US2335180A - Television system - Google Patents

Description

,NV- 23, 1943 l A. N. GoLDsMn-H 2,335,180

TELEVISION SYSTEM Filed Jan. 28, 1942 ATTORNEY Patented Nov. 23, 1943 i UNITED STATES PATENT oFFicE- :335,180 rELEvTsxoN srs'rau aurea N. Genomen. New vork. N. r. Application January ss, i942, sensi No. 42am This invention relates to image transmission systems and, in particular, to method and apparatus for` transmitting color television pictures by the additive process. 1

'I'he reproduction of colored objects by television is based on the experimental fact that substantially all colors can be visually simulated in reproduction by the addition inproper proportions or brlghtnesses of three primary" colors.A

'I'hese colors ordinarily are a somewhatorangered, a nearly pure green, and a violet blue. For brevity they will be referred to hereinafter as red, green, and blue.

In any color reproduction system it is necessary ilrst to make a tri-color analysis of the depicted object. This ordinarily is accomplished by passing light from the object through red, green and blue filters, respectively. The light transmitted through the lters is thereafter utilized to form appropriate color component images by a suitable optical system on a photographic or photosensitive group of surfaces. Each of the tri-color analytical records thus obtained is then used to control a corresponding color positive and light from the three positives is then combined to form the reproduced color view of the original subject. It will be appreciated that accurate registration and correct relative brightnesses of light from the three positives are necessary in order that the reproduction be faithful. This is the so-called additive process and is utilized here merely by way of illustration of my invention because my invention applies as well to four-color additive reproductions, according to the Vfourcolor reproduction theories of Zander, Hering,

and Ladd-Franklin.

While additive television processes are known in which the red, green and blue analytical pictures of a given scene are made in rapid succession, my invention makes the tri-color analytical pictures simultaneously and assembles them also, as it were, simultaneously. This simultaneity has the advantages that the photosensitive surface generating electrical signals representative of each of the tri-color images is active continuously. Each of the photosensitive surfaces may be given an appropriate spectral sensitivity to the color of the image falling thereon, and, most important, relative displacements between the images resulting from the motion of the subject are completely avoided. The avoidance of relative displacements between the images which occur in a sequential type of system results in objectionable action fringes" or color margins which 15 Claims. ('CL 17d-5.2i

are seen around the edges of moving colored objects.

` In the reproduction of colored pictures by my additive method, the red. green and blue component pictures being viewed simultaneously results in a further advantage of providing greater luminous emciency because each of the component image screens is viewed substantially continuously instead of one-third of the time as in the case of a sequential system reproduction.

Brieily, my invention provides a method and apparatus by which light from the colored object is simultaneously passed through three appropriate filters and each image falls on its own separate photoelectric surface. Scanning of each of the images is provided in the conventional fashion. The output of each of the camera tubes embodying the photosensitive surface is suitably amplied. A low-pass filter follows each of the amplifiers to limit the band of frequencies to a predetermined maximum value, say, for example, 4 megacycles. For purposes of modulating the transmitter, the output of one of the filter channels is passed on to the modulator. The output of the lter of the second channel is shifted in frequency so that its lowest frequency is adjacent to the highest frequency of the ilrst channel, as determined by the cutoil characteristic of the filter in the first channel. The output of the third channel is also shifted in frequency, but to a greater extent than that Vof the second channel so that the lowest frequency of the third channel is adjacent to the highest shifted frequency of the second channel. The shifted frequencies of the second and third channels are then fed to the modulator, the output of which serves to actuate the transmitter for transmitting the channels.

At the modulator, the total band width of the signal frequencies will be equal to the sum of the band widths of the three individual channels. Thus, for example, if each of the filters is given a cutoff frequency of 4 megacycles then the band width of-slsnals used to actuate the modulator will be 4+4+4=12 megacycles. At the receiver it is only necessary to provide a receiver which will faithfully reproduce a band width of signals equal l to the total band Width used in the modulator.

'I'he output of the receiver is then fed to appropriate filters which segregate each band of frequencies representative of one of the primary color images and, in the example shown above, the ilrst filter may be a low-pass filter having a band pass from 0 to 4 megacycles, while the second channel may include a band pass lter pass ing from 4 to 8 megacycles, while the third channel may include either a high-pass or band pass filter which passes the 8 to IZ-megacycle signals. The output of the filters in the second andthird channels is thereafter shifted downward in frequency so that, following the shift in frequency, both channels have an output whose frequency band runs from to 4 megacycles.

When the received signals have thus been split into three channels and each occupy a band width of from 0 to 4 megacycles, then each of these signals may be fed each to its individual reproducer, and by suitable colored phosphors oi' the reproducing kinescope or by the use of white phosphors with appropriate filters, or by the combination of different phosphors and filters, the three images are given proper brightness: and spectral quality. 'I'he three images are optically reassembled so that the viewer sees all three images simultaneously superimposed on each other. It will be appreciated that in talking of the wave filters in the three channels of the receivers that the frequencies mentioned were merely by way of example and were appropriate where the detected signal was utilized from the receiver. On the other hand, if it is desirable to utilize the signal before final detection, it will be appreciated that it is only necessary to provide the 12 megacycles required by the first described method of transmission in which each color channel had the same band width of 4 megacycles. It may be practicable still further to reduce the band width assigned to the blue channel in the 10 example here given. It is to be noted that no vnoticeable deterioration of the image results from this gain in reducing the width of the frequency spectrum.

Other advantages immediately ow from my method of unequal band widths of transmission in view of the fact that since two of the channels do not require such a wide band of frequencies the video amplifiers can be simplied, as it is well known that increasing the band of frequencies whichl a video amplifier must handle re'- band pass iilters, each having a band width of 4 megacycles and in which the adjacent frequenso cies of any two filters are substantially contiguous. synchronizing and control of the background brightness may be accomplished by any of the known conventional methods.

It Willof course be recognized that' such a color television system requires for a reproduced picture of high definition a much wider band of frequencies than is currently used for high definition monotone pictures. However, my invention provides the further benefit of actually reducing the total band width required for a given definition, because I have found that it is not necessary to transmit the same band width of frequencies for each of the primary colors in order to obtain high definition of pictures. I have found that the delineatory capabilities of a primary color are determined by the contrast be tween the color of the light projected on the screen and the color of the screen. In my additive process of reproducing color images, the screen is normally black. Consequently, the delineatory capabilities of the primary blue color on such a screen are less than those of the red image, which, in turn, are less than those of the green image. Since the delineatory capabilities determine the definition of an image, it will be appreciated that it is important that all of' the frequencies of the green image must be faithfully ytranslated into light. 0n the other hand, the

electrical currents representative of the red image will'not reduce the definition of the picture noticeably if the higher frequencies are suppressed, and this is also true to an even greater extent of the signal currents representative of the 'blue image, Simple tests have indicated that at least a`40% reduction in band width of the blue and the red image band of frequencies may be provided without any noticeable change in definition. It will be readily seen therefore that the filters in the channels of the red and the blue images no longer require the same band width as that of the green image channel, and, consequently, in the example given above the band widths for the green channel may remain at '4 megacycles while the blue and red channel band widths need.

quires a more complex and costly circuit. My system, therefore, simplifies the transmitter and the receiver, and at the same time reduces the cost in maintenance of the same. With the in- 5 creasing needs of communication the frequency spectrum becomes more and more valuable and, consequently, the reduction in band width required is a very important advantage.

Accordingly, it is my main object to provide a new, improved method and apparatus for electronically reproducing color images.

Another object of my invention is to provide a simultaneous electronic color television transmission and reception system.

Another object of my invention is to provide a color television system in which action fringes due to object motion cannot occur.

Another object of my invention is to provide a color transmission system which affords improved efliciency of conversion of light images into electrical signals by substantially continuous use of the photoelectric surface of the camera tubes.

Still another object of my invention is to increase the reproducing efficiency by utilizing each of the reproducing screens or images substantially continuously.

Another object of my invention is to provide an improved television reproducing system wherein each component color of screen material has selective color radiation, of maximum eflciency for its corresponding color image and further using minimal color filtering consistent with the fproduction of the component image.

Other objects of my invention will become apparent upon reading the following detailed description of my invention taken together with the drawing in which there is shown a schematic arrangement in block diagram form of apparatus embodying the principles of my invention, l

In the figure, the object I, of which a color representation is to be transmitted and reproduced, is focused by an optical system 3 upon the mosaics 20, 22, and 2| of the pickup tubesv I9, 2|, and 23. 'Ihe partially silvered mirrors I4 and I5, positioned in the path of the image projected on the mosaic 24, serve to reflect images on the mosaics 20 and 22, respectively. 'I'he mosaics 20, 22 and 2l are so positioned that each has a total length of light path which is equal to each other so as to insure identical-size images of the object I. Interposed in the light path are filters I6, I1, I8 which in combination with the selected color sensitivities of their respectively associated pickup tubes give a suitable range in blue component channel.

intensity of chromatic response. It will be noted that all three images on the mosaics 20, 22, and

. 24, assumed to be, by way of example, the green,

blue and red component photosensitive surfaces respectively, are present at all time and so avoid any possibility of action fringes."

' tubes may be substituted for that shown in the figure without affecting the principles of the method of operation. It will further be appreciated that the insertion of the filters I6, I1, and I3 may require readjustment of the tubes positioned in order to insure that the optical paths are identical in length. Moreover, the filters, in certain cases, for example in the case of tube 2|, may not be necessary if the mosaic surface 22 is so sensitized as to be only sensitive to blue light, as, for example, would occur in a potassium hydride surface. Thus, it will be appreciated that the important feature to `be obtained is that the combination of the spectral response of the mosaic taken together with its associated filter must provide the spectral distribution required for the particular component of color to be transmitted by the tube.

The outputs of the tubes I9, 2|, and 23 are amplified respectively by the amplifiers 28, 34,43. The succeeding mixing amplifiers 29, 35, 44 receive the outputs from amplifiers 28, 34, 43, respectively, Vas well` as the synchronizing-signals inputs from the synchronizing generators 30, 36, and 45. `It will be recognized that the synchronizing generators may be a single unit supplying the mixing ampliers 29, 35, and 44. Likewise, background brightness control signals are fed to the mixing amplifiers 29, 35, 44 from the background control 3|, 31, 46, respectively. vThe mixed signals are then passed through low- pass filters 32, 38, 41 and in the first case, for example, each of `the filters may be provided with a cutoff frequency vof such a'value as to pass frequencies up to 4 megacycles substantially'unb formly and without appreciable phase distortion. Where, however, it is desired to decrease the totalband width of frequencies to be transmitted the filters 33 and 41 would be given such a cutoff frequency as to pass only frequencies up to 2.5 megacycles, while filter 32 would pass frequencies up to 4 megacycles, it being assumed that filter 32 is in the green component channel, filter 38 in the red component channel, and filter 41 in the It is understood that these are values merely by way of example and in a particular .system it may be desirable to actually decreasethe width of the blue channel to a figure less than 2.5 megacycles and conceivably the band width ofthe red channel filter may be increased without affecting the principles of operation of my invention. Y

The output of the filter 32 corresponding to the green component image passes through into the modulator mixer 52. The output of filter 39 is mixed with energy from an 8-megacycle oscillator 4| and the output of the mixer stage detected and filtered to provide a 4 to 8 megacycle signal, which is then passed into the mixer 52, assuming that the output of the filter 38 is for the first described condition ofoperation in which al1 channels have the same band width. It may be desirable to insert a low-pass filter cutting oi at 8 megacycles (not shown) into conductor 42. The output of the filter 41 is heterodyned against 12 megacycle energy from the oscillator 50, detected and filtered so as to provide an output having frequencies lying within the band 8 to 12 megacycles. This energy is fed to the modulator receiver 52. If required, a lowpass filter cutting off at 12 megacycles (not shown) may be inserted into conductor 5|. Thus, it will be observed that the modulator is fed with energy having frequency components lying between 0 and 12 megaeycles and split into three equally sized bands of frequencies.

It the second kind of operation is provided then the oscillators 4| and 59 have different values of heterodyning frequencies. For the channels assumed above the frequency of the oscillator 4| would be 6.5 megacycles so as to provide output energy lying between 4 and 6.5 megacycles, while the frequency of oscillator 50 would be 9 megacycles so as to provide output energy lying within the frequency band of 6.5 to 9 megacycles. The cutoff low-pass filters which might be inserted into conductors 42 and 5| would then have cutos at 6.5 and 9 megacycles respectively. The total band width of frequencies fed to the modulator mixer 52 would therefore be 9 megacycles. The output of the mixer is then fed to a suitable modulator 53, which modulator serves to modulate the transmitter |54 and energy from which is thereafter radiated by the antenna |55. It will be understood that while an antenna is shown for transmitting the energy that the output of the transmitter may be a suitable coaxial cable or wave guide.

The energy radiated from vthe antenna |55 is then pickedup by the' receiving antenna 6| and fed to a suitable receiver 6|. The demodulated receiver output from the receiver 6| is then fed to the three filters 65, 66, 61, which filters have, for the rst condition of operation, pass bands of 0 to 4 megacycles, 4 to 8 megacycles, and 8 to 12 megacycles, respectively. For the second condition of operation the output of the filters Vwould'be 0 to 4 megacycles, 4 to 6.5 megacycles, and 6.5 to` 9 megacycles, respectively. 'I'he output of the filter is passed directly to the green image reproducer 15. The output of filter 66, for the first condition of operation, is beat against an 8 megacycle oscillator in the mixer 69 so as to provide an output whose frequency components lie between 0 and 4 megacycles, while the output of lter 61 is beat against a twelve-megacycle oscillator 12 in the mixer 1| so as to provide an output having two frequency components lying between 0 and 4 megacycles, The output from the mixers 69 and 1| is thereafter fed to revproducers 16 and 11, respectively. Appropriate lowJ-pass filters (not shown) may, as before, be inserted into conductors 13 and 14, respectively.

For the second condition of operation the frequencies of the oscillators 10 and 12 would be 6.5

' and 9 megacycles, respectively, so as to provide output from both of the mixers 69 and 1|, having frequency components lying between 0 and 2.5 megacycles. appropriate type may be used in conductors 13 and 14. The kinescopes 15, 11, and 16 have screens selectively producing light in the green, blue, and red portions of the spectrum. Minimal color filters 18, 80, and 19 are providedso as to insure that the spectral quality of output of each of the tubes is suitable for recombining the three color images into a single image in which the component colors faithfully reproduce the colors of the original object I. Half-silvered Here again low-pass filtering of mirrors 8| and 82 are provided and arranged with respect to the reproducer tubes 16, 11, and 15 so as to bring the three images from the reproducer tubes into exact registration with respect to the eye of the observer at 88. It will be apparent that a suitable optical system may be used for projecting the three images upon a screen for observation. Moreover, the half-silvered mirrors I4 and i5, 8| and 82 may be other types of partially transmitting and partially reflecting optical elements. For example, the element I may be a plane parallel piece of glass coated with a salt having a suitable index of refraction compared to that of the plane parallel piece of glass so that it substantially reflects blue light and transmits the red light. Such partial reflecting and partial transmitting elements are well-known and are used in monitoring equipment for producing sound records on film. 'Ihe important feature to be remembered in this connection is that the combination of the mirror elements and the lters and the spectral response of the mosaics and of the luminescent screens must provide a suitable overall spectral response for the additive process of color transmission. It will be noted that in so far as the receiver is concerned, that conventional method of synchronizing and brightness control are utilizedl and that-the only departure from conventional receiver circuits is the provision of the filters, mixers, and oscillators. Accordingly, there is provided by my invention a simple all-electronic color television reproducing system having improved .quality, absence of action fringes, and high over-all-efliciency. I

Various alterations and modifications of the present invention may become apparent to those skilled in the art and it is desirable that any and quency spectrum, and means for simultaneously transmitting the altered signals together with the unaltered signals.

3. A color television system comprising means for forming three primary color images of the picture to be reproduced, means for scanning the separate primary color images to produce groups of electrical image signals each normally representative of one of the produced primary color images, means for altering the frequency range of two of the groups of generated signals, means for shifting the range of frequency of at least one group of signals relative to the others so that the several groups occupy substantially contiguous ranges in the frequency spectrum, means for transmitting the altered signals together with the unaltered-signals, means for receiving the transmitted signals, means for segregating the all such modifications and alterations be conf sidered within the purview of the present invention except as limited by the hereinafter appended claims.

What I claim is:

1. A color television system comprising means for forming a plurality of primary color images of the pictureto be reproduced, means for generating separate groups of. normally substantially like banc` Width electrical signals representative of each of the selected primary color images, means for altering the frequency range and band width of at least one of the Agroups of generated signals, means for transmitting the altered signals together with the unaltered signals, means for receiving the transmitted signals, means for segregating the altered signals from the unaltered signals, means for altering the frequency range of the originally altered signals to place them in their original frequency band, means for producing a plurality of primary color light images y in accordance with the received unaltered signals and the altered signals, and means for superimposing the produced light images upon each other.

2. A color television system comprising means altered signals from the unaltered signals, means for altering the frequency range of the originally altered signals to place them in their original frequency band, means for producing three primary color light images in accordance with the received unaltered signals and the altered signals, andmeans 'for superimposing the produced light images upon each other.

4. A color television system comprising means for forming a plurality of primary color images of the picture to be reproduced, means for scanning the separate primary color images to produce Vgroups of electrical image signals each normally occupying a. substantially uniform frequency range and each representative of one of the produced primary color images, means for reducing the frequency` range of at least one of the groups of generated signals, means for shifting the range of frequency of at least one group of signals relative to the others so that the sev eral groups occupy substantially contiguous ranges in the frequency spectrum, means for simultaneously transmitting the reduced frequency range signals together with the unaltered signals, means for receiving the transmitted signals, means for segregating the reduced signals from the unaltered signals, means for shifting the received reduced signals in the frequency spectrum to place them'in their original frequency band, means for producing a plurality of primary color light images in accordance with the received reduced signals and the altered signals, and means for superimposing the produced light images upon each other.

5. A color television receiving system comprising means for receiving groups of signals representative of primary color images, said groups occupying contiguous portion of the frequency spectrum, means for segregating the groups of signals, means for shifting the frequency range of the groups of signals of higher frequency to place all groups in the same frequency band, means for producing a plurality of primary color light images in accordance with the received groups of signals, and means for superimposing the produced light images upon each other.

6. A color television system comprising means for'forming a plurality of primary color images of the picture to be reproduced, means for scanning the separate images for generating groups of electrical signals which each include a substantially uniform range of frequencies representative of each of the produced primary color images. means for reducing the frequency range of at least one of the groups of generated signals,

. means for shifting the reduced frequency band of signals to a spectral location adjacent the group of signals produced by a second primary color scanning, means for transmitting the reduced and shifted signals together with the unaltered signals, means for receiving the transmitted signals, means for segregating the reduced and shifted signals from the unaltered signals, means for shifting the frequency range of the originally reduced and shifted signals to place them in the same frequency spectrum as the unaltered signals, means for producing a plurality of primary color light images in accordance with the shifted signals and the altered signals, and means for superimposing the produced light images upon each other.

'7. The method of reproduction of color pictures which comprises the steps of forming a plurality of primary color images of the picture to be reproduced, scanning the separate color images for generating groups of electrical signals, each group representative of one of the produced color images, suppressing a portion of the frequency range of at least one of the groups of generated signals, means for shifting the range of frequency of at least one group of signals relative to the others so that the several groups occupy substantially contiguous ranges in the frequency spectrum, transmitting the altered signals together with the unaltered signals, receiving the transmitted signals, segregating the altered signals from the unaltered signals, altering the frequency range of the originally altered signals to place them in their original frequency band respectively, producing a plurality of primary color light images in accordance with the received unaltered signals and the altered signals, and superimposing the produced light images upon each other.

8. The method of reproduction of color pictures which comprises the steps of forming a plurality of primary color images of the picture t be reproduced, scanning the independent and'separate primary color images for generating groups of electrical signals, each group representative of one of the produced color images, altering the frequency range of at least one of the groups of generated signals by suppressing a portion of the developed frequencies, and simultaneously transmitting the altered groups of generated signals together with the unaltered group of signals.

9. The method of reproduction of color pictures which comprises the steps of forming three primary images of the picture to be reproduced, scanning the independent and separate primary color images for generating a group of electrical signals representative of each of the produced color images, altering the frequency spectrum of two of the groups of generated signals by suppressing a portion of the frequency band normally developed, shifting the frequency range of the altered signals so that all of the signals occupy adjacent frequency bands, and simultaneously transmitting the altered and frequency shifted signals together with the unaltered -signals, receiving the transmitted signals, segregating the altered signals from the unaltered signals, altering the frequency spectrum of the orig- 'inally altered signals to place them in their original frequency spectrum, producing primary color light images in accordance with each of the groups of signals, and superimposing the produced light images upon each other.

10. The method of reproduction of color pictures which comprises the steps of forming a plurality of primary color images of the picture to be reproduced, scanning the independent and separate primary color images for generating groups of electrical signals, each group representative of oneof the produced color images, reducing the frequency range of at least one of the groups of generated signals, simultaneously transmitting the reduced signals together with the unaltered signals, receiving the transmitted signals, segregating the reduced signals from the unaltered signals, shifting the received reduced signals in the frequency spectrum to place them in their original frequency band, producing a plurality of primary color light images in accordance with the received reduced signals and the altered signals, and superimposing the produced light images upon each other.

11. The method of reproduction of color pictures which comprises the steps of receiving groups of signals representative 0f primary color images, said groups occupying contiguous portion of the frequency spectrum, segregating the groups of signals, shifting the frequency range of' the groups of signals of higher frequency to place all groups in the same frequency band, producing a plurality of primary color light images in accordance with the received groups of signals, and superimposing the produced light images upon each other.

12. The method of reproduction of color pictures which comprises the steps of forming a plurality of primary color images of the picture to be reproduced, scanning the independent and separate primary color images for generating groups of `electrical signals, each group representative of one of the produced color images, reducing and shifting the frequency range of at least one of the groups of generated signals, transmi-tting the reduced and shifted signals together with the unaltered signals, receiving the transmitted signals, segregating the reduced and shifted signals from the unaltered signals, shifting the frequency range of the originally reduced and shifted signals to place them in the same frequency spectrum as the unaltered signals, producing a plurality of primary color light images in accordance with the shifted signals and the altered signals, and superimposing the produced light images upon each other.

13. A color television system comprising means for forming a plurality of primary color images of an image tobe reproduced, means for scanning the separate primary color images to pro- 'duce trains of electrical signals each occupying predetermined frequency bands relative to each other and each representative of one of the produced primary color images, heterodyning means for altering the spectralfrequency range of at least one of the groups of produced signals and for placing the signals representative of said primary colors in substantially contiguous bands in the frequency spectrum, and means for simultaneously ,transmitting all of the groups of produced signals.

14. The method of transmitting color television image signals which comprises the steps of ltering the incident light forming an image to provide a plurality of primary color image representations of the image to be reproduced by forming each primary color image with minimal absorption of the image-forming light, scanning the independently and separately produced primary color images so as to generate by each scanning separate groups of electrical signals' of groups of signals occupy substantially contiguous ranges in the frequency spectrum, and then simultaneously transmitting all of the developed groups oi' signals.

15. A color television receiving system comprising means for receiving groups of signals representative of selected primary color images, said groups of signals occupying substantially contiguous portions of the frequency spectrum. means for segregating the several groups of received signals, means for shitting the frequency range of predetermined segregated groups of signals to place all ofthe groups in substantially the same assunse g frequency band, a plurality or image forming screens of a number corresponding to the number of sianal groups for selectively producing light oi' approximately the selected primary colors, a illter means associated with each o1' the image forming screens, each o! said illter means having minimal absorption o't the light emanating from the image forming screen with which it is associated so that the passed light substantially corresponds to the desired primary color, and means for superimposing the several produced primary color light images one upon the other.

ALFRED N. GOLDSMITH.

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