US2211066A - Television system - Google Patents

Television system Download PDF

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Publication number
US2211066A
US2211066A US240824A US24082438A US2211066A US 2211066 A US2211066 A US 2211066A US 240824 A US240824 A US 240824A US 24082438 A US24082438 A US 24082438A US 2211066 A US2211066 A US 2211066A
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scanning
zone
picture
zones
light
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Expired - Lifetime
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US240824A
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English (en)
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Maguire Irwin Leonard
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Individual
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
    • H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
    • H04N3/30—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical otherwise than with constant velocity or otherwise than in pattern formed by unidirectional, straight, substantially horizontal or vertical lines
    • H04N3/34—Elemental scanning area oscillated rapidly in direction transverse to main scanning direction

Definitions

  • This invention relates to cathode ray and mechanical methods of scanning in television systems, and it has been devised to simplify difficulties which arise in photocell response, ampli- 5 fiers and the like in both transmission and reception.
  • the present invention provides for reduction of transmission frequency with increased degree of definition of a facsimile to thereby simplify diiliculties of transmission reception and amplification of signals.
  • the light emitted by each picture point actuates thephotocell during the time taken for a scanning spot to traverse one of said points and the response of gas filled types of photocell to this light is proportional to the time during which the light is incident upon it.
  • the greater the definition of the picture the smaller is the response of the photocell for a given brilliance of the individual picture points.
  • the picture points of the facsimile are recreated during the time taken to scan corresponding points of the picture and the apparent brightness to the eye of the recreated picture points of the facsimile depends, for a given source of light, upon the time taken for the scanning spot to traverse the picture point.
  • the photocell response depends upon the total amount of light flux emitted by the scanning spot and since the light of the scanning spot utilised for the recreation of the picture points of the facsimile is more or less uniform and of a size equivalent to that of a picture point, it follows that no definite detail 35, of the picture or facsimile which is smaller in.
  • frequency of the video signal is proportional to the ratio of the area of the picture frame to the area of the scanning spot and to the number of picture frames scanned in a given time and thus the frequency of the video signal is proportional to the definition of the picture and the greater the definition the higher the video signal frequency.
  • the present invention has for its objects the improvement of definition in the facsimile reconstructed at the receiver and reduction of the video signal frequency, and according to this invention the first mentioned object is attained by modulation of the light for the creation of facsimiles by means of a signal which is derived from the diiference in effects of two similar signals subject to be transmitted which are successively scanned in serial order.
  • the definition of the facsimile is rendered independent of the video signal frequency with resultant increase in the definition of the facsimile.
  • Reduction of transmission frequency is attained by a scanning method comprising the successive scanning of zones of the subject to be transmitted, said zones being equivalently proportioned and dimensioned to comprise a group of picture points whereby the individual picture points recreated in the facsimile at the receivermay be appreciably smaller in area than the zones scanned at the transmitter.
  • the relative dimensions of said group of picture points and individual picture points are determined by the size of the zone scanned at the transmitter and the difierence in phase provided and utilized as above described at the receiver.
  • each zone above- A mentioned are equivalently proportioned to a to single line of the picture frame at the transmitter.
  • each picture point within a zone of scanning is presented to the photo-cell for a period of time equivalent to that occupied in the scanning of the complete zone, and thus the response of the photocell per picture point is increased.
  • This advantage is obtained by progressively revealing each zone to the photocell until maximum disclosure is reached, following which the zone is progressively concealed to zero before commencement of the scanning of the next zone.
  • the scanning of the picture may be efiected by known means such as a cathode ray beam focussed on a photosensitive mosaic, but the image of the beam in lieu of being a spot is a zone or rectangular shaped area equivalent in proportions to a line of the picture, and in scanning, the beam image is caused to traverse the picture frame along the lines of the picture so as first to progressively reveal the picture points and then to progressively conceal said points.
  • the image of the cathode ray beam may be focussed to a spot as usual and the beam oscillated at high frequency to cause the spot to traverse backwardsand forwards along a line and by superimposing a suitable sweep movement to this oscillatory movement of the cathode ray beam the scanning zone produced by the oscillatory movement of the spot is caused to advance across the picture frame in the same manner and with the same equivalent effect as when the cathode ray beam image was focussed to a line and the line was caused to advance across the picture frame and further, this scanning zone so produced by the oscillatory movement of the spot can be caused to fly back quickly as in known methods of spot scanning with cathode ray tubes.
  • a scanning disc may be employed in which a series of arcuate slots is arranged, said slots preferably being equivalently proportioned to a line of picture frame and angularly spaced so that each slot progressively reveals a line of the picture to a photocell and then progressively conceals the line from the photocell before the next succeeeding slot commences to reveal the next succeeding line zone.
  • the points are numbered I, 2, 3, etc. starting from the end of the zone when the first picture point is disclosed to the photocell.
  • the time taken to fully disclose the zone is nt seconds and that the time taken to traverse a picture point from one end of the picture point to the other is seconds.
  • the light flux emitted by the picture points I, 2, 3, etc. in t seconds is W1, W2, W3, etc. respectively.
  • the amplitude of the photocell currents at any instant is proportional to the light which is incident at this instant upon the cell so that at the respective instants that the number of picture points I or 2 or 3 etc. are simultaneously disclosed, the amplitude of the photocell currents is proportional to etc. respectively.
  • Fig. 1 in the drawings accompanying this specification shows the variations in amplitude of the photocell current with time of scanning a zone of the picture.
  • the abscissae shows the number of picture point revealed at any instant, and the ordinates show amplitude of the photocell current when the zone discloses I or 2 or 3 or more eto., picture points to the photocell.
  • the video signal current is equivalent to the photocell currents and the amplitude of the photocell currents and the video signal currents at any instant is thus proportional to the integrated eifect of the picture points which at that instant are incident upon the photocell.
  • the effects of the video signal are differentiated to obtain an effect which is proportional to the rate of change in amplitude of the video signal.
  • This instantaneous rate of change in amplitude of the video signal corresponds to the change in amplitude of the photocell currents due to the disclosure at that instant of a picture point to the photocell.
  • the effects so obtained correspond to the individual effects of the picture points disclosed to the photocell.
  • Fig. 1 is a graph showing variations in amplitude of photocell current with time of scanning a picture zone.
  • Fig. 2 shows a circuit arrangement for transmitter and receiver equipment organised to incorporate an embodiment of the invention in which scanning operations are performed by a cathode ray method.
  • Fig. 3 shows a mechanical scanning disc devised for use at a transmitter shown diagrammatically in Fig. 4, While Figs. 5 and 6 are views, similar to Figs. 3 and 4, of a modified mechanical scanning arrangement.
  • Fig. '7 is a schematic lay-out of a cathode ray tube arranged for optical creation of facsimiles Within the scope of the present invention.
  • Fig. 8 is a diagrammatic representation of the operation of the triple beam produced by the cathode ray tube shown in Fig. 7.
  • Fig. 9 is a graph showing two curves plotted in the manner of the curve in Fig. l and illustrating difference in amplitude of duplicate signals differing in phase relationship.
  • Figs. 10, 11, 12 and 13 are circuit diagrams illustrating different networks for obtaining phase differences between duplicate signals.
  • the essential characteristic of the invention resides in utilizing the difference in effects of two similar signals, which differ in phase and are generated from a single video signal produced at the transmitter, to modulate the light used for creating facsimiles at the receiver, and consequently it will be convenient first to refer to the group of figures of drawings marked Figs. 10 to 13 inclusive illustrating phasing methods.
  • the received single video signal is applied at VS being the input terminals of the network, one branch Bl consisting of a potential dividing resistance VR and the second branch 132 which may be arranged as a constant impedance comprising resistance and capacity and inductance at SR, SC, and Si respectively, or it may be arranged as a reactance comprising a capacity and resistance SC and SR respectively.
  • Figs. 10 to 13 each provide a duplicate of the video signal in each of the branches Bl, B2 and by adjustment of the capacity and/or inductance in the latter branch the current therein can be caused to lead or lag behind that in branch Bl to set up the required phase difference at the output terminals at OS, which terminals bear similar reference characters in Fig. 2 and are connected to the amplifier at RAZ in that figure.
  • Resistance VR may conveniently constitute the grid leak resistance of the input tube of amplifier RA2.
  • the subject to be televised is indicated as a travelling film at TF and is scanned by the cathode ray generated by cathode ray tube CR.
  • Reduction of video signal frequency in accordance with the invention and to obtain the ad vantages of low frequency transmission is attained by so scanning zones successively, each zone being equivalent to a line of the subject, that each zone is progressively revealed to the photocell until maximum disclosure is reached following which the zone is progressively concealed to zero before scanning commences of the next succeeding zone.
  • the amplitude of the photocell currents at any instant is equivalent to the sum of the picture points revealed to the photocell at the same instant.
  • Scanning means for carrying out the scanning method stated may consist of conventional cathode ray tube apparatus or mechanical scanning devices such as a Nipkow type of disc having its scanning apertures dimensioned as hereinafter described.
  • the image of the beam is focussed to a rectangular area equivalent in proportions to one line of the subject and the beam is caused to sweep along the line to progressively reveal and conceal the line as before stated.
  • the said image of the beam may be focussed to a spot as usual and the beam oscillated at high frequency along a path equivalent to a line of the subject and a sweep movement is imparted to said path to eifect said progressive revealment and concealment.
  • thescarming at the transmitter is performed by the cathode ray methods above described by the cathode ray tube OR, the resultant beams being directed by a lens L to the photocell at PC.
  • the photocell currents are led to the coupled ampliflerunits at Al and A2 thence to modulator unit at M where the output current from the latter is superimposed upon a carrier frequency and the modulated carrier frequency is applied to the transmitting aerial at TA via oscillator-power amplifier OPA.
  • the line sweep oscillator is indicated at LG and the line sweep-synchronising signal generator at SGI and these are connected to the deflecting plates at LD of the cathode ray tube CR, while the frame deflecting plates FD of the latter are connected to'the frame sweep-synchronising signal generator 8G2.
  • the pick-up at RA of the incoming low frequency impulses from TA are received and amplified at RA! and then applied to a phasing network (comprising branches BI and B2) for the purposes previously described and as ascertained by reference to Figs. 10 to 13 inclu sive.
  • a phasing network comprising branches BI and B2
  • the output from the phasing network terminals OS is applied to the amplifier RA2 and thence to the cathode ray modulating electrode of the cathode ray tube at CRl.
  • the line sweep potentials are applied to the deflecting plates at LDI and the frame sweep potential to the deflectingplates at FDl,
  • the synchronising signals are applied from RA! to 8G3 and SGQ.
  • a scanning-disc SD having scanning apertures SDI, arranged in a single spiral path.
  • Each of said scanning apertures SD! is proportioned so as to be equivalent in shape to one line of the picture frame and said apertures are spaced apart a distance. at least equivalent to the length of said line.
  • the scanning disc SD is shownin Fig. i asso ciated with its related photocell PC and subject at S.
  • Fig. 5 showing an alternative arrangement of the scanning apertures SDI in Fig. 3, the scanning apertures are disposed in a circular path in the scanning disc SD for scanning a continuously travelling film TF as shown in Fig. 6 in juxtaposition with an associated photocell PC and light source at US.
  • FIG. 8 three illuminated zones are indicated at Z, Zl, and Z2, one of said zones Z! being assumed as illuminated to double the brilliance of each of the zones Z and Z2.
  • Fig. 7 depicts a cathode ray tube CR2 arranged to create the zones Z, Zl, Z2 related and functioning as above described.
  • the tube CR2 is shown provided with three electron guns EG directed towards a common focal point on the screen at CS.
  • the rays EG! emanating from the guns EG are oscillated at high frequency by the deflecting plates LS to illuminate superimposed overlapped zones equivalent to Z, .Zl, Z2 on the screen at CS.
  • the deflecting plates at LS also effect the line sweep motion and deflecting plates FS effect the frame sweep motion of the zone Z0.
  • the deflecting plates EG2 are utilized to relatively locate the overlapped zones Z, Z! and Zii.
  • At the receiver differentiation of the effects of the video signal may be obtained electrically or optically.
  • the amplitude of the modulating signal obtained by taking the difference in potential of the currents flowing in the two branches of the network at the time of scanning the picture points I, 2, 3 etc., is thus proportional to W1, W2, W3 etc.
  • This signal is thus equivalent to the signal generated by scanning the picture point by point in accordance with the usual method of picture scanning at the present time.
  • a known type of scanning device such as the oathode ray tube is used as a receiver and its beam is modulated by the modulating signal and the focussed spot of the cathode ray is moved to correspond with the movements of the scanning zone at the transmitter and so that the focussed spot at the receiver corresponds in location with the leading end of the scanning zone at the transmitter then the facsimile will be created to correspond with the picture scanned at the transmitter.
  • an area equivalent in proportions to the corresponding zone at the transmitter, is uniformly illuminated by a modulated light Whose brilliance is proportional to the amplitude of the photocell currents.
  • this illuminated zone at the receiver is revealed to the eye of an observer in a manner corresponding to the revealment of the picture zones at the transmitter, i. e. at instants corresponding to the revealment of respective picture points I, 2, 3, etc. there are revealed to the observer at the receiver corresponding respective zone points I, 2, 3, etc.
  • the effect upon the eye, of the light emitted at points I, 2, 3 etc., is that due to persistance of vision and the brilliance of the points of the zone appears to the eye as being proportional to the total flux revealed per picture point of the zone during the time that the zone is scanned or revealed to its maximum extent.
  • the light of the brightest zone when the light of the brightest zone is modulated so as to increase in brightness, the light of the other two zones is modulated so as to decrease in brilliance, and if the images of the zones are superimposed so that the first disclosed picture point of each of the zones is a picture point out of phase in the order shown by the formula for W1, W2, W3 etc., then the light of the zones becomes differentiated due to the effects of persistence of vision so that the mind is rendered conscious of the creation of the picture points I, 2, 3 etc. If the zones are scanned and located at the receiver in a manner coresponding to the scanning of the zone at the transmitter then the facsimile will be created.
  • the method consisting of progressively and continuously scanning, in seriatum, individual zones of the subject to be transmitted, completing the scanning of one zone before commencing to scan the next zone of the series, converting the light effects from each zone into an equivalent electric signal, amplifying the latter, applying the amplified signal to a carrier frequency which is transmitted to a receiver,
  • the method consisting of progressively and continuously scanning, in seriatum, individual zones of the subject to be transmitted, completing the scanning of one zone before commencing to scan the next zone of the series, converting the light effects from each zone into an equivalent electric signal, amplifying the latter and applying the amplified signal to a carrier frequency which is transmitted to a receiver, amplifying the received video signal, duplicating the latter with a phase diflerence between the duplicate signals, and applying the potential of a signal due to said phase difference to modulate light used for the creation of a facsimile of the subjecttransmitted, whereby an optical effect is created corresponding with the light values constituting the elementary picture points present in each zone scanned at the trans- I mitter.
  • a transmitter comprising scanning means for continuously scanning, 'in seriatum, individual zones of the subject to be transmitted and completing the scanning of one zone before commencing the scanning of the next zone of the series, a photo-electric cell, means for applying the light effects from each of said zones to the photo-electric cell, means for amplifying the output from the photoelectric cell, means for applying the amplified signal to a transmissible carrier frequency, a receiver for said amplified signal comprising means for amplifying and means for multiplying the received signal, means for creating a phase difference between the multiple signals, means for simultaneously converting said multiple differentially phased signals into equivalent superimposed visible signals, and means for locating the latter signals in a common zone, whereby the beforementioned phase difference creates an optical effect corresponding with the light values constituting the elementary picture points present in each zone scanned at the transmitter.
  • a television system consisting of a transmitter comprising scanning means for continuously scanning, in seriatum, individual zones of the subject to be transmitted and completing the scanning of one zone before commencing the scanning of the next zone of the series, a photoelectric cell, means for applying the light effects from each of said zones to the photo-electric cell, means for amplifying the output from the photoelectric cell, means for applying the amplified signal to a transmissible carrier frequency, a receiver for said amplified signal comprising means for amplifying and means for duplicating the received signal, means for creating a phase difference between the duplicate signals, and means for applying the potential of a signal due to said phase difference to modulate light used for the creation of a facsimile of the subject transmitted, whereby an optical effect is created corresponding with the light values constituting the elementary picture points present in each zone scanned at the transmitter.
  • a television system consisting of a transmitter comprising scanning for continuously scanning, in seriatum, individual zones of the subject to be transmitted, a photo-electric cell, means for applying the light effects from each of said zones to the photo-electric cell, means for amplifying the output from the photo-electric cell, means for applying the amplified signal to a transmissible carrier frequency, a receiver for said amplified signal comprising means for amplifying and means for duplicating the received signal, and means for creating a phase difference between the duplicate signals, consisting of a phasing network constituted of two branches connected to the amplified output of the receiver, one of said branches comprising a potential dividing resistance and the other of said branches comprising a constant impedance or reactance, the output potential from said phasing network being applied to modulate light used for the creation of a facsimile of the subject transmitted, whereby an optical effect is created corresponding with the light values constituting the elementary picture points present in each zone scanned at the transmitter.
  • a television system consisting of a transmitter comprising scanning means for continuously scanning, in seriatum, individual zones of the subject to be transmitted, a photo-electric cell, means for applying the light effects from each -of said zones to the photo-electric cell, means for amplifying the output from the photoelectric cell, means for applying the amplified signal to a transmissible carrier frequency, a receiver for said amplified signal comprising means for amplifying and means for duplicating the received signal, means for creating a phase difference between the duplicate signals, consisting of a phasing network constituted of two branches connected to the amplified output of the receiver, one of said branches comprising a potential dividing resistance and the other of said branches comprising a constant impedance or reactance, a cathode ray tube, ray deflecting plates in said tube, means for amplifying the output from said phasing network, means for applying said amplified output potential to modulate the ray generated by said cathode ray tube, and means for applying frame sweep and line
  • a transmitter comprising scanning means for continuously scanning, in seriatum, individual zones of the subject to be transmitted, a photo-electric cell, means for applying the light effects from each of said zones to the photo-electric cell, means for amplifying the output from the photo-electric cell, means for applying the amplified signal to a transmissible carrier frequency, a receiver for said amplified signal comprising means for amplifying and means for multiplying the received signal, consisting of a cathode ray tube comprising ray generating electrodes to each of which the received amplified signal is simultaneously applied to modulate said rays, means for deflecting said modulated rays to impart overlap or phase shift thereto, and means for applying frame sweep and line sweep to said deflected rays, whereby an optical effect is created corresponding with the light values constituting the elementary picture points present in each zone scanned at the transmitter.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
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US240824A 1937-12-03 1938-11-16 Television system Expired - Lifetime US2211066A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2595548A (en) * 1947-02-24 1952-05-06 Rca Corp Picture reproducing apparatus
US3198881A (en) * 1962-03-19 1965-08-03 Avien Inc Film scanning transmission system using fiber optics

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2595548A (en) * 1947-02-24 1952-05-06 Rca Corp Picture reproducing apparatus
US3198881A (en) * 1962-03-19 1965-08-03 Avien Inc Film scanning transmission system using fiber optics

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FR846979A (fr) 1939-09-28

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