CA1169546A - Color-signal detection system for a color-television receiver - Google Patents

Abstract

ABSTRACT

A color-signal detection system for a three-color television receiver is disclosed. A first circuit supplies a signal primarily representative of the brightness of a tele-vised color image. A second circuit supplies a wave signal effectively modulated at different phases by color-difference signals defining the chrominance of the image. A first signal-detection circuit is coupled to the second circuit for deriving from one phase of the wave signal a component representative of one of the color-difference signals. A second signal-detec-tion circuit is coupled to the second circuit for deriving from another phase of the wave signal a component representative of another of the color-difference signals. A signal-combining system which is responsive jointly to the brightness signal and the derived components representative of the color-difference signals develops at least three effects for use by a three-color dis-play of a three-color television receiver.

Description

The present invention relates, in general, to color-signal detection systems for color-television re-ceivers of a three-color television system and, particularly, to such detection systems in television systems which translate brightness information as one signal and chro-maticity information as modula-tion components oE a sub-carrier wave signal. The present application is a divi-sion of application No. 796,598 which is a division of application No. 614,465.
In a form of a color-television system, as more fully described in the above-mentioned Canadian application Serial No. 61~,465, color signals individually represent:-ative of the primary colors, specifically, green, red, and blue, of a color image being televised are devaloped at a transmitter. Components of these color signals are applied as modulation signals to a subcarrier wave signal ef-fectively to multiplex-modulate the wave signal by de-veloping in a predetermined phase sequence at different phase points thereof modulation components individually representative of the primary color signals. Conventionally, the modulated subcarrier wave signal has a predetermined mean frequency within the video-frequency range and has amplitude and phase characteristics related to the primary colors of the televised image. In a specific form of such color-television system the subcarrier wave signal is ef-fectively modulated at 120 phase intervals by successive ones of the three color signals. In another specific form of such color-television system the subcarrier wave signal !

may be efEecti~rely modulated at 0~, 180, and 270 by dif-ferent ones of the three color signals. In addition to the modulated subcarrier wave signal, a signal representative of the brightness of the image, in other words a signal in-cluding the detail information of the image in terms ofshades of black and white, is also developed at the trans-mitter. The multiplex modulated subcarrier wave signal, effectively comprising the chromaticity information, and the brightness signal, effectively comprising the brightness and detail information of the televised image, are combined in an interleaved manner to form in a pass band common to both signals a resultant video-Erequency signal which is transmitted in a con~entional manner.
A color-television receiver in such color-television system intercepts the transmitted signal and initially the video-frequency detector derives therefrom the modulated subcarrier wave signal and the brightness signal, in a conventional manner, as components of a video-frequency signal. The brightness signal has many of the 2Q characteristics of a conventional monochrome signal and is conventionally applied directly to one of the beam-intensity control circuits of a picture tube. The modulated sub-carrier wave signal is applied to a color-signal detection system to which there is also applied a locally generated signal having a frequency equal to the mean-frequency of the subcarrier wave signal and having a phase related in phase therewith. A number of color-signal detection devices respond jointly to the locally generated signal and the modulated subcarrier wave signaI individually to derive s'~
from -the subcarrier wave signal signals represen-tative of different ones of the three primary colors utilized in the color-television system. The derived signals representative of the chromaticity of the televised image are then in-dividually combined with the brightness signal to developin the picture tube a color reproduction of the televisecl image.
Color-television receivers of the type just de-scribed normally include conventional radio-frequency and intermediate-frequency amplifier sections and a conventional detector for deriving video-frequency signals including the brightness and chromaticity information. Such receivers differ from the conventional monochrome receivers in the design oE that portion oE the receiver ollowin~ the video-frequency signal detector. In addition to other circuitswhich need not be considered in detail for the purposes of the present invention, the portion of the receiver to which reference has JUSt been made includes the color-signal de-tection devices, previously mentioned hereinl and which in combination with one another comprise a color-signal detec-tion system. The present invention is particularly directed to new and improved such detection svstems.
As previously mentioned, a number of these color-signal detection devices are utilized for deriving the chromaticity information from the multiplex-modulated sub-carrier wave signal. In three-color television receivers where the chromaticity of an image is represented by signals individually representative of three primary colors, three color-signal detection devices for deriving three signals individually representative of the three primary colors are conventionally employed. These three signals and -the signal representative of brightness comprise four components of information which are utilized to provide the complete color information for the three primary colors. Since a composite color composed of three primary colors is capable of being defined by information rela-ting to the brightness, hue, and color saturation thereof, it appears more desirable and more economical to develop only three independent com-ponents of information to define a composite color in place of the four components derived in previous receivers. Since a color-television receiver of the type previously described herein derives a signal representative of brightnessl it appears desirable -to utilize in such a receiver a colox-signal detection system which will de~ive two signals which deine the chromaticity of the image and which in com-bination with the brightness signal will define the composite colors of a reproduced color image. Such a color-signal detection system will utili7e less components and, therefore, be more economical to manufacture than prior such detection systems. Therefore, the present invention is directed to a color-signal detect-on system which derives only two in-dependent signals representative of the chromaticity of a televised image.
It is, thereforel an object of the present in-vention to provide a new and improved color-signal detection system for a color-television receiver which avoids the aforementioned disadvantages of prior color-signal detection systems.

It is another object of the present invention to provide a new and improved color-signal detection system Eor a color-television receiver in which relatively few color-signal detection devices are utilized to derive the S color information.
It is still another ob~ect of the present in-vention to provide a new and improved color-signal detection system for a three-color television receiver in which only two color-signal detection devices are employed to derive all of the color information.
It is still a further ob~ect of the present in-vention to provide a color-signal detection system for a three-color television receiver which is sim~le, economical, and utilizes a relatively small number o circuit components.
In accordance with the present invention, in a three-color television receiver responsive to a received composite television signal having a subcarrier component effectively modulated hy color-difference signals defining the chrominance of the ima~e to be reproduced, a color-difference signal-detection system comprises circuit means for supplying a ~ave signal effectively modulated at dif-ferent phases by color-difference signals defining the chrominance of the image. The detection system also in-cludes first signal-detection circuit means coupled to the supply circuit means for deriving from one phase of the ave signal a component representative of one of the color-difference signals. The detection system also includes second signal-detection circuit means coupled to the supply circuit means for deriving ~from another phase of the aforesaid wave signal a component representative of another of the color-difference signals. The detection syste~ also includes circuit means responsive jointly to the aforesaid derived components representative o the color-dif~erence signals for developing a component representative of a third oE the color-difference signals at a third phase of the wave signal.
For a better understanding of the present invention, together with other and further objects thereo~, reference is had to the following description -taken in connection with the accompanying drawing, and its scope wi11 be pointed out in the appended claims.
In the drawing, the Eigure is a schematic diagr~m of a three-color -television receiver including a color-signal detection system embodying the invention in one form.

GENERAL DESCRIPTION OF THE THREE-CO~OR TELEVISION RECEIVER
Referring to the drawing, there is represented a color-television rec~iver embodying a color-signal detec-tion system in accordance with one form of the present in-vention and comprising portions of Fig. 1 and Fig. 5 of theabove-mentioned Canadian application Serial No. 614,465 of which this application is a division. The receiver is of a constant-luminance type as described-in the above-mentioned Canadian application Serial No. 614,465. In other words, it is of a type wherein the monochrome or hrightness signal determines the brightness of the image, while the chroma-ticity signals determine only color and do not affect brightness. The receiver represented also is of a type which utilizes information representative of the relative proportions of three primary colors to be combined to reproduce a color image and is, -therefore, desianated a three-color television receiver. The rece;.ver includes a radio-frequency amplifier 10 of any desired number of stages having its input circuit connected to an antenna system 11,11. Coupled in cascade with the output circuit of the ampliPier 10, in the order named, are an oscillator-modulator 12, an intermediate-frequency amplifier 13 of one or more stages, a detector and automatic-gain-control lQ (AGC) circuit 1~, and a signal-translating system including a color-signal detection system 15", to be ~escribed in more detail hereinafter, and a color image-reproducin~ ap-paratus 16 of the cathode-ray tube type.
As explained more fully in thc above-mentionecl Canadian application Serial Mo. 61~,~65, the apparatus 16 comprises cathode-ray tubes 17a, 17b, 17c individually arranged to respond, respectively, to signals developed in the output circuits of the unit 15" representative of the green, red, and blue colors of the image being televised.
70 In other words, the bubes 17a, 17b and 17c are arranged to develop, respectively, green, red, and blue images on the respective image screens thereof. The axes of the tubes 17a, 17b, and 17c are physically positioned at right angular relationships with respect to each other, and an optical system 18, which may consist of a well-~nown dichroic mir-ror type arrangement,is so positioned as optical]y to com-bine the images on the screens of the cathode-ray tubes 17a, 17b, and 17c into a color reproduction of the televised color image. Conventional beam-deflecting windings are 0 associated with each cathode-ray tube.

There is also coupled to the detector 14 a synchronizing-signal separator 19 having output circuits coupled through a line-scanning generator 20 and a fieId-scanning generator 21 to each o~ the beam-deflecting windings of the cathode-ray tubes 17a, 17b and 17c. An output circuit of the separator 19 is also connected to a color wave-signal generator 22" in the system 15".
" The output circuit of the AGC supply included in the unit 14 is connected to t~ input circuits of one or more of the tubes of the radio- requency amplifier 10, the oscillator - modulator 12, and the intermediate-frequency amplifier 13 in a well-known manner. A sound-signal r~-producing unit 23 is also connected to the output circuit of the intermediate-requenc~ ampliEier 13 and may :Lnclude one or more stages o intermediate-frequency ampliEication, a sound-signal detector, one or more stages of audio-frequency amplification, and a sound-repxoducing device.
It will be understood that the various units thus far described with respect to the receiver represented in the drawing, with the exception of the color-signal de-tection system 15", correspond to units described in Fig.
1 of the above-mentioned Canadian application Serial No.
614,465 and may have any conventional cons~ruction and de-sign, the details of such units being well known in the art, thus rendering a further description thereof unnecessary.
.
GENERAL OPERATION OF THE TELEVISION RECEIVER
Considering briefly the operation of the receiver of Fig. 1 as a whole, and assuming for the moment that the , :

3~ ~

unit 15" is a means for developing separate signals rep~resentati~e, respectively/ of the green, ~ed, and blue colors of the image being reproduced, the desired -tele-vision signal is intercepted by the antenna 11 and selected S and amplified in the radio-frequency amplifier 10. The la-tter signal is then applied to the oscillator-modulator 1~ wherein it is converted into an intermediate-frequency signal which is then selectively amplified in the amplifier 13 and supplied to the detector 14 wherein its modulation components are derived. The derived composite video-frequency components are applied to the system 15" wherein signals representative of the green, red, and blue colors of the televised image are derived from the applied signal.
Individual ones of the deri~ed aolor signals are applied to different ones of the control electrodes o the cathod~-ray tubes 17a, 17b, and 17c in the unit 16 to modulate the in-tensity of the electron beams in these tubes. The synchro-nizing-signal components of the received s.ignal are separa-ted from thevideo-frequency components in the unit 19 and are utili~ed to synchronize the operation of the line-scanning and field-scanning generators 20 and 21. These generators supply signals of saw-tooth wave form which are properly phased with reference to the transmittea television signal . and which are applied to the deflection windings of the cathode-ray tubes 17a-17c, inclusive, in the unit 16, thereby to deflect the cathode-ray beams in each tube in two.directions normal to each other. There is thus re-produced on the image screens of the tubes 17a, 17b and 17c, respectively, green, red, and blue images representative _ 9 _ of the respective primary colors of the image bein~ televised at the transmitter. The dichroic mirror arrangement l8 optically combines the green, re~, and blue images on the several image screens and presents the complete reproduced color lma~e to the observer.
The automatic-gain-control or AGC signal derived in the unit 14 is effective to control the amplification of one or more of the units 10, 12, and 13 to maintain the signal applied to the detector 14 and to the sound-signal reproducing unit 23 within a relatively narrow range for a wide range of received signal intensities.
The sound-signal modulated wave signal aacompa-nying the desired television signal is also intercep-ted by the antenna syst~m 11,11 and, after amplification in the amplifier 10 and conversion to an intermediate-frequency signal in the unit 12, it is further amplified in the amplifier 13 and applied to the sound-signal reproducing unit 23. In the unit 23 it is amplified and the sound-signal modulation components derived. The latter compo-nents are further amplified b~ the reproducing device ina conventional manner.

DESCRIPTION OF COLOR-SIGN~L DETECTION SYSTEM 15"

. .
Referring now in particular to the color-signal detection system 15", this system corresponds to the system described with reference to Fig. 5 of the above-mentioned Canadian application Serlal No. 614,465 and com-prises a first circuit for supplying a signal primarily representative of the brightness of a televised color image.

Specifically, -this :Eirs~ circui-t includes a 0-4 megacycle low-pass filter network 64 coupled between the terminals 25,25 and an input circuit of each of adder circults 65a, 65b, and 65c. The color-~ignal detection system 15" also 5 includes a second circu.it Eor supplying a wave signal ef-Eectively having amplitude-modulat:ion components a-t dif-erent phase points thereo representative of individual ones of signals defining the chromaticitv of the televised image. Speciically, the second circuit comprises à 2-4 10 megacycle band-pass filter network 27 coupled between the input terminals 25,25 and an input circuit in each of a pair O:e synchronous detectors 28b' and 28c' or applyiny to the latter detectors a 3.5 megacycle subcarrier wave sicJnal modu:l.ated by color-si~nal components representative o:E
15 green, red, and blue o a televised image~

The system 15" also includes a generator for de-veloping a signal having a frequency which is an integral multiple o the requency o the modulated subcarrier wave signal, specifically, a color wave-signal generator 22".
20 The generator 22" may be a conventional sine-wave generator including automatic-frequency-control circuits for develop-ing a signal having a frequency of substantially 3.5 meg-acycles if the frequency o the subcarrier wave signal is 3.5 megacycles. Though not considered in detail herein, 25 the requency of the generator 22" may in some embodiments be a harmonic of the subcarrier wave-signal frequency. An input circuit of the generator 22", as previously mentioned, is connected to an output circuit of the separator 19 for applica-tion oE a synchroniæing signal thereto to control the operation thereof in synchronism with the operation of a corresponding generator in the ~.ransmitter.
The system 15" also ineludes a signal-deteetion apparatus including as detectors for the modulation com-ponents of the suhcarrier wave signal only two signal de-teetion devices, speeifically the units 28b' and 28c' or deriving from the modulated wave signal different modulation components which substantially completely define the chro~ati^citY
of the image. The units 28b' and 28e' are essentially mod-ulators for developing in the output eircuits thereof Ereq-ueney difference signals resulting ~rom the heterodynlng of the modul.ated subcarrier wave si~nal and the locall~ de-veloped wave signal~ The output cixeuit of the unit 28b' is eoupled through a 0-2 megacycle low-pass filter network 29b and an amplifier 30b' to an input eircuit of an adder cir-cuit 65h, while the output cireuit of the detector 28c' is similarly coupled through a 0~2 megacycle filter network 29c and an ampli~ier 30c' to an input circuit of an adder circuit 65c. The circuit elements of the amplifiers 30b' and 30c' are so proportioned that these amplifiers in-dividually have gains complementary to gains in corresponding signal translating channels at the transmitter in order to make the total gains of the separate channels for translating the signals representative of the color of an image from the transmitter through the receiver equal for all such channels. These gains are related to the constant-luminance correction employed at the receiver in the form of channel gains, as more fully explained hereinafter and in the above-J'~mentioned Canadian application Serial No. 61~,~65. As described in the above-mentioned Canadian application Serial No. 6]~,465, the gain of the channel for translating the signal representative of green can be considered to be unity or one. With relation to such gain the channel at the transmitter, for tran~lating the signa:L representative of red may have a gain oE 1 23- and, also at the transmitter, the channel for translating the signal representative of blue may have approximately a gain of 1/5. As one factor in the system under consideration to assure that all of the primary colors have the same hrightness eEeects at the re-ceiver so that the chromaticity signa.ls control only the~
color and do not affect the brightness of the reproduced image and to cause the colors in the reproduced image ~aith-fully to represent the colors in the televised image, thegain of the channel translating the signal representative of green is proportioned to be unity, that of the channel trans lating the signal representative of red is proportioned to be 2.23, and that of the channel translatinq the signal representative of blue is proportioned to be 5. Thus, if the total gain of each channel is considered to be in one unit in each channel, the amplifier 30b' in the channel for translating the signal representative of red may be such a unit and is therefor~ proportioned to have a gain of

2.23. For a similar reason~ the amplifier 30c' is pro-portioned to have a gain of 5.
The signal-detection apparatus also includes a signal-translating system coupled to the aforesaid second circuit for applying the previously mentioned subcarrier wave signal to the devices 28b' and 28c', specifically,the two signal paths coupling an input circu.it oE each of the last-mentioned units to different ones of the output circuits of the filter network 27. Additionally, the 5 signal-detection apparatus includes a si~nal-translating system coupled to the unit 22" for applying the above-mentioned generated signal developed in the unit 22" to the units 28b' and ~8c' for effecting the derivation of the components of the subcarrier wave signal, specifically, 10 two signal paths individually connecting different ones of separate output circuits of the generator 22" to another input circuit of each of the detectors 28b' and 28c', At le~st one of the signal-translating systems for applying signals to the units 28b' and 28c' has circuit elements SO
15 proportioned for modi:Eylng the phase o:~ the signals trans-lated therethrough that the generated signal is in phase with a predetermined phase of the wave signal as applied to one of the devices 28b', 28c', and i9 substantially in quadrature phase with this predetermined phase of the wave 20 signal as applied to the other of the devices 28b', 28c'.
For example, the signal path coupling an output circuit of the generator 22" to an input circuit of the detector 28b' may be considered to include circuit elements so proportioned that substantially no phase delay with respect to an ar-25 bitrary predetermined phase thereof occurs in translatinga signal from the generator 22" to the input circuit of the detector 28b' coupled to the unit 22", while the signal path coupling the generator 22" to an input circuit of the detector 28c' includes circuit elements at the latter input circuit tha-t are so proportioned tha-t the signal translated through the latter path is delayed by 90 in phase with respect to the above-mentioned predetermined phase. Though, in such example, the delay is considered as occurri.ng with respect to -the signa] ~pplied ~rom the generator 22" -to the detector 28c', it should he understood that the delay cou.ld equally well occur i.n one of the paths connecting the output circuit of the filter network 27 to the detectors 28b' and 28c'. In the latter case, the signal applied to each of the last-mentioned detectors from the generator 22"
would have the same phase with respect to the predetermined phase. Additionally phase delays may occur both in the path from the generator 22" to the detector 28c' and the path Erom the ne~work 27 to the same detector -to cause the quadrature relationship o~ the signal.s applied to the de-tector 28c' to occurO As described more fully in the above-mentioned Canadian application Serial No. 614,465, the de-tectors 28b' and 28c' are conventional units arranged to cause the signals applied thereto from the generator 22"
and the network 27 to heterodyne and develop signals rep-resentative of any frequency di.fference in the applied sig-nals specifically caused by the modulation components of the subcarriex wave signal.
Finally, the system 15" includes a signal-combinina means responsive jointly to the brightness signal and the modulation components derived in the unit 15" for developing at least three effects for use by a three-color display of a three-color television receiver. More specif-ically, such combining means includes the adder circuits 65a, 65b, and 65c, each having an ou-tput circuit coupled ! throùgh terminals 26a, 26b, and 26c, respectively, to the control electrode circuits of the tubes 17a, 17b, and 17c, respectively, in the image-reproducing device 16. Each of the adder circuits 65a-65c, inclusive, has an input circuit coupled to the output circuit of the ~ilter network 6~.
Additionally, the adder circuit 65a has an input circuit coupled through a phase-inverter circuit 66a to the output circuit of the filter network 29b and has another input circuit coupled through a voltage divider 67 and a phase-inverter circuit 66b to the output circuit of the filter network 29c. As will be explained more fully herein~ter, the phase inverters 66a and 66b are o~ a conventional tvpe or inverting the phase oE the signals in the output cir~uits of the networks 29b and 29c, respectively. The voltage divider 67 is proportioned to apply to the unit 65a a pre-determined portion of the signal develo~ed in the output circuit of the network 29c. The adder circuits may have any conventional design~ for example, each may comprise a plurality of similar tubes having separate input circuits and a common output circuit.

EXPLANATION OF OPERATION OF COLOR-SIGNAL DETECTION SYSTEM
.
In general, the received signal components der-ived in the detector 14 and representing the composite video-frequency signals, including brightness and color information, are applied to the terminals 25,25 of the net-work 15". The signals primarily representative o~ bright-ness and having frequencies of ap~roximately 0-~ megacycles are translated through the filter network 6~ and appliedt.o the input circu;.ts of the adder circuits 65a, 65b, and 65c. The subcarrier wave signal havin~ amplitude-modulation components at different phase points thereof representa-tive : S of individual ones of the signals defining the chroma~icity of the image and having, for example, a mean freauency of

3.5 megacycles~ is translated through the band-pass filter network 27 and applied to input circuits of the detectors 28b' ~nd 28c'. The detec~ors 28b' and 28c' also have a local].y generated 3.5 megacycle wave signal applied thereto from the generator 22", that signal applied to the detector 28b' from the unit 22" be;.ng in quadrature with the signal applied ~rom the same unit to the detector 28c'. The de-tectors 28b' and 28c' are ef~ectively modul.ators, since the modulated subcarrier wave signal and the locally gen-erated signal heterodyne in each detector to derive the low-frequency modulation components of the wave signal.
The detector 28b' develops an output signal representative of the modulation components at, for example, the 0 phase point of the subcarrier wave signal while the detector 28c' develops output signals representative of the components, for example, at the 90 phase point of the subcarrier wave signal. These low-frequency components are then translated through the networks 29b and 29c, respectively, and ~he amplifiers 30b' and 30c', respectively, and applied to input circuits of the adder circuits 65b and 65c wherein they combine with the brightness signals to produce color signals representative of red and blue, respectively. As has pre-viously been ~enticned, the a~pLifier 3~b~ has a gain of 2.23 with reference to a reference gain of the signal rep-resentative of green, whereas the amplifier 30c' has a gain of 5 with reference to the reference gain. Thus, as explained in the above-mentioned Canadian application Serial No. 614,465, these gains are effec-tive to cause the ~` color signals developed in the output circuits of the adder circuits 65b and 65c faithfully to represent the red and blue colors, respectively, of the televised image. These gains together with the gain of the channel including the unit 65a for translating the signal representative of green and, as will be explained ~ore fully hereina~ter, the relative proportions o~ the signal component.s in the output circui-ts o~ the un:its 29b and 29c wh.ich combine to develop the signal representative of green, are efective to cause the signals representative of the chromaticity of the image to develop the color thereof while not affecting the brightness of the . image.
As will be more fully understood from a con-sideration of signals of specific composition to be con-sidered hereinafter, portions of the signals developed inthe output circuits of the networks 29b and 29c are in-verted in phase in the networks 66a and 66b, respectively, and applied to input circuits of the adder circuit 65a to develop in the output circuit of the latter unit the signal representative of green. The path through the system 15"
for the signal representative of green has an amplification factor of unity with respect to the amplification of the path for translating the brightness signal. The signal . ~
representative of green is then translated through the ter-minal 26a and applied to the control electrode c.ircuit of the cathode-ray tube 17a.

Considering the general e~planation of the op-eration of the ~ystem 15" as presented above, it is apparent that three components of information are derived from the composite video-frequency signal bY means of the two de~
tection devices 28b' and 28c' and utilized to develop the three signals represen-tative of the colors green, red, and blue in t.he image to be reproduced. Thus, the signal trans-lated through the network 64 is representative of the brightness information of the image, while the signals trans-lated through the networks 29b and 29c, having been derivedfrom the subcarrier wave signal solely by the two detectors 28b', 28c', are collectively representative of the chro-maticit~ or color information of the image. Specifically, the signal translated through the n~twork 29b i.s a ~olor difference signal R-Y representative of red while the signal translated through the network 29c is a color dif~erence signal B-Y representative of blue where the letters R and B
represent, respectively, red and blue and the letter Y rep-resents the brightness signal. More detail with respect to these signals will be presented hereinafter. In addition to being representative of the primary colors red and b~ue, these signals include components which when properly combined develop a color difference signal G-Y representative of green in the reproduced image. The units 66a and 66b and the voltage divider 67 are effect;.ve to derive the latter components in proper proport;on from the signals translated through the networks 29b and 29c for combination in the adder circuit 65a to develop the color difference signal G-Y
representative of the green of the image. Thus, the net-work 15" includes only two signal-de-tection devices or deriving from the modulated wave signal different modulation components which substantially completely define the chro-maticity of the image.
It is helpful to consider a specific example to indicate the manner in which inEormation relative to bright-ness and the three colors greenl red, and blue of an image may be derived from the composite video-frequency signal with the utilization o~ one channel Eor developing the bright-ness signal and only two si~nal-detection devices for de-veloping the signals representative of the green, red, and blue colors of the image. In a constant-lumlnance ty~e of color-television recelver such as described in the abov~-mentioned Canadian application Serial No. 614,465, there are developed color signals G, R, B representative, re-spectively, of the green, red, and blue colors of the image in the output circuits of the adder circuits 65a, 65b, and 65c, respectively. The signals G, R, B are developed in - the adder circuits just mentioned by combining a brightness si~nal Y in each of these adder circuits with a color dif-ference signal representative of a component of the chro-maticity of the image. As defined by Equation (1) in the above-mentioned Canadian application Serial No. 614,465, the brightness signal M is:
M = 0.67G + 0.30R + 0.03B (1) The reasons for the relative portions of the G, R, B signals which are combined to develop the brightness ~ignal M are fully exp]ained in the above-mentioned Canadian application Serial No. 614,465 and relate to the constant-luminance 5~
; charac-teris~ic of the -television system. The brightness signal M defined by Equation (1) is translated through the network 64 and applled to each of the adder circuits 65a, 65b, and 65c.
In addition to the brightness signal M, there are also applied to the adder circuits 65a, 65b, and 65c signals representative of the chromaticity of the image, specifically, color difference signals g, r, and b. Signals representative of the latter signals are defined bY Equations (7), (9), and (lO) of the above-mentioned Canadian application Serial No.
614,465 as ~he signals at the output circuits oE the detectors 28a, 28b, and 28c of Fig. 1 of that application. The latter signals modified by the gains of ~he channels thro~lgh which they are translated, become the color difEerence signals g, rl and b and are defined as follows:
g = 0.33G - 0.30R - 0.03B (2) r = 0.70R - 0.67G - 0.03B (3) b = 0.~7B - 0.67G - 0.30R ~4) The signals g, r, and b are applied to the units 65a, 65b, and 65c, respectively. It is apparent that as the signal g is added to the signal M in the unit 65a the signal G is developed. Similarly, the signals R and B are developed in the units 65b and 65c, respectively.
Signals rl and bl representative of r and b prior to the amplification in the units 30b' and 30c' are derived directly at quadrature phase points, for example, at the 130 and 270 phase points, respectively, of the subcarrier wave signal by the detectors 2Rb' and 28c', respectively.

These signals are defined by ~quations (11! and (12) of the above-mentioned C~nadian application Seria:l No. 614,465 and, for the present purpose, may be defined in a rearranged form of the latter Equations, as follows:
rl = 0.31R - 0.30G - O.OlB (5) hl = O.l9s - 0.13G - 0.06R (6 As described in the above-mentioned Canadian application Serial No. 6~.4,465, an~ as i.s evident from an examination of Equation (2), the signal g is composed of porti.ons of the G, R, and B slgnals in the proportions expressed by Equation (2)~ These proportions as defined in one form by Equation (17) in the above-mentioned Canaclian application ~er;.al No. 614,465 may be defi.ned as fol].ow~:
g = -r - kb (7) where 15 k is the fraction~l porti.on of the signal b to be combined with the signal r to develop the signal g.
As defined by Equation (17) in the above-mentioned Canadian application Serial No. 614,465:
k = 0.22 (8) With such value for k, substituting the values of rl and bl as defined by Equations (5) and (6), in F.quation (7) the signal g as defined by Equation (2) is developed.
To accomplish the operation defined by Equation 25 (7), the phase inverters 66a and 66b are utilized to develop the signals -rl and -bl, and the voltage di.vider 67 is adjusted to apply the fractional portion 0.22 of the signal -bl to the adder circuit 65a, the signal -rl ~eing applied to the same adder circuit hy the unit 66a.

Though the example just considered is directed to the derivation of the signals -rl and -kbl by means of actual phase-inverter circuits 66a and 66b and the voltage divider 67, as explained in the above-ment.ioned Canadian applicat.ion Serial No. 61~,465, at least some of the latker units may be re~laced by an asymetrical arrangement for deriving the signa~s g, r, and b~ Briefly by deriving color difference signals representative of red and blue at the proper phase angles it is possible to cause a color differ-ence signal representative of green to be equal to theinverse of the derived co.lor dieerence signal representa-tive of red, thereby eliminati.ng the need for more than one phase-inverting circuit.
The embodiment of the i.nvention just described is one wherein information relating to the three primary colors green, red, and blue is derived from the subcaxrier wave signal solely hy utili.zing the two synchronous de-tectors 28b' and 2ac'. By utilizing approximately two-thirds of the co].or-sianal detection apparatus that would normally be utilized directly to derive signals repxesenta-tive of the three primary colors, all of the information needed to develop signals representative of the three primary colors is obtained. This information is obt.ained without any 105s in the quality of the image reproduced from the derived signals and with evident increased economy in the number of circuits utilized. Though there has heen described a specific system for developing signsrepresent-ative of the three primary colors from two signs derived from the subcarrier wave signal, it is to be understood that signals other than -those described herein as bein~ deri.ved from ~he s~lbcarrier wave si~nal may be developed and utilized to provide information relative to the three pri~ary colors in accordance with the teaching o the in-vention.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In color television receiver apparatus having a tricolor picture reproducing means, the combination of a monochrome signal source, a first color-difference signal source, a second color-difference signal source, a first mixer circuit having a plurality of inputs, a second mixer circuit having a plurality of inputs, a third mixer circuit having a plurality of inputs, with said monochrome signal source connected to one of the inputs of each of said mixer circuits, with said first color-difference signal source connected to another input of said first mixer circuit, and with the second color-difference signal source connected to another input of the third mixer circuit.