JP2001186534A - Solid-state image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image pickup device that can effectively suppress color false signal, in the case of employing a solid-state image pickup element which consists of complementary color filters. SOLUTION: A color separation processing section 16 receives an image signal of each pixel of a solid-state image pickup element 10 having a complementary color filter array, a G signal component obtained from a target pixel or its surrounding is added to a Cy signal obtained from the target pixel or to a mean value of Cy pixels obtained from the pixels around the target pixel and are substrated from a luminance signal component obtained from the target pixel and its surrounding pixels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single-chip solid-state imaging device used in a video camera, a digital camera, and the like, and more particularly to a single-chip solid-state imaging device having a color separation processing circuit having an effect of suppressing a false color signal. About.

[0002]

2. Description of the Related Art In a so-called single-panel video camera or digital camera using only one solid-state image pickup device, a specific color filter such as magenta (Mg), cyan (Cy), yellow (Ye),
A green (G) color filter is provided. There are various arrangements of color filters for each pixel, and many signal processings for color separation corresponding to the arrangement of the color filters have been considered.

A conventional color filter arrangement and signal processing for color separation will be described with reference to FIG.

FIG. 2A shows an arrangement using complementary color filters. For example, an odd line is repeatedly arranged with a Mg filter and a G filter in a two-pixel cycle, and an even line is a Cy filter and a Ye filter is arranged with a two-pixel cycle. It has a repetitive structure in which 2 × 2 pixels repeatedly arranged in a pixel cycle are regarded as one unit.

[0005] A color separation process is performed to separate and generate a red (R) signal, a green (G) signal, and a blue (B) signal for each pixel from the image signals output from the solid-state imaging device having this arrangement.

For example, when attention is paid to the central pixel of the 3 × 3 pixel area in FIG. 2B, the pixel of interest is a Ye pixel,
That is, since the pixel is provided with the Ye filter, R, G, and B signals cannot be generated as it is.

Therefore, generally, the Ye color is obtained by adding R and G colors (Ye = R + G), the Cy color is obtained by adding B and G colors (Cy = B + G), and the Mg color is obtained by adding R and B colors. R, G, and B using the color (Mg = R + B)
To generate a signal.

That is, the R signal of the target pixel is obtained by adding the average value of the signals of the four Mg pixels adjacent to the target pixel from the Ye signal of the target pixel, and calculating the average value of the signals of the two Cy pixels adjacent to the target pixel. Is generated by subtracting.

R signal = Ye signal + Mg signal−Cy signal The G signal is obtained from a G pixel adjacent to the pixel of interest.
The average value of two Cy signals obtained from the Cy pixels adjacent to the target pixel is added to the average value of the two G signals, and the Ye signal obtained from the Ye pixel of the target pixel is added. It is generated by subtracting the average value of the four Mg signals obtained from the calculated Mg pixels.

G signal = G signal + Ye signal +
Cy signal-Mg signal The B signal is obtained from the Cy pixel adjacent to the pixel of interest.
It can be generated by adding the average value of the four Mg signals obtained from the Mg pixels adjacent to the target pixel to the average value of the two Cy signals, and subtracting the Ye signal obtained from the Ye pixel of the target pixel.

B signal = Cy signal + Mg signal−Ye signal However, in such a color separation process, a boundary between a bright pixel and a dark pixel when a bright pixel and a dark pixel are adjacent to each other on a solid-state imaging device, that is, There is a problem that a so-called false color signal different from the original color is generated at the edge portion of the pixel. The mechanism of this false color signal is shown in FIG.
This will be briefly described with reference to FIG.

In FIG. 3A, Mg, G, Cy, Y
The numerical value written below e indicates the signal level, and the signal level is 0 to 255 with 8-bit resolution.

When the signal level of each pixel has a sharp level difference in the horizontal direction as shown in FIG. 3 (a), when the R, G, B signals for each pixel are obtained by the above-mentioned normal processing formula, Assuming that the target pixel is the second line in FIG. 3A, the R signal is as shown in FIG. 3B, the G signal is as shown in FIG. 3C, and the B signal is as shown in FIG.

As can be seen from the signal level before the color separation shown in FIG. 3A, when the signal whose level is greatly increased from left to right in the horizontal direction is used in the above processing equation, Paying attention to the B signal, it can be seen that the signal level is turned upside down at a location where there is a sharp level difference (from level 36 to level 29 and from level 29 to level 45). . The inversion of the level of the B signal causes a false color signal.

This is because, in the color separation processing unit of 3 × 3 pixels, when the G pixel or the Ye pixel has the arrangement of the center pixels, there is no spatial sampling frequency of the B component in the horizontal direction.

[0016]

As described above, the conventional solid-state imaging device has a problem that a false color signal is generated.

The present invention has been made in order to solve the above-described problems, and has as its object to provide a solid-state imaging device that suppresses a false color signal.

[0018]

(First Solution) A red signal, a blue signal, and a green signal are output for each pixel from a solid-state image sensor having a color filter array having a cycle of two pixels in the horizontal direction and two pixels in the vertical direction. In a solid-state imaging device that performs a color separation process that generates a signal, a cyan signal obtained from the pixel for each pixel or an average value of a cyan signal obtained from a pixel around the pixel is applied to the pixel or the periphery of the pixel. The method is characterized in that a green signal component obtained from a green pixel is added, and a luminance signal component generated from the pixel or the periphery of the pixel is subtracted to generate a broadband blue signal.

(Second Solution) Color separation for generating a red signal, a blue signal, and a green signal for each pixel from an output signal from a solid-state imaging device having a color filter array having a cycle of two pixels in the horizontal direction and two pixels in the vertical direction. In the solid-state imaging device that performs the processing, for each pixel, the yellow signal obtained from the pixel or the average value of the yellow signal obtained from the pixel around the pixel, the green value obtained from the pixel or the green pixel around the pixel A solid-state imaging device that adds a signal component and subtracts a luminance signal component generated from the pixel or a periphery of the pixel to generate a broadband red signal.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the solid-state imaging device according to the present invention. In the solid-state imaging device 10, Mg, Cy, Ye, and G color filters are arranged in each pixel arranged in a matrix.

In this arrangement, as shown in FIG. 2A, for example, an Mg filter and a G filter are repeatedly arranged at odd-numbered lines at a two-pixel cycle, and a Cy filter and Ye filter are repeated at even-numbered lines at a two-pixel cycle. 2x2 placed
This is a color filter array having a repeating structure in which a pixel is one unit.

Among the pixels of the solid-state imaging device 10, a pixel on which an Mg filter is disposed is an Mg pixel, a pixel on which a Ye filter is disposed is a Ye pixel, a pixel on which a Cy filter is disposed is a Cy pixel, and a G filter is disposed. The pixel obtained is referred to as a G pixel.

The solid-state imaging device 10 is not limited to this, but is composed of, for example, a two-dimensional CCD image sensor or a CMOS image sensor.

The image signal output from the solid-state imaging device 10 is input to an analog signal processing unit 11, where processing such as generation of a video signal and noise reduction is performed. The image signal output from the analog signal processing unit 11 is A /
After being converted into a digital signal by the D converter 12, gamma correction is performed by a gamma correction circuit 13.

The digital image signal output from the gamma correction circuit 13 is divided into 3 lines × 3 columns of pixel signals by two 1H delay circuits 14 and six 1-pixel delay circuits 15 to perform color separation processing. Input to the unit 16.

The 1H delay circuit 14 generates a 1H signal of the digital image.
A memory or a delay line capable of recording (one horizontal period) can be used to obtain an output signal delayed by 1H. One-pixel delay circuit 15 is a delay circuit having a delay time equal to the time required to transmit one pixel.

That is, a digitized image signal,
The image signal that has passed through the one-stage 1H delay circuit 14 and the two-stage
An image signal of three lines including the image signal passed through the H delay circuit 14 is generated. Further, by providing the two-stage one-pixel delay circuit 15 for each line, signals of 3 lines × 3 columns are input to the color separation processing unit 16 at the same time.

In the color separation processing section 16, Ye, Cy, M
g, G color separation processing is performed, and the R signal,
The G signal and the B signal are generated. Details of the processing in the color separation processing unit 16 will be described later.

The R signal, the G signal, and the B signal generated by the color separation processing section 16 are input to the masking correction section 18 to eliminate the signal leakage from the adjacent pixels on the solid-state imaging device 10. Is input to the color processing unit 19 after the masking correction for the

The color processing unit 19 converts the R, G, and B signals into a low-frequency luminance signal (YL) and color difference signals (U, V).

Automatic white balance processing unit (AWB) 2
0 is a coefficient used for white balance processing based on the color difference signals (U, V) obtained from the color processing unit 19 and a luminance signal (Y) to be described later. It feeds back to the signal and automatically performs white balance processing.

For example, when the R, G, B signal ratio of the digital signal output from the color separation processing section 16 when a certain subject is photographed is R: G: B = 2: 2: 1, the white region of the subject is Detected by the automatic white balance processing unit 20,
A correction coefficient is generated so that the R, G, B signal ratio becomes R: G: B = 1: 1: 1, and the correction coefficient is fed back to the multiplier 17.

On the other hand, the contour extraction unit 21
A high-frequency luminance signal (YH) is generated from the g signal, the Cy signal, the Ye signal, and the G signal, and a horizontal contour signal (HDTL) and a vertical contour signal (VDTL) are further generated.

The first adder 22 outputs a high-frequency luminance signal (Y
H), the horizontal contour signal (HDTL) and the vertical contour signal (VD
TL) is added to obtain an outline correction signal (DTL).

In the second adder 23, the contour correction signal (D
TL) and the low-frequency luminance signal (YL),
A luminance signal (Y) is generated and output.

Next, the color separation processing unit 1 which is a feature of the present invention.
The processing in 6 will be described in detail.

The method for generating the B signal of the color filter array shown in FIG.

B signal = Cy signal + G signal component−luminance component Specifically, the arrangement of 3 × 3 pixels of the digital image signal input to the color separation processing unit 16 is shown in FIGS.
(C) There are four types of sequence A, sequence B, sequence C and sequence D shown in (d). In order to represent each pixel position of 3 × 3 pixels, the horizontal direction is x and the vertical direction is y as shown in FIG.
Is used. Here, it is assumed that a pixel at the coordinates (x, y) at the center of the 3 × 3 pixels is set as a target pixel and a color signal of the target pixel is obtained.

The digital image signal input to the color separation processing unit 16 has four types of arrangement of 3 × 3 pixels (array A, array B,
The generation formula of the B signal of the pixel of interest corresponding to the array C and the array D) is shown below.

In these four types of arrangements, there are columns without B components in the horizontal direction, so only the B signal generation formula is shown.

The method of generating the R signal and the G signal is the same as in the conventional method.

In this color signal generation method, the image signals output from each pixel and the initials (M, G,
C, Y, R, B) and the x, y coordinates indicate the position of each pixel. B (x, y) is B in which the pixel of interest is generated
The signal Y (x, y) indicates the Ye signal of the pixel of interest.

<B signal generation equation corresponding to array A> B (x, y) = (C (x−1, y) + C (x + 1, y)) / 2+ (G (x, y−1) + G ( x, y + 1) / 2- (Y (x, y) / 4 + (G (x, y-1) + G (x, y + 1) + C (x-1, y) + C (x + 1, y) / 8 + ( M (x−1, y−1) + M (x + 1, y−1) + M (x−1, y + 1) + M (x + 1, y + 1)) / 16) · (1) <B signal generation corresponding to array B Formula> B (x, y) = C (x, y) + (G (x-1, y-1) + G (x + 1, y-1) + G (x-1, y + 1) + G (x + 1, y + 1)) / 4- (C (x, y) / 4 + (M (x, y-1) + M (x, y + 1) + Y (x-1, y) + Y (x + 1, y))) / 8+ (G (x- 1, y-1) + G (x + 1, y-1) + G x−1, y + 1) + G (x + 1, y + 1)) / 16) · (2) <B signal generation equation corresponding to array C> B (x, y) = (C (x−1, y−1) ) + C (x + 1, y-1) + C (x-1, y + 1) + C (x + 1, y + 1)) / 4 + G (x, y)-(G (x, y) / 4 + (C (x, y-1) ) + C (x, y + 1) + M (x-1, y) + M (x + 1, y)) / 8+ (C (x-1, y-1) + C (x + 1, y-1) + C (x-1, y + 1) + C (x + 1, y + 1)) / 16) · (3) <B signal generation equation corresponding to array D> B (x, y) = (C (x, y−1) + C (x, y + 1) ) / 2 + (G (x-1, y) + G (x + 1, y)) / 2- (M (x, y) / 4 + (C (x, y-1) + C (x, y + 1) + G (x −1, y) + G (x + 1, y)) / 8 (Y (x-1, y-1) + Y (x + 1, y-1) + Y (x-1, y + 1) + Y (x + 1, y + 1)) / 16)... (4) given to the color separation processing unit 16 The 3 × 3 pixel array is array A
The case will be described.

Ye (x, y), G (x, y-1) and G
(X, y + 1) is where the blue component does not exist. Therefore, G (x, y-1) and G (x, y + 1)
Means that the horizontal high-frequency component of the G signal is added to the target pixel.

By performing this processing, the spatial sample frequency in the horizontal direction of the pixel of interest can be supplemented.

However, since the signal obtained by adding the G signal to the Cy signal is not the B signal, the G signal is substantially equal to the luminance signal component, and the luminance signal generated from the target pixel or the peripheral pixels of the target pixel is used. A B signal is generated by subtraction with the component.

The method of generating the luminance signal component is a 3 × 3 pixel in which the target pixel is 1/4 times, the pixel adjacent to the upper, lower, left and right sides of the target pixel is 1/8 times, and the other pixels are 1/16 times. It is realized by adding.

The method of generating the luminance signal component is not limited to array A, but is the same for array B, array C and array D.

Next, the case where the 3 × 3 pixel array provided to the color separation processing section 16 is the array B will be described.

C (x, y), M (x, y-1) and M
Since the blue component exists at (x, y + 1), the target pixel has a high frequency component in the horizontal direction.
However, to match the signal levels with the arrays A and C, G (x-1, y-1), G (x + 1, y-1), G (x-1, y + 1) and G (x + 1, y + 1) Add the average value of This means that the low frequency component of the G signal has been added.

That is, the value is obtained by adding the high frequency component of the cyan signal and the low frequency component of the G signal. Here, looking at the array A, the value is the sum of the low-frequency component of the cyan signal and the high-frequency component of the G signal, and the signal level matches.

In the B signal generation in the case of array B, the luminance signal component is subtracted in the same manner as in array A.

Next, in the case of the array C, the Cy and Mg pixels in the array A are in the form in which the Ye and G pixels are inverted, respectively.
Is replaced with the formula.

Similarly, the processing of the array D is a formula in which the Ye and G pixels and the Cy and Mg pixels in the color filter array B are reversed.

The B signal processed as described above complements the spatial sample frequency in the horizontal direction by adding the G component, so that the color false signal is suppressed.

The effect will be described with reference to FIG. The processing equation for the B signal has 8-bit precision as in the description of FIG.

In this case, the color separation processing section 16 generates the B signal shown in FIG. As you can see from this,
The reversal of the signal level generated in FIG. 3D is eliminated. That is, the cause of the generation of the false color signal is improved.

By the way, in the above-described color signal generation processing,
Although the color filter arrangement of FIG. 2A has the effect of suppressing the false color signal of the B signal, the color filter arrangement shown in FIG. 2C in which the Cy and Ye pixels of the color filter arrangement are reversed. is there.

In the case of this arrangement, since a column having no R signal component is formed in the horizontal direction, a false color signal is generated in the R signal.

Therefore, the B signal generation formula of the color separation processing section 16 described above is used this time when generating the R signal.

That is, R of the color filter array shown in FIG.
The signal generation method is represented by the following equation.

R signal = Ye signal + G signal component−luminance component As described above, even if the Cy pixel and the Ye pixel are reversed, the concept of the B signal generation formula is used when generating the R signal, and thus the R signal is obtained. A color false signal suppression effect can be obtained for the signal.

By the way, it is known that the color reproducibility changes depending on the spectral distribution characteristics of the color filters arranged in each pixel of the solid-state imaging device and the color temperature under photographing illumination.

Therefore, in the color signal generation processing in the color separation processing section 16 described above, the coefficient α
And a signal obtained by subtracting a luminance signal component multiplied by a coefficient α from a G signal component to be added to a Cy signal or a Ye signal is multiplied by a coefficient β, thereby obtaining a color reproducibility according to a shooting state or a spectral distribution characteristic of a color filter. Can be changed.

In the case of the color filter arrangement shown in FIG. 2A, the B signal generation formula is as follows.

B signal = Cy signal + (G signal component
-Luminance signal component x α) x β In the case of the color filter array of Fig. 2C, the R signal generation formula is as follows.

R signal = Ye signal + (G signal−luminance signal × α) × β For example, the data in FIG.
Although it is 0 degree, if α = 1.44 and β = 1, the result of FIG. 7 is obtained, and the signal level becomes the same level as that of FIG. As described above, various characteristics of a color temperature change due to shooting illumination or a spectral distribution of a color filter arranged in a solid-state imaging device can be freely set by having the above two types of coefficients.

[0069]

As described above, according to the present invention, a false color signal which is a problem in a solid-state imaging device such as a video camera or a digital camera can be effectively reduced, and the image quality can be improved.

When a B signal or an R signal is generated, a luminance signal component is multiplied by a coefficient α, and a signal obtained by subtracting a luminance signal component multiplied by a coefficient α from a G signal component is converted to a coefficient β
, The saturation of the generated B signal or R signal can be changed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a diagram illustrating a color filter array of a solid-state imaging device according to the present invention.

FIG. 3 is a diagram for explaining a generation mechanism of a color false signal in the related art.

FIG. 4 is a diagram showing types of a color filter array of an image signal input to a color separation processing unit 16 in FIG. 1;

FIG. 5 is a diagram showing a correspondence relationship between a color filter array and coordinates of each pixel position.

FIG. 6 is a diagram for explaining a color false signal suppression effect in the color separation processing unit 16 of FIG. 1;

FIG. 7 is a diagram for explaining the correspondence between coefficients in a shooting situation in the color separation processing unit 16 in FIG. 1;

[Explanation of symbols]

10. solid-state image sensor, 11 analog signal processing unit,
12 A / D converter, 13 gamma correction circuit, 14
1H delay circuit, 15 1-pixel delay circuit, 16 color separation processing unit, 17 multiplier for automatic white balance processing, 18 masking correction circuit, 19 color processing unit
20... Automatic white balance processing section, 21... Contour extraction circuit, 22... First addition section, 23.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) KC07 KC11 KE02 KE19 KM02

Claims (4)

[Claims] 1. A solid-state imaging device that performs a color separation process for generating a red signal, a blue signal, and a green signal for each pixel from an output signal from a solid-state imaging device having a color filter array having a cycle of two horizontal pixels and two vertical pixels. In the device, for each pixel, a green signal component obtained from the pixel or a green pixel around the pixel is added to a cyan signal obtained from the pixel or to an average value of cyan signals obtained from pixels around the pixel. A solid-state imaging device that subtracts a luminance signal component generated from the pixel or a periphery of the pixel to generate a broadband blue signal. 2. A solid-state imaging device that performs a color separation process for generating a red signal, a blue signal, and a green signal for each pixel from an output signal from a solid-state imaging device having a color filter array having a cycle of two horizontal pixels and two vertical pixels. In the device, for each pixel, a green signal component obtained from the pixel or a green pixel around the pixel is added to a yellow signal obtained from the pixel or to an average value of yellow signals obtained from pixels around the pixel. A solid-state imaging device that subtracts a luminance signal component generated from the pixel or a periphery of the pixel to generate a broadband red signal. 3. The solid-state imaging device according to claim 1, wherein the color filter having a cycle of two horizontal pixels and two vertical pixels is a combination of magenta, cyan, yellow, and green. 4. An operation used for color separation processing includes a first luminance signal component generated from the pixel or a periphery of the pixel.
Multiplying a signal obtained by subtracting the luminance signal component multiplied by the first coefficient from a green signal component obtained from the pixel position or a green pixel around the pixel, by a second coefficient, The solid-state imaging device according to claim 1, wherein the first and second coefficients are dependent on a color temperature under illumination at the time of photographing or a spectral distribution characteristic of the color filter.