JP5271201B2 - Image signal processing apparatus and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the accuracy of shading correction so as to improve image quality of an image after the correction. <P>SOLUTION: An imaging apparatus includes: a pixel array having an effective area, a first light shielding area, and a second light shielding area on a second side opposite to a first side; a first generation means for generating first reference data corresponding to output signals from first light shielding pixels; a second generating means for generating second reference data corresponding to output signals from second light shielding pixels; a third generating means for generating correction data using either of a first value obtained by averaging the first and second reference data and a second value obtained by linearly interpolating between the first and second reference data; and a correction means for correcting a reference level of output signals from effective pixels using the correction data. The third generation means determines whether to use the first value or the second value (S611, S610) corresponding to photographing conditions (S1) and/or a state of the reference signals output from each of the first and second light shielding pixels (S2). <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an image signal processing device and an imaging device.

  An imaging device such as a CCD image sensor or a CMOS image sensor for capturing a still image or a moving image may be used in an imaging device such as a digital camera. In this image sensor, the output signal from each pixel in a pixel array in which a plurality of pixels are arranged in a direction along a row and a direction along a column is fluctuated due to the influence of fluctuations in various supplied reference power supply voltages. May be. Among these, the level of the fluctuation of the output signal caused by a relatively gradual power fluctuation or the like having a period longer than the readout time of one row in the pixel array varies across a plurality of rows. For this reason, in the image corresponding to the output signal, the shading in the vertical direction appears as horizontal stripe noise. Further, among them, those with relatively fast fluctuations appear as finer horizontal stripe noise.

  By the way, the noise due to the vertical shading caused by the power supply fluctuation does not occur in a pattern determined for each shooting, but appears in a different shape for each shooting. For this reason, if correction data prepared in advance is used, the accuracy of correction is reduced. Therefore, correction must be performed simultaneously with shooting, or correction data must be created and corrected from at least the shot image itself. Further, considering the usability of the imaging apparatus, it is not possible to spend much time for the correction.

  On the other hand, there is a method of correcting the vertical shading component whose shape changes for each imaging using the output value of the horizontal optical black area (horizontal OB area) optically shielded in the imaging device. is there.

  Specifically, in a digital signal processing circuit such as an image engine, the average value for each row is calculated for the output of the horizontal OB region, and the calculated correction value is uniformly calculated from the output signal of the corresponding region in the effective row. Subtract. Alternatively, by using a horizontal OB clamp circuit of an analog signal processing circuit that performs analog signal processing on the output signal of the image sensor, the level is shifted so that the average output value of the horizontal OB area of each row becomes the dark level of that row. To go.

  In this way, if the output signal for each row is corrected so that the output signal of the horizontal OB region becomes a dark level, the vertical shading component can be corrected when the vertical shading component is uniform in the horizontal direction. .

  By the way, the horizontal OB area is often arranged on one side corresponding to the leading side in the reading direction, but there is also an image sensor in which the horizontal OB area is arranged on the opposite side. When the vertical shading shape differs depending on the horizontal position in the pixel array, the correction is made based on the output signals of the horizontal OB regions on both the left and right sides, rather than performing the correction based on the output signals of the horizontal OB region on one side. It is considered that the correction effect becomes larger when it is performed. At this time, a method of correcting the effective area of the row using the average value of the output signals of the left and right horizontal OB areas for each row is generally used.

  As a technique related to the background art described above, there is a technique described in Patent Document 1. Patent Document 1 describes that in the CCD image pickup chip 3, OB regions 22 a are arranged above and below the area portion 21 to detect shading components in the upper and lower OB regions 22 a. Based on the detected shading component, the black level in the entire area unit 21 is estimated and calculated, and the black level is subtracted from the image signal. Thereby, according to Patent Document 1, it is supposed that image information obtained by calibrating a shading component can be obtained.

Japanese Patent Laid-Open No. 06-078224

  On the other hand, all of the above-described vertical shading corrections are performed in a uniform process regardless of shooting conditions. However, the degree to which the accuracy of vertical shading correction is affected by the magnitude of the noise component included in the output signal in the horizontal OB region is considered to vary depending on the shooting conditions. For this reason, depending on the shooting conditions, the vertical shading correction process that is being performed may not be appropriate, and the image quality of the corrected image may deteriorate compared to the image before correction.

  For example, consider a case where the amount of incident light is small and the sensitivity setting is set to high sensitivity. In this case, as the output signal of the horizontal OB region is amplified with a high gain, the noise component included in the output signal of the horizontal OB region is also amplified with a high gain. May vary from line to line. As a result, the level of the reference data of each row generated based on the output signal of the horizontal OB region also varies, and by performing correction using the reference data, the corrected image itself varies from line to line. There is a possibility.

  For example, let us consider a case where shooting is performed under conditions where a large amount of dark current is generated, such as in a high-temperature environment or during long-second shooting. In this case, there is a higher probability that a so-called scratch pixel that generates more dark current than the other surrounding pixels will occur, so that the correction of a row with a scratch pixel becomes a value that deviates from the correction value of another row. When vertical shading correction is performed using correction data, there is a possibility that an image including a horizontal line in a line having a scratch in the horizontal OB area may be generated.

  In either case, if the horizontal OB area is sufficiently large and a large number of pixels can be used for the average value for creating correction data, the variation in the average output value can be suppressed to some extent. However, increasing the horizontal OB area unnecessarily increases the chip size and increases costs. For this reason, the size of the horizontal OB area is limited. In particular, as described above, when the horizontal OB areas are arranged on the left and right sides of the effective area, the size of each area is further restricted as compared with the case of only one side.

  FIG. 7 is a diagram for briefly explaining the processing contents and effects of various vertical shading corrections. FIGS. 7A and 7D are diagrams for explaining the vertical shading correction processing and the effect when the horizontal OB region is arranged only on the left side of the effective region in the pixel array. In the vertical shading correction shown in FIGS. 7a) and d), an average value for each row is calculated for the output of the left horizontal OB region in the pixel array. Then, the calculated correction value is uniformly subtracted from the output signal in the effective area. As a result, when the level of the vertical shading component is different between the left and right in the effective area as shown in FIG. 7a), the vertical shading component is effectively reduced in the pixels close to the horizontal OB area in the effective area as shown in FIG. 7d). Is done. However, in the pixel far from the horizontal OB area in the effective area, the level of the correction value becomes too large with respect to the level of the shading component, and overcorrection is performed. As a result, the image quality of the corrected image (see FIG. 7d) is worse than that of the image before correction (see FIG. 7a).

  FIGS. 7B) and 7E are diagrams for explaining the processing contents and effects of vertical shading correction in the case where horizontal OB areas are arranged on the left and right sides of the effective area in the pixel array. In the vertical shading correction shown in FIGS. 7B) and 7E), an average value for each row is calculated for each region for the output signals of the left and right horizontal OB regions in the pixel array. Then, a value obtained by further averaging the two calculated average values is uniformly subtracted for each row with respect to the output signal of the effective region.

  When the level of the vertical shading component is different between the left and right in the effective area as shown in FIG. 7b), the image quality of the image after correction is improved as a whole compared with the image quality of the image before correction as shown in FIG. 7e). Yes. That is, in the correction processes shown in FIGS. 7b) and e), overcorrection in the correction processes shown in FIGS. 7a) and d) is suppressed. However, since the correction value is uniform in the horizontal direction for each row, in the row in which the correction in the effective area is performed, there are pixels in which the shading component cannot be completely removed in a part of the horizontal direction, and the correction remains. .

  FIGS. 7c) and 7f) are diagrams for explaining processing contents and effects of another vertical shading correction when horizontal OB areas are arranged on the left and right sides of the effective area in the pixel array. In the vertical shading correction shown in FIGS. 7c) and 7f), an average value for each row is calculated for each region with respect to the output signals of the left and right horizontal OB regions in the pixel array. Then, a value (shading component) to be subtracted in the effective area is calculated by interpolating the calculated left and right average values for the output signal in the effective area, and the interpolated value is subtracted in the horizontal direction.

  When the level of the vertical shading component is different between the left and right in the effective area as shown in FIG. 7c), the correction residual of the vertical shading component in the effective area is reduced as shown in FIG. 7f). That is, in the correction process shown in FIGS. 7c) and f), the remaining correction in the correction process shown in FIGS. 7b) and e) is suppressed.

  Here, for example, consider a case where the amount of incident light is small and the sensitivity setting is set to high sensitivity. In this case, as the output signal of the horizontal OB area is amplified with a high gain, the noise component included in the output signal of the horizontal OB area is also amplified with a high gain, and the left OB reference data and the right OB reference data are obtained. Generated. As a result, the noise component included in the left OB reference data and the right OB reference data is increased, so that the correction value level is too large with respect to the shading component level in all pixels in the corrected row in the effective region. Overcorrection is performed. This overcorrection becomes more prominent as the sensitivity of the imaging device is higher, and deteriorates the image quality of the corrected image.

  On the other hand, if the sensitivity of the imaging device is sufficiently low, the effect of overcorrection on the image quality of the image after correction is small, so the image quality of the image after correction can be improved by the correction processing shown in FIGS. 7c) and f). It is done. However, since the number of pixels in the OB area used to calculate the correction value is halved compared to the method described with reference to FIG. This increases the risk of generating horizontal stripes. In addition, since a correction value must be calculated for each pixel, there is a problem in that the amount of calculation for correction increases and processing time increases.

  For the reasons described above, the conventional vertical dark shading correction has a problem that there is no universal correction processing for various shooting conditions and the state of output signals in the left and right OB areas.

  An object of the present invention is to improve the accuracy of shading correction and improve the image quality of the corrected image.

  An image signal processing device according to one aspect of the present invention includes an effective area in which a plurality of effective pixels that respectively generate image signals corresponding to light are arranged, and a first of the effective areas adjacent to the effective area. A first light-shielding area in which a plurality of first light-shielding pixels each generating a reference signal are arranged, and the first light-shielding area adjacent to the effective area and sandwiching the effective area The image signal output from the image sensor having a pixel array having a second light-shielding area in which a plurality of second light-shielding pixels are arranged, which is an area disposed on the opposite side of the area and generates a reference signal. An image signal processing device that performs a predetermined correction process, wherein the first generation means generates first reference data in accordance with a first reference signal output from the plurality of first light-shielding pixels; Output from multiple second shading pixels Second generation means for generating second reference data in response to the second reference signal to be generated; a first value obtained by averaging the first reference data and the second reference data; Third generation means for generating correction data using any one of the second value obtained by linear interpolation between the first reference data and the second reference data; and the correction data A correction unit that corrects an image signal output from the plurality of effective pixels, and a third generation unit that uses the first value or the second value to generate the correction data. And a control means for determining.

  According to the present invention, the accuracy of shading correction can be improved and the image quality of the corrected image can be improved.

1 is a diagram illustrating a configuration of an imaging apparatus according to an embodiment. FIG. 3 is a diagram illustrating a configuration of an image sensor according to an embodiment. The figure explaining the 1st vertical shading correction process. The figure explaining the 2nd vertical shading correction process. 2A and 2B illustrate a structure of a digital signal processing circuit. The flowchart which shows a vertical dark shading correction process. The figure explaining background art.

  A configuration of an imaging apparatus 100 according to an embodiment of the present invention will be described with reference to FIG. An optical system 101 includes a lens and a diaphragm. Reference numeral 102 denotes a mechanical shutter (shown as a mechanical shutter). Reference numeral 103 denotes an image sensor that converts a subject image into an image signal. As will be described later, the image sensor 103 includes a plurality of pixels each performing a charge accumulation operation. Reference numeral 104 denotes an analog signal processing circuit that performs analog signal processing on an image signal output from the image sensor 103. Reference numeral 105 denotes a CDS circuit that performs correlated double sampling (CDS) processing inside the analog signal processing circuit 104.

  Reference numeral 106 denotes a signal amplifier that amplifies an analog signal inside the analog signal processing circuit 104. A clamp circuit 107 performs horizontal OB clamping inside the analog signal processing circuit 104. Reference numeral 108 denotes an A / D converter that converts an analog signal into a digital signal inside the analog signal processing circuit 104. A timing signal generation circuit 110 generates a signal for operating the image sensor 103 and the analog signal processing circuit 104.

  Reference numeral 111 denotes a drive circuit for the optical system 101, the mechanical shutter 102, and the image sensor 103. Reference numeral 112 denotes a digital signal processing circuit that performs digital signal processing necessary for captured image data. Reference numeral 113 denotes an image memory for storing image processed image data. Reference numeral 114 denotes an image recording medium (shown as a recording medium) that is removable from the imaging apparatus 100. Reference numeral 115 denotes a recording circuit for recording the signal-processed image data on the image recording medium 114.

  Reference numeral 116 denotes an image display device that displays image data subjected to signal processing. Reference numeral 117 denotes a display circuit that displays an image on the image display device 116. Reference numeral 118 denotes a system control unit that entirely controls each unit of the imaging apparatus 100. 119 stores a program describing a control method executed by the system control unit 118, control data such as parameters and tables used when the program is executed, and correction data such as a scratch address. It is a storage part. The first storage unit 119 is, for example, a nonvolatile memory such as a ROM.

  Reference numeral 120 denotes a second storage unit that transfers and stores the program, control data, and correction data stored in the first storage unit 119 and is used when the system control unit 118 controls the imaging apparatus. . The second storage unit 120 is a volatile memory such as a RAM, for example. Reference numeral 121 denotes a temperature detection circuit (temperature detection means) that detects the temperature around the pixel array in the image sensor 103 and its peripheral circuits. Reference numeral 122 denotes an accumulation time setting unit that sets an accumulation time for each of a plurality of pixels in the image sensor 103 to perform a charge accumulation operation. Reference numeral 123 denotes a shooting mode setting unit (sensitivity setting means) for setting shooting conditions such as ISO sensitivity (shooting sensitivity) setting and switching between still image shooting and moving image shooting.

  Next, a photographing operation using the imaging device 100 configured as described above will be described. Prior to the photographing operation, necessary programs, control data, and correction data are transferred from the first storage unit 119 to the second storage unit 120 when the operation of the system control unit 118 is started, such as when the imaging apparatus 100 is turned on. And remember it. These programs and data are used when the system control unit 118 controls each unit of the imaging apparatus 100. At the same time, these programs and data are transferred as necessary from the first storage unit 119 to the second storage unit 120, or the system control unit 118 directly transmits the first storage unit. The data in 119 is read out and used.

  The drive circuit 111 drives the diaphragm and the lens in the optical system 101 according to the control signal received from the system control unit 118. The optical system 101 forms a subject image set to an appropriate brightness on the imaging surface (pixel array) of the imaging element 103.

  The drive circuit 111 drives the mechanical shutter 102 so as to expose / shield the image sensor 103 with a necessary exposure time in accordance with a control signal from the system control unit 118 at the time of still image shooting. At this time, when the image sensor 103 has an electronic shutter function, the mechanical shutter 102 and the electronic shutter function may be used together to ensure a necessary exposure time.

  Further, the drive circuit 111 maintains the mechanical shutter 102 in an open state so that the image sensor 103 is always exposed during shooting according to a control signal from the system control unit 118 during moving image shooting. The image sensor 103 is driven according to the operation pulse supplied from the timing signal generation circuit 110, converts the subject image into an image signal by photoelectric conversion, and outputs it as an analog image signal.

  The analog signal processing circuit 104 performs analog signal processing on the analog image signal output from the image sensor 103 in accordance with the operation pulse supplied from the timing signal generation circuit 110. Specifically, the CDS circuit 105 performs CDS processing for removing clock synchronization noise from the analog image signal and outputs the result to the signal amplifier 106.

  The signal amplifier 106 amplifies the received signal with an amplification factor (gain) set according to the amount of incident light, and outputs the amplified signal to the clamp circuit 107. The clamp circuit 107 performs a clamp operation on the received signal in accordance with the reference signal (reference voltage) output from the horizontal OB region, and outputs the clamped signal to the A / D converter 108. The A / D converter 108 performs A / D conversion processing on the received signal, thereby generating a digital image signal and outputting the digital image signal to the digital signal processing circuit 112.

  The digital signal processing circuit 112 generates image data by performing various types of digital signal processing on the received digital image signal in accordance with the control signal received from the system control unit 118. The various digital signal processing includes vertical shading correction data generation by averaging the signals in the horizontal OB region in the digital image signal according to the present embodiment, and vertical shading correction processing using the correction data.

  Various digital signal processing includes image processing such as color conversion, white balance, and gamma correction, resolution conversion processing, image compression processing, and the like for digital image signals. At this time, the image memory 113 temporarily stores a digital image signal during signal processing, or stores image data that is a digital image signal subjected to signal processing. The image data signal-processed by the digital signal processing circuit 112 and the image data stored in the image memory 113 are converted into data suitable for the image recording medium 114 by the recording circuit 115 and recorded on the image recording medium 114.

  Data suitable for the image recording medium 114 is, for example, file system data having a hierarchical structure. Alternatively, the image data is subjected to resolution conversion processing by the digital signal processing circuit 112, and then converted into a signal suitable for the image display device 116 (for example, an NTSC analog signal) by the display circuit 117, and the image display device 116. Is displayed.

  Here, the digital signal processing circuit 112 does not perform signal processing on the received digital image signal according to the control signal received from the system control unit 118, and uses the digital image signal as image data as it is as the image memory 113. Or may be output to the recording circuit 115.

  Further, the digital signal processing circuit 112 may output various kinds of information related to digital image signals and image data generated in the signal processing process when requested by the system control unit 118. The various types of information include, for example, information such as the spatial frequency of the image, the average value of the designated area, the data amount of the compressed image, or information extracted from them. Further, the recording circuit 115 outputs information such as the type and free capacity of the image recording medium 114 to the system control unit 118 when requested by the system control unit 118.

  Further, a reproduction operation when image data is recorded on the image recording medium 114 will be described. The recording circuit 115 reads image data from the image recording medium 114 in accordance with a control signal received from the system control unit 118. In response to the control signal received from the system control unit 118, the digital signal processing circuit 112 performs image expansion processing when the image data is compressed image data, and stores the expanded image data in the image memory 113. . The image data stored in the image memory 113 is subjected to resolution conversion processing by the digital signal processing circuit 112, converted to a signal suitable for the image display device 116 by the display circuit 117, and displayed (reproduced) on the image display device 116. )

  Next, the configuration of the image sensor 103 will be described with reference to FIG. The image sensor 103 includes a pixel array PA. The pixel array PA includes an effective area 204, a first horizontal OB area (first light shielding area) 202, a second horizontal OB area (second light shielding area) 203, and a vertical OB area 201. In the effective area 204, a plurality of effective pixels are arranged in a direction along a row and a direction along a column. Each of the plurality of effective pixels includes a photoelectric conversion unit that is not shielded from light.

  The photoelectric conversion unit accumulates electric charges according to the dark current component, and generates and accumulates electric charges according to the light. That is, the photoelectric conversion unit in the effective pixel generates an image signal corresponding to light. The photoelectric conversion unit is, for example, a photodiode. The first horizontal OB area 202 is arranged adjacent to the effective area 204 on the left side (first side) in the direction along the row.

  In the first horizontal OB region 202, a plurality of first light-shielding pixels are arranged in a direction along a row and a direction along a column. Each of the plurality of first light shielding pixels includes a photoelectric conversion unit that is shielded from light (by a light shielding film such as aluminum). Since the photoelectric conversion unit receives almost no light, it accumulates electric charges according to the dark current component. That is, the photoelectric conversion unit in the first light-shielding pixel generates a reference signal. If the first light-shielding pixel is configured to generate and output a reference signal, the first light-shielding pixel does not include the photoelectric conversion unit or includes the photoelectric conversion unit, but the photoelectric conversion unit It may be configured so as not to output a signal corresponding to the electric charge generated in step 1.

  The first horizontal OB area 202 includes a first calculation area 205. The first calculation area 205 is configured by the whole or a part of the first horizontal OB area 202. The first calculation area 205 is an area used to create first reference data (to be described later) used in the vertical shading correction according to the present embodiment. The second horizontal OB area 203 is arranged adjacent to the effective area 204 in the direction along the row on the right side (opposite to the first horizontal OB area 202 across the effective area 204).

  In the second horizontal OB region 203, a plurality of second light-shielding pixels are arranged in a direction along a row and a direction along a column. Each of the plurality of second light shielding pixels includes a photoelectric conversion unit that is shielded from light (by a light shielding film such as aluminum). Since the photoelectric conversion unit receives almost no light, it accumulates electric charges according to the dark current component. That is, the photoelectric conversion unit in the second light-shielding pixel generates a reference signal. The second light-shielding pixel does not include the photoelectric conversion unit or includes the photoelectric conversion unit as long as the second light-shielding pixel is configured to generate and output a reference signal. It may be configured so as not to output a signal corresponding to the electric charge generated in step 1.

  The second horizontal OB area 203 includes a second calculation area 206. The second calculation area 206 is configured by the whole or a part of the second horizontal OB area 203. The second calculation area 206 is an area used to create second reference data (to be described later) used in the vertical shading correction according to the present embodiment. A specific method for properly using the first calculation area 205 and the second calculation area 206, etc., will be described with reference to the vertical shading correction processing of the present embodiment described later with reference to FIG. 3 and with reference to FIG. This will be referred to in the description of the flowchart of the present embodiment.

  The vertical OB area 201 is adjacent to the effective area 204 in the direction along the column on the upper side (third side). In the vertical OB region 201, a plurality of third light-shielding pixels are arranged in a direction along a row and a direction along a column. Each of the plurality of third light shielding pixels includes a photoelectric conversion unit that is shielded from light (by a light shielding film such as aluminum). Since the photoelectric conversion unit receives almost no light, it accumulates electric charges according to the dark current component. That is, the photoelectric conversion unit in the third light-shielding pixel generates a reference signal. If the third light-shielding pixel is configured to generate and output a reference signal, it does not include the photoelectric conversion unit or includes the photoelectric conversion unit, but the photoelectric conversion unit It may be configured so as not to output a signal corresponding to the electric charge generated in step 1. The vertical OB area 201 is an area used for generating correction data used in horizontal shading correction.

  Next, the first vertical shading correction process in the imaging apparatus according to the embodiment of the present invention will be described with reference to FIG. The first vertical shading correction process described with reference to FIG. 3 is a process for performing correction using an average value of reference data generated from two horizontal OB areas.

  FIG. 3A) is an original image on which vertical shading correction is performed in the vertical shading correction processing described with reference to FIG. In FIG. 3 a), in order to explain the effect of correction using the left and right horizontal OB regions, the image has vertical shading components with different levels on the left and right in the pixel array. 3b) and FIG. 3c) are generated by calculating the average value for each row with respect to the reference signal output from each of the first calculation area 205 and the second calculation area 206 in FIG. 3a). Reference data.

  FIG. 3d) shows a correction generated by calculating an average value for each row of the reference data (first reference data) in FIG. 3b) and the reference data (second reference data) in FIG. 3c). It is data. FIG. 3e) is a corrected image generated by uniformly subtracting the correction data of FIG. 3d) from the output signal of the effective area of each row with respect to the original image of FIG. 3a). As described above, the first vertical shading correction process is performed by a series of procedures.

  Here, if the horizontal OB area is sufficiently large and a large number of pixels can be used for the average value for creating correction data, the variation in the average output value can be suppressed to some extent. As a result, it is possible to reduce the influence of the accuracy of vertical shading correction processing due to noise components generated in the horizontal OB region. However, increasing the horizontal OB area unnecessarily increases the chip size and increases costs.

  On the other hand, in the first vertical shading correction process, one correction data is generated from the area obtained by adding the first calculation area 205 and the second calculation area 206. For this reason, the degree of influence of the accuracy of the vertical shading correction processing on the noise component generated in the horizontal OB area is the same as when the horizontal OB area is combined on one side with the same number of columns in the horizontal OB area. It is considered equivalent. As a result, it is possible to reduce the left-right difference in vertical shading without increasing the chip size as compared with the case where the horizontal OB area is only on one side. That is, it can be said that the first vertical shading correction is an effective correction process at the time of photographing conditions where noise is likely to occur such as high sensitivity and high temperature.

  In the first vertical shading correction process, the correction value is uniform in the horizontal direction for each row. For this reason, as shown in FIG. 3e), in the row in which the correction in the effective region is performed, there is a pixel in which the shading component cannot be completely removed in a part in the horizontal direction, and the correction remains. For this reason, in a situation where the level difference between the left and right vertical shading components in the effective region is large, there is a possibility that a sufficient correction effect cannot be obtained by the first vertical shading correction processing.

  Next, the second vertical shading correction process in the imaging apparatus according to the embodiment of the present invention will be described with reference to FIG. The second vertical shading correction process described with reference to FIG. 4 is a process for correcting the reference data generated from the two horizontal OB regions by linearly interpolating between the two.

  FIG. 4A) is an original image on which vertical shading correction is performed in the vertical shading correction processing described with reference to FIG. In FIG. 4a), in order to explain the effect of correction using the left and right horizontal OB regions, an image having vertical shading with different levels on the left and right in the pixel array is shown. 4b) and FIG. 4c) are respectively generated by calculating the average value for each row for the reference signals output from the first calculation area 205 and the second calculation area 206 in FIG. 4a). First reference data and second reference data.

FIG. 4d) shows corrected image data obtained by performing linear interpolation for each row with respect to the reference data in FIGS. 4b) and 4c) and providing a slope in the horizontal direction. For example, the value (correction data) of the corrected image data in the column of the horizontal address x shown in FIG. 4D is (correction data) = ({(first reference data) × b
+ (Second reference data) × a} / (a + b) Equation 1
It becomes. In Equation 1, a is the distance from the center of the first calculation area 205 to the pixel at the horizontal address x, and b is the distance from the center of the second calculation area 206 to the pixel at the horizontal address x.

  FIG. 4e) is a corrected image generated by subtracting the corrected image data of FIG. 4d) for each pixel from the output signal of each row in the effective area with respect to the original image of FIG. 4a). . As described above, the second vertical shading correction is performed by a series of procedures.

  Here, in the second vertical shading correction process, correction is performed using a correction value generated by linearly interpolating between reference data generated from the left and right OB areas according to the horizontal address. For this reason, in a situation where the noise component included in the reference data is small and the change in the horizontal direction of the vertical shading is linearly shifted, the remaining correction is not included as in the image of FIG. In addition, an image in which overcorrection is not noticeable can be acquired.

  On the other hand, in the second vertical shading correction process, reference data is generated from each of the first calculation area 205 and the second calculation area 206. These reference data are generated from data of about half of the pixels compared to the correction data used in the first vertical shading correction. Accordingly, the reference data is greatly influenced by noise components generated in the horizontal OB region, and may be image data including a large noise component. In other words, a large noise component remains in the corrected image data generated based on these two reference data, and this correction may generate an image with conspicuous overcorrection. That is, it can be said that the second vertical shading correction is an effective correction process under shooting conditions in which noise hardly occurs.

  In the second vertical shading correction process, the correction value changes according to the horizontal address of the pixel. For this reason, as shown in FIG. 4e), even when the level difference between the left and right vertical shading components in the effective region is large, a sufficient correction effect can be obtained by the second vertical shading correction processing. That is, the second vertical shading correction can be said to be an effective correction process in a state where the vertical shading components are greatly different on the left and right in the pixel array.

  Next, the configuration of the digital signal processing circuit 112 (image signal processing apparatus) will be described with reference to FIG. The digital signal processing circuit described with reference to FIG. 5 has a signal processing circuit that realizes vertical shading correction processing in the present embodiment. The digital signal processing circuit 112 (see FIG. 1) includes a first digital signal processing unit 501, a vertical shading correction circuit 502, and a second digital signal processing unit 503. The first digital signal processing unit 501 receives the digital image signal output from the analog signal processing circuit 104.

  The first digital signal processing unit 501 performs horizontal shading correction on the received digital image signal by using the reference signal output from the vertical OB area 201 (see FIG. 2), and outputs it to the vertical shading correction circuit 502. To do. The vertical shading correction circuit 502 performs vertical shading correction on the received digital image signal by using the reference signals output from the first calculation area 205 and the second calculation area 206, and performs second digital signal processing. Output to the unit 503.

  The second digital signal processing unit 503 is configured by a second digital signal processing unit 503 that performs gamma processing, white balance processing, and the like on the received digital image signal. Here, the vertical shading correction circuit 502 includes a first switch 504, a second switch 505, a first generation unit 506, a second generation unit 507, a first calculation unit 513, a second calculation unit 514, A third generation unit 508, a memory unit 509, and a correction unit 512 (correction means) are included.

  The first switch 504 is configured to connect / disconnect the first digital signal processing unit 501 and the first generation unit 506 by turning on / off. The second switch 505 is configured to connect / disconnect the first digital signal processing unit 501 and the second generation unit 507 by turning on / off.

  The first generation unit 506 is connected to the first calculation unit 513, the second calculation unit 514, and the third generation unit 508. The second generation unit 507 is connected to the first calculation unit 513, the second calculation unit 514, and the third generation unit 508. The third generation unit 508 is connected to the first generation unit 506, the second generation unit 507, the first calculation unit 513, the second calculation unit 514, the memory unit 509, and the correction unit 512. The correction unit 512 is connected to the first digital signal processing unit 501, the third generation unit 508, and the second digital signal processing unit 503. The correction unit 512 includes a subtracter 510 and an adder 511.

  Next, vertical shading correction processing according to this embodiment will be described with reference to FIG. In the imaging apparatus according to this embodiment described with reference to FIG. 5, the output order of the pixels in each row is the order of the pixels in the second horizontal OB area 203, the first horizontal OB area 202, and the effective area 204. It is assumed that the data is read and driven so as to be output. The first digital signal processing unit 501 performs basic various corrections such as horizontal shading correction on the image signal output from the analog signal processing circuit 104. Subsequently, the vertical shading correction circuit 502 performs vertical shading correction on the image signal output from the first digital signal processing unit 501.

  Specifically, the first switch 504 is off during the period in which the reference signal of the second calculation area 206 in the second horizontal OB area 203 is output from the first digital signal processing unit 501, 2 switch 505 is on. Thereby, the second generation unit 507 (second generation means) receives the reference signal of the second calculation area 206. The second generation unit 507 generates second reference data according to the second reference signal output from the second calculation area 206. For example, the second generation unit 507 generates the second reference data according to the representative value of the reference signal for each row in the second calculation area 206, and generates a third generation unit 508 (third generation means). Output to. The representative value is, for example, an average value or a median value.

  The first switch 504 is on during the period in which the reference signal of the first calculation area 205 in the first horizontal OB area 202 is output from the first digital signal processing unit 501, and the second switch 505 is turned on. Is off. Thereby, the first generation unit 506 (first generation means) receives the reference signal of the first calculation area 205. The first generation unit 506 generates first reference data according to the reference signal output from the first calculation area 205. For example, the first generation unit 506 generates first reference data according to the representative value of the first reference signal for each row in the first calculation region 205 and outputs the first reference data to the third generation unit 508. The representative value is, for example, an average value or a median value.

  The third generation unit 508 generates correction data by using the received first reference data and second reference data. Specifically, the third generation unit 508 calculates the interval between the first value obtained by averaging the first reference data and the second reference data, and the first reference data and the second reference data. The correction data is generated by using any one of the second values obtained by linear interpolation. That is, the third generation unit 508 uses either the first value or the second value to generate correction data according to the shooting conditions.

  For example, when the temperature detected by the temperature detection circuit 121 is equal to or higher than the first threshold, the third generation unit 508 generates correction data using the first value, and is detected by the temperature detection circuit 121. When the temperature is lower than the first threshold, correction data is generated using the second value.

  Alternatively, for example, when the sensitivity set by the shooting mode setting unit 123 is equal to or higher than the second threshold, the third generation unit 508 generates correction data using the first value. When the sensitivity set by the shooting mode setting unit 123 is less than the second threshold, the third generation unit 508 generates correction data using the second value.

  Alternatively, for example, the third generation unit 508, when the accumulation time for each of the plurality of effective pixels in the image sensor 103 set by the accumulation time setting unit 122 to perform the charge accumulation operation is equal to or greater than the third threshold value, Correction data is generated using the first value. The third generation unit 508 sets the second value when the accumulation time set by the accumulation time setting unit 122 for each of the plurality of effective pixels in the image sensor 103 to perform the charge accumulation operation is less than the third threshold. Is used to generate correction data.

  The third generation unit 508 further generates correction data according to the state of the reference signal output from the first calculation area 205 and the reference signal output from the second calculation area 206. Either one of the first value and the second value is used.

  For example, the first calculation unit 513 receives the reference signal output from the first calculation region 205 via the first generation unit 506 when the first switch 504 is turned on. The first calculation unit 513 receives the reference signal output from the second calculation region 206 via the second generation unit 507 when the second switch 505 is turned on. The first calculation unit 513 calculates a variation between the reference signal output from the first calculation area 205 and the reference signal output from the second calculation area 206. The first calculation unit 513 outputs the calculation result to the third generation unit 508. The third generation unit 508 generates correction data using the first value when the variation calculated by the first calculation unit 513 is greater than or equal to the fourth threshold value. When the variation calculated by the first calculation unit 513 is less than the fourth threshold, the third generation unit 508 generates correction data using the second value.

  Alternatively, for example, the second calculation unit 514 receives first reference data from the first generation unit 506 and receives second reference data from the second generation unit 507. The second calculation unit 514 calculates a correlation coefficient between the first reference data and the second reference data. The second calculation unit 514 outputs the correlation coefficient information to the third generation unit 508. When the correlation coefficient calculated by the second calculation unit 514 is less than the fifth threshold, the third generation unit 508 generates correction data using the first value. The third generation unit 508 generates correction data using the second value when the correlation coefficient calculated by the second calculation unit 514 is greater than or equal to the fifth threshold.

  Then, the third generation unit 508 generates correction data using either the first value or the second value and outputs the correction data to the correction unit 512. Note that the third generation unit 508 further adjusts the value of the correction data based on the generated correction data value and the history information regarding the correction data read in advance stored in the memory unit 509. May be.

  Based on information from the temperature detection circuit 121, the accumulation time setting unit 122, the shooting mode setting unit 123, and the like, the third generation unit 508 corrects the correction data so as to have an appropriate value according to shooting conditions and shooting mode settings. The value of may be further adjusted. The third generation unit 508 stores various information used when generating the correction data value in the memory unit 509 as history information regarding the correction data.

  During the period in which the image signal of the effective area 204 is output from the first digital signal processing unit 501, the correction unit 512 uses the correction data, thereby using the reference level (darkness) of the image signal output from the plurality of effective pixels. Level). Specifically, the subtractor 510 of the correction unit 512 receives the image signal of the effective area 204 from the first digital signal processing unit 501 and the correction data from the third generation unit 508. The subtractor 510 subtracts the correction data from the image signal in the effective area 204 and outputs the result to the adder 511. The adder 511 adds a predetermined offset value to the image signal from which the correction data is subtracted, and outputs the added image signal to the second digital signal processing unit 503 as an image signal subjected to vertical shading correction.

  Next, the procedure of the vertical shading correction process of the present embodiment will be described using the flowchart of FIG. The flowchart in FIG. 6 is executed under the control of the system control unit 118 (control means) based on the program stored in the first storage unit 119. When the system control unit 118 receives an instruction to start shooting from the user via an input unit (not shown), first, driving conditions such as moving image shooting, a still image and a trimming region, sensitivity, aperture value, exposure time, etc. Are initially set (S601). The system control unit 118 controls the mechanical shutter 102 to perform an exposure process for exposing the image sensor 103 (S602).

  Next, the system control unit 118 switches the correction data creation method of the vertical dark shading correction executed in the digital signal processing circuit 112 according to the shooting conditions (S1). That is, the system control unit 118 determines which of the first value and the second value should be used to generate correction data according to the shooting conditions. The first value is a value obtained by averaging first reference data and second reference data described later. The second value is a value obtained by performing linear interpolation between the first reference data and the second reference data.

  Specifically, the shooting mode set by the shooting mode setting unit 123 is determined (S603). If it is determined that the set shooting mode is a mode for performing high-speed reading, such as a live view mode or a moving image recording mode, it is determined that the first value should be used to create correction data, and processing To S610. If it is determined that the set shooting mode is not a mode for performing high-speed reading, it is determined that the second value should be used to create correction data, and the process proceeds to S604.

  It is determined whether or not the temperature in the shooting environment detected by the temperature detection circuit 121 is high (S604). When it is determined that the temperature detected by the temperature detection circuit 121 is equal to or higher than the first threshold (high temperature), it is determined that the first value should be used, and the process proceeds to S610. When the temperature detected by the temperature detection circuit 121 is lower than the first threshold (not high temperature), it is determined that the second value should be used, and the process proceeds to S605.

  It is determined whether or not the accumulation time for each of the plurality of effective pixels in the image sensor 103 set by the accumulation time setting unit 122 to perform the charge accumulation operation is longer than the third threshold (whether or not the long-second exposure setting is set). (S605). If the accumulation time is greater than or equal to the third threshold, it is determined that the first value should be used, and the process proceeds to S610.

  If the accumulation time is less than the third threshold, it is determined that the second value should be used, and the process proceeds to S606. It is determined whether or not the ISO sensitivity set by the shooting mode setting unit 123 is higher than the second threshold (whether or not the sensitivity setting is high) (S606).

  If the sensitivity set by the shooting mode setting unit 123 is greater than or equal to the second threshold, it is determined that the first value should be used, and the process proceeds to S610. If the sensitivity set by the shooting mode setting unit 123 is less than the second threshold, it is determined that the second value should be used, and the process proceeds to S607.

  Further, the system control unit 118 further generates the correction data in order to generate correction data according to the state of the reference signal output from the first calculation area 205 and the reference signal output from the second calculation area 206. It is determined which one of the value 1 and the second value should be used (S2). Specifically, after calculating the standard deviation σ between the reference signal output from the first calculation area 205 and the reference signal output from the second calculation area 206, it is determined whether the value is large. (S607).

  If the calculated standard deviation (variation) σ is equal to or greater than the fourth threshold value, it is determined that the first value should be used, and the process proceeds to S610. If the calculated standard deviation (variation) σ is less than the fourth threshold value, it is determined that the second value should be used, and the process proceeds to S608.

  In step S <b> 608, the digital signal processing circuit 112 generates first reference data according to the reference signal output from the first calculation area 205, and the first signal is output according to the reference signal output from the second calculation area 206. 2 reference data is generated. Then, the digital signal processing circuit 112 calculates a correlation coefficient between the first reference data and the second reference data (S608).

  Subsequently, it is determined whether or not the correlation coefficient calculated in S608 is larger than the fifth threshold (S609). If the calculated correlation coefficient is less than the fifth threshold, it is determined that the first value should be used, and the process proceeds to S610. If the calculated correlation coefficient is equal to or greater than the fifth threshold, it is determined that the second value should be used, and the process proceeds to S611.

  In S610, the digital signal processing circuit 112 uses the first value obtained by averaging the first reference data and the second reference data, and the vertical image data for the first vertical dark shading correction method. (Correction data) is created (see FIG. 3d). In S611, the digital signal processing circuit 112 uses the second value obtained by linearly interpolating between the first reference data and the second reference data, so that the corrected image data (inclined in the horizontal direction) ( Correction data) is created (see FIG. 4d).

  In S612, the digital signal processing circuit 112 performs vertical dark shading correction on the effective area using the correction data generated in S610 or S611. In S613, the digital signal processing circuit 112 outputs the image data of the corrected image to the image memory 113, the recording circuit 115, or the display circuit 117, and the main photographing is finished.

  As described above, it is possible to provide an imaging apparatus that performs higher-precision vertical dark shading correction suitable for shooting conditions and the state of reference signals from the left and right horizontal OB regions.

  In addition, this invention is not limited to said embodiment, It can take various forms. For example, in the procedure shown in FIG. 6, it is possible to determine the correction process based on only the exposure time, or to determine the correction process based on two conditions of ISO sensitivity and environmental temperature. It is also possible to adopt a configuration in which the correction process is determined only from the state.

  Similarly, it is also possible to switch the calculation area using the shooting environment and shooting conditions other than the environmental temperature, the exposure time during imaging, and the ISO sensitivity setting as judgment materials. For example, the correction data generation method can be switched in shooting under conditions where the dark current is large even at high temperatures and other than during long-second exposure, such as shooting immediately after using the liquid crystal monitor for a long time.

  Further, in the procedure shown in FIG. 6, for example, both the first value and the second value are generated in advance, and then, based on the determination result of the shooting condition at the time of shooting and the state of the horizontal OB portion. Also, which value is used to perform vertical dark shading correction may be selected. Further, in the first and second vertical shading correction processes, for example, an average value or an interpolated value of output signals from the calculation areas of two horizontal OB areas may be calculated for each row. It is also possible to calculate the correction data for each row from there, and at the same time read the row, correct the output signal of the effective area of the row.

Claims (9)

An effective area in which a plurality of effective pixels each generating an image signal corresponding to light is arranged, and an area arranged on the first side of the effective area adjacent to the effective area, each generating a reference signal A first light-shielding region in which a plurality of first light-shielding pixels are arranged, and a region adjacent to the effective region and disposed on the opposite side of the first light-shielding region with the effective region interposed therebetween. An image signal processing device that performs a predetermined correction process on the image signal output from an image sensor having a pixel array having a second light-shielding region in which a plurality of second light-shielding pixels that are generated are arranged,
First generation means for generating first reference data in response to a first reference signal output from the plurality of first light-shielding pixels;
Second generation means for generating second reference data in response to a second reference signal output from the plurality of second light-shielding pixels;
The obtained by linear interpolation between the first value and the first reference data and the second reference data obtained by averaging the first reference data and the second reference data Third generation means for generating correction data using any one of the values of 2,
Correction means for correcting image signals output from the plurality of effective pixels using the correction data;
Control means for determining whether the third generation means uses the first value or the second value to generate the correction data;
An image signal processing apparatus comprising: The control unit determines whether the third generation unit uses the first value or the second value to generate the correction data according to an imaging condition. Item 2. The image signal processing device according to Item 1. In accordance with the state of the first reference signal and the second reference signal, the control means uses the first value or the second value to determine whether the third generation means uses the correction data. The image signal processing apparatus according to claim 1, wherein it is determined whether to generate the image signal. Temperature detecting means for detecting a temperature around the pixel array;
The control unit determines whether the third generation unit uses the first value or the second value to generate the correction data according to the temperature detected by the temperature detection unit. The image signal processing apparatus according to claim 1. Sensitivity setting means for setting the shooting sensitivity is further provided,
The control unit determines whether the third generation unit generates the correction data using the first value or the second value according to the photographing sensitivity set by the sensitivity setting unit. The image signal processing apparatus according to claim 1, wherein the determination is performed. Each of the plurality of effective pixels generates an image signal by performing a charge accumulation operation,
The control means may be configured such that the third generation means uses either the first value or the second value according to an accumulation time during which each of the plurality of effective pixels performs a charge accumulation operation. The image signal processing apparatus according to claim 1, wherein it is determined whether to generate the image signal. The control unit calculates a variation between the first reference signal and the second reference signal, and the third generation unit determines whether the first value and the second value are in accordance with the variation. The image signal processing apparatus according to claim 1, wherein which one is used to generate the correction data is determined. The control means calculates a correlation coefficient between the first reference data and the second reference data, and according to the correlation coefficient, the third generation means causes the first value and the first reference data to be calculated. The image signal processing apparatus according to claim 1, wherein which of the two values is used to determine whether to generate the correction data. An image sensor;
The image signal processing apparatus according to claim 1, wherein a predetermined correction process is performed on the image signal output from the image sensor.
An imaging device comprising: