US2412098A - Color television film scanning system - Google Patents

Description

Dec. 3, 1946. N Z I 2,412,098

COLOR TELEVISION FILM SCANNING SYSTEM Filed y 1, 1944 2 Sheets-Sheet 1 l8 2| FIG! I v I LINE a scmumg L TELEVISON -i LJNMGETGE 1 AMP! a-TRANs.

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SYNC. PULSE SEPARATOR REO.&AMP.

27 INVENTOR FIG. 2 JOSEPH QSCHANTZ ATTORNEY Dec. 3, 1946. J. D. SCHANTZ 2,412,098 I COLOR TELEVISION FILM SCANNING SYSTEM Filed July 1, 1944 2 Sheets-SheepZ TO FIELD SCANNING T' WAVE GENERATOR VIDEO SIGNAL OUTPUT INVEINTOR ATTORNEY Patented Dec. 3, 1946 COLOR TELEVISION FILM SCANNING SYSTEM Joseph D. Schantz, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application July 1, 1944, Serial No. 543,075

13 Claims. (Cl. 178-52) This invention relates to a method of and apparatus for transmitting and receivin television pictures in natural colors and particularly relates to a method and apparatus for color television transmission and reproduction in which interlaced scanning is employed.

It is customary in television to employ interlaced scanning where each complete scanning pattern or picture frame comprises a plurality of fields of scanning lines which are geometrically displaced with respect to each other. The present television standard adopted in the United States requires thetransmission of images at a field frequency of 60 per second twice interlaced to provide a frame frequency of thirty per second. This standard has been adopted to coordinate the field scanning period of 60 cycles with the standard 60 cycle alternating current prevalent throughout most of this country. On the other hand, the standard rate of transmission of motion picture film is 24 frames per second.

Various scanning systems have been suggested for properly coordinating the standard television transmission rate of 60 field scansions per second twice interplaced, and the present motion picture standard of 24 pictures per second. To this end, it has been proposed to scan successive pairs of picture frames five times while the picture transmission rate is 24 per second. Thus, the field scansion period is at the standard rate of 60 cycles per second while the picture transmission rate corresponds to the motion picture standard of 24 pictures per second.

Usually the first picture frame is scanned three times and the succeeding frame is scanned twice.

In both cases, the interlace ratio is two-to-one. In the frames which are scanned three times, the third scansion is a duplicate of one of the other two. However, it is also feasible to scan each third line only during each field scansion period.

For transmitting scenes in natural colors, it has been proposed to interpose a rotating disk containing three or six color filters into the path of the light rays impinging upon the transmitter tube for transmitting consecutive series ofrthree fields, each being representative of another color. Usually the three primary colors red, green and blue are chosen for a three-color filter disk, and the colors are repeated when a six-color disk is used. However, such a scheme is not adapted for the transmission of color motion picture film where five fields are employed to scan each successive pair of picture frames. It will beeasily seen that with such an arrangement one of the three primary colors will occur only once during scansion of the first five fields, while during scansion of the next five fields another of the primary colors will occur only once, and so forth. This will produce a very marked color flicker, due to the low frequency of this lack of color balance which repeats after every fifteen fields correspondin to one-quarter of a second.

The principal object of this invention is, therefore, to provide a novel method of and apparatus for transmitting and receiving television pictures in natural colors.

Another object of the present invention is to provide a method of and apparatus for transmitting and receiving television pictures in natural colors employing an interlaced scanning pattern having five field scansion cycles for each recurring group of two consecutive picture frames and further interposing five light filters into the path of the light so that a different color characteristic prevails for at least three fields of every periodically recurring group of five field scansion periods. I

A further object of this invention is to provide a method of and apparatus for televising color motion picture film and correlating the televising scanning rate and the color scanning rate with the film speed.

In accordance with the present invention, there is provided a method of and apparatus for transmitting and receivin television pictures in natural colors. Means are provided for scanning an optical image in accordance with aninter.- laced scanning pattern comprising groups of five field scansion cycles. Five light filters of different light transmission characteristics are provided which are successively interposed in predetermined sequence between the optical image to be transmitted and the television transmitter tube so that a different filter is interposed into the path of the light rays for each field scansion cycle. Preferably, the light filters are arranged as segments of a disk rotating in synchronism with the field scansion cycle. A similar disk synchronized with the disk of the transmitter is arranged in front of the receiving tube between the tube and the observer.

The system of the present invention is particularly adapted for televising color motion picture film, for instance, of the Kodachrome or Technicolor type. However, it is also feasible to use the color television scanning system of the present invention for direct pickup of an object to be transmitted.

The color television scanning system of the game 3 present invention has been shown in connection with a transmitter tube of the image-dissector type. As will be readily understood, the method and apparatus of the present invention may also be used in connection with a television transmitter tube of the light storage type.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 shows a transmitter and receiver system embodying the invention;

Fig. 2 is an end view along line 22 of Fig. 1

and shows a color filter disk for use in the apparatus of Fig. 1; and

Fig. 3 shows schematically a transmitter in accordance with the invention adapted for direct pickup of the object to be transmitted.

Referring now to Fig. 1, there is shown a television transmitter tube li! and a cathode-ray television receiving tube Ii. Television transmitter tube i is of the image-dissector type and comprises a photosensitive electrode l2 which receives light from light source i3 through lens system H. Color film i5, which may be of the Kodachrome or Technicolor type, is arranged between light source It and lens system 14 and may be moved'either with uniform speed or intermittently, as desired. Lens system 14 projects an image of succeeding film frames on photosensitive electrode l2.

Two different methods have been developed for televising motion picture film. In one suggested arrangement, the film moves with uniform speed in front of the television pickup tube, and optical means, such as moving lenses or prisms are employed for projecting intermittently stationary images of the uniformly moving film on the television transmitter tube. Another suggested method employs intermittent film feed similar to the one used for projecting motion picture films. Either one of these methods can be used for televising color motion picture film fl in accordance with the present invention.

Through the action of the light projected on photosensitive electrode 12, photoelectrons are emitted therefrom. These photoelectrons are focused by magnetic coil 16 energized from battery 11. Magnetic coil 15, arranged outside of transmitter tube Ill, produces an axial magnetic field. A pair of magnetic coils schematically indicated at #8, it is connected with field-scanning wave generator 25). Coils I8, 18 generate 'a transverse magnetic field and serve for deflecting the photoelectrons emitted from photosensitive electrode l2 in accordance with the field scanning cycle. The field scanning frequency obtained from gnerator 20 is 60 cycles per second; Another pair of magnetic coils schematically indicated at 2i, 2| is connected with line-scanning generator 22 to give the photoelectrons their linescanning deflection by generating a transverse magnetic field arranged at right angles to the field generatedby coils |8,'l'8. The photoelectrons are focused at scanning aperture 23 of target or anode finger 24 and collected in a conventional manner. The output signal representative of brightness and color values of the film to be transmitted, is impressed upon resistor I9, and voltage variations appearing thereacross are fed through lead 25 to television amplifier and transmitter 26.

In accordance with the invention, there is provided a color disk 21 which is rotated by electric motor 28. Leads 30, 3| connect electric motor with field-scanning wave generator 20 through frequency divider or reducer 29. Fieldscanning generator 20 delivers an alternating current of cycles. Motor 28 is designed to rotate with 12 revolutions per second by the intermediary of frequency divider 29.

Rotatable disk 21, shown particularly in Fig. 2, comprises five segments 32, 33, 34, 35 and 36. Segments 32 to 38 consist of light filters of different light transmission characteristics. Three of the five segments 32 to 36, are designed to transmit individually the three primary colors; that is, red, green and blue. The two remaining segments may consist of light filters designed to transmit individually two of the primary colors. However, it may be preferred to select two intermediate colors for the two remaining filter segments. This scheme may be particularly useful for balancing the color of the entire system. As is well understood, the wavelength range of white light passing through the optical system into the transmitter tube is dependent upon the composition of the projected light used to illuminate the scene to be transmitted, the color absorption of the light filters, and the color sensitivity of the photosensitive electrode. Hence, it will be obvious that by selecting suitable intermediate colors for the two remaining segments of rotating disk 21', a much better color balance of the transmitted color television picture may be obtained.

It is also feasible to use two transparencies for the two remaining segments of disk 27., The effect of the transparencies upon the composite color of the transmitted picture Will be described hereinafter.

The transmitter system shown in Fig. 1 operates as follows: light from light source I3 passes through film'l'5 and is projected by lens system M on' photosensitive electrode l2. This produces in a well-known manner a cloud of photoelectrons representative of the brightness of individual portions of the optical image. This electron cloud is focused by means of coil 16 and deflected by coils i8 and 2| into aperture 23 of target 24 to produce the video signals.

Motor 28 rotates disk 21Iat the rate of 12 revolutions per second. Hence, each of segments 3-2 to '36 will be in front of transmitter tube [0 for one-sixtieth of a second corresponding to the field scanning period. The motion picture frames on film I 5 are moved in front of transmitter tube ill at the rate of 24 pictures per second. As explained hereinbefore, it is customary .to scan the first film frame three times and the second frame two times for coordinatingthe picture transmission rate of 24 pictures persecond with the'field scanning period of 60 fields per second.

We may now assumethat the first film frame which is scanned three times receives its light from light source 13 through three consecutive filter segments which are designed to transmit individually the three primary colors, red, green and blue. The succeeding. picture frame is scanned twice and receives its light through the two remaining sectors of 'disk 21. As explained above, these sectors may bev designedato transmit individually twoof the primary colors or any suitable intermediate color to give the proper color balance to the system. In case the two remaining sectors of disk21 are transparencies, the video signal corresponding to these two picture scansions is representative of the brightness in black and white of th object to be'tra'nsmitted. In view of the high rate of transmission of the fields, the eye would still receive'the impression of a picture in natural colors in spite of the fact that twopictures out of every five are transmitted in black and white only. It will be understood that the term light filters of different light transmission characteristics includes transparencies. The sequence in which the five light filters are arranged on disk 21 is of course entirely immaterial to the operation of the transmitter and receiver system of the invention.

Cathode-ray television receiving tube ll comprises an electron gun 40. Electron gun 40includes indirectly heated cathode 4|, a control element 42, a first anode 43 and a second anode 44. The connections of these elements being well known in the art, have notbeen shown in the drawings to prevent confusion. For modulating the electron beam in accordance with the received picture signals, control element 42 is operatively connected to the output of receiver 52, to receive the demodulated picture signals therefrom. Cathode-ray receiver tube II has an inner Wall coating 45 and a fluorescent screen 46 designed for emitting white light upon electron bombardment. Magnetic coils 4?, 47 are connected with field. scanning generator 48 for deflecting the electrons produced by electron gun 40 in accordance with the field-scanning period. Magnetic coils '50, are connected with line-scanning wave generator 51 for deflecting the electrons according to the line-scanning period.

The video signals produced by transmitter structure III are received and amplified by television receiver and amplifier 52. As shown in Fig. 1, the video signal is transmitted by radio carrier waves, but it is to be understood that transmitter I0 may be connected with receiver ll through a suitable cable. Television receiver and amplifier 52 is connected with synchronizing pulse separator 53 which in turn is connected with field scanning generator 48 and line scanning generator 5| for synchronizing purposes;

Electric motor 54 is connected with field scanning generator 48 through frequency divider 49 so that motor 54 rotates with 12 revolutions per second. The particular arrangement is such that motor 54 rotates in synchronism with motor 28 of the transmitter. Hence, disk 55, driven by motor 54, will also rotate in synchronism with disk 27 of the transmitter. Disk 55 bears five segments of light filters of the same light transmission characteristics and arranged in the same manner as the light filters of transmitter disk 21.

Receiver tube I l operates as follows: The electrons produced by electron gun 40 are focused, controlled in accordance with the received video signals and deflected. Depending upon the intensity of the electron bombardment, successive elemental areas of fluorescent screen 46 are excited to give white light representative of the brightness of corresponding points of the film to be transmitted. This light is now seen by the observer through the intermediary of filter disk 55,

an image instead of scansion of a colorfilm; Such an arrangement has been shown schematically in Fig. 3. In Fig. 3, there is provided a television transmitter tube schematically indicated at 60. Transmitter tube has a photosensitive electrode 6! which receives light from object 62 through-lens system 63; The photoelectrons pro: duced by the action of the light on photosensitive electrode 6| are collected in anode finger 64. The video signal is impressed on lead 65 and may then be amplified and transmitted. Electric motor 65 is connected with the field scanning wave generator in the manner previously explained. It rotates at the rate of 12 revolutions per second and drives filter disk 61 which is arranged in the same manner as explained in connection with Fig. 2. The operation of the television transmitter shown in Fig. 3 is the same as the one illustrated in Fig. 1. The receiver for the transmitter in Fig. 3 may be identical with the one shown in Fig. l.

Although the television transmitter tube shown herein is of the image-dissector type, it will be understood that television receivers of the light storage type may be used in connection with the system of the present invention.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from-the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. Television apparatus for transmitting pictures in natural colors comprising a picture signal generating device having a photosensitive member, means for projecting an optical image of the object to be transmitted on said member, means for efieotively scanning successive elemental areasof said image in accordance with an interlaced scanning pattern comprising pe-. riodically recurring groups of field scansion cycles to produce a train of picture signals representative of the brightness of said elemental areas, a plurality of light filters of difierent light transmission characteristics, equal in number to the number of field scansion cycles in each of said groups, and means for successively interposing said filters in predetermined sequence between said optical image and said photosensitive memher so that a different filter is interposed between said image and said member for each field scansion cycle.

2. Television apparatus for transmitting pictures in natural colors comprising a picture signal generating device having a photosensitive member, means for projecting an optical image of the object to be transmitted on said member, means in synchronism with the field scanning periods ans-as in such a manner that the same segment traverses &id' photosensitive member, during each field scanning period of successive pairs of frames.

V '3. Television apparatus for transmitting pictures in "natural colors comprising a picture signal generating device having a photosensitive member, means for projecting an optical image of the object to be transmitted on said member, means for effectively scanning successive elementa'lareas of. said image in accordance with an interlaced scanning pattern having three fields of consecutively scanned lines for one frame and two fields of consecutively scanned lines for the succeeding frame to produce a train of picture signals representative of the brightness of said element-a1 areas, a disk having five segments of different light transmission characteristics, three of said segments being designed to transmit individually light of one of the three primary colors and the remaining two of said segments being designed to transmit individually light of intermediate colors, said disk being arranged between said-optical image and said photosensitive memher, and means for rotating said disk whereby said disk segments in rotating traverse successively said photosensitive member in synchronism with 'the field scanning periods.

4. Television apparatus for transmitting pictures in natural colors comprising a picture signs generating device having a photosensitive member, means for projecting an optical image of the object to be transmitted on said member, means for effectively scanning successive elemental areas of said image in accordance with an interlaced scanning pattern having three fields of consecutively scanned lines forone frame and two fields of consecutively scanned lines for the succeeding frame to produce a train of picture signals representative of the brightness of said elemental areas, a disk having five segments of different light transmission characteristics, three of said segments being designed to transmit individually light of one of the three primary colors and the remaining two of said segments being transparencies, said disk being arranged between said optical image and said photosensitive member, and means for rotating said disk in synchronism with the field scanning periods whereby each' of said disk segments in rotating traverses said photosensitive member during one field scanning period.

5. A television receiving system for reproducing television pictures in natural colors comprising a cathode ray picture reproducing tube, 7 including means for developing a beam of electrons anda target adapted to be scannedby said beam, means for controlling said beam in accordance'with received picture signals representative of .picture brightness and color components thereof, means for defiecting said beam across said target in accordance with an interlaced scanning pattern, thereby to produce a luminous image of substantially white light, said scanning pattern comprisingpairs of successive frames, each pair of frames having five field Lscansion cycles, five light filters of diiTerent light transmission characteristics, andmeans for successively interposing said five filters in predetermined sequence in the path of said luminous white image so that a diiferent filteris interposed in .said path for each field scansion cycle and that the same filter is interposed in said ,path for each film scansion cycle of'successive pairs of frames. 7

6. A'television receiving system for reproducing television pictures in natural colors comprismg a cathode ray picture reproducing tub e,.ineluding means fordeveloping a beam of electrons and a target adapted to be scanned by said beam, means for controlling said beam in accordance with received picture signals representative of picture brightness and color components thereof, means for deflecting said beam across said target in accordance with an interlaced scanning pattern, thereby to produce a luminous image of substantially white light, saidscanning pattern comprising successive frames, one of said frames having three fieldsof 'oonsecutivelyscanned lines and the succeeding frame having two fields of consecutively scanned lines, a disk having five segments of different light transmission characteristics three of said segments being designed to transmit individually light of one of the three primary colors and the remaining two of said segments being designed to transmit individually light of intermediate colors, said disk being arranged in the path of said luminous white image and in front of said target, and means for irotating said disk whereby said disk segments in rotating traverse successively said target in synchronism with the field scanning periods.

7. A television receiving system for reproducing television pictures in natural colors comprising a cathode-ray picture reproducing tube, including means for developing a beam of electrons and a target adapted to be scanned by said beam, means for controlling said beam in accordance with received picture signals representative of picture brightness andcolor components thereof, means for deflecting said beam across said targetin accordance with an interlaced scanning pattern, thereby to produce aluminous image of substantially white light, said scanning pattern comprising successive frames, one of said frames having three fields of consecutively scanned-lines and the succeeding frame having two fields of consecutivelyscanned lines, a disk having five segments'of difierent light transmission characteristics, "three of said segments being designed to transmit individuallylight of one of the three primary colors and the remaining ,two of said segments bein transparencies, said disk being arrangedin the path of said luminous white image and in .front of said target, and means for rotating said .diskin synchronism with the field scanning periods whereby each of said disk se ments infrotating traverses said target during one field scanning period.

8. A television system'foritransmitting pictures innatural colors comprising a picture signal generating device having a photos'ensitive member, mean-s 'forprojecting an optical image of the 0biect to bert'ransmitted on said member, means for effectively scanning successive elemental areas of "said image'in accordance with :an interla'cedscanningpattern"to produce a train of picture signals "representative of picture brightness and color components thereof, meansjfortransmitting said signalsJmeans for receiving said signals, a cathode-ray'picture reproducing tube including means .for developing a "beam of electrons and a'target adapted to be scanned by said beam, means for controlling said beam in accordance with the ireceivedipicture signals, means for deflecting "said beam across said target in accordance with said interlaced scanning pattern, thereby to producea' luminous image of substantially white light, said pattern comprising successive frames, each .pair of frames having five fields of. consecutively scanned paralleljlines, five lightfilters of different light transmission characteristics, and means for successively interposing said five filters in predetermined sequence in the path of said luminous white light image so that a different filter is interposed in said path for each film scansion cycle and that the same filter is interposed in said path for each film scansion cycle of successive pairs of frames.

9. A television system for transmitting pictures in natural colors comprising a pictur signal generating device having a photosensitive member, means for projecting an optical image of the ob- .iect to be transmitted on said member, means for effectively scanning successive elemental areas of said image in accordance with an interlaced scanning pattern having three fields of consecutively scanned lines for one frame and two fields of consecutively scanned lines for the succeeding frame to produce a train of picture signals representative of picture brightness and color components thereof, means for transmitting said signals, means for receiving said signals, a cathode-ray picture reproducing tube including means for developing a beam of electrons and a target adapted to be scanned by said beam, means for controlling said beam in accordance with the received picture signals, means for deflecting said beam across said target in accordance with said interlaced scanning pattern, thereby to produce a luminous image of substantially White light, said pattern comprising successive frames, one of said frames having three fieldsof consecutively scanned lines and the succeeding frame having two fields of consecutively scanned lines, five light filters of different light transmission characteristics, three of said light filters being designed to transmit individually light of one of the three primary colors, and means for successively interposing said five filters in predetermined sequence in the path of said luminous white light image so that a different filter is interposed in said path for each film scansion cycle and that the same filter is interposed in said path for each film scansion cycle of successive pairs of frames.

10. The method of transmitting television pictures in natural colors comprising the steps of producing an optical image of the object to be transmitted, deriving from said image a train of picture signals representative of the brightness and color of successive elemental areas of said image by effectively scanning said image in accordance with an interlaced scanning pattern, said pattern comprising successive frames, each pair of frames having five fields of consecutively scanned parallel lines, and changing the color characteristic of said image for each scanning field in such a manner that a different color characteristic prevails for at least three fields of every periodically recurring group of five scanning periods and that the same color characteristic prevails for every field of successive ones of said recurring groups.

11. The method of transmitting television piotures in natural colors comprising the steps of producing an optical image of the object to be transmitted, deriving from said image a train of picture signals representative of the brightness and color of successive elemental areas of said image by effectively scanning said image in accordance with an interlaced scanning pattern, said pattern comprising successive frames, one frame having three fields of consecutively scanned parallel lines and the succeeding frame having two fields of consecutively scanned parallel lines, and changing the color characteristic of said image for each scanning field in such a manner that a different color characteristic prevails for each scanning field of every periodically recurring group of five scanning periods corresponding to one pair of consecutive frames and that the same color characteristic prevails for every field of successive ones of said recurring groups.

12. The method of reproducing television pictures in natural colors comprising the steps of developing a beam of electrons and scanning the target by said beam, controlling said beam in accordance with received picture signals representative of picture brightness and color components thereof, deflecting said beam across said target in accordance with an interlaced scanning pattern to produce a luminous image of substantially white light, said pattern comprising successive frames, each pair of frames having five fields of consecutively scanned parallel lines, and changing the color characteristic of said image for each scanning field in such a'manner that a different color characteristic prevails for at least three fields of every periodically recurring group of five scanning periods and that the same color characteristic prevails for every field of successive ones of said recurring groups.

13. The method of reproducing television pictures in natural colors comprising the steps of developing a beam of electrons and scanning the target by said beam, controlling said beam in ac cordance with received picture signals representative of picture brightness and color components thereof, deflecting said beam across said target in accordance with an interlaced scanning pattern to produce a luminous image of substantially white light, said pattern comprising successive frames, one frame having three fields of consecutively scanned parallel lines and the succeeding frame having two fields of consecutively scanned parallel lines, and changing the color of said image for each scanning field in such a manner that a different color prevails for each scanning field of every periodically recurring group of five scanning periods corresponding to one pair of consecutive frames and that the same color prevails for every field of successive ones of said recurring groups.

JOSEPH D. SCHANTZ.

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