JP2010034744A - Imaging device and imaging control method - Google Patents

Abstract

Image quality degradation is reduced even under a situation where image quality degradation occurs due to a pixel defect in an OB pixel region without changing the structure of an image sensor.
An analog signal processing unit calculates a black level of a readout line 13e in a photosensitive pixel area 13a from an average value of black levels of pixels in a TP pattern 13f in an OB pixel area 13b, and performs a clamping process. The digital camera is provided with a normal TG pattern shown in (a) and a TG pattern having a larger number of clamp pixels than the normal TG pattern shown in (b), and the CPU determines the photosensitive pixel from which TG pattern depending on the situation. It is determined whether to calculate the black level of the area 13a. For example, a TG pattern with a large number of clamp pixels is used when the ISO sensitivity is 800 or more, and a normal TG pattern is used when the ISO sensitivity is less than 800.
[Selection] Figure 6

Description

  The present invention relates to an image pickup apparatus and an image pickup control method, and more particularly to an image pickup apparatus and an image pickup control method that reduce image quality deterioration when a pixel defect is present in an OB pixel area.

  It is known that noise due to dark current components is included in the output of an image sensor such as a CCD. This noise occurs even when no light is incident, and the noise signal voltage is proportional to the accumulation time and has temperature dependence.

  In order to compensate for this dark current component, an optical black pixel area (OB pixel area), which is a set of light-shielded light receiving elements, is arranged outside the effective pixel area of an image sensor such as a CCD, and acquired from the OB pixel area. The image signal of the effective pixel region is clamped using the average value of the black level as a reference level.

  However, if there is a large pixel defect (especially a line flaw) in the OB pixel area to be clamped, the reference level will fluctuate if the black level is acquired from the OB pixel area including the pixel defect. Degradation of image quality due to noise (in the case of line scratches, black sinking after the line scratch generation line) occurs. In addition, the above problem appears more prominently depending on shooting conditions such as high ISO sensitivity and low brightness subject.

Patent Document 1 discloses a technique in which the dark current integration signal is averaged before reading by the common connection of the reset terminals of the photodiodes of the pixels in the OB region with the potential averaging line, and does not need to be averaged in the clamp circuit. Are listed. According to this technique, it is possible to prevent the clamp level from varying due to a pixel defect or the like, and to obtain the black level in a shorter time.
JP 2001-285572 A

  However, the technique of Patent Document 1 has a problem that the conventional image sensor structure cannot be used.

  The present invention has been made in view of such circumstances, and an imaging apparatus capable of reducing image quality degradation even in a situation where image quality degradation occurs due to pixel defects in the OB pixel region without changing the structure of the image sensor. An object is to provide an imaging control method.

  In order to achieve the above object, an image pickup apparatus according to claim 1 is an image pickup element in which light receiving elements are two-dimensionally arranged, a photosensitive pixel region for converting received light of an object into an image signal, and the photosensitive element. An image sensor that is provided adjacent to the side of the pixel area and is shielded from light by a light shielding member, and a pixel in an arbitrary horizontal line in the photosensitive pixel area, the pixels in the optical black area An obtaining means for obtaining a clamp level of pixels in a horizontal line of the photosensitive pixel region from an output signal of pixels having a predetermined number of lines including a horizontal position line that is the same as a horizontal line of the photosensitive pixel region; Clamping means for clamping an output signal of a pixel in a horizontal line of the photosensitive pixel area based on the clamp level acquired by the acquisition means; and the clamp Means for generating a photographed image based on the signal clamped by the stage, and detection means for detecting a photographing condition and / or photographing environment in which image quality deterioration of the photographed image is likely to occur due to a pixel defect in the optical black region. And a switching means for increasing the predetermined number of lines when the detection means detects a photographing condition and / or photographing environment in which the image quality deterioration is likely to occur.

  According to the first aspect of the present invention, the number of lines in the OB pixel area for acquiring the clamp level is increased in the photographing conditions and the photographing environment in which the image quality is likely to deteriorate. Even under a situation where image quality deterioration occurs, the image quality deterioration can be reduced.

  According to a second aspect of the present invention, in the imaging apparatus according to the first aspect, the imaging device further includes a unit that sets a shooting ISO sensitivity, and the detection unit is configured to perform the operation when the set shooting ISO sensitivity is higher than a first predetermined value. It is characterized in that it is detected as a shooting condition in which image quality deterioration is likely to occur.

  As a result, it is possible to appropriately detect a shooting condition in which image quality deterioration is likely to occur.

  The imaging apparatus according to claim 1 or 2, further comprising means for measuring the temperature of the imaging element, wherein the detecting means has a temperature of the measured imaging element that is a second predetermined value. If it is higher, it is detected as a shooting environment in which the image quality deterioration is likely to occur.

  As a result, it is possible to appropriately detect a shooting environment in which image quality deterioration is likely to occur.

  The imaging apparatus according to any one of claims 1 to 3, wherein the image pickup apparatus according to any one of claims 1 to 3 is configured to select one drive frequency from a plurality of drive frequencies, and to synchronize with the selected drive frequency. Means for reading out an output signal of the image sensor, and the detection means detects the photographing condition that is likely to cause the image quality degradation when the drive frequency is lower than a third predetermined value.

  As a result, it is possible to appropriately detect a shooting condition in which image quality deterioration is likely to occur.

  5. The imaging apparatus according to claim 1, further comprising means for calculating subject brightness, wherein the detecting means has the calculated subject brightness lower than a fourth predetermined value. In this case, it is detected that the image quality is likely to deteriorate.

  As a result, it is possible to appropriately detect a shooting condition in which image quality deterioration is likely to occur.

  The imaging apparatus according to any one of claims 1 to 5, further comprising means for calculating a horizontal and / or vertical resolution of a subject, wherein the detection means is the calculated resolution. Is lower than the fifth predetermined value, it is detected as a photographing condition in which the image quality deterioration is likely to occur.

  As a result, it is possible to appropriately detect a shooting condition in which image quality deterioration is likely to occur.

  The imaging apparatus according to any one of claims 1 to 6, further comprising means for calculating an R gain and a B gain for adjusting white balance, wherein the detection means is the calculated When the R gain is higher than a sixth predetermined value or the calculated B gain is higher than a seventh predetermined value, the imaging condition is detected as a shooting condition in which the image quality deterioration is likely to occur.

  As a result, it is possible to appropriately detect a shooting condition in which image quality deterioration is likely to occur.

  In order to achieve the above object, the imaging control method according to claim 8 is an imaging device in which light receiving elements are two-dimensionally arranged, and includes a photosensitive pixel region that converts received light of an object into an image signal, and The pixels of the optical black region are pixels of an arbitrary horizontal line of the photosensitive pixel region of the imaging element that is provided adjacent to the side of the photosensitive pixel region and is shielded by the light shielding member. An acquisition step of acquiring a clamp level of pixels in a horizontal line of the photosensitive pixel region from an output signal of pixels having a predetermined number of lines including a line at the same horizontal position as the horizontal line of the photosensitive pixel region; A clamping step of clamping an output signal of a pixel in a horizontal line of the photosensitive pixel region based on the clamping level acquired in the acquisition step; A step of generating a photographed image based on the signal clamped in the ramp step, and a detection step of detecting a photographing condition and / or photographing environment in which image quality deterioration of the photographed image is likely to occur due to a pixel defect in the optical black region And a switching step of increasing the predetermined number of lines when a photographing condition and / or photographing environment in which the image quality is likely to deteriorate is detected in the detecting step.

  According to the eighth aspect of the present invention, the number of lines in the OB pixel area for obtaining the clamp level is increased under the photographing conditions and the photographing environment in which the image quality is likely to be deteriorated. Even under a situation where image quality deterioration occurs, the image quality deterioration can be reduced.

  According to the present invention, since the number of lines in the OB pixel area for acquiring the clamp level is increased in shooting conditions and shooting environments in which image quality is likely to deteriorate, image quality deterioration is caused by pixel defects in the OB pixel area. Even under such circumstances, image quality degradation can be reduced.

  The best mode for carrying out the present invention will be described below.

<First Embodiment>
FIG. 1 is a diagram showing an example of an electrical configuration of a digital camera 10 according to the present invention. As shown in the figure, the digital camera 10 includes a lens 11, a motor driver 12, a CCD 13, a timing generator 14, an analog signal processing unit 15, a CPU 16, a clock generator 17, an operation unit 18, an image signal processing unit 19, and a compression processing unit. 20, AE / AF / AWB processing unit 21, memory 22, video encoder 23, image display device 24, sound input processing unit 25, microphone 26, media recording control unit 27, recording medium 28, sound output processing unit 29, speaker 30 , A bus 31, a power supply block 32, a battery 34, and the like.

  Each unit operates under the control of the CPU 16, and the CPU 16 controls each unit of the digital camera 10 by executing a predetermined control program based on an input from the operation unit 18.

  The digital camera 10 includes a ROM (not shown), and various data necessary for control are recorded in the ROM in addition to a control program executed by the CPU 16. The CPU 16 controls each unit of the digital camera 10 by reading the control program recorded in the ROM into the memory 22 and executing it sequentially.

  The memory 22 is composed of SDRAM and is used as a program execution processing area, a temporary storage area for image data and the like, and various work areas.

  The operation unit 18 includes a shutter release button, an ISO sensitivity changeover switch, and the like (not shown), and outputs a signal corresponding to each operation to the CPU 16.

  The lens 11 includes a zoom lens and a focus lens (not shown), and is driven by a driver 12 to perform zooming and focusing.

  The CCD 13 is arranged at the rear stage of the lens 11 and receives subject light transmitted through the lens 11. FIG. 2 shows a schematic diagram of the CCD 13. As shown in the figure, the CCD 13 includes a photosensitive pixel region 13a, an OB pixel region 13b, a horizontal transfer path 13c, an amplifier 13d, and the like.

  A large number of light receiving elements (not shown) are two-dimensionally arranged on the light receiving surface (photosensitive pixel region 13a) of the CCD 13, and red (R), green (G), blue (B) (not shown) corresponding to each light receiving element. ) Primary color filters are arranged in a predetermined arrangement structure. The subject light imaged on the photosensitive pixel region 13a is converted into an electric signal by each light receiving element.

  Further, on the right side of the photosensitive pixel area 13a, an OB pixel area 13b is provided adjacent to the photosensitive pixel area 13a. In the OB pixel region 13b, a large number of light receiving elements similar to those in the photosensitive pixel region 13a are two-dimensionally arranged. These light receiving elements are covered with a light shielding member (not shown) such as aluminum.

  The electrical signals accumulated in the light receiving elements in the photosensitive pixel area 13a and the OB pixel area 13b are read out to a vertical transfer path (not shown). The vertical transfer path transfers this signal to the horizontal transfer path 13c line by line in synchronization with the clock supplied from the timing generator 14. Further, the horizontal transfer path 13 c outputs the signal for one line transferred from the vertical transfer path to the amplifier 13 d in synchronization with the clock supplied from the timing generator 14.

  The output of the image signal is started when the digital camera 10 is set to the shooting mode. That is, when the digital camera 10 is set to the photographing mode, output of an image signal is started to display a through image on the image display device 24. The output of the image signal for the through image is temporarily stopped when the instruction for the main photographing is given, and is started again when the main photographing is finished.

  The analog image signal output from the amplifier 13d is input to the analog signal processing unit 15. The analog signal processing unit 15 includes a correlated double sampling circuit (CDS), a clamp processing circuit, and an automatic gain control circuit (AGC) (not shown).

  The CDS removes noise generated by the amplifier 13d included in the image signal. The clamp processing circuit performs processing for removing dark current components, and the signal of the photosensitive pixel region 13a is clamped to a clamp level based on the electrical signal of the OB pixel region 13b. Specifically, the output signal of the horizontal line 13e in the photosensitive pixel area 13a is clamped using the average value of the black level of the TG pattern 13f in the OB pixel area 13b as a reference value.

  FIG. 3 is a diagram showing a positional relationship between the horizontal line 13e and the TG pattern 13f with respect to the horizontal line. The horizontal line 13e from which the black portion of the photosensitive pixel region 13a is read is shown, and the black portion of the OB pixel region 13b shows the TG pattern 13f. As described above, the photosensitive pixel area 13a and the OB pixel area 13b are read out by the horizontal transfer path 13c by one horizontal line. Therefore, the TG pattern 13f is composed of a horizontal line at the same position as the horizontal line 13e in the OB pixel region and a plurality of lines read before the horizontal line, and is composed of, for example, about 512 pixels. Is done. The clamp processing circuit calculates an average value of the black level from each pixel of the TG pattern, and clamps the signal of the corresponding horizontal line using the calculated average value as a reference level.

  Further, the AGC amplifies the image signal from which the dark current component has been removed with a predetermined gain corresponding to the set ISO sensitivity.

  The analog image signal subjected to the required signal processing in the analog signal processing unit 15 is converted into a digital image signal having a gradation width of a predetermined bit by an A / D converter (not shown). This image signal is so-called RAW data, and has a gradation value indicating the density of R, G, and B for each pixel. This digital image signal is stored in the memory 22 via the bus 31.

  In addition to the CPU 16 and memory 22, the bus 31 includes an image signal processing unit 19, a compression processing unit 20, an AE / AF / AWB processing unit 21, a video encoder 23, a media recording control unit 27, a sound input processing unit 25, a sound An output processing unit 29 and the like are connected, and these can exchange information with each other via a bus 31.

  The image signal processing unit 19 performs predetermined signal processing on the image signals of R, G, and B colors stored in the memory 22, and an image signal (Y / Y) composed of a luminance signal Y and color difference signals Cr and Cb. C signal).

  The AE / AF / AWB processing unit 21 fetches R, G, and B image signals stored in the memory 22 according to a command from the CPU 16 and calculates an integrated value necessary for AE control. The CPU 16 calculates a luminance value from the integrated value and obtains an exposure value from the luminance value. Further, the aperture value and the shutter speed are determined from the exposure value according to a predetermined program diagram.

  Further, the AE / AF / AWB processing unit 21 calculates a focus evaluation value necessary for AF (Automatic Focus) control based on an image signal stored in the memory 22 in accordance with an instruction from the CPU 16. The AE / AF / AWB processing unit 21 includes a focus region extraction unit that extracts a signal within a predetermined focus region set on the screen, and an integration unit that integrates absolute value data within the focus region. The integrated absolute value data in the focus area is output to the CPU 16 as a focus evaluation value. During the AF control, the CPU 16 searches for a position where the focus evaluation value output from the AE / AF / AWB processing unit 21 is maximized, and moves the lens 11 to that position, thereby focusing on the main subject. Do.

  The AE / AF / AWB processing unit 21 includes a white balance gain calculation circuit for calculating a gain value for white balance gain adjustment, and a gain variable amplifier for increasing / decreasing the levels of the R, G, and B color signals. Based on a command from the CPU 16, gain adjustment corresponding to the white balance gain of each color signal is performed.

  The compression processing unit 20 performs compression processing of a predetermined format (for example, JPEG) on the image signal (Y / C signal) composed of the input luminance signal Y and color difference signals Cr and Cb in accordance with a compression command from the CPU 16. Generate compressed image data. Further, in accordance with a decompression command from the CPU 16, the input compressed image data is subjected to decompression processing in a predetermined format to generate non-compressed image data.

  The video encoder 23 controls display on the image display device 24 in accordance with a command from the CPU 16.

  The media recording control unit 27 controls reading / writing of data with respect to the recording medium 28 in accordance with a command from the CPU 16. The recording medium 28 may be detachable from the main body of the digital camera 10 such as a memory card, or may be built in the main body of the digital camera 10. In the case of detachable, a card slot is provided in the main body of the digital camera 10, and the card slot is used by being loaded.

  The sound input processing unit 25 converts the voice input input from the microphone 26 into a digital signal of a predetermined format in accordance with a command from the CPU 16. This audio signal is stored in the memory 22 via the bus 31.

  The sound output processing unit 29 outputs a sound signal of a predetermined format from the speaker 30 in accordance with a command from the CPU 16.

  The power supply block 32 includes a DC / DC converter 33, converts a power supply voltage supplied from the battery 34 into a desired voltage in accordance with a command from the CPU 16, and supplies power to each device.

  Next, the black level clamping process of the digital camera 10 will be described.

  FIG. 4 is a diagram showing the black level after clamping of each horizontal line in the case where a linear defective pixel column (line scratch 13g) due to a defect in the vertical transfer path of the OB pixel region 13b of the CCD 13 exists. . As described above, the black level of each horizontal line is calculated from a TG pattern including a line at the same horizontal position in the OB pixel region 13b and a plurality of lines read before that. As shown in FIG. 4, when the line defect 13g is present in the OB pixel region 13b, the black level becomes abnormal from the horizontal line position including the line defect 13g. Therefore, as compared with the captured image in the case where there is no line flaw 13g shown in FIG. 5A, image quality deterioration in which the black level changes horizontally occurs as shown in FIG. 5B.

  Here, when there is a line flaw 13g in the vertical transfer path of the OB pixel region 13b, the black level after clamping when the black level is calculated with the TG pattern shown in FIG. 6A is indicated by a solid line in FIG. . On the other hand, as shown in FIG. 6B, when the black level is calculated with the TG pattern in which the number of clamp pixels is increased by increasing the number of lines in the OB pixel region 13b as compared with the TG pattern in FIG. 6A. The black level after clamping is indicated by a dotted line in FIG. FIG. 5C shows a captured image when the clamp level is calculated using the TG pattern shown in FIG. When the number of clamp pixels in the TG pattern is increased in this way, the time constant for calculating the black level increases, so that the fluctuation of the black level due to line scratches is reduced. As a result, a sudden change in the black level is alleviated, and image quality deterioration (blackening) is reduced as an image. The digital camera 10 is configured to be able to switch between the TG pattern shown in FIG. 6A and the TG pattern shown in FIG.

  Next, the operation of the digital camera 10 will be described with reference to FIG.

  The CPU 16 issues a command to the analog signal processing unit 15 so as to select a TG pattern having a large number of clamp pixels shown in FIG. 6B as necessary before the actual photographing (step S1). Before the actual photographing, as described above, the through image is displayed on the image display device 24, and the normal TG pattern (TG pattern with a small number of clamp pixels) shown in FIG. 6A is selected. The TG pattern is switched at the timing of one vertical period, that is, when the scanning for one screen is completed.

  Thereafter, when the shutter release button of the operation unit 18 is operated, actual shooting is started (step S2).

  Thus, by changing the pattern as necessary, it is possible to reduce image quality degradation due to scratches or the like of the image sensor.

  When it is known that the OB pixel area 13b of the CCD 13 has a pixel defect, a setting for selecting a TG pattern having a large number of clamp pixels may be made as an initial setting. In this case, it is recorded that there is a pixel defect in the memory 22.

  Note that it is originally preferable that the number of clamp pixels is not too large. This is because the black level of the OB pixel away from the readout line is considered to be different from the original black level value to be clamped.

  In this embodiment, an instruction to change the TG pattern is given before the start of photographing. However, if it can be set before the signal capture of the CCD 13 starts, a command may be sent from the CPU 16 during exposure.

<Second Embodiment>
The digital camera 10 of the second embodiment selects a TG pattern according to the ISO sensitivity.

  FIG. 9 is a diagram showing the ratio between the exposure signal and the clamp level (black level) at each ISO sensitivity of the CCD 13. The shaded portion indicates the signal amount due to exposure, and the black portion indicates the signal amount (black level) when light is blocked. To express. As shown in the figure, as the ISO sensitivity increases, the exposure signal amount decreases (and is increased by the corresponding gain), and the ratio of the dark current in the entire signal amount increases. Therefore, the higher the ISO sensitivity, the more the black level changes. It will be greatly affected. That is, as the ISO sensitivity increases, the influence of pixel defects in the OB pixel region 13b increases. Therefore, the digital camera 10 according to the second embodiment selects a TG pattern having a high ISO sensitivity and a large number of clamp pixels with severe image quality deterioration conditions.

  FIG. 10 is a flowchart illustrating the operation of the digital camera 10 according to the second embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the flowchart shown in FIG. 8, and the detailed description is abbreviate | omitted.

  The analog signal processing unit 15 performs black level clamping processing of a captured image using a TG pattern having a normal number of clamping pixels shown in FIG.

  The CPU 16 determines whether or not the ISO sensitivity set by the ISO sensitivity changeover switch of the operation unit 18 is ISO sensitivity A = 800 or more (step S11).

  When the set ISO sensitivity is 800 or more, the CPU 16 instructs the analog signal processing unit 15 to use the TG pattern with a large number of clamp pixels shown in FIG. 6B (step S1). . When the set ISO sensitivity is less than 800, the normal TG pattern of the number of clamp pixels shown in FIG. This is because, as described above, it is originally preferable that the number of clamp pixels is not too large.

  Thereafter, when the shutter release button of the operation unit 18 is operated, the main photographing is started based on the selected TG pattern (step S2).

  In this embodiment, the TG pattern is selected using the ISO sensitivity. However, the TG pattern may be selected using the analog gain value of the automatic gain control circuit (AGC) of the analog signal processing unit 15.

  Further, a plurality of TG patterns may be provided and a TG pattern corresponding to the ISO sensitivity may be selected. Also in this case, a TG pattern having a larger number of clamp pixels is selected as the ISO sensitivity is higher.

<Third Embodiment>
The digital camera 10 according to the third embodiment selects a TG pattern according to the temperature of the CCD 13.

  FIG. 11 shows a block diagram of a digital camera 10 according to the third embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the block diagram shown in FIG. 1, and the detailed description is abbreviate | omitted. It differs from the block diagram shown in FIG. 1 in that a thermistor 13h is provided.

  The thermistor 13h is disposed in contact with the back surface of the CCD 13, and can measure the temperature of the CCD 13 (particularly, the OB pixel region 13b).

  The higher the temperature of the image sensor at the time of shooting, the higher the output level of the pixel defect, so that it is greatly affected by the fluctuation of the black level. Therefore, the digital camera 10 according to the third embodiment selects a TG pattern having a large number of clamp pixels when an image sensor having severe image quality degradation conditions is at a high temperature.

  FIG. 12 is a flowchart illustrating the operation of the digital camera 10 according to the third embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the flowchart shown in FIG. 8, and the detailed description is abbreviate | omitted.

  The CPU 16 determines whether or not the temperature of the CCD 13 is equal to or higher than B from the output signal of the thermistor 13h (step S12).

  When the temperature of the CCD 13 is equal to or higher than B, the CPU 16 instructs the analog signal processing unit 15 to select a TG pattern having a large number of clamp pixels (step S1). If it is less than B, the TG pattern having the normal number of clamp pixels is used.

  Thereafter, when the shutter release button of the operation unit 18 is operated, the main photographing is started based on the selected TG pattern (step S2).

  Thus, by measuring the temperature of the CCD 13 with the thermistor 13h and selecting a TG pattern according to the measured temperature, it is possible to reduce image quality degradation due to pixel defects in the OB pixel region 13b.

<Fourth embodiment>
The digital camera 10 according to the fourth embodiment selects a TG pattern according to the frequency of the drive clock of the CCD 13 supplied from the timing generator 14.

  The slower the drive frequency of the image sensor at the time of shooting, the greater the output level of pixel defects on the transfer path, and thus the greater the influence of black level fluctuations. Therefore, the digital camera 10 according to the fourth embodiment selects a TG pattern with a large number of clamp pixels when the drive frequency of an image sensor with severe image quality deterioration conditions is low.

  FIG. 13 is a flowchart illustrating the operation of the digital camera 10 according to the fourth embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the flowchart shown in FIG. 8, and the detailed description is abbreviate | omitted.

  The CPU 16 determines whether or not the drive frequency of the CCD 13 output from the timing generator 14 is C MHz or less (step S13).

  When the drive frequency of the CCD 13 is CMHz or less, the CPU 16 instructs the analog signal processing unit 15 to select a TG pattern with a large number of clamp pixels (step S1). If it is faster than CMHz, the TG pattern with the normal number of clamp pixels is used.

  Thereafter, when the shutter release button of the operation unit 18 is operated, the main photographing is started based on the selected TG pattern (step S2).

  The drive frequency of the CCD 13 may be used by reducing the frequency by dividing the original drive clock in order to reduce power consumption. By selecting a TG pattern according to the drive frequency of the CCD 13 output from the timing generator 14 as in the present embodiment, it is possible to reduce image quality degradation due to pixel defects in the OB pixel region 13b.

<Fifth embodiment>
The digital camera 10 according to the fifth embodiment selects a TG pattern according to the subject brightness.

  As shown in FIG. 14, when the subject brightness is low, the amount of exposure signal decreases, and the fluctuation of the black level becomes dominant. Therefore, the digital camera 10 according to the fifth embodiment selects a TG pattern with a large number of clamp pixels when the imaging subject luminance is low and the conditions for image quality degradation are severe.

  FIG. 15 is a flowchart illustrating the operation of the digital camera 10 according to the fifth embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the flowchart shown in FIG. 8, and the detailed description is abbreviate | omitted.

  The CPU 16 acquires subject luminance information from the AE / AF / AWB processing unit 21 (step S14). It is determined whether or not the acquired luminance is D or less (step S15).

  When the luminance is D or less, the CPU 16 instructs the analog signal processing unit 15 to select a TG pattern with a large number of clamp pixels (step S1). If it is higher than D, the TG pattern having the normal number of clamp pixels is continuously used.

  Thereafter, when the shutter release button of the operation unit 18 is operated, the main photographing is started based on the selected TG pattern (step S2).

  As described above, by acquiring the luminance information of the subject and selecting the TG pattern according to the luminance, it is possible to reduce the image quality deterioration due to the pixel defect in the OB pixel region 13b.

<Sixth Embodiment>
The digital camera 10 according to the sixth embodiment selects a TG pattern according to the resolution of the subject.

  FIG. 16 is a diagram illustrating high-frequency components of an image in the vertical direction of the image. When the frequency component of the exposure signal is extracted, the higher the resolution, the higher the high frequency component. When a flat subject with low resolution is photographed, the fluctuation of the black level becomes noise on the horizontal stripes, and the image is easily noticeable. Therefore, the digital camera 10 according to the sixth embodiment selects a TG pattern having a large number of clamp pixels when the subject resolution is severe in the condition of image quality deterioration.

  FIG. 17 is a flowchart illustrating the operation of the digital camera 10 according to the sixth embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the flowchart shown in FIG. 8, and the detailed description is abbreviate | omitted.

  The CPU 16 acquires subject resolution information from the AE / AF / AWB processing unit 21 (step S16). The resolution information may be the vertical resolution of the image as shown in FIG. 16, the horizontal resolution, or both. It is determined whether or not the acquired resolution is equal to or less than E (step S17).

  If the resolution is E or less, the CPU 16 instructs the analog signal processing unit 15 to select a TG pattern with a large number of clamp pixels (step S1). If it is higher than E, the normal TG pattern with the number of clamp pixels is used.

  Thereafter, when the shutter release button of the operation unit 18 is operated, the main photographing is started based on the selected TG pattern (step S2).

  As described above, by acquiring the resolution information of the subject and selecting the TG pattern according to the resolution, it is possible to reduce the image quality deterioration due to the pixel defect in the OB pixel region 13b.

<Seventh embodiment>
The digital camera 10 according to the seventh embodiment selects a TG pattern according to the white balance gain of the subject.

  18A shows a case where there is no pixel defect in the OB pixel region 13b, and FIG. 18B shows a case where there is a pixel defect in the OB pixel region 13b and the black level fluctuates, and the RGB signal and black at the time of photographing the gray subject. FIG. 4 is a diagram illustrating a level relationship, in which the left side shows a signal before white balance gain and the right side shows a signal after white balance gain.

  The RGB signal of a gray subject obtained with a general imaging device has the largest G and R and B are small. Therefore, in order to match the white balance, it is necessary to raise the small R and B signals to the same level as G. is there. For this reason, the gains of R and B are larger. Further, when the subject light source is a light source biased to either the R or B wavelength such as tungsten, the white balance gain is also a gain biased to either the B or R accordingly. When the black level fluctuates due to a pixel defect in the OB pixel area 13, a signal with a large white balance gain also has a large decrease amount of the signal after the white balance gain, and the portion where the sun sinks as a color is colored. Deterioration in image quality will be more noticeable. Therefore, the digital camera 10 of the seventh embodiment selects a TG pattern with a large number of clamp pixels when the white balance gains R and B are larger than a certain gain.

  FIG. 19 is a flowchart illustrating the operation of the digital camera 10 according to the seventh embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the flowchart shown in FIG. 8, and the detailed description is abbreviate | omitted.

  The CPU 16 acquires the white balance gain information of the subject from the AE / AF / AWB processing unit 21 (step S18). For the acquired white balance gain, it is determined whether or not the gain of R is F or more, or the gain of B is H or more (step S19).

  When the gain of R is F or more or the gain of B is H or more, the CPU 16 instructs the analog signal processing unit 15 to select a TG pattern having a large number of clamp pixels (step S1). When the gain of R is less than F and the gain of B is less than H, the TG pattern having the normal number of clamp pixels is continuously used.

  Thereafter, when the shutter release button of the operation unit 18 is operated, the main photographing is started based on the selected TG pattern (step S2).

  As described above, by acquiring the white balance gain information of the subject and selecting the TG pattern according to the white balance gain, it is possible to reduce the image quality deterioration due to the pixel defect in the OB pixel region 13b.

  In the present embodiment, the white balance gain information corresponding to the subject is acquired from the AE / AF / AWB processing unit 21, but the same determination may be performed even in a shooting mode in which the white balance gain is fixed. Further, when the G gain also fluctuates, the G gain may be similarly determined.

FIG. 1 is a diagram showing an example of an electrical configuration of a digital camera 10 according to the present invention. FIG. 2 is a schematic diagram of the CCD 13. FIG. 3 is a diagram showing a positional relationship between the horizontal line 13e and the TG pattern 13f with respect to the horizontal line. FIG. 4 is a diagram showing the black level after clamping of each horizontal line when there is a line scratch in the vertical transfer path. FIG. 5 is a diagram illustrating a difference in image quality degradation due to a difference in TG patterns. FIG. 6 is a diagram showing a TG pattern. FIG. 7 is a diagram illustrating a difference in black level after clamping due to a difference in TG pattern. FIG. 8 is a flowchart showing the operation of the digital camera 10. FIG. 9 is a diagram showing the ratio between the exposure signal and the clamp level (black level) at each ISO sensitivity of the CCD 13. FIG. 10 is a flowchart illustrating the operation of the digital camera 10 according to the second embodiment. FIG. 11 is a block diagram of a digital camera 10 according to the third embodiment. FIG. 12 is a flowchart illustrating the operation of the digital camera 10 according to the third embodiment. FIG. 13 is a flowchart illustrating the operation of the digital camera 10 according to the fourth embodiment. FIG. 14 is a diagram showing the relationship between subject brightness and exposure signal amount. FIG. 15 is a flowchart illustrating the operation of the digital camera 10 according to the fifth embodiment. FIG. 16 is a diagram illustrating high-frequency components of an image in the vertical direction of the image. FIG. 17 is a flowchart illustrating the operation of the digital camera 10 according to the sixth embodiment. FIG. 18 is a diagram showing the relationship between the RGB signal and the black level when shooting a gray subject. FIG. 19 is a flowchart illustrating the operation of the digital camera 10 according to the seventh embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Digital camera, 13 ... CCD, 13a ... Photosensitive pixel area, 13b ... OB pixel area, 13c ... Horizontal transfer path, 13d ... Amplifier, 13e ... Reading horizontal line, 13f ... TG pattern, 13g ... Line scratch, 13h ... Thermistor , 14 timing generator, 15 analog signal processing unit, 16 CPU, 18 operation unit, 19 image signal processing unit, 21 AE / AF / AWB processing unit, 22 memory

Claims (8)

An image sensor in which light receiving elements are two-dimensionally arranged, and is provided adjacent to a photosensitive pixel region for converting received light of an object into an image signal, and adjacent to the side of the photosensitive pixel region, and is shielded by a light shielding member. An image sensor comprising an optical black region,
For pixels in any horizontal line in the photosensitive pixel area, output signals from pixels in the optical black area, and output signals from pixels having a predetermined number of lines including lines at the same horizontal position as the horizontal lines in the photosensitive pixel area. Obtaining means for obtaining a clamp level of a pixel in a horizontal line of the photosensitive pixel region;
Clamping means for clamping output signals of pixels in a horizontal line of the photosensitive pixel area based on the clamping level acquired by the acquiring means;
Means for generating a captured image based on the signal clamped by the clamp means;
Detection means for detecting a shooting condition and / or a shooting environment in which image quality deterioration of the shot image due to a pixel defect in the optical black region is likely to occur;
Switching means for increasing the predetermined number of lines when the detection means detects a photographing condition and / or photographing environment in which image quality deterioration is likely to occur;
An imaging apparatus comprising: Means for setting the shooting ISO sensitivity,
The imaging apparatus according to claim 1, wherein the detection unit detects an imaging condition in which the image quality deterioration is likely to occur when the set imaging ISO sensitivity is higher than a first predetermined value. Means for measuring the temperature of the image sensor;
3. The imaging apparatus according to claim 1, wherein the detection unit detects the imaging environment in which the image quality deterioration is likely to occur when the measured temperature of the imaging device is higher than a second predetermined value. . Means for selecting one drive frequency from a plurality of drive frequencies;
Means for reading out an output signal of the image sensor in synchronization with the selected drive frequency,
4. The imaging apparatus according to claim 1, wherein the detection unit detects an imaging condition in which the image quality deterioration is likely to occur when the driving frequency is lower than a third predetermined value. 5. Means for calculating subject brightness,
5. The imaging according to claim 1, wherein the detection unit detects an imaging condition in which the image quality deterioration is likely to occur when the calculated subject luminance is lower than a fourth predetermined value. 6. apparatus. Means for calculating the horizontal and / or vertical resolution of the subject;
6. The imaging apparatus according to claim 1, wherein the detection unit detects an imaging condition in which the image quality deterioration is likely to occur when the calculated resolution is lower than a fifth predetermined value. . Means for calculating an R gain and a B gain for adjusting the white balance;
The detection means detects as an imaging condition in which the image quality deterioration is likely to occur when the calculated R gain is higher than a sixth predetermined value or when the calculated B gain is higher than a seventh predetermined value. The imaging apparatus according to claim 1, wherein: An image sensor in which light receiving elements are two-dimensionally arranged, and is provided adjacent to a photosensitive pixel region for converting received light of an object into an image signal, and adjacent to the side of the photosensitive pixel region, and is shielded by a light shielding member. An output signal of a pixel in the optical black area of a pixel in an arbitrary horizontal line of the photosensitive pixel area of the imaging device configured with the optical black area, and a line at the same horizontal position as the horizontal line of the photosensitive pixel area Obtaining a clamp level of pixels of a horizontal line of the photosensitive pixel region from an output signal of pixels of a predetermined number of lines including:
A clamping step of clamping an output signal of a pixel in a horizontal line of the photosensitive pixel region based on the clamping level acquired in the acquisition step;
Generating a captured image based on the signal clamped in the clamping step;
A detection step of detecting a shooting condition and / or a shooting environment in which image quality deterioration of the shot image due to pixel defects in the optical black region is likely to occur;
A switching step of increasing the predetermined number of lines when detecting a shooting condition and / or shooting environment in which the image quality deterioration is likely to occur in the detection step;
An imaging control method comprising:

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