch for accommodating the light-pen 40 when the light-pen
`40 is not in use. This switch is nonnally off and comprises
`movable contacts 43 and 44 which are mechanically ganged
`together. The normally off position of contacts 43 and 44 is
`shown by the dotted lines, and is the position of the contacts
`when the light-pen 40 is not in use. The on position of the con-
`tacts is shown by the full lines and is effected by taking off the
`light-pen from the switch. These contacts are mechanically
`operated to close the circuit shown by the full lines.
`Each television telephone set houses a synchronizing signal
`oscillating circuit 50, by which an independent synchronizing
`signal is produced per each set and the signal is supplied to a
`synchronizing signal mixing circuit 54 via the fixed contact 45
`and movable contact 43 which is in its normally off position
`when the light-pen is not in use. 53 is a wire for supplying the
`synchronizing signal to the deflecting circuit (not shown) of
`
`l0
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`I5
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`20
`
`25
`
`30
`
`35
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`4
`the camera equipment of the set and is branched from the
`conductor leading to the mixing circuit 54. 51 is a camera
`tube, for instance, a vidicon tube consisting of the camera por-
`tion of the television telephone set of the party B. This camera
`tube supplies an output to a preamplifier 52, which in turn
`supplies the output to the mixing circuit 54 via the fixed con-
`tact 46 and movable contact which is in its normally off posi-
`tion when the light-pen is not in use. The output of the mixing
`circuit 54 is further amplified in the video amplifier 55 and is
`sent out to the exchange 20 via transmitting line 21. The as-
`sociated circuits of the camera tube 51 are known and not
`shown, since they have no particular importance for the un-
`derstanding of the present invention.
`If this subscriber B wishes to obtain a certain information
`service, he must make a necessary selection by dialing. Then
`this party B is connected by the exchange 20 to a transmitting
`party A, the details of which will be given later on. and a com-
`posite video signal a is transmitted via lines 25 and 22. This
`signal a is amplified by a video amplifier 60 and supplied to the
`displaying cathode ray tube 30 via an output amplifier 61. In
`FIG. 1, the display screen 31 of the cathode ray tube 30 is dis-
`playing an image of a picture of train seats indicated by 32 and
`33.
`The details of the transmitting side A will be described
`hereinafter, but briefly, 100 is, for instance, an on-line type
`electronic computer, which may be reached by a predeter-
`mined service code of the system and transmits requested in-
`fomiation in response to additional selecting digits sent from
`the party B. 70 shows generally a voice transmitting device of
`the computer 100, 80 is generally an output device, and 90 is
`an input device of the computer. The details of these equip-
`ments will be described hereinafter. 24, 25 and 26 are the con-
`necting circuits of these equipments in the exchange, wherein
`24 and 25 are wideband circuits and 26 is a voice frequency
`circuit.
`The operation of the system of the invention is as follows:
`As mentioned above, if the television telephone subscriber
`B makes an information service call, his telephone set 10 is
`connected by the exchange 20 to the computer 100. Then a
`composite video signal a typically shown in FIG. 2a is sent out
`from the output equipment 80 of the transmitting side via lines
`25 and 22 to the video amplifier 60 and supplied to the
`cathode ray tube 30 via the output amplifier 61 and displayed
`as visual picture information. In FIG. 2a s indicates a horizon-
`tal synchronizing signal. In this condition the light-pen 40 is in
`the normal or the housed position and the movable contacts
`43 and 44 are in their normally off positions shown by the
`dotted lines. The output signal of the camera tube 51 is sent
`through the preamplifier 52, contacts 44 and 46 and circuits
`54 and 55 to the line 21. The local synchronizing signal
`produced by the synchronizing signal oscillator 50 is fed on
`one hand to the camera deflecting circuit (not shown) and on
`the other hand to the synchronizing signal mixing circuit 54
`and thereafter sent to line 21 via the video amplifier S5. A
`synchronizing signal separating circuit 62 is connected in
`branch from a circuit between the video amplifier 60 and the
`output amplifier 61. This circuit 62 separates the synchroniz-
`ing signal s shown in FIG. 2b from the received composite
`video signal a shown in FIG. 2a. A part of the separated
`synchronizing signal 5 is fed to a monitor deflecting circuit
`(not shown) via wire 63.
`If the party B wishes to send back a position indication
`signal in the received picture information according to the
`present invention, he first picks up the light-pen 40. By this ac-
`tion, the normally off contacts 43 and 44 are mechanically
`moved into the positions shown by the full lines and close the
`light-pen circuit. The top of the light-pen 40 is then pressed
`against the display screen receiving the video information. For
`instance, if it is pressed against point 34 in the screen, the
`switch 42 provided at the top of the light-pen 40 operates by
`the contact pressure, and the photoelectric element 41, con-
`sisting of photo diode, photo transistor, etc., is turned on.
`
`

`
`3,668,312
`
`6
`
`5
`By the operation of the movable contact 43 the synchroniz-
`ing signal oscillating circuit 50 for the subscriber’s own trans-
`mitting system is cut off, and the synchronizing signal b
`separated from the received composite image signal a sent
`from the transmitting party A by the synchronizing signal
`separating circuit 62 as shown ‘in FIG. 2b is instead supplied to
`the synchronizing signal mixing circuit 54. Also by the opera-
`tion of contact 44 the camera tube 51 and the preamplifier 52
`are cut off from the transmitting circuit of the subscriber’s set,
`and the light-pen 40 connected in series with a pulse shaping
`circuit 64 is connected to the synchronizing signal mixing cir-
`cuit 54.
`FIG. 3 is a diagram showing the relation between the in-
`dicating point 34 of the light-pen 40 and raster of the picture
`31’ of the cathode ray tube 30. While receiving picture infor-
`mation, the scanning is made from left to right of the picture
`31' and from top to bottom thereof, and the cathode ray spot
`moves cyclically. At the same time a composite video signal a
`sent from the transmitting side A and shown in FIG. 2a is sup-
`plied to the control circuits of the cathode ray tube. Ac-
`cordingly, the spot is moving on the screen while producing a
`variation of the brightness. In FIG. 3, l_-I,,_,
`is the (n—l) th
`scanning line, and H,,
`is the nth and H,,,,,
`the (n+1) th
`scanning lines, respectively. 34 indicates the position of con-
`tact of .the top of the lighit-pen 40 onto the surface of the
`cathode ray tube. By making the size of top of the light-pen
`slightly larger than the scanning interval, it must cross at least
`one of the scanning lines. The figure shows the nth scanning
`spots crossing the contact point or the indicating point 34. In
`case of interlacing scanning, the passing position of each spot
`in each successive field of an image frame is different, but by
`making the top size of the light-pen the size mentioned as
`above, each scanning interval of the spot
`is sufficiently
`covered by the top of the light-pen. If the nth scanning spot
`passes the indication point 34 of the light-pen 40, a damped
`pulse signal c as shown in FIG. 2c is produced at an output of
`the photoelectric element 41 of the light-pen 40. Since the ele-
`ment 41 consists of a photo transistor or photo diode, which
`may be made sufficiently highly sensitive, it is possible to
`make the light-pen "sufficiently sensitive even at the lowest
`brightness of the raster of the picture. Therefore, even if the
`crossing point between’ the indicating point 34 and the nth
`spot H,. is a black level of the signal, the element 4! produces
`an indication output. However, if required, the circuit of the
`contact switch 42 may additionally be made to include a cir-
`cuit for varying the brightness of the raster of the cathode ray
`tube in the black level. The reason of forming an exponential
`damping of the pulse form shown in FIG. 2c is that the output
`decreases according to an after image character of the
`phosphorescence material of the cathode ray tube.
`The output of the photoelectric element 41 of the light-pen
`40 is- supplied to the pulse shaping circuit 64 and, after apply-
`ing necessary amplification and wave form shaping therein, a
`pulse d having a constant
`level as shown in FIG. 2d is
`produced, and the pulse d is supplied to the synchronizing
`signal mixing circuit 54 via the movable contact 44. In the out-
`put of the synchronizing signal mixing circuit 54, a superposed
`signal of the separated synchronizing signal 12 derived from the
`composite video signal -a transmitted from the transmitting
`party A and the pulse d constituting an indication signal is
`produced in the form of a composite indicating signal e shown
`in FIG. 2e. In this composite signal e the indication pulse
`signal d is superposed in the nth horizontal scanning period,
`and this signal e is used as the position indicating composite
`signal. This composite signal e is applied the necessary amplifi-
`cation by the video amplifier 55 and sent back to the exchange
`20 via line 21. Then the signal e is supplied via line 24 and
`input circuit 90 to the computer 100 and treated as an indica-
`tion information. The operation in the central equipment will
`be described more fully later on. During these period, necessa-
`ry voice information v is sent from the computer by means of
`the voice responsive device 70 to the telephone set 10.
`
`FIG. 4 is a block diagram showing principle of operation of
`an information center A of a television telephone system ac-
`cording to the present invention. There are various types of
`such information centers, and accordingly, the figure illus-
`trates only one possible embodiment, and the present inven-
`tion is not limited to this embodiment.
`In FIG. 4, 20 is the telephone exchange. 21 to 26 are the
`lines tenninating at the exchange and are also shown in FIG. 1
`by the same reference numerals. As mentioned before, 21, 22,
`24 and 25 are the video circuits, and 23 and 26 are the voice
`or audio circuits.
`If this television telephone information
`center A is connected from a subscriber B, such as shown in
`FIG. 1, at first a selecting information code m, for instance,
`consisting of a multifrequency coded audio signal is received
`via line 23, exchange 20 and line 26, by an audio signal
`receiver 71. Then this signal is fed to the computer 100 via
`line 101, thereby transmitting the required selecting informa-
`tion to the computer.
`The computer 100 responds to the received selecting infor-
`mation, and if a pattern or a picture is to be sent according to a
`predetermined program, it sends out an instruction to a video
`signal producing device 80, mainly consisting of a video
`memory device 81, via data controlling lines 104 and 105. In
`' this respect, the computer 100 sends out data containing the
`information content and the associated controlling signal to
`the video memory device 81, which comprises, for instance,
`magnetostriction type delay lines, so as to store the content of
`the picture in the memory device. The memorized information
`content is converted into a video image signal by a converting
`circuit 82. Then this image signal is added with a synchroniz-
`ing signal in a synchronizing signal mixing circuit 83 to form a
`composite video signal a, such asvshown in FIG. 2a, and this
`composite video signal a is sent out to the line 25. If a moving
`picture or an image varying with the progress of time is to be
`supplied to the information requesting subscriber, the com-
`puter sends out a controlling signal to a video tape recorder 84
`via a command line 106 to send out a prerecorded composite
`image signal.
`It
`is also possible to connect a character
`memorizing device (not shown),
`in addition to the video
`memorizing device, to the output of the computer, so that
`desired character patterns are read out by an indicating output
`of the computer to form an independent video information
`signal or to superpose on the desired video information.
`The previously mentioned position indicating composite
`signal e sent back from the television telephone subscriber B is
`supplied via line 21, exchange 20, and line 24 to a video ampli-
`fier 27. This signal e is amplified in the amplifier 27 and sup-
`plied to a video signal separating circuit 28 and to a
`synchronizing signal separating circuit 29, respectively. By the
`above circuits 28 and 29 the signal e is separated into a video
`signal, namely, a position indicating pulse d shown in FIG. 2d
`and synchronizing pulses b shown in FIG. 2b. The synchroniz-
`ing pulses b are further separated into horizontal and vertical
`synchronizing signals by a horizontal synchronizing signal
`separating circuit 91 and a vertical synchronizing signal
`separating circuit 92. These signals are supplied to the cor-
`responding set-input terminals S of flip-flop circuits 93 and 94,
`respectively. The position indicating information signal d
`separated in the videosignal separating circuit 28 is supplied
`to both of the reset terminals R of the flip-flop circuits 93 and
`94. The outputs of the flip-flop circuits 93 and 94 are supplied
`to one of the input terminals of AND gate circuits 95 and 96,
`respectively. The other input terminals of these AND gate cir-
`cuits are supplied with output pulses from pulse signal genera-
`tors 107 and 108, respectively. These generators 107 and 108
`produce pulses having repetition frequencies determined by a
`requirement for the discrimination accuracy of the horizontal
`and vertical positions of the indicating point in the display pic-
`ture. The pulse generator 108 producing vertical position dis-
`criminating pulses may obviously be replaced by a pulse
`source derived from the source producing the horizontal
`synchronizing pulses. The outputs of the AND gates 95 and 96
`are supplied to the inputs pulse counter circuits 97 and 98,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`70
`
`75
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`4:1!
`
`I n 1 tun
`
`

`
`7
`
`3,668,312
`
`8
`
`other circuits. This signal f is displayed on the screen 231 of
`the cathode ray tube 230 of the subscriber C and produces an
`identical image 236 which is exactly same with that of the
`image 36 except that a white dot is indicated on the point 234
`corresponding to the indicating point 34 of the light-pen 40 on
`the picture screen 31 of the receiving set. In this case the sub-
`scriber C can supervise the transmitted imate picture in a loop
`manner through the circuit of the set of the receiving sub-
`scriber B. Therefore, a perfect supervision and confirmation is
`possible over the whole transmission path, and it is very con-
`venient for a very important information transmission.
`As shown in FIG. 6f, the indication of the light-pen at the
`receiving party may be effected in a white image area of the
`picture having a very high brightness. This is convenient in ob-
`taining the output of the photoelectric element of the light-
`pen, but this is inconvenient to the discrimination or identifi-
`cation of the indicated point by the subscriber C. If necessary,
`the output pulse from the pulse shaping circuit 64 is further
`treated, for instance, by an astable type multivibrator which
`detects the wave height of the produced pulse c to alternately
`reverse the polarity of the pulse to a full white level and black
`level. Then the subscriber C can observe an alternately
`switching black and white spot, so that the identification of the
`position indicating signal is easily effected irrespective of the
`brightness of the background picture.
`The present system shown in FIG. 5 is particularly con-
`venient to permit a discussion among several subscribers by
`using the same picture or diagram in a conference conversa-
`tion mode.
`
`10
`
`I5
`
`20
`
`25
`
`30
`
`respectively, whose clearing signal input terminals are sup-
`plied with the horizontal and vertical synchronizing signals,
`respectively. Each of the flip-flop circuits 93 and 94 is set by
`the horizontal or the vertical synchronizing signal, and is reset
`by the arrival of the position indicating information signal d. In
`this manner, by the number or count of pulses in the pulse
`counters at the time when the flip-flop circuits are reset by the
`position indicating signal d, horizontal position information
`and a vertical position information corresponding to the point
`indicated by the light-pen in the received picture of the party
`B are derived. This position information is derived from the
`horizontal position indication lines 110 and the vertical posi-
`tion indicating lines 111. For instance, in the example shown
`in FIG. 3, the information showing the horizontal position of
`the indicating point of the light-pen 40 of the subscriber B on
`the nth scanning line H,, is obtained at the counter output lines
`110. The horizontal position counter 97 counts continuously
`in each of the horizontal scanning periods, however, it is con-
`structed to send out the horizontal position information to the
`computer 100 only when the flip-flop 93 is reset by the arrival
`of the position indicating pulse 11, and the counter 97 is
`stopped accordingly. Through this input device the computer
`100 can receive information concerning the indicated position
`as a continuous digital code having the required accuracy. Ac-
`cordingly, the computer 100 can now respond with the infor-
`mation corresponding to the indicated position, and according
`to the need it may respond to a further command or selecting
`signal In received by the receiver 71 and make the necessary
`operation according to a predetermined program.
`FIG. 5 is a block diagram showing a modified embodiment
`of the present invention. This figure shows a possible embodi-
`ment wherein a television telephone subscriber B commu-
`nicates with another television telephone subscriber C, while
`the subscriber C is sending video information concerning a
`table or a picture 200, that is the both parties B and C commu-
`nicate each other observing an identical picture. In this figure,
`the parts corresponding with those of FIG. 1 are shown by the
`same reference numerals.
`
`35
`
`The equipment of the subscriber B is nearly the same as that
`shown in FIG. 1. The only difference is that the received video
`signal a, sent from the other party C, at the output of video
`amplifier 60 is further supplied by a connection wire 65 to the
`output of the pulse shaping circuit 64. The received image
`signal a is superposed on the output of the photoelectric ele-
`ment 41 of the light-pen 40, and synchronizing signals are
`added at the synchronizing signal mixing circuit 54 for the
`sake of completeness to produce a composite signal shown in
`FIG. 6f, which is