US2661392A - Color television - Google Patents

Description

1953 H. G. LUBSZYNSKI ET AL 2,66

COLOR TELEVISION Filed Dec. 15, 1947 /nven7brs: HANS GERHARD LUBSZYNSKI' REGINALD SIDNEY WEBLEY W 64m ,4 for/19y 93 lea COLOP TELEVISION Hans Gerhard Lubszynski, N orthwootl, and Reginald Sidney Webley, Hayes, England, assignors to Electric & Musical Industries Limited, Hayes, England, a company of Great Britain Application December 13, 1947, serial No. 791,542

12 Claims,

This invention relates to electron discharge apparatus for generating signals suitable for use in colour television.

Various proposals have heretofore been made 2 colour mixed with said first colour, and signal generating means which is arranged to utilise said groups of electrons so as to generate one set of picture signals representative of compofor generating colour television signals, but most 5 nents of said iinage of said first colour and a of these prior proposals have relied upon the use second set of picture signalsrepresentative of of colour filters through which an image of an components of said image of said second colour. object for transmission is projected onto a suit- The apparatus employed in the invention may able screen from which picture signals can be decomprise an electron discharge device following rived. The use of colour filters for generating m the same general construction as has been propicture signals for colour television purposes is posedfor generating monochromatic picture sigundesirable from many points of View and the nals, the apparatus, however, being modified by object of the present invention i to provide an the provision of said electron separating means. improved apparatus for generating picture sig- Preferably, the group of electrons is caused to nals for colour television in which the use of (201- impinge on a target electrode of the charge-storour filters for generating signals is avoided. age type, the target electrode being scanned by When a light image of mixed colour is proa cathode ray beam so as to restore the elements jected onto a photo-electric cathode, photo-elecof the target electrode to datum potentials, the trons are released from the cathode and the vearrangement being such that the image is 'ultilocity of the electrons so released depends on the niately effectively separated into sets of picture colour of the elemental areas of the image illusignals representative of the primary colour (361.cminating the photo-electric cathode. Thus, if ponents of the image. one elemental area of the photo-electric cathode In order that the said invention may be clearly is illuminated with blue light then the maximum understood and readily carried into effect, the emission energy of the photo-electrons released 5 same will now be more fully described with refiroin thi elemental area will be greater than the crease to the drawings, in which maximum emission energy of photo-electrons re Figure 1 illustrates diagrammatically an elecleesed from another elemental area of the phototron'discharge' device suitable for use in the inelectric cathode which is being illuminated for vention, example with green light, and a substantial irac- Figure 2 is a block diagram of a television tion of the electrons released by the blue light transmitter operating in accordance with one will have emission energies exceeding the maxlembodiment of the invention,

emission energy of the electrons released Figure 8 is a diagrammatic View of a modifiby the green light. Similarly the maximum emiscation of the discharge device shown in Figure 1, energy of the electron released by the green 5 Figure 4 is a diagram illustrating a diiierent light will be greater than the maximum emission manner of operating the device shown in Fig energy of photo-electrons released from an eleure '1, mental area of the photo electric cathode which Figure 5 illustrates diagrammatically a Inc-db is being illuminated by red light and substantial ficationof the device hawn in Figure 1 for usg fraction of the electrons released by green light 40 with the manner of. operation shown in Figure 4, will have emission energies exceeding the max- Figure 6 illustrates diagrammaticmly a further I ssion energy of electrons released by red embodiment of the invention, and

t. present invention i based on the Figure 7 illustrates a modification of the arpnnoiple of utilising the difference of emission rangement shown in Figure 6. energies of electrons released by light of difierent The present invention is based on the phenomcolours in order to gener t picture signals for enon that when a light image of mixed colours is colour television. projected onto a photo-electric cathode the emis The presgnt ti n rovides apparatus for sion energies of the electrons released from the generating picture signals for colour television hoto-electric cathode depends on the colour of wherein means re provided for utilising the the incident light. By setting up a suitable field difieren c in energy between electrons released it is possible to exercise a control on the released y light of one colour compared with light of electrons which is dependent upon their emission another colour to generate picture signals repreenergies and thereby separate released elec rons sentative of different colour components of an into groups according to the emission energies of image, the electrons and hence according to the colour m aratus for carrying the invention into of incident light. For example, the controlmay eiiect may comprise means for separating eleobe effective to produce one group containing elec trons released by a light image of mixed colours trons released by light of a first colour, another into one group containing electron released by group containing electrons released by light of light (me 1 and into a second group cona second colour mixed with said firstcolour and taming electrons released by light of a second a third group containing electrons releasedby light of a third colour mixed with said first and second colours, the first group of electrons can then be employed to obtain a set of picture signals corresponding to said first colour, the first and second groups can be employed to obtain a set of picture signals corresponding predominantly to said second colour by substantially balancing out said first colour, and similarly the second and third groups can be employed to obtain a set of picture signals corresponding predominantly to said third colour. The control may for example be exercised by applying potentials to a control electrode disposed adjacent to a photo-electric cathode such that effectively only electrons released with energies exceeding a predetermined value are permitted to pass said electrode. Figure 1 of the drawings illlustrates an electron discharge device suitable for use in one form of the invention and which, when used in conjunction with the circuit shown in block form in Figure 2, enables television signals to be obtained which are representative of the three primary colours of a coloured image.

Figure 1 illustrates an electron discharge device which constitutes a pick-up tube similar to a device known as an image orthicon. The discharge device shown comprises an evacuated envelope I having at one end a photo-electric cathode 2 onto which a light image of mixed colours can be projected cal system indicated at d. On projecting an optical image onto the photo-electric cathode 2 photo-electrons are released which are projected and focussed onto a charge-storage target electrode 5. Adjacent to the cathode 2 is disposed a control electrode t in the form of a grid which, in operation, is biasscd in such a way as to allow, first, only electrons liberated from the oathode 2 by blue light with energies exceeding the maximum emission of by green light, then electrons liberated by blue light mixed with green light with energies exceeding the maximum emission energy of electrons released by red light and finally all the electrons liberated by blue light mixed with green and red light to be transmitted through the interstices of the electrode 6 and caused to impinge on the target 5. It will be convenient to refer to electrons liberated with energies exceeding the maximum emission energy of electrons released by green light as blue electrons, to refer to electrons liberated with energies not exceeding the latter maximum but exceeding the maximum emission energy of electrons released by red light as green electrons, and to refer to electrons liberated with energies not exceeding the last-mentioned maximum as red electrons. It will of course be appreciated that a number of the green electrons may in fact be liberated by blue light, while a number of the red electrons may in fact be liberated by blue and green light, but these should not prevent satisfactory operation of the apparatus. The target is of the so-called double-sided type and on the side of the target 5 facing the cathode 2 is a collector electrode 1 in the form of a grid for collecting secondary electrons released from the target 5 whilst on the side of the target 5 remote from the photo-electric cathode "2 is an electron gun indicated conventionally at 8 which serves to generate a beam of electrons for scanning the target 5, scanning of the target 5 by the beam of the gun 8 serving in known manner to restore the elements of the target 5 to an equilibrium potential, electrons which are not employed for through a suitable optienergy of electrons released d restoring the elements being returned to multiplying electrodes indicated at 6 which serve in known manner effectively to multiply the returned electrons, the final electron stream serving to develop picture signals. The discharge device shown in Figure 1 is arranged within a coil It: which serves to set up a substantial axially symmetrical magnetic field which is necessary for the operation of discharge devices of the kind shown in Figure l. A pair of coils H is provided between the cathode 2 and the target 5, these coils having applied thereto, in operation, a rectangular pulse Waveform in such a manner that the photo-electrons released from the cathode 2 are caused to be projected alternately onto the upper and lower portions of the target 5, as indicated by the dotted lines, the photo-electrons being projected on to each portion for the duration of a colour frame. The electron beam from the gun 8 is arranged to scan the electron images applied to the target 5 in such a phase that during one colour frame the beam always scans that portion of the target which has been charged by photo-electrons during the previous colour frame. The electron image from the cathode 2 is focussed by the coil is and is accelerated onto the target electrode 5 by a cylindricai anode i2 applied to the wall of the tube l. The electron beam from the gun 3 is also focussed by the coil it! while deflecting coils, some of which are shown at it impart the line and frame scanning deflections to said beam from the gun 8, the electrons from the gun 3 being accelerated by a cylindrical anode 54 applied to the wall of the tube i, as shown.

The control electrode 6 as aforesaid is arranged to be biased by means of potential pulses in such a manner that first blue electrons are released for a predetermined interval equal to the duration of a colour frame, these blue electrons being projected say onto the upper portion of the target 5 and the charges produced by said electrons being stored by the target 5. Then the Potential applied to control electrode 6 is changed so that it allows blue and green electrons to be released, the electron image resulting from these blue and green electrons being projected onto the lower portion of the target 5 for an interval of equal duration and during the projection of blue and green electrons onto the target 5 the upper portion of the target is scanned by the beam emanating from the gun 8. Then the potential applied to the control electrode 6 is again changed so that it allows blue, green and red electrons to be released, these electrons being projected onto the upper portion of the target 5 during which period the lower portion of the target is scanned by the beam of the gun 8 and so on, so that the output of the tube derived from the multiplying electrodes 9 consists of three sets of signals. The first set of signals is generated during one colour frame and is representative of the blue component of the image, the next set of signals is generated during the next colour frame and is representative of the blue and green components of the image, whilst the third set of signals, which is generated during the following colour frame is representative of the blue, green and red components of the image, the said sets being generated in the same sequence during successive colour frames.

Referring now to Figure 2 of the drawings, the signal output from the device shown in Fig 1 is amplified by an amplifier i5 and the three sets of signals aforesaid are passed to a switching device it, the construction of which is such that the signals are passed in accordance with the.

phasing of the intervals in which they are generated to a transmitter ll or to a storage device it? iii, or to a combination of them.

The devices 58 and is may each comprise for example an electron discharge device having a target electrode which can store charges and which can be scanned on one side with a high velocity beam of electrons and on the other side with a low velocity beam of electrons. If with this arrangement, the first set of picture signals caused to modulate the high velocity beam of electrons in the device it during one colour frame, a positive charge image is produced on the storage electrode representative of said set of signals, and during the subsequent colour frame the signals are reproduced. by scanning with the low velocity beam of electrons so as to discharge the storage electrode, a signal plate being provided capacitatively with the storage electrode from which the reproduced signals are derived. The reproduced signals can then be combined on opposite phase with the second set of signals in a suitable amplifier the resultant of the combined signals being signals which are representative effectively only of the green electrons, the second set of signals being simultaneously caused to modulate the high velocity beam of electrons in the device it so that after storage they can subsequently be combined in opposite phase with the third set of signals, so as to produce signals representative effectively only of red electrons. Alternatively the storage devices it and It may each comprise an electron discharge device having a charge storage electrode provided at one side with a signal plate capacitatively associated with the storage electrode and at the other side with a control electrode in the form of a grid or grill which means being provided for scanning the storage electrode with an unmodulated beam of electrons from the side at which the grid is located. If, with this arrangement, the first set of signals is applied to the signal plate of the device It durone colour frame while the storage electrode is being scanned by said beam of electrons, a charge image will be produced in said storage electrode representative of said first set of signals. During the subsequent colour frame, the second set of signals can then be applied to the signal plate while the storage electrode is being again scanned by the beam of electrons, and a is maintained at a uniform potential,

resultant signal derived from thesignal plate which is representative of the difierence of the two sets of signals, and therefore representative predominantly of the green component of the original image. The second and third sets of can similarly be combined in appropriate phase with the aid of the other storage device i9 whereby signals are obtained from the latter device which are representative predominantly of the red component of the original image.

The sequence ofoperation of the switching device it may be as follows: the first set of signals is caused by the device it to be fed to the transmitter ll during said first colour frame, said set of signals being simultaneously fed to the storage device it. The second set of signals is then fed during said second colour frame by the device it to the storage device It and also to the storage device It whilst the output of the device is is fed to the transmitter H. The output signals from the device [8 will then be representative-of the green component of theoriginal image.

unmixed with the blue component. Then the third set of signals is fed during said third colour frame to the storage device E9, the output signals of this device then consisting only of the red components of the original image. At the same time the storage device I 8 is conditioned to receive the first set of signals of another colour frame by discharging the elements of the storage electrode. Similarly, during the next colour frame the storage device I 9 is conditioned for commencing the next cycle. Since the first set of signals, which are representative of the blue component of the image, is fed directly to the transmitter ll, whilst the signals representative of the green and red components of the original image are derived from the storage devices It and It, it will of course be necessary to employ suitable amplifying or attenuating means in the channels feeding the transmitter l7 and the devices ft and is so that the respective signal amplitudes are effectively proportional to the original signals derived from the device shown in Fig. 1. These amplifying or attenuating means can also be used to correct if required the colour response of the photo-electric cathode 2. It is possible that imperfect signals will be derived from the devices It and it when a moving object is projected onto the cathode 2, but since the frame frequency for a colour television transmission will necessarily be increased compared with a monochromatic system, these imperfect signals may not be a serious disadvantage.

The type of discharge device shown in Figure 1 is usually operated with cathode potential stabilisation; that is to say, the target 5 is discharged with a low velocity beam of electrons from the gun 8. With this mode of operation, it is necessary to set up positive charge images on the target 5. The photo-electrons from the photo-electric cathode 2 are therefore projected on the target 5 with sufiicient velocity to release secondary electrons, these secondary electrons being absorbed by the electrode 5.

The invention is however, not limited in its use to the general type of discharge device shown in Figure 1 since the invention can also be employed with other kinds of devices. For example it may be applied to discharge devices wherein the electron image from the photo-cathode 2 is projected with a low velocity on the target 5 so as to charge the elemental areas of the storage electrode to negative potentials in dependence upon the intensity of the projected electron image, i. e. so as to form a negative charge image on the target 5,

r and wherein a control electrode in the form of a mesh is disposed immediately in front of the scanned side of the target 5. Potential differences are thus set up between the elemental areas of the target 5 and the control electrode in dependence upon said negative charge image, the control electrode being maintained at a constant potential. One proposed form of device of this kind is described in United States patent application Serial No. 792,576, and according thereto the target 5 is scanned by means of a beam of electrons of sufiicient velocity to release secondary electrons from the target 'i.

released from the target 5 escape through the control electrode and are utilised for generating electrical signals by directing them to an electron multiplier, the number of electrons which escape from each elemental area being dependent upon the potential difierence established, as aforesaid, between the respective elemental area and the control electrode. In another form of device of The electrons this kind, the target is rendered photo-sensitive on the scanned side thereof, scanning being effected by means of a light spot projected, for example, from the fluorescent screen of a cathode ray tube. The light spot releases electrons from the target 5, the release being controlled as aforesaid by the control electrode. If either form of device of this kind is employed, the grid 6, instead of being disposed adjacent to the cathode 2, may alternatively be disposed as shown in Fi ure 3 adjacent to the target 5 since the photoelectrons have a low velocity in the vicinity of the target 5. In this case, the photo-electrons released from the cathode 2 are accelerated by a grid 2?.- and pass through the grid 6 before impinging on the target 5 so as to charge it negatively. By applying suitable potential pulses to the control electrode 6, the target 5 can be charged respectively by blue electrons, blue and green electrons, and blue, green and red electrons.

Instead of deriving signals representative of the three primary colours of the image by the use of the devices i8 and 19 it is possible to obtain signals representative of said primary colours from the aforesaid blue, blue and green, and blue, green and red electrons by causing said electrons to impinge on the target 5 with such energies that the primary/secondary electron emission ratio is varied according to whichever of the three sets of electrons is being projected. For example, the blue electrons released from the photo-electric cathode 2 of Figure 1 can be caused to impinge on the target 5 with such energy that they release more than one secondary electron for each primary electron. The blue and green electrons can be caused to impinge on the target electrode with low energies so that they release substantially no secondary electrons and if the image of the blue and green electrons is superimposed on the target which has been charged by the blue electrons, then the charges due to the blue electrons will eifectively cancel one another so that a charge image will result corresponding efiectively only to green electrons. Similarly a charge image can be ultimately obtained which is representative only of red electrons. The change in energy of the electrons in order to cause the primary/secondary electron emission ratio to vary may be effected by applying suitable rectangular potential pulses to the photo-electric cathode 2 and the grid 6 of Figure 1 thus effectively varying the potential of the source of electrons. The sense of the pulses may be arranged so that the charge images resulting from the mutual cancellation are either positive or negative according to the type of electron discharge device employed.

The sequence of operations when operating the device shown in Figure l in this manner is represented in Figure 4 from which it will be observed that, firstly, as shown at a, a blue electron image is focussed onto the upper portion of the target 5 for the duration of half a colour frame so as to form on said target electrode a positive charge image. The electron image is then completely cut off for the remainder of the frame interval, for example, by applying a strong negative bias to the grid 6 as represented at b. Then a blue electron image is focussed onto the lower portion of the target 5 for the duration of half a colour frame, so as to form on the lower portion of said target electrode a negative charge image as represented at 0. Then an image resulting from blue and green electrons is superimposed on the negative blue image for the duration of the remaining half of the colour frame so as to form a positive charge image, the charges resulting from the blue components effectively cancelling and leaving a charge image corresponding only to green electrons. This step is shown at d. Then blue and green electrons are focussed onto the upper portion of the target for the duration of half the n xt colour frame so as to form a negative charge image of blue and green electrons, as shown at e. Then a charge image of blue, green and red electrons is superimposed on the negative charge image formed by blue and green electrons for the duration of the remaining half of the last-mentioned colour frame so as to form a positive charge image so that the ultimate charge image set up on the screen 5 is a charge image resulting only from red electrons, as shown at f. The scanning of the cathode ray beam from the gun 8 is so phased that the beam always scans the charge image stored during the previous colour frame. Thus, during the sequences 0 and d the beam is caused to scan the portion of the target upon which the blue image is formed at a in Figure 4 and during the sequences e and f the beam is caused to scan the green image at d in Figure 4 and so on. If any this-matching of colour occurs due to incorrect secondary emission factors it may be possible to compensate for such nus-matching by varying the ratio of the exposure time of the charge images. Colour fringes resulting from fast-moving objects could be transformed into slightly blurred edges of the correct colour by alternately projecting the images onto the target electrode at a high frequency instead" of projecting them separately each for a duration of half a colour field.

In addition, the apparatus illustrated can be operated in such way that interlaced scanning is efiected. In that case, each complete scanning raster traced by the beam on the target 5 is effected in two frames or sequences of lines one of which i traced on the lower portion of the target 5 and the other of which is traced on the upper portion of the target 5. By displacing the upper charge image relatively to the lower charge image on the target 5, or vice versa, in the vertical directicn by half the vertical displacement which the scanning beam undergoes during a line period, it is arranged that the lines traced on the charge image on the lower portion of the target 5 interlace With the lines traced on that on the upper portion of the target 5. Alternatively, the

- same result can be achieved by relatively displacing the two sequences of lines which are traced respectively on the upper and lower portions of the target 5. lhe lines of each sequence are spaced apart to allow the lines of the other sequence to interlace therewith and, in order to remove the charges stored in the gaps between the lines of each sequence, the scanning beam can be caused to discharge these gaps during the return times between successive lines. Since the return times are appreciably shorter than the line times, the beam current may be increased during the return times to assist in discharging the gaps, for example by applying positive potential pulses to the modulating electrode of the gun 8. Simultaneously, the signal output may be suppressed in the amplifier or in the electron multiplier during the line return times. The d scharge of the gaps can also be assisted by sllghtly defocussing the beam during the line return times and simultaneously superimposing rectangular pulses of line frequency on the vertical scanning waveform so that the beam, during the line return times, is shifted slightly backwards in the vertical direction.

Instead of applying pulses to the cathode 2 and grid as aforesaid, the changeover required to afford the positive and negative charge images may be eiiected by means of a grid 2|, as shown in Figure 5, this grid being arranged in front of Figure ,6 of the drawings illustrates a, further embodiment of the invention. As shown in this figure there is disposed at the end of the onred electrons.

Assuming that the maximum emission energies of red, green and blue electrons are a, b and c electron volts respectively, where a is smaller than I: and b is smaller than c, then the potential applied to the electrode 22 is maintained in sequence for each colour field at -c volts, b volts and u volts respectively, and the potential of the electrode 2d is maintained in similar sequence at -29 volts, a volts and Zero Volts. When the potential of the elec trode 22 is -c volts and the potential of the elec trode 24 is volts, cannot collect any or the released electrons so that the released electrons pass through the grid it, and red and green electrons are then repelled by the electrode 28 and caused to return to the electrode 23, blue electrons being however permitted to pass through the interstices of the electrode 2 3 to the target 5. When the potential of the electrode 22 is -29 volts, and the potential of the electrode 2d is a 5' volts, blue electrons are collected by the electrode 22 while red and green electrons pass through the electrode 23, red electrons being finally reflected to the electrode by the electrode while the green electrons to the target 5. When the potential of the electrode 22 is -a volts and the potential of the electrode 24 is zero volts, then blue and green electrons are collected by the electrode 22 and only red electrons pass through the electrode 23 and no electrons are reflected to the electrode 23 by the electrode 2 in this way, red, green and blue electron images are formed in sequence on the target electrode 5. By applying suitable poten tial pulses to the deflecting coils H in timed relationship with the change of potentials on the electrodes 22 and 2d, a red image can be formed on the lower portion of the target then a green image on the middle portion of the target 5 and then a blue image on the upper portion of the target 5. The red image is arranged to be scanned by the beam from the gun 8 whilst the green image is being applied to the middle portion of the target, and so on.

If desired, the grid electrodes 23 and E l may be combined as .sho n in Figure 7. For example, a mesh 25 of aluminium may be provided which is insulated by the provision of an anodised layer the right-hand side of the mesh 25, as shown in Figure '7, being suitably lapped that it is not covered by the layer fit and on the left-hand side of the mesh 25 there is provided a sputtered or evaporated metal layer 2? which replaces the electrode Whilst the right-hand side of the mesh is provided with a photo-electric layer which replaces the electrode The electrodes 2? and are thus shown facing the 013-- n it direction from that in Figure 6.

hough the invention has been described as applied to several kinds of electron discharge deit will be understood that the invention is not limited in its use to electron discharge devices oi the kinds described as it can be applied to any suitable device such as has been proposed for generating television signals, such as the socalled image dissectcrs or electron discharge devices in which the optical image projected onto a target electrode is converted into an electron stream by scanning a photo-electric cathode with a light spot so as to derive from the photo-elem trio cathode a beam of electrons which scans said targe We claim:

1. In apparatus for generating picture signals for colour television, an electron discharge pickup tube having a photo-electrically sensitive surface arranged for exposure to light images of mixed colours, means for establishing a potential field for differentially controlling the electrons released by a light image from said photosensitive surface in dependence upon the energies of said electrons, and means for generating from said differentially controlled electrons picture signals representative of diiferent colour components of a light image.

2. In apparatus for generating picture signals for colour television, an electron discharge pickup tube having a photo-electrically sensitive surface arranged for exposure to light images of mixed colours, means for separating electrons re leased by a light image from said photo-electrically sensitive surface, in dependence upon their energies, into one group containing electrons released with emission energies exceeding one level and a second group containing electrons r and means I01 generating from said groups of electrons one set of picture signals representative of components of said light image of a first colour and a second set of picture signals representative of components of said light image of a second colour.

In apparatus for generating picture signals for colour television according to claim 2, said tube having means for generating one set of picture signals from said first group of electrons, means for generating further signals from said second group of electrons, and means for combining said further signals with said first set of picture signals in phase opposition to generate thereby said second set of signals.

4. In apparatus for generating picture signals for colour television according to claim 2, said tube having a charge storage electrode, means for causing said groups of electrons to produce superimposed charge images of opposing polarity on said charge storage electrode to effectively balance out charges representative of electrons having emission energies exceeding said first level components from the resultant charge image, and means for generating picture signals from the re sultant charge image to generate thereby said second set of picture signals.

5. In apparatus for generating picture signals for colour television, an electron discharge pickup tube comprising a photo-electrically sensitive surface arranged for exposure to light images of mixed colours, means for separating electrons released by a light image from said photo-e1ectri cally sensitive surface, in dependence upon their energies, into one group containing electrons released with emission energies exceeding one level and a second group containing electrons released with emission energies exceeding another and lower level but not exceeding said first level, means for generating one set of picture signals representative of components of said light image of a first colour from said first group of electrons and for generating a second set of picture signals representative of said light image of a second colour from said second group of electrons.

6. In apparatus according to claim 5, said electron separating means comprising a first control electrode, means for applying one potential to said control electrode during intervals to repel all electrons released with emission energies exceeding said lower level and for applying a different potential to said control electrode at other intervals to collect electrons with emission energies exceeding said first level and to repel electrons with lower emission energies, a second control electrode arranged in the path of electrons repelled by said first control electrode and means for applying potentials to said control electrode to allow only the passage of electrons with emission energies exceeding said first level at said first intervals and to allow the passage of all elec trons with emission energies exceeding said lower level at said other intervals.

'7. In apparatus for generating picture signals for colour television, an electron discharge pickup tube having a photo-electrically sensitive surface arranged for exposure to light images of mixed colours, means dependent upon the energies of the electrons released from said surface for separating the released electrons alternately into one group containing electrons released with predetermined energies and a second group con.- taining electrons released'with different energies, a charge storage electrode, means for directing said groups of electrons alternately to different portions of said charge storage electrode to mduce charge images alternately on said portions, means for causing a beam of electrons to scan said portions of the charge storage electrode alternately in reverse order from that in which said charge images are produced in said portions, and means for deriving picture signals represent ative of different colour components of a light image from the scanning of said charge storage electrode.

8. In apparatus for generating picture signals for colour television, an electron discharge pickup tube having a photo-electrically sensitive surface arranged for exposure to a light image of mixed colours, potential-operated meansfor differentially controlling electrons released by a light image from said surface in dependence upon the energies of said electrons, means for applying potentials to said potential-operated means to separate electrons released from said surface alternately into one group containing electrons of predetermined energies and into a second group containing electrons of diiierent 12 energies, andmeans for sequentially generating from said groups of electrons one set of picture signals representative of a first colour component of a light image and a second set of picture signals representative of a different colour component of the light image.

9. In apparatus for generating picture signals for colour television according to claim 8, said potential-operated means comprising a control electrode pervious to electrons and arranged in the path of electrons released from said photoelectrically sensitive surface. 10. 111 a'paratus for generating picture signals for color television, an lectron discharge pick-up tube comprising aphoto-electrically sensitized surfacearranged for exposure to a light image oi mixed-colorsfnieans for controlling the path m. the m t ress released from said surface by a light imageind'ependence upon the energiesof the released electrons, and means for generating from the controlled electrons picture signals representative of difierent color components of a lightimage to which said surface is exposed.

ll. In apparatus for generating picture signals for eolontelevision, an electron discharge picliup tube having a photo-electrically sensitive surfacearranged'for exposure to light images of mixed colors, means for separating electrons released'lfro'm'said surface by a light image in dependence upon the energies of said electrons into groups containing electrons with energies in different energy ranges, and means for generating picture signals representative of different color components of the light image from said groups of electrons.

' 12. In apparatus for generating picture signals for color television, an electron discharge pickup tube comprising a photo-electrically sensitive surface arranged for exposure to light images of mixedcolors, electrode means effective in the path of electrons released by a light image from said surface, means for applying potentials to said electrode means during one set of periodic intervals to separate electrons with emission err-- ergies'in one energy range from electrons re leased by a light image from said surface, means for applying different potentials to said electrode means during another set of intervals inter calated with said first set to separate electrons with emission energies in. a different energy range from electrons released by a light image from said surface, and means for generating pic ture signals representative of different color components of said light image from the electron:

' separated during said different sets of intervals.

HANS GERHARD LUBSZYNSKI. REGINALD SIDNEY WEBLEY.

References Cited in the file of this patent UNITED STATES PATENTS

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