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WO1991011887A1 - Transfert ameliore de signaux d'affichage video - Google Patents

Transfert ameliore de signaux d'affichage video Download PDF

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Publication number
WO1991011887A1
WO1991011887A1 PCT/AU1991/000034 AU9100034W WO9111887A1 WO 1991011887 A1 WO1991011887 A1 WO 1991011887A1 AU 9100034 W AU9100034 W AU 9100034W WO 9111887 A1 WO9111887 A1 WO 9111887A1
Authority
WO
WIPO (PCT)
Prior art keywords
reference voltage
computer
signal
network
station
Prior art date
Application number
PCT/AU1991/000034
Other languages
English (en)
Inventor
Harri Evert Astrom
Original Assignee
Ketex Pty. Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ketex Pty. Ltd. filed Critical Ketex Pty. Ltd.
Publication of WO1991011887A1 publication Critical patent/WO1991011887A1/fr
Priority to FI923454A priority Critical patent/FI923454A7/fi

Links

Classifications

    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/14—Digital output to display device ; Cooperation and interconnection of the display device with other functional units
    • G06F3/1454—Digital output to display device ; Cooperation and interconnection of the display device with other functional units involving copying of the display data of a local workstation or window to a remote workstation or window so that an actual copy of the data is displayed simultaneously on two or more displays, e.g. teledisplay
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G09G5/10—Intensity circuits
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/64—Circuits for processing colour signals
    • H04N9/68—Circuits for processing colour signals for controlling the amplitude of colour signals, e.g. automatic chroma control circuits

Definitions

  • THIS INVENTION relates to improvements in video display for a multicomputer network.
  • the invention is directed to apparatus and method for transferring video signals between computers in a multi-computer network, with automatic level control.
  • a typical multi-computer teaching system comprises a number of student computer stations connected in a network which includes a teacher computer station.
  • An interface circuit is provided between each computer station and the network bus, and a control unit is normally associated with the teacher computer station.
  • the interface circuit may be housed on an adaptor card in each micro-computer.
  • each student computer station can display either an output from its own computer or an output transmitted through the network from either the teacher computer station or another selected student computer station.
  • Each computer station is provided with an adaptor card containing a video logic circuit to enable video display signals to be transferred to and from that computer station.
  • the teacher can communicate with the whole class of students without moving away from the teacher's computer station.
  • the teacher may transfer displays, information and data files, use the computer screen as a blackboard, correct the student's work, use a "mouse" as a pointer, and give different degrees of assistance to students with different abilities.
  • the teacher can also obtain a full picture of the students' progress by scanning their displays. This can be done automatically, or by manual control so that the teacher may observe the individual students' displays for different periods.
  • the multi-computer network therefore provides an efficient teaching tool.
  • the present invention provides a method of transferring video signals between computer stations in a multi-computer network, wherein said video signals include synchronising signals and colour signals, characterised in that a reference voltage is transmitted during at least some of the synchronising signals and said reference voltage is used by the receiving computer station(s) to control the amplification of the received colour signals so as to provide a substantially constant video display level at the monitor of the receiving comp ⁇ ter station(s).
  • a reference voltage is derived at the transmitting station and transmitted during the horizontal synchronising pulses of the video display signals.
  • the reference voltage is sampled and held by each receiving station, and is used to provide a reference level for a plication of the received colour signals. (The reference voltage is removed before the received video display signal is sent to the monitor) .
  • the present invention provides apparatus for transferring video signals between computer stations in a multi-computer network, wherein the video signals comprise synchronising signals and colour signals, said apparatus comprising means for detecting the occurrence of a synchronising signal; means for deriving and transmitting a reference voltage during the detected synchronising signal; means for receiving and retaining the transmitted reference voltage; and means for amplifying the received colour signals in accordance with the retained reference voltage in order to provide a substantially constant video display level.
  • the apparatus is embodied as a logic circuit on an adaptor card fitted to each computer to enable the computer to both transmit and receive a video display.
  • the means for retaining the reference voltage may suitably comprise a sample and hold circuit, but any other equivalent circuit will suffice.
  • the present invention overcomes the abovedescribed problem of known video display transfer systems since a reference voltage is transmitted with the displays, and this reference voltage is used to enable a constant display level to be achieved at the receiving station irrespective of cable and equipment loadings and other factors influencing the level of the received video signals.
  • Fig. 4 illustrates the timing signals at the station receiving a transmitted video display
  • Fig. 5 illustrates the timing signals at the station transmitting the video display.
  • the video display signals transmitted between computer stations in a network consist of analog colour video signals (R, G, B) representing the red, green and blue primary colours together with horizontal (Hsync) and vertical (Vsync) synchronising signals.
  • R, G, B analog colour video signals
  • Hsync horizontal
  • Vsync vertical
  • the method of automatically maintaining constant brightness and quality of the video display according to this invention involves the transmission of a reference voltage to the receiving monitor during a synchronising signal. This reference voltage is retained by the receiving station and is used to provide the correct level of amplification to the received video colour signals. This is achieved by an improved video display transfer circuit, an embodiment of which is shown in Figs. 1 to 3.
  • each circuit comprises a multiplexer 1 which, in use, receives a select signal ("sel o") from the control unit (not shown) to cause the multiplexer 1 to select either the Hsync signal transmitted by its own display adaptor card (H-VGA) or the Hsync signal transmitted through the network bus (H-Net) .
  • the waveform of the Hsync signal selected by the multiplexer 1 is shown as signal Sync A in the timing diagrams of Figs. 4 and 5.
  • the output signal sync A of the multiplexer 1 is fed to an exclusive-or gate 2 which provides an output pulse on each positive or negative level change in the sync A signal.
  • the waveform of the output signal of gate 2 (Exor B) is also shown in Figs. 4 and 5.
  • the Exor B signal pulses output from the exclusive- or gate circuit 2 are fed to a one-shot circuit 3 which acts as a masking circuit.
  • the one-shot circuit 3 provides an output pulse on detecting a pulse from the exclusive-or gate 2, and the length of the output pulse from the one-shot circuit 3 is long enough to mask out the next received pulse from the exclusive-or circuit 2, thereby securing the front edge of the sync A pulse independent of polarity.
  • the output of the one-shot circuit 3 is shown as the wave form "Sync Mask D" in figures 4 and 5.
  • the output signal of the one-shot circuit 3 is fed to a flip-flop 4 which acts as a sample control circuit.
  • the flip-flop 4 provides an output timing pulse C which is fed to the multiplexer circuit 1 and is used to form a Sample signal provided by the multiplexer 1 to a sample and hold circuit 11 via a level translator 10 (Fig. 2).
  • the Sample signal is used to indicate to the sample and hold circuit 11 when the signal from the network is to be sampled, namely, during the synchronising pulse.
  • the wave form of the output signal from the flip-flop 4 is shown as "Sample control FF C" in Fig. 4.
  • the output of the one-shot circuit 3 is also fed to a reference one-shot circuit 17 which outputs a reference signal pulse "Tx Ref E" whose waveform is shown in Figures 4 and 5.
  • the Tx Ref signal has a pulse length of preferably about 20% more than sync pulse sync A so as to ensure that the reference signal is transmitted for sufficient time to be sampled by all receiving circuits.
  • the output of the one-shot circuit 3 is also fed to AND gate 5 the output of which controls switches for the analog video signals R, G, B (as described later) to prevent the reception of the video colour signals during the transmission of a reference voltage as well as preventing the transmission of the reference voltage from one station to its own monitor.
  • the AND gate also receives "select own display” or “select network display” signals from the control unit.
  • the blue, red and green colour signals are fed from the VGA controller of the transmitting computer station to the network.
  • a switch 6 disconnects the transfer circuit from the blue colour signal B from the VGA controller card of the micro-computer during the Hsync signal, thereby allowing a reference voltage to be sent on the Blue line to the LAN network. That is, the reference voltage is not affected by the blue signal.
  • the reference voltage is derived from a voltage reference circuit 7 which is switched into the network by a transistor switch 7A controlled by the output signal Tx Ref E of one-shot circuit 17. Thus the reference voltage is transmitted on the blue line during the duration of the pulses on the Tx Ref E waveform.
  • the reference voltage signal is passed through video buffer circuit 8A and a transmit switch 8B.
  • the transmit switch 8B is controlled by a transmit display signal from the control unit to connect only the transmitting computer station to the network, i.e. the transmit display signal disconnects transmitting portions of all other computer stations from the network so that only one station may transmit at a time.
  • An analog switch 9 controlled by the "own direct" output signal from AND gate circuit 5 also ensures that the transmitted reference voltage is not fed to the monitor of the transmitting computer station while the reference signal is transmitted to the network during the sync pulse.
  • the "sample” signal from the multiplexer 1 indicates when the received signal is to be sampled and held so as to capture the reference voltage being transmitted during the sync pulse of the received video signal.
  • the sample signal from multiplexer 1 is fed to a level translator circuit 10, the output of which is connected to sample and hold circuit 11.
  • the sample and hold circuit 11 will sample the received reference voltage by charging a capacitor through FET switches throughout the sample signal, and hold the charged voltage at the negative going edge of the sample signal.
  • An amplifier 12 is used to amplify the voltage level held by the sample and hold circuit 11, and the amplifier output is then buffered to provide a reference level to the individual video amplifiers for the R, G, and B colour signals.
  • the amplifier 12 has gain adjustment and reference adjustment to allow the proper voltage levels for the video amplifiers of the R, G and B colour signals to be pre-set.
  • the colour video signal received from the network on the blue line (after the sync pulse) is then amplified by amplifier 13.
  • the previously sampled and buffered reference voltage is now used to control a gain control FET switch which acts as a voltage controlled resistance and varies the amplification provided to the blue colour video signal by the amplifier 13 so as to produce a substantially constant level signal.
  • the blue colour signal output from amplifier 13 is then transmitted to the monitor of the computer station via video buffer 15.
  • the output of the amplifier 13 will be of substantially consistent level as determined by the reference voltage transmitted during the sync pulse.
  • the variable degree of amplification thereby compensates for variations to the video signal, for example, as a result of the network cable loading.
  • a network analog switch 14, controlled by the "net display" signal from the AND gate circuit 5, is interposed between amplifier 13 and the monitor to prevent the reference voltage transmitted during the sync signals from being transmitted to the monitor.
  • the video logic circuits 16 for the red and green colour signals are shown in Fig. 3. These logic circuits are similar to the logic circuit for the blue colour signal, except that there is no need to include circuitry for transmitting, or receiving and capturing, the reference voltage as the output of the gain amplifier 12 in the blue signal logic circuit is used to control the individual colour signal amplifiers in the red and green signal circuits as well.
  • a reference voltage is transmitted by that computer station during the synchronising pulses of the video signal.
  • the receiving computer stations use that reference voltage to maintain a substantially constant output display level, irrespective of factors such as cable and equipment loading on the transmitted video signals.
  • the displays at all of the computer stations are of substantially constant level and quality.
  • the reference voltage may be transmitted during the vertical synchronising signals rather than the horizontal synchronising signals.
  • the reference voltage may be transmitted on the red or green colour signals rather than the blue colour signal.
  • the invention may also be used for monochrome video displays, and the term "colour" as used in this specification is to be interpreted accordingly when used in reference to monochrome video signals.

Landscapes

  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Human Computer Interaction (AREA)
  • General Engineering & Computer Science (AREA)
  • Testing, Inspecting, Measuring Of Stereoscopic Televisions And Televisions (AREA)
  • Details Of Television Systems (AREA)
  • Controls And Circuits For Display Device (AREA)

Abstract

Des signaux vidéo sont transmis entre les ordinateurs d'un réseau d'ordinateurs multiples, avec commande automatique des niveaux. Une tension de référence est transmise par l'ordinateur effectuant l'émission des signaux pendant les impulsions de synchronisation horizontales ou verticales desdits signaux vidéo. La tension de référence est détectée par les postes de réception, et est utilisée par chacun d'eux pour procurer le niveau d'amplification correct des signaux couleur vidéo reçus. De cette manière, un niveau d'affichage constant est obtenu à l'écran du poste récepteur, malgré le nombre d'équipements et de câbles branchés et les autres facteurs pouvant influencer le niveau des signaux vidéo reçus.
PCT/AU1991/000034 1990-02-02 1991-02-01 Transfert ameliore de signaux d'affichage video WO1991011887A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
FI923454A FI923454A7 (fi) 1990-02-02 1992-07-30 Foerbaettrad videobild oeverfoering.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPJ842290 1990-02-02
AUPJ8422 1990-02-02

Publications (1)

Publication Number Publication Date
WO1991011887A1 true WO1991011887A1 (fr) 1991-08-08

Family

ID=3774480

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/AU1991/000034 WO1991011887A1 (fr) 1990-02-02 1991-02-01 Transfert ameliore de signaux d'affichage video

Country Status (2)

Country Link
FI (1) FI923454A7 (fr)
WO (1) WO1991011887A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0490502A3 (en) * 1990-12-11 1992-12-30 International Business Machines Corporation Analog image signal processor circuit for a multimedia system
WO1993020660A1 (fr) * 1992-03-31 1993-10-14 Minnesota Mining And Manufacturing Company Etalonnage de couleur pour panneau d'affichage a cristaux liquides
US5367340A (en) * 1990-10-19 1994-11-22 Gec-Marconi Limited Apparatus and method for noise reduction of video signal dependent upon video gain
US5410363A (en) * 1992-12-08 1995-04-25 Lightwave Communications, Inc. Automatic gain control device for transmitting video signals between two locations by use of a known reference pulse during vertical blanking period so as to control the gain of the video signals at the second location

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2908748A (en) * 1954-09-14 1959-10-13 Rca Corp Color television chroma control system
GB1018715A (en) * 1963-02-27 1966-02-02 Fernseh Gmbh Method for controlling the black level of television signals
US3780218A (en) * 1971-08-20 1973-12-18 Zenith Radio Corp Circuit for establishing correct hue setting in color television using virs signal
US4303986A (en) * 1979-01-09 1981-12-01 Hakan Lans Data processing system and apparatus for color graphics display
WO1987007810A1 (fr) * 1986-06-03 1987-12-17 Scientific Atlanta, Inc. Format mac avec signaux alternes de niveau de courant continu et de recuperation d'horloge

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2908748A (en) * 1954-09-14 1959-10-13 Rca Corp Color television chroma control system
GB1018715A (en) * 1963-02-27 1966-02-02 Fernseh Gmbh Method for controlling the black level of television signals
US3780218A (en) * 1971-08-20 1973-12-18 Zenith Radio Corp Circuit for establishing correct hue setting in color television using virs signal
US4303986A (en) * 1979-01-09 1981-12-01 Hakan Lans Data processing system and apparatus for color graphics display
WO1987007810A1 (fr) * 1986-06-03 1987-12-17 Scientific Atlanta, Inc. Format mac avec signaux alternes de niveau de courant continu et de recuperation d'horloge

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5367340A (en) * 1990-10-19 1994-11-22 Gec-Marconi Limited Apparatus and method for noise reduction of video signal dependent upon video gain
EP0490502A3 (en) * 1990-12-11 1992-12-30 International Business Machines Corporation Analog image signal processor circuit for a multimedia system
US5526017A (en) * 1990-12-11 1996-06-11 International Business Machines Corporation Analog image signal processor for a multimedia system
WO1993020660A1 (fr) * 1992-03-31 1993-10-14 Minnesota Mining And Manufacturing Company Etalonnage de couleur pour panneau d'affichage a cristaux liquides
US5369432A (en) * 1992-03-31 1994-11-29 Minnesota Mining And Manufacturing Company Color calibration for LCD panel
US5410363A (en) * 1992-12-08 1995-04-25 Lightwave Communications, Inc. Automatic gain control device for transmitting video signals between two locations by use of a known reference pulse during vertical blanking period so as to control the gain of the video signals at the second location

Also Published As

Publication number Publication date
FI923454A0 (fi) 1992-07-30
FI923454A7 (fi) 1992-07-30

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