US2487641A - Electronic pointer for television images - Google Patents

Description

Nrw., 19459 W. E. DENK ELECTRONIC POINTER FOR TELEVSION IMAGES Filed Sept. 7, 1946 Patented Nov. 8, 1949 ELECTRONIC POINTER FOR TELEVISION IMAGES William E. Denk, Haverford Township, Delaware County, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application September ,7, 194.6, SerialNo. 695,542

6 Claims.

The invention herein described and claimed relates to television systems and circuits. More particularly, the instant invention appertains to a novel arrangement of apparatus through the agency of which an unseen television announcer or lecturer is enabled visually to direct the attention of the television audience to a specific point of interest in a televised scene or picture.

In the telecasting of certain types of television program material, in which the announcer does not himself appear before the camera, it is sometimes important that the announcer be enabled to direct attention to a specific individual or point o1 interest by means which are clearly visible to theftelevision audience, but which do not distract the televised subject or subjects. For example, in telecasting a football scene an announer may Wish to point out a particular player, or, during a= time-out period, he may desire to direct attention to an important public gure in the stands. Ideally, this is accomplished through the agency of means having no direct association with the televised scene, but which function instead in cooperation with control circuits and apparatus remote from the cameras eld of View.

To the foregoing general ends, the present invention provides apparatus by means of which an announcer may superpose an attention-directing arrow, spot, or line, directly upon the appropriate region of the transmitted picture. This superposition is conveniently accomplished at video frequency, and at any convenient stage between the television camera and the television transmitter-preferably in the television control room with which the pickup camera is associated.

In accordance with one embodiment of the invention, there is provided` in the control room overlooking the televised scene a conventional picture monitor tube on the fluorescent screen of which the televised scene or action is reconstituted. The announcer whose duty it is to describe the televised scene is provided with a special pointer which he brings into contact with that portion ot the glass face of the tube directly overlying the regionof the reconstituted picture to which attention is to be directed. The pointer includes, at the tube-engaging end thereof, means responsive to the passage of the electron beam thereby (or to the presence of the electron beam thereunder) for synchronously generating a short electrical impulser This electrical impulse is preferably amplified, limited, or shaped to give it a desired wave-form and duration. It is then combined with the video signal and transmitted as a part thereof. Depending upon the polarity of the inserted electrical impulse, the received television picture will include either a bright spot or a dark spot whose position corresponds to the point indicated by the announcer. The shape and the intensity of the bright (or dark) spot may be controlled in part by the shape of the tube-engaging end of the pointer, and in part by the electrical circuits employed.

The tube-engaging portion of the pointer may, for example, comprise a conductive terminal portion which derives an electrical impulse from the cathode ray beam, by capacitive coupling thereto, whenever said beam passes directly beneath the pointer. Regardless of the specic means employed, the invention contemplates the derivation of electrical impulses from selected areas of a reconstituted television picture, substantially synchronously with the scanning thereof, the electrical impulses thus derived being thereafter combined with the video signal prior to transmission. Because the circuits employed in accomplishing these ends produce negligible delay, the inserted impulses appear in the nal picture at a position corresponding substantially identically with the position of the impulse-deriving pointer.

Accordingly it is a principal object of the present invention to provide an improved apparatus by means of which a television announcer, himself unseen by the television audience, may visually direct the attention of that audience to specic points of interest in the transmitted picture.

It is another object of the invention to provide television announcers with the electronic equivalent of the optically-projected arrow or spot commonly used by lecturers in describing details shown in lantern slides, moving pictures, and the like.

These and other objects of the invention, and the manner in which they are attained, will appear from the following detailed description and the accompanying drawings, in which Figure 1 is a schematic diagram of one embodiment of the invention; and r Figure 2 is a cross-sectional drawing, on an enlarged scale, of a preferred embodiment of the pointer illustrated schematically in Figure 1.

The television system of Figure 1 comprises, inter alia, a television camera 3 (including its related synchronizing and deecting circuits), and a video frequency amplier 4 by means of which the video output signal of camera 3 is amplified. The amplied signal is applied to one of the input terminals of a conventional signal combining amplier 5 (the purpose of which will appear hereinafter), and also to the intensity control grid 6 of a picture monitor tube l, upon the screen 8 of which the scene viewed by camera 3-is reconstituted. The deflecting yoke 9 is supplied with suitable deecting signal currents derived from the deflecting signal circuits I0. In order that the scanning action of the television camera 3 and the monitor tube 1 be precisely synchronized, the delecting signal circuits of the camera and of the monitor tube may be driven from a common source of synchronizing signals. In the figure the synchronizing signals used to drive the deflecting signal circuits I are derived from television camera 3 by way of path II.

In accordance with the present invention there is provided a suitable pointer, or indicating device, I2 having a tube-engaging portion I4 with which an announcer or lecturer may engage the face portion I5 of the monitor tube 1. The tube-engaging portion I4 comprises means, or has means associated therewith, for generating an electrical impulse synchronously with the passage of the electron beam thereunder or thereby. The electrical impulse thus generated is transferred, via the conductor I6, to a conventional video frequency ampliiier I'! in which the impulse is amplified to any desired level.

Preferably,` though not necessarily, the voltage impulses derived from the video frequency amplifier I'I are next passed through a pulse-shaping device I8. This device may comprise conventional pulse-shaping circuits constructed and arranged to yield, in response to pulses from- Y amplifier I1, output pulses of a predetermined quency signal derived from the television camera 3 with the impulse signal derived from the pointer I2. The combined video output signal derived from the signal combining amplier 5 may be applied, by way of the conductor 21, to subsequent video frequency amplifier stages, and thence to the television transmitter, or to any other signal utilization means (not shown).

Since the television camera 3 and the picture monitor tube 1 are synchronized in their scanning operations, and since the time delay produced by devices I 1, I8 and I9 is ordinarily negligible, the voltage impulses derived from pointer I2 appear in the nal picture in a position corresponding substantially to the position of the pointer I2 with respect to the screen 8 of the monitor tube 1. However, should the time delay be of a magnitude suiiicient to be disadvantageous, its eifect may easily be eliminated by lengthening the conductor 24 (to the right of junction 25) to an extent such that the delay therein corresponds to the delay inherent in the path comprising the conductor 26, monitor tube 1, pointer I2, devices I1, IB'and I9, and the conductor 23.

In the operation of the system of Figure 1, the speaker or announcer, in referring to points of interest in the television picture, employs the uniform amplitude and duration. By way of eX- ample, the device I8 may comprise amplitude limiters, amplifiers, voltage differentiating circuits, and the like, in known combination and for the purpose set forth. The pulse-shaping device I8 may advantageously include an Eccles- Jordan trigger circuit, a known device which may be employed to convert pulses of random amplitude and duration into pulses of uniform amplitude and duration. A circuit of this type is described, for example, in Hoag, Basic Radio, 1942. l0. 235.

The pulses derived from the pulse-shaping device I8 are preferably applied to a conventional paraphase amplier I9, i. e. an amplier which is capable of converting a single-side input signal into a push-pull output signal. A known form of paraphase amplifier, suitable for the present purpose, comprises a triode having output loads in both the plate and cathode circuits, and across which there appear like signals of opposite phase or polarity. Regardless of the specic design of the paraphase amplier, the device I9 provides a pair of output connections 20 and 2l from which there may be selectively obtained either positive or negative voltage impulses respectively. A desired impulse-polarity may be secured at will by operation of the singlepole double-throw switch 22. The electrical impulses thus selected are applied, by way of path 23, to the lower of the two input terminals of signal combining amplier 5. The device 5 may comprise any conventional circuit arrangement which is capable' of adding a plurality of input signals to produce a resultant signal possessing the combined characteristics of the input signals. In the present instance the signal combining amplifier 5 combines the amplified Video frepointer I`2 to point out significant details of the picture appearing on the face of the monitor tube 'I. As indicated above, terminal I4 of the pointer derives an electrical impulse from" the face of the tube synchronously with the passage of the cathode ray beam thereby. Terminal I4 may comprise simply a conducting point Which derives an electrical impulse from the cathode ray beam, by capacitive coupling thereto, as the said beam passes directly beneath the pointer. This electrical impulse, or pulse, is combined with the video signal supplied by camera 3, in the manner hereinbefore explained, and appears as a spot or dot in the reconstituted picture. Whether this spot or dot reproduces in black or in white depends upon the polarity of the pulse inserted in the signal combining amplifier 5 by way of the conductor or path 23. Assuming that the polarity of the video signal supplied by the amplifier 4 is such that white is represented by a positive signal and black by a negative signal, then adjustment of switch 22 to its upper position will produce a white spot, while adjustment of the switch to its lower position will reproduce the voltage impulse as a black spot. Where the attention-directing spot appears in a portion of the picture which is largely black or gray, it will usually be desirable to employ a white spot. However, where the attention-directing spot is to appear in a portion of the picture which is largely White it may be preferable to employ a black spot.

In the operation of the monitor tube 1 care should be taken never to cut off the cathode ray beam entirely, even during completely black portions of the picture, since otherwise the pointer I 2 could derive no impulse from such areas of the picture. In practice this ordinarily will require that the tube be operated over a somewhat restricted contrast range, and that the background level be adjusted to a value suiiiciently high to insure that black elements of the picture be reproduced as gray rather than black. Alternatively, however, monitor tube 1 may be operated with no video signal voltage whatever on its control grid 6, i. e. with zero contrast range.

`'Iube 1 may then `be `regarded as merely .a `means *for synchronously reproducing the scanning pattern of camera 3. Since, under these conditions, no picture or image appears on screen 8, the anrnouncer may most readily `locate pointer i2 rela- -tive to screen .8 vby observing the position of the pointer spot Vin a conventional monitor tube (not Sho-wn) operating from the combined signal supp'lied by signal combining amplifier f5.

In general, it will be desirable to make `the terminal `I4 of pointer l2 rof suilicien-t size that voltage impulses are induced therein at appropriate points in a sufficient number of lines to enable the electronically inserted light spot to be readily seen and interpreted by those viewing the transmitted picture. rWhere the pulse shapingdevice I8 designed to provide a narrow output :pulse in response to `the electrical impulse derived -by terminal M, the attention-directing "indication, as `seen in the reconstituted picture, will consist of a narrow, generally vertical line extending over `a number of picture lines corresponding `to the number of lines actually covered the pointer terminal. On the other hand, if the pulse shaping device I8 comprises only a voltage limiter, or is omitted entirely, the size and shape of the `resulting bright (or dark) area will correspond generally to that of the facecontacting portion of the pointer.

`A preferred embodiment of .the impulse-pickup portion of pointer I2, is illustrated in section, on an enlarged scale, Ain Figure 2 Certain electrical features vthereof are illustrated schematically. The main body portion of the pointer comprises a hollow `metal tubular member 28 which, as will be explained hereinafter, also serves as the outer `.conductor of .the coaxial line employed in transmitting electrical impulses to the video frequency amplifier l1 of Figure 1. An insulating bushing 29, in threaded engagement with tubular member 28,*serves as a support for the picture-tubecontacting, impulse-pickup element 30. Element 38 preferably comprises a flexible, spring-steel wire, bent in the region 3| to enable one employing the pointer to place the straight portion of the wire 30 in contact with the face of the monitor tube 1. If desired the free end of element 30 may be provided with a flattened, arrow-shaped point in order to improve the directional indication of the pointer.

While the voltage impulse may be passed directly through tubular member 28 and thence by way of a flexible coaxial cable (not shown) to video amplifier I1 (Figure l), I prefer to apply the derived voltage impulse to the grid of a cathode follower circuit, in order that the high input impedance of the pickup wire 3U may be properly matched to the low impedance presented by the coaxial line forming the main body portion of the pointer. The cathode follower circuit may conveniently comprise a triode 32 having a cathode load resistor 33 connected between cathode 34 and tubular member 28. Pickup wire 3U is coupled to grid 35 by way of capacitor 36. A grid lead 3l is connected in conventional manner between grid 35 and tubular member 28. Capacitor 36 is preferably small, and so related to the resistance of grid leak 3l that these elements (3G-31), acting as a high-pass lter, greatly attenuate signals of horizontal sweep frequency and less. Anode 38 is bypassed to member 28 by means of a video bypass condenser 39.

An output signal is derived from the cathode follower stage by means of conductor 40 which, as indicated in Figure l, serves as the inner 6 conductor of the coaxial line which comprises the main body portion of pointer l2. A plurality of apertured linsulating discs 4| may be employed to center `the inner conductor 40 with respect to the -outer tubular conductor '28. Discs `4| may be suitably notched at their periphery `to permit passage therethrough of a conductor 42 by means .of which the Ausual fixed positive potential may be applied to anode 38. The tubular conductor 28 is, of course, preferably maintained at ground potential. Details having to do with the physical arrangement of vacuum tube 32 within the tubular member 28 have not been illustrated, but will be apparent to those familiar with the construction of radio test instrument probes, certain types of which include a vacuum tube detector or amplifier stage housed within the tubular body thereof. The tube 32 should, of course, be of a miniature or sub-miniature variety in order to reduce to a minimum the space-requirements of the circuit.

Although the present invention is herein illustrated and described with particular reference to certain specific physical embodiments it will be apparent to those skilled in the art that Various alternative arrangements may be employed within the scope of the invention defined in the appended claims.

I claim:

1. In a television system, a television camera, meansfor deriving a video frequency signal therefrom, a cathode ray tube having means for generating a cathode ray beam and having means 4for d eecting said beam over a wall of said tube synchronously with the scanning operation of said camera, a pointer having a terminal portion adapted to be brought into direct contact with any point on the outer surface of said wall, said terminal portion comprising means responsive to the passage thereby of said cathode ray beam for generating an electrical impulse, and means for combining said impulse with a video frequency signal from said camera.

2. In a television system, a television camera, means for deriving a video frequency signal therefrom, a picture tube having a screen and means for sweeping a cathode ray beam over said screen synchronously with the scanning operation of said camera, means for applying said video signals to said picture tube whereby the scene televised by said camera is reconstituted on said screen, a pointer having a terminal portion adapted to be brought into adj acency with said screen, said terminal portion comprising means responsive to that region of the reconstituted image adjacent thereto for generating an electrical impulse synchronously with the movement of said beam thereby, and means for combining said impulse with said video signal.

3. In a television system, a television camera, a picture tube having a uorescent screen and having means for sweeping a cathode ray beam over said screen synchronously with the scanning operation of said camera, means for applying video signals generated in said camera to said picture tube whereby to reconstitute on' said screen the scene televised by said camera, a pointer having a conductive terminal portion adapted to be brought into adjacency with said screen and thereby into cooperative relation with said cathode ray beam, a signal combining device having a plurality of signal input circuits, means for applying video signals generated in said camera to the rst of said circuits, and means coupling said conductive terminal portion to the second of said circuits.

4. In a television system, a television camera, means for deriving a video frequency signal therefrom, a cathode ray tube having means for generating a cathode ray beam and having means for deecting said beam over a Wall of said tube synchronously with the scanning operation of said camera, a pointer having an indicating portion terminating in an electrically conductive capacity-element, said capacity-element being adapted to be brought into direct contact with any point on the outer surface of said Wall, said capacity element deriving an electrical impulse from said cathode ray beam, by capacitive coupling thereto, coincidentally with the sWeep` ing of said beam past said capacity-element, and means for combining said electrical impulse with a video frequency. signal from said camera.

5. In a television system, a television camera, means for deriving a video frequency signal therefrom, a cathode ray tube having a face and having means for directing an electron beam at said face, beam deflection means cooperating with said cathode ray tube and electrically controlled by said television camera for synchronously reproducing on the face of said cathode ray tube the scanning pattern of said television camera, position indicating apparatus wholly external to said television camera and to lsaid cathode ray tube, said apparatus including an indicator-portion which is adapted to be brought into adjacency with any point on the face of said cathode ray tube, said apparatus comprising means responsive to the generation of that portion of the reproduced scanning pattern which is immediately adjacent said indicatorportion for generating an electrical impulse "8 coincidentally with the movement of said electron beam past said indicator-portion, and means for combining said impulse with a video frequency signal derived from said television camera.

6. In a television system, a television camera, means for deriving a video frequency signal therefrom, a picture tube having a screen and means for sweeping a cathode ray beam over said screen synchronously with the scanning operation of said camera, means for applying said video signals to said picture tube whereby the scene televised by said camera is reconstituted on said screen, a pointer having a terminal portion adapted to be brought into adjacency with any selected point on said screen, said terminal portion comprising means responsive to that region of the reconstituted image adjacent thereto for generating an electrical impulse synchronously with the movement of said beam thereby, a pulseshaping device constructed and arranged to develop, in response to applied pulse voltages, uniform output pulses of predetermined Waveform, means for applying said generating electrical impulses to said pulse-shaping device, and means for combining the output pulses of said pulseshaping device with said video frequency signal.

WILLIAM E. DENK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,047,533 Von Ardenne July 14, 1936 2,225,032 Carbonara Dec. 17, 1940 2,275,026 Bedford Mar. 3, 1942

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