JPH03205992A - Solid-state color camera - Google Patents

Abstract

PURPOSE:To satisfactorily reproduce colors by providing a means to separate the colors of linear sequence signals to be outputted from an image pickup element and a means to generate three primary colors R, G and B from the four kinds of chrominance signals which colors are separated. CONSTITUTION:Prescribed color separation filters are arranged at an image pickup element 1 and the output signals become the dot sequence signals of the chrominance signals corresponding to the kinds of the color separation filters. A color separating circuit 3 separates the colors of the dot sequence signals corresponding to the kind of the corresponding color separation filters. The linear sequence signal to be outputted from the color separating circuit 3 is synchronized with a signal delaying the linear sequence signal for one horizontal period by 1H delay circuits 41 and 42 by a switch circuit 5 and a matrix circuit 6 calculates the synchronized chrominance signal and generates the R, G and B signals. Thus, even when a ratio among three primary color components is slightly changed in the beam splitting characteristic of the color filter, the R, G and B signals can be exactly reproduced and satisfactory color reproducibility can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state color camera using a solid-state imaging device such as a COD.

[Conventional technology]

Solid-state color cameras for home use are generally single-chip cameras configured to obtain color video signals using a single solid-state image sensor. As one method of a single-chip solid-state camera, a method is known in which signals from two vertically adjacent pixels in a light receiving section of an image sensor are mixed inside the device and output. Regarding signal processing of this type of solid-state color camera,
For example, it is described in Japanese Patent Application Laid-Open No. 57-203387.

In the solid-state color camera described above, color signals are generated in the following manner. The color signal component superimposed on the high frequency component of the output signal of the image element is extracted by a bandpass filter, and the obtained color signal is delayed by one horizontal period. The red and blue primary color signals are obtained by generating a signal obtained by adding the delayed color signal and the color signal before the delay, and a signal obtained by subtracting the signal, and detecting these signals.

FIG. 6(a) shows a color filter arrangement of an image sensor used in such a solid-state color camera. The color filters are provided corresponding to the light receiving elements on the image sensor, and the same pattern is repeatedly arranged with the arrangement shown in FIG. 6 as one period. Since the output signal of the image sensor is read by adding the signals of two pixels in the vertical direction, Y e + C y and 2G are output point-sequentially in one horizontal scanning period, and Ye + G is output in the next horizontal scanning period. A point sequential signal of a and cy is output. Here, Ye, Cy, and G indicate yellow, cyan, and green signals, respectively.

High frequency components included in the output signal of the image sensor (horizontal direction 2
The pixel period component) is modulated by the difference signal between two adjacent pixels, and every horizontal period, (Ye+Cy) -2G
, (Ye+G) (G+Cy). Here, Ye, Cy, G are 3 [color components r (red), g (green), b
(blue), it becomes as shown in equations (1) to (3).

Ye=r+g・・・・・・・・・・・・・・・・・・
・(1) cy=g×b ・・・・・・・・・・・・・・・
・・・・・・(2) G=g ・・・・・・・・・
・・・・・・・・・(3) Using formulas (1) to (3),
If the high frequency component of the image sensor output is expressed as r+gy b, (Ye+Cy)-20=r+b -=-(4)(Ye
10G)-(G0Cy)=r-b-.=(5), and signals expressed by equations (4) and (5) are obtained for each upper horizontal period. Color signals R (red) and B (
blue).

[Problem to be solved by the invention]

However, in the conventional example described above, there is a problem in that color reproducibility deteriorates when the spectral characteristics of the color filter applied to each pixel deviate from ideal characteristics.

For example, in equations (1) to (3), Ye, Cy, and G are
Although it is assumed that each green signal has an equal predetermined value g, in reality, it is difficult to obtain an ideal characteristic in which the transmittance of the g component of each color filter for Ye, Cy, and G pixels is all equal. Therefore, the g components of equations (1) to (3) are slightly different, and the g component also appears as an error on the right sides of equations (4) and (5). Therefore, (4), (5
) The g component is also mixed into the R and B signals obtained by adding and subtracting the equations, deteriorating color reproducibility.

In other words, the above problem is equivalent to finding a solution using two equations (7) and (8) for three unknowns r + g + b, and it is impossible to reproduce the correct < R, B signal. It is.

The purpose of the present invention is to solve the above problems and provide a solid-state color camera with good color reproducibility. [Means to solve the problem]? In order to achieve the above object, the present invention includes an image sensor that outputs a line sequential signal, a means for color separating the line sequential signals output from the image sensor, and a three primary color signal R from four color separated color signals. , G, and B, a solid-state color camera was constructed.

[Effect]

The image sensor outputs different types of line sequential signals every horizontal period. This line sequential signal is a point sequential signal according to the type of color filter arranged in the light receiving part of the image sensor, and is a point sequential signal consisting of S1 and S2 in one horizontal period, and in the next horizontal period. This is a point sequential signal consisting of S3 and S. A means for color separation separates these four types of signals, and a means for generating R, G, and B signals calculates the color-separated signals S1 to S4 to generate R, G, and B signals.

81 to S4 are signals represented by the sum of ayK color signal components, and separating these four types of signals corresponds to having four linear equations for the three unknowns R, G, and B. Therefore, among 81-S4? By calculating at least three signals, it is possible to accurately reproduce R, G, and B signals and obtain good color reproducibility even if the ratio of the 3M color components in the spectral characteristics of the color filter changes slightly. can.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a block diagram showing the configuration of a solid-state camera according to the present invention, in which 1 is an image sensor, 2 is a preamplifier, 3 is a color separation circuit, 4■, 4■ are IH delay lines, 5 is a switch circuit,
6 is a matrix circuit, 7■ to 74 are low-pass filters,
8 is a signal processing circuit, 9 is an encoder, and 10 is an image sensor driving circuit.

The operation of each block in FIG. 1 will be explained. The image sensor 1 photoelectrically converts an incident optical signal and outputs it, and the preamplifier 2 amplifies the output signal of the image sensor 1. As will be described later, predetermined color separation filters are arranged in the image sensor 1, and the output signal thereof is a point-sequential color signal corresponding to the type of color separation filter. What is the color separation circuit 3? A point-sequential signal such as the following is color-separated according to the type of the corresponding color separation filter. The line sequential color signal output from the color separation circuit 3 and this line sequential color signal are sent to the LH delay circuit 4.
The signals delayed by l horizontal period by 1, 4■ are synchronized by the switch circuit 5.

The matrix circuit 6 calculates the synchronized color signals,
Generate R, G, B signals. The R, G, and B signals are input to the signal processing circuit 8 after being band-limited by low-pass filters 72 to 74 in the color signal band.

The signal processing circuit 8 performs white balance correction and gamma correction on each of these R, G, and B signals, and outputs two color difference signals B-Y and R-Y. Furthermore, the luminance signal output from the low-pass filter is also subjected to known signal processing such as clamping and gamma correction.

In the encoder 9, this luminance signal Y and color difference signal R-
A television signal of NTSC system or the like is generated from Y and B-Y.

The operation of this embodiment will be explained in more detail below.

FIG. 2 shows the structure of the image sensor 1 in FIG. 12 is a plan view showing a horizontal transfer section. 13 is an output section, 14 is a pixel, and 15 is a vertical transfer section.

This image sensor is generally called an interline CCD image sensor, and has a horizontal transfer section 12 and a vertical transfer section 15.
C C D (Charge Coupled D
evice).

Next, the operation of this image sensor will be explained using FIG. 2. In this image sensor, signals accumulated in pixels are read out at field intervals. Q in the horizontal row in the pixel array from top to bottom
．． ．． Assuming Q2, Q, ......, in the odd field, the signals of the pixels corresponding to Q2, Q■Q6 are first transferred to the vertical transfer section adjacent to each pixel during the vertical retrace period, and then The signal is transferred one stage in the vertical transfer section.

Next, the pixel signals corresponding to k et Q31 QS . . . are transferred to the vertical transfer section adjacent to each pixel.

As a result, the signals of the pixels corresponding to Q2, Q4, Q1, . . . and the signal charges of the pixels corresponding to n,, Q3, Q, .

Thus obtained (t■+Qz, Qs+Q<-Qs+Q
The signals corresponding to s... are transferred one stage at a time within the vertical transfer section during the horizontal retrace period. The signal thus transferred vertically upward is transferred to the top stage of the vertical transfer section, and then transferred to the horizontal transfer section 12. The signals transferred to the horizontal transfer section 12 are sequentially transmitted from the output section 13 during the scanning period.
Output.

For even fields, change the combination of rows to add,
Read out the signals of Q, +n, , Q4+ms, . . . . In this way, by changing the combination of rows to be added for each field, pseudo interlaced scanning is performed.

Next, a method of generating a color video signal from the signals read out in this manner will be described. The signals Q and Q2 output during the first horizontal period in the odd field are dot sequential signals corresponding to pixel columns arranged in the horizontal direction. This dot sequential signal can be expressed as 2W, Ye+G, 2W, Ye+G, . . . depending on the type of color filter arranged on the pixel.

However, W, Ye, Cy, and G indicate color filters that transmit all colors, yellow, cyan, and green light, respectively. Ru. below,
Similarly, in the next horizontal period, W+C y, 2 Y
e, W + C y, 2 Y e ”' ”
' A dot sequential signal is output.

FIG. 3 is a diagram showing the output signal waveform of the image sensor. In the figure, reference numeral 16 indicates a signal corresponding to the flood row of the image sensor, and reference numeral 17 indicates a signal waveform corresponding to D, +Q, which is output in the next horizontal period. However, W', G', C
y' and Ye' are respectively 2W, Ye + G, W
+ C y and 2 Y e are abbreviated. Further, in FIG. 3, 18 and 19 are output to even fields, respectively, and show signal waveforms corresponding to h+1, +n S and +n S d. Both signals, like the signals output in odd fields, are
, G', W', G'... and Ye',
Cy', Ye, Cy' --= are output alternately.

When these signals are decomposed into three primary color signal components rr gt b, they are expressed as follows.

W' =2W=2 (r+g+b) −・−(7)G
' =Ye1G=(r+g)+g=r+2g・-=(8
) Cy'=W+C y=(r+g+b)+(g+b)=
r+2g+2b-(9)Ye'=2Ye=2(r+g)
・・・=・−”・(10) The average composition of the output signal of the image sensor is (W' + G') / every horizontal period.
It can be expressed as 2s (C y' + Y e ') / 2, and when expressed in terms of 'pgyb component, (11)
It becomes like the expression.

(W' + G')/2=(C y' + Y e
)/2='-r+2g+b- (11)2 The composition shown in equation (11) is relatively close to the visibility characteristic,
The output signal of the image sensor can be used as a luminance signal. On the other hand, to generate color signals, W', G', Cy', and Ye' shown in equations (7) to (9) may be calculated by calculating R, G, and B signals according to the equations shown below.

R= a (W'-Cy')+(1-α)(Ye'-G
')=r-(12)B=β(W'-Ye')
+(1-β)(Cy'-G')=2b-(13)G=
y (Cy'+-LYe'-W')+ (1-
y) (G'-LYe')=g- (14)22 However, in equations (12) to (14), α, β, and γ are arbitrary constants.

In order to generate a color signal using equations (12) to (l4), W', G', Cy included in the output signal of the image sensor
'? It is necessary to separate e'. Therefore, the color separation circuit 3 in FIG. 1 samples and holds the amplified output signal of the image sensor and performs color separation. FIG. 4 is a diagram showing a signal waveform after the signal shown in FIG. 3 is color-separated. In FIG. 4, 20 is a signal obtained by sampling and holding W' in the signal 16 or 18 shown in FIG. 3 and separating it, and 21 is a signal obtained by sampling and holding G' and separating it. Similarly, 22 and 23 indicate waveforms obtained by sample-holding and separating Cy' and Ye' in the signal engineer 7 or 19 shown in FIG.

By separating the colors in this way, W
Two types of line sequential signals are obtained which alternately repeat ' and Cy' or G' and Ye'.

In the delay lines 4■ and 4■ in FIG. 1, the switch circuit 3 switches these two types of line sequential signals and the signal delayed by the horizontal period every horizontal period.
Each signal of W', G', Cy', and Ye' is made available in every horizontal period. W' thus synchronized
, G' , Cy , Ye'? If the calculations of equations (I2) to (I4) are executed in the matrix circuit 6,
Three primary color signals R, G, and B can be obtained.

FIG. 5 is a block diagram showing the configuration of the matrix circuit 6 in FIG.
3-61■ are adder circuits, 6■8-6. . is a subtraction circuit.

In the amplifier circuits 61 to 61■, according to equations (l2) to (13). Each signal of W', G', Cy', and Ye' is amplified. The amplified signals are each operated by an adder circuit and a subtracter circuit to generate R, G, and B signals.

By doing the above, the R, G, and B signals are accurately reproduced, so that good color reproducibility can be obtained.

In the explanation of this example, W', G', (:y'Y
The composition of e' was assumed to be expressed by equations (7) to (IO), but this is true when the color filter has ideal characteristics as expressed by equations (1) to (3). Only stand up. In equations (7) to (9), the coefficients r, g, and b on the right side are integers between O and 2, but in the case of actual filters, they contain a certain amount of error, so if they take integer values, is not limited. However, even in such a case, if you do the following,
It can accurately reproduce R, G, and B signals. r + g on the right side of (7) to (IO) to represent the actual color filter characteristics.
After correcting the coefficients of pb, the arithmetic expressions corresponding to equations (l1) to (14) may be found and executed. In this way, this method can achieve good color reproducibility even when the characteristics of the color filter deviate somewhat from ideal characteristics.

Furthermore, since this method can accurately reproduce R, G, and B signals, it is possible to accurately adjust the white balance even if the color temperature of the light source changes, and it always maintains good color reproducibility under any lighting conditions. Obtainable.

The color filter array in the embodiment described above is shown in FIG. 2, but an image sensor having color filters whose basic units are the arrays shown in FIGS. 5(.) to (d) is used. The present invention can be similarly applied to this case. In other words, each color filter arrangement? From the formula showing the composition of r + g + b corresponding to formulas (7> to (10)), reg
Find r b and perform the operations corresponding to (11) to (l4). It is possible to reproduce R, G, and B signals.

〔Effect of the invention〕

According to the present invention, since R, G, and B signals can always be faithfully reproduced, a solid-state color camera with good color reproducibility can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a solid-state color camera that is an embodiment of the present invention, FIG. 2 is a plan view showing the configuration of the image sensor, FIGS. 3 and 4 are signal waveform diagrams, and FIG. 5 6 is a block diagram showing the configuration of the matrix circuit, and FIG. 6 is a plan view showing the color filter arrangement. Engineering...Image sensor, 3...Color separation circuit, 4
■,4■...IH delay line, 5...switch circuit, 6
...Matrix circuit, 71-74...Low-pass filter, 8...Signal processing circuit, 14...Pixel, ? 1~
6■2...Amplification circuit, ? ■, ~6■7...addition circuit, ? 1, l~6■. ...Subtraction circuit. 3rd flash l4 +l)+ jshinbaJ\erJgen----p3+i, 11〉t Fig. 4 2θ Fig. 5 Fig. 6 Fig. 6

Claims (1)

[Claims] 1) It has a two-dimensional array of pixels consisting of a photoelectric conversion element and a color separation filter provided on the photoelectric conversion element, and the color separation filter is basically 2 pixels in the horizontal direction x 4 pixels in the vertical direction. The signals accumulated in two vertically adjacent horizontal rows of pixel groups, which are arranged periodically as a unit, are mixed and read out for every two vertically adjacent pixels, and the signals are read out by the color separation filter. A solid-state image sensor configured to alternately output first and second video signals corresponding to two adjacent pixels among four vertical pixels in a basic unit and another two adjacent pixels, respectively, for each horizontal scan. and a signal processing circuit that generates a color video signal using the first and second video signals, wherein the output signal of the solid-state image sensor is included in the first video signal, Signals S_1 and S_2 each correspond to two pixels in the horizontal direction in the basic unit of the color separation filter, and signals S_1 and S_2 are included in the second video signal and each correspond to two pixels in the horizontal direction in the basic unit of the color separation filter. Signal S_3
a first means for separating signals into four types of signals S_1, S_2, and S_4; and a first means for separating signals S_1, S_2,
A solid-state color camera characterized in that a second means for generating three primary color signals R, G, and B from S_3 and S_4 is provided.