Solid-state color imaging apparatus for preventing color alias

A color solid-state imaging apparatus includes a color solid-state image sensor that produces a color image output signal. This output signal includes horizontal scanning line signals. Different signals are produced by amplifying the levels of these horizontal scanning line signals by different amounts. By substracting the amplified signals, a difference signal can be produced. The amount of amplification is adjusted such that this difference signal is zero when the solid-state image sensor is detecting an image of a predetermined color.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention relates to a solid-state color imaging apparatus 
arranged to obtain a color television signal by the use of a solid-state 
image sensor such as a CCD (Charge Coupled Device) or a MOS type color 
image sensor. 
Various types of solid-state color image sensors each combined with a color 
filter have hitherto been developed. The output signals of the solid-state 
color image sensor include luminance information and chrominance 
information. The former information is obtained by passing the output 
signal of the solid-state color image sensor through a low-pass filter, 
and is used as a luminance signal (Y). The latter information, the 
chrominance is obtained by passing the output signal from the solid-state 
color image sensor through a band-pass filter. This latter information, 
i.e., chrominance information, is separated into red information and blue 
information, by a separating means. This separating means includes a one 
horizontal line period (hereinafter, referred to simply as 1-H) delay 
circuit, an adder, and a subtractor. In the adder non-delay chrominance 
information constituting an output of the band-pass filter and delay 
chrominance information constituting an output of the 1-H delay circuit 
are added together, whereby red information is obtained from this adder. 
On the other hand, in the subtractor, subtraction is performed between the 
non-delay chrominance information and the delay chrominance information. 
Blue information is obtained from this subtractor. The red and blue 
information are subjected to detection by a detector, to become a red 
signal (R) and a blue signal (B), respectively. The red signal (R), blue 
signal (B), and luminance signal (Y) are inputted into an encoder, in 
which a color video signal is composed with the use of these input 
signals. 
In order to obtain a color signal from the output signal of the solid-state 
color image sensor in the above-mentioned way, it is necessary to perform 
an operation between the chrominance information of one horizontal line 
and that of another horizontal line which is adjacent thereto. That is to 
say, the red signal (R) and the blue signal (B) are obtained using 
vertical correlation between the two adjacent horizontal lines. 
Accordingly, a means for performing said operation generates a color alias 
with respect to that portion of the foreground to be picked up which has 
no vertical correlation. Namely, a conventional color signal separation 
circuit carries out its operation based on the assumption that a vertical 
correlation exists between the colors and brightness of the foreground. 
When the foreground contains a portion where no vertical correlation 
exists between its color and that of the background (i.e. when the color 
and/or brightness of that particular portion of the foreground are in 
sharp contrast with the color and/or brightness of the background) the 
video images of the foreground and background contain a color alias at 
their boundaries. 
Further, as mentioned above, the conventional circuit is arranged so that 
the red information and blue information are subjected to detection by a 
detector, to become a red signal (R) and a blue signal (B), respectively, 
which are inputted into the encoder. In the encoder, the red signal (R) 
and the blue signal (B) are matrixed, whereby a green signal (G) is 
prepared. In the encoder, thereafter, the red signal (R), blue signal (B), 
green signal (G), and luminance signal (Y) are composed. According to 
circumstance, in order to simplify the circuit, the red signal (R), the 
blue signal (B) and the luminance signal (Y) may be directly used for 
obtaining the TV iignal without the green signal being made. In such 
cases, the linearity of the signals are important factors in determining 
the white tracking, white balance, and hue correction of the picture. 
However, since the conventional color signal separation circuit is such 
that the blue information and red information are subjected to AM 
detection, where a signal having a low brightness level in particular is 
processed, the white balance deteriorates because the linearity of the 
detector circuit (diode detector circuit) is bad. That is, it is difficult 
to obtain a uniform white balance from high to low illumination portions 
of a subject. Further, for the R, G, B and Y signals, corresponding to 
signals (which are obtained through filters having good spectrum 
sensitivity), a color adjustment circuit is provided in many cases. The 
color adjustment circuit use the R, G, B and Y signals in its 
calculations. However, the white balance deteriorates because the signal 
ratio is hhanged by the calculations. Further, if all combinations between 
R, G, B and Y signals are calculated, the calculation circuit becomes 
complicated and the adjustment is complex. For this reason, the adjustment 
can not be achieved in a limited adjusting width. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the above-mentioned 
circumstances and its object is to provide a solid-state color imaging 
apparatus which is capable of eliminating the color alias, thereby 
improving the quality of the picture. 
Another object of the present invention is to provide a solid-state color 
imaging apparatus which permits the white balance to be stably maintained 
in the picture and which makes it possible to easily adjust the hue 
correction. 
In order to achieve the above objects, the present invention provides a 
solid-state color imaging apparatus comprising: a solid-state color image 
sensor intended for outputting color image information, and a color signal 
information processing means, intended for obtaining first and second 
difference signals. The solid state color image sensor has a color filter 
in which the first and second horizontal scanning picture element array 
are alternately set in the vertical direction. First and second color 
signal information is obtained from the first horizontal scanning picture 
element array, and third and fourth color signal information is obtained 
from the second horizontal scanning picture element array. The color 
signal information processing means includes; a separating means coupled 
to the solid-state color image sensor which is intended to separate the 
first, second, third and fourth color signal information pieces, an 
amplifying means in which said four color signal information pieces are 
grouped into two sets each consisting of two arbitrarily selected color 
signal information pieces, and in which the gains of the respective color 
signal information pieces constituting each set are so set that when a 
foreground portion having one color is photographed, the first difference 
signal (which indicates the difference between the color signal 
information pieces constituting a first set of said two sets), and the 
second difference signal (which indicates the difference between the color 
signal information pieces constituting a second set of said two sets), may 
be zero. It also has subtracting means to which are inputted thsse signals 
from the amplifying means which are subjected to gain control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a solid-state color imaging apparatus according to an 
embodiment of the present invention. A solid-state color image sensor 11 
has a color filter array 20 shown in FIG. 2 with respect to its picture 
elements. In the color filter array 20, W, G, Ye, and Cy represent the 
following filter portions, respectively. 
W . . . white color light transmission filter portion, 
G . . . green color light transmission filter portion, 
Ye . . . yellow color light transmission filter portion, and, Cy . . . cyan 
color light transmission filter portion. The filter portions W, G, Ye, and 
Cy correspond to the picture elements which constitute photoelectric 
conversion elements. 
The output signal of the solid-state colo image sensor 11 is inputted into 
a one horizontal line period delay circuit 17 and an adder 18, which 
together constitute a composing means, and also inputted into a signal 
separation circuit 12. The adder 18 adds the output signal of the 
solid-state color image sensor 11 to the output signal of the 1-H delay 
circuit 17. Assuming now that the output signal of the adder 18 is S3, 
##EQU1## 
The S3 indicates a fundamental composite signal for demodulating the R, G 
and B signals at an aftermentioned operation circuit 19. In the above 
formula (1), the Ws, Gs, Ys, and Cs represent the following signal 
amounts. 
Ws=white signal amount (=R+G+B) 
Gs=green signal amount (=G) 
Ys=yellow signal amount (=R+G), and 
Cs=cyan signal amount (=G+B) 5 
Letters R, G, and B represent the red, green and blue signal amounts, 
respectively, which are contained in the output signals of the picture 
elements. The signal separation circuit 12 can be constituted, for 
example, by a sample and hold circuit or a gate circuit. 
The signal separation circuit 12 separates the output signal from the 
solid-state color image sensor with respect to each individual picture 
element. That is to say, with respect to the nth line, the circuit 12 
separates the output signal Ws of the picture element corresponding to th 
whole color light transmission filter portion (W) and the output signal Gs 
of the picture element corresponding to the green color light transmission 
filter portion (G). With respect to the (n+1)th line, the circuit 12 
separates the output signal Ys of the picture element corresponding to the 
yellow color light transmission filter portion (Ye) and the output signal 
Cs of the picture element corresponding to the cyan color light 
transmission filter portion (Cy). Namely, with respect to the nth line, 
the signals: 
##EQU2## 
are obtained from the signal separation circuit 12. With respect to the 
(n+1)th line, the signals: 
##EQU3## 
are obtained from this circuit 12. 
The signals (a1) and (b1) of the above formula (2) or (3) which have thus 
been obtained from the signal separation circuit 12 are inputted into a 
gain control circuit 13. This gain control circuit 13 gain-controls one or 
both of the two input signals (a1) and (b1) and produces the two 
gain-controlled output signals (a2) and (b2) which are inputted into a 
subtractor 14. In the gain control circuit 13, gain control is previously 
made so that the difference between the output signals (a2) and (b2), when 
an image having some color is picked up by the image sensor, is zero. The 
"image having some color" is nne having a white (achromatic) color, for 
example. 
Accordingly, when the white object has been imaged on the entire screen of 
the solid-state image sensor 11, gain control is made such that a2 (Ws)=b2 
(Gs) with respect to the nth line; and a2 (Ys)=b2 (Cs) with respect to the 
(n+1)th line, by previously rearranging the characteristic of the gain 
control circuit 13. In these formulae, the symbols parenthesized indicate 
the filter portions corresponding to the output signals a2 and b2, 
respectively. The gain control circuit 13 contains a first amplifier for 
amplifying the signal (a1) and a second amplifier for amplifying the 
signal (b1), the gain of said second amplifier being changed over to 
.alpha. or .beta. with respect to each horizontal line so as to cause the 
formulae (6) and (7), as later described, to be established. The gain 
control circuit 13 may contain a first amplifier for amplifying the signal 
(a1) and second and third amplifiers for amplifying the signal (b1). In 
this case, the second and third amplifiers have their gains set to .alpha. 
and .beta. respcctively, as later described, and (with respect to the nth 
line) the output of the second amplifier is drawn out by a switch while 
(with respect to the (n+1)th line) the output of the third amplifier is 
drawn out by a switch. 
Assume now that the entire screen of the solid-state image sensor is 
photographed with a white colored image and that the signal amounts 
contained in the output signals of the picture elements are represented by 
Ws(wh), Gs(wh), Ys(wh), and Cs(wh). At this time, the two output signals 
a2 and b2 of the gain control circuit 13 are expressed as follows: with 
respect to the nth line, 
##EQU4## 
(the reference signal is Ws); and with respect to the (n+1)th line, 
##EQU5## 
(the reference signal is Ys). Hereinafter, for simplification, 
##EQU6## 
Assume now that the difference signal of the subtractor 14 obtained with 
respect to the nth line is S1 while the difference signal of the 
subtractor 14 obtained with respect to the (n+1)th line is S2. Then, these 
difference signals S1 and S2 are expressed as follows. Namely, 
EQU S1=Ws-.alpha.Gs . . . (6) 
EQU S2=Ys-.beta.Cs . . . (7) 
Accordingly, from the subtractor 14, the signal S1 or S2 is alternately 
obtained with respect to each horizontal line. 
The color signals R, G and B are prepared with the use of the 
above-mentioned signals S1 and S2 and the above-mentioned signal S3 from 
the adder 18. However, since the signal S1 or S2 is alternately obtained 
with respect to each line, these signals S1 and S2 are required to be 
synchronized with each other so as to be simultaneously inputted into 
specified terminals of an operation circuit 19 with respect to whatever 
line on which the scanning operation is being performed. The means whereby 
suc synchronization is performed is a one horizontal line period delay 
circuit 15 and a one horizontal line period changing over switch 16. That 
is to say, the output signal from the subtractor 14 is inputted into one 
input terminal of the 1-H changing over switch 16 as well as into the 1-H 
delay circuit 15. To the other input terminal of the 1-H changing over 
switch 16 is inputted an output signal from the 1-H delay circuit 15. The 
1-H changing over switch 16 has an output terminal for the signal S1 and 
an output terminal for the signal S2. Its input signal is alternately 
changed over to a mode shown in FIG. 1 by a broken line, or a second mode 
shown in FIG. 1 by a one-dot chain line, with respect to each scanning 
line. Thus, the signals S1 and S2 are synchronized and then inputted into 
the operation circuit 19. For example, a horizontal synchronizing pulse 
which is used to drive the color image sensor 11 is used as a control 
signal for controlling the 1-H changing over switch 16. Thus, the signals 
S1, S2 and S3 are inputted into the operation circuit 19. 
Preparing the signal S3 is possible without using the 1-H delay circuit 17. 
In this case, the line from the solid-state image sensor to the 1-H delay 
circuit 17 and the adder 18 is cut off, then the signals S1, S2 are 
inputted into the adder 18 as shown FIG. 1 by one-dot chain lines. 
That is, it is also possible to prepare the signal S3 with the use of the 
not gain-controlled signals al and bl which constitute the output signals 
of the sample and hold circuit 12. In this case, with respect to the nth 
line, 
EQU S3=Ws+Gs=R+2G+B . . . (8) 
and, with respect to the (n+1)th line, 
EQU S3=Ys+Cs=R+2G+B . . . (9). 
Another way of preparing the signal S3 is possible without using the 1-H 
delay circuit 17 and the adder 18. In this case, the output signal from 
the solid-state image sensor is used, as it is, as the signal S3. The 
signal S3 can be disclosed by the formulas (8), (9). 
The color signal information processing circuit which is enclosed by a 
broken line of FIG. 1, and which has been explained above, effectively 
works to prevent the generation of a color alias. That is to say, in the 
gain control circuit 13, the gains .alpha. and .beta. of the amplifiers 
which have previously been explained in connection with the formulas (4) 
to (7) are controlled. Namely, the gain control circuit 13 is so set that 
when the screen of the sensor 11 obtains an image which is a white-colored 
image, Ws=.alpha.Gs and Ys=.beta.Cs with the result that the difference 
signals S1 and S2 are zero. These difference signals S1 and S2 are 
prepared from the output signals obtained by scanning a single horizontal 
line. At the stage where the signals S1 and S2 have been obtained, 
therefore, even if a foreground portion having no vertical correlation in 
brightnsss is imaged in a video screen, the output signal obtained by 
scanning an adjacent horizontal line is prevented from affecting the 
output signal obtained by scanning the present horizontal line. As a 
result, the generation of a color alias is prevented. The gains .alpha. 
and .beta. of the amplifiers contained in the gain control circuit 13, as 
stated before, were controlled so that, in the state wherein the entire 
hhite color image is picked up by the image sensor, the signals S1 and S2 
may become zero. The reason for this is that the reproduction of false 
colors in the white-colored picture image in particular is prominent. 
The operation circuit 19 is a circuit which is intended to obtain the 
signals R, G, and B necessary for composing color video signals by using 
the signals S1, S2, and S3. The operation coefficients in the operation 
circuit 19 are determined when the respective color signals outputted 
therefrom are SR, SG and SB, as follows. 
The signals S1, S2 and S3 can be expressed, as follows using the 
expressions in formulae (1)-(7). 
##EQU7## 
Assume now that M is defined as follows. 
##EQU8## 
Then, the signal amounts SR, SG, and SB of the signals R, G, and B are 
expressed with the use of the inverse matrix, as follows. 
##EQU9## 
Accordingly, by setting into the operation circuit 19 the operation 
coefficients shown in the formula (12) above, it is possible to obtain the 
signals R, G and B necessary for composing the color video signals. The 
signals SR, SG, and SB which have been composed through the calculation 
made in the operation circuit 19 are inputted into an encoder 20 and thus 
become color video signals of standard format. 
In the above-mentioned signal processing operation, where the white color 
image is pick up by the image sensor, S1=S2=0 even when a difference 
exists between the nth line add the (n+1)th line in respect of brightness 
level. Accordingly, in this case, each of the signals SR, SG, and SB is 
prepared from the signal S3 in the following form. 
##EQU10## 
The respective coefficients of the signals S3 in the above formula (13) are 
intended to make the ratio between the signals SR, SG, and SB 1:1:1 under 
the state of white balance. 
Further, as is obvious from the formula (13), if the respective 
coefficients of the signals S3 are set to 1, the ratio between the signals 
SR, SG, and SB is 1:1:1. Therefore, in the formula (12), when the 
respective coefficients of the signals S3 are set to 1 and the other 
coefficients are normalized according to the signals S3, the white balance 
can be obtained in a balanced state. 
In this case, the signal amounts of SR, SG, and SB of respective signals R, 
G and B are shown in the following formula (14). 
##EQU11## 
In the present invention, as long as the color of a foreground subject is 
white, the requirement of S1=S2=0 is satisfied. Therefore, the formula of 
SR:SG:SB=1:1:1 is established even when a difference exists between the 
portions of the foreground as vertically viewed in respect of brightness 
level. The color of the reproduced foreground portion is white and it is 
not possible for any false signal to be generated. That is, at the stage 
where the output signals SR, SG and SB have been obtained from the 
operation circuit 19, a good state of white balance is already obtained. 
Usually, a final hue adjustment in the camera is performed by photographing 
a standard color chart such as, for example, a color bar chart in advance 
and viewing a color monitor. This adjustment is performed by adjusting the 
signal amounts of the signals Y, R and B inputted into the encoder, 
through the operation between these signals Y, R and B. In the prior art 
color signal processing circuit, however, in some cases when the hue 
adjustment is performed, since the signal ratios between signals Y, R and 
B are changed, the white balance is lost. Therefore, the white balance 
adjustment is again required. As a result, the adjustment is complicated 
and the width of adjustment latitude is small. 
In contrast, according to the present invention, the hue correction is 
achieved at the same time as the color separation by the coefficients of 
S1, S2 in the M.sup.-1 of formula (12), which are changed. In this case, 
the width of adjustment for the color signal is large and the adjustment 
can be performed independently corresponding to eahh color signal. 
Further, since the formula S1=S2=0 has been obtained for the foreground, 
the hue correction can be provided iddependent of the white being 
balanced. 
Accordingly, the latitude with which the hue adjustment can be performed is 
made wider. Thus, the present invention can contribute to obtaining a 
video image having good reproduced colors. 
The standard color television signal is made by using the above-mentioned 
R, G and B signals. However, when the number of picture elements in the 
horizontal direction of the solid-state image sensor becomes small, the 
resolution in the horizontal direction may be insufficient. In this case, 
R, G, B and Y signals are produced by using an output signal which is 
obtained from every other picture element in the horizontal direction. The 
resolution in the horizontal direction is thereby improved by the output 
from the solid-state image sensor. The resolution is improved, when R, G 
and B signals obtained from the invention system are used as the 
chrominance signal, and when the output signal from the solid-state image 
sensor is used, as it is, as the luminance signal. 
The solid-state color image sensor and color filter which are used in the 
present invention are not limited to those which have been used in the 
above-mentioned embodiment. 
In the above-mentioned embodiment, the solid-state color image sensor 
wherein its picture element and the filter portion of its color filter 
array are 1:1 was explained. However, the arrangement of the picture 
elements may be of the type wherein, as shown in FIG. 3 by broken lines, 
one picture element in one horizontal line is shifted 180.degree. from its 
corresponding picture element in an adjacent horizontal line. In this 
case, the color filter 23 is such that strip-like filter portions Ye, W, 
Cy and G are repeatedly arranged side by side in the horizontal direction. 
In this type of color picture image sensing means as well, the operation 
processing is carried out by using the output signals of 2.times.2 picture 
elements as the operation units, i.e., horizontal two picture elements and 
vertical two picture elements. In this type of color picture image sensing 
means, the output signal of, for example, the picture element 24 is a 
composite signal of the signals sensitive to the lights passed through the 
filter portions (Ye) and (W). The output signal of the picture element 25 
is a composite signal of the signals sensitive to the lights passed 
through the filter portions (Cy) and (G). The output signal of the picture 
element 26 is a composite signal of the signals sensitive to the lights 
passed through the filter portions (W) and (Cy). Further, the output 
signal of the picture element 27 is a composite signal of the signals 
sensitive to the lights passed through the filter portions (G) and (Ye). 
The output signals of these picture elements 24, 25, 26 and 27, in 
combination, are used as the basic operation units, whereby the processing 
of the operation involved is carried out. Where said color picture image 
sensing means is used, a good horizontal resolution is obtained. Since the 
strip-like color filter portions are arranged in the form of a stripe, 
manufacture of the filter is easy. 
In the above example, the operation processing was carried out by using the 
output signals of 2.times.2 picture elements as the basic operation units, 
i.e., horizontal two picture elements and vertical two picture elements. 
However, the operation processing can also be performed by using as the 
basic operation units the output signals of 2.times.4 picture elements. In 
this case, color filters 28 and 29 which are shown in FIGS. 4A and 4B are 
used. 
According to the image sensor having the color filter 28 or 29, output 
signals from two picture elements (divided into high and low signals 
adjacent to one another) are added and read out as horizontal signals, and 
the combination of the picture elements, to be interlaced, is changed in 
each field. 
Where the image sensor which uses the color filter 28 or 29 is used with 
respect to an odd field, the information in the nth line, the (n+1)th 
line--are read out as shown and, with respect to an even field, the 
information in the (n+263)th line, the (n+264)th line --are read out as 
shown. Therefore, the cyclic period in which the information of the 
picture elements in this image sensor is read out is 1/2 of the cyclic 
period in which the information of the picture elements in the image 
sensor having the filter array of FIG. 2 is read out. Accordingly, in the 
case of this color image sensing means, the time period in which the 
information of each picture element is accumulated is 1/2 of the time 
period required in the case of the image sensor described in the preceding 
first embodiment (FIG. 1). In this color image sensing means, therefore 
offers the advantage that the residual images are lessened. 
The color image sensor used in the present invention is not limited to the 
type which has been used in the preceding first embodiment. That is to 
say, the technical concept of the present invention is not limited to the 
above-mentioned method whereby the output signals are drawn out from the 
picture elements and the above-mentioned method whereby such signals are 
gain-controlled. 
FIG. 5 shows another embodiment of the present invention. In FIG. 5, the 
same parts or sections as those which appear in FIG. 1 are denoted by like 
reference numerals. The solid-state color image sensor 31 used in this 
second embodiment is one which is capable of reading out the output 
signals of picture elements corresponding to four picture elements (two 
horizontal picture elements and two vertical picture elements), through 
four lines, simultaneously. Accordingly, tee use of this type of image 
sensor eliminates the necessity of providing the sample and hold means and 
synchronizing means provided in FIG. 1. By composing the signals (Ws, Gs, 
Ys and Cs) read out from the image sensor 31 having the color filter array 
shown in FIG. 2 through the operation of an adder 36, the signal S3 is 
obtained. Further, if the signal Gs is gain-controlled in a gain control 
circuit 32 and the operation of (Ws-.alpha.Gs) is performed in a 
subtractor 34, the signal S1 will be obtained. Further, if the signal Ys 
is gain-controlled and the arithmetic operation of (Ys-.beta.Cs) is 
carried out in a subtractor 35, then the signal S2 will be obtained. That 
is, in the subtractors 34 and 35, the operations in the above-mentioned 
formulae (6) and (7) are performed. It should be noted here that the gains 
.alpha. and .beta. of the gain control circuit 32 are previously 
controlled so that S1=S2=0 under the condition wherein a white-colored 
foreground portion is picked up by the image sensor over the entire screen 
of the image sensor. 
In the foregoing description, when subtraction is performed, the output 
signals of two horizontally adjacent picture elements were used as one set 
of signals. This indicates that, for example under the condition wherein 
the white-colored foreground portion is entirely picked up by the image 
sensor, generation of color alias is prevented even when a great 
difference in brightness exists between the vertical portions of the video 
image. 
The present invention is not limited to said combination of operational 
factors (output signals of picture elements). That is, as shown in FIG. 5 
by broken lines, the output signal of the gain control circuit 33 is 
inputted into the subtractor 34 and the output signal of the gain control 
circuit 32 is inputted into the subtractor 35, as another combination. In 
this case as well, the gain of each gain control circuit 33 or 32 is so 
controlled that S1=S2=0 under the condition wherein the white colored 
foreground portion is entirely picked up by the image sensor. When the 
operational factors are combined in that way, the following operations are 
performed. Namely, 
EQU S1=Ws-.alpha.'Ys 
EQU S2=Cs-.beta.'Gs, and 
EQU S3=Ws-Ys-Cs-Gs 
Since the operational factors for obtaining the difference signals S1, S2 
and S3 are the output signals of the picture elements as vertically 
arranged, the generation of color alias is lessened even when a great 
difference in brightness exists between the horizontal portions of the 
video image. That is, the color alias which may appear at the vertical 
edge portions of a reproduced picture image can be decreased. Further, 
when a difference signal is obtained by using the signals corresponded to 
the picture elements on the diagonal line, the color alias in the inclined 
direction can be eliminated. 
The type of output signal of the present invention is not limited to said 
standard color TV signal. That is, the type of output signal may be 
transformed according to the apparatus which needs the outuut signal of 
the color image system. R, G, B signals are used as they are, for example, 
when a monitor television set has terminals that can be input R, G and B 
signals. Further, when a magnetic recording reproducing apparatus needs 
the output signal of the color image system, the preferred type of output 
signal is the chrominance and luminance signal. 
As stated above, according to the present invention, the false signals 
which may be generated from the edges of a foreground portion as viewed in 
a specified direction can be lessened in accordance with the method of 
combination of the two difference signals. Further, the degradation in the 
detection characteristic of the detector conventionally used in the signal 
processing of such things as the frequency separation process, can be 
covered by the high linearity of the signal separation circuit, whereby 
the color displacements when the image is low in illumination are 
improved. Further, hue corrections can be individually performed according 
to each color signal without disturbing the white balance. 
Further, in the case of the on-wafer filter wherein color filters are 
directly formed on the solid-state image sensor, it is generally known 
that the lens-like effect is produced due to the variation in shape of its 
surface with the result that a balanced signal, from the respective 
picture elements, is lost. This phenomenon is also prevented from 
occurring, at the stage where the difference signals are gain-controlled. 
As a result, a picture signal of good quality can be obtained. As stated 
above, the present invettion can solve the problems which are inherent in 
the prior art and contribute to obtaining a high grade of reproduced color 
picture images.