US2423770A - Color television system - Google Patents

Description

' July 8, 1947.

A. N. GOLDSMITH COLOR TELIEVISION SYSTEM originalFiled Aug. 21, 1942' l ATTORNEY Patented July 8, 1947 ooLon TELEvsIoN SYSTEM Alfred N. Goldsmith, New York, N. Y., assignor to Radio Corporation of America,-a corporation of Delaware Original application 455,556. Divided August 21, 1942, Serial No. and this application April 7, 1945, Serial No. 587,061

This invention relates to color television systems, and methods, and more particularly, to a color television method and system in which the general effect of a key image is kprovided to augment and improve the color rendition and brilliancy of the finally reproduced television image or picture. This invention constitutes a division of my copending U. S. application for Letters Patent, Serial No. 455,556, filed August 21, 1942.

In a color television system, it is usual to employ three primary color component images superimposed either cyclically or simultaneously to reproduce a color image having the same colors as the object of which the image is a representation. Two-component pictures are also known, but suffer from relatively inferior iidelity of color reproduction and, thus, color television systems usually employ the three-color process.

While it is theoretically possible to achieve nearly perfect color reproduction under idealized conditions by the three primary color component method, there is, actually, considerable divergence from such ideal conditions in practice, due to the fact that the analyzing filters, the spectral sensitivity of the light sensitive medium, and the spectral response characteristics of the reproducing medium, do not have the required characteristics necessary to meet the theoretical requirements for reproduction. For example, it is well known in the theory of three color reproduction that three properly chosen pure spectral colors are suiiicient to reproduce substantially all of the colors lying within the trichromatic color triangle. However, light sensitive mediums have an irregular spectral response, and color reproducing mediums are far from pure spectral colors. The color ltersrequired for analyzing the colors of the object likewise do not have sharp cutoiis with a band of uniform transmission, but have sloping cutoffs and non-uniform transmissions through the passbands. This departure from ideal conditions, therefore, tends to degrade the quality of the color reproduction,

By my invention, in which I follow a predetermined period of transmission of the three primary color component images by an orthochromatic image transmission whereby I improve the color reproduction of television images or pictures b-y obtaining the eiect of increasing brilliancy of the highlights, and increasing density of the shadow areas.

Accordingly, it is an object of my invention to provide an improved method of transmitting color television images or pictures.

Another object of my invention is to provide Claims. (Cl. 178-5.2)

apparatus for improving the delity oi color television images.

Still a further object of my invention is that of improving the detail, resolution and delineation of color television pictures by adding to the realism and naturalness of the color reproduction and, as well, by increasing the contrast and gradation ranges in color reproduction.

Another object of my invention is to provide the effect of an addition of a key picture to color component pictures in additive or subtractive color television systems in which the color component pictures are either simultaneouslyk scanned or cyclically scanned. n

Again, it is an object of my invention to provide the effect of a key image of substantially neutral tint to be added to each group of color component images in a color television system.

A further object of my invention is the production of key images and the use of a color lter, which in conjunction with the chromatic photosensitivity of the mosaic produces anorthochromatic rendition of the picture, that is to say, a rendition in which brightness values correspond to the apparent brightness as viewed by the normal eye, of the various colors in the scanned image i'ield.

Another object of my invention is to provide a color television system in which key pictures are produced by the equalized transmission and reception of each of the tri-color component images.

Other objects of my invention will become apparent to those skilled in the art upon a reading of the following detailed description, taken in conjunction with the drawing.

The drawing constitutes a schematic representation of a color television system wherein the several component color images or pictures are simultaneously transmitted for simultaneous reproduction at receiving points and an equalized or key image or picture correspondingv to the orthochromatic image, and thus the intrinsic brilliance of the several colored images, is trans- 45-,mitted in a cyclic manner.

In the arrangement shown by the drawing, a color television system is disclosed wherein the channel Width to transmit the color image representation may be regarded ashaving beenincreased over that usually provided for sequential color operation. This is rbecause provisions are made for separate channels to transmit simultaneously the image representations corresponding tothe red, the green and the blue component color images, and, after a plurality of such images or picture fields representing such colors have been transmitted, a key image field corresponding to an orthochromatic image may be simultaneously transmitted over all of the several channels.

In the arrangement diagrammatically represented by the drawing, the light of the image (not shown) is adapted to be directed along the optical path |3| and through the optical system |33, and thence, by means of a, plurality of half-silvered mirrors |35 and |31, a portion of the light is permitted to pass directly along the initial optical path 3| or in a direction at right angles thereto. The half silvered mirror |35 thus permits the orthochromatic image rays |`3| to split into two paths, of which the light reflected from the mirror surface |35 is directed along a path |36 into an image scanning tube |39 through an appropriate iilter |4| which is adapted to direct upon the mosaic electrode |43 of the image scanning tube |39 a light image of red characteristics, for instance. The unreiiected rays which pass through the half-silvered mirror |35 are then directed along the path |45 to impinge upon the second half-silvered mirror |31, from which a portion of the rays is directed along a path |41 and another portion of the rays is passed directly through the half -silvered mirror surface |31 along a path |49. Y

It will be assumed, for instance, that the refiected rays traveling along the light path |41 impinge upon the 4mosaic electrode |5| of the scanning tube |53 after passing through a lter |55 which is adapted to direct rays corresponding to the green picture image upon the mosaic electrode of the scanning tube |53. Likewise, the light rays passing along the light path |49 are adapted to enter the image scanning tube |51 and to fall upon the mosaic electrode |59 .thereof after having passed through the light lter I6| which is adapted to segregate the blue imageY from the orthochromatic image directed along the light path |49. Thus, a light image is simultaneously impressed upon all of the image scanning tubes |39,'|53 and |51, but the light image upon tube |39 is that corresponding to the red image; the light image upon the tube 53 is that corresponding tothe greenimage, and the light image upon the` tube |51 is that corresponding to the blue image, assuming the selection of filters as hereinabove outline. Y

Since light losses occur in the half-silvered mirrors |35 and |31, the density of the filters |4| and |55 is such as to compensate for the loss and make the general intensity of the optical image impinging upon the mosaic electrodes |43 and |5 Y of tubes |39 and |53 respectively substantially of the same order as that of the image cast upon the mosaic |59 of the scanning tube |51. In this manner, equalization of the outputs is reasonably well maintained.

The tubes 31, 53 and |51 have been illustrated in a most schematic form, but it is to be understood that the tubes are generally of the type. known as the Iconoscope and described by Zworykin and others, or the scanning tube may be of the type known in the art as the image Y Iconoscope or the Orthicon, or it may be one of the type known as theY image dissectorgall'of which have been disclosed both directly and by footnote Vreference in the book Principles of Television' Engineering by D. G. Fink and published in 1940 by McGraw-Hill Book Co. For conven-Y ience, referencev herein will be made to a scanning tube of the Iconoscope, type as illustrative of the principles of operation. The optical image, in traveling to the mosaic electrode 43, for instance, of tube |39 passes through the filter element |4| which means that the red component influences the tube to produce a charge on the mosaic in known manner. In the tube |39 an electron gun (not shown) produces an electron beam which scans the mosaic |43 to provide, through the means of released electrons, the video signal, which signal is carried by the signal plate of the mosaic. Thus, when the mosaic electrodes |43, |5| and |59 of all of these tubes |39, |53 and |51 are scanned by the usual cathode ray scanning beam, output signals will result which appear in the output conductors |6I, |62 and |63 connected respectively to the collecting electrode of the mosaics. These output video signals are appropriately amplified in the ampliers |64, |65 and |66, from which output energy is supplied to the several commutators |61, |68 and |69 by way of the commutator brushes |18, |1| and |12 connected respectively to the conductors |13, |14 and |15. The signal outputs in these respective conductors are those representative of the simultaneously scanned red, green and blue images.

The various commutator elements |61, |68 and |69 are appropriately driven from a suitable prime mover (not shown), so that they revolve in synchronism and co-phaseally.

Since it was assumed, from what was hereinabove stated, that the transmission of the images would take place in such a manner that three image i'lelds representing diierent color images would be transmitted simultaneously and in a sequence of three to be followed by a single transmission of an orthochromatic image on all transmission channels, the commutators |61, |68 and 69 are provided with commutating segments |16 and |11 each respectively, which extend for substantially 270 of the periphery and 90 of the periphery with suitable insulating segments |16 and |18 separating each section of the commutator. The longer segment |16 of the commutator is connected to a second commutator ring |19 for each commutator, from which, by meansd of the brushes |86, I8! and |82, the respective red, green and blue image signals are derived to be fed to the separate transmitter amplifiers |84, |85 and |86 connected respectively thereto by way of the' conductors |81, |88 and |89. The rings |19 have insulating segments (as shown) to correspond in position to the insulating segments |18 and |18 of the outer rings |16, |11, it being appreciated that the brushes are aligned (as schematically indicated). The smaller section |11 of each of the commutators is connected to an inner slip ring member |99, |9| and |92 from which'energy is picked up by means of a series of brushes |93, |94 and |95 and then fed by way of the conductor |96 connected to all of the brushes |93, |94 and |95 to energize simultaneously all of the transmitter amplifiers |84, |85

and |86.

Vquarters of any unit time period corresponding,

Y for instance,` to the time to scan four image i'lelds.

During the remaining one-quarter of the assumed unit time period, the various transmitter ampliiiers are energized by the combined output of all of the image scanning tubes |39, |53 and |51 as derived from the ampliers |64; |65 and |66, so that the energy appearing on the conductor |96,

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for mstance., is that Corresponding to an orthochromatic image, and thus, over each channel corresponding to the various colors chosen, there will be transmitted signals both of individual color and of the combined color representing the three selected components. The output from the various transmitter ampli-fiers |84, |85 and |86 is then fed byway of conductors i9?, |98 and |59, for instance, to any suitable form of transmission channel, such as a radio link or a wire line transmission link, or to a suitable monitor instrumentality.

It has not been shown by the diagrammatic representa-tion of the drawing but is to be understood that scanning beams in all of the tubes |39, |53 and |57 for scanning the respective.

mosaic electrodes thereof are to operate simultaneously so as to strike the various mosaic elements in substantially identical spacial relationships. E'ach scanned raster is to be homologous and equidimensional. To this end, it is preferable to provide a single source of beam deecting energy to be applied to deflect the cathode ray beams, in order that synchronous and co-phaseal relationship shall be maintained between each. It is, of course, to be understood that to achieve this objective it is desirable that the geometry of the scanning tubes substantially coincides, and that the applied operating voltages to each tube likewise substantially correspond in order that the general operating parameters for all the scanning tubes shall be alike. This, however, forms no specific part of the present .invention except insofar as it co-operates with the remaining elements to produce the complete system. The arrangement for obtaining Vcontrolled movements of the scanning beams will be discussed more particularly ,in a companion application (Docket 20,907), Serial No. 548,238, nled August 5, 1944, for instance.

1t is to be appreciated, in the arrangement illustrated by the drawing, that what is herein termed an orthochromatic or key image is merely one of several forms which might be used and represents one acceptable form. Other forms of key images may be derived from signal output of separate pickup or camera tubes receiving `the light image from any of the optical paths |3| |31, |45 and |49 prior to the time when the light of the image has passed through any lter. The

key image signals thus derived may, as heretofore stated, correspond to the Visual luminosity response, or to ultra-violet, or infra-red versions of the image which is picked up, or to any other selected form of key image signal, In any of these cases, such key image signal will be used identically in the manner hereinbefore set forth, that is, such key image signals will be impressed upon the conductor |96 and thus caused to energize all of transmitter amplifiers `and channels during the period corresponding to the passage of such segments as |11 under the corresponding contact brush.

It is thus apparent, from what has been pointed out, that the system disclosed herein provides for simultaneously transmitting the red, the green and the blue component color images for simultaneous reproduction at receiving or monitoring points. Then, after a predetermined number of image fields has thus been transmitted, an equalized transmission, representing `the combined red, green and blue component pictures, which corresponds to the key image will be transmitted and reproduced at receiving .points for a time period of one image field, after which the sequence 4is repeated again and again. Thus, the system disclosed may be termed a combined simultaneous and cyclic method, since it is a simultaneous method for the separate color transf missions but cyclic between the color images and the key pictures.

For receiving the images transmitted by the system disclosed, various arrangements may be provided which would consist, for instance, of a single electron tube having a laminated luminescent target which would respond to reproduce the various picture colors, andffin which the laminations would be so located that independent electron guns within the receiving cathode ray tube might operate to direct scanning beams thereagainst, or, alternatively, the system may be of the type disclosed by my applications, Serial Numbers 548,238 and 548,239, each filed August 5, 1944, relating to color television. Further, as known in the art, the receiving instrumentality may comprise a plurality of separate cathode ray image reproducing tubes individually having target areas adapted to reproduce the red, the green and the blue images and arranged to direct the issuinglight simultaneously upon a single viewing target area at which the light image of all tubes is superimposed.

The receiver instrumentality is not herein specifically illustrated since it does not form a speciiic part of the invention. It will be understood however that the receiver instrumentality is generally such that it comprises a plurality of separate cathode ray image reproducing tubes each being adapted to reproduce ,a pure black and white image and having a filter disc coordinated with each to portray at proper times the separate component color images.

Synchronization between the scannings of the receiver and the transmitter for the system described is, of cour-se, to be maintained in known ways.

Further, in connection with the arrangement herein described, it is apparent that if the choice of time duration for transmitting the color images, such as those representing the red, the green and the blue images, is made equal to a time period required to scan and transmit one image held only, then appropriate time delay means, similar to that disclosed in connection with my parent application, Serial No. 455,556, supra, and particularly the .delay circuit 69 .disclosed thereby may be combined with the transmitter ampliers ld, 485 and |85 to provide the ke-y image transmission, but otherwise the transmission should be of the general form hereinabove outlined.

It will be appreciated that while mechanical commutation has been illustrated herein as representative of the principles of the invention and for the purpose of indicating the switching operations, an all-electronic switching method may readily be utilized. Such circuits are well known in the art as illustrated, for instance, by patents heretofore granted to C. C. Shumard, No. 2,146,862, and C. S. Roys and H. F. Mayer, No. 2,089,430, as well as the application of Whitaker, Serial No. 436,983, led March 31, 1942 for an invention entitled Electrical circuits.

,It is to be understood that any representa- Having now described the invention, what is claimed is:

l.Y The method of color television transmission which comprises the steps of producing independent series of signals representative f each of a predetermined plurality of primary colors of the object whose image is to be reproduced, producing a further independent series of signals to represent the combined intrinsic brightness of the several colors of the object, simultaneously transmitting the independent series of signals representing the primary colors as color signal indicia, also transmitting the combined intrinsic brilliance signals, and alternating the signal transmission of the primary color indicia signals and the combined intrinsic brilliance signals according to a selected time cycle.

2. The method of color television transmission which comprises the steps of producing independent series of signals representative of predetermined component colors of the object Whose image is to be reproduced, producing a series of signals representative only of the intrinsic brightness of the colors of the object, and sequentially and simultaneously transmitting the produced series of signals representative of the individual component colors and then alternating in succession with the transmission of the individual component color signals the produced intrinsic brightness signals.

3. The method of color television transmission which comprises the steps of producing independent series of signals representative of predetermined primary colors of the object whose image is to be reproduced, producing a series of signals representative of a key picture of the object whose image is to be reproduced, simultaneously transmitting all of the produced color series of signals, then interrupting the color signal transmissions and transmitting the key image signals during the color signal series interruption period only, and alternating the transmissions of each of the color signal series with the key image signal series.

4. The method of color television transmission which comprises the steps of producing independent series of signals representative of predetermined component colors of the object whose image is to be reproduced, producing a series of signals representative only of the visual brightness of the colors of the object, transmitting all of the produced series of component color signals simultaneously and then interrupting said transmission for transmitting the visual brightness signals and repeating the sequence of each transmission at a selected rate of alternations between signal transmissions. Y

5. The method of color television transmission which comprises the steps of producing independent series of signals representative of predetermined primary colors of the object whose image is to be reproduced, producing a series of signals representative only of a function of the intrinsic brightness of the combined component colors of the object, transmitting all of the produced series of signals in an alternating manner such that contemporaneous transmissions of component color signal series occurs with alternate transmissions of intrinsic brightness sig- Y nals.

6. In a color television system a plurality of scanning devices, and means interposed relative to the several scanning devices so that each device scans an image of an object in one only of a plurality of selected primary colors,` meansV for supplying all of the signals to independent transmission channels simultaneously, and distributor means operating to supply to all of the transmission channels, after a predetermined time period, the signals of each of the independent scanning systems in combined relationship.

7. In a color television system, a plurality of scanning devices, means rfor energizing each of the several scanning devices by the light of only one primary color image of an object, means for scanning the images impressed upon the independent scanning devices to produce a series of signals representative of the images thereon, means for supplying all of the signals to independent transmission channels simultaneously, and distributor means operating to energize all of the transmission channels, after a predetermined time period, by the signals of all of the independent lscanning systems in combined relationship.

8. In a multi-color television system, a plurality ofV scanning camera tubes, means for directing upon the plurality of camera tubes independently of one another light images of different selected component color images of an object collectively representing the object in substantially its natural color, means for scanning the image directed upon each independent camera tubes to develop video signals independently representing the said selected component color images of an object, means Vfor simultaneously energizing separate load circuits by the output video signals from one only of the camera tubes for a iirst predetermined time period, means for collectively energizing each of the load circuits by the video signal output of all of the camera tubes for a second predetermined time period, and distributor means for sequentially switching the energization of the independent load circuits between the individual component color video signal output and the combined video signal outputs which collectively represent substantially monochromatic transmission.

9. In a color television system, a plurality of scanning camera tubes, means for energizing the plurality of camera tubes independently of one vanother by light images representing selected and different component color images of an object, means for scanning the image directed upon each independent camera tube to develop video signals independently representing each selected component color image of an object, means for simultaneously energizing separate load circuits by the output video signals from one only of the camera tubes for one predetermined time period, means for collectively energizing each of the load circuits by the video signal output of all of the camera tubes for a time period which is a fractional part only of the period of energization of the load circuits by the individual video signal output, and distributor means for sequentially switching the energization of the independent load circuits between the individual component color video signal output and the combined video signal outputs.

10. In a multi-color television system, a plurality of scanning camera tubes, means for energizing the plurality of camera tubes independently of one another by light images 0f a different selected component color image of an object, means for synchronously and cophaseally scanningthe image directed upon each independent camera tube to develop video signals independently representing the selected component color brilliance at like pointsV of the said image, means 9 for simultaneously energizing separate load circuits by the output video signals from the camera. tubes for one predetermined time period to provide simultaneous multicolor image signal transmissions, means for collectively energizing each of the said load circuits by the output of all of the camera tubes for a time period which is a fractional part only of the period of energization of the load circuits by the individual video signal output to provide effectively monochromatic signals in each load circuit, and distributor means for sequentially switching the energization of the independent load circuits between the individual REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Valensi May 15, 1945 Number

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