US2452293A

US2452293A - Color television system

Info

Publication number: US2452293A
Application number: US572863A
Authority: US
Inventors: Forest Lee De
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-01-15
Filing date: 1945-01-15
Publication date: 1948-10-26
Anticipated expiration: 1965-10-26

Description

wwo a... DE FOREST COLOR TELEVISION SYSTEM 3 Sheets-Sheet 1 Filed Jan. 15, 1945 INVENTOE LEE 5 Foessr .B/ Hana/5,1? cw, Ever-2 &/%wm5 @d. 26, 39%. 1.. DE FOREST 3 COLOR TELEVISION SYSTEM Filed Jan. 15, 1945 3 Sheets-Sheet 2 sww- Saw/c OSCILLATOR AMPLIFIER 1N vzwroz LEE DE F0225? .W ana/s, lf/zcdfbsrm 6t HARE/5 Quiz. 26, 3948.. L. DE FOREST COLOR TELEVISION SYSTEM 3 Sheets-Sheet 3 Filed Jan. 15, 1945 [NVENTDE L5: as FbREsT F02 7745 Hem JQTTO/QNEY? Patented Oct. 26, 1948 UNITED STATES PATENT OFFICE COLOR TELEVISION SYSTEM Lee de Forest, Los 'Angelea, Calif.

Application January 15, 1945, Serial No. 572,863

9 Claims. 1

My invention relates to a new and useful television system for transmitting, receiving, and projecting in natural colors objects presented before a television pick-up camera or iconoscope at the transmitting station.

Heretofore systems for televising objects in their natural colors with any substantial degree of accuracy have usually employed revolving color sector discs comprising color filter sections of either two or three colors. In such television systems the color filter disc is located at the transmitter between the object and the pick-up camera or iconoscope and at the receiver between the fluorescent screen of the kinescope or cathode beam projection tube and the observer. Such systems require that the diameter of the rotating disc be considerably more than twice the diameter of the cathode beam receiving tube. when such tube is large enough to give a satisfactory picture without projection upon the fluorescent end of the tube, e. g., a picture at least 6" x 8" in dimensions, such rotating color disc must be approximately 2 feet in diameter and obviously requires a relatively large synchronous motor, involving excessive power and disturbing noise, for the rotation of the disc at the required speed.

Furthermore, in such systems which require color filter sectors of substantial dimensions, at least somewhat larger than the dimensions of the picture itself upon the end of the kinescope tube,

the picture is completely viewed in color sequence; that is, one complete frame is viewed through each of the three color sectors, 1. e., the red, blue, and green sectors, or one picture field, made up of alternate lines only, is viewed in succession through each of such three color sectors. In either case and in order to avoid the highly objectionable color fringes or flicker, particularly when the object viewed at the transmitter is rapidly moving, it is necessary that the number 40 increases, the width of the required video frerate of 30 per second. Usually such increase required is double the foregoing rate, or 60 comquency band for such projection must be correspondingly increased. Thus, where a frequency band of 6 or 6.5 megacycles is considered adequate for satisfactory projection in present television systems projecting 525 line pictures in black and white, a band width of two or three times the black and white band width is required for three color televison transmission employing color sector discs. Such increase in the frequency band requires that the main or carrier frequency of such television transmisson be increased from the present standard frequency region of 50 to 70 megacycles to several hundred megacycles.

Further, when the carrier frequency is raised to these upper limits, new difliculties and problems in transmission arise, such as overcoming the greatly diminished efficiency of the transmitting tube at such frequencies, the substantial increase in the number of shadow casting obstacles, and .the increased number of ghost images presented by the higher reflectivity of objects to the higher carrier frequencies.

Among the objects of my invention is the provision of a system of transmitting and projecting television pictures in natural colors which avoids such difliculties and problems, which eliminates the necessity for an increase in the number of pictures transmitted per second, and which employs the portion of the frequency spectrum now employed for the transmission of black and white television pictures with its numerous and great advantages.

Embodiments of my invention are described in the following specification, which may be more readily understood by reference to the accompanying drawings. In the drawings Fig. 1 is a vertical sectional view of a pick-up camera, or iconoscope tube employed as a part of the television system of my invention;

Fig. 2 is a horizontal sectional 'view of the apparatus illustrated in Fig. 1:

Fig. 3 is a side elevational view of the appaplete picture scans per second, and such an inratus illustrated in Fig. 1;

crease in.pictures makes necessary a corresponding increase in the speed of rotation of the color sector discs at the transmitter and receiver.

It will be seen, therefore, that the present television systems for transmitting and receiving images in natural colors, and including such rotating color sector discs, involve substantial obstacles and objections preventing or impairing their public acceptance.

Furthermore, as is well recognized, as the num- Fig. 4 is an enlarged fragmentary plan view of the light-transparent curtain used with the apparatus illustrated in Figs. 1 to 3, inclusive;

Fig. 5 is an enlarged fragmentary sectional view of the curtain illustrated in Fig. 4;

Fig. is a side elevational view, partially sectioned, of the kinescopetube and the remainder of the synchronizing apparatus for the synchronizing of the curtains in accordance with my invention;

Fig. 8 is a fragmentary plan view of the end of the kinescope tube illustrated in Fig. 7;

Fig. 9 is a vertical sectional view, partially diagrammatic, of the apparatus illustrated in Fig. '7;

Fig. 10 is a side elevational view, partially sectioned, of a modified form of apparatus of my invention;

Fig. 11 is a diagrammatic view illustrating the relationship between the colored stripes upon the light-transparent curtain and the sweeps of the cathode beam; and

Fig. 12 is a diagrammatic view illustrating the relationship between the color stripes upon the transparent curtain and the cathode beam sweep when the stripes are horizontally disposed and the curtain is moved vertically.

With reference to the drawings, which are for illustrative purposes only, the numeral 2| indicates a pick-up camera or iconoscope or cathode beam'tube of conventional construction, and including an enlarged portion 22 and an elongated cated by the numeral 21 and are brought out of the tube through the end of the elongated cylindrical portion 23.

The enlarged portion 22 of the cathode beam tube is enclosed within or surrounded by an endless band, screen, or curtain 28. The curtain 28 isosupported upon

rollers

29, 30, 3i, and 32 suitably mounted for rotation, is held taut by a teni sion spring 33 connecting the roller 32 to a suitable base, and is maintained in firm contact with the roller 31, which is the driving roller, by

idle rollers

34 and 35. The driving roller 3| is driven by an electric motor 36 through a geared connection 31 with its shaft I8 at a speed which may be very low, as, for example, of the order of 9 to 13 inches per minute of linear movement of the curtain 28. If desired for any reason, the speed of movement of the curtain as may be made much greater than this order, there being no definite relationship between thespeed of travel of the curtain and that of the cathode beam sweep or the number of sweeps per second of the cathode beam across the mosaic plate 24. The broken line indicated by the numeral a indicates an object, light rays from which are passed through a collecting lens 40 and a colllmating lens' 4| in a housing 42, so that the light rays passing from the lens 4| to the mosaic plate 24 are parallel.

The curtain 28 is light-transparent and provided over its entire surface with contiguous, narrow vertical stripes 43. These stripes are in groups of three colors, red, blue, and green, as indicated by the letters R, G, and B in Fig. 4, the exact shades of such colors being so selected that, when viewed in rapid motion, the impression of white is conveyed to the retina of the eye, 1. e.. the

combination of shades of the three colors coiliprises the entire spectrum visible to the human eye.

The width of each individual stripe is determined by the diameter of the area of the mosaic plate 24 impinged upon by the cathode beam at any position of its travel; for example, if the dimeter of the cathode beam at its impingement upon the mosaic plate 24 is .002 inch, the width of each individual stripe 43 upon the curtain 28 is equal to at least .002 inch and may be somewhat greater. 1,

The curtain 28 is preferably constructed of flexible material, such as cellophane, celluloid, or

thin white silk made transparent. as by impreg-.

nation with a suitable glazing material. To provide additional mechanical strength I prefer to provide to each edge of the curtain 28 a reinforcement or hem 44 formed of linen or thin flexible material, such as steel or bronze. The lower hem 44 is provided with a plurality of perforations 45 which may be of any desired form and are 11-. lustrated as substantially square in the drawings. These perforations 45 serve to transmit light through the hem 44 which is opaque in order to synchronize the movement of the curtain 24 with the movement of a similar curtain at the receiving station utilizing apparatus illustrated in Fig. 6.

The numeral 48 indicates a lamp so positioned with respect to a reflector "that light rays from the lamp 46 are directed through a lens 48 and one of the perforations 45 when it is directly aligned with the lamp 4i, reflector 41, and lens 48. A photoelectric cell 49 is positioned upon the opposite side of the hem 44 and so shielded that light can fall upon the cathode electrode thereof only when it is transmitted through one of the perforations 48 and a collector lens 50. When a flash of light is thus passed through one of the delivered to the generator of the audio-carrier high frequency and is radiated therefrom in the form of a pulse of supersonic frequency to be picked up by the receiving antenna. The circults involved in the amplifier II and supersonic oscillator 52. being well known to those skilled in the art, are not illustrated or described in detall, nor for the same reason is the ampllfler or filter circuit at the receiving station by which this supersonic pulse is received. v

The received supersonic pulse is detected and amplified by an amplifier 53 and led to a thyratron tube 54, the output of which is connected to a gaseous glow or flash lamp 5!. The lamp II is so positioned with respect to a reflector N and a 7 lens 51 that light from the lamp is is projected through one of the perforations 45a in a curtain 28a, identical with the curtain 28 previously described, when such perforation is in alignment with the lamp '5, reflector 5i, and lens 51.

' All of the light from the lamp 55 which passes through one of the perforations 45a, when it is in advance of its proper position with resp ct to the curtain 28 at the transmitter, light from the lamp 88, when it is flashed, passes through one of the perforations 48a and enters the transparent wedge 88 and is conducted therefrom to a photoelectric cell 8|. Similarly, if the curtain 28a at the receiver is slightly behind its proper position to be synchronized with the curtain 28 at the transmitter, when the lamp 55 is flashed, light passes therefrom through one of the perforations 45c and falls upon the transparent wedge 88 and is conducted therefrom to a photoelectric cell 82.

The output of cells 8| and 82 is connected through

amplifiers

88 and 84, respectively, to a supersonic oscillator 88 having a circuit arrangement well known in the art, such that its output responsive to the amplified impulse from cell 8| is of one supersonic frequency, for example I! kilocycles, while its output responsive to the amplified impulse from the cell 82 is a different supersonic frequency, for example 20 kilocycles.

These amplified supersonic impulses of and kilocycles are filtered out through appropriate fllter circuits, well known in the art and hence not described in detail, and the resultant pulses are detected and amplified through

amplifiers

88 and 81. The rectified output of the

amplifiers

88 and 81 is led to the coils of two

relays

88 and 88, respectively, the operation of which is described hereinafter.

The numeral In in Fig. '7 indicates an iconoscope or cathode beam tube at the receiving station. The cathode beam tube I8 is of conventional construction and includes a cathode beam gun II and deflecting plate I2 for causing the cathode beam to scan a fluorescent picture area II to provide an illuminated image of the object 88 at the transmitter.

The curtain 28a is arranged immediately adjacent the fluorescent picture area I8, and on the opposite side of the curtain 280. a reflector 14 is positioned at an angle of substantially with the plane of the picture area It to project the light therefrom vertically upon a second inclined reflector I8. The second reflector I5 is so positioned as to reflect the light against a viewing screen I8 from the reflector I4 substantially parallel to the light rays directed from the picture area I8 against the reflector I4. The picture may be viewed either from the front or rear of the viewing screen I6, according to the type of viewing screen employed.

It would, of course, 'be possible to pass the color curtain 28a completely around the cathode beam tube 18 in the manner that it passes around the smaller cathode beam tube 2! at the transmitter. However, the reflector arrangement described avoids such an inconveniently great length for the curtain 28a by permitting this curtain to pass around only the reflector 14. In such travel the curtain 28a is supported by rollers 'I'l similar to the rollers supporting the curtain 28 and previously described.

In the apparatus previously described it is desireable that the curtain 28a pass very close to the picture area I8 in order to avoid color confusion resulting from diflusion of the light rays from various elements of the picture image through stripes 43 other than the stripes of the appropriate color. In the apparatus as illustrated this color confusion is avoided by positioning the curtain 28a practically in contact with the flattened surface of the cathode beam tube 18 upon which the picture area I8 is located. If the curtain 28a 6 is spaced some distance from the picture area 18, the color confusion referred to may be avoided by the use of an optical projection system located between the picture area I8 and the curtain 28a as is hereinafter described.

As best illustrated in Fig. 'I, 'the cathode beam tube I8 is mounted upon a fiat support I8 pivoted at its rearward end on a, pin I8 supported upon a base 88. The tube I8 is supported upon this support I8 by clamps 8| which extend around a portion of the periphery of the tube. At its forward end the support I8 rests upon two rollers 82 mounted upon an upright 88 attached to the base 88. Adapted for rolling contact with the

cesses

88 and 81 provided in the tops of

armature members

88 and 88, respectively. As illustrated in Fig. 9, the

recesses

88 and 81 are provided with downwardly converging bottom walls.

. It will be seen that, when the armature member 88 is attracted by current passing through the relay coil 88, th ball 88 is forced into close'and propelling contact with the support |8 so as to propel the support I8 toward the right. Likewise, when the armature member 88 is attracted by current passing through the relay coil 68, the ball 88 is forced into driving contact with the support 18 so that the support I8 with the cathode beam tube 18 is moved to the left.

When one of the balls 84 or 85 is in propelling contact with the support I8, the other of such balls is disengaged from the support I8 so that the support is free to move either to the right or to the left in response to contact with one ball or the other. By this arrangement the cathode beam tube 18 is shifted slightly to the right or left so that the vertical color stripes 48 in the curtain 28a will register perfectly with the corresponding color stripes in the curtain 28 at the transmitter.

Where both the transmitter and the receiver are operated from the same power network, there is only a practically negligible tendency on the part of the

curtains

28 and 28a to become displaced from each other. even by the width of half of a single stripe 43, so that no automatic synchronizing device is necessary under such circumstances. Such adjustment as is required for such an arrangement may be effected by an adjusting screw 88 threaded through an upright 8| of the base 88 and engaging one side or the support II and a spring 82 resiliently engaging the other side of the support I8 and an upright 88 secured to the base 88. The adjusting screw 88 is not employed if the automatic synchronizing apparatus herein described is used.

It is in any event necessary that the lateral location of the cathode beam picture upon the picture area I8 of the cathode beam tube I8 be at all times positive and exact. However with the existing methodsof line sweep synchronization the dimensions and location of the cathode beam picture are maintained with extreme accuracy.

Illustrated in Fig. 10 is a modified form of apparatus in which the curtain 28a is spaced from the picture area I3 and the flattened end of the cathode beam tube 18. In this

apparatus lenses

88 and 88 are provided in a housing 91a in position to collect the rays of light from the picture area I8 and to transmit them as horizontal rays through the curtain 28a in close proximity to the lens 88 and against an inclined reflector 81. The reflector 8I reflects these rays against a second reflector 88, which in turn reflects the rays'in a direction substantially parallel to the rays which pass from the picture area I2 through the lens 88. The curtain 28a is looped around the reflector 81 and may be supported and driven in the manner previously described.

In the apparatus illustrated in Fig. the synchronization of the stripes of corresponding color in the curtain 28:: at the receiver and the curtain 28 at the transmitter are accomplished with the same apparatus as that described in connection 10 with Figs. 7, 8 and 9 by moving the lens housing 81:: parallel to th direction of movement of the curtain 28a.

Referring to Fig. 11, if it be assumed that light rays from a small blue object pass through the area indicated by the numeral I88 upon the curtain 28 in front of the cathode beam tube 2 i, and that such area is included within one of the stripes 42 which is red, the light rays from this blue object will not be transmitted through the curtain 28 for /30 of a second. This is for the reason that, if the curtain is travelling from right to left, and the next adjacent stripe 43 is green, the secqnd sweep of the cathode beam will be on the line indicated by the numeral 2 in Fig. 11 rather than upon the line indicated by the numeral I. When the cathode beam again arrives at the sweep indicated by the numeral I, a stripe 48 of blue color on the curtain 28 will be interposed between the rays of light from such 30 blue object, and such rays will therefore be transmitted to the spot on the mosaic plate 24 corresponding to the area Hill.

The shift of the curtain 28 from .the first red stripe to the second blue stripe will represent /30 of a second. if, on the other hand, a green object were presented to the area indicated by. the numeral Hi8, instead of a blue object, /is of a second would elapse before a stripe 48 on the curtain which is green will be in position to trans- 4o mit the rays of green light upon the area of the mosaic plate 24 corresponding to the area indicated by the numeral I80.

Therefore, it will be seen that any color spot of the image is delayed not longer than /15 of a second for a stripe 42 on the curtain 28 of corresponding color to appear before it and thus permit light rays from such color spot to pass through the curtain 28 to the mosaic plate 24.

-As the horizontally travelling cathode beam 50 scans the picture from left to right and from top to bottom, unless the object 38 before the oathode beam tube 2| is moving with extreme rapidity, every individual element or section of the object optically projected upon the curtain 28 will find a stripe 48 of corresponding color on the curtain 28 for the transmission of its proper 'color to the mosaic plate 24 of the cathode beam screen 18, the rapid horizontal interlaced sweep of the cathode beam across the curtain 28 upon the face of the mosaic plate 24 and the very slow and transverse movement of the current 28 providing a 'varl-colored projected image in which extremely small properly colored elements appear all over the face of the mosaic plate 24. These properly colored elements upon the mosaic plate 24 are, as will be apparent from the foregoing, reproduced with the same fidelity upon the viewing screen 18.

Instead of employing

curtains

28 and 28a with stripes .43 extending vertically, I may employ a curtain of the same character with the stripes of color extending horizontally, the arrangements of mirrors, lenses, and drive means being the same as described in connection with the curtains 28 and 2842 except that they are rotated through The horizontal arrangement of stripes 48, however, is not as satisfactory as the vertical arrangement. I

This is illustrated in Fig. 12, where I hav shown a cross section of a vertically moving our.- tain 28b having stripes 43b extending horizontally. These stripes 42b are like the stripes 42, previo lfl y described, as to color and sequence.

In the column headed C there is illustrated the successive sweeps of the horizontally moving cathode beam of the cathode beam tube 2|, assuming for the purpose of simplification that the beam scans successive lines and not alternate lines as in actual practice. In the column headed D I have shown the relative positions of the successive sweeps oi the cathode beam and the curtain 28b when the curtain has moved upwardly a distance equal to half of the diameter of the cathode beam'at its impingement upon the mmsaic plate 24. K

With the relative positions of the cathode beam sweeps in the column D and the stripes 4812, it will be evident that the cathode beam sweeping path i is travelling along both a red and a blue horizontal stripe. This results in the projection upon the mosaic plate 24 of a section of the obiect 29 through half a red stripe and half .a

blue stripe 42b. giving the sensation of purple upon the retina of the observer's eye, thus incorrectly presenting the true color of the corresponding section of the object.

Thus, if the corresponding section of the oblect were red and the scanning beam of the oathode beam tube 2l were astride a red and blue stripe 42b of the curtain 28b, the resultant electron impulse from the cathode beam tubeli will be that resulting from the red light transmitted to the curtain 28b, being only half transmitted through the curtain 28b. Therefore, at the receiving cathode beam tube 18 the intensity of the scanning beam at that section of the image will be reduced by half, and this reduced illumination will be divided between the red and blue stripes, resulting in a dim purple colored section of the image, instead of a bright red colored sec tion.

The diminution of light intensity at this instant in such a' small section might be overlooked, because within /30 or not to exceed /15 of a second thereafter or less a succeeding red stripe 43b of the curtain 28b would be in proper position to give the proper eye sensation of color and the proper intensity of illumination. However, as hereinbefore stated, there would be a sensation of purple projected along the entire sweep of the cathode beam represented by the path i, if it be assumed that a horizontal red stripe existed on the object 38 at the area being scanned, so that the integrated sensation of the eye would be a blending of a red line followed by a purple line giving distorted color sensation for that section of the object.

.It will thus be apparent that color errors or distortions are involved in the use of a curtain 9,. with horizontal stripes of color which do not occur when the curtain is provided with vertical color stripes.

The disadvantage of a curtain with the horizontal stripes may be reduced or eliminated by moving the curtain 28b vertically step-by-step with sufiicient suddenness rather than by slow continuous motion. In such a manner the paths of the beam sweep indicated by the numeral I, for example, coincides successively with stripes 43 of red, blue, and green color. In such a manner there may be secured an effect in general similar to that obtained by the conventional three-color rotating filter disc, except that the colors of the projected image will be intermingled during any single scanning. Such intermingling will result in far less color fringing and flicker than in the use of the conventional rotating color disc, and likewise provides the extremely important advantage of providing color images at a scanning rate of thirty pictures .per second equal in excellence to those obtained with the conventional rotating color disc and a scanning rate two or three times this figure.

However, such intermittent motion of the cur tain 28b with the stripes 43b extending horizontally presents mechanical difficulties in view of the frequency with which such motion must occur.

It will be obvious that, instead of employing stripes 43 or 43b upon the curtains 28. 28a. and 28b of three colors in sequence, as hereinbeiore described, I may employ stripes in two-color se quences, thus permitting an even slower movement of the continuously or intermittently propelled curtains. However, it is well known that the reproduction of natural colors by the use of a two-color process or apparatus is only approximately perfect and not entirely satisfactory, and I therefore prefer to employ the three colors in sequence to cause the projected image to truly present the natural colors of the object.

The numerous advantages of my invention hereinbefore described are not restricted to a television scanning system employing 525 or any precise number of lines to a picture and or any precise number of complete frames, or 60 or any precise number of scanning fields per second.

The advantages of my invention hereinbefore described are enhanced if the number of lines of the picture be substantially increased. Obviously, if the number of lines to the picture be increased, the width of the stripes 43 and 43b should be proportionately reduced. It is not necessary for the reasons set forth to increase the number of picture scans per second in order -to obtain satisfactory reproduction of the image in correct natural colors. It will be apparent that various mechanical arrangements and devices other than those I have illustrated and described may be employed to efiect the modes of operation and the results of the mechanical arrangements and constructions I have illustrated and described for illustrative purposes. Such arrangements and many variations and modifications of the apparatus illustrated and described will readily occur to those skilled in the art to which the invention is related, and my invention should therefore be understood as not restricted to the specific embodiments illustrated and described but as including all arrangements, modifications, and additions coming within the scope of the claims which follow.

I claim as my invention:

1. In a color television system wh ch includes a 10 cathode beam tube having means for generating a cathode beam and having means for moving the beam along parallel paths, the combination of: a movable filter disposed adjacent the cathode beam tube, said filter comprising a plurality of sequentially arranged stripes of different colors, said stripes being perpendicular to the direction of movement of the cathode beam; and means for moving said filter at a uniform speed in a direction perpendicular to said stripe 2. Ina color television system including a pair of cathod beam tubes one of which is associated with a transmitter and the other of which is associated with a receiver, the cathode beam tube at the receiver being movable, the combination of: a first multi-color filter disposed adjacent the cathode beam tube at the transmitter and provided with a plurality of perforations therethrough; first light-producing means adapted for directing light rays through one of said perfora tions through said first multi-color filter; first light-responsive mean-s in the path of said light rays from said first light-producing means; means for moving said first multi-color filter; a second multi-color filter disposed adjacent the cathode beam tube at the receiver and provided with a plurality of perforations therethrough; second light-producing means adapted for directing light rays through one of said perforations through said second multi-color' filter whenever light rays from said first light-producing means fall on said first light-responsive means; second light-responsive means in the path of light rays from said second light-producing means; means for moving said second multi-color filter; and

means actuable by said second light-responsive means for moving the cathode beam tube at the receiver whenever light rays from said second light-producing means fall on said second lightresponsive means.

3. In a color television system which includes a tube having means for generating an electron stream, means for causing said electron stream to scan a field in said tube in a plurality of parallel paths and means providing a light path for said field, a movable light filter disposed in said light path, said filter having a plurality of sequentially arranged stripes of different colors extending transversely of said parallel paths, and means for moving said filter at a uniform speed in one direction to move said stripes transversely of themselves across the light path for said field and at a speed causing the scanning of said field to cross a multiplicity of said stripes in each of said parallel paths.

4. In a color television system which includes a cathode beam tube for generating a cathode beam, means for moving the end of the beam to cause said end to scan a field in said tube in a plurality of parallelpaths and means providing a light path for said field, a movable light filter disposed adjacent said cathode beam tube and in said light path, said filter having a plurality of sequentially arranged stripes of different colors extending transversely of said parallel paths, and means for moving said filter at a uniform speed in one direction to move said stripes transversely of themselves across the light path for said field and at a speed causing said end of said beam to cross a multiplicity of said stripes while moving along each of said parallel paths.

5. In a color television system which includes a tube having means for generating an electron stream, means for causing said electron stream to scan a field in said tube in a plurality of parll allel paths and means providing a light P th for said field, a movable light filter disposed in said light path, said filter having a plurality of sequentially arranged stripes of difierent colors extending transversely of said parallel paths, and means for moving said filter at a uniform speed in one direction to move said stripes transversely of themselves across the light path for said field and at a speed causingthe scanning of saidfield to cross a multiplicity of said stripes in each of said parallel paths, said tube having an image receiving surface constituting said field scanned by said electron stream, said filter being positioned closely adjacent and substantially parallel to said surface.

6. In a color television system which includes a tube having means for generating an electron stream, means for causing said electron stream to scan a field in said tube in a plurality of parallel paths and means providing a light path for said field, a movable light filter disposed in said light path, said filter having a plurality of sequentially arranged stripes of diil'erent colors extending transversely of said parallel paths, and means-for moving said filter at a uniform speed in one direction to move said stripes transversely of themselves across the light path for said field and at a speed causing the scanning of said field to cross amultiplicity of said stripes in each of said parallel paths, said filter being an endless fiexible curtain extending around said tube.

7. m a color television system which includes a tube having means for generating an electron stream, means for causingsaid electron stream to scan a field in said tube in a plurality of parallel paths and means providing a light path for said field, a movable light filter disposed in said light path, said filter having a plurality of sequentially arranged stripes of different colors extending transversely of said parallel paths, and means for moving said filter at a uniform speed in one direction to move said stripes transversely of themselves across the light path for said field and at a speed causing the scanning of said field to cross a multiplicity of said stripes in each of said parallel paths, said filter being an endless flexible curtain forming a closed loop with a portion of said curtain adjacent said tube and a portion remote from said tube and an angularly positioned mirror within said loop to cause said light path to pass through said adiacent portion only of said curtain.

8. In a color television receiver which includes. a cathode beam tube for generating a cathode beam, means-for moving the end of the beam to cause said end to scan a field in saidwtube in a plurality of parallel paths and means providing a light path for said field, a movable light filter disposed adjacent said cathode beam tube and said light path, said filter having a plurality of sequentially arranged stripes of different colors extending transversely of said parallel paths, means for moving said filter at a uniform speed in onedirectionto move said stripes transversely of themselves across the light path for said as v 434,368

assaaos field and at a speed causing said end of said beam to cross a multiplicity of said stripes while moving along each of said parallel paths, means for receiving and detecting light filter synchronizing pulses. means for converting said synchronizing pulses into light pulses and directing said light pulses toward said filter, said filter having light interrupting and light transmitting portions in the path of said light pulses, the position of said portions of said filter being correlated with the position of said stripes and means including a photoelectric device responsive to light from said lizht pulses transmitted through said light transmit'ting portions for moving said filter and tube relative to each other in a direction transversely of said stripes to maintain color synchronization of said receiver.

9. In a color television receiver which includes, a cathode beam tube for generating a cathode beam, means for moving the end 01' the beam to cause said end to scan a field in said tube in a plurality of parallel paths and means providing a light path for said field, a movable light filter disposed adjacent said cathode beam tube and said light path, said filter having a plurality of sequentially arranged stripes of difi'erent colors extending transversely of said parallel paths, means for moving said filter at a uniform speed in one direction to move said stripes transversely of themselves across the light path for said field and at a speed causing said end of said beam to-cross a multiplicity of said stripes while moving along each of said parallel paths, means for receiving and detecting light filter synchronizing pulses, means for converting said synchronizing pulses into light pulses and directing said light pulses toward said filter, said filter having light interrupting and light transmitting portions in the path of said light pulses, the position of said 0 portions of said filter being correlated with the receiver.

LEE l: FOREST.

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

UNITED STATES PATENTS Number Name Date 1,130,221 ,Van Riper Mar. 2, 1915 2,310,863 ,Leverenz Feb. 9, 1943 2,317,989 Goldmark May 4, 1943 2,319,803 Dyer May 25, 1943 2,319,805 Dyer May 25, 1943 2,389,979 I-Iufi'nagle Nov. 27, 1945 FOREIGN PATENTS Number Country Date Great Britain Sept. 9, 1995