JP2011114474A - Imaging apparatus and method for driving solid-state imaging element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of preventing image quality deterioration accompanying the reduction of smears. <P>SOLUTION: The imaging apparatus is provided with a CCD type solid-state imaging element 5 having a plurality of photoelectric conversion elements. The plurality of photoelectric conversion elements includes: a driving part 5a including an effective photoelectric conversion element for generating charge corresponding to object light and a photoelectric conversion element for smear detection to drive the solid-state imaging element 5; and a smear occurrence ratio calculating part 18 for calculating the ratio (hereafter called as a smear occurrence ratio) of a smear occurrence area to the entire area where effective pixels are arranged on the basis of a signal output from a pixel for smear detection. The driving part 5a drives the solid-state imaging element 5 with smear reduction driving to read a signal when the smear occurrence ratio is equal to or more than a threshold, and drives the solid-state imaging element 5 with normal driving to read a signal when the smear occurrence ratio is not higher than the threshold, wherein the smear reduction driving is driving that reduces the number of photoelectric conversion elements for reading charge than during the normal driving. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an imaging apparatus and a method for driving a solid-state imaging element.

  In an imaging device such as a digital camera or digital video camera equipped with a CCD (Charge Coupled Device) type image sensor as an imaging device, smear that is a phenomenon peculiar to CCD occurs when shooting is performed without using a mechanical shutter. Is a problem.

  As a method of reducing smear, as disclosed in Patent Document 1, a method of transferring charges at high speed by performing thinning driving is known. Since this method transfers charges at high speed, there is a possibility that the remaining transfer of charges occurs in a transfer path where smear does not occur, and the image quality may deteriorate. If smear occurs in a wide range to some extent, the effect of reducing smear due to high-speed transfer is greater than the deterioration in image quality due to this transfer residue, so the final image quality should be good. it can. However, when smear occurs locally (for example, when smear occurs only in one vertical charge transfer path), image quality degradation due to the transfer residue is reduced due to high-speed transfer. In some cases, the final image quality deteriorates.

  As disclosed in Patent Document 2, smear reduction driving is generally performed only when it is determined that smear has occurred. However, when the thinning drive is adopted as the smear reduction drive in such a method, the image quality deteriorates due to the above-described reason when the smear is generated locally.

JP 2003-234964 A JP 2009-89075 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an imaging apparatus and a solid-state imaging element driving method capable of preventing image quality deterioration due to reduction of smear.

  The imaging device of the present invention is an imaging device including a CCD type solid-state imaging device having a plurality of pixels, and the plurality of pixels detect effective pixels and smears that generate charges according to subject light. A drive unit that drives the solid-state imaging device to read signals from the plurality of pixels, and an area in which the effective pixels are arranged based on signals output from the smear detection pixels A smear generation ratio calculation unit that calculates a ratio of a smear generation region to the whole (hereinafter referred to as a smear generation ratio), and the drive unit performs smear reduction driving when the smear generation ratio is equal to or greater than a threshold value. The signal is read out by driving the solid-state imaging device by the normal drive when the smear occurrence ratio is less than the threshold value, and the signal is read out by the solid-state imaging device. A drive with a reduced number of pixels to read out the charge than when driving.

  The solid-state imaging device driving method of the present invention is a CCD-type solid-state imaging device driving method having a plurality of pixels, and the plurality of pixels detect effective pixels and smears that generate charges according to subject light. And calculating a ratio of the smear generation area to the entire area where the effective pixels are arranged (hereinafter referred to as a smear generation ratio) based on a signal output from the smear detection pixel. A smear occurrence ratio calculating step; when the smear occurrence ratio is equal to or greater than a threshold value, the solid-state image sensor is driven by smear reduction driving to read a signal; and when the smear occurrence ratio is less than the threshold value, the solid-state image sensor is normally driven And the smear reduction drive is a drive in which the number of pixels from which charges are read is reduced as compared with the normal drive.

  According to the present invention, it is possible to provide an imaging apparatus and a solid-state imaging element driving method capable of preventing image quality deterioration due to reduction of smear.

The figure which shows schematic structure of the imaging device for describing one Embodiment of this invention FIG. 1 is a schematic plan view showing a schematic configuration of a solid-state image sensor in the digital camera shown in FIG. The figure which showed the example of an arrangement | sequence of the pixel contained in the light-receiving part of the solid-state image sensor shown in FIG. The figure explaining the method of reading a signal by normal drive from the solid-state image sensor in the digital camera shown in FIG. The figure which shows the timing chart example of the drive pulse at the time of the normal drive of the solid-state image sensor in the digital camera shown in FIG. The figure explaining the method to read a signal by the smear reduction drive (1st field) from the solid-state image sensor in the digital camera shown in FIG. The figure which shows the example of a timing chart of the drive pulse at the time of the smear reduction drive (1st field) of the solid-state image sensor in the digital camera shown in FIG. The figure explaining the method to read a signal by the smear reduction drive (2nd field) from the solid-state image sensor in the digital camera shown in FIG. The figure which shows the example of a timing chart of the drive pulse at the time of the smear reduction drive (2nd field) of the solid-state image sensor in the digital camera shown in FIG. The figure which showed typically the imaging signal output at the time of the normal drive of the solid-state image sensor in the digital camera shown in FIG. The figure which showed typically the imaging signal output at the time of a smear reduction drive from the solid-state image sensor in the digital camera shown in FIG. The figure explaining the method to synthesize | combine two image pick-up signals output in each field at the time of smear reduction drive from the solid-state image sensor in the digital camera shown in FIG. The figure which showed the operation | movement flow when the digital camera shown in FIG. 1 implements the imaging for recording for recording image data on a recording medium. The figure which showed another example of arrangement | sequence of the pixel contained in the light-receiving part of the solid-state image sensor shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an imaging apparatus for explaining an embodiment of the present invention. Examples of the imaging device include an imaging device such as a digital camera and a digital video camera, an imaging module mounted on an electronic endoscope, a camera-equipped mobile phone, and the like. Here, a digital camera will be described as an example.

  A digital camera shown in FIG. 1 includes a photographing lens 1, an aperture 2, a mechanical shutter 3, a CCD solid-state imaging device 5, an analog signal processing unit 6, an AD conversion unit 7, a lens driving unit 1a, Aperture drive unit 2a, shutter drive unit 3a, image sensor drive unit 5a, system control unit 11, auxiliary light emission unit 10, light emission drive unit 10a, operation unit 12, main memory 16, and main memory 16, a memory control unit 15, a digital signal processing unit 17, a smear occurrence ratio calculation unit 18, a compression / decompression processing unit 19, and an external memory control unit 20 to which a removable recording medium 21 is connected, And a display control unit 22 to which a liquid crystal display unit 23 mounted on the back of the camera or the like is connected.

  The diaphragm 2 and the mechanical shutter 3 are provided in this order between the photographing lens 1 and the solid-state imaging device 5.

  The auxiliary light emitting unit 10 emits auxiliary light for illuminating a subject at the time of photographing, and emits auxiliary light (flash light) by a xenon tube, an LED, or the like.

  The system control unit 11 controls the lens driving unit 1a to adjust the position of the photographing lens 1 to the focus position or to perform zoom adjustment. The system control unit 11 adjusts the exposure amount by controlling the aperture amount of the aperture 2 via the aperture drive unit 2a, and controls opening and closing of the mechanical shutter 3 via the shutter drive unit 3a. The system control unit 11 drives the solid-state imaging device 5 via the imaging device driving unit 5a, and outputs a subject image captured through the photographing lens 1 as an imaging signal. The system control unit 11 causes the auxiliary light emitting unit 10 to emit auxiliary light via the light emission driving unit 10a. An instruction signal from the user is input to the system control unit 11 through the operation unit 12.

  The analog signal processing unit 6 performs correlated double sampling processing and signal amplification processing on the imaging signal output from the solid-state imaging device 5. The AD conversion unit 7 converts the imaging signal processed by the analog signal processing unit 6 into a digital signal. The digital signal processing unit 17 generates image data by performing white balance correction, synchronization processing, gamma correction calculation, RGB / YC conversion processing, and the like on the imaging signal output from the AD conversion unit 7. The digital signal processing unit 17 also performs processing for generating wide DR image data in which the dynamic range is expanded by combining two generated image data having different sensitivities.

  The smear occurrence ratio calculation unit 18 calculates data for determining whether or not smear reduction driving that can be performed by the digital camera is performed during imaging.

  The compression / decompression processing unit 19 compresses the image data generated by the digital signal processing unit 17 into the JPEG format or decompresses the compressed image data. The processed image data is recorded on the recording medium 21 under the control of the external memory control unit 20.

  The memory control unit 15, the digital signal processing unit 17, the smear occurrence ratio calculation unit 18, the compression / decompression processing unit 19, the external memory control unit 20, and the display control unit 22 are connected to each other by a control bus 24 and a data bus 25. It is controlled by a command from the system control unit 11.

  FIG. 2 is a schematic plan view showing a schematic configuration of the solid-state imaging device in the digital camera shown in FIG. A light receiving portion 51, a horizontal charge transfer path 52, and an output portion 53 are formed on a semiconductor substrate such as silicon.

  In the light receiving unit 51, a plurality of lines in which a plurality of pixels including photoelectric conversion elements such as photodiodes are arranged in the horizontal direction X are arranged in the vertical direction Y orthogonal to the horizontal direction X.

  The charges generated in each pixel of the light receiving unit 51 are read out to a vertical charge transfer path (not shown) in the light receiving unit 51 and transferred here in the vertical direction Y. The charge for one line transferred through the vertical charge transfer path is transferred in the horizontal direction X by the horizontal charge transfer path 52. An end portion of the horizontal charge transfer path 52 is provided with an output unit 53 such as a floating diffusion amplifier (FDA) that converts the charge into a voltage signal (imaging signal) proportional to the charge amount and outputs the voltage signal. The electric charge transferred to is converted into a voltage signal by the output unit 53 and output to the outside.

  At least one line adjacent to the horizontal charge transfer path 52 among the plurality of lines arranged in the light receiving portion 51 is configured such that light is not incident on the light shielding film in order to detect smear. Each pixel in the shielded line is called a smear detection pixel. In addition, pixels other than the smear detection pixel are referred to as effective pixels that generate charges according to subject light because light is incident thereon. In addition, since smear is mainly generated in the vertical charge transfer path, the smear detection pixel does not need to be a photoelectric conversion element, and only the vertical charge transfer path is provided without providing the photoelectric conversion element. Also good. When the photoelectric conversion element is omitted, the charge existing in the vertical charge transfer path adjacent to the area where the photoelectric conversion element is omitted is treated as the charge read from this area.

  In addition, there are pixels that are shielded from light for detecting the black level for black level correction around the effective pixels of the light receiving unit 51, but the illustration is omitted here.

  When smear occurs in any vertical charge transfer path in the light receiving section 51, the signal level obtained from the smear detection pixel from which charge is read out to the vertical charge transfer path is the level when black smear is not generated (black Level). For this reason, by detecting the level of the signal obtained from the smear detection pixel, it is possible to know at which effective pixel the smear is generated in the effective region where the effective pixel is arranged. . The smear occurrence ratio calculation unit 18 uses this fact to calculate a smear occurrence ratio that is a ratio of the smear occurrence area to the effective area.

  Specifically, the smear occurrence ratio calculation unit 18 detects the level of the signal obtained from the smear detection pixel line, and determines whether the level exceeds a level (smear level) that can be determined as smear. To do. When there is a smear detection pixel that exceeds the smear level, the position in the horizontal direction of the pixel is set as a smear generation position. When the number of pixels in the horizontal direction in one line of effective pixels (synonymous with the number of pixels in the horizontal direction in one line of smear detection pixels) is M, and the number of detected smear occurrence positions is N, the smear occurrence ratio calculation unit 18 (N / M) is calculated as a smear generation ratio.

  FIG. 3 is a diagram illustrating an example of the arrangement of pixels included in the light receiving unit 51 of the solid-state imaging device illustrated in FIG. The blocks with “R1” and “R2” shown in FIG. 3 indicate pixels having a red color filter above the light receiving surface. The blocks with “G1” and “G2” indicate pixels having a green color filter above the light receiving surface. The blocks with “B1” and “B2” indicate pixels having a blue color filter above the light receiving surface.

  In the example shown in FIG. 3, the pixels 5a arranged in a square lattice in the horizontal direction and the vertical direction, and the pixels 5b arranged in a square lattice at the same pitch and the same number as the pixels 5a The arrangement is arranged so as to be shifted in the horizontal and vertical directions by 1/2 of the arrangement pitch. In FIG. 3, the blocks to which R1, G1, and B1 are attached are the pixels 5a, and the blocks to which R2, G2, and B2 are attached are the pixels 5b.

  As shown in FIG. 3, the color filter array above the pixel 5a is a Bayer array, and the color filter array above the pixel 5b is also a Bayer array. With such an arrangement, a pixel 5b having a color filter of the same color as the color filter above the pixel 5a is present obliquely next to the pixel 5a.

  A vertical charge transfer path 54 is provided correspondingly to a pixel column composed of pixels arranged in the vertical direction. The vertical charge transfer path 54 is arranged on the right side of the corresponding pixel column, and transfers the charges read from each pixel of the corresponding pixel column in the vertical direction. Between the vertical charge transfer path 54 and each pixel in the corresponding pixel column, a charge read region 56 (in the figure, schematically indicated by an arrow) for reading charge from the pixel to the vertical charge transfer path 54. Is formed).

  When pixel rows composed of pixels arranged in the horizontal direction are referred to as lines, transfer electrodes V1 to V16 to which drive pulses are supplied from the image sensor driving unit 5a are meandered in the horizontal direction between the lines.

  Of the GB line in which the pixel 5a having the G filter above and the pixel 5a having the B filter above are arranged, the transfer electrode V16 is on the upper side of the odd-numbered line counted from the side opposite to the horizontal charge transfer path 52. The transfer electrode V1 is formed on the lower side. Of the GB line of the pixel 5a, the transfer electrode V8 is formed on the upper side of the even-numbered line counted from the side opposite to the horizontal charge transfer path 52, and the transfer electrode V9 is formed on the lower side. .

  Of the RG line in which the pixel 5a having the R filter above and the pixel 5a having the G filter above are arranged, the transfer electrode V4 is disposed on the upper side of the odd-numbered line counted from the side opposite to the horizontal charge transfer path 52. The transfer electrode V5 is formed on the lower side. Of the RG line of the pixel 5a, the transfer electrode V12 is formed on the upper side of the even-numbered line counted from the side opposite to the horizontal charge transfer path 52, and the transfer electrode V13 is formed on the lower side. .

  Of the GB line of the pixel 5b, the transfer electrode V6 is formed on the upper side of the odd-numbered line counted from the side opposite to the horizontal charge transfer path 52, and the transfer electrode V7 is formed on the lower side. . Of the GB line of the pixel 5b, the transfer electrode V14 is formed on the upper side of the even-numbered line counted from the side opposite to the horizontal charge transfer path 52, and the transfer electrode V15 is formed on the lower side. .

  Of the RG line of the pixel 5b, the transfer electrode V2 is formed on the upper side of the odd-numbered line counted from the side opposite to the horizontal charge transfer path 52, and the transfer electrode V3 is formed on the lower side. . Of the RG line of the pixel 5b, the transfer electrode V10 is formed on the upper side of the even-numbered line counted from the side opposite to the horizontal charge transfer path 52, and the transfer electrode V11 is formed on the lower side. .

  The transfer electrodes V1, V5, V9, and V13 also cover the charge readout region 56 adjacent to the pixel 5a and also serve as a readout electrode. By applying a read pulse to the transfer electrodes V1, V5, V9, and V13, charge can be read from the pixel 5a to the vertical charge transfer path.

  The transfer electrodes V3, V7, V11, and V15 also cover the charge readout region 56 adjacent to the pixel 5b and also serve as a readout electrode. By applying a read pulse to the transfer electrodes V3, V7, V11, and V15, charges can be read from the pixel 5b to the vertical charge transfer path.

  Thus, since the readout electrode of the pixel 5a and the readout electrode of the pixel 5b can be driven independently, it is possible to control the exposure times of the pixel 5a and the pixel 5b to be different. With such a configuration, it is possible to output signals having different sensitivities from the pixels 5a and 5b, while the pixels 5a and 5b have the same structure.

  Hereinafter, the pixel 5a illustrated in FIG. 3 is also referred to as a main pixel, and the pixel 5b is also referred to as a sub-pixel. A combination of a main pixel and a sub-pixel which are adjacent main pixels and sub-pixels and have a color filter of the same color above the light receiving surface is called a pair. The arrangement shown in FIG. 3 can be said to be a regular arrangement of a plurality of pairs.

  This digital camera can be set to a normal shooting mode, a high-sensitivity shooting mode, and a wide DR shooting mode for shooting with an expanded dynamic range.

  In the normal imaging mode, the system control unit 11 performs imaging with the same exposure time for the main pixel and the sub-pixel. Then, the digital signal processing unit 17 generates image data using all signals read from the main pixel and the sub-pixel. This image data is recorded on the recording medium 21 after being compressed.

  In the high-sensitivity shooting mode, the system control unit 11 performs imaging with the same exposure time for the main pixel and the sub-pixel. Then, the digital signal processing unit 17 combines the signal obtained from the main pixel and the signal obtained from the sub-pixel in the pair, and generates high-sensitivity image data using the combined signal. This image data is recorded on the recording medium 21 after being compressed.

  In the wide DR shooting mode, the system control unit 11 performs imaging with different exposure times for the main pixel and the sub-pixel. The digital signal processing unit 17 generates main pixel image data from a signal obtained from a main pixel, and generates subpixel image data from a signal obtained from a subpixel. The digital signal processing unit 17 combines these main pixel image data and subpixel image data to generate wide DR image data with an expanded dynamic range. The wide DR image data is recorded on the recording medium 21 after being compressed.

  In the normal shooting mode, the system control unit 11 determines a signal readout driving method at the time of imaging the next frame according to the smear generation rate calculated by the smear generation rate calculation unit 18 at the time of imaging the previous frame. Specifically, if the smear occurrence rate is equal to or greater than a threshold (for example, 0.1), the smear reduction drive is adopted as a signal readout method at the time of imaging the next frame, and if the smear occurrence rate is less than the threshold, the next Normal driving is adopted as a signal readout method at the time of imaging of the frame.

  In the configuration example of the solid-state imaging device illustrated in FIG. 3, each pixel of at least two lines adjacent to the horizontal charge transfer path 52 among the pixel lines is a smear detection pixel. Then, the smear occurrence ratio calculation unit 18 detects the level of the signal obtained from each pixel of these two lines, and sets the horizontal position of the signal exceeding the smear level as the smear detection position. Then, the total number of pixels included in these two lines is M, the number of detected smear occurrence positions is N, and (N / M) is calculated as the smear occurrence ratio.

  When the pixel array is a square array, that is, in the configuration in which the pixel 5b is omitted in FIG. 3, each pixel of at least one line adjacent to the horizontal charge transfer path 52 is set as a smear detection pixel. (M / M) may be calculated as a smear generation ratio, where M is the total number of pixels included in the pixel, N is the number of smear occurrence positions detected.

  Here, “imaging” refers to the start of exposure of each pixel of the solid-state imaging device 5, and the charge accumulated in a part or all of the pixels of the solid-state imaging device 5 by the exposure after the exposure is completed. This is a series of processing for reading out to 54, transferring this, and outputting a signal corresponding to the charge from the solid-state imaging device 5.

  Further, the smear reduction drive is a drive in which the number of pixels from which charges are read is reduced compared to the normal drive. Hereinafter, the normal drive and the smear reduction drive will be specifically described.

  FIG. 4 is a diagram for explaining a method of reading a signal from the solid-state imaging device by normal driving. FIG. 5 is a diagram illustrating an example of a timing chart of pulses supplied to the transfer electrode of the solid-state imaging device 5 during normal driving. FIG. 5A in FIG. 5 shows a timing chart for reading out charges from a pixel and transferring the charges several stages. FIG. 5B in FIG. 5 shows a timing chart when charges are transferred through the vertical charge transfer path 54.

  As shown in FIGS. 4 and 5, at the time of normal driving, the system controller 11 applies a read pulse to the transfer electrodes V1, V3, V9, V11 after the exposure is completed, and every two lines from the lines of all pixels. Charge is read out to the vertical charge transfer path 54. Then, this charge is transferred, and a signal corresponding to the charge is output from the solid-state imaging device 5. In FIG. 4, the pixel from which charges are read is hatched.

  On the other hand, at the time of smear reduction driving, the system control unit 11 divides into a plurality of (two in the following example) fields from the pixels (pixels indicated by oblique lines in FIG. 4) from which signals are read out during normal driving. The signal is read out.

  FIG. 6 is a diagram for explaining a method of reading a signal from the solid-state imaging device in the first field of smear reduction driving. FIG. 7 is a diagram illustrating an example of a timing chart of pulses supplied to the transfer electrode of the solid-state imaging device 5 in the first field of smear reduction driving. FIG. 7A in FIG. 7 shows a timing chart for reading out charges from a pixel and transferring the charges several stages. FIG. 7B of FIG. 7 shows a timing chart when charges are transferred through the vertical charge transfer path 54.

  FIG. 8 is a diagram for explaining a method of reading a signal from the solid-state imaging device in the second field of smear reduction driving. FIG. 9 is a diagram illustrating an example of a timing chart of pulses supplied to the transfer electrode of the solid-state imaging device 5 in the second field of smear reduction driving. FIG. 9A in FIG. 9 shows a timing chart for reading out charges from a pixel and transferring the charges several stages. FIG. 9B of FIG. 9 shows a timing chart when charges are transferred through the vertical charge transfer path 54.

  At the time of smear reduction driving, first, the system control unit 11 applies a read pulse to the transfer electrodes V1 and V3 after the exposure is completed, and is a half of the lines to be read at the time of normal driving (the hatched lines are shown in FIG. 6). Charge is read from the pixel) to the vertical charge transfer path 54. Then, the electric charge is transferred, and a signal corresponding to the electric charge is output from the solid-state imaging device 5 to complete the first field (see FIGS. 6 and 7).

  After the end of the first field, the system control unit 11 applies a read pulse to the transfer electrodes V9 and V11, and performs vertical operation from the remaining half of the lines to be read during normal driving (pixels indicated by diagonal lines in FIG. 8). The charge is read out to the charge transfer path 54. Then, this charge is transferred, and a signal corresponding to the charge is output from the solid-state imaging device 5 (see FIGS. 8 and 9).

  FIG. 10 is a diagram schematically illustrating an imaging signal output from the solid-state imaging device 5 during normal driving. When signals obtained from two adjacent lines among the lines from which signals are read during normal driving are defined as normal lines, n normal lines (1) to (n) are displayed during normal driving, as shown in FIG. Is obtained.

  FIG. 11 is a diagram schematically illustrating an imaging signal output from the solid-state imaging device 5 during smear reduction driving. FIG. 11A shows the image pickup signal read out in the first field, and FIG. 11B shows the image pickup signal read out in the second field.

  Of the lines from which signals are read out in the first field during smear reduction driving, signals obtained from two adjacent lines are defined as thinning lines A, and from among the lines from which signals are read out in the second field during smear reduction driving, If the signal obtained from the two lines is defined as a thinning line B, as shown in FIG. 11, (n / 2) thinning lines are obtained in each field during smear reduction driving.

  Thus, at the time of smear reduction driving, the number of charges read out to the vertical charge transfer path 54 in each field is half that during normal driving. Therefore, as can be seen by comparing FIG. 5 with FIG. 7 and FIG. 9, the vertical charge in each field is longer in the smear reduction drive, although the time until all signals are read out is longer than in the normal drive. The charge transfer time in the transfer path 54 can be shortened. Since the amount of smear depends on the charge transfer time in the vertical charge transfer path 54, the smear can be reduced by shortening the charge transfer time.

  In this digital camera, the digital signal processing unit 17 combines the imaging signal obtained in the first field at the time of smear reduction driving with the imaging signal obtained in the second field at the time of smear reduction driving. Two imaging signals are recorded on the recording medium 21 as one frame data (data for generating one image).

  That is, as shown in FIG. 12, by performing the process of interpolating the thinning line B between the thinning lines A, the same imaging signal as the signal array obtained during normal driving is obtained. By doing so, the resolution can be made the same as that during normal driving, and the resolution can be maintained while reducing smear.

  Since both the first field and the second field can independently acquire color data of three colors of RGB, only the imaging signal obtained from either one may be recorded as one frame data. In this case, the first field or the second field can be omitted, and the signal can be read out in substantially the same time as in normal driving.

  In the above description, signals are read from half of all the lines during normal driving. However, the lines to be read may be determined according to the resolution of the image data to be recorded and the imaging mode. For example, in the still image capturing mode, signals may be read from all or part of the line so that the set resolution is obtained. In the moving image capturing mode, high-speed image capturing is required, so that a signal may be read from a part of the line.

  The operation of the digital camera configured as described above will be described.

  FIG. 13 is a diagram showing an operation flow when the digital camera shown in FIG. 1 performs recording imaging for recording image data on a recording medium. FIG. 13 illustrates an example of an operation when capturing an image for recording a moving image.

  When a release button included in the operation unit 12 is pressed and a moving image imaging instruction is issued, the system control unit 11 performs imaging of the first frame with the solid-state imaging device 5. In this imaging, the system control unit 11 reads the signal by driving the solid-state imaging device 5 by normal driving (step S1).

  When the imaging of the first frame is completed, the smear occurrence ratio calculation unit 18 acquires the imaging signal output from the solid-state imaging device 5 by this imaging, and detects the smear occurrence position based on the imaging signal (step S2). . The smear occurrence ratio calculation unit 18 calculates a smear occurrence ratio based on the detected smear occurrence position (step S3).

  Next, the system control unit 11 compares the smear occurrence ratio calculated in step S3 with a threshold value, and if the smear occurrence ratio is equal to or greater than the threshold value (step S4: YES), the signal is read when the next frame is imaged. As a method, smear reduction driving is set (step S5), and when the smear occurrence ratio is less than the threshold value (step S4: NO), normal driving is set as a signal reading method at the time of imaging of the next frame (step S6). .

  After steps S5 and S6, the system control unit 11 starts imaging the next frame (step S7). In this imaging, a signal is read by the drive set in steps S5 and S6.

  When the imaging in step S7 is completed, the digital signal processing unit 17 generates frame data from the imaging signal output from the solid-state imaging device 5 by this imaging, and records this frame data on the recording medium 21 (step S8). When the signal is read out by normal driving, the digital signal processing unit 17 performs digital signal processing on the imaging signal obtained from the solid-state imaging device 5 to generate frame data. In addition, when the signal is read by smear reduction driving, the digital signal processing unit 17 synthesizes the imaging signal obtained in each field to generate an imaging signal having the same arrangement as the imaging signal obtained during normal driving. After that, the image signal is subjected to digital signal processing to generate frame data. In parallel with the processing in step S8, the smear occurrence ratio calculation unit 18 acquires the imaging signal output from the solid-state imaging device 5 by this imaging and detects the smear position (step S9).

  When imaging is continued after step S9 (step S10: NO), the process proceeds to step S3, and the smear occurrence ratio calculation unit 18 performs imaging in step S7 based on the imaging signal acquired in step S9. Calculate the smear generation rate at. Then, based on this smear occurrence ratio, a signal readout method at the time of imaging of the next frame is set. After step S9, when the imaging is finished (step S10: YES), the system control unit 11 finishes the imaging operation.

  Here, moving image imaging is taken as an example, but at the time of still image imaging, the release button included in the operation unit 12 is half-pressed to instruct AE (automatic exposure) / AF (automatic focus adjustment) processing. At the time, the imaging in step S1 is performed as temporary imaging, and the system control unit 11 performs AE / AF processing based on the imaging signal obtained by the temporary imaging, and also performs processing in steps S2 to S6. Then, when the release button is fully pressed, the imaging (main imaging) in step S7 is performed. In still image capturing, step S10 is omitted after step S9, and the image capturing operation is terminated.

  As described above, according to this digital camera, when smear occurs locally, normal driving is performed, and when smear occurs over a wide area, smear reduction driving is performed. . For this reason, image quality deterioration can be prevented in both cases where smear has occurred locally and smear has occurred in a wide range.

  In addition, according to this digital camera, smear reduction driving is realized by reading a signal into a plurality of fields from a photoelectric conversion element that is a target for reading a signal during normal driving. Further, since the signals obtained in each field of the smear reduction drive are processed so as to be the same as the signal arrangement obtained during the normal drive, it is possible to reduce the smear without reducing the resolution. In addition to reducing smear, dark current and dark vertical shading can also be suppressed.

  In addition, according to this digital camera, it is possible to reduce smear while maintaining the resolution with the configuration of a general solid-state imaging device, so that the cost can be reduced.

  Note that the pixel arrangement of the solid-state imaging element 5 is not limited to that shown in FIG. For example, as shown in FIG. 14, a general configuration in which Bayer array color filters are provided on photoelectric conversion elements PD arrayed in a square lattice pattern may be used. In the case of the configuration shown in FIG. 14, for example, during normal driving, signals are read every two lines with hatching in the figure, and during smear reduction driving, signals are divided into a plurality of fields from the hatched lines in the figure. What is necessary is just to read.

  As described above, the following items are disclosed in this specification.

  The disclosed imaging device is an imaging device including a CCD type solid-state imaging device having a plurality of pixels, and the plurality of pixels detect effective pixels and smears that generate charges according to subject light. A drive unit that drives the solid-state imaging device to read signals from the plurality of pixels, and an area in which the effective pixels are arranged based on signals output from the smear detection pixels A smear generation ratio calculation unit that calculates a ratio of a smear generation region to the whole (hereinafter referred to as a smear generation ratio), and the drive unit performs smear reduction driving when the smear generation ratio is equal to or greater than a threshold value. To read the signal, and when the smear occurrence rate is less than a threshold value, the solid-state image sensor is driven by normal driving to read the signal. Than during normal driving is a drive with reduced number of pixels to read out the charge.

  With this configuration, when smear is locally generated, normal driving is performed, and when smear is generated in a wide range, smear reduction driving is performed. For this reason, image quality deterioration can be prevented in both cases where smear has occurred locally and smear has occurred in a wide range.

  In the disclosed imaging device, when the smear occurrence ratio is equal to or greater than a threshold value, the drive unit reads a signal from a pixel that is a target for reading a signal during the normal drive in a plurality of fields, and In each of the pixels from which signals are to be read out, the pixels from which the signals are read out by the smear reduction drive, the signals read out by dividing into the plurality of fields are combined, and the signals from which the signals are read out during the normal drive A signal synthesizer that generates signals having the same signal arrangement as the signal arrangement read out from.

  With this configuration, even when smear reduction driving is performed, frame data having the same resolution as that during normal driving can be obtained.

  The disclosed imaging apparatus includes a control unit that performs control to perform provisional imaging before actual imaging, and at the time of the provisional imaging, the driving unit reads a signal from the solid-state imaging device by the normal driving, and the smear The generation ratio calculation unit calculates the smear generation ratio based on a signal output from the smear detection pixel in the provisional imaging, and the driving unit is configured to detect the smear generation ratio at a threshold value or more during the main imaging. Reads out a signal from the solid-state imaging device by smear reduction driving, and reads out a signal from the solid-state imaging device by normal driving when the smear generation ratio is less than a threshold.

  In the disclosed imaging apparatus, when the driving unit captures the nth frame, the smear reduction ratio is calculated when the smear occurrence ratio calculated based on a signal obtained by imaging the (n−1) th frame is equal to or greater than a threshold. A signal is read from the solid-state image sensor by driving, and when the smear occurrence ratio calculated based on a signal obtained by imaging of the (n−1) th frame is less than a threshold value, the signal is output from the solid-state image sensor by normal driving. read out.

  The disclosed method for driving a solid-state imaging device is a method for driving a CCD solid-state imaging device having a plurality of pixels, and the plurality of pixels detect effective pixels and smears that generate charges according to subject light. And calculating a ratio of the smear generation area to the entire area where the effective pixels are arranged (hereinafter referred to as a smear generation ratio) based on a signal output from the smear detection pixel. A smear occurrence ratio calculating step; when the smear occurrence ratio is equal to or greater than a threshold value, the solid-state image sensor is driven by smear reduction driving to read a signal; and when the smear occurrence ratio is less than the threshold value, the solid-state image sensor is normally driven And the smear reduction drive is a drive in which the number of pixels from which charges are read is reduced as compared with the normal drive. .

  In the driving method of the disclosed solid-state imaging device, in the driving step, when the smear generation ratio is equal to or higher than a threshold value, the signal is read out from a pixel to be read out during the normal driving in a plurality of fields, In each of the plurality of fields, the signal is read by the smear reduction driving in which the pixel from which the signal is to be read is different, and the signals read by dividing into the plurality of fields are combined to read the signal at the time of the normal driving. A signal synthesis step of generating a signal having the same signal arrangement as the signal arrangement read from the target pixel;

  The disclosed method for driving a solid-state imaging device includes a control step for performing control to perform provisional imaging before the main imaging, and reading the signal from the solid-state imaging device by the normal driving during the provisional imaging, and generating the smear In the ratio calculation step, the smear generation ratio is calculated based on a signal output from the smear detection pixel in the temporary imaging, and in the driving step, when the smear generation ratio is equal to or greater than a threshold value during the main imaging. A signal is read from the solid-state imaging device by smear reduction driving, and a signal is read from the solid-state imaging device by normal driving when the smear generation ratio is less than a threshold value.

  In the driving method of the disclosed solid-state imaging device, in the driving step, the smear occurrence ratio calculated based on a signal obtained by imaging of the (n−1) th frame is greater than or equal to a threshold value when imaging the nth frame. When the smear reduction drive reads out the signal from the solid-state imaging device, and the smear occurrence ratio calculated based on the signal obtained by imaging of the (n-1) th frame is less than the threshold, the solid-state imaging with normal drive Read the signal from the element.

5 Solid-State Image Sensor 5a Image Sensor Drive Unit 11 System Control Unit 18 Smear Generation Ratio Calculation Unit

Claims (8)

An imaging device including a CCD type solid-state imaging device having a plurality of pixels,
The plurality of pixels include an effective pixel that generates an electric charge according to subject light and a smear detection pixel for detecting smear,
A driving unit that drives the solid-state imaging device and reads signals from the plurality of pixels;
A smear occurrence ratio calculation unit that calculates a ratio of a smear occurrence area to an entire area where the effective pixels are arranged (hereinafter referred to as a smear occurrence ratio) based on a signal output from the smear detection pixel;
The drive unit reads the signal by driving the solid-state image sensor with smear reduction driving when the smear occurrence ratio is equal to or greater than a threshold value, and drives the solid-state image sensor with normal drive when the smear occurrence ratio is less than the threshold value. Read out the signal,
The smear reduction drive is an image pickup device in which the number of pixels from which charges are read is reduced compared to the normal drive. The imaging apparatus according to claim 1,
When the smear occurrence ratio is equal to or greater than a threshold value, the driving unit reads signals in a plurality of fields from a pixel from which signals are read during the normal driving, and reads signals in each of the plurality of fields. Read out the signal with the smear reduction drive with different target pixels,
An imaging apparatus comprising: a signal synthesis unit that synthesizes signals read out in a plurality of fields and generates a signal having the same signal arrangement as a signal arrangement read from a pixel from which signals are read out during the normal driving. The imaging apparatus according to claim 1 or 2,
A control unit that performs control to perform provisional imaging before the main imaging;
At the time of the provisional imaging, the driving unit reads a signal from the solid-state imaging device by the normal driving,
The smear occurrence ratio calculation unit calculates the smear occurrence ratio based on a signal output from the smear detection pixel in the temporary imaging,
The driving unit reads signals from the solid-state image sensor by smear reduction driving when the smear occurrence ratio is equal to or greater than a threshold value during the main imaging, and performs normal driving when the smear occurrence ratio is less than the threshold value. An imaging device that reads signals from. The imaging apparatus according to claim 1 or 2,
When the drive unit picks up the nth frame, when the smear occurrence ratio calculated based on the signal obtained by the (n-1) th frame image pickup is equal to or greater than a threshold value, smear reduction driving is performed from the solid-state image sensor. An imaging apparatus that reads out a signal and reads out the signal from the solid-state imaging device by normal driving when the smear occurrence ratio calculated based on the signal obtained by imaging of the (n−1) th frame is less than a threshold. A method for driving a CCD type solid-state imaging device having a plurality of pixels,
The plurality of pixels include an effective pixel that generates an electric charge according to subject light and a smear detection pixel for detecting smear,
A smear occurrence ratio calculating step for calculating a ratio of a smear occurrence area to the entire area where the effective pixels are arranged (hereinafter referred to as a smear occurrence ratio) based on a signal output from the smear detection pixel;
When the smear occurrence ratio is equal to or higher than a threshold value, the solid-state image sensor is driven to read out signals by smear reduction drive, and when the smear occurrence ratio is less than the threshold value, the solid-state image sensor is driven to read signals from the normal drive. A driving step,
The smear reduction driving is a driving method of a solid-state imaging device, which is driving in which the number of pixels from which charges are read is reduced compared to the normal driving. A method for driving a solid-state imaging device according to claim 5,
In the driving step, when the smear occurrence ratio is equal to or greater than a threshold value, the signal is read into a plurality of fields from a pixel from which a signal is read during the normal driving, and the signal is read out in each of the plurality of fields. Read out the signal with the smear reduction drive with different target pixels,
A solid-state imaging device comprising a signal combining step of combining signals read out in a plurality of fields and generating a signal having the same signal arrangement as a signal arrangement read from a pixel from which signals are read out during the normal driving Driving method. A method for driving a solid-state imaging device according to claim 5 or 6,
Including a control step for performing control to perform provisional imaging before main imaging;
At the time of the provisional imaging, a signal is read from the solid-state imaging device by the normal driving,
In the smear occurrence ratio calculation step, the smear occurrence ratio is calculated based on a signal output from the smear detection pixel in the temporary imaging,
In the driving step, when the smear occurrence ratio is equal to or greater than a threshold value during the main imaging, a signal is read from the solid-state image sensor by smear reduction drive, and when the smear occurrence ratio is less than the threshold value, the solid-state image sensor is normally driven. For driving a solid-state imaging device for reading out a signal from an image. A method for driving a solid-state imaging device according to claim 5 or 6,
In the driving step, when the smear occurrence ratio calculated based on a signal obtained by imaging of the (n−1) th frame is greater than or equal to a threshold during imaging of the nth frame, smear reduction driving is performed from the solid-state imaging device. A method of driving a solid-state imaging device that reads out a signal and reads out the signal from the solid-state imaging device by normal driving when the smear occurrence ratio calculated based on the signal obtained by imaging of the (n-1) th frame is less than a threshold value .

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