JP2000069491A - Image pickup element and image pickup device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a dynamic range. SOLUTION: The signals of four pixels in respective color pixel groups 6 being four pixel units having the color filters of the same color components are synthesized and outputted from a color pixel matrix having 2m pixels in a horizontal direction and 2n pixels in a vertical direction. In such a case, the color filters having similar transmissivity are loaded on the upper and lower pixels in the color picture element groups 6, and the color filters having different transmissivity are loaded on right and left pixels. Thus, a wide dynamic range is obtained by the synthesis of the signals of the right/left picture elements and the signal of high sensitivity is obtained by the addition of the charges of the upper/lower pixels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image pickup device and an image pickup device using the same, and more particularly to an image pickup device capable of outputting an image pickup signal having a wide dynamic range and an image pickup device using the same.

[0002]

2. Description of the Related Art Conventionally, in a color electronic camera using an IT-CCD, an electric charge accumulated in pixels arranged above and below is added to double the electric charge signal amount. The range is being improved.

On the other hand, when a color image is obtained using a color filter having a complementary color system, color filters having different spectral transmission characteristics are arranged at pixels at predetermined positions, and an image pickup device for adding and reading out the pixel charges is provided. There is.

When a color image is obtained by using a color filter having primary color components, a color filter having the same spectral transmission characteristic is arranged at a pixel at a predetermined position, and the pixel charges are added and read out. There is a device.

[0005]

However, the amount of charge handled by the pixel on the image sensor, that is, the photoelectric conversion element is from the dark current level to the saturation level, and this range has a great influence on the dynamic range of the photoelectric conversion characteristic. As a result, there is a problem that an image cannot be captured with a wide dynamic range.

In this case, even if the spectral transmittance of the color filter is increased to increase the amount of charge and the sensitivity is increased, the dynamic range does not change, and conversely, the spectral transmittance of the color filter is decreased to reduce the amount of charge. And the sensitivity is lowered, the dynamic range itself does not change.

Therefore, the present invention eliminates such a problem,
It is an object of the present invention to provide an imaging device capable of obtaining an imaging signal having a wide dynamic range and an imaging device using the same.

[0008]

According to a first aspect of the present invention, in an image pickup device, a plurality of pixels arranged in a matrix are provided, and the pixels are provided with a plurality of color filters having the same color but different transmittances. Features. In the first invention, since a plurality of color filters having the same color but different transmittances are mounted, the dynamic range can be widened by adding the charges of the mounted pixels or synthesizing the signals from the pixels. it can.

A second invention is characterized in that, in the first invention, the color filters of the same color but different in transmittance are arranged adjacent to each other. Thus, the same operation as that of the first invention can be obtained without significantly lowering the resolution.

A third invention is characterized in that, in the first or the second invention, the spectral characteristics of the pixels mounted with the color filters having the same color but different transmittances are the same. Thereby, the photoelectric conversion characteristics can be changed only by the transmittance, and the same operation as in the first or second aspect can be obtained by using the color filters having different transmittances.

According to a fourth aspect of the present invention, in the image pickup apparatus, an image pickup device having a plurality of pixels arranged in a matrix and having a plurality of color filters of the same color but different in transmittance is provided. A driving circuit capable of supplying a driving signal to read out a signal obtained by adding electric charges of pixels each having a color filter having a different transmittance. As a result, the signal amount can be increased, the dynamic range can be widened, and a highly sensitive signal can be obtained.

In a fifth aspect based on the fourth aspect, the color filters having the same color but having different transmittances are arranged adjacent to each other and can be read by adding charges corresponding to the color filters having the same color but having different transmittances. It is characterized by being.
Thus, a signal with high sensitivity and a wide dynamic range can be obtained without significantly lowering the resolution.

According to a sixth aspect of the present invention, in the image pickup apparatus, an image pickup device having a plurality of pixels arranged in a matrix and having a plurality of color filters of the same color but different in transmittance is provided. And a drive circuit capable of supplying a drive signal for independently reading out the charges of the pixels on which the color filters having different transmittances are mounted without adding the charges. Thereby, a high-sensitivity signal and a low-sensitivity signal can be obtained simultaneously.

According to a seventh aspect of the present invention, in the image pickup apparatus, an image pickup device having a plurality of pixels arranged in a matrix and having a plurality of color filters of the same color but different in transmittance is provided. A driving circuit capable of supplying a driving signal for adding signal charges obtained from pixels having the same transmittance and having the same transmittance and reading out without adding signal charges obtained from pixels having different transmittances, A signal processing device that combines signals obtained from adjacent same-color pixels having different transmittances and converts the signals into one light-dark signal by combining the signals so as to continuously change in accordance with the amount of incident light. I do. This makes it possible to obtain an imaging device that can operate with a wide range of incident light amount and has an extremely wide dynamic range.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram illustrating a configuration of an imaging device according to an embodiment of the present invention. The image pickup device 10 forms a color pixel matrix in which a plurality of 2m pixels 1 in a horizontal direction (row direction) and 2n pixels in a vertical direction (column direction) are arranged. The color components of all the pixels in the color pixel group 6 composed of four adjacent 2 × 2 pixels are the same,
It is composed of m × n color pixel groups 6.

When the color pixel matrix is viewed in units of the m × n color pixel group 6, an RGB Bayer arrangement is obtained. For example, M (1,1), M (1,2), M (2,2) in a 2m × 2n color pixel matrix M
The four pixels 1) and M (2, 2) are arranged as pixels having a color filter of a color component G, and M (1, 3),
The four pixels M (1,4), M (2,3), and M (2,4) are arranged as pixels having a color filter of a color component R, and M (3,1), M (3 , 2), M (4,1),
Each of the four pixels of M (4,2) is arranged as a pixel having a color filter of color component B, and furthermore, M (3,3),
The four pixels M (3,4), M (4,3) and M (4,4) are arranged as pixels having a color filter for the color component G.

These pixels 1 as photoelectric conversion elements such as photodiodes function as pixels of R, G, and B color components, respectively.
The above-described color filter that transmits light of G and B color components is provided. Therefore, for example, the pixel 1 of the color pixel matrix M (1, 1) transmits, receives, and photoelectrically converts only light of the G (green) color component. Note that m and n are natural numbers.

Further, as shown in FIG. 2, the color filters of the four pixels in each color pixel group 6 have the same transmittance for the adjacent upper and lower pixels 1a, 1b and pixels 1c, 1d. However, as shown by oblique lines, adjacent left and right pixels 1a and 1c and pixels 1b and 1d have different transmittances. However, the spectral characteristics of the left and right pixels are the same. Therefore, in each of the color pixel groups 6, the left and right pixels are provided with a color filter having the same color component but different sensitivity.
The upper and lower pixels are provided with color filters having the same color components and the same sensitivity.

In FIG. 2, a high-sensitivity color filter of a color component G is mounted on the pixels 1a and 1b,
In 1d, a low-sensitivity color filter of the color component G is mounted. When the charges of the upper and lower pixels having the same sensitivity are added, the charge amount increases, and the signal amount can be doubled. A virtual pixel obtained by adding and reading the charges of two pixels can be regarded as a single pixel located at the center of gravity of the two pixels. Further, the dynamic range can be widened by simultaneously reading out the charges of the high-sensitivity pixels and the charges of the low-sensitivity pixels separately and combining them by a signal processing circuit, which will be described later.

The charge stored in each of the four pixels in each color pixel group 6 is obtained by adding the upper and lower two pixels of the same color, for example, on the image sensor 10, and the added charges are sequentially transferred side by side. As an output signal 5.

When the output signals adjacent to the left and right of the same color are combined by an external signal processing circuit among the output signals of the upper and lower two pixels thus added, the color components of the color pixel group 6 as shown in FIG. Is obtained. The virtual pixel 8 when the signals of the four pixels of each color pixel group 6 are synthesized is
It can be regarded as a single pixel located at the center of gravity of four pixels. By sequentially obtaining an output signal for each color pixel group 6 in this manner, as shown in FIG.
M having an RGB Bayer array pixel arrangement in units of
× n color images can be obtained.

There are the following modes for reading the charge or signal of the pixel. The first is to read out each pixel independently. The second is the upper and lower pixels 1a, 1b or pixels 1c, 1d in one vertical column in the color pixel group 6.
Are added to and read out to the vertical transfer circuit 2, and are sequentially read from the vertical transfer circuit 2 via the horizontal transfer circuit 3 and the output amplifier 4. Third, the upper and lower pixels 1a and 1b or the pixels 1c and 1d in one vertical column in the color pixel group 6 are sequentially transferred to the vertical transfer circuit 2 and added in the vertical transfer circuit 2 respectively. The added charges of the upper and lower pixels are sequentially transferred to the horizontal transfer circuit 3 and output via the output amplifier 4. Such addition can be easily achieved by controlling the charge transfer operation by the driving circuit of the image sensor.

It should be noted that the charges of four pixels of the same color in each color pixel group 6 having the pixel configuration as shown in FIG. 2 are added in the image pickup device 10 and a signal corresponding to the added charges is output signal 5. Can also be obtained as In this case, as compared with the case of a single pixel, the ratio of the signal charge amount to the noise charge amount can be increased, the sensitivity can be improved, and the dynamic range can be improved.

In order to add the electric charges of four pixels in the image pickup device, the electric charges of two pixels vertically adjacent to each other among the four pixels are added and read out to a vertical transfer circuit. What is necessary is just to add the added charges of two pixels together and to output them. Alternatively, the charges of two vertically adjacent pixels may be read out and then added in the vertical transfer circuit, and the added charges of the two pixels further horizontally adjacent in the horizontal transfer circuit may be added to each other.

Next, referring to FIG. 4, left and right pixels having color filters having different transmittances, that is, pixels 1a, 1
The principle that the dynamic range is widened by the combination of b and the pixels 1c and 1d will be described.

FIG. 4 is a diagram showing the relationship between the amount of photoelectric conversion charge and the amount of light of a pixel. In FIG. 4, line L1 is
The photoelectric conversion relationship of a pixel having high sensitivity by a color filter having an increased transmittance corresponds to the sum of the pixels 1a and 1b. At a light amount larger than the point P1,
The converted charge amount is saturated. On the other hand, the line L2 corresponds to the pixel 1
It corresponds to the sum of c and 1b, and shows the photoelectric conversion relationship of a pixel whose sensitivity has been reduced by a color filter having a small transmittance. Although there is no saturation in the light amount range shown in FIG. 4, the converted charge amount is small.

When signals corresponding to the charges of the high-sensitivity pixels 1a and 1b and the low-sensitivity pixels 1c and 1d are combined by an external signal processing circuit, the linear portions of the lines L1 and L2 are connected. The output, that is, the photoelectric conversion relationship of the line L. In the range of the light amount shown in FIG. 4, the incident light amount in a wide range can be converted into the converted charge amount without being saturated, and the dynamic range can be widened. Moreover, in this case, the sensitivity can be improved by adding the electric charges of the upper and lower pixels. Note that the gradient of the light quantity versus the converted charge quantity of the left and right pixels is
It is preferable to have a difference of two times or more.

Therefore, by combining the signals of the four pixels in each color pixel group 6 as described above, the dynamic range can be widened by combining the signals of the left and right pixels, and the electric charge of the upper and lower pixels is added. The amount is twice or more, and the sensitivity can be greatly improved.

Further, as shown in FIG. 5, the arrangement of the four pixels in the color pixel group 6 may be such that the transmittance of the left and right pixels is the same and the transmittance of the upper and lower pixels is different. In FIG. 5, pixels with high transmittance are arranged on the upper side, and pixels with low transmittance are arranged on the lower side. However, the arrangement may be reversed.

Next, a case where the transmittance of all the four pixels in the color pixel group 6 is made different will be described. FIG.
, Each of the pixels 1a to 1d has a pixel 1a → 1b → 1c
→ The transmittance is set to be lower in order of 1d. Therefore, the signals of the four pixels 1a to 1d are read out independently and connected by a signal processing circuit, whereby the signals shown in FIG.
A very wide dynamic range can be obtained as shown in FIG. That is, the pixel 1a with high sensitivity has the light amount of the point P
The pixel 1b with the next highest sensitivity has the photoelectric conversion relationship of the line LL1 that saturates above P1 and the photoelectric conversion relationship of the line LL2 that saturates when the light amount exceeds the point PP2. , The line LL where the light intensity is saturated at or above the point PP3
The pixel 1d having the photoelectric conversion relationship of 3 and having the lowest sensitivity is
In the range of the light amount shown in FIG. Therefore, if the signals of the respective pixels 1a to 1d are combined so that a line graph is connected, it is possible to obtain a photoelectric conversion characteristic having a very wide dynamic range like a line LL. Note that even in the case where the color pixel groups shown in FIGS. 5 and 6 are provided, it is possible to add and read out the charges of the four pixels in each color pixel group in the image sensor.

Here, in the above-described image pickup device 10, the color pixel group is composed of four 2 × 2 pixels. Next, an image pickup device 10A in which the color pixel group is composed of two 1 × 2 pixels will be described. I do. 1 × 2 color pixel group 7 shown in FIG.
Is a set of pixels of the same color component as in the 2 × 2 color pixel group 6 shown in FIG. This color pixel group 7
Has an RGB Bayer arrangement when viewed from the entire color pixel matrix. The upper and lower pixels 7a and 7b in the color pixel group 7 are provided with color filters having different transmittances as shown in FIG. Pixel 7a
Is a pixel provided with a color filter having a high transmittance, and the pixel 7b is a pixel provided with a color filter having a low transmittance. Therefore, the virtual pixel 9 obtained by combining the signals from the pixels 7a and 7b by the signal processing circuit has a wide dynamic range. Further, since two pixels are not added for improving the sensitivity as in the imaging device 10 shown in FIG. 1, the sensitivity cannot be greatly improved.
The resolution increases accordingly. That is, as shown in FIG. 10, the set of virtual pixels 9 is a 2m × n color matrix.

Each of the color pixel groups 6 in the color image matrix in the image pickup devices 10 and 10a is 2
4 pixels of 2 × 2 pixels or 2 pixels of 1 × 2, but not limited thereto, 2 pixels of 1 × 2, 9 pixels of 3 × 3, 6 pixels of 3 × 2
An arbitrary number of pixels and the like, and an arrangement of an arbitrary arrangement mode can be adopted. However, in order to improve the dynamic range, it is necessary to provide color filters having different transmittances in the color pixel group.

Further, the above-described image pickup device 10 has been described on the assumption that the CCD solid-state image pickup device is used. However, the present invention is not limited to this. Obviously, this is applicable.

Next, an electronic camera as an image pickup apparatus using the image pickup device 10 shown in FIG. 1 or the image pickup device 10A shown in FIG. 8 will be described. In the following description, an apparatus using the image sensor 10 will be described.

FIG. 11 is a block diagram showing a configuration of an electronic camera using the image pickup device 10. In FIG. 11, an image sensor 10 is a subject 2 input through an optical system 11.
8 is converted into an electric signal. This optical system 11 has an infrared cut filter.

The CDS / AGC circuit 12
Is subjected to a CDS function for reducing noise components by correlated double sampling or the like and an AGC function for performing automatic amplification according to sensitivity, and outputs the signal to the A / D converter 13.

The A / D converter 13 converts an analog signal from the CDS / AGC circuit 12 into a digital signal of, for example, 10 bits or more, and converts the analog signal into a digital signal processor (DS).
P) 14.

The DSP 14 performs image interpolation processing, black level adjustment, gamma correction, knee correction, and the like on the input 10-bit digital data, and processes the digital data converted from 10 bits to 8 bits. A signal processing circuit that performs processing such as matrix and contour correction, and performs processing such as generation of 16-bit digital data composed of 8-bit luminance components and 8-bit color difference components, and is a one-chip LSI for digital signal processing. is there. Also, D
The SP 14 also performs a drive timing pulse generation process for the image sensor 10.

The compression / decompression unit 15 performs compression / decompression processing based on the JPEG standard, which is an international standard for still images, and specifically includes discrete cosine transform (DCT) and inverse DCT.
T, a one-chip decoder that performs logical processing such as Huffman encoding / decoding. Further, the compression / decompression unit 15 takes in and accesses data to and from the buffer memory 16 and also refreshes the buffer memory 16 composed of a DRAM.

The buffer memory 16 includes a compression / decompression unit 15
Is a memory for temporarily storing image data of one frame before compression, and is composed of a DRAM as described above.

The SRAM 22 has a function as a buffer memory before adding the header information as a JPEG file to the image data compressed by the compression / decompression unit 15 before storing it in the flash memory 26.

The flash memory 26 is a nonvolatile memory for finally storing an image file which is a JPEG file to which header information has been added.

The external interface 27 is an interface for transferring data between an external processing device such as a personal computer and the electronic camera body.

The digital encoder 17 is a chip for modulating digital data into an analog video signal.

The display 18 is realized by an LCD or the like, and displays and outputs a video signal generated by the digital encoder 17.

The speedlight section 24 has a function of independently controlling external light control. That is, the speedlight unit 2
In 4, light emission, charge, and the like are controlled by a CPU 21 described later, and light emission amount control is performed by external light control by the speedlight unit alone.

The LCD 23 has various shooting modes, remaining frames,
The status of erase (erase), battery detection, etc. is displayed on the LCD.

The CPU 21 is composed of, for example, a microprocessor, and controls the above-described units as a whole.

The timing generator 20 generates various pulses for driving the image pickup device 10 and various timing pulses for each of the above-described units.

The image pickup device 10 is controlled by the drive timing pulse from the DSP 14 described above. The horizontal transfer pulse for horizontal charge transfer of the image sensor 10 is DS
The image pickup device 10 is directly driven from P 14 via the timing generator 20, and a vertical transfer pulse for vertical charge transfer is input to the timing generator 20, and the image pickup device is driven by a signal which is voltage-converted via the drive unit 19. 10 is driven.

Here, the operation unit 25 includes a photographing mode changeover switch for switching various photographing modes and a command dial for setting various commands.

That is, the photographing mode changeover switch of the operation unit 25 switches between a high dynamic range mode in which a wide dynamic range is set, a normal mode in which each pixel is individually transferred from the image pickup device 10, and a high sensitivity mode. Be instructed.

When the normal mode is instructed, the CPU 21
Indicates that the normal mode has been set to the DSP 14, and the DSP 14 drives the four pixels in each color pixel group 6 according to the normal charge transfer control to sequentially transfer the horizontal pixel groups one by one. A timing pulse is generated to drive the image sensor 10 and perform signal processing corresponding to a color image output on an output signal input via the A / D converter 13. Further, the CPU 21 also performs instruction control for other units corresponding to the normal mode.

When the high dynamic range mode is instructed, the CPU 21 instructs the DSP 14 that the high dynamic range mode has been set. DSP14 is
In each color pixel group 6, two pixels having the same sensitivity are added, and a driving timing pulse for independently reading out signals from pixels having different sensitivities is generated to drive the image sensor. In addition, a synthesis process is performed on output signals of pixels having different sensitivities input through the A / D converter 13. In addition, the CPU 21 also performs instruction control for other units corresponding to the high dynamic range mode. Alternatively, in the case of the pixel arrangement in FIG. 6, each pixel is read independently without adding in the image sensor, and the signal of each pixel is synthesized.

When the high sensitivity mode is designated,
The DSP 14 drives the image sensor by generating a drive timing pulse for adding charges of four pixels in each color pixel group in the image sensor.

FIG. 12 is a plan view of the electronic camera described above. The electronic camera body 31 has a shooting mode changeover switch 32, a command dial 33, an LCD
34, and a release switch 35. The shooting mode switch 32, command dial 33, and release switch 35 are connected to the operation unit 25 shown in FIG.
LCD 34 is the LCD 2 in FIG.
Equivalent to 3. The photographing mode changeover switch 32 is a switch for switching each mode.
It is displayed in D34. Command dial 33
Is a dial used for setting operations such as a shutter speed and an aperture value, and the result of the setting is displayed on the LCD 34.

As described above, in the electronic camera shown in FIG. 11, by using the same image pickup device 10, a color image having a wide dynamic range can be obtained in addition to the color image in the normal mode and the high sensitivity mode. it can.

[0058]

As described above in detail, according to the present invention, since a plurality of color filters having the same color but different transmittances are mounted, the signal of the pixel having the color filters different in transmittance is mounted. The dynamic range can be greatly improved by independently connecting by the readout signal processing, and there is an effect that a color image having an extremely wide dynamic range can be obtained. In addition, by adding the charges of a plurality of pixels of the same color in the image sensor, the signal charge amount can be increased with respect to the noise charge amount, and the sensitivity and the dynamic range can be increased. Furthermore, by combining the addition of electric charges in the imaging device and the synthesis by signal processing, imaging with a very wide dynamic range and high sensitivity can be performed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a configuration of an imaging device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the principle of obtaining a high-sensitivity signal with a wide dynamic range by combining signals of a color pixel matrix.

FIG. 3 is an explanatory diagram showing a high-sensitivity image having a wide dynamic range by combining signals of a color pixel matrix.

FIG. 4 is an explanatory diagram showing a photoelectric conversion characteristic of each pixel and a photoelectric conversion characteristic obtained by combining signals of pixels having different transmittances.

FIG. 5 is an explanatory diagram showing an example of a pixel arrangement mode in a color pixel group.

FIG. 6 is an explanatory diagram showing an example of an arrangement of each pixel when the transmittance of all pixels in a color pixel group is different.

FIG. 7 is an explanatory diagram showing photoelectric conversion characteristics having a wide dynamic range obtained by synthesizing signals when transmittances of all pixels in a color pixel group are different.

FIG. 8 is an explanatory diagram showing a configuration of an image sensor according to another embodiment of the present invention.

FIG. 9 is an explanatory diagram showing an example of a pixel arrangement mode of a color pixel group in the embodiment of FIG. 8;

FIG. 10 is an explanatory diagram showing a matrix of addition pixels having a wide dynamic range by combining signals of a color pixel matrix.

11 is a block diagram illustrating a configuration of an electronic camera using the imaging device illustrated in FIG.

12 is a schematic plan view of the electronic camera shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 pixel 2 vertical transfer circuit 3 horizontal transfer circuit 4 output amplifier 5 output signal 6 color pixel group 8 addition pixel 10 imaging device 14 digital signal processing unit (DSP) 19 drive unit 20 timing generator 21 CPU 25 operation unit

Claims (7)

[Claims] 1. An image sensor comprising a plurality of pixels arranged in a matrix, wherein the pixels are provided with a plurality of color filters having the same color but different transmittances. 2. The image sensor according to claim 1, wherein the color filters having the same color but different transmittances are arranged adjacent to each other. 3. The imaging device according to claim 1, wherein the pixels equipped with the color filters having the same color but different transmittances have the same spectral characteristics. 4. An image sensor having a plurality of pixels arranged in a matrix and having a plurality of color filters of the same color but different transmittances, and a color filter having the different transmittances mounted on the image sensor. And a driving circuit capable of supplying a driving signal to read out the sum of the electric charges of the pixels. 5. A color filter having the same color but different transmittances is arranged adjacently and readable by adding charges corresponding to color filters of the same color but different transmittances. An imaging device according to claim 1. 6. An image sensor having a plurality of pixels arranged in a matrix and having a plurality of color filters of the same color and different transmittances, and a color filter having a different transmittance for the image sensor. A driving circuit capable of supplying a driving signal for independently reading out the electric charge of the mounted pixel without adding the electric charge. 7. An image pickup device having a plurality of pixels arranged in a matrix and having a plurality of color filters of the same color and different transmittances, and an image of the same color adjacent to the image pickup device and having the same transmission. A driving circuit capable of supplying a driving signal to add signal charges obtained from pixels having different transmittances and read out without adding signal charges obtained from pixels having different transmittances; A signal processing device that combines the obtained signals so that the signals change continuously according to the amount of incident light and converts the signals into one light / dark signal.