JP2002185854A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device that attains effective defect correction where deterioration in the resolution cannot substantially be caused by utilizing information of effective pixels without waste, so as to minimize the deterioration in the S/N, without the need for provision of a complicated hardware circuit needing much load. SOLUTION: The imaging device the sensitivity of which is enhanced through summation of pixel values, is provided with a read section that is placed in a pre-process circuit 107 receiving a detection signal from a CCD imaging element 105 taking an image of an object to process the signal and uses a CCD driver 106 to read summed pixel information items of unit pixels in the unit of photoelectric conversion of the imaging element 105, with a memory that stores unit pixel defect information being pixel defect information with respect to the unit pixel, and a pixel information correction section that applies correction to the pixel information of pixels after the summation reading.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus whose sensitivity is improved by adding pixels, and more particularly to an image pickup apparatus having a defect compensation function.

[0002]

2. Description of the Related Art In recent years, digital still cameras (electronic cameras) for capturing a subject image with an image sensor such as a CCD and obtaining a video signal have been actively developed. In an image pickup apparatus used in this type of electronic camera, compensation for pixel defects and pixel addition readout are known. That is, the former makes it possible to use even an imaging device having a defect, and realizes a cost that can be provided to the market.
In addition, the latter can improve the SN ratio and the dynamic range.

At this time, for example, when one pixel (this is referred to as a multi-pixel and the original pixel is referred to as a unit pixel) is obtained by adding and reading four pixels in two rows and two columns, one pixel is included in the multi-pixel. However, if a defective pixel is included, the multiple pixels become defective pixels. For this reason, if the conventional defect compensation technology is applied, the defective multi-pixel is applied (substituted) with information of the adjacent multi-pixel.

[0004]

In the above example, the defective pixel information is mixed with the defective pixel information by addition reading even though the defective multiple pixels include valid pixels that are not defective in the unit pixel. Therefore, these pieces of pixel information become invalid. Then, the correction for the defective multi-pixel is performed not based on the adjacent unit pixel closest to the defective unit pixel, but on the information of the farther adjacent multi-pixel. Therefore, the resolution was greatly deteriorated.

[0005] In order to solve this problem, in the case of using a signal readout unit from an image sensor, that is, a pixel signal addition using a sample and hold circuit, as a pixel signal addition and readout method, only a portion including a defective pixel is used in a normal manner. A technique has been proposed in which information corresponding to an effective unit pixel can be obtained by performing a sample-and-hold process different from the addition operation, thereby preventing resolution degradation. (Japanese Patent Application Laid-Open No. H11-122538) However, this type of system has the following problems. In other words, it is a delicate hardware circuit that contains technically advanced elements, and it is extremely difficult to ensure performance because a sample-and-hold circuit, which may be difficult to ensure stable basic performance, requires a more special switching operation. Could be Also, since it can be applied only to addition in the horizontal direction, for example, considering the above-described four-pixel addition in which this technique is applied most generally after addition of two vertical lines,
Even if there is only one defective pixel, the information that can be effectively used is information of at most two pixels, which is wasteful.
At this time, if, for example, two diagonal pixels among the four pixels are defective, the multiple pixels are defective pixels.

The present invention has been made in consideration of the above circumstances, and has as its object to eliminate the need for a complicated and heavy hardware circuit and to use the information of effective pixels without waste. It is an object of the present invention to provide an image pickup apparatus capable of performing effective defect correction with practically no resolution degradation while minimizing SN degradation.

[0007]

(Structure) In order to solve the above-mentioned problem, the present invention employs the following structure.

That is, according to the present invention, in an imaging apparatus in which sensitivity is improved by pixel addition, an imaging element for imaging a subject, driving means for driving the imaging element, and photoelectric conversion of the imaging element using the driving means. A reading unit capable of performing addition and reading while adding a plurality of pieces of pixel information of a unit pixel that is a conversion unit pixel; a storage unit that stores unit pixel defect information that is pixel defect information regarding the unit pixel; Pixel information correcting means for correcting the pixel information of the multi-pixels, which are the pixels after addition read out by the above-mentioned method, based on the unit pixel defect information.

Here, preferred embodiments of the present invention include the following. (1) The pixel information correction means, when the black-based defect unit pixel is included in the multi-pixel, based on the number of constituent pixels of the multi-pixel and the number of black-based defective pixels for the pixel information of the multi-pixel. It is configured to perform coefficient correction for multiplying by a predetermined coefficient.

(2) The pixel information correction means, when the white pixels are included in the multi-pixels, determines the pixel saturation level, the number of pixels constituting the multi-pixels, and the white-based defect for the pixel information of the multi-pixels. Based on the number of pixels, coefficient correction for multiplying by a predetermined coefficient after subtracting the pixel saturation level is performed.

(3) The pixel information correcting means is configured to perform correction according to the following equation: S = (A−w · n _w ) × N / (N−n _w −n _b ). Here, S is the corrected multi-pixel signal value, A is the pre-correction (correction target) multi-pixel signal value, w is the saturation level of the unit pixel, N is the number of constituent pixels of the multi-pixel, and n _w is the white color of the multi-pixel. defective pixel count, n _b is a black-defect pixel number of multi-pixel.

(4) If the constituent unit pixels of the multi-pixel are all defective pixels, the pixel information correction means determines this as a defective multi-pixel, and uses the information of the adjacent non-defective multi-pixel to determine the defective multi-pixel. Is configured to apply to the information in

(5) The reading means performs vertical two-pixel addition of unit pixels in the image sensor, performs horizontal two-pixel addition on the added pixels, and adds pixel information of four unit pixels. Reading pixel information of multiple pixels.

(6) If none of the unit pixels constituting the multi-pixel has a defect, the pixel information of the multi-pixel obtained by the reading means is used as it is, and if any of the unit pixels has a defect, the pixel information is corrected. Calculating the correction formula by means.

(Operation) According to the present invention, when pixel addition reading is performed in an image sensor having a black flaw or a white flaw, predetermined pixel correction based on pixel defect data is performed on the read pixel data. Thereby, defect correction becomes possible. Then, the correction for the defective multi-pixel is performed based on the information of the unit pixel in the same multi-pixel instead of the adjacent multi-pixel information, so that the deterioration of the resolution can be suppressed.
In the case of a black defect, only coefficient correction is performed.
In the case of a white defect, the coefficient correction is performed after performing the saturation level subtraction according to the number, so that the black defect and the white defect can be accurately corrected.

As a result, there is no need for a complicated and heavy hardware circuit, and the effective pixel information is used without waste. Therefore, it is possible to effectively prevent the resolution from deteriorating while minimizing the SN deterioration. Defect correction becomes possible.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a block diagram showing a schematic configuration of an electronic camera according to an embodiment of the present invention.

In the figure, reference numeral 101 denotes a lens system including various lenses; 102, a lens driving mechanism for driving the lens system 101; 103, an exposure control mechanism for controlling the aperture of the lens system 101; A filter for cutting, 105 is a CCD color image sensor having a built-in color filter, and 106 is a CCD for driving the image sensor 105.
CD driver 107, a pre-processing circuit including an A / D converter, etc., 108, a digital processing circuit for performing color signal generation processing, matrix conversion processing, and other various digital processing, 109, a card interface, 11
0 denotes a memory card such as a CF, and 111 denotes an LCD image display system.

In the figure, reference numeral 112 denotes a system controller (CPU) for comprehensively controlling each unit, 113 denotes an operation switch system composed of various SWs, and 114 denotes an operation display for displaying an operation state, a mode state, and the like. System, 115 is a lens driver for controlling the lens driving mechanism 102, 116 is a strobe as a light emitting means, 117 is an exposure control driver for controlling the exposure control mechanism and the strobe 116, and 118 is various kinds of setting information and the like. Non-volatile memory (EEPROM) is shown.

In the electronic camera according to the present embodiment, the system controller 112 performs overall control, and the CCD driver 106 controls the CCD image pickup device 10.
5 is controlled to perform exposure (charge accumulation) and signal readout, which are taken into a digital process circuit 108 via a preprocess circuit 107, subjected to various signal processings, and then subjected to a card interface 109 via a card interface 109. The data is recorded on the memory card 110.

FIG. 2 is a plan view showing the element structure of the CCD image pickup device 105. Photodiodes 201 are arranged in a matrix as light receiving elements.
A plurality of vertical CCDs 202 are arranged in the column direction between them,
One horizontal CCD in the row direction at the end of the vertical CCD 202
203 are arranged. And the photodiode 2
The signal charge stored in the first CCD 01 is read out to the vertical CCD 202 by the charge transfer pulse TG, and is transferred inside the vertical CCD 202 downward in the drawing. The signal charges transferred from the vertical CCD 202 are transferred to the horizontal CCD 203,
D203 is transferred leftward on the paper, and finally output via an FDA (floating diffusion amplifier) 204 which is a readout amplifier.

The basic configuration up to this point is the same as that of the conventional apparatus, but in this embodiment, in addition to this, an addition reading means for reading out the pixel information of the unit pixel while adding a plurality of pieces of pixel information to the CCD 105; And a pixel information correcting unit for correcting the pixel information. Note that the addition reading in the image sensor 105 is performed by the CCD driver 106 under the control of the system controller 112, and the correction processing is performed in the pre-processing circuit 107 or the digital processing circuit 108 under the control of the system controller 112. I have.

The image sensor 105 used in the present embodiment is, for example, a progressive scanning type, and is a square pixel type having an equal vertical and horizontal pixel pitch (p is a value). Then, the image sensor 105 is configured as shown in FIG.
As shown in (2), addition and readout are performed with 2 × 2 pixels as the minimum unit. When the minimum unit of the substantial image information is composed of a plurality of pixels (unit pixels) of the image sensor 102, this is referred to as a multi-pixel.

Next, the operation of reading out a pixel addition signal and correcting a defect in this embodiment will be described.

The reading is an adjacent four-pixel addition reading by adopting the well-known simultaneous addition of two vertical pixels and two horizontal pixels. As shown in FIG. 4A, the vertical two-pixel addition is performed by outputting a V transfer clock for two pixels (two rows) in each horizontal blanking period. As shown in FIG. 4B, horizontal two-pixel addition is performed by outputting two units of horizontal transfer pulses between sampling gates in a CDS (correlated double sampling circuit), that is, between each reset gate pulse. Will be

In the process of correcting a defective pixel, the only "defects" to be processed are a black defect (output 0) and a white defect (output is at saturation level w). When the defective pixel is included in the multi-pixel image information, the defective pixel is corrected based on the following correction formula.

A multi-pixel signal value before correction (to be corrected) is A,
The number of black defects included in the single pixel (four pixels) is represented by n _b ,
Assuming that the number of white defects is n _W , the corrected multi-pixel signal value S is S = (A−w · n _w ) × 4 / (4-n _b −n _w ) (1). This equation is obtained when no defective pixel is included (S
= A).

In the case of general N pixel addition, not limited to four pixels, S = (A−w · n _w ) × N / (N−n _b −n _w ) (2)

Although the acquisition of defect information is not described above, any known method can be used. For example, data (including temperature and exposure time dependency) previously checked in the manufacturing process may be stored in a memory and used with reference to the temperature and exposure time during use. In particular, this method is desirable for black defects. Further, data obtained by performing test imaging immediately before shooting, for example, in a light-shielded state at the expected exposure time may be used. In particular, this method is excellent for white defects.

Here, the data registered as a black defect (black-based defect) or a white defect (white-based defect) is the address data of each of the corresponding pixels. Where "white defect (output is the saturation level w)" is written, the output is always 0,
Needless to say, the output w is not essential, and may be approximately regarded as such a pixel.

Instead of always using the above equation (1), a necessary equation may be selected depending on the presence or absence of a defect. For example, as shown in FIG. 5, after obtaining a multi-pixel signal value A, it is determined whether or not a defective pixel is included in the multi-pixel. If no defect is included, A is set to S as it is. If a defect is included, S is obtained by performing the calculation of the above equation (1). S obtained in this manner is used as a corrected multi-pixel signal value. Since the presence or absence of a defect is known in advance, the amount of calculation can be minimized by this method.

As described above, according to the present embodiment, in a method of obtaining one multi-pixel by adding and reading four pixels,
When even one defective pixel is included in the multiple pixels, the defective pixel can be easily compensated by performing the correction operation based on the above equation. In this case, the correction for the defective multi-pixel is performed based on the information on the unit pixel in the same multi-pixel, not on the adjacent multi-pixel information. Therefore, the information of the effective pixels can be used without waste, and the deterioration of the resolution can be suppressed while the deterioration of the SN is minimized. Further, the present invention can be realized only by performing calculations using a simple calculation formula without requiring a complicated hardware configuration such as providing a special switching operation to the sample-and-hold circuit.

The present invention is not limited to the above embodiment. In the embodiment, the description has been given of the monochrome image sensor. However, the present invention can be similarly applied to a color image sensor. In the case of color, the original addition is usually the same color addition processing. Depending on the coding pattern, addition other than adjacent addition is used, but the same can be applied to multiple pixels to be added. Further, the present invention is not limited to an electronic camera such as a digital still camera, and can be applied to a movie such as a video camera in the same manner.

Further, the pixel addition is not limited to the internal addition, but can be external. For example, for horizontal addition, adjacent pixels may be added by digital operation after a signal is read from the image sensor. In addition, various modifications can be made without departing from the scope of the present invention.

[0036]

As described above in detail, according to the present invention, in an image pickup apparatus in which sensitivity is improved by pixel addition,
A storage unit that stores unit pixel defect information that is pixel defect information relating to the unit pixel; and a pixel information correction unit that performs correction based on the unit pixel defect information on pixel information of a multi-pixel that is a pixel after addition. With this arrangement, an effective defect that does not require a complicated and heavy hardware circuit, uses information of effective pixels without waste, and thus does not cause degradation of resolution while minimizing degradation of SN. Correction becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of an electronic camera according to an embodiment of the present invention.

FIG. 2 is a plan view showing an element structure of a CCD image sensor.

FIG. 3 is a diagram showing a relationship between a unit pixel and multiple pixels in a CCD image sensor.

FIG. 4 is a timing chart showing a pulse phase of addition driving.

FIG. 5 is a flowchart for selecting a correction calculation based on the presence or absence of a defect.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Lens system 102 ... Lens drive mechanism 103 ... Exposure control mechanism 104 ... Filter system 105 ... CCD color image sensor 106 ... CCD driver 107 ... Pre-process part 108 ... Digital process part 109 ... Card interface 110 ... Memory card 111 ... LCD image Display system 112 ... System controller (CPU) 113 ... Operation switch system 114 ... Operation display system 115 ... Lens driver 116 ... Strobe 117 ... Exposure control driver 118 ... Non-volatile memory (EEPROM) 201 ... Photodiode 202 ... Vertical CCD 203 ... Horizontal CCD 204: readout amplifier

Claims (6)

[Claims] An image pickup device for picking up an image of a subject, a driving unit for driving the image pickup device, and a plurality of pixel information of a unit pixel which is a pixel of a photoelectric conversion unit of the image pickup device are added by using the driving unit. Reading means capable of performing addition and reading while reading, storage means for storing unit pixel defect information which is pixel defect information relating to the unit pixel, and pixel information of a multi-pixel which is an added pixel read by the addition reading And a pixel information correcting unit for performing correction based on the unit pixel defect information. 2. The method according to claim 1, wherein the pixel information correcting means determines the number of constituent pixels of the multi-pixel and the black system pixel information with respect to the pixel information of the multi-pixel when the multi-pixel includes a black defect unit pixel. 2. The image pickup apparatus according to claim 1, wherein the image pickup apparatus is configured to perform coefficient correction for multiplying the coefficient by a predetermined coefficient based on the number of defective pixels. 3. The method according to claim 1, wherein said pixel information correcting means determines a pixel saturation level, a number of constituent pixels of the multi-pixel, and a pixel information of the multi-pixel when the multi-pixel includes a white defect unit pixel. 3. The imaging apparatus according to claim 1, wherein a coefficient correction for multiplying a predetermined coefficient is performed after subtracting a pixel saturation level based on the number of white defect pixels. 4. The pixel information correcting means is configured to perform the correction according to the following equation: S = (A−w · n _w ) × N / (N−n _w −n _b ). The imaging device according to claim 1. (Where S is the corrected multi-pixel signal value, A is the uncorrected (corrected) multi-pixel signal value, w is the saturation level of the unit pixel, N is the number of constituent pixels of the multi-pixel, and n _w is the multi-pixel The number of white defective pixels, n _b is the number of black defective pixels of multiple pixels) 5. When all of the constituent pixels of the multi-pixel are defective pixels, the pixel information correction means determines that the pixel is a defective multi-pixel, and uses the information on the adjacent non-defective multi-pixel to determine the defective multi-pixel. The imaging device according to any one of claims 1 to 4, wherein the imaging device is configured to apply to pixel information. 6. The reading means performs vertical two-pixel addition of a unit pixel in the image sensor, performs horizontal two-pixel addition on the added pixel, and adds pixel information of four unit pixels. The imaging device according to claim 1, wherein the pixel information of the plurality of pixels is read.