US2418414A

US2418414A - Television color mixing system

Info

Publication number: US2418414A
Application number: US570229A
Authority: US
Inventors: Christian C Larson
Original assignee: Farnsworth Television and Radio Corp
Current assignee: Farnsworth Television and Radio Corp
Priority date: 1944-12-29
Filing date: 1944-12-29
Publication date: 1947-04-01
Anticipated expiration: 1964-04-01
Also published as: GB620132A

Description

April 1, 1947; V c. c. LARSON 2,413,414

' TELEVISION COLOR MIXING SYSTEM .F'i led Dec. 29, 1944 2 Sheets-Sheet 1 KEYING PULSE GENERATOR I U I! O.

PHOTO'CELL MULTIPLI HORLDEFLECTION VERT. DEFLECTION GENERATOR) GENERATOR FIG.I

ATTORNEY April 1 1947. c, 'c, LARSON 2,418,414

TELEVISION COLOR MIXiNG SYSTEM 7 Filed Dec. 29, 1944 2 Sheets-Sheet z n I a: a:

: I; 3 I: 3 n: i E a =2 INVENTOR g t; CHRISTIAN c. LARSON L.F. SYNC. INPUT ATTORNEY Patented Apr. 1, 1947 TELEVISION COLOR MIXING'SYSTEM Christian C. Larson, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application December 29, 1944, Serial No. 570,229

18 Claims. 1

This invention relates generally to a system for transmitting pictures in natural colors and particularly to a color mixing control for color television systems.

According to conventional television practice the transmission of pictures in color is accomplished by projecting a light image through color filters upon a light responsive electrode. The color filters are arranged successively to transmit the primary colors contained in the light image or at least such a combination of colors which will give a reasonably faithful and pleasing reproduction of the object or scene to be transmitted. In this manner groups of picture signals are transmitted to succession, each group representing a certain color contained in the light image to be transmitted. For reproducing color film it is customary to employ an arc lamp as the light source which, as is Well known in the art, contains a preponderance of energy of certain wave lengths particularly in the inira-red spectral region. For ordinary studio illumination various types of light sources are used which also have an uneven distribution of the light energy over the visible spectral range. It is further known that the photosensitive electrodes or mosaic screens used in conventional television pickup tubes are more sensitive to certain wave lengths of the visible range of the spectrum than to others. In order to obtain a faithful or pleasing reproduction of the object to be transmitted the response of the human eye to light energy of different wave lengths must be taken into consideration. Moreover, it sometimes happens that the color filters used for filtering the light image do not pass light exactly within the desired wave length range and, therefore, the intensity of the filtered light is not truly indicative of the light or color values of the object.

For these reasons it is obviouslyvery desirable to provide means for controlling the transmission level of each group of picture signals associated with one of the primary colors to be transmitted in order to control the relative brightness of the reproduced colors. It is furthermore desirable to modify this control of the transmission level of the groups of picture signals associated with each color to be transmitted in accordance with the average light intensity of the image for each individual color. 7 i To illustrate the problem further we may consider, as an example, an object to be transmitted which lacks entirely one color such as red. On the other hand, the object to. be transmitted may be additionally illuminated with a red light. In order to reproduce each of these objects with their proper color values it is essential to transmit separate information of the average light level during each color transmission period. The light intensity of the object averaged for all colors obviously could not supply this information.

For effecting a color mixing control it has been suggested to control the intensity of the scanning beam in a pickup tube of the light storage type in synchronism with the color transmission periods. However, such an arrangement does not permit a control of the transmission level in accordance with the average intensity of the light of the object. It has also been suggested to employ a separate amplifier channel for each of the colors transmitted, the amplifier channels being associated with electronic switching means. In this way the amplification factor of one group of picture signals associated with one color can be modified by the energy contained in another picture channel. This scheme, however, has the drawback that as many amplifier channels are needed as there are colors to be transmitted.

It is an object of the present invention, therefore, to provide a television color mixing system for controlling the transmission level of groups of picture signals, each being representative of an individual color in an optical image, in such a way that the relative brightness values of the individual colors may be adjusted at will, and further, so that an automatic control is obtained or" each group of picture signals in dependence upon the average light intensity during the individual transmission periods and in dependence upon the preselected relative color values.

In accordance with the present invention there is provided a television system for transmitting an object in natural colors. Means are provided for generating groups of picture signals in succession whereby each of the groups represent a selected color component of the object to be transmitted. These groups of picture signals are now amplified, and a photocell multiplier is arranged which is responsive to the average light of th object to be transmitted during each color transmission period. Further means are provided for adjusting at will the gain of the photocell multiplier to a desired value during each color transmission period. Finally, the gain of the picture signal amplifier is controlled by the output current of th photocell multiplier.

Accordingly, the output of the photocell multiplier depends upon the light received thereby during each color transmission period, as well as on its gain. The first relationship between the multiplier output and the light level during each color transmission period results in an autosnatlc color control. The dependence of the multiplier output upon the adjustable multiplier gain, on the other hand, produces an adjustable picture signal amplifier gain control which is separately adjustable for each of the colors to be transmitted. In this manner the gain of each group of picture signals is controlled not battery 12.

only to reproduce each color with a predetermined brightness in comparison with the other colors, but also in accordance with the average intensity of the light image for each individual color to be transmitted.

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 is a schematic circuit diagram, partly in block form, of a television color mixing system embodying the present invention; Fig. 2 isa schematic circuit diagram of portions of the circuit of Fig. 1, including keying impulse generators and a color mixer and their connections to a photocell multiplier for controllingthe gain thereof; and

Fig. 3 is a set of curves illustrating the time relation between the field frequency synchronizing impulses and the keying impulses applied to the photocell multiplier.

Referring now more particularly to Fig. 1 or" the drawings, there is shown a picture signal transmitting system including a television pickup tube I. A scene or object represented by arrow 2- is projected upon photosensitive or light responsive electrode 3, arranged in pickup tube I, through lens system 4. Color disk 5 driven by synchronous motor 6 is arranged between object 2 and photosensitive electrode 3. As shown in Fig. 1, photosensitive electrode 3 is of the mosaic screen type. Color disk 5 consists of a number of color filters each of which is arranged to transmit one. of the primary colors. It is customary .to provide filters for transmitting the colors red, green and blue.

'Photosensitive electrode 3 is scanned by an electron scanning beam generated by electron gun 1. Electron gun 1 includes an indirectly heated cathode 8 and a first anode It which is supplied with positive potential with respect to cathode 8 by potentiometer H connected with Second anode it may be grounded asshown and is held at a still higher positive potential with respect to cathode 8. Anode I3 is integral with collector electrode I4. A pair of coils 1:5, connected with horizontal deflection generator 16, deflect the scanning beam horizontally across photosensitive electrode 3 in accordance with the line scanning frequency. An-

other pair of deflecting coils H is connected with vertical deflection generator it and serves for deflecting the electron beam vertically in accordance with the field scanning frequency.

The electron scanning beam generated by electron gun I and deflected by coils l5 and Ill drives photosensitive electrode 3 to a normal or equilibrium potential to neutralize the charge deficiency caused by the emission of photoelectr-cns freed by the action of the light impinging on photosensitive electrode 3. By driving electrode 3 to its equilibrium potential voltage variations are impressed upon signal plate 19 coupled to photosensitive electrode 3 through an insulating layer. These voltage variations are developed as picture signals across grounded resistor Eli and impressed through coupling condenser 2! upon preamplifier or video amplifier 22.

In accordance with the present invention photocell multiplier 25 is arranged adjacent television pickup tube I. The light from object 2 is projected upon photocell multiplier 25 through lens system 26. However, if desired, lens system 4 may be used for projecting the light from object 2 into photocell multiplier 25. Color disk 5 is arranged between object 2 and photocell multiplier 25 and, therefore, photocell multiplier 25 receives light from object 2 which is filtered through the color filters of disk 5.

Keying pulse generators 27, controlled by vertical deflection generator 18, are connected through color mixer 28 with photocell multiplier 25'. The connections of keying pulse generators 2'! and color mixer 28 with photocell multiplier- 25 are shown in detail in Fig. 2 in which like components are designated by the same reference numerals as were used in Fig. l. Keying pulse generators 2'5 may have the construction described in the copending application to John A. Buckbee, Serial No. 431,645, filed February 20, 1942, and assigned to the same assignee as is this application. As illustrated in Fig. 2, three keying pulse generators or impulse generators lit, 3! and 32 are provided. Each of the

impulse generators

3G, 35 and 32 may include a multivibrator element as described in the Buckbee application above referred to.

We may assume that fields are transmitted each second. If we further assume, as is conventional, that three primary colors are transmitted, each of the three colors will reoccur at a frequency of 40 cycles per second. Impulse generators 3%, 3| and 32 are arranged to generate substantially square pulses of a duration of /120 of a second each corresponding to the field scanning frequency. The pulses generated by each impulse generator are spaced /40 of a second corresponding to the reoccurrence period of each color. The shape of the pulses generated by

impulse generators

30, 3! and .32 is shown in Fig. 3. Curve 33 represents the output of generator 3t and may, for instance, be present during the period or, in other words, each keying impulse has a duration equal to'that between the leading edges of two successive field scannin impulses illustrated at the top of Fig. 3. For synchronizing purposes impulse generators Bil, 3i and 32 are coupled to the low frequency synchronizing input developed by vertical deflection generator l8, shown in Fig. 1.

Color mixer 28, shown in detail in Fig. 2, includes three channels, one for each of the three primary colors to be transmitted. The output of impulse generator 3i! is connectedto potentiometer 36 through coupling condenser .31. Similarly, the output of impulse generator 3| is coupled to potentiometer 38 through coupling condenser t6, and the output of impulse generator 32 to potentiometer ti through coupling condenser t2.

Potentiometers

36, 38 and 4 are connected, respectively, to the grids of vacuum'tube amplifiers d3, 44 and 5.

Photocell multiplier 25 includes photocathode 4t and six multiplier stages 48, 49., 59, 5|, 52 and E3. The photoelectrons emitted by photocathode 46 are multiplied by being fed through the consecutive multiplier stages 48 to 53 and are finally collected by electron collector 54. Photocell multiplier stages 58 to 53 receive their voltages from potentiometer 55 ener ized by, for example, a battery 56 in such a manner that the voltage of each succeeding stage is more positive than the voltage of the preceding stage. Usually, a potential of about 90 volts is required between two successive multiplier stages. The output of electron collector 54 is connected to resistor 51 and thence to the grid of amplifier tube 60, shown in Fig. 1 for a purpose to be described hereinafter.

The output of vacuum tube amplifier 43 is connected between the first and second stage of photocell multiplier 25, that is, to

stages

48 and 49. Similarly, the output of amplifier tube 44 is connected between multiplier stages 50 and 5|, and the output of amplifier 45 is connected between multiplier stages 52 and 53.

It will now be evident that during the transmission period of one color a keying pulse such as 33 is generated by impulse generator 30 and amplified by tube 43. The degree of amplification is controlled by potentiometer 36 and can thus be adjusted. at will. The output of tube 43 connected between multiplier stages 48, 49 controls the biasing voltage therebetween, and hence the total gain of photocell multiplier 25 is thus controlled during the transmission period of the red light.

The biasing voltage between the multiplier stages of photocell multiplier 25 is controlled in the following manenr. Supposing a positive keying pulse 34 is now generated by impulse generator 3! and amplified by tube 44. This causes a voltage drop both at the cathode and anode of tube 44. Consequently, multiplier stage 5| is driven more negative and stage 50 more positive than in its normal state. As a result the potential difference between multiplier stages 49 and 53, as well as the one between stages 5! and 52, is increased, while at the same time the potential difierence between stages 50 and 5| is decreased. Consequently, the electron multiplication on stages 53 and 52 is increased, while the multiplication on stage 5! is decreased. The net result, that is, whether the output current of electron multiplier 25 is increased, or decreased will depend upon the voltages applied to the individual stages. If the amplitude of keying pulse 34 is suficiently large, the total gain of the multiplication in electron multiplier 25 will be decreased. The exact amount of the decrease of the total gain can be adjusted by setting potentiometer 38 to a suitable value.

Keyin pulses

33 and 35 amplified by

tubes

43 and 45, respectively, act in a similar manner to modify the total gain of electron multiplier 25. Although tube 43 acts on the initial multiplier stages and tube 45 on the final multiplier stages of electron multiplier 25, their efiect on the total gain is the same because the total gain of an electron multiplier is the product of the gains of the individual multiplier stages. Q

In this way the gain of photocell multiplier 25 is cyclically controlled in synchronism with the color transmission periods or the field scanning cycles. At the same time the output obtained from electron collector 54 also depends upon the average intensity of the light of object 2 during each color transmission period. The light projected through lens system 26 upon photocathode 46 is filtered through successive color filters of disk 5 in synchronism with the field scanning cycle.

In accordance with the invention the output of electron collector 54 may be connected to one of the amplifier stages of video amplifier 22 such as 6 to amplifier 60. As set forth hereinabove the output of electron collector 54 is connected through resistor 57 to the grid of vacuum tube amplifier 60 to provide a variable grid bias. The grid of tube 60 is further controlled by preamplifier 22 and the output thereof is connected to amplifier, .modulator and transmitter 6|. Amplifier, modulator and transmitter BI is also connected to horizontal deflection generator l6 and vertical deflection generator l8 for combining the video signal with the synchronizing signals to obtain a composite television signal which is then used for modulatinga carrier wave in a conventional manner. Transmitter Bl supplies energy to transmitter antenna 62. Tube 30 may be a variable i or remote cutoff tube which then operates as in an automatic volume control system well known in the art.

According to the television standards adopted by the Radio Manufacturers Association, the polarity of transmission is such that an increase in the initial light intensity of the object causes a decrease in the radiated power. Accordingly, tube 59 is connected to photocell multiplier 25 in such a manner that an increase of the light level of each color transmission period will decrease the gain of tube 60.

We will first consider the automatic control of each color transmission level by means of photocell multiplier 25. Assuming that at a particular moment the object to be transmitted contains relatively more red light than light of the other primary colors, the output of photocell multiplier 25 will be larger during the transmission period of the red light. The output current of photocell multiplier 25 causes a voltage drop across resistor 59 connecting electron collector -54 to potentiometer 55. This voltage reduction drives the grid of tube 6!! more negative, resulting in a decrease of the amplificationfactor of tube 5!] during the transmission period of the red light. On the other hand, when the object to be transmitted contains less light energy of one of the transmitted colors such as red, in come parison to the other colors, the grid of tube 63 is driven more positive, thus causing an increase However, it is also possible to change at will the color transmission level of any one color with respect to the other colors. Supposing the transmitted picture, as seen for instance on a monitor screen, contains more red light than is desired for a pleasing appearance, it is possible to reduce the red color transmission level at will. To this end potentiometer 35, associated with the red color transmission period, may be adjusted manually to reduce the gain of-photocell multiplier 25 during the red color transmission period. This new color transmission level for the red color will then be automatically maintained with respect to the relative brightness of the other colors contained in the object to be transmitted.

In this mannera color mixing control is obtained Where the relative brightness of one color, with respect to the relative brightness of any one of.

Thus a control ofthe transmission level of each color above the black level is effected.

It is also feasible to supply the grid of tube (58 with a positive bias so that When no light is received by photocathode 46 of photocell multiplier 25, the gain of tube till is at its maximum. in this manner the black level may be established as the common or reference level of all colors to be reproduced. The output current from photocell multiplier 25 Will then reduce the positive grid bias of tube 50 to reduce the gain thereof in accordance With the light values of the object during each color transmission period.

Although the television color mixing system of the invention has been shown in connection With an iconoscope it will be evident that the inventive concept disclosed herein may be applied to any type of television picture signal generating tube including other pickup tubes of the light storage type as Well as image dissector tubes.

While there has been described what is at pres- =ent considered the referred 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: i

1. In a. television system for transmitting a object in natural colors, means for generating groups of picture signals in succession, each of said groups representing a selected color component of said object, means for amplifying said groups of picture signals, a photocell multiplier responsive to the average light of said object during each color transmission period, means for establishing a predetermined gain in said multiplier during transmission of each color component, and means for controlling the gain of said amplifying means by the output of said photocell multiplier.

2. In a television system for transmitting an object in natural colors, means for generating groups of picture signals in succession, each of said groups representing a primary color of said object, an amplifier comprising successive stages for amplifying said groups of picture signals, a photocell multiplier responsive to the average light of said object during each color transmission period, means for establishing a predetergain in said multiplier during transmission of each primary color, and means for controlling the gain in one of said amplifier stages by theoutput of said photocell multiplier in synchronism with said color transmission periods.

3. In a television system for transmitting an object in natural colors, means for generating groups of picture signals in succession, eachof said groups representing a selectedcolor component of said object, means for amplifying said groups of picture signals, a photocell multiplier responsive to the average light of said object during each color transmission period, means for adjusting at Wlll the gain of said photocell multiplier to a desired value during each of said color transmission periods, and'means for controlling the gain of said amplifying means by the output of said photocell multiplier.

, 4. In a television system for transmitting an object in natural colors, means for generating groups of picture signals in succession, each of said groups representing a primary color of said "object, 'an' amplifier comprising successive stages for amplifying said groups of picture signals, a photocell multiplier responsive to the average light of said object during each color transmission period, means for adjusting at will the gain of said photocell multiplier to a desired value during each of said color transmission periods, and means for controlling the gain in one of said amplifier stages by the output of said photocell multiplier in synchronism with said color transmission periods.

5. In a television system for transmitting an object in natural colors, means for generating roups of picture signals in succession, each of said groups representinga selected color component of said object, means for amplifying said groups of picture signals, a photocell multiplier responsive to the average light of said object during each color transmission period, a source oi keying impulses for producing successive pulses in synchronism with said color transmission periods, a color mixer controlled by said keying impulses comprising a keyed amplifier for each of said color components connected to said multiplier stages for automaticall controlling the gain therein during said color transmission periods, and means operatively connected with the output of said photocell multiplier for controlling the gain of said picture signals in said amplifying means in synchronism with saidcolor transmission periods.

6. In a television system for transmitting an object in natural colors, means for generating groups of picture signals in succession, each of said groups representing a selected color component of said object, means for amplifying said groups of picture signals, a photocell multiplier responsive to the average light of said object during each color transmission period, a source of keying impulses for producing successive pulses in synchronism with said color transmission periods, a color mixer controlled by said keying impulses comprising a keyed amplifier for each of said color components connected to said multiplier stages for automatically establishing a predetermined gain therein during said color transmission periods, means associated with said keyed amplifiers for individually adjusting the gain thereof, thereby to control at Will the gain in said photocell multiplier during each color transmission period, and means operatively connected with the output of said photocell multiplier for controlling the gain of said picture si nals in said amplifyingmeans. in synchronism withsaid color transmission periods.

7. In a television system for transmitting pictures in natural colors, a light responsive electrode, means for projecting alight image upon saidlight responsive electrode, a photocathode' arranged adjacent said electrode, a plurality of electron multiplier stages associated with said photocathode, a plurality of 1ight filters of different light transmittingcharacteristics, means for successively interposing said filters in a predetermined sequence between said light image andsaid light responsive electrode and photocathode, means associated with said light responsive electrode for generating groups of picture signals each being representative of an individual color in said light image, means .for amplifying said picture signals, a source of keying impulses for producing successive pulses in synchronism with the successive interposition of said light filters, a color mixer controlled by said keying impulses comprising a keyed amplifier for' each of said colors connected to said multiplier stages for controlling the gain therein during the transmission period of each color, and means operatively connected with the output of said multiplier stages for controlling the gain of said picture signals in said amplifying means in synchronism with said color transmission periods, thereby to control the gain of said picture signals in accordance with the average intensity of the light passing through said filters and impinging on said photocathode.

8. In a television system for transmitting pictures in natural colors, a light responsive member, means for projecting a light image upon said light responsive member, a photocathode arranged ad- 'jacent said member, a plurality of electron multiplier stages associated with said photocathode, a plurality of color filters, means for successively interposing said filters in a predetermined sequence between said light image and said light responsive member and photocathode, means associated with said light responsive member for generating groups of picture signals each being representative of an individual primary color in said light image, means for amplifying said picture signals, a source of keying impulses for producing successive pulses in synchronism with the successive interposition of said color filters, a color mixer controlled by said keying impulses comprising a keyed amplifier for each of said primary colors connected to said multiplier stages for controlling the gain therein during the transmission period of each color, and means operatively connected with the output of said multiplier stages for individually controlling the gain of each group of said picture signals in said amplifying means, thereby to control the gain of said picture signals in accordance with the average intensity of the light passing through said filters and impinging on said photo-cathode.

9. In a television system for transmitting pictures in natural colors, a, light responsive member, means for projecting a light image upon said light responsive member, a photocathode arranged adjacent said member, a plurality of electron multiplier stages associated with said photocathode, a plurality of color filters, means for successively interposing said filters in a predetermined sequence between said light image and said light responsive member and photocathode, means associated with said light responsive member for generating groups of picture signals each being representative of an individual primary color in said light image, means for amplifying said picture signals, a source of keying impulses for producing successive pulses in synchronism with the successive interposition of said color filters, a color mixer controlled by said keying impulses comprising a keyed amplifier for each of said primary colors connected to said multiplier stages for controlling the gain therein during the transmission period of each color, means associated with said keyed amplifiers for individually adjusting the gain thereof, thereby to control at will the gain of said multiplier stages during each color transmission period, and means operatively connected with the output of said multiplier stages for individually controlling the gain of each group of said picture signals in said amplifying means, thereby to control the gain of said picture signals in accordance with the average intensity of the light, passing through said filters and impinging on said photocathode.

10. In a television system for transmitting pictures in natural colors, 9, photo-sensitive member,

means for projecting a light image upon said ll) photosensitive member, a photocathode arranged adjacent said electrode, a plurality of electron multiplier stages associated with said photocathode, a plurality of color filters, means for successively interposing said filters in a predetermined sequence between said light image and said photosensitive member and photocathode, means associated with said photosensitive memher for generating groups of picture signals each being representative of an indivdual primary color in said light image, an amplifier comprising successive stages for amplifying said picture signals, a source of keying impulses for producing successive pulses in synchronism with the successive interposition of said color filters, a color mixer controlled by said keying impulses comprising a keyed amplifier for each of said primary colors connected to individual multiplier stages for establishing a predetermined gain therein during the transmission period of each color, and means operatively connected with the output of said multiplier stages for individually controlling the gain of each group of said picture signals in one of said amplifier stages, thereby to control the gain of said picture signals in accordance with the average intensity of the light passing through said filters and impinging on said photocathode.

11. In a television system for transmitting pic tures in natural colors, a photosensitive member, means for projecting a light image upon said photosensitive member, a photocathode arranged adjacent said electrode, a plurality of electron multiplier stages associated with said photocathode, a plurality of color filters, means for success sively interposing said filters in a predetermined sequence between said light image and said photosensitive member and photocathode, means associated with said photosensitive member for generating groups ofpictur signals each being representative of an individual primary color in said light image, an amplifier comprising successive stages for amplifying saidpicture signals, a source of keying impulses for producing successive pulses in synchronism with the successive interposition of said color filters, a color mixer controlled by said keying impulses comprising a keyed amplifier for each of said primary colors connected to individual multiplier stages for controlling the gain therein during the transmission period of each color, means associated with said keyed amplifiers for individually adjusting the gain thereof, thereby to control at will the gain ofsaid multiplier stages during each color transmission period, and means operatively connected with the output of said multiplier stages for individually controlling the gain of each group of said picture signals in one of said amplifier stages, thereby to control the gain of said picture signals in accordance with the average intensity of the light passing through said filters and impinging on said photocathode. r

12. In a television system for transmitting pictures in natural colors, a photosensitive member,

means for projecting a light image upon said photosensitive member, a photocell multiplier including a photocathode arranged adjacent said electrode and a plurality of electron multiplier stages, a color disk having a plurality of color filters, means for rotating said color disk to successively interpose said filters in a predetermined sequence between said light image and said photosensitive member and photocathode, means associated with said photosensitive member for generating groupsof picture signals eachbeing rep 'resentative' of an individual primary color in said light image, means for amplifying said picture signals, a source of keying impulses for producing successive pulses in synchronism with the successive interposition of said color filters, a color mixer controlled by said keying impulses comprising a keyed amplifier for each of said primary colors connected to individual multiplier stages for controlling the gain therein during the transmission period of each color, and means operatively connected with the output of said multiplier stages for controlling the gain of said picture signals in said amplifying means in synchronism with said color transmission periods, thereby tocontrol the gain of said picture signals in accordance with the average intensity of the light passing through said filters and impinging on said photocathode.

13. A method of transmitting an object in natural colors comprising generating groups of picture signals in succession, each of said groups representing a selected color component of said object, amplifying said groups of picture signals, projecting light from said object upon a photocell multiplier, deriving an output current from said photocell multiplier representative of the average light of said object during each color transmission period, and controlling the amplification gain of said picture signals by the output current of said photocell multiplier.

14. A method of transmitting an object in natural colors comprisin generating groups of picture signals in succession, each of said groups p s ti a selected color component of said object, amplifying said groups of picture signals, projecting light from said object upon a photocell multiplier, deriving an output current from said photocell multiplier representative of the avag'e light of said object during each color transmission period, establishing, a predetermined gain in said photocell multiplier during each of said colortransmission periods, and controlling the amplification gain of said picture signals by the output current of said photocell multiplier.

15. A method of transmitting pictures in nat ural color-s comprising projecting a light' image upon a photo-sensitive electrode and a, photocell multiplier, successively interposing color filters in predetermined sequence between said light image and said photosensitive electrode" and photocell multiplier, deriving groups of picture signals from said electrode each being representative of an individual color in said light image, deriving a keying pulse in synchronism with, each change of color, utilizing said keying pulse for automatically controlling the gain of said photocell multiplier during the transmission period of each color, amplifying said picture signals, and; utilizing the output of said photocell multiplier for controlling the amplification gain of said picture signals, thereby to control the gain of said picture signals in accordance with the intensity of said light image. during each color transmission period. a

16. A method of transmitting pictures in natural colors comprising projecting a light image upon a photosensitive electrode and a photocell multiplier, successively interposing color filters in predetermined sequence between said light image and said photosensitive electrode and photocell multiplier, deriving groups of picture si nals fro said electrode each beingrepresentative of an, individual color in said light image, deriving a keying pulse'in synchronism with eachc'hahge 'of 'c o-lor, utilizing said keying .ural colorsv comprising the steps of projectinga pulse for automatically controlling the gairrol' said photocell multiplier during the transmission period of each color, individually adiustin the gain of said photocell multiplier during ea color transmission period, amplifying said picture signals, and utilizing the output of, said photocell multiplier for controlling theamplification gain of said picture signals, thereby tocontrol the gain of said picture signals in accordancerwith the intensity of said light, image during each color transmission period.

17. A method of; transmitting pictures natural colors comprising the steps of projecting a light image upon a photosensitive electrode and a photocell multiplier, successively interposing color filters in predetermined sequence between said light image and said photo-sensitive electrode and photocell multiplier, deriving groups of picture signals from said electrode each being representative of an individual primary color in said light image, deriving a keying pulse in synchronism wi h each change of primary color, utilizing said keying pulse for automatically controlling the gain of individual stages of said photocell multiplier during the transmission period of each color, amplifying said picture signals, and utilizing the'output of said photocell multiplier representative of the average intensity of said light image during each color transmission period for individually controlling the amplification gain of each group of said picturesignal's, thereby to control the gain of said picture signals in accordance with the intensity of saidlight image during each transmission period.

18. A method o-f-transmitting pictures in natlight image upon a photosensitive electrodeand a photocell multiplier, successively interposing col-or filters in predetermined sequence between said light image and said photo-sensitive ,electrode and photocell multiplier, deriving groups of picture signals from said electrode each-being representative of an individual primary color in said light image, deriving'a keying, pulse in synchronism with each change of primary color, utilizing said keying pulse for automatically controlling the gain of individual stages of said photocell multiplier during the transmission period of each color, individually adjusting the gain of said photocell multiplier during each color transmission period, amplifying said pic ture signals, and utilizing the output of said photocell multiplier representative of the average intensity of said light image during each color transmission period for individually controlling the amplification gain of each group of said picture signals, thereby to control the gain of said picture signals in accordance with the intensity of said light image during each color transmission period.

CHRISTIAN C. LARSON.

REFERENCES CITED The following references are of record; in the Australian Jan. 16, 1945