US2438269A - Color television system - Google Patents

Description

March 23, 1948. BUCKBEE 2,438,269

COLOR TELEVISION SYSTEM Filed Feb. 20, 1942 2 Sheets-Sheet 2 24 27 FIG.3

BLANKING SIGNAL INVENTOR I BKBEE ATTORNEY I Patented Mar. 23 1948 pnrrrzo stares rarest OFFICE (101.01% TELEVISION SYSTEM John A. Buckbee, Fort Wayne, Ind., assignor, by mesne assignments, to Farnsworth Research- Corporation, a corporation'of Indiana Application February 20, 1942, Serial No. 431,645

8 Claims. 1

This invention relates generally to a system for transmitting color pictures and more particularly to a method and apparatus for accomplishing mixing of color images.

In general, color pictures are reproduced electrically by forming an optical image and scanning the image to obtain electron images corresponding to each of the primary colors therein or at least enough of the primary colors to reproduce a reasonably faithful image at the receiving end of the system. It is difficult, however, to obtain faithful reproduction of the primary colors particularly with regard to their relative brightness and shading. In the case of reproduction of color lrn, it is the usual practice to employ an arc projection lamp for forming the optical image and these lamps emit more light in the infra-red portion of the spectrum than for the other parts of the visible spectrum. It is also true that studio illumination contains disproportionate quantities of light of certain wave lengths. Also, it frequently happens that the photosensitive screen of dissector pickup tube or the light sensitive screens of other types oi picture signalling generating tubes are more sensitive to certain colors than to others, notably, to the infra-red portion of the spectrum. Further difficulty arises from the fact that the response of the human eye is greater for some colors than for others and further complication arises from the effects of artificial light in the vicinity of the picture receiver. These difficulties which arisein the reproduction of color images, render it necessary to control the electrical signals representative of each individual color image by adjusting the level of transmission to obtain the most pleasing or most faithful combination of the primary color images in the picture to be transmitted. Furthermore, after providing apparatus for obtaining this result, it. is also possible to even improve the reproduced color picture over the original by shading the respective primary colors to obtain an eventual picture which is more pleasing from the artistic point of vlew.

Color mixing is accomplished by generating a keying impulse 'for each primary color scanning field of the picture and impressing the keying impulse on an amplifier, the gain of which depends upon the nature of the keying impulse. Thus,- as signal currents representative of each color form are amplified, this keying impulse controls the eventual intensity of a particular color at the receiving end of the system. These impulses create a further problem by generating a transient impulse in the transmittedim-age signal train during the time interval in which the blanking sig= nal normally occurs and, therefore, in certain types of color-mixing systems, it is necessary to eliminate the transient impulse and reintroduce the blanking signal in the signaltrain. The use of color-mixing has also been made diihcult because of the necessity of maintaining the direct current or 'black'level of each primary color at the same values. This diificulty, of course, arises from the fact that the amplitude gain for each primary color image may-be adjustedto havedif ferent values thereby changing the direct current level of each primary color image.

It is an object of the present invention, therefore, to provide, in' a color television system, a novel method and apparatus for controlling transmission and reproduction of image signals representative of each of theprimary colors in'an optical image. g

Another object or the invention is to provide a novel means in a color television system for controlling the transmission level of image signals representative of'each primary color in an optical image.

Still another object or" this invention is simplificatioh of the electrical circuits necessary for transmission of pictures or optical images in their natural colors.

-A still further object or this invention is to provide in a color television system, a means for color-mixing wherein the gain for each color image may be controlled without disturbing the direct current level of each color image.

A still further object of this invention is to provide a color-mixing system wherein the gain for each color imag may be controlled without introducing blanking signals in the video ampliof a transmission pickup tube such as a dissecto'r.

Each color image is converted into what corresponds to a black and white electron image, the intensity of which corresponds to the shading of that particular primary color in the optical imthe field-scanning frequency divided by the number of primary colors which it is desired to reproduce in the receiving system; The keying pulses for each color are successively impressed on one of a number of keying amplifier channels equal to the number of primary colors to be reproduced in the received picture. Each channel of the keying amplifier may be connected to a separate stage of the electron multiplier in the dissectortube for controlling the potential across that stage and, therefore, the gain therein. Thus, as each primary color image passes through the multipler in the form of a stream of electrons, the keying, impulse generated during that particular field-scanning period of the picture, controls. the gain of the multiplier and the intensity of that particular color in the transmitted and received color image.

It is to be noted that blankingimpulses may also be impressed on one stage of the multiplier in the dissector tube'to stop the electron emission during the return period of scanning and thus, therecan be no transient pulse in the output'of, the multiplier during the blanking period. Also the black or direct current level of each color image must be the same since during the transmission of the black portion of each color image, there is no flow of electrons through the multiplier.

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

In the accompanying drawing,

Fig. 1 is a block diagram of a color system,

Fig. 2 is a circuit diagram of a generator illustrated in Fig. 1,

Fig. 3 is a cross-section view of a dissector transmission tube including an electron multiplier, V r

Fig.4 is a circuit diagram illustrating a keying amplifier and its connection to the electron multiplier, shown in Fig. 3,

Fig. 5,is a diagram illustrating the time relatelevision keying pulse .tion between the low frequency synchronizing impulses and the keying impulses which are applied to the multiplier.

Referring now more particularly to Fig. 1 of the drawing, the system illustrated therein comprises a dissector transmitting tube I, and a light projecting device 2, comprising an arc projection lamp together with whatever other apparatus may be necessary for producing an optical image. There is provided a timer chain'3 connected for driving color disc 4 through a synsources comprise the multiplier divider I for eii-' ergizing the multiplier in tube I, a dissector cathode and multiplier supply l2 and a dissector f0- cus supply I 3. Tube 1, which includes an electron multiplier, as mentioned hereinbefore, is' connected to intermediate amplifier l4 and video amplifier for amplifying the tube output and chronous motor '5 and also connected with the scanning frequency generator 6. In accordance with this invention, there is provideda keying "pulse generator I, a color-mixer and dissector blanking signah amplifier 9.. The potential feeding signals to a transmitter of conventional form which is not shown. 7

The important portion of the system so far as this invention is concerned includes the keying pulse generator 1 and color-mixer 9 for controlling the gain in the multiplier of tube I, as shown in detail in Figs. 2, 3 and 4. Fig. '3 is a detailed'illustration of a dissector transmitting tube for converting an optical image first into an electron image and then into a train of electrical signals adapted for transmission over'a radio'channel or a physical line channel, as is Well known in the art; The details of the multiplier portion of dissectortube l are illustrated inFig.4. i a

The television dissector tube 1' comprises an envelope 20, a cathode 2| at one end thereof,

the opposite end 23 being transparent and preferably in the form of a planar window so that an optical image, as represented by the optical path lines 25, may be projected on cathode 2! by an outside lens or equivalent pptical system 26; Close to" the window 23 is positioned an anode finger assembly comprising a hollow conductive tube 28, preferably havinga square section. This tube is made sufiiciently small in diameter so that it does not appreciably distort, the

optical image. Inasmuch as it is not in thefo-' cus of the lens system, its only action is to reduce the over-all light on cathode 2 l The anode tube 28 is provided with aprimary scanning aperture 30 facing cathode 2|, and ax-,

ially positioned with regard to the tube envelope and the cathode, as clearly shown in Fig. 4 of the drawing. Extending into the interior of the anode tube 28 from the edges of primary aperture 30 is acylindrical cup 3l,,the bottom of which is provided with a secondary scanning aperture 33 also axiallypositionedwith respect to envelope and cathode. Immediately back of aperture 33 is firstmultiplier element 35, in the form of a box having a fiat side facing secondaryaperture 33, and provided witha tertiary scanning aperture 36.

alignment, and diminish in size, tertiary aperture 36 being the smallest of the three. 7 3

The back of the mulitplier element 35 is curved, and the side at right angles-to the one carrying aperture 33 is open, and second multiplier element 38 is positioned with a screened side 39 presented to the open'side of element 35. The open side of second. element 38 opens to the screenedside 40 of multiplier element 42, and the same constructionand position holds with the fourth, fifth, sixth, seventh, eighth and ninth multiplier elements. of the ninth multiplier element 43 is an output screen 45 backed by final multiplier'element 46.

The leads from each individual element are.

brought out separately through the press of" stem 48,011 which oneend of the anode tube 28 is.

drawn toward anode finger 28, and the electrons are maintained in electron image array bymeans offs. longitudinal magnetic field Provided by The primary, secondary,. and tertiary apertures are concentric and in Parallel to the open side aesaeee focusing-coil -22. This focusing coil isenergized, preferably, by asource of direct current 24. The electron image is moved in the direction across aperture 39, and, consequently, across apertures 33 and 3G, by scanning generators 21 andZQ supplying .scanning currents to the magnetic defiection coils 32 and 34.

Thus it can be arranged, as is well known in the art, to successively scan each elementary area of the electron image corresponding to each elementary area of the optical image producing the electron image, The stream of electrons entering primary scanning aperture 39 is still further selected by passing through secondary scanning aperture 33 and tertiary aperture 36, and will finally, within the first multiplier element, give a stream of electrons representing the dissection or analysis of the image on cathode 2 5.

However, it is obvious that in dissecting such an image the number of electrons entering the first multiplier stage will be small, After passing through scanning aperture 36, however, in the first multiplier element, they impact the back surface of multiplier element 35 and there produce secondary electrons, because the multiplier elements, as shown in Fig. 4, are supplied with successively increasing positive potentials from source The secondary electrons produced in the first multiplying element are drawn through the accelerating screen 39 on the second multiplier element 33, and there again produce secondaries. Electrons then pass successively through the following multiplier elements, creating secondaries at each impact, the stream finally passing out of the ninth multiplier element 43 to impact the final multiplying element it. The secondaries produced by impacting the final mutiplier element 26 are collected by collection screen 55, which is at the highest positive potential, and which is connected to source 5% through an output resistor 5 l, and the output may be then taken directly from the output electrode #35 through output condenser 52.

The keying pulse generator 7, shown in Fig. 1, may comprise a number of multivibrator elements such as illustrated, by way of example, in Fig. 2. The timer chain 3 is coupled to an amplifier stage 55 the output of which is coupled to the first multivibrator element 58. This consists of a double element vacuum tube 6! of the type designated in the drawings, and is adjusted to generate oscillations of a frequency slightly less than one-third of the field scanning frequency, the reason for which will be apparent in subsequent parts of this description, The output of tube 59 is coupled to an amplifier 6|, in the output of which is tapped oil a keying impulse of the type indicated at 63 in Fig. 5. Tube (ii is coupled to the second multivibrator tube 65 of multivibrator element 66, and since tube 65 is oscillating at a period slightly longer than the desired period, impulse 63 pulls tube 65 into synchronism and the second impulse 63 is generated in the output of tube 65. Tube it! is coupled to tube 65 for amplifying impulse 68.- This is a second keying impulse timed to occur at the trailing edge of impulse 63, which was generated in multivibrator element 58. Tube H1 is coupled to a third multivibrator element '32, wherein the tube 13 is tripped by tube and pulled into synchronism to generate the third impulse 75, beginning at the trailing edge of impulse 68. Impulse 15 is amplified in tube 76 and appears in its output as a third keying impulse.

If the timer chain 3 i adjusted to generate low-frequency field-scanning impulses at, the rate of 120 cycles per second and if it is desired to reproduce three primary color images, each of the keying impulses 63, 68 and,15 should be generated in the multivibrator shown in Fig. 2 at the rate of 40 cycles per second andeach of these impulses should have the duration-of /120 of a second, that is, each impulse should have maximum amplitude for theduration ofone field-scanning period, or, in other words, each keying impulse should have a period equal to that between the leading edges of successive fieldscanning impulsesasillustrated in Fig. 5.

Color mixer 9, shown in Fig. 1, is illustrated in detail in Fig. 4 of the drawings and comprises three channels, one for each of the primary colcrs to be reproduced. The output of tube 6| of Fig, 2 is connected to conductor 62 and potentiometer Bil. The output of tube ID inFig. 2 is connected to conductor H and potentiometer 8!, while the output of tube 16 inFig. 2 isconnected to conductor TI and potentiometer 82.

' The keying impulses from each of the multivibrators 58, 6% and E2 of Fig, 2, are respectively fed through the channels including vacuum tube amplifiers 3t, and 85, tube 84 being-connected across the second and third stages38 and 42-of th multiplier in the dissector tube, the output of tube 85 being connected across the-fourth and fifth stages of-the multiplier, and the output of tube 85 being connected across thesixth and seventh stages of the multiplier. The blanking signal Which is taken from the timer chain 3 is shown as impressed on the eighth stage-of the multiplierthrough the conductor-88.

As illustrated in Fig. lot the drawings, the source as is connected to each stage of the multiplier in a known manner to supply a voltage drop between the stages of approximately volts, whereby the electron stream emitted by cathode 25 of the dissector tube is accelerated between successive stages of the multiplier and amplified in each stage in accordance with the teachings of the prior art@ Suitable couplings and voltage sources are incorporated in each channel in a known manner and of suitable manner and of suitable values as illustrated in In operation, the cathode 2i oi the dissector tube i is exposed to an opticalimage produced in arc projector 2 and modified-by the color disc whereby individual colors which may be present in the optical image, are converted into what corresponds to a black and white electron image on cathode '2! each elemental area of said image representing the intensity of a particularcolor in that areaof the optical image. Color disc 4 is driven by motor 5, which is energized from the timer chain 3 for producing successive primary color images, for instance, red, blue andgreen, on the cathode of the dissector tube l in synchronism with the field-scanning, whereby a complete field representation of different color image is scanned, line by line. If interlaced scanning is desired, a first series of' linesrepre senting, for instance, red, is scanned during the period that the color disc produces a red image, and then a subsequent field is scanned between the lines of the first scanning field during the time that the color disc exposes. the screen to a blue image. The next scanning field scans the original line trace during the time that the color disc exposes the screen togreem Thus; aftersix complete field scannings, the entireareaofift'he screen 2t has beenscanned for each otthree primary colors in the optical image. It will be obvious to'those skilled in the art, that it, is also possible to reproduce more than three primary colors.

' The electron images are scanned under control of a dissectorscanning element in the conventional manner as described hereinbefore in connection with the dissector tube illustrated in Fig. 3. vAny desired rate of scanning is suitable so long as sufiicient detail of picture reproduction is obtained but for purposes of illustration, it is assumed that the particular rate of field-scanning is 120 fields per second. The signal output of the dissector is fed through the multiplier elements in tube 23 and amplified in the intermediate amplifier M and video amplifier I after which the signal may be transmitted over a radio or wire-line channel.

In accordance Withthis invention, each signal train representative of an electron image is individually controlled for the purpose of obtaining the desired brightness of each primary color in the optical image. When the color disc dexposes screen 2| to a red image, the low-frequency field-scanning impulse starts the line tracing of the electron image. At the same time, this impulse acts ontube 55 to control'the multivibrator 58. This element normally oscillates ata period somewhat slower than the period of the into channel 62 from amplifier BI and through potentimeter 80 to tube 84, the amplification of the impulse depending upon the setting of potentimeter 80. Amplifier tube 84 is connected across the second and third multiplier stages 38 and s2, its output opposing the normal accelerating potential so that the gain of the multiplier is governed by the voltage of the keying impulse and thus, the red image signal train is controlled and transmitted at a certain brightness level.

If necessary, the multiplier tube can be com pletely blocked by the keying impulse to eliminate red from the reproduced picture.

When the color disc exposes cathode 2| of the dissector l to a blue image, a second field-scanning period is started by a second field-scanning impulse and at this time the tube Bl keys the multivibrator element 66 which is also oscillating at a period slightly longer than the desired period so that tube El pulls tube 65 into step and it generates a second cycle impulse 68 which is fed through tube 1'0, conductor ll, potentiometer 8| and tube 85; to the fourth and fifth stages of themultiplier. Here, as described above, in connection with the red image, the gain of the multiplier is controlled in accordance withthe' set- .ting of potentiometer. 8! to amplify the blue image and transmit it at any desired level of brightness.

When the color disc 4-exposes cathode 2| of the dissector I, to the green image, a third low "frequency field-scanning impulse starts the line trace of the green image and tube 10 keys the multivibrator element 12 to generate'a third 40 7 cycle impulse 15 which is fed through the con- 8 ductor l1, potentiometer 82, and tube 86 to the sixthand seventh stages of the electron multiplier and thus, the gain of the multiplier is controlled by potentiometer 82 during the period of transmission of the green image and it is trans-' mitted at any desired level of brightness. Thus, the primary color images are successively scanned and transmitted, each color image having the degree of brightness corresponding to the settingof its related potentiometer. If the conditions of illumination of the optical image are changed, it is only necessary to readjust the potentiometer settings to again obtain the desired brightness of each primary color.

The blanking signal may be 'fed through'channel 88 from the timer chain 3 and impressed on the eighth stage of the multiplier with'suflicient potential'to completely block the flow of electrons through the multiplier, whereby the signal train which is eventually transmitted, can contain nothing but the blanking impulse during the blanking period.

This invention should not be limited to the specific structural elements and circuits .diS. closed herein, as it is possible to apply the inventive concept disclosed herein in any form of dissector tube which comprises a multiplier. 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. 7

What is claimed is: 1. In a television system, means for forming optical images representative of individual, pri-.

mary colors in an image,means for generating electrical signal groups each of which is representative of an individual, primary color ;inthe image; means associatedwith said generating means comprising successive electron-multiplier stages for amplifying said signals; and means for sequentially controlling the gain in said multiplier in synchronism with said'signal groups.

2. In a television system, means for forming optical images representative of individual, primary colors in an image; means for generating electrical signal groups each of which is representative 0f anindividual, primary color in the image; means associated with said generating .means comprising successive electron-multiplier stages for amplifying said signals; means. for

, producing keying pulses insynchronism with said signal groups and means responsive to' said keying pulses for controlling the gain insaid multicolors in' an image; means for generating electrical signal groups each of which is representative of an individual, primary color in the'image;

means associated with said generating means comprising successive electron-multiplier stages with said generating means for producing keying pulses in synchronism with said signal groups and means responsive to said keying pulses for providing a predetermined gain in said multiplier for each signal group.

4. In a television system, means for forming optical images representative of individual, primary colors in an image; means for generating electrical signal groups each of which is representative of an individual, primary color in the image; means associated with said generating means comprising successive electron-multiplier stages for amplifying said signals; a source of keying pulses for producing a pulse in synchronism with said signal groups and means including an amplifier individual to each color and responsive to said keying pulses for controlling the gain in said multiplier,

5. In a television system, means for forming optical images representative of individual, primary colors in an image; means for generating electrical signal groups each of which is representative of an individual, primary color in the image; means associated with said generating means comprising successive electron-multiplier stages for amplifying said signals; a source of keying pulses associated with said generating means for producing pulses in synchronism with said signal groups and means including an amplifier individual to each color and responsive to said keying pulses for providing a predetermined gain in said multiplier for each signal group.

6. In a color television system including an electron-multiplier device, a method of producing color pictures comprising the steps of forming groups of electrical signals representative of each primary color in an optical image, amplify ing each group of signals by electron multiplication and sequentially controlling the degree of said electron multiplication in synchronism with the formation of said signal groups.

7. In a color television system including :an electron-multiplier device, a method of producing color pictures comprising the steps of forming groups of electrical signals representative of each primary color in an optical image, amplifying each group of signals by electron multiplication, deriving a keying pulse in synchronism with each change of primary color, controlling the amplitude of said pulse in accordance with the desired level of transmission and utilizing said keying pulses to control the degree of multiplication of each group of signals.

8. In a color television system including an electron-multiplier device, a method of producing color pictures comprising the steps of forming groups of electrical signals representative of each primary color in an optical image, producing a stream of electrons representative of each group of signals, amplifying said stream of electrons by a series of steps of electron multiplications producing a keying pulse in predetermined time relation with said groups of signals and utilizing said keying pulse to control the degree of multiplication of said stream in at least one step of said electron multiplications.

JOHN A. BUCKBEE.

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

UNITED STATES PATENTS Number Name Date 1,725,710 Hammond Aug. 20, 1929 2,259,884 Goldsmith Oct. 21, 1941

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