Color television signal generating apparatus for use in a single camera tube

A color television signal generating apparatus comprises a color-resolving striped filter, in a camera tube, for separating the output signal of the camera tube into required signals. Detecting means detects the envelopes of specific positive wave and negative wave signals thus separated. The output of the camera tube is a superimposed signal of a direct wave signal containing signals of three primary colors, of additional mixed colors, and a high-band component signal comprising a group of modulated color signals. This camera output signal results from the amplitude modulation of a carrier wave responsive to filter stripes in the color-resolving striped filter. The carrier wave components have a high harmonic relation relative to two primary color signals. The separating means comprises first separating means for separating the direct signal from the above mentioned superimposed signal and second separating means for separating the high-band component signal. The envelope detecting means comprises a first detector for producing a demodulated output signal in accordance with an envelope resulting from a successive connection of peak values of the positive wave of the thus separated high-band component signal. A second envelope detection means produces a demodulated output signal in accordance with an envelope resulting from a successive connection of peak values of the negative wave of the thus separated high-band component signal.

BACKGROUND OF THE INVENTION 
This invention relates generally to an apparatus for generating color 
television signals and more particularly to such an apparatus for use in a 
color television image-pickup device, such as a color television camera. 
Among the simple types of known color television cameras, there is a 
so-called single-tube type in which a single pickup or camera tube, having 
a color-resolving striped filter in its optical system, is used to 
generate luminance signals and color signals. Also, a color television 
camera has two tubes in one pickup or camera tube. One tube is used for 
generating luminance signals, and the other tube has a color-resolving 
striped filter within its optical system to generate color signals. 
In either of the above mentioned color television camera types, the 
color-resolving striped filters are of the phase-separation or the 
frequency-separation system. 
In a color-resolving striped filter of the phase-separation type, however, 
there has been the disadvantageous requirement that the color-resolving 
striped filter have a complicated organization, including index stripes. 
Another disadvantageous requirement is that a complicated has been 
required for generating sampling pulses on the basis of information 
obtained from these index stripes. A further problem is that noise results 
in the conversion of color information signals by a "sampling hold" of a 
dot-sequential system. In this system, a signal is obtained by sampling 
and inadvertently introducing noise of high frequency into simultaneous 
color information signals included in the dot-sequential. The color 
information signals become stretched along the time axis and are converted 
into noise of conspicuously low frequency, whereby the signal-to-noise 
ratio becomes low. 
A color-resolving striped filter of the frequency-separation system does 
not encounter the above described difficulties accompanying a known 
color-resolving striped filter of the phase-separation system. However, 
there are interference fringes (moire), due to various causes, since two 
sheets of striped filters of different space frequency values are 
fabricated in combination. In addition, the frequency fluctuation of a 
carrier wave generated in the output signal, as a result of non-linearity 
of the deflection system of the camera tube, is a large problem. Often, 
there are further difficulties, such as shading due to a difference in 
degrees of modulation, at the peripheral region and the central region in 
the target surface of the camera tube. 
SUMMARY OF THE INVENTION 
It is a general object of the present invention to provide a new and useful 
color television signal generating apparatus which overcomes the above 
described difficulties. 
More specifically, an object of the invention is to provide a color 
television signal generating apparatus which does not require index 
stripes in the color-resolving striped filter, as found in a 
phase-separation system. Here, an object is to avoid interference fringes 
(moire), shading, and other deleterious effects, as found in a 
frequency-separation system. 
Another object of the invention is to provide a color television signal 
generating apparatus having means for detecting the envelopes of the 
positive wave and negative wave of a separated high-band component signal. 
In particular, an object is to obtain two two-color mixture signals with a 
simple circuit. 
Still another object of the invention is to provide a color television 
signal generating apparatus having means for eliminating noise in an 
existing frequency band portion which is unnecessary for reproduction of 
color signals and means for separating a high-band component signal. By 
means of the apparatus of the present invention, color signals of large 
S/N ratio can be obtained. 
Other objects and further features of the present invention will be 
apparent from the following detailed description with respect to preferred 
embodiments of the invention when read in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION 
One embodiment of a color-resolving striped filter for use in the apparatus 
of the present invention is illustrated in FIG. 1. The color-resolving 
striped filter 10 is made up of first, second, and third filter stripes 
F1, F2, and F3 of equal widths a. Each stripe has an oblong, narrow shape 
in the vertical direction. The stripes are laid consecutively and 
contiguously in the order named above, stripes F1, F2, and F3 constituting 
one group. A plurality of such groups are laid consecutively and 
contiguously side-by-side in a single place. The widths of these filter 
stripes may be selected at will. These filter stripes F1, F2 and F3, of 
all groups, extend in the direction (direction Y in FIG. 1) which is 
perpendicular to the horizontal scanning direction (direction X in FIG. 
1). The stripes are arrayed in an orderly manner in the above mentioned 
sequence, and all filter stripes have the same spatial frequency. 
The light transmitting characteristics respectively of these filter stripes 
F1, F2 and F3 are as follows. The first filter stripe F1 is adapted to 
transmit light of one primary color from among the three primary colors 
(red, green, and blue) of addition mixed colors. The second filter stripe 
F2 is adapted to transmit light of mixed colors of the primary color 
transmitted through the first filter stripe and one of the two remaining 
primary colors (i.e. not the primary color transmitted through the first 
filter stripe). The third filter stripe F3 is adapted to transmit the 
light of all colors (e.g. white light). 
More specifically, the second filter stripe F2 is capable of transmitting 
light of colors respectively having the following relationships, depending 
on whether the primary color transmitted through the first filter stripe 
F1 is red, green or blue. 
______________________________________ 
Primary color light 
Color of light transmitted 
transmitted through 
through second filter 
first filter stripe 
stripe 
F1 F2 
______________________________________ 
red light magenta (red blue) or 
yellow (red green) 
green light yellow (red green) or 
cyan (blue green) 
blue light magenta (red blue) or 
cyan (blue green) 
______________________________________ 
In one example of a color-resolving striped filter 10 of the above 
described organization, the first filter stripe F1 is adapted to have a 
transmission characteristic I (FIG. 2) to transmit green light (G). The 
second filter stripe F2 is adapted to have a transmission characteristic 
II to transmit the light of a mixture color of blue light (B) and green 
light (G) (that is, cyan (C)). The third filter stripe F3 is adapted to 
have a transmission characteristic III to transmit the light of all 
colors, that is, white light (W) or a mixed color light of red light (R), 
green light (G), and blue light (B). 
If these filter stripes F1, F2, and F3 have such light transmitting 
characteristics, the energy state of the light transmitted when a white 
light (W) is projected onto the color-resolving striped filter 10 is as 
illustrated by one example in FIG. 3, in which the horizontal direction 
(X-axis direction) represents energy distribution. That is, green light 
(G) is continuously distributed since it is transmitted through all filter 
stripes F1, F2 and F3. Blue light (B) is distributed over a width 2a 
separated by space intervals a, since it only passes through the filter 
stripes F2 and F3. Red light (R) is distributed over a width a separated 
by space intervals of 2a since it is only transmitted through the filter 
stripe F3. 
The color television signal generating apparatus, according to the present 
invention, in which the above described color-resolving striped filter 10 
is used will now be described with respect to one embodiment thereof and 
with reference to FIG. 4. 
In the apparatus diagrammatically represented in FIG. 4, the image light 
from an object 11 to be televised passes through the camera lens 12 of a 
single tube type color television camera and forms an image on the 
color-resolving striped filter 10. The optical image thus formed on this 
filter 10 is transmitted by way of a relay lens 13 and forms an image on 
the photoconductive surface (or photoelectric surface) of a camera tube 
14. 
When a color-resolving striped filter 10 of the characteristic indicated in 
FIG. 2 is used, and a white light image is introduced as incident light 
passing through the camera lens 12, the resulting output signal S obtained 
from the camera tube 14. This light can be represented as a periodic 
function having a fundamental repetitive period described by the pitch of 
the respective stripes of the color-resolving striped filter. This signal 
is represented by the following Fourier series: 
##EQU1## 
The output signal S represented by the above equation (1) is also 
represented as S = Sd + Sh . . . (2), where the signal Sd is a direct wave 
(DC component) signal comprising a mixture of a luminance signal Y, a 
green light signal Sg, a blue light signal SB, and a red light signal SR. 
The resulting signal can be represented by 
EQU Sd = SG + 2SB/3 + SR/3 (3) 
the signal Sh is a high-band component (AC component) signal comprising a 
group of modulated color signals having forms resulting from amplitude 
modulation of specific carrier wave and other carrier waves with a mixture 
signal. The specific carrier wave has a frequency which is the same as the 
space frequency determined by the number of groups of filter stripes F1, 
F2 and F3 of the color-resolving striped filter 10. The other carrier 
waves have frequencies which are the same as higher harmonics of the 
specific carrier wave. The mixture signal is made up of two primary colors 
other than the primary (which is green color light in the instant example) 
passing through the first filter stripe F1. 
The above mentioned output signal S of the camera tube 14 is amplified by a 
preamplifier 15. Then, it is supplied to low-pass filters 16 and 17 and a 
high-pass filter 18. The low-pass filter 16 has a filtering characteristic 
shown by curve IV (FIG. 5), which is an upper-limit cut-off frequency fy 
of approximately 2.5 MHz. A luminance signal Y is derived from the output 
signal of filter 16 (curve IV). The low-pass filter 17 has a filtering 
characteristic shown by curve V, with an upper-limit cut-off frequency fc 
of approximately 0.5 MHz, from which the above mentioned direct signal Sd 
is derived. The high-pass filter 18 has a filtering characteristic shown 
by curve VI with a lower-limit cut-off frequency fh. The above mentioned 
high-band component signal Sh is derived from the signal of curve VI. 
In FIG. 5, frequency f1 indicates a carrier wave of a frequency which is 
determined by the number and space frequency of filter stripe groups of 
the color-resolving striped filter 10, this frequency being approximately 
3.25 MHz, for example, when there are 170 groups of the filter stripes. 
The frequency f2 indicates the second harmonics (of approximately 6.5 MHz) 
of the carrier wave of the above mentioned frequency f1. 
If a color-resolving striped filter having the characteristic indicated in 
FIG. 3 is used, only a modulated color signal having a component of the 
signal SB due to blue light B and a modulated color signal having a 
component of the signal SR due to red light R exist in the signal Sh. A 
signal component due to green light G is not contained therein. The 
angular frequencies .omega. and 2.omega. and the above mentioned 
frequencies f1 and f2 have the relationships .omega. = 2.pi.f1 and 
2.omega. = 2.pi.f2. 
When only red light reaches the camera lens 12, the high-band component 
signal Sh is only the red signal SR indicated in FIG. 6(A). When only a 
blue light is imparted, the high-band component signal Sh becomes only the 
blue signal SB indicated in FIG. 6(B). Furthermore, when a white light is 
imparted to the camera, the high-band component signal Sh becomes a signal 
of a waveform as indicated in FIG. 6(C). 
Here, the interval on the time axis within which the red signal SR and the 
blue signal SB can be generated is determined by the positions of the 
filter stripes F1, F2, and F3. For this reason, there is a constant phase 
relationship between the blue signal SB and the red signal SR when these 
two signals are simultaneously present, at any point on the time axis. 
Accordingly, if the red signal SR of the waveform indicated in FIG. 6(A) 
and the blue signal SB of the waveform indicated in FIG. 6(B) are mixed, 
the resulting signal is a high-band component signal Sh of the waveform 
indicated in FIG. 6(C). In FIGS. 6(A), 6(B), and 6(C), the lines 0-0 
represent the average zero level (alternating current axis) of the 
respective signals. The peak value of the positive wave of the red signal 
SR (FIG. 6(A)) is 2/3SR. The peak value of the negative wave thereof is 
-1/3SR. The peak value of the positive wave of the blue light SB (FIG. 
6(B)) is 1/3SB, while the peak value of the negative wave thereof is - 
2/3SB. Furthermore, the peak value of the positive wave of the high-band 
component signal Sh (FIG. 6(C)) is (2/3SR + 1/3SB), while the peak value 
of the negative wave thereof is - (1/3SR + 2/3SB). 
The high-band component signal Sh is indicated in FIG. 6(C) which has been 
derived from the high-pass filter 18. Signal Sh is supplied respectively 
to envelope detector circuits 19 and 22, where the positive wave and 
negative wave, respectively, are envelope detected. For example, FIG. 7A 
shows the envelope detector circuit 19 comprising a forward-direction 
diode D1, a capacitor C1, and a resistor R1. A demodulated output 
corresponds to an envelope resulting from a successive connection of peak 
values of the positive wave of the high-band component signal Sh. For 
example, FIG. 7B shows the envelope detector circuit 22 comprising a 
reverse direction diode D2, a capacitor C2, and a resistor R2. A 
demodulated output corresponds to an envelope resulting from a successive 
connection of peak values of the negative wave of the high-band component 
signal Sh. 
The output demodulated signals of the envelope detector circuits 19 and 22 
are supplied to a matrix circuit 21 by way of low-pass filters 20 and 23, 
as signals Sh1 and Sh2. The low-pass filters 20 and 23 may be provided, if 
necessary, and their pass-band width may be the same as that of the above 
mentioned low-pass filter 17. 
The signals Sh1 and Sh2 thus supplied from the envelope detector circuits 
19 and 22 to the matrix circuit 21 correspond respectively to the 
envelopes of the positive and negative waves of the high-band component 
signal Sh. For this reason, these signals can be expressed by the 
following equations: 
EQU Sh1 = (2/3SR + 1/3SB) (4) 
EQU sh2 =-(1/3SR + 2/3SB) (5) 
the matrix circuit 21 receives these signals Sh1 and Sh2 together with the 
direct-wave signal Sd, which is represented by Eq.(3), from the low-pass 
filter 17. As a result, the matrix circuit 21 produces three primary color 
output signals SG, SR, and SB for green, red, and blue. 
EQU SG = Sd + Sh2 (6) 
EQU SR = (Sh1 .times. 2) + Sh2 (7) 
EQU SB = -{(Sh2 .times. 2) + Sh1} (8) 
The apparatus of the present invention has the following advantageous 
features. 
1. Since a filter comprising filter stripes F1, F2, and F3 of respectively 
equal space frequency are used for the color-resolving striped filter, 
moire does not occur. 
2. Since the system is not a phase separation system, stripes are not 
necessary for generating index pulses in the color-resolving striped 
filter, the camera tube, and other parts. Therefore, the color-resolving 
striped filter and the camera tube become simple and can be readily 
fabricated. Furthermore, since the rate of utilization of the incident 
light is improved, a bias light is unnecessary. 
3. By adjusting the spectral response characteristics of the filter stripes 
F1, F2 and F3 of the color-resolving striped filter and the spectral 
response characteristic of the camera tube, the output levels of the three 
primary color signals SR, SG and SB respectively become equal when there 
is a pick up of an all-color light (white light). It is easy to reduce the 
shading which is due to the modulation degree characteristic of the camera 
tube. 
4. The positive and the negative waves of the high-band component signal 
are, respectively, envelope detected to obtain two 2-color mixture 
signals. Thus, it is possible to provide a color television signal 
generating apparatus with an excellent performance, which is simple and 
can be produced at low cost. 
It is desirable for the high-pass filter 18 to have uniform amplitude and 
phase characteristics, over the entire region of its pass band. In actual 
practice, however, it is difficult to obtain a high-pass filter having 
such ideal characteristics. Furthermore, other factors prevent an ideal 
characteristic. For example, the diameter of the electron beam of the 
camera tube is not infinitely small. Also, the degree of modulation of the 
camera tube decreases in the high-frequency band. As a result of these 
various causes, the high-band signal component Sh, obtained from the 
high-pass filter 18, has many waveform distortions. 
On one hand, the alternating-current component contained within the output 
signal of the camera tube is not distributed uniformly throughout the 
entire band. Instead, it has a distribution wherein, as indicated in FIG. 
5, a carrier wave f1 has a fundamental frequency value f1 determined by 
the number of groups of filter stripes of the color resolving striped 
filter 10. The information content exists only in the vicinity of this 
fundamental and the vicinity of the higher harmonics thereof. In contrast, 
the noise present within the output signal S of the camera tube is 
distributed uniformly over the entire band. For this reason, when the 
high-pass filter 18 separates the high-band signal component Sh from the 
camera tube output signal S, the S/N ratio of the resulting high-band 
signal component Sh deteriorates greatly. 
Furthermore, in a color television system, in general, the band of a color 
signal considered to be necessary for color reproduction may be relatively 
narrow, for example, .+-. 500 KHz for an NTSC system. For this reason, it 
is more advantageous from the viewpoint of the S/N ratio to limit the band 
if this will not have a deleterious effect on color reproduction, with 
respect to also the high-band signal component Sh. 
Next to be described is a second embodiment (FIG. 8) of the invention, in 
which the above described problems associated with the high-pass filter 18 
have been solved. In FIG. 8, those parts which are the same as 
corresponding parts in FIG. 4 are designated by like reference numerals, 
and a detailed description of such parts will be omitted. 
In FIG. 8, a signal composing circuit 30 is used in place of the high-pass 
filter 18 shown in FIG. 4. The output signal S of the preamplifier 15 is 
supplied to the low-pass filters 16 and 17 and, at the same time, to 
band-pass filters 31 and 32 of the signal composing circuit 30. The 
band-pass filter 31 has a center frequency, a pass-band width, and cut-off 
characteristic required for extracting from the output signal S of the 
camera tube those frequencies which are in the vicinity of the carrier 
wave (fundamental signal) f1, which is a frequency determined by the 
number of groups of the filter stripes of the color-resolving striped 
filter. The band-pass filter 32 has a center frequency, pass-band width, 
and cut-off characteristic required for extracting from the output signal 
S of the camera tube those frequencies which are in the vicinity of the 
second harmonic wave signal f2. 
The fundamental wave output signal component of the band-pass filter 31 is 
supplied through a delay circuit 33 to an adder 34. The second harmonic 
wave output signal component of the band-pass filter 32 is supplied 
directly to the adder 34. 
In this case, the delay circuit 33 may be provided, if necessary, so that 
the output signals of the band-pass filters 31 and 32 supplied to the 
adder 34 will have the same time delay. Accordingly, the delay circuit 33 
may be provided on either the input side of the band-pass filter 31 or the 
output side of the band-pass filter 31. Furthermore, if the delay 
characteristics of the band-pass filters 31 and 32 are equal, this delay 
circuit 33 is unnecessary. 
The adder 34 mixes, in suitable proportions, and amplifies the fundamental 
wave signal component and the second harmonic signal component supplied 
thereto. The adder output is a composed harmonic signal component Shp, 
which is supplied to envelope detector circuits 19 and 22. This composed 
harmonic signal component Shp can be used in place of the above mentioned 
high-band signal component Sh, as will now be explained. 
When the high-band component signal Sh (FIG. 6(C)) is expanded in a Fourier 
expansion to determine the component up to and including the second 
harmonic, the following expression is obtained. This equation represents 
the content of the composed harmonic component signal Shp having a 
waveform as indicated in FIG. 9. 
##EQU2## 
When this Eq.(9) is arranged in the form of the sum of the fundamental wave 
signal component and the second harmonic component signal, the following 
equation is obtained: 
##EQU3## 
The envelope detector circuits 19 and 22 detect the peak value of the 
positive wave and the peak value of the negative wave of the composed 
harmonic signal component Shp, represented by the above Eq.(10). These 
peak values of the positive wave and the negative wave of the composed 
harmonic signal component Shp are determined in correspondence with the 
above Eq.(10). When this signal is differentiated, the resulting 
differential becomes zero. 
##EQU4## 
Eq.(11) becomes zero when .omega.t is .pi./3, -.pi./3, (.pi. + 2.phi.), or 
(2.phi. - .pi.). Of these cases, that wherein .omega.t is (.pi. + 2.phi.) 
or (2.phi. - .pi.) corresponds to the point of inflection, of intermediate 
value. Therefore, the value of .omega.t for maximum and minimum values of 
Eq.(10) are .pi./3 and -.pi./3. 
When .omega.t = -.pi./3 is substituted in Eq.(9), the peak value Shp1 of 
the positive wave of the composed harmonic signal component Shp becomes as 
represented by Eq.(12), below. When .omega.t = .pi./3 is substituted in 
Eq.(9), the peak value Shp2 of the negative wave becomes as represented by 
Eq.(13), below; 
##EQU5## 
When the signals Shp1 and Shp2 in these Eqs.(12) and (13) are compared with 
the signals Sh1 and Sh2 of Eqs. (4) and (5), it is seen that the signals 
Shp1 and Shp2 are merely the signals Sh1 and Sh2 respectively multiplied 
by a specific coefficient 9.sqroot.3/4.pi.. The mixture ratios of the two 
primary color signals respectively in Eqs.(4) and (12) and Eqs.(5) and 
(13) are the same. It is apparent, therefore, that merely by appropriately 
changing the circuit of the matrix circuit 21, three primary color signals 
SR, SG, and SB can be obtained. These color signals are the same as those 
obtained in the first embodiment as illustrated in FIG. 4 and the second 
embodiment as shown in FIG. 8. 
The instant embodiment of the invention affords the following advantageous 
features. 
1. In the composed harmonic signal component obtained by the signal 
composing circuit 30, there is no admixing of noise existing in a 
frequency band part which is unnecessary for reproduction of color 
signals. Therefore, color signals of a large S/N ratios can be obtained. 
2. By merely causing the fundamental wave signal component and the second 
harmonic signal component to have the same time delay and by adding these 
two signals, it is possible to carry out a delayed phase compensation of 
the signals of the entire color television camera system. 
3. The amplitudes of the two signals to be added by the adder 34 can be 
respectively adjusted to obtain a good color reproduction. 
Then, it is apparent from Eq.(10) that the amplitude component coefficient 
A of the fundamental wave component of the first term on the right side of 
the equation and the amplitude component coefficient A/2 of the second 
harmonic component of the second term on the right side are always in the 
ratio of 2:1. Furthermore, the phase angle .phi. is (+.phi.) with respect 
to the fundamental wave component and is (-.phi.) with respect to the 
second harmonic component. 
In general, the modulation characteristic of the camera tube is such that 
the degree of modulation drops abruptly as the frequency becomes high, the 
drop being a result of effects such as the beam aperture. Furthermore, 
because of effects such as the output capacity of the camera tube and the 
input capacity of the preamplifier, the attenuation increases with 
increasing frequency. The amplitude coefficient of the second harmonic 
component signal within the harmonic component signal derived from the 
camera tube output signal S is a value which is less than the value of 
A/2, which is necessary for faithful color reproduction. Consequently, the 
S/N ratio of the second harmonic signal component is smaller than the S/N 
ratio of the fundamental wave signal component. 
As a consequence, deterioration of the S/N ratio due to the above described 
cause will be present in this signal even if the fundamental wave signal 
component and the second harmonic signal component are added in specific 
proportions. The proportions are such that the amplitude component 
coefficients will become 2:1 with respect to the fundamental wave 
component and the second harmonic component, thereby forming a combined 
harmonic signal component. 
Accordingly, it was observed that the requirements which should be 
fulfilled by the combined harmonic signal components are: (1) that the 
amplitude component coefficients in the fundamental wave signal component 
and the second harmonic signal component always have the relationship of 
2:1, and (2) that the phase angle in the fundamental wave signal component 
and the phase angle in the second harmonic signal component have the 
relationship of (+.phi.), (-.phi.). 
Next, a third embodiment (FIG. 10) of the invention will be described. 
Color television signals having an even better S/N ratio than the ratio in 
the second embodiment can be generated by using only the phase variation 
part of a second harmonic signal component of a deteriorated S/N ratio. An 
amplitude variation is formed of the second harmonic signal component from 
the amplitude component of the fundamental wave signal component of good 
S/N ratio. In FIG. 10, those parts which are the same as corresponding 
parts in FIG. 4 are designated by like reference numerals. Description of 
such parts will be omitted. 
The output signal S of the preamplifier 15 is supplied to low-pass filters 
16 and 17 and, at the same time, to band-pass filters 41 and 42 of a 
signal combining circuit 40. Thus, the camera tube output signal S is 
applied to the band-pass filter 41 which has a pass-band filtering 
characteristic whereby it passes only a fundamental wave signal component 
in the vicinity of the carrier wave f1. The frequency f1 is determined by 
the number of groups of filter stripes of the color-resolving striped 
filter 10. The band-pass filter 42 has a pass-band filtering 
characteristic whereby it passes only a second harmonic signal component 
in the vicinity of the second harmonic f2 of the fundamental wave. 
The output fundamental wave signal component of the band-pass filter 41 is 
supplied by way of a delay circuit 43 to an adder 44 and, at the same 
time, to an amplitude demodulator 45, which supplies an amplitude signal 
component corresponding to an amplitude component coefficient A in 
Eq.(10). This amplitude signal component is sent through a low-pass filter 
46, which removes the undesirable signal component. The resulting signal 
is then supplied to a balanced modulator 48. 
The second harmonic signal component from the band-pass filter 42 is 
supplied to an amplitude limiter 47, where a phase-modulated wave 
component is extracted and supplied to the above mentioned balanced 
modulator 48. The balanced modulator 48 carries out a balanced modulation, 
with the amplitude signal component from the low-pass filter 46 acting as 
a signal wave and the phase-modulated wave component from the amplitude 
limiter 47 acting as a carrier wave. The balanced modulated wave output 
signal passes through a band-pass filter (low-pass filter) 49, where its 
undesired signal component is removed. Thereafter it is supplied to the 
adder 44, where it is mixed with a specific ratio and amplified with the 
fundamental wave signal component from the delay circuit 43. 
In this case, the phase modulated wave signal component extracted from the 
second harmonic signal component is balanced modulated in the balanced 
modulator 48 responsive to an amplitude signal component extracted from a 
fundamental wave signal component of large S/N ratio. For this reason, a 
second harmonic signal component is obtained, as represented by 
(A/2)sin(2.omega.t - .phi.), which is the second term on the right side of 
the above given Eq.(10). Therefore, from the adder 44, there is obtained a 
combined harmonic signal component which has the same signal constitution 
as the combined harmonic signal components obtained from the adder 34. 
Moreover, the adder output has an S/N ratio which has been improved over 
that of the latter signal. 
In Eq.(10), furthermore, the fundamental wave signal component and the 
second harmonic signal have a relationship of 2:1. For this reason, color 
reproduction, with a large S/N ratio, is possible without the occurrence 
of large color errors, even if only the amplitude component of either one 
of the two signals is used as the amplitude component. 
FIG. 11 shows an embodiment of the invention wherein the frequency 
component and the phase component are respectively used directly as they 
are, with respect to the fundamental wave signal component, the second 
harmonic signal component, and the amplitude component. In FIG. 11, those 
parts which are the same as corresponding parts in FIG. 4 are designated 
by like reference numerals, and description of these parts will be 
omitted. 
The output signal S of the preamplifier 15 is supplied to low-pass filters 
16 and 17 and, at the same time, to band-pass filters 51 and 52 of a 
signal composing circuit 50. A fundamental wave signal component (carrier 
wave) Shf1 in the vicinity of a fundamental frequency f1, is obtained from 
the band-pass filter 51 and supplied to an adder 53. A second harmonic 
signal component Shf2, in the vicinity of a second harmonic wave f2 of a 
carrier wave f1, is obtained from the band-pass filter 52. Signal Shf2 is 
amplitude limited by an amplitude limiter 54 and thus made a phase 
modulated signal component having a constant amplitude. This phase 
modulated signal component is added to the above mentioned fundamental 
wave signal component in the adder 53. 
In this instance, the second harmonic signal component is represented by 
the second term of the right side of Eq.(10). It is amplitude limited by 
the amplitude limiter 54. As a consequence, its amplitude coefficient A/2 
is a constant amplitude K, determined by amplitude limiter 54. 
Accordingly, the extracted phase modulated signal Shf2 is represented by 
the following equation: 
EQU Shf2 = Ksin(2.omega.t - .phi.) 
Therefore, the composed harmonic signal component Shf, which is led out of 
the adder 53, is represented as follows: 
EQU Shf = Shf1 + Shf2 = Asin(.omega.t + .phi.) + Ksin(2.omega.t - .phi.) (14) 
This composed harmonic signal component Shf is supplied to envelope 
detector circuits 19 and 22, where its positive wave and negative wave are 
envelope detected, and first and second demodulated primary color signals 
are respectively led out. In this instance, the signals obtained by the 
envelope detection are determining the maximum and minimum values of the 
above given Eq.(14). By differentiating this Eq.(14), 
##EQU6## 
is obtained. Then, the value of .omega.t which makes Eq.(15) equal to zero 
is substituted into Eq.(14). 
The mixing ratio of the adder 53 is set so that the coefficients A and K in 
Eq.(15) have the relationship A &lt;&lt; K. Then, the conditions for producing 
maximum and minimum values are: .omega.t = .phi./2 - .pi./4 and .omega.t = 
.phi./2 + .pi./4, by which cos (2.omega.t - .phi.) in Eq.(15) becomes 
zero. By substituting the above condition .omega.t = .phi./2 - .pi./4 for 
.omega.t in Eq.(14), the envelope detection output Shfp1 is determined 
with respect to the positive wave, as indicated by the following Eq.(16). 
By substituting the above condition .omega.t = .phi./2 + .pi./4 for the 
.omega.t in Eq.(14), the envelope detection output Shfp2 (with respect to 
the negative wave) is indicated by the following Eq.(17): 
##EQU7## 
The envelope detection outputs represented by these Eqs.(16) and (17) are 
demodulated primary-color signals. However, merely by observing these two 
equations, it is difficult to perceive immediately that they are 
demodulated primary-color signals. Accordingly, in order to facilitate an 
understanding, an example will be taken when a light of a specific color 
is introduced as incident light into the camera. Next to be described is 
the nature of the signals obtained from the envelope detector circuits 19 
and 22, respectively, at the time when this light of the specific color is 
introduced as incident light. 
The following table indicates the output signals Shfp1 and Shfp2 obtained 
respectively from the envelope detector circuits 19 and 22 when the 
incident light entering the camera is: a red light (the same with a yellow 
light, that is, the case where blue light is zero); a blue light (the same 
with a cyan light, that is, the case where red light is zero); and a 
magenta light (the same with a white light, that is, the case where red 
light and blue light are equally included). 
__________________________________________________________________________ 
Incident 
light 
Detection 
Red light Blue light 
Magenta light 
output (SB = 0) (SR = 0) 
(SR = SB) 
__________________________________________________________________________ 
Shfpl 
##STR1## - K 
##STR2## 
Shfp2 K 
##STR3## 
##STR4## 
__________________________________________________________________________ 
it is apparent that the coefficient K is a DC component; therefore, if K is 
zero, the DC component in the signal is removed. A red color signal SR 
will then be obtained by itself from the envelope detector circuit 19, and 
a blue color signal SB will be obtained by itself from the envelope 
detector circuit 22. 
If a comparison is made of the levels of the output signals produced by the 
envelope detector circuits 19 and 22 when a white light (or a magenta 
light) enters the camera as incident light and when a red light (or a blue 
light) only enters the camera as incident light, it is observed that the 
level in the former case becomes .sqroot.3/2 = 0.816 times the level in 
the latter case. This is apparent from the above table. Conversely stated, 
the level in the latter case is approximately 18 percent lower than that 
in the latter case, and the degree of saturation decreased by 
approximately 18 percent. However, a decrease of this order has almost no 
adverse effect in actual practice. 
The detected signals produced as outputs of the envelope detector circuits 
19 and 22 are respectively passed through low-pass filters 20 and 23. 
There, their carrier wave components are amply attenuated. Thereafter, the 
signals are respectively led out as a red light signal SR and blue light 
signal SB through output terminals 57 and 58 and, at the same time, 
supplied to a matrix circuit 55. The matrix circuit 55 matrixes a 
three-color mixture signal from the low-pass filter 17 and the demodulated 
primary-color signals SR and SB from the low-pass filters 20 and 23, with 
a specific amplitude ratio and polarity. As a result, in this instance, a 
green signal SG is produced as an output from the matrix circuit 55 and is 
led out through an output terminal 56. 
The spectral sensitivities of the lenses 12 and 13 used in the optical 
system of the camera may differ in parts. Fabrication errors may exist in 
the color-resolving striped filter 10. There may be irregularities in the 
spectral sensitivity of the photoelectric conversion layer of the camera 
tube 14. The shape of the spot of the electron beam of the camera tube 14 
may vary during scanning. The scanning velocity of the electron beam may 
vary in parts. A fluctuation having a detrimental effect on color 
reproduction may be produced in the phase of the modulated signal wave in 
the output signal S of the camera tube 14. In such a case, undesirable 
color shading is produced in the reproduced picture. 
Accordingly, the occurrence of this color shading can be prevented by 
eliminating the various causes mentioned above. However, carrying out 
countermeasures with respect to each of these causes is quite difficult in 
actual practice, and the apparatus becomes very expensive. In one 
embodiment of the present invention as described below, this color shading 
is prevented by a color shading correction circuit. 
FIG. 12 is a block schematic diagram showing one embodiment of a color 
shading correction circuit applied to the apparatus of the invention 
illustrated in FIG. 8. In FIG. 12, parts which are the same as 
corresponding parts in FIG. 8 are designated by like reference numerals. 
Detailed description of such parts will not be repeated. 
A signal generating circuit 60 generates a color shading correction signal 
and supplies it to a variable phase shifter 61. This variable phase 
shifter 61 also receives a fundamental wave signal component from the 
band-pass filter 31. A delay time imparted to this fundamental wave signal 
component is controlled in accordance with the color shading correction 
signal thus supplied. The variable phase shifter 61 comprises, for 
example, as shown in FIG. 15, coils L1 and L2 and a variable capacitance 
diode VC. Accordingly, a signal is supplied from the band-pass filter 31 
to an input terminal 62 of this variable phase shifter 61. During the 
interval before it reaches an output terminal 63 of this circuit, it 
receives a time delay in accordance with the capacitance value of the 
variable capacitance diode VC, which is varied by the correction signal 
applied through a terminal 64. 
The amount of time delay (i.e., the variation of phase) of the fundamental 
wave signal component constituting one part of the combined harmonic 
signal component is controlled in a manner to eliminate color shading in 
the reproduced picture. For this purpose, as described above, a color 
shading correction signal is generated by circuit 60 for controlling the 
amount of time delay. For this color shading correction signal, a wave 
such as, for example, a triangular wave or parabolic wave of horizontal 
scanning period, a triangular or parabolic wave of vertical scanning 
period, or a composite wave of these waves is used in accordance with the 
state of generation of color shading in the reproduced picture. 
FIG. 13 shows a modification of the apparatus shown by block diagram in 
FIG. 8 in which a variable phase shifter 61a is interposed between the 
preamplifier 15 and the signal combining circuit 30. 
In another embodiment of the apparatus as shown in FIG. 14, a variable 
phase shifter 61b is interposed between the preamplifier 15 and the 
high-pass filter 18 of the apparatus shown by block diagram in FIG. 4. 
Further, this invention is not limited to these embodiments but various 
variations and modifications may be made without departing from the scope 
and spirit of the invention.