JP2012191379A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus that generates no noise such as horizontal stripes to suppress deterioration of quality of an image even when the temperature of an imaging element increases.SOLUTION: An imaging apparatus includes: an imaging element; a setting part; a dark image acquisition part; a real image acquisition part; a first calculation part; and a first correction part. The imaging element has an effective pixel region in which a plurality of pixels that photoelectrically converts incident light is arranged two-dimensionally. The setting part sets a sub-region by dividing the effective pixel region along the column direction of an arrangement. The dark image acquisition part acquires the dark image of the sub-region by driving the imaging element under a state where incident light is shaded. The first calculation part obtains the output value of a dark current for each column unit of the sub-region along the row direction of the arrangement to calculate an inclination showing the rate of change in the dark current. The real image acquisition part acquires a real image by driving the imaging element. The first correction part corrects noise generated in the row direction caused by the dark current in the real image based on the inclination.

Description

  The present invention relates to an imaging apparatus.

  2. Description of the Related Art Conventionally, in an electronic camera that is one of imaging devices, as noise caused by an imaging device, for example, shading (output unevenness) due to dark current when signal charges are read is known. As the shading correction method, a so-called clamping process is performed using a light-shielded pixel region (an optical black pixel region having a photodiode, hereinafter referred to as an “OB region”) arranged adjacent to the effective pixel region of the image sensor. It is known. (For example, see Patent Document 1).

JP 2001-268448 A

  However, in the above correction method, for example, when the temperature of the image sensor rises, the variation in the output of each pixel in the OB region increases, and the clamping process does not operate normally, and noise such as horizontal stripes occurs. There is.

  Therefore, in view of the above circumstances, an object of the present invention is to provide an imaging device that suppresses image quality deterioration of an image without generating noise such as horizontal stripes even when the temperature of the imaging device rises. To do.

  An imaging apparatus according to a first invention includes an imaging device, a setting unit, a dark image acquisition unit, a main image acquisition unit, a first calculation unit, and a first correction unit. The imaging device has an effective pixel region in which a plurality of pixels that photoelectrically convert incident light are two-dimensionally arranged. The setting unit sets the partial region by dividing the effective pixel region along the row direction of the array. The dark image acquisition unit acquires the dark image of the partial region by driving the imaging element in a state where the incident light is shielded. The first calculation unit analyzes the dark image to obtain an output value of the dark current for each row unit of the partial region along the column direction of the array, and calculates an inclination indicating a change rate of the dark current. The main image acquisition unit acquires a main image for recording by driving the image sensor. The first correction unit corrects noise in the row direction caused by dark current in the main image based on the inclination.

  In a second aspect based on the first aspect, the second aspect further includes a second calculation unit and a second correction unit. The second calculation unit obtains an output value of dark current for each column unit of the partial region along the row direction of the array by analyzing the dark image. The second correction unit corrects the noise in the column direction caused by the dark current in the main image based on the output value of the dark current in the column direction of the dark image.

  According to a third aspect, in the first or second aspect, the setting unit sets the partial region including at least a central line in the row direction of the effective pixel region.

  According to a fourth invention, in any one of the first to third inventions, a determination unit is further provided. The determination unit determines whether or not to correct the first correction unit according to the magnitude of the inclination. When the determination unit determines that correction is to be performed, the first correction unit performs the correction.

  In a fifth aspect based on any one of the first to fourth aspects, the first calculation unit obtains an average value of dark current output values for each row unit along the column direction, and calculates a slope.

  An imaging device according to a sixth aspect includes an imaging device, a main image acquisition unit, a calculation unit, and a correction unit. The imaging device has an effective pixel region in which a plurality of pixels that photoelectrically convert incident light are two-dimensionally arranged, and a light-shielded pixel row including a light-shielded pixel that blocks incident light within the effective pixel region is an array row. There are multiple along the direction. The main image acquisition unit acquires a main image for recording by driving the image sensor. The calculation unit analyzes the main image to obtain an output value of the dark current of the light-shielded pixel for each light-shielded pixel row, and calculates an inclination indicating a change rate of the dark current. The correction unit corrects noise in the column direction caused by dark current in the main image based on the inclination.

  In a seventh aspect based on the sixth aspect, the imaging device has two light-shielding pixel rows, and sandwiches one and the other of the light-shielding pixel rows with a central line in the row direction of the effective pixel region. It is arranged near the line.

  According to an eighth invention, in the sixth or seventh invention, a determination unit is further provided. The determination unit determines whether to correct the correction unit according to the magnitude of the inclination. When the determination unit determines to perform correction, the correction unit performs the correction.

  In a ninth aspect based on any one of the sixth to eighth aspects, the calculation unit obtains an average value of the dark current output for each light-shielded pixel row and calculates a slope.

  The present invention can provide an imaging apparatus that suppresses image quality deterioration of an image due to noise such as horizontal stripes.

Side view showing a configuration example of a main part of the electronic camera 1 The figure which shows the internal structural example of the electronic camera 1 shown in FIG. The figure explaining an example of the setting process of the partial area by the setting part 22a, and the output of dark current Partial enlarged view of the partial area shown in FIG. The figure explaining an example of the relationship between the drive state of the image pick-up element 11, and dark current A flowchart showing an example of the operation of the electronic camera 1 The block diagram which shows the structural example of the electronic camera 2 of 2nd Embodiment. The figure which shows an example of the effective pixel area | region of the image pick-up element 31 The figure explaining an example of the relationship between the drive state of the image pick-up element 31, and dark current A flowchart showing an example of the operation of the electronic camera 2

(First embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a side view illustrating a configuration example of a main part of the electronic camera 1. The electronic camera 1 is an embodiment of the imaging apparatus of the present invention. The electronic camera 1 is, for example, a single-lens reflex type electronic camera, and includes a camera body 10 and a photographing lens unit 2. The photographic lens unit 2 is detachably attached to a lens mount 10 a formed on the front surface of the camera body 10 in order to guide incident light (subject light) to the camera body 10. The camera body 10 and the photographic lens unit 2 are electrically connected via a contact point of the lens mount 10a when the photographic lens unit 2 is mounted.

  The taking lens unit 2 includes a lens system 3 and a diaphragm 4. The lens system 3 includes a plurality of lens groups including a zoom lens that adjusts the focal length and a focus lens that adjusts the imaging position on the imaging surface of the image sensor 11. Thereby, the lens system 3 can adjust the focus and the focal length. In FIG. 1, the lens system 3 is shown as a single lens for convenience of explanation. The diaphragm 4 adjusts the amount of incident light by opening and closing the diaphragm blades. As a result, the diaphragm 4 adjusts the light quantity of the light beam that forms an image on the image sensor 11 described later.

  The camera body 10 includes a quick return mirror 5, a pentaprism 6, an eyepiece lens 7, an optical finder 8, a mechanical shutter 9, an image sensor 11, and a display monitor 17.

  The quick return mirror 5 is rotatably provided on an optical axis L indicated by a one-dot chain line in the drawing. When photographing a subject, the quick return mirror 5 is retracted to a position indicated by a dotted line in the figure by rotation. As a result, incident light incident on the camera body 10 from the subject is guided to the image sensor 11. On the other hand, when the subject is not photographed, the quick return mirror 5 is disposed at an oblique position with respect to the optical axis L. In this case, the quick return mirror 5 guides incident light to the pentaprism 6. The pentaprism 6 reflects incident light and guides it to the eyepiece lens 7.

  The eyepiece 7 forms incident light guided by the pentaprism 6 as a subject image. The photographer can determine the composition of the subject by viewing the subject image formed by the eyepiece lens 7 via the optical viewfinder 8.

  The mechanical shutter 9 includes an openable / closable shutter curtain, and switches between a light shielding state in which incident light to the image sensor 11 is shielded and a non-light shielding state in which incident light reaches the image sensor 11 by opening and closing the shutter curtain. The image sensor 11 is, for example, a complementary metal-oxide semiconductor (CMOS) type color image sensor (details will be described later). The display monitor 17 is composed of, for example, a liquid crystal display medium. The display monitor 17 displays a playback still image, an operation menu of the electronic camera 1, and the like.

  FIG. 2 is a diagram illustrating an internal configuration example of the electronic camera 1 illustrated in FIG. 1. 2, illustration of the pentaprism 6, the eyepiece 7, the optical finder 8, the lens mount 10a, and the like shown in FIG. 1 is omitted for convenience of explanation.

  In FIG. 2, the camera body 1 includes a photographing lens unit 2 including a lens system 3 and a diaphragm 4, a mechanical shutter 9, an image sensor 11, a timing generator (hereinafter referred to as “TG”) 12, an analog front An end unit (hereinafter referred to as “AFE”) 13, a signal processing unit 14, an image processing unit 15, a RAM (Random Access Memory) 16, a display monitor 17, a flash memory 18, a recording interface unit (hereinafter, referred to as “AFE”). 19, an operation unit 20, a release button 21, a CPU (Central Processing Unit) 22, and a data bus 23.

  Among these, the AFE 13, the signal processing unit 14, the image processing unit 15, the RAM 16, the display monitor 17, the flash memory 18, the recording I / F unit 19, and the CPU 22 are connected to each other via the data bus 23. The lens system 3, the diaphragm 4, the mechanical shutter 9, the image sensor 11, the TG 12, the operation unit 20, and the release button 21 are connected to the CPU 22.

  The image sensor 11 has an effective pixel region in which a plurality of pixels that photoelectrically convert incident light are two-dimensionally arranged. Furthermore, the image sensor 11 can read out signal charges on an arbitrary line by XY addressing. The image sensor 11 captures an image of incident light and acquires an analog image signal (signal charge). An analog image signal output from the image sensor 11 is input to the AFE 13. Note that three types of color filters of R (red), G (green), and B (blue) are arranged in, for example, a Bayer array in the effective pixel region (imaging surface) of the image sensor 11. The TG 12 controls the charge accumulation time of the image sensor 11 and the reading of the image signal.

  The AFE 13 performs processing such as gain control and noise removal on the analog image signal input from the image sensor 11. Further, the AFE 13 performs a process of converting an analog image signal into a digital image signal (A / D conversion). The image signal output from the AFE 13 is temporarily recorded in the RAM 16 as image data.

  The signal processing unit 14 calculates first correction data and second correction data to be described later for the image data temporarily recorded in the RAM 16. Further, the signal processing unit 14 corrects noise generated due to dark current in the image data based on the first correction data and the second correction data. The signal processing unit 14 includes a first calculation unit 14a, a first correction unit 14b, a second calculation unit 14c, and a second correction unit 14d in order to correct noise generated due to dark current (details). Will be described later).

  The signal processing unit 14 may include an internal memory (not shown) that temporarily stores an image signal therein. In this case, the signal processing unit 14 corrects the image data temporarily recorded in the internal memory.

  The image processing unit 15 reads the image data recorded in the RAM 16 and performs various image processing (gradation conversion processing, white balance processing, etc.). The RAM 16 is a volatile memory. The flash memory 18 is a rewritable nonvolatile semiconductor memory. A program for controlling the electronic camera 1 is recorded in the flash memory 18 in advance. In accordance with this program, the CPU 22 executes a flow process shown in FIG.

  The recording I / F unit 19 is formed with a connector (not shown) for connecting a detachable recording medium 30. Then, the recording I / F unit 19 accesses the recording medium 30 connected to the connector according to an instruction from the CPU 22 and performs a recording process of a still image. The recording medium 30 is, for example, a non-volatile memory card. FIG. 2 shows the recording medium 30 after being connected to the connector.

  The operation unit 20 includes, for example, a command dial for command selection, a power button, and the like. Further, the operation unit 20 receives an instruction input for operating the electronic camera 1, for example.

  The release button 21 is an instruction for a half-press operation (an instruction input for starting an operation such as autofocus (AF) or automatic exposure (AE) before photographing) and a full-press operation (starting an imaging operation for acquiring a main image). Accept input.

  The CPU 22 is a processor that performs overall control of the electronic camera 1. The CPU 22 controls each part of the electronic camera 1 by executing a program stored in advance in the flash memory 18. The CPU 22 also functions as a setting unit 22a, a dark image acquisition unit 22b, a main image acquisition unit 22c, and a determination unit 22d.

  The setting unit 22a sets the partial region by dividing the effective pixel region of the image sensor 11 along the row direction of the array.

  FIG. 3 is a diagram for explaining an example of partial area setting processing and dark current output by the setting unit 22a. FIG. 4 is a partially enlarged view of the partial region shown in FIG. FIG. 3A shows an example of the horizontal output characteristics of dark current in the effective pixel region 11 a of the image sensor 11. FIG. 3B is a diagram illustrating an example of the effective pixel area 11 a of the image sensor 11. FIG. 3C illustrates an example of output characteristics in the vertical direction of dark current in the effective pixel region 11 a of the image sensor 11.

  As shown in FIG. 3A, the horizontal dark current tends to increase in the periphery of the effective pixel region 11a. Further, the dark current in the vertical direction tends to increase linearly in proportion to the time for sequentially reading from the 1st line to the nth line in the figure.

  As illustrated in FIG. 3B, the setting unit 22a divides the effective pixel area 11a (an imaging area including pixels in X rows and Y columns) in the X direction (row direction), and sets the partial area 11b. In FIG. 3B, the partial region 11b is indicated by a region surrounded by oblique lines. The setting unit 22a preferably sets the partial region 11b (for example, a partial region including 512 lines) including at least the center line in the row direction of the effective pixel region. Thereby, the setting part 22a can make it difficult to receive the influence of the temperature rise of the circuit etc. which are arrange | positioned around the effective pixel area | region 11a with respect to the partial area | region 11b. The partial region 11b is not limited to 512 lines, and may be an arbitrary number of lines such as 256 lines or 1024 lines. The setting unit 22a may set the entire effective pixel area as a partial area.

  After the shutter curtain of the mechanical shutter 9 is closed, the dark image acquisition unit 22b acquires the dark image of the partial region 11b by driving the image sensor 11 with the incident light blocked. When FIG. 3B is taken as an example, the dark image acquisition unit 22b instructs to read the image signal of the partial region 11b by designating the address of the partial region 11b via the TG 12. The main image acquisition unit 22c acquires the main image for recording by driving the image sensor 11 after the shutter curtain of the mechanical shutter 9 is opened and is in a non-light-shielding state.

  The determination unit 22d determines whether or not to correct the first correction unit 14a in accordance with the magnitude of the gradient indicating the rate of change in dark current. For example, the determination unit 22d determines that the first correction unit 14a performs correction when the inclination is equal to or greater than a preset threshold value. This threshold value is recorded in the flash memory 18 in advance. That is, the determination unit 22d reads the threshold value recorded in the flash memory 18 and determines whether or not the first correction unit 14a is to be corrected.

  The first calculation unit 14a analyzes the dark image to obtain an output value of dark current for each row unit of the partial region 11b along the column direction of the array, and calculates the inclination. Specifically, as shown in FIG. 4, the first calculation unit 14 a integrates pixel output values for each horizontal row (line) unit of the partial region 11 b and divides the average by the number of pixels for one line. Each value is calculated along the column direction (vertical direction) of the array. Here, since each RGB pixel is imaged in a light-shielded state, a dark current signal component is output. And the 1st calculation part 14a calculates the inclination of a perpendicular direction based on each average value as shown in FIG.3 (c). The first calculation unit 14a may calculate an average value for each predetermined number of lines.

  The first correction unit 14b corrects the noise in the column direction caused by the dark current in the main image based on the inclination (details will be described later).

  The second calculation unit 14c obtains an output value of dark current in the column direction of the partial region 11b along the row direction of the array by analyzing the dark image. Specifically, as shown in FIG. 4, the second calculation unit 14 c calculates the average value obtained by integrating the output values of the pixels for each column unit of the partial region 11 b and dividing by the number of pixels for one column. The second correction unit 14d corrects the noise in the column direction caused by dark current in the main image based on the average value for each column unit calculated by the second calculation unit 14c (details will be described later). .

  Next, an example of the operation of the electronic camera 1 will be described. FIG. 5 is a diagram illustrating an example of the relationship between the driving state of the image sensor 11 and the dark current. FIG. 5A is a diagram illustrating a driving state of the image sensor 11 when the main image is captured. The CPU 22 resets (A1) the data accumulated in the pixels in the image sensor before driving the image sensor 11 via the TG 12. The image sensor 11 then reads out (A2) in a light-shielded state. Thereby, the image sensor 11 outputs an output signal (dark image signal) in a state where the image sensor 11 is shielded from light prior to the exposure operation for obtaining the main image.

  Thereafter, the CPU 22 temporarily stops driving the image sensor 11 via the TG 12 (A3). Subsequently, the CPU 22 resets (A4) the data accumulated in the pixels in the image sensor before driving the image sensor 11 through the TG 12 in the same manner as the acquisition of the dark image signal. Next, the main image acquisition unit 22c of the CPU 22 performs shutter control according to the exposure value based on the exposure calculation result by AE control, and acquires the image signal of the main image. Thereby, the image sensor 11 performs exposure (A5) and reading (A6), and outputs the main image signal.

  FIG. 5B is a diagram showing a change with time of dark current accumulated in the image sensor 11. The image sensor 11 starts dark current accumulation after pixel reset (A1). As a result, dark current output proportional to time is accumulated during shading & reading (A2), exposure (A5), and reading (A6). It is known that the increase rate (slope) of dark current depends on temperature.

  However, the increase rate (slope) of the dark current in the dark image and the increase rate (slope) of the dark current in the main image are such that the time difference between the dark image acquisition (A2) and the main image acquisition (A6) is, for example, long seconds. If it is smaller than exposure etc., it can be regarded as the same. Taking FIG. 5 as an example, if the time from A1 to A6 is about 300 milliseconds as an example, the slopes of both can be regarded as the same.

  That is, since the increase rate of the dark current is linear, the first calculation unit 14a, as shown in FIG. 3C, based on the difference between the dark current output values in the vertical direction (vertical direction) of the screen, If the inclination in the dark image corresponding to 11b is calculated, the inclination from the 1st line to the nth line of the main image is calculated as a result. Accordingly, the first correction unit 14a corrects the noise in the column direction caused by the dark current in the main image based on the inclination calculated from the dark image, and consequently suppresses the horizontal stripe noise. It becomes possible to do. Hereinafter, an example of the operation of the electronic camera 1 will be described using a flowchart.

  FIG. 6 is a flowchart showing an example of the operation of the electronic camera 1. In the following operation example, after the power is turned on, the CPU 22 first drives the imaging device 11 to start capturing a through image having a resolution lower than that of the main image, and displays the through image on the display monitor 17 so-called live view display. Let Here, in the present embodiment, it is assumed that the temperature of the image sensor 11 is increased by live view display. Thereafter, when the release button 21 receives an instruction input for a full-press operation, the CPU 22 starts the processing of the flow shown in FIG.

  Step S101: The setting unit 22a of the CPU 22 performs partial area setting processing. Specifically, first, the CPU 22 disposes the quick return mirror 5 at an oblique position with respect to the optical axis L and closes the mechanical shutter 9. The setting unit 22a sets, for example, 512 rows of lines as the partial region 11b including the center line in the row direction of the effective pixel region as the data reading region (see FIG. 3B).

  Step S102: The dark image acquisition unit 22b of the CPU 22 starts imaging processing of a dark image (image signal of the partial region 11b). Specifically, the dark image acquisition unit 22b performs reset (A1) via the TG 12, as shown in FIG. Thereafter, the image sensor 11 performs reading (A2) in a state where light is shielded. The AFE 13 performs A / D conversion on the image signal of the partial region 11b read by the image sensor 11. The image signal of the partial area 11b output from the AFE 13 is temporarily recorded in the RAM 16 as image data of a dark image.

  Step S103: When the CPU 22 issues an instruction to the first calculation unit 14a of the signal processing unit 14, the first calculation unit 14a calculates the first correction data (the increase rate (slope) of the dark current in the dark image). . Specifically, the first calculation unit 14a analyzes the dark image, thereby calculating the average value of the dark current output value for each row (horizontal direction in FIG. 4) of the partial region 11b in the column direction of the array (FIG. 4), the first correction data (tilt) is calculated. At this time, the first calculation unit 14a may apply a median filter to each pixel of one line, for example. Alternatively, for example, for a registered defective pixel, the first calculation unit 14a may employ a value obtained by performing an interpolation process using output values of surrounding pixels.

  By calculating the first correction data (gradient) from the average value of the dark current output value by the first calculation unit 14a, the accuracy of the correction process of the first correction unit 14b is improved.

  Step S104: When the CPU 22 issues an instruction to the second calculation unit 14c of the signal processing unit 14, the second calculation unit 14c calculates the second correction data. Specifically, the second calculation unit 14c analyzes the dark image, thereby calculating the dark current output value for each column unit (vertical direction in FIG. 4) of the partial region 11b in the row direction of the array (horizontal in FIG. 4). Direction). That is, as shown in FIG. 4, the second calculation unit 14c integrates the output values of the pixels for each column unit of the partial region 11b, and calculates the average value. Thus, the average value for each column unit is calculated for one line in the horizontal direction. That is, the second calculation unit 14c calculates each horizontal average value for one line as the second correction data.

  Step S105: The main image acquisition unit 22c of the CPU 22 starts imaging processing of the main image (exposure (A5) shown in FIG. 5). Specifically, first, the CPU 22 retracts the quick return mirror 5 from the optical axis L and opens the mechanical shutter 9. Then, the main image acquisition unit 22c performs shutter control via the TG 12 based on the exposure value based on the exposure calculation result at the time of half-press operation. Then, after the exposure time ends, the CPU 22 closes the mechanical shutter 9. Thereafter, the image sensor 11 reads the image signal of the main image (read (A6) shown in FIG. 5). The AFE 13 A / D converts the image signal of the main image read by the image sensor 11. The image signal of the main image output from the AFE 13 is temporarily recorded in the RAM 16 as image data of the main image. Through this series of processing, the main image acquisition unit 22c acquires the main image.

  Step S106: When the CPU 22 issues an instruction to the second correction unit 14d of the signal processing unit 14, the second correction unit 14d corrects vertical streak and horizontal shading noise based on the second correction data. Specifically, the second correction unit 14d uses the second correction data for one line calculated in step S104 to output the output value of the pixel of the main image for each line of the main image (1 line to n lines). Then, the average value of the second correction data in the same row as the dark image is subtracted. Thereby, since the horizontal component of the dark current is offset, the second correction unit 14d can reduce noise common to the column direction such as vertical stripes and horizontal shading.

  Step S107: The determination unit 22d of the CPU 22 determines whether or not the first correction data (tilt) is equal to or greater than a preset threshold value. When the first correction data (tilt) is equal to or greater than a preset threshold value (step S107: Yes), the CPU 22 proceeds to the process of step S108.

  On the other hand, when the first correction data (tilt) is less than the preset threshold value (step S107: No), the CPU 22 proceeds to the process of step S109. In this case, the first correction unit 14b of the signal processing unit 14 does not need to perform unnecessary correction processing.

  Step S108: When the CPU 22 issues an instruction to the first correction unit 14b of the signal processing unit 14, the first correction unit 14b corrects the horizontal stripe noise based on the first correction data (tilt). Specifically, the first correction unit 14b sets the correction value to zero with the first line of the main image as a reference, and sets the correction value to a value obtained by sequentially multiplying the number of lines and the slope for the second and subsequent lines.

  Then, the first correction unit 14b subtracts the correction value corresponding to the line number from the output value of each pixel for each line (2 to n lines) of the main image, and performs correction processing for all lines. Thereby, since the vertical component of the dark current is offset, the first correction unit 14b does not need to generate horizontal stripe noise. That is, as shown in FIG. 5, the first correction unit 14b calculates the inclination in the main image because the inclination in the dark image and the inclination in the main image can be regarded as the same if the time from A1 to A6 is short. Processing can be omitted.

  Step S109: When the CPU 22 issues an instruction to the image processing unit 15, the image processing unit 15 performs various types of image processing (gradation conversion processing, White balance processing).

  Step S110: The CPU 22 records the image data of the main image after the image processing on the recording medium 30 via the recording I / F unit 19.

  As described above, the electronic camera 1 according to the first embodiment does not need to perform shading correction based on the dark current using the output of each pixel in the OB region arranged around the effective pixel region. That is, the electronic camera 1 calculates the increase rate (slope) of the dark current without being affected by the temperature rise of the image sensor 11, and corrects the horizontal stripe noise based on the increase rate (slope). Is possible. Thereby, in the electronic camera 1, when the temperature of the image sensor 11 rises, there is no problem that the output variation of each pixel in the OB region becomes large and noise such as horizontal stripes is generated.

  Further, the electronic camera 1 can correct fixed pattern noise common to the column direction, such as vertical stripes and horizontal shading. That is, in the electronic camera 1, when acquiring dark region image data in a partial area in order to correct fixed pattern noise, the driving of the image sensor 11 is not newly added to correct lateral stripe noise. The noise of the horizontal stripes can also be corrected using the dark image data.

Therefore, according to the first embodiment of the present invention, it is possible to suppress image quality deterioration due to noise such as horizontal shading, vertical stripes, horizontal stripes, and the like.
(Second Embodiment)
Next, an electronic camera according to a second embodiment of the present invention will be described. In the first embodiment of the present invention and the second embodiment of the present invention, the description of the same components is omitted, and the differences are mainly described. The electronic camera 2 according to the second embodiment is characterized by correcting the horizontal stripe noise without acquiring a dark image.

  FIG. 7 is a block diagram illustrating a configuration example of the electronic camera 2 according to the second embodiment. In the electronic camera 2, an image sensor 31 is used in place of the image sensor 11 of the electronic camera 1 of the first embodiment. In the electronic camera 2, the setting unit 22a, the dark image acquisition unit 22b, the second calculation unit 14c, and the second correction unit 14d illustrated in FIG. 1 are excluded.

  FIG. 8 is a diagram illustrating an example of the effective pixel area of the image sensor 31. As shown in FIG. 8, the imaging element 31 has an effective pixel region 31a in which a plurality of pixels that photoelectrically convert incident light are two-dimensionally arranged. Furthermore, the image sensor 31 has two light-shielding pixel rows 32 and 33 including light-shielding pixels that shield incident light within the effective pixel region along the array row direction (horizontal direction in the drawing). For example, the effective pixel is shielded from light by a metal such as aluminum. In FIG. 8, the light-shielded pixels are indicated by a region surrounded by diagonal lines. Note that the number of light-shielding pixel rows is not limited to two, and may be increased as needed. Further, the light-shielding pixel rows 32 and 33 may have a length corresponding to one line. In FIG. 8, the reason why the light-shielded pixels are arranged in a checkered pattern is to correct the output value of the light-shielded pixels using the output values of the surrounding effective pixels.

  Further, it is assumed that the image sensor 31 has a circuit configuration that is less likely to generate fixed pattern noise common in the column direction such as vertical stripes and horizontal shading than the image sensor 11. For this reason, in the image pickup device 31, it is sufficient to generate noise that does not require correction of the fixed pattern noise. Therefore, the electronic camera 2 can reduce the acquisition of the second correction data for correcting the fixed pattern noise described in the first embodiment.

  Here, the electronic camera 1 according to the first embodiment is configured to obtain a dark image of a partial region in a state where the image sensor 11 is shielded from light prior to the exposure operation. On the other hand, the electronic camera 2 of the second embodiment does not require acquisition of a dark image. Therefore, in the image pickup device 31, one of the two light-shielding pixel rows 32 and 33 and the other side of the effective pixel region in the row direction (horizontal direction in FIG. 8) are sandwiched in the vicinity of the line. Is arranged. With such an arrangement, the light-shielded pixels in the two light-shielded pixel rows 32 and 33 are less susceptible to the temperature rise of circuits and the like existing around the effective pixel region.

  As an example, the first calculation unit 14a of the second embodiment analyzes the main image to obtain the dark current output value of the light-shielded pixel for each of the light-shielded pixel rows 32 and 33, and the slope indicating the change rate of the dark current. Is calculated. Note that the first calculation unit 14a may calculate the average value of the dark current output for each of the light-shielded pixel rows 32 and 33 and calculate the inclination. At this time, for example, when the registered defective pixel is a light-shielded pixel, the first calculation unit 14a may adopt a value obtained by performing an interpolation process using output values of surrounding light-shielded pixels. By calculating the first correction data (gradient) from the average value of the dark current output value by the first calculation unit 14a, the accuracy of the correction process of the first correction unit 14b is improved.

  The first correction unit 14b of the second embodiment corrects noise in the column direction generated due to dark current in the main image based on the inclination. Specifically, the first correction unit 14b calculates the output difference of dark current in the screen column direction (vertical direction in FIG. 8) from the light-shielded pixel rows 32 and 33 arranged in the image sensor 31. Then, the first correction unit 14b calculates the inclination in the screen row direction based on the dark current output difference. Hereinafter, an example of the operation of the electronic camera 2 will be described.

  FIG. 9 is a diagram illustrating an example of the relationship between the driving state of the image sensor 31 and the dark current. Compared to the electronic camera 1 of the first embodiment, in FIG. 9, the driving process in a light-shielded state is reduced compared to FIG.

  FIG. 9A is a diagram illustrating a driving state of the image sensor 31 when the main image is captured. FIG. 9B is a diagram showing a change with time of dark current accumulated in the image sensor 31. The CPU 22 resets (B1) the data accumulated in the pixels in the image sensor before driving the image sensor 31 via the TG 12. In the image pickup device 31, accumulation of dark current starts after data reset (B1), and dark current proportional to time is accumulated during exposure (B2) and readout (B3). The first calculation unit 14 a calculates the increase rate (gradient) of the dark current based on the outputs from the light-shielded pixel rows 32 and 33. As a result, the first correction unit 14b can correct the gradient of the dark current output generated during the reading (B3).

  Next, the main image acquisition unit 22a performs shutter control according to the exposure value based on the exposure calculation result by AE control, and acquires the main image. That is, when the main image acquisition unit 22a instructs through the TG 12, the image sensor 31 performs exposure (B2) and reading (B3), and outputs a main image signal. Hereinafter, an example of the operation of the electronic camera 2 will be described using a flowchart.

  FIG. 10 is a flowchart illustrating an example of the operation of the electronic camera 2. In the following operation example, after the power is turned on, the CPU 22 first drives the imaging device 31 to start capturing a through image and causes the display monitor 17 to display the through image. Here, also in the second embodiment, it is assumed that the temperature of the image sensor 31 is increased by live view display. Thereafter, when the release button 21 receives an instruction input for a full-press operation, the CPU 22 starts the processing of the flow shown in FIG.

  Step S201: The main image acquisition unit 22a of the CPU 22 starts imaging processing of the main image. Specifically, first, the CPU 22 retracts the quick return mirror 5 from the optical axis L and opens the mechanical shutter 9. Then, the main image acquisition unit 22a performs shutter control via the TG 12 based on the exposure value based on the exposure calculation result at the time of half-press operation. Then, after the exposure time ends, the CPU 22 closes the mechanical shutter 9. Thereafter, the image sensor 31 reads the image signal of the main image (read (B3) shown in FIG. 9). The AFE 13 A / D converts the image signal of the main image read by the image sensor 31. The image signal of the main image output from the AFE 13 is temporarily recorded in the RAM 16 as image data of the main image.

  Step S202: When the CPU 22 issues an instruction to the first calculation unit 14a of the signal processing unit 14, the first calculation unit 14a calculates first correction data (dark current increase rate (slope)). Specifically, the first calculation unit 14a analyzes the main image to obtain the average value of the dark current output values of the light-shielded pixels for each of the light-shielded pixel rows 32 and 33. Subsequently, as shown in FIG. 9, an output difference occurs between the average value of the dark current output value in the light-shielded pixel row 32 and the average value of the dark current output value in the light-shielded pixel row 33. Calculates first correction data (slope).

  Step S203: The determination unit 22b of the CPU 22 determines whether or not the first correction data (tilt) is greater than or equal to a preset threshold value. When the first correction data (tilt) is larger than a preset threshold value (step S203: Yes), the CPU 22 proceeds to the process of step S204.

  On the other hand, when the first correction data (tilt) is less than the preset threshold value (step S203: No), the CPU 22 proceeds to the process of step S205. In this case, the first correction unit 14b need not perform unnecessary correction processing.

  Step S204: When the CPU 22 issues an instruction to the first correction unit 14b of the signal processing unit 14, the first correction unit 14b corrects the horizontal stripe noise based on the first correction data (tilt). Specifically, the first correction unit 14b sets the correction value to zero with the first line of the main image as a reference, and sets the correction value to a value obtained by sequentially multiplying the number of lines and the slope for the second and subsequent lines. Then, the first correction unit 14b subtracts the correction value corresponding to the line number from the output value of each pixel for each line (2 to n lines) of the main image, and performs correction processing for all lines. Thereby, since the vertical component of the dark current is offset, the first correction unit 14b does not need to generate horizontal stripe noise in the main image. In addition, the first correction unit 14b interpolates the output value of the light-shielded pixel using the output value of the surrounding effective pixels.

  Step S205: When the CPU 22 issues an instruction to the image processing unit 15, the image processing unit 15 performs various types of image processing (gradation conversion processing, White balance processing).

  Step S206: The CPU 22 records the image data of the main image after the image processing on the recording medium 30 via the recording I / F unit 19.

  As described above, the electronic camera 2 according to the second embodiment, like the electronic camera 1 according to the first embodiment, uses the output of each pixel in the OB area arranged around the effective pixel area to perform shading correction based on dark current. You don't have to. Further, as compared with the electronic camera 1, the electronic camera 2 can acquire the main image signal and the dark image signal for correction as a single image at the same time, so that more accurate correction can be performed.

  Therefore, according to the second embodiment of the present invention, it is possible to perform correction that does not require acquisition of a dark image with respect to the correction of the noise of the horizontal stripe, and it is possible to suppress deterioration in image quality of the image.

DESCRIPTION OF SYMBOLS 1, 2 ... Electronic camera 11, 11, ... Image pick-up element, 22a ... Setting part, 22b ... Dark image acquisition part, 22c ... Main image acquisition part, 14a ... 1st calculation Part, 14c ... 1st correction part

Claims (9)

An image sensor having an effective pixel region in which a plurality of pixels that photoelectrically convert incident light are arranged in a two-dimensional manner;
A setting unit for setting a partial region by dividing the effective pixel region along the row direction of the array;
A dark image acquisition unit that acquires a dark image of the partial region by driving the imaging element in a state where the incident light is shielded;
A first calculation unit that obtains an output value of dark current for each row unit of the partial region along the column direction of the array by analyzing the dark image, and calculates an inclination indicating a change rate of the dark current When,
A main image acquisition unit for acquiring a main image for recording by driving the image sensor;
An image pickup apparatus comprising: a first correction unit configured to correct noise in the column direction generated due to the dark current in the main image based on the inclination. The imaging device according to claim 1,
A second calculation unit that obtains an output value of dark current in the column direction of the partial region along the row direction of the array by analyzing the dark image;
And a second correction unit that corrects the noise in the column direction caused by the dark current in the main image based on the output value of the dark current for each column unit. apparatus. In the imaging device according to claim 1 or 2,
The image pickup apparatus, wherein the setting unit sets the partial region including at least a central line in the row direction of the effective pixel region. In the imaging device according to any one of claims 1 to 3,
A determination unit that determines whether to correct the first correction unit according to the magnitude of the inclination;
When the determination unit determines to perform the correction, the first correction unit performs the correction. In the imaging device according to any one of claims 1 to 4,
The imaging apparatus according to claim 1, wherein the first calculation unit calculates an average value of the output values of the dark current for each row unit along the column direction, and calculates the inclination. A plurality of pixels that photoelectrically convert incident light have an effective pixel region that is two-dimensionally arranged, and a light-shielding pixel row that includes the light-shielding pixels that shield the incident light within the effective pixel region is arranged in the row direction of the array. An image sensor having a plurality of
A main image acquisition unit for acquiring a main image for recording by driving the image sensor;
By analyzing the main image, an output value of the dark current of the light-shielded pixel is obtained for each light-shielded pixel row, and a calculation unit that calculates an inclination indicating a change rate of the dark current;
An image pickup apparatus comprising: a correction unit configured to correct noise in the column direction generated due to the dark current in the main image based on the inclination. The imaging device according to claim 6,
The image sensor has two light-shielding pixel rows, and one and the other of the light-shielding pixel rows are arranged in the vicinity of the lines with a center line in the row direction of the effective pixel region interposed therebetween. An imaging apparatus characterized by comprising: In the imaging device according to claim 6 or 7,
A determination unit for determining whether to correct the correction unit according to the magnitude of the inclination;
The imaging apparatus, wherein when the determination unit determines to perform the correction, the correction unit performs the correction. In the imaging device according to any one of claims 6 to 9,
The said calculating part calculates | requires the average value of the said output value of the said dark current for every said light-shielding pixel row, and calculates the said inclination, The imaging device characterized by the above-mentioned.

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