JPH11122625A - Solid-state image pickup device and its signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a black/white video output with high gradation and high resolution in the case of photographing a character in addition to a conventional color video output by having only to mount a color solid-state image pickup element. SOLUTION: This device is provided with a color solid-state image pickup element 1, a pre-processing circuit 2, a color signal processing circuit 3, a correction coefficient calculation circuit, a black/white information generating circuit 5, a black/white signal processing circuit 6, and a selector circuit 4. Then the color signal processing circuit 3 generates a color video signal from R, G, B signals of color information of the color solid-state image pickup element 1 processed by the pre-processing circuit, and the black/white signal processing circuit 6 generates a black/white video signal generated by the black/white information generating circuit 5 based on the R, G, B signals of the color information of the color solid-state image pickup element 1 processed by the pre-processing circuit 2 and the correction coefficient calculated by the black/ white generating circuit 5. The selector circuit 4 selects a color video signal or a black/white video signal depending on a photographed object and outputs the selected video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device.

[0002]

2. Description of the Related Art In recent years, in the field of image processing, with the diversification of image information to be processed and the enhancement of functions of the image processing itself, solid-state imaging devices used for image input have also been improved in performance and functions. Is required. Resolution, which is one of the performances of the solid-state imaging device, is determined by the structure of the solid-state imaging device mounted on the solid-state imaging device. When comparing the resolution of a color solid-state image sensor with the same number of pixels as the resolution of a black-and-white solid-state image sensor, a luminance signal is obtained by forming a plurality of color filter patterns on each photoelectric conversion element and calculating the output signal of an adjacent photoelectric conversion element. The resolution of a color solid-state imaging device for generating color signals is inferior to the resolution of a monochrome solid-state imaging device in which the output signal of each photoelectric conversion element becomes a luminance signal as it is. Therefore, when a high resolution is required as in the case of reading a character, the use of a monochrome solid-state image sensor can provide a monochrome image signal but a high-resolution image.

Generally, a solid-state imaging device for inputting an image includes:
A solid-state imaging device equipped with a color solid-state imaging device that emphasizes color reproducibility and a solid-state imaging device equipped with a black-and-white solid-state imaging device that emphasizes resolution are used. A solid-state imaging device equipped with a color solid-state imaging device capable of selecting and outputting a black and white video signal has also been developed.

The principle of operation of a conventional solid-state imaging device having such a function will be described with reference to FIG. FIG. 2 is a schematic block diagram of a solid-state imaging device showing a signal flow of the conventional solid-state imaging device. In FIG. 2, reference numeral 8 denotes a color solid-state imaging device, 9 denotes a preprocessing circuit, 10 denotes a color signal processing circuit, and 11 denotes a color signal processing circuit.
Is a binarizing circuit, 12 is a black and white signal processing circuit, and 13 is a selector circuit.

Here, a color solid-state image pickup device forming three types of color filters of red, green and blue (hereinafter abbreviated as R, G and B, respectively) will be described as an example. R, G, and B color filters are formed in each photoelectric conversion element of the color solid-state imaging device 8, and a signal component photoelectrically converted from each photoelectric conversion element according to the spectral characteristics of the corresponding color filter. That is, a color output signal composed of the R signal component, the G signal component, and the B signal component is output.

The preprocessing circuit 9 comprises a CDS (correlated double sampling) circuit, an AGC / gamma circuit, and an AD converter. The CDS circuit removes noise components of the color output signal, the AGC / gamma circuit performs gain control (auto gain control) and gamma correction of the color output signal, and the AD converter samples the color output signal with a clock and converts it from an analog signal. The signal is converted into a digital signal and output to the color signal processing circuit 10 and the binarization circuit 11 at the next stage.

The color signal processing circuit 10 converts an R signal component, G
After detecting the signal component and the B signal component, a luminance signal (Y) is created from the relational expression of Y = 0.3R + 0.59G + 0.11B based on the R signal component, the G signal component, and the B signal component, Further, an RY signal and a BY signal are created from the luminance signal (Y), the R signal component, and the B signal component, and a double balance modulation is performed at the sub-carrier frequency to create a chroma signal (C). Finally, a color video signal in which the luminance signal (Y), the chroma signal (C), and the synchronizing signal are superimposed is created and output to the selector circuit 13 at the next stage.

[0008] In the binarization circuit 11, the digital signal is output by the preprocessing circuit 9.
R signal component and G signal from color-converted color output signal
After detecting the component and the B signal component, respectively, the R signal component,
The signal levels of the G signal component and the B signal component are set for each signal component.
Binarized by comparing with the threshold value
Output to the signal processing circuit 12. Here, the R signal component is R
, G signal component is G, B signal component is B, R signal
The threshold of the component _TAnd the threshold value of the G signal component is
G_TAnd the threshold value of the B signal component is B_TAnd the white output signal
Issue S_WAnd the black output signal is S_BIf you say
It is binarized as follows. In this case, signals above the threshold
Output signal S_WAnd the signal below the threshold value is output as the black signal output S
_BOutput as

[0009] R <when the G → S _W B <B _T when the G → S _B G ≧ G _T at the time when the _{R T R → S B R ≧} R T R → S W G <G T B → S _B B ≧ B _T B → S _W The monochrome output signals (white output signal _SW , black output signal S _B ) created in this way are output to the monochrome signal processing circuit 12 at the next stage. In general, when a black-and-white signal processing circuit performs black-and-white signal processing on a color output signal as it is, the black-and-white signal processing is performed for the purpose of preventing a repeated pattern of a color filter from appearing in a video output as FPN (fixed pattern noise). Because a filter is inserted in the circuit,
The frequency characteristics deteriorate, and as a result, the resolution deteriorates. The binarizing circuit 11 is used to solve this problem.
That is, when the binarization circuit is inserted, the FPN is eliminated, and it becomes unnecessary to insert a filter into the black and white signal processing circuit.

In the monochrome signal processing circuit 12, the binarizing circuit 1
The black and white output signal (white output signal _SW and black output signal S
Create a luminance signal from _B ). Then, a black-and-white video signal in which the luminance signal and the synchronizing signal are superimposed is created and output to the next-stage selector circuit 13. The selector circuit 13 can arbitrarily output a color video signal and a black-and-white video signal that are input depending on whether the target subject is a color image or a monochrome image. A color video signal is selected when capturing a normal color subject, and a monochrome video signal is selected when capturing a subject composed of white and black shades represented by characters on a document.

With such a configuration, it is possible to arbitrarily output a color video signal and a black-and-white video signal input to the selector circuit 13 depending on whether the target subject is a color image or a monochrome image.

[0012]

However, in the conventional solid-state imaging device, the R signal component and the G signal component of the color solid-state imaging device are used.
Since each output signal of the signal component and the B signal component is binarized by comparing the output signal with a threshold value, the resolution is the same as that of a solid-state image pickup device equipped with a normal black-and-white solid-state image pickup device, but the gradation is dark and light. There is a problem that an image is output without images.

An object of the present invention is to provide a solid-state imaging device capable of obtaining a high-resolution and high-gradation black-and-white video signal while mounting a color solid-state imaging device.

[0014]

To achieve this object, a solid-state imaging device according to the present invention comprises a color solid-state device in which photoelectric conversion elements each having a color filter are arranged two-dimensionally to detect different color information. An image sensor, a color signal processing circuit that creates a color video signal from the color information, and a monochrome information creation circuit that converts color information into monochrome information using a correction coefficient for converting the color information into monochrome information,
A black-and-white signal processing circuit for generating a black-and-white video signal from black-and-white information and a selector circuit for selecting a color video signal and a black-and-white video signal are provided.

According to this configuration, a color image signal can be output in the case of a color subject only by mounting a color solid-state image pickup device, and an image of a subject on which characters or the like requiring high resolution are displayed is taken. In this case, it is possible to provide a solid-state imaging device capable of obtaining a black-and-white video output with high resolution, and to realize a high-quality, high-performance image input camera.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram of a solid-state imaging device showing a signal flow of the solid-state imaging device according to the embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a color (CCD) solid-state imaging device in which photoelectric conversion elements on which color filters (RGB filters) are formed are two-dimensionally arranged to detect different color information; 2, a preprocessing circuit; A color signal processing circuit for creating a color video signal from the information; 4A, RGB for detecting R, G, B color information;
A detection circuit, 4B is a correction coefficient creating circuit for creating a correction coefficient based on R, G, B color information, 4C is a storage means (memory) for storing the correction coefficient, and 5 is color information based on the color information and the correction coefficient. A black-and-white information processing circuit for generating a black-and-white video signal from the black-and-white information, and a selector circuit 7 for selecting a color video signal and a black-and-white video signal.

Here, the operation will be described by taking a color solid-state image pickup device forming three kinds (R, G, B) of color filters as an example. The basic signal flow is the same as in a conventional solid-state imaging device. R, G, and B color filters are formed in each photoelectric conversion element of the color solid-state imaging device 1, and a signal component photoelectrically converted from each photoelectric conversion element according to the spectral characteristics of the corresponding color filter. That is, a color output signal composed of the R signal component, the G signal component, and the B signal component is output.

The pre-processing circuit 2 comprises a CDS circuit, an AGC / gamma circuit, and an AD converter. The CDS circuit removes noise components of the color output signal, and
The gamma circuit performs gain control (auto gain control) and gamma correction of the color output signal, and the AD converter samples the color output signal with a clock and converts the analog signal into a digital signal. Output to the RGB detection circuit 4A.

The color signal processing circuit 3 detects an R signal component, a G signal component, and a B signal component from the digitally converted and input color output signal, and then, based on the R signal component, the G signal component, and the B signal component. , Y = 0.3R + 0.59G + 0.11B, a luminance signal (Y) is generated, and an RY signal and a BY signal are generated from the luminance signal (Y), the R signal component, and the B signal component. Then, the chroma signal (C) is created by performing double balanced modulation with the subcarrier frequency. Finally, a color video signal in which the luminance signal (Y), the chroma signal (C), and the synchronizing signal are superimposed is created and output to the next-stage selector circuit 7.

The RGB detection circuit 4A detects an R signal component, a G signal component, and a B signal component from the color output signal that has been digitally converted and input, and sends them to the monochrome information creating circuit 5 and the correction coefficient creating positive circuit 4B. In the correction coefficient creating circuit 4B,
An R signal component, a G signal component, and a B signal component, which are color information of a color output signal, are converted into black and white information to generate a correction coefficient for generating a black and white signal. The method of creating this correction coefficient is as follows. That is, when the light of the same luminance is incident, the output signal level for each color component of the corrected color information is equalized or approximated by multiplying the output signal level different for each color component of the color information by the correction coefficient. Are calculated based on output signal levels that are different for each color component of color information when light of the same luminance is incident. Specifically, for example, an all-white subject is illuminated with a light source having a predetermined color temperature, and an R signal component, a G signal component, and a B signal component are detected from a color output signal obtained at this time, and each color is detected. By multiplying the output signal level of the component by the correction coefficient, a correction coefficient such that the output signal level of each color component of the corrected color information becomes equal to or approximates to each other is calculated by the R signal component, the G signal component, and the B signal component.
By finding the reciprocal of the ratio of the output signal level of the signal component,
calculate.

Here, the method of calculating the correction coefficient will be described for the case where the color temperature of the light source of the illumination is 3200K. The output signal of a solid-state imaging device equipped with a color solid-state imaging device when an object composed of white and black shades represented by characters of a document is imaged using a light source having a color temperature of 3200K for illumination,
A color output signal is output based on the spectral characteristics of the color filter corresponding to each photoelectric conversion element, and after being processed by the preprocessing circuit 2, an R signal component, a G signal component, and a B signal component are created. At this time, the ratio of the output signal of the R signal component, the G signal component, and the output signal of the B signal component is always constant irrespective of the gradation, that is, the shading of the subject, when the light source has the same color temperature of 3200K.

Therefore, for example, if an image of an all-white subject is taken
R signal component_WAnd the G signal component is G_WWhen
And the B signal component_WAnd the color temperature of the light source of the lighting
Is the R signal component and the G signal
K corresponding to each of the_3200R, K
_3200G, K_3200BAnd k_3200R・ R_W= K_3200G・ G_W= K_3200B・ B_W The R signal component, the G signal component,
Correction coefficient k for B signal component _3200R, K_3200G, K_3200BTo
Calculates and corrects the signal level of the signal component for each color component.
k_3200R, K_3200G, K_3200BBy correcting with
The subsequent R, G, and B signal components have the same signal level.
Can be aligned with the bell. This makes it seem the same
It becomes an output signal of a photoelectric conversion element having optical characteristics. That is,
When imaging with a solid-state imaging device equipped with a black and white solid-state imaging device
It can be converted to a monochrome output signal.

Although the method of calculating the correction coefficient has been described using the color temperature of 3200K as an example, in practice, several kinds of correction coefficients for each color temperature are calculated in advance and stored in a memory or the like. It can correspond to the light source considered above. The storage unit 4C stores the values created by the manual setting in the correction coefficient creation circuit 4B or the values calculated in advance for each color temperature as the correction coefficients k _R , k _G , and k _B. In the case of the manual setting, as described above, a white screen is imaged (over the entire surface), the correction coefficient creation circuit 4B calculates the value of the correction coefficient by an external trigger, and stores it in the storage unit 4C. Let it. Also, the values of the correction coefficients for each color temperature are, for example, 3000 K, 500
It can be simply calculated from the spectral characteristics of the CCD at 0K and 9000K, and the value is stored in the storage means 4C in advance.

In the black and white information generating circuit 5, the correction coefficients k _R , k _G , and k _{B for} each color component read from the storage means 4C.
Is converted into black and white output signals r, g, and b based on. Specifically, in the black and white information creating circuit 5, RG
The R signal component R, G signal component G, and B signal component B detected by the B detection circuit 4A are multiplied by the correction coefficients k _R , k _G , and k _B for each color component read from the storage unit 4C. To convert them into black and white output signals r, g, b. That is,
The following equation holds.

K _R · R = r k _G · G = g k _B · B = br = g = b The monochrome output signals r, g, b created in this way are sent to the next stage monochrome signal processing circuit 6. Output.

The black-and-white signal processing circuit 6 generates a black-and-white video signal by encoding a synchronization pulse and the like based on the black-and-white output signals r, g, and b input from the black-and-white information generation circuit 5. Output to The selector circuit 7 can arbitrarily output a color video signal and a black-and-white video signal that are input depending on whether the target subject is a color image or a monochrome image. In this case, select a color video signal to capture a normal color subject, and select a black-and-white video signal to capture a subject composed of white and black shades represented by characters on a document. For example, using a color solid-state imaging device, it is possible to obtain a high-gradation, high-resolution black-and-white video signal comparable to a normal black-and-white video signal.

In the above description, the embodiment of the solid-state imaging device having the color solid-state imaging device having the three color filters of R, G, and B has been described. The present invention is not limited to this, and can be applied to a solid-state imaging device having a color solid-state imaging device having four color filters (for example, yellow, magenta, green, and cyan). In this case, only the correction coefficient increases by one in response to the increase in the number of colors, and the configurations of the RGB detection circuit, the correction coefficient generation circuit, the storage means, and the monochrome information generation circuit are basically three-color cases. Is the same as

[0028]

As described above, according to the solid-state imaging device of the present invention, a color video signal can be output for a color subject only by mounting a color solid-state imaging device, and high resolution can be obtained. It is possible to provide a solid-state imaging device capable of obtaining a black-and-white video output with high resolution when capturing an image of a subject on which required characters and the like are displayed, and realize a high-quality and high-performance image input camera. be able to.

[Brief description of the drawings]

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

FIG. 2 is a schematic block diagram of a conventional solid-state imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Color solid-state imaging device 2 Preprocessing circuit 3 Color signal processing circuit 4A RGB detection circuit 4B Correction coefficient creation circuit 4C Storage means 5 Black and white information creation circuit 6 Black and white signal processing circuit 7 Selector circuit

Claims (3)

[Claims] 1. A color solid-state imaging device in which photoelectric conversion elements provided with color filters are arranged two-dimensionally to detect different color information, a color signal processing circuit to create a color video signal from the color information, A black-and-white information generation circuit for converting the color information into black-and-white information using a correction coefficient for converting the color information into black-and-white information; a black-and-white signal processing circuit for generating a black-and-white video signal from the black-and-white information; A solid-state imaging device comprising a selector circuit for selecting a signal and the monochrome video signal. 2. A color solid-state imaging device in which photoelectric conversion elements provided with color filters are arranged two-dimensionally to detect different color information, a color signal processing circuit to create a color video signal from the color information, A black-and-white information generation circuit for converting the color information into black-and-white information using a correction coefficient for converting the color information into black-and-white information; a black-and-white signal processing circuit for generating a black-and-white video signal from the black-and-white information; What is claimed is: 1. A signal processing method for a solid-state imaging device, comprising: a selector circuit for selecting a signal and the monochrome video signal, wherein a correction coefficient for converting the color information into monochrome information is calculated based on the color information. A signal processing method for a solid-state imaging device, comprising: 3. A color solid-state imaging device in which photoelectric conversion elements provided with a color filter are arranged two-dimensionally to detect different color information, a color signal processing circuit to create a color video signal from the color information, A black-and-white information generation circuit for converting the color information into black-and-white information using a correction coefficient for converting the color information into black-and-white information; a black-and-white signal processing circuit for generating a black-and-white video signal from the black-and-white information; A signal processing method for a solid-state imaging device, comprising: a selector circuit for selecting a signal and the black-and-white video signal, wherein when light having the same luminance is incident, a different output signal level is provided for each color component of the color information. The correction section for multiplying the correction coefficient to equalize or approximate output signal levels for each color component of the color information after correction. The signal processing method of the solid-state imaging device, and calculates, based on respective different output signal levels for each color component of the color information when the light of the same brightness was incident.