Color TV camera with circuit for adjusting the white balance of red, green, and blue signals generated from a narrow-band luminance signal and line-sequential color-difference signals

A solid-state image sensor with a color separation, filter generates a luminance signal component and line-sequential color-difference signal components. Low-pass filters produce wide-band and narrow-band luminance signals from the luminance signal component. A synchronous detection circuit, a delay circuit, and a switching circuit produce simultaneous color-difference signals from the line-sequential color-difference signal components. A level control circuit adjusts the white balance of red, green, and blue signals produced from the narrow-band luminance signal and the simultaneous color-difference signals. A narrow-band luminance signal and simultaneous color-difference signals produced from the white-balanced red, green, and blue signals together with the wide-band luminance signal are encoded into a color video signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a solid state color television camera having a 
solid state image sensing device wherein an image signal processing is 
executed for generating a composite color video signal. 
2. Description of the Prior Art 
It has been customary in a color video camera to achieve a white balance 
control in order not to cause changes in a white part of an image due to 
the temperature of a light source. Also, in a single plate television 
camera, wherein the single solid state imager performs a color image 
sensing, a complementary color filter with a high light utilization 
efficiency is provided to an image sensing optical system as a color 
separating filter to perform a color iamge sensing by a field-accumulated 
image sensing device so as to improve an image sensing sensitivity or a 
dynamic resolution, etc. 
In such type of a color television camera, an imaging operation is 
performed using an image sensing element with a complementary color filter 
for color coding provided on its image sensing plane in which color 
filters of magenta (Mg), green (G), cyan (Cy), yellow (Ye), for example, 
are arranged in a mosaic pattern as seen in FIG. 2. Thus there is obtained 
an image sensing output which is an additive synthesis of signal electric 
charges of L.sub.(N) line and L.sub.(N+1) line as an image sensing output 
of an odd field. Similarly, an image sensing output which is an additive 
synthesis of signal electric charges of L.sub.(N+1) line and L.sub.(N+2) 
line is obtained as an image sensing output of an even field. From the 
aforementioned image sensing element with the complementary color filter, 
an image output (S.sub.o) wherein (Mg+Cy) output and (G+Ye) output are 
repeatedly produced and an image output (S.sub.E) wherein (Mg+Ye) output 
and (G+Cy) output are repeatedly produced are line sequentially produced. 
As shown in FIG. 3, in the conventional devices, a color video signal was 
formed by supplying the image sensing output obtained by the 
above-described image output element to an image sensing signal processing 
circuit. 
In FIG. 3, the numeral 20 indicates the image sensing element with said 
complementary color filter, 21 indicates a first low-pass filter 
(LPF.sub.H) that picks up a wide band luminance signal Y (Y.sub.H) from 
the image sensing output (S.sub.O)/(S.sub.E) obtained as a line sequential 
output by the image sensing element 20, 22 indicates a second low-pass 
filter (LPF.sub.L) that picks up a narrow band luminance signal (Y.sub.L 
') from the image sensing output, and 23 indicates a band-pass filter 
(BPF) that picks up a chroma signal (C) from the image sensing output. 
The first low-pass filter 21 forms a wide band luminance signal Y (Y.sub.H) 
by excluding a space sampling carrier component produced by the 
complementary color filter from the image sensing output 
(S.sub.O)/(S.sub.E). The wide band luminance signal Y (Y.sub.H) is 
supplied to a color encoder 39. 
Also, the second low pass filter 22, the cut-off frequency of which is 
lower than that of the first low-pass filter 21, forms a narrow band 
luminance signal (Y.sub.L ') by excluding a space sampling carrier 
component. This narrow band luminance signal (Y.sub.L ') is supplied to a 
signal adder 27, 28 as a white balance control signal (.+-..DELTA.Y) via a 
variable gain amplifier 24, 25. 
Further, in the band-pass filter 23, the space sampling carrier component 
produced by the complementary color filter, i.e. a chroma signal, is 
picked up from the image sensing output (S.sub.O)/(S.sub.E) to be supplied 
to a synchronous detection circuit 26. 
The synchronous detection circuit 26 performs a synchronous detection of 
the chroma signal picked up from the image sensing output 
(S.sub.O)/(S.sub.E) with a carrier signal corresponding to the space 
sampling carrier component so as to produce an output of a line sequential 
color difference signal (R-Y')/(B-Y'), hereinafter denoted by 
(C.sub.1)/(C.sub.2). 
Then, there is provided an additive synthesis of the white balance control 
signal (.+-..DELTA.Y) in the signal adder 27, 28 to the line sequential 
color difference signal (C.sub.1)/(C.sub.2) that was outgoing from the 
synchronous detection circuit 26, which is supplied to the simultaneous 
circuit 31 direct from a signal selecting circuit 29 or via a one 
horizontal period (1H) delay circuit 30. 
The line sequential color difference signal (C.sub.1)/(C.sub.2) to which a 
white balance control has been already achieved is converted from the line 
sequential system to the simultaneous system due to the simultaneous 
circuit 31. 
It is to be noted that when the color temperature of the object the image 
of which is picked up in the image sensing element 20 varies from the 
normally-set color temperature to the higher one, each color difference 
signal (C.sub.1)/(C.sub.2) changes the state indicated by a line to the 
state indicated by a chain-dotted line, both of which are shown in FIGS. 
4(A) and 5(A). Also, the luminance signal (Y) changes the state indicated 
by a line to the state indicated by a chain-dotted line in FIG. 6. 
Therefore, it is possible to execute a white balance control as shown in 
FIGS. 4(C) and 5(C), by generating a white balance control signal 
(.+-..DELTA.Y) indicated by the chain-dotted lines in FIGS. 4(B) and 5(B) 
from the narrow band luminance signal (Y.sub.L '), and by performing an 
additive and subtractive synthesis of said white balance control signal 
(.+-..DELTA.Y) with each color difference signal (C.sub.1)/(C.sub.2) such 
that the waveformed integral value shown in FIGS. 4(A) and 5(A) becomes 
zero. 
However, even by this white balance control, each color difference signal 
(C.sub.1)/(C.sub.2) changes its sensitivity due to the wave length, and 
results to have characteristics different from a spectral sensitivity 
(response) at the normally-set color temperature. 
Hence, in regard to the respective color difference signals 
(C.sub.1)/(C.sub.2) that were outgoing from the simultaneous circuit 31, 
it has been customary to perform a compensation beforehand to the changes 
of the color temperature in a color temperature control circuit 38, and 
then to generate a color video signal of a standard television system, 
such as an NTSC system, in a color encoder 39 to let it outgo from a 
signal output terminal 40. In this connection, the color temperature 
control circuit 38 is also called as a linear matrix circuit, where there 
is performed an additive synthesis of the respective color difference 
signals (C.sub.1)/(C.sub.2) in each signal adder 36, 37 via variable gain 
amplifiers 32, 33, 34, 35 wherein the gain varies according to the color 
temperature so as to control the spectral sensitivity characteristics. 
As earlier noted, with the known image sensing signal processing circuit 
wherein the white balance is controlled by providing an additive and 
subtractive synthesis of the white balance control signal (.+-..DELTA.Y) 
to each color difference signal (C.sub.1)/(C.sub.2), it becomes impossible 
to maintain the color reproducibility because of the change in the 
spectral sensitivity characteristics caused by the change of the color 
temperature. So it is necessary to provide a color temperature control 
circuit having complicated circuit structure in order to control the 
changes of the spectral sensitivity characteristics. 
OBJECTS AND SUMMARY OF THE INVENTION 
In view of the foregoing, it is an object of the present invention to 
provide a solid state color television camera with a novel structure, 
according to which, a composite color video signal with superior color 
reproducibility and luminance reproducibility against the color 
temperature changes can be generated without using a color temperature 
control circuit. 
More specifically, it is a feature of the present invention to provides a 
solid state color television camera having a solid state image sensing 
device with a color filter comprising a signal converting means, a signal 
separating means, a level control means, a matrix means and an encoding 
means. 
In a solid state color television camera of the present invention, a 
three-primary-color signal is generated from an image sensing output of a 
color difference line sequential system color video camera and a white 
balance control is achieved thereon, thus it requires no color temperature 
compensation. 
Other objects and advantages of the invention will be apparent in the 
following description, the appending claims and the accompanying drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT 
The invention of a solid state color television camera will now be 
described by way of example with reference to the accompanying drawings. 
In a schematic block diagram of FIG. 1, the numeral 1 indicates an image 
sensing element having a complementary color filter, 2 indicates a first 
low-pass filter (LPF.sub.H) by which a wide band luminance signal 
(Y.sub.H) is picked up from an image sensing output (S.sub.O)/(S.sub.E) 
obtained as a line sequential output by the image sensing element 1, 3 
indicates a second low-pass filter (LPF.sub.L) by which a narrow band 
luminance signal (Y.sub.L ') is picked up from the image sensing output, 
and 4 indicates a band-pass filter (BPF) by which a chroma signal (C) is 
picked up from the image sensing output. 
In the present embodiment, a complementary color filter for color coding 
with the arrangement shown in FIG. 2 is provided on the image sensing 
plane of the image sensing element 1 so as to produce a line sequential 
output of an image sensing output (S.sub.O)/(S.sub.E) of an object image. 
The aforementioned first low-pass filter 2 generates a wide band luminance 
signal (Y.sub.H) by excluding a space sampling carrier component produced 
by the complementary color filter from the image sensing output 
(S.sub.O)/(S.sub.E). This wide band luminance signal (Y.sub.H) is supplied 
to a color encoder 14. 
The second low-pass filter 3 has a cut-off frequency lower than that of the 
first low-pass filter 2, and forms a narrow-band luminance signal (Y.sub.L 
') by excluding the space sampling carrier component. This narrow band 
luminance signal (Y.sub.L ') is supplied to a first matrix circuit 8 for 
separating a three-primary-color signal. 
Also, in the band-pass filter 4, the space sampling carrier component 
produced by the complementary color filter, i.e. a chroma signal, is 
picked up from the image sensing output (S.sub.O)/(S.sub.E) and is 
supplied to a synchronous detection circuit 5. 
In the synchronous detection circuit 5, the chroma signal (C) picked up 
from the image sensing output (S.sub.O)/(S.sub.E) is synchronously 
detected by a carrier signal corresponding to the space sampling carrier. 
In such manner, there is generated a composite color difference signal 
(C.sub.1) that is given by 
##EQU1## 
to the image sensing output. Also, there is generated a composite color 
difference signal (C.sub.2) that is given by 
##EQU2## 
to the image sensing output (S.sub.E), thus, producing an output of a line 
sequential color difference signal (C.sub.1)/(C.sub.2) or (B-Y')/(R-Y'), 
hereinafter denoted as (R-Y')/(B-Y'). 
It should be noted that said (Y') is a luminance signal obtainable by 
excluding the space sampling carrier component from the image sensing 
output (S.sub.O)/(S.sub.E), and can be indicated as 
##EQU3## 
The line sequential color difference signal (C.sub.1)/(C.sub.2) that was 
outgoing from the synchronous detection circuit 5 is supplied directly or 
via 1H delay circuit 6 to a simultaneous circuit 7, wherefrom conversion 
from the line sequential system to the simultaneous system is executed. 
The simultaneous color difference signal (C.sub.1), (C.sub.2) thus obtained 
in the simultaneous circuit 7 is supplied to the first matrix circuit 8. 
In the first matrix circuit 8, in regard to the low-pass luminance signal 
(Y.sub.L ') and each color difference signal (C.sub.1), (C.sub.2), a 
matrix processing as 
##EQU4## 
is executed to separate a three-primary-color signal (R).(G).(B). For the 
respective matrix constants, the spectral characteristics of each signal 
(Y.sub.L ').(R-Y').(B-Y') is taken into consideration, for example, 
setting a value such that when in search of R signal, G and B elements are 
restricted. 
The three-primary-color signal (R).(G).(B) separated by the first matrix 
circuit 8 is supplied to the second matrix circuit 13 via a level control 
circuit 12 for a white balance control constructed by the amplifier 10 and 
the variable gain amplifiers 9 and 11. 
From the aforementioned second matrix circuit 13 there is formed a narrow 
band luminance signal (Y.sub.L) and each color difference signal 
(R-Y).(B-Y) both of which are supplied to a color encoder 14 by executing 
a reverse matrix processing of the first matrix circuit 8 on the 
three-primary-color signal (R).(G).(B) supplied via the level control 
circuit 12 to which a white balance control being already executed. 
Also, said color encoder 14 forms a color video signal of a standard 
television system, such as an NTSC system, based on a narrow band 
luminance signal (Y.sub.L) and each color difference signal (R-Y).(B-Y) 
supplied from the second matrix circuit 12 to which a white balance 
control being already executed and a wide band luminance signal (Y.sub.H) 
supplied from the first low-pass filter 2. The color video signal thus 
formed is outgoing from the signal output terminal 15. 
In this embodiment, three-primary-color signal (R).(G).(B) is separated 
from the line sequential color difference signal (C.sub.1)/(C.sub.2) and a 
narrow band luminance signal (Y.sub.L ') obtained from an image sensing 
element 1 as an image sensing output, and a white balance control is 
achieved on the thus separated three-primary-color signal (R).(G).(B). 
Then, based on the narrow band luminance signal (Y.sub.L ') and each color 
difference signal (R-Y).(B-Y) reformed from the three-primary-color signal 
(R).(G).(B) to which the white balance control being already achieved, a 
composite color video signal is generated. Hence, because of the white 
balance control it follows that a control against the color temperature 
change is also achieved. In this manner, without providing a specific 
color temperature compensation circuit, it is possible to realize a high 
color reproducibility and high luminance reproducibility closely related 
to a color image sensing device using a primary color filter. 
As is evident from the description given above with the embodiment, in the 
solid state color television camera of the present invention, a composite 
color video signal is formed by forming a three-primary-color signal from 
an image sensing output of a color difference sequential system color 
video camera, executing a white balance control to a primary color signal, 
and obtaining a luminance signal (Y.sub.L) and respective color difference 
signals (R-Y).(B-Y) from the three-primary-color signal on which the white 
balance control being already achieved. Accordingly, without providing a 
specific color temperature compensation circuit, the control to the color 
temperature changes is executed by the aforementioned white balance 
control. As a result, it is possible to attain the desired end of a high 
color reproducibility and high luminance reproducibility closely related 
to a color image sensing device using a color filter. 
Although an illustrative embodiment of this invention has been described in 
detail herein with reference to the accompanying drawings, it is to be 
understood that the invention is not limited to that precise embodiment, 
and that various changes and modifications could be effected therein by 
one skilled in the art without departing from the scope or spirit of the 
invention as defined in the appended claims.