JP4662343B2 - Imaging apparatus and correction method - Google Patents

Description

  The present invention relates to an imaging apparatus and a correction method using an imaging element such as a CCD or a CMOS image sensor, and more particularly to dark current correction of a captured image.

  2. Description of the Related Art Conventionally, imaging devices such as digital cameras and video cameras using imaging elements such as CCDs and CMOS image sensors have become widespread.

  In an image pickup apparatus using an image pickup device, for example, when taking a dark subject, the influence of dark current cannot be ignored in shooting with long accumulation. The dark current component is proportional to the accumulation time and increases as the temperature increases.

  On the other hand, a peripheral circuit for driving the image sensor and outputting an image signal exists around the pixel region of the image sensor. Since these peripheral circuits generate heat when they operate, a temperature gradient is generated in which the temperature of the image sensor increases toward the periphery.

  Due to this temperature gradient, the dark current characteristics of the image sensor have unevenness depending on the position in the screen. In other words, due to the influence of the heat of the peripheral circuit, the pixel region of the image sensor has a dark current characteristic in which the peripheral portion is raised compared to the central portion of the screen because the pixel region of the image pickup device has a higher temperature and is more likely to generate dark current. FIG. 10 is a diagram showing the concept of an image signal obtained in a state where the image sensor is shielded from light, and the signal value is expressed in darker color as the signal value becomes lower.

  As a method for correcting this dark current unevenness, in Patent Document 1, reference dark data for one frame is stored in advance, and data obtained from a light-shielding portion (optical black: OB) of a photographed image to be corrected is stored. A method is disclosed in which the reference dark data stored based on the average value is corrected and subtracted from the captured image.

JP 2004-88306 A

  However, the method of Patent Document 1 requires a memory for one frame in order to store the reference dark data.

  In an imaging apparatus using the above-described imaging device, an OB clamp circuit is generally provided in the imaging device or in an A / D converter in order to correct an offset error due to dark current and ensure a dynamic range. is there. Since the average value of the OB portion is always constant in the image after the OB clamping process is performed, the dark current amount of the image sensor when the image to be corrected is captured from the information, and the reference dark time data is obtained. It is difficult to calculate an appropriate coefficient for correcting.

  The present invention has been made in view of the above problems, and realizes highly accurate dark current unevenness correction and reduces the memory capacity necessary for storing dark current reference data used for dark current unevenness correction. This is the first purpose.

  It is a second object of the present invention to appropriately perform dark current unevenness correction even after performing OB clamping processing on an image signal to be corrected.

In order to achieve the first object, the imaging apparatus according to the present invention averages the image signals output from the entire area of the imaging element in the horizontal direction and the vertical direction in a state where the opening of the imaging element is shielded from light . Storage means for storing the dark current distribution data in the vertical direction and the dark current distribution data in the horizontal direction, each representing polynomial distribution of the data and calculated using the obtained approximate expression; Expansion means for generating dark current correction data by two-dimensionally developing the dark current distribution data in the vertical direction and the dark current distribution data in the horizontal direction stored in the means, and the generated by the expansion means using dark current compensation data, and a correcting means for correcting the dark current unevenness of an image signal obtained when photographing an object, said horizontal direction and said vertical dark current distribution data In particular, the boundary between the central portion and the peripheral portion in the horizontal direction and the vertical direction is set as the minimum point in the approximate expression, and the dark current distribution data corresponding to the peripheral portion is used as the minimum point in the approximate expression. And the value of the dark current distribution data corresponding to the central portion is set to zero .

In addition, the dark current non-uniformity correction method in the image pickup apparatus having the image pickup element is obtained by averaging the image signals output from the entire area of the image pickup element in the horizontal direction and the vertical direction in a state where the opening of the image pickup element is shielded from light . Performing a polynomial approximation of the data, the readout step of reading out the dark current distribution data in the vertical direction representing the distribution characteristics of the dark current and the dark current distribution data in the horizontal direction calculated from the obtained approximate expression from the storage medium, A developing step for generating dark current correction data by two-dimensionally developing the dark current distribution data in the vertical direction and the dark current distribution data in the horizontal direction read in the reading step, and generated by the developing means using said dark current correction data, and a correction step of correcting the dark current unevenness of an image signal obtained when photographing an object In each of the dark current distribution data in the horizontal direction and the vertical direction, a boundary between the central portion and the peripheral portion in the horizontal direction and the vertical direction is set as a minimum point in the approximate expression, and the peripheral portion is set as the boundary Is calculated using the approximate expression, and the value of the dark current distribution data corresponding to the central portion is set to zero .

  Preferably, the imaging apparatus according to the present invention is configured so that the dark current correction data is based on the image signal to be corrected and the dark current correction data corresponding to a predetermined area set as a constantly shielded area of the imaging element. The correction means further corrects dark current unevenness by subtracting the product of the dark current correction data and the coefficient from the image signal to be corrected. In the correction method of the present invention, the dark current correction data is obtained on the basis of the image signal to be corrected and the dark current correction data corresponding to a predetermined area set as a constantly shielded area of the image sensor. The method further includes a calculation step of calculating a coefficient to be adjusted. In the correction step, dark current unevenness is corrected by subtracting a product of the dark current correction data and the coefficient from the image signal to be corrected.

  In order to achieve the second object, there are a plurality of the predetermined areas, and the difference between the average values of the image signals to be corrected between the plurality of predetermined areas and the plurality of predetermined areas are used as the coefficients. The ratio of the difference between the average values of the dark current correction data is calculated.

  According to the present invention, highly accurate dark current unevenness correction can be realized, and the memory capacity required for storing dark current reference data used for dark current unevenness correction can be reduced.

  Further, even after the OB clamping process is performed on the image signal to be corrected, the dark current unevenness correction can be appropriately performed.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a block diagram showing a configuration of an imaging apparatus such as a digital camera or a digital video camera according to the first embodiment. Reference numeral 101 denotes an imaging element, which uses a CCD or CMOS sensor. Reference numeral 102 denotes an A / D converter that converts an analog signal from the image sensor 101 into a digital signal. Reference numeral 103 denotes a DSP (Digital Signal Proseccer) that performs various correction processes and development processes on data from the A / D converter 102. In the DSP 103, various memories such as the ROM 106 and the RAM 107 are controlled and image data is written to the recording medium 108.

  A timing generation circuit 104 supplies a clock signal and a control signal to the image sensor 101, the A / D converter 102, and the DSP 103, and is controlled by the CPU 105. Reference numeral 105 denotes a CPU that controls the DSP 103 and the timing generation circuit 104, and controls camera functions using various units (not shown) such as photometry and distance measurement. Switches 109 to 111, which will be described later, and a mode dial 112 are connected, and processing corresponding to each state is executed.

  A ROM 106 stores a camera control program executed by the CPU 105 and various correction data used by the DSP 103, and a RAM 107 temporarily stores image data and correction data processed by the DSP 103. Further, dark current distribution data, which will be described later, is stored in the ROM 106, and is developed in the RAM 107 and used for dark current unevenness correction, which will be described later. The RAM 107 can be accessed at a higher speed than the ROM 106. Reference numeral 108 denotes a recording medium such as a compact flash (registered trademark) card for storing a photographed image, which is connected to a camera via a connector (not shown).

  Reference numeral 109 denotes a power switch (SW) for activating the camera, and 110 is turned on by a first predetermined operation (for example, half-press) of a shutter button (not shown), and instructs to start operations such as photometry processing and distance measurement processing. The shutter switches SW 1 and 111 are turned on by a second predetermined operation (for example, full press) of a shutter button (not shown), drive a mirror and a shutter (not shown), and a signal read from the image sensor 101 is converted into an A / D converter. 102, a shutter switch SW2 for instructing the start of a series of imaging operations to be written to the recording medium 108 via the DSP 103.

  FIG. 2 is a flowchart showing the control of the image pickup apparatus having the configuration shown in FIG. First, in step S101, it is determined whether or not the power SW 109 for starting the camera is turned on. If it is off, step S101 is repeated. If the power SW 109 is turned on, the dark current distribution data stored in the ROM 106 is developed in the RAM 107 in step S102 in preparation for photographing (hereinafter, the developed data is referred to as “dark current correction data”). Then, the process proceeds to step S103. In step S103, it is determined whether or not the mode dial 112 is set to the shooting mode. If the other mode is set, the process corresponding to the mode selected in step S104 is performed and then the process returns to step S101. If the shooting mode is set, the process proceeds to step S105.

  In step S105, it is determined whether or not the shutter switch SW1 (110) is ON. If SW1 (110) is OFF, the process returns to step S101 and the above-described processing is repeated. If SW1 (110) is ON, the process proceeds to step S106.

  In step S106, photometry processing for determining the aperture value and shutter speed and distance measurement processing for adjusting the focus of the photographing lens to the subject are performed using a photometry control unit and a distance measurement control unit (not shown).

  When the photometry / ranging process in step S106 is completed, the state of the shutter switch SW2 (111) is determined in a subsequent step S107. If SW2 (111) is OFF, the process returns to step S105 and the above-described processing is repeated. If SW2 (111) is ON, the photographing process is executed in step S108. Details of this photographing process will be described later.

  When the photographing process in step S108 ends, the process proceeds to step S109, dark current unevenness correction is performed, and after the process ends, the process proceeds to step S110. Details of the dark current unevenness correction will be described later. In step S110, the DSP 103 performs development processing on the captured image data. In step S <b> 111, compression processing is performed on the image data that has undergone development processing, and the compressed image data is stored in an empty area of the RAM 107.

  In step S112, the image data stored in the RAM 107 is read, and recording processing on the recording medium 108 is executed. After the recording process is completed, the process returns to step S101 to prepare for the next process.

  Next, details of the photographing processing operation performed in step S108 will be described with reference to FIG.

  First, in step S201, the mirror is moved to the mirror up position, and in step S202, the aperture is driven to a predetermined aperture value based on the photometric data obtained by the photometric processing in step S106 of FIG. In step S203, the charge clear operation of the image sensor 101 is performed, and charge accumulation is started in step S204. After the start of charge accumulation, the shutter is opened in step S205, and exposure of the image sensor 101 is started (step S206).

  Thereafter, in step S207, the process waits for the end of exposure according to the photometric data, and the shutter is closed in step S208. In step S209, the aperture is driven to the open aperture value, and in step S210, the mirror is driven to the mirror down position. In step S211, the process waits until the set charge accumulation time elapses, and ends the charge accumulation of the image sensor 101 (step S212). Finally, in step S213, the signal of the image sensor 101 is read out, and a series of processing is terminated and the processing returns to the main processing. In the first embodiment, in order to obtain a coefficient used for dark current unevenness correction described later, the area a in the OB portion of the pixel area of the image sensor 101 shown in FIG. The signal is read without performing the OB clamping process. The signal read from the image sensor 101 in this way is temporarily stored in the RAM 107 or an image memory (not shown).

  Next, dark current distribution data stored in the ROM 106 will be described with reference to FIG.

  The dark current distribution data is acquired in advance at a predetermined timing, for example, at the time of manufacturing the imaging device or at the time of calibration of the imaging device that is performed prior to actual shooting, and is stored in the ROM 106. When acquiring at the time of calibration, the dark current distribution data may be stored in the RAM 107, or may be stored in the ROM 106 if the ROM 106 is rewritable. Since it is preferable to acquire the dark current distribution data in a state where the dark current is conspicuous, photographing is performed in a high temperature state by shading the image sensor 101 and accumulating charges for a long time, and without performing the OB clamping process. Is read.

  The concept of dark image data obtained in this way is shown in FIG. In FIG. 5A, the lower the signal value, the darker the color. As can be seen from FIG. 5A, due to the above-described reasons such as heat from the peripheral circuit, dark current unevenness occurs in which the signal value is low in the central region of the image sensor 101 and the signal value is high in the periphery. FIGS. 5B and 5D are graphs showing data of arbitrary columns and rows in FIG. 5A with respect to pixel positions, respectively.

  In the first embodiment, the signal values of the respective pixels are not stored, but data representing the characteristics of the graphs shown in FIGS. 5B and 5D is obtained and stored in the ROM 106 as dark current distribution data. Keep it. By doing so, the amount of data to be stored can be reduced as compared with the case where all the signal values of each pixel are stored, so that the capacity of the ROM 106 can be saved.

  An example of how to obtain dark current distribution data representing this characteristic will be described in detail below.

  First, the data of each column and each row as shown in FIGS. 5B and 5C are added and averaged for each pixel while offset correction is performed so that the data value of the central pixel portion substantially matches zero. The reason why the data value of the central pixel portion is set to 0 is to prevent the image quality after correction in the imaging apparatus from being unnecessarily deteriorated due to the influence of pixel defects and local dark current unevenness. The local dark current unevenness referred to here does not indicate a tendency with horizontal / vertical addition average data as the correction target of the present invention, and for example, dark current is concentrated in one place near the center of the image. This is a case where a large pixel exists. If the data is to deal with such a place, the image quality deteriorates due to the influence of the pixel having a problem up to the other problem-free area, so the data value near the central pixel portion is set to zero.

  Of the obtained averaged data values, the averaged data values corresponding to the peripheral parts (upper and lower, left and right regions) that deviate from 0 are approximated by polynomials and shown by the thick lines in FIGS. 5B and 5C. Find an approximate curve. The approximate expression is obtained independently for the upper side, the lower side, the left side, and the right side. The order of approximation is determined by the characteristics of the dark current unevenness shape. Here, for example, a fourth-order approximation is used.

Then, using the obtained approximate expression, horizontal values [dx1, dx2, ..., dxm] and vertical values [dy1, dy2, ..., dyn] are calculated for each pixel position, and dark current distribution data is calculated. And At this time, an approximate expression is used when obtaining the data of the peripheral portion of the screen, and the boundary between the peripheral portion and the central portion where the data value is 0 is a minimum point of the approximate expression. That is, in the vertical direction, when y = 0 in the top row, the upper curve approximate expression is f _u (y), and the lower curve approximate expression is f _d (y). Of the local minimum points that appear twice due to the approximation, the local minimum point of f _u (y) near y = 0 is p _u , and the local minimum point of f _d (y) farther from y = 0 is p _d . Then
For 0 ≦ y < _pu , f _u (y)
For p _u ≦ y ≦ p _d , f (y) = 0
For y> _pu , f _d (y) (1)

To calculate the vertical value for each y. FIG. 5C shows the dark current distribution data in the vertical direction thus obtained.
Similarly, in the horizontal direction, when the leftmost column is x = 0, the approximate expression of the left curve is f _r (x), the approximate expression of the right curve is f _l (x), and f _r (x the minimum point _p r close to x = 0 of _x), and the distant minimum point from x = 0 of _f l (x) and _{p l,}
For 0 ≦ x < _pr , f _r (x)
For p _r ≦ x ≦ _pl , f (x) = 0
If x> _pr , f _l (x) (2)

To calculate a horizontal value for each x. The dark current distribution data in the horizontal direction thus obtained is shown in FIG.
As a result, the continuity of the boundary between the peripheral portion where the data actually exists and the central portion where the data is 0 is maintained, and the image quality after correction becomes higher.

In the example described above, [dx1, dx2,..., Dxm], [dy1, dy2,..., Dyn] are described as being stored as dark current distribution data, but equations (1) and (2) are stored. In addition, the calculation may be performed when dark current data is developed in step S102 of FIG. Further, in the expansion process in step S102, the dark current correction data Dij at the pixel position (i, j) uses dark current distribution data [dx1, dx2, ..., dxm], [dy1, dy2, ..., dyn]. ,
Dij = dxi × dyj, i = 0 ~ m, j = 0 ~ n

Is expanded in two dimensions.
Next, dark current unevenness correction performed in step S109 of FIG. 2 will be described with reference to the flowchart of FIG.

  First, in step S301, an average value ave_a of the area a of the photographed image shown in FIG. 4 is calculated. As described above, in an image pickup apparatus using an image pickup device, an OB clamp operation is generally performed in the image pickup device or the A / D converter in order to remove a dark current component and secure a dynamic range of a signal. is there. In the pixel area read after performing this OB clamping operation, the amount of dark current generated in the image sensor cannot be known from the image data. Accordingly, the area a is an area where image data is acquired without performing the OB clamping operation, and the amount of dark current generated during photographing can be known by calculating the average value of this area.

In a succeeding step S302, it is determined whether or not the average value ave_a of the region a exceeds a predetermined value. If it is less than the predetermined value, the dark current amount itself is small and the process is terminated without correction. If it is equal to or greater than the predetermined value, a conversion coefficient α for adjusting the dark current correction data in accordance with the actual photographing conditions is calculated in step S303. Here, the ratio of ave_a calculated from the image data of the area a and the average ave_A of the dark current correction data in the area corresponding to the area a in the dark current correction data developed in step S102 in FIG. . That is,
α = ave_a / ave_A

In this way, the ratio between the dark current amount under actual photographing conditions and the dark current amount at the time of dark current distribution data acquisition is the conversion coefficient α.
In the next step S304, the dark current correction data D (x, y) developed in the RAM 107 in step S102 of FIG. 2 is multiplied by the conversion coefficient α to convert to dark current correction data that matches the actual photographing conditions. Then, correction is completed by subtracting the converted dark current correction data D (x, y) from the captured image data S (x, y) in step S305.

  As described above, according to the first embodiment, the dark current distribution data stored in the ROM 106 is only [dx1, dx2,..., Dxm], [dy1, dy2,. The amount of data is small, and it is possible to realize highly accurate dark current unevenness correction.

  In the first embodiment, two-dimensional correction is performed using horizontal and vertical dark current distribution data. However, depending on the characteristics of dark current unevenness, only either horizontal or vertical is corrected. You may do it.

  Also, ave_A may be calculated at the time of development into dark current correction data in step S102 of FIG. 2 and stored in the RAM 107, or may be calculated in advance when dark current distribution data is acquired, and dark current distribution data is obtained. At the same time, it may be stored in the ROM 106 or may be obtained at the time of dark current unevenness correction, and the present invention is not limited by the calculation timing.

  Further, in the dark current unevenness correction shown in FIG. 6, the case where the dark current correction data is once converted by α in step S304 and then the converted dark current correction data is subtracted from the captured image data to be corrected has been described. However, the calculation procedure is not limited to this, and it goes without saying that the product may be subtracted while multiplying the dark current correction data by α during the correction calculation of each pixel.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.

  In the first embodiment, the correction coefficient α is calculated based on the average values of the captured image data and dark current correction data in the area a, that is, the dark current absolute value. However, as described above, since it is necessary to know the value before OB clamping as the captured image data of the region a, the OB clamping operation is not performed from the read first pixel of the image sensor 101 at the time of image capturing. It must start after the reading is finished, and the pixels cannot be used effectively.

  Therefore, in the second embodiment, as shown in FIG. 7, the correction coefficient α is calculated by the dark current relative value from the average value of the image data in the two areas of the image sensor 101. That is, the correction coefficient is obtained from the vertical region b of the OB portion and the vertical region c in the OB portion which is different from the region b in the horizontal direction.

  Note that the configuration of the imaging apparatus, the basic control of the imaging apparatus, and the imaging process in the second embodiment are substantially the same as those described in the first embodiment, and thus detailed description thereof is omitted. However, unlike the first embodiment, the readout process in step S213 in FIG. 3 obtains a signal obtained by performing the OB clamping process for all the areas including the area a in the second embodiment.

  Next, dark current unevenness correction performed in step S109 of FIG. 2 in the second embodiment will be described with reference to the flowchart of FIG.

  First, in step S401 and step S402, the average value ave_b of the area b and the average value ave_c of the area c of the image data obtained by photographing are calculated. The difference between these two values (ave_b−ave_c) represents the degree of peripheral floating due to dark current unevenness itself.

In a succeeding step S403, it is determined whether or not the difference between ave_b and ave_c exceeds a predetermined value. If it is less than the predetermined value, the peripheral floating due to dark current unevenness is small, and the process is terminated without correction. If it is equal to or greater than the predetermined value, a coefficient α for calculating the dark current correction data according to the actual photographing conditions is calculated in step S404. Here, the difference between the ave_b and ave_c calculated from the image and the average ave_B and ave_C of the dark current correction data in the regions corresponding to the region b and the region c in the dark current correction data developed in step S102 in FIG. The ratio to is α. That is,
α = (ave_b-ave_c) / (ave_B-ave_C)

  The subsequent processing is the same as in FIG. 6. In the next step S304, the dark current correction data D (x, y) developed in the RAM 107 in step S102 is multiplied by the conversion coefficient α, and the darkness that matches the actual photographing conditions is obtained. Convert to current correction data. Then, correction is completed by subtracting the converted dark current correction data D (x, y) from the captured image data S (x, y) in step S305.

  Thus, according to the second embodiment, dark current unevenness can be corrected without knowing the dark current absolute value.

<Third Embodiment>
Next, a third embodiment of the present invention will be described.

  When the correction coefficient α is calculated from the values of the two vertical areas in the OB portion as in the second embodiment described above, if the number of pixels in the OB portion is not large to some extent, the two regions are too close and the value difference is large. There is a possibility that it becomes small and a problem occurs in accuracy.

  Further, when there is a clear difference in the characteristics of the dark current distribution between the horizontal direction and the vertical direction, as shown in FIG. 9, the average value of the horizontal area and the average value of the vertical area of the OB portion It is also effective to obtain a dark current relative value from the above and calculate a correction coefficient. According to this method, it is possible to calculate the conversion coefficient with high accuracy even if the number of pixels in the OB portion of the image sensor is small.

  Note that the configuration of the imaging apparatus, the basic control of the imaging apparatus, and the imaging process in the third embodiment are the same as those in the second embodiment, and the detailed description thereof is omitted. . However, in the third embodiment, unlike the above-described second embodiment, a region b is set in the vertical OB portion and a region c is set in the horizontal OB portion.

  As described above, according to the third embodiment, the dark current unevenness correction can be performed with high accuracy even in an imaging apparatus in which the dark current absolute value is unknown and the number of pixels in the OB portion is small.

<Other embodiments>
An object of the present invention is to supply a storage medium (or recording medium) in which a program code of software for realizing the functions of the above-described embodiments is recorded to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus. Needless to say, this can also be achieved by reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an operating system (OS) running on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included. Examples of the storage medium for storing the program code include a flexible disk, hard disk, ROM, RAM, magnetic tape, nonvolatile memory card, CD-ROM, CD-R, DVD, optical disk, magneto-optical disk, MO, and the like. Can be considered. Also, a computer network such as a LAN (Local Area Network) or a WAN (Wide Area Network) can be used to supply the program code.

  Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. It goes without saying that the CPU or the like provided in the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

1 is a block diagram illustrating a schematic configuration of an imaging apparatus according to an embodiment of the present invention. It is a flowchart which shows operation | movement of the digital camera in embodiment of this invention. It is a flowchart which shows the imaging process operation | movement in embodiment of this invention. It is the figure which represented typically the pixel area | region of the image pick-up element in the 1st Embodiment of this invention. It is explanatory drawing of the acquisition process of the dark current distribution data in embodiment of this invention. It is a flowchart of the dark current nonuniformity correction process in the 1st Embodiment of this invention. It is the figure which represented typically the pixel area | region of the image pick-up element in the 2nd Embodiment of this invention. It is a flowchart of the dark current unevenness correction process in the second and third embodiments of the present invention. It is the figure which represented typically the pixel area | region of the image pick-up element in the 3rd Embodiment of this invention. It is a figure explaining the dark current nonuniformity of an image sensor.

Explanation of symbols

101 Image sensor 102 A / D converter 103 DSP
104 Timing generation circuit 105 CPU
106 ROM
107 RAM
108 Recording medium 109 Power switch 110 Switch SW1
111 Switch SW2
112 mode dial

Claims (12)

A dark approximation calculated by using the approximate expression obtained by performing polynomial approximation of data obtained by adding and averaging the image signals output from the entire area of the image sensor in the horizontal direction and the vertical direction in a state where the aperture of the image sensor is shielded from light. Storage means for storing dark current distribution data in the vertical direction representing current distribution characteristics and dark current distribution data in the horizontal direction;
Developing means for generating dark current correction data by two-dimensionally developing the vertical dark current distribution data and the horizontal dark current distribution data stored in the storage means;
Using the dark current correction data generated by the developing means, and correcting means for correcting dark current unevenness of an image signal obtained when a subject is photographed ,
In each of the dark current distribution data in the horizontal direction and the vertical direction, a boundary between the central portion and the peripheral portion in the horizontal direction and the vertical direction is set as a minimum point in the approximate expression, and the peripheral portion is set as the boundary The dark current distribution data corresponding to is calculated using the approximate expression, and the value of the dark current distribution data corresponding to the central portion is set to 0 . A coefficient for adjusting the dark current correction data based on an image signal obtained when the subject is photographed and a dark current correction data corresponding to a predetermined area set as a constantly shielded area of the image sensor. It further has calculation means for calculating,
The imaging apparatus according to claim 1, wherein the correction unit corrects dark current unevenness by subtracting a product of the dark current correction data and the coefficient from the image signal to be corrected.   The calculating means calculates, as the coefficient, a ratio between an average value of image signals obtained when the subject in the predetermined area is photographed and an average value of the dark current correction data in the predetermined area. The imaging device according to claim 2.   There are a plurality of the predetermined areas, and the calculating means calculates, as the coefficient, a difference between average values of image signals obtained when the subject is photographed between the plurality of predetermined areas, and the plurality of predetermined areas. The imaging apparatus according to claim 2, wherein a ratio with a difference between average values of dark current correction data is calculated.   The imaging apparatus according to claim 4, wherein the plurality of predetermined areas are two areas set in a horizontal direction and a vertical direction, respectively. Wherein the horizontal dark current distribution data, the imaging apparatus according to any one of claims 1 to 5, characterized by further comprising a calculating means for calculating a dark current distribution data of the vertical direction. A method for correcting dark current unevenness in an imaging apparatus having an imaging element,
Performed polynomial approximation of the data obtained by adding and averaging the image signals output from the entire area of the image sensor in the horizontal direction and the vertical direction in a state where the aperture of the image sensor is shielded, and calculated using the obtained approximate expression . A reading step of reading out dark current distribution data in the vertical direction representing the distribution characteristics of dark current and dark current distribution data in the horizontal direction from the storage medium, and
A developing step for generating dark current correction data by two-dimensionally developing the vertical dark current distribution data and the horizontal dark current distribution data read in the reading step;
Using the dark current correction data generated by the developing means, and correcting the dark current unevenness of the image signal obtained when the subject is photographed ,
In each of the dark current distribution data in the horizontal direction and the vertical direction, a boundary between the central portion and the peripheral portion in the horizontal direction and the vertical direction is set as a minimum point in the approximate expression, and the peripheral portion is set as the boundary The dark current distribution data corresponding to is calculated using the approximate expression, and the value of the dark current distribution data corresponding to the central portion is set to 0 . A coefficient for adjusting the dark current correction data based on an image signal obtained when the subject is photographed and a dark current correction data corresponding to a predetermined area set as a constantly shielded area of the image sensor. It further has a calculation step for calculating,
The correction method according to claim 7 , wherein in the correction step, dark current unevenness is corrected by subtracting a product of the dark current correction data and the coefficient from the image signal to be corrected. In the calculating step, as the coefficient, a ratio of an average value of image signals obtained when the subject in the predetermined area is photographed and an average value of the dark current correction data in the predetermined area is calculated. The correction method according to claim 8 . There are a plurality of the predetermined areas, and in the calculation step, as the coefficient, a difference between average values of image signals obtained when the subject is photographed between the plurality of predetermined areas, and the difference between the plurality of predetermined areas. The correction method according to claim 8 , wherein a ratio with a difference between average values of dark current correction data is calculated. The correction method according to claim 10 , wherein the plurality of predetermined areas are two areas set in a horizontal direction and a vertical direction, respectively. Wherein the horizontal dark current distribution data, the correction method according to any one of claims 7 to 11, wherein the further comprising a vertical calculation step of calculating a dark current distribution data.

Images