JP5241596B2 - IMAGING DEVICE, IMAGING DEVICE CONTROL METHOD, AND PROGRAM - Google Patents

Description

  The present invention relates to an imaging apparatus having an imaging element, a control method thereof, and a program.

  Imaging devices such as CCD image sensors and CMOS image sensors are used in imaging devices such as digital still cameras and digital video cameras. In recent years, the trend toward downsizing and increasing the number of pixels of an image pickup device has rapidly progressed, and accordingly, the area per unit pixel of the image pickup device has been reduced. Some items are difficult to maintain. As one of such items, there is a characteristic related to leakage of electric charge to adjacent pixels.

The reason why it has become difficult to maintain the characteristics related to the leakage of electric charges to adjacent pixels to the same level as in the past will be described.
FIG. 13 is a plan view showing a configuration of a general CCD image sensor. FIG. 13 shows a part of a CCD image sensor, that is, 16 pixels of 4 vertical pixels × 4 horizontal pixels.

  In FIG. 13, reference numeral 601 denotes a photodiode portion that converts light into electric charges (performs photoelectric conversion). Reference numeral 602 denotes a vertical transfer register unit that transfers charges accumulated by photoelectric conversion in the photodiode unit 601 in the vertical direction. Reference numeral 603 denotes a separation region unit that separates the regions. FIG. 14A shows a horizontal sectional view taken along line AA ′ shown in FIG. 13 and FIG. 14B shows a vertical sectional view taken along line BB ′ shown in FIG. Yes. In FIG. 14, 604 is a light shielding film, and 605 is a vertical transfer electrode.

  Here, in recent image sensors, sensitivity is another item that is difficult to maintain the same level of characteristics as conventional ones. As a method for improving the sensitivity of the image sensor, for example, there is a method of expanding the photoelectric conversion region (photodiode portion) in the depth direction of the semiconductor substrate as indicated by a dotted arrow in FIG. By this method, the sensitivity of light on the long wavelength side, that is, the sensitivity to light on the red side is improved, and as a result, it is possible to improve the sensitivity as a luminance signal. However, when the photoelectric conversion region is expanded in the depth direction of the semiconductor substrate, as indicated by the solid line arrow in FIG. 14, when the charge is saturated, a portion where the pixel separation is partially weak in the deep portion occurs and the charge leaks to the adjacent pixel. It is known that a phenomenon occurs.

  As described above, there is a current situation that it is difficult to maintain the characteristics related to the leakage of charges to the adjacent pixels in the recent image sensor, but the leakage of charges to the adjacent pixels is difficult. When the error occurs, the following two problems occur in the imaging apparatus.

  The first problem as an image pickup apparatus is a color mixing characteristic which is a problem in an image pickup device having a signal output for each color, and when the characteristic relating to charge leakage into adjacent pixels of the image pickup device is inferior, When the accumulated charge becomes close to saturation, charge leaks to adjacent pixels.

  FIG. 15 is a diagram in which color filters are represented on the plan view shown in FIG. 13. As an example, a general Bayer array of R (red), Gr (green), Gb (green), and B (blue) is used. . For example, when leakage of charge from the Gr pixel 901 to the adjacent pixel occurs in the image sensor shown in FIG. 15, the charge leaks from the Gr pixel 901 as shown by the dotted arrow. That is, the charge from the Gr pixel 901 leaks into the upper and lower B pixels of the Gr pixel 901 and the right and left R pixels of the Gr pixel 901. When such charge leakage into adjacent pixels occurs, the linearity (linearity) between the light amount and the output level associated with each R, Gr, Gb, B output signal cannot be maintained.

  16 and 17 are diagrams illustrating an example of the relationship between the light amount (incident light amount) and the output level of the output signal in the CCD image sensor. 16 and 17, the horizontal axis represents the light amount, and the vertical axis represents the output level of the output signal. FIGS. 16 and 17 show output levels of R, Gr, Gb, and B output signals output from the R, Gr, Gb, and B pixels, respectively.

  In general, a photodiode generates a charge proportional to the amount of light. Therefore, if there is no leakage of charge to the adjacent pixels, the relationship between the light amount and the output level of each R, Gr, Gb, B output signal is saturated until the accumulated charge is saturated (as shown in FIG. 16). Until it is reached). In each R, Gr, Gb, and B output signal, the slope of the straight line indicating the relationship between the light amount and the output level is different because the sensitivity varies depending on the wavelength of incident light.

  On the other hand, when charge leakage to an adjacent pixel occurs near any of the R, Gr, Gb, and B output signals, the output level of the output signal with respect to the amount of light changes in the pixel where the charge has leaked, The linearity of the relationship between the amount of light and the output level of the output signal is impaired. For example, FIG. 17 shows a case where charge leaks from the Gr and Gb pixels to the R and B pixels, and the vicinity where the Gr output signal and the Gb output signal are saturated (the broken line portion shown in FIG. 17). ), The linearity of the R output signal and the B output signal is lost, and the inclination changes.

  This phenomenon varies in degree depending on the image sensor. For this reason, the actual image cannot be designed as desired in the color change (how to bend the color) of the high-luminance part and the high-chroma part, and the color change (color Will be different).

  As a countermeasure against the first problem described above, for example, the following method has been proposed. By performing correction processing on the signal of the target pixel using each signal of a plurality of surrounding pixels adjacent to the target pixel of the image sensor and the correction parameter independent of each signal, the correction amount of the surrounding pixel There has been proposed a method of giving directionality to the image (see, for example, Patent Document 1).

  The second problem as an imaging device is a phenomenon in which charges generated by defective pixels of the imaging element leak into adjacent pixels. The amount of electric charge generated by a defective pixel usually doubles every time the temperature rises by 8 ° C. to 10 ° C., and the shutter speed has a characteristic proportional to time. Therefore, if the characteristics related to the leakage of charge to the adjacent pixels of the image sensor are inferior, depending on the temperature and shutter speed at the time of shooting, the charge generated by the defective pixel reaches near the saturation of the pixel, and the charge to the adjacent pixel Leakage may occur.

  Regarding the second problem, the phenomenon itself of the charge leaking into the adjacent pixels is the same as the first problem described above. However, the leakage of charges generated by defective pixels into adjacent pixels occurs only in a single pixel, so if the subject is a dark scene such as a night scene, Electric charge leaks, resulting in a cross-shaped very characteristic and conspicuous scratch. As a countermeasure against such a cross-shaped scratch, when dealing with a general white spot scratch correction method, the address of the white spot scratch is detected by factory adjustment before product shipment and stored in a memory such as a FROM. This is a method of interpolating from adjacent pixels of the target white point scratch address.

Japanese Patent Laid-Open No. 2007-142697

As a countermeasure against the first problem described above, for example, when the method described in Patent Document 1 is used, the following problem occurs.
Regarding the first problem described above, the leakage of charge to adjacent pixels occurs near the point where the accumulated charge of the pixel is saturated, and conversely does not occur when the accumulated charge of the pixel is small. That is, it is very difficult to estimate the amount of charge leakage from the pixel of interest because whether or not charge leakage to the adjacent pixel occurs depends on the amount of charge of the pixel. Therefore, even if the correction amount of the peripheral pixels is given directionality, correction becomes difficult.

  Further, when the above-mentioned second problem is dealt with by a general white spot defect correction method, there is the presence or absence of charge leakage to adjacent pixels and the level difference depending on the temperature and shutter speed. It is difficult to detect cross-shaped white scratches. Even if detection by factory adjustment is possible, scratches that span multiple pixels, such as cross-shaped white scratches, will be interpolated from neighboring pixels that are considerably distant from the target pixel. It becomes difficult to faithfully reproduce the subject image.

  The present invention has been made in view of such circumstances, and an object of the present invention is to suppress the occurrence of charge leakage to adjacent pixels in an image sensor and obtain a good image.

An image pickup apparatus according to the present invention includes an image pickup device having a plurality of pixels, a color mixture rate detection unit that detects a color mixture rate between pixels of the image pickup device, and a color mixture rate detected by the color mixture rate detection unit. And substrate voltage control means for controlling the substrate voltage of the image sensor.
An imaging apparatus according to the present invention includes an imaging device having a plurality of pixels, an address detection unit that detects an address of a defective pixel having a maximum output level of an output signal among defective pixels of the imaging device, and the address detection unit A leakage amount detecting means for detecting a leakage amount of electric charge to an adjacent pixel at an address detected by the control, and controlling a substrate voltage of the imaging device according to the leakage amount detected by the leakage amount detection means. Substrate voltage control means.
An image pickup apparatus control method according to the present invention includes: an output level of an output signal of the image pickup device detected by uniform luminance light source photographing under an exposure condition in which all output signals of respective colors of an image pickup device having a plurality of pixels are not saturated; Based on the output level of the output signal of the image sensor detected by uniform luminance light source photographing under an exposure condition where at least one of the output signals of each color of the image sensor is saturated, between pixels of the image sensor And a substrate voltage control step of controlling a substrate voltage of the image sensor in accordance with the color mixture rate detected in the color mixture rate detection step.
An image pickup apparatus control method according to the present invention includes an address detection step of detecting an address of a defective pixel having a maximum output level of an output signal among defective pixels of an image pickup device having a plurality of pixels, and the address detection step. A leakage amount detection step for detecting the amount of charge leakage to the adjacent pixel of the detected address, and the substrate voltage of the image sensor is controlled according to the leakage amount detected in the leakage amount detection step. And a substrate voltage control step.
The program according to the present invention includes an output level of an output signal of the image sensor detected by uniform luminance light source photographing under an exposure condition in which all output signals of each color of the image sensor having a plurality of pixels are not saturated, and the image sensor Based on the output level of the output signal of the image sensor detected by uniform luminance light source photographing under an exposure condition in which at least one of the output signals of each color is saturated, the color mixing ratio between the pixels of the image sensor is calculated. It is characterized by causing a computer to execute a color mixing rate detection step to be detected and a substrate voltage control step to control the substrate voltage of the image sensor in accordance with the color mixing rate detected in the color mixing rate detection step.
The program according to the present invention includes an address detection step of detecting an address of a defective pixel having a maximum output level of an output signal among defective pixels of an image sensor having a plurality of pixels, and an address detected in the address detection step. A leakage amount detecting step for detecting a leakage amount of electric charge to adjacent pixels of the pixel, and a substrate voltage control for controlling a substrate voltage of the image sensor according to the leakage amount detected in the leakage amount detection step And causing the computer to execute the steps.

  According to the present invention, by controlling the substrate voltage of the image sensor according to the detection result related to the leakage of charge to the adjacent pixel, it is possible to suppress the occurrence of charge leakage to the adjacent pixel, which is favorable. It becomes possible to obtain a simple image.

It is a figure which shows the structural example of the imaging device in embodiment of this invention. It is a figure which shows the structural example of the board | substrate voltage control part in this embodiment. It is a figure which shows an example of the board | substrate voltage setting table of the image pick-up element in this embodiment. It is a flowchart which shows the flow of the saturation voltage adjustment process in this embodiment. It is a figure which shows an example of the relationship between the substrate voltage of an image sensor, saturation voltage, and sensitivity. It is a flowchart which shows the flow of the color mixing rate detection process in this embodiment. It is a figure for demonstrating the calculation method of the color mixing rate in this embodiment. It is a flowchart which shows the flow of the largest white crack address detection process in this embodiment. It is a flowchart which shows the flow of a process in imaging | photography operation | movement in this embodiment. It is a figure which shows an example of the black image photography determination table in this embodiment. It is a figure for demonstrating an example of the calculation method of the leakage amount of the electric charge to the adjacent pixel in this embodiment. It is a figure which shows an example of the board | substrate voltage change table in this embodiment. It is a top view which shows the structure of a CCD image sensor. It is sectional drawing which shows the structure of a CCD image sensor. It is the figure which described the color filter with respect to FIG. It is a figure which shows the example of the relationship between the light quantity in a CCD image sensor, and the output level of an output signal. It is a figure which shows the example of the relationship between the light quantity in a CCD image sensor, and the output level of an output signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The imaging apparatus according to the embodiment of the present invention is suitable for use in a digital still camera, a digital video camera, or the like that can record and reproduce an image taken by an imaging device such as a CCD image sensor or a CMOS image sensor. In the following description, a case where the imaging apparatus according to the embodiment of the present invention is applied to a digital still camera will be described as an example, but the present invention is not limited to this.

  FIG. 1 is a block diagram illustrating a configuration example of a digital still camera to which an imaging apparatus according to an embodiment of the present invention is applied.

  In FIG. 1, reference numeral 101 denotes an imaging optical system that forms a subject image. Reference numeral 102 denotes an image pickup element that has a plurality of pixels and converts subject light imaged by the image pickup optical system 101 into an electric signal. The image sensor 102 is, for example, a CCD image sensor or a CMOS image sensor, and is hereinafter referred to as a CCD image sensor. Note that in this embodiment, the image sensor 102 has each color (R, Gr, Gb, B) by a color filter of a general R (red), Gr (green), Gb (green), B (blue) Bayer array. ) Is output. In the image pickup apparatus according to the present embodiment, the image pickup optical system 101 has a light blocking mechanism that blocks the incidence of subject light on the image pickup element 102, and black image shooting (dark image) is performed with the image pickup element 102 blocked. Photography).

  Reference numeral 103 denotes an image pickup drive unit for driving the image pickup element 102. A substrate voltage control unit 104 controls the substrate voltage of the image sensor 102. The substrate voltage control unit 104 responds to, for example, the color mixture ratio between the pixels of the image sensor 102 and the amount of charge leaking to the adjacent pixels of the defective pixel having the maximum output signal output level among the defective pixels of the image sensor 102. The substrate voltage of the image sensor 102 is changed and controlled.

  An analog signal processing unit 105 processes an output signal output from the image sensor 102. Reference numeral 106 denotes an A / D conversion unit (ADC unit) that converts an analog image signal, which is an output of the analog signal processing unit 105, into a digital image signal. A signal processing unit 107 performs image processing such as white balance adjustment, γ correction, and pixel interpolation on the digital image signal converted by the ADC unit 106.

  Reference numeral 108 denotes a frame memory unit for temporarily storing digital image signals. The frame memory unit 108 is composed of, for example, a DRAM. A signal compression unit 109 compresses the digital image signal stored in the frame memory unit 108 using a technique such as JPEG. The compression operation by the signal compression unit 109 is started with a release operation at the time of shooting, for example. Reference numeral 110 denotes a recording media unit such as a flash memory for storing the image signal compressed by the signal compression unit 109.

  Reference numeral 111 denotes an NTSC / PAL encoder that converts a digital image signal stored in the frame memory unit 108 into an NTSC signal or a PAL signal. Reference numeral 112 denotes an electronic viewfinder as a display unit that displays an image signal converted into an NTSC signal or a PAL signal.

  A system control unit 113 controls each unit of the digital still camera according to the present embodiment. A memory unit 114 stores constants, variables, shooting conditions, programs, and the like for operation of the system control unit 113. For example, in the present embodiment, the system control unit 113 executes a (computer) program stored in the memory unit 114 to include a color mixture rate detection unit (a first level detection unit and a second level detection unit). ) Function is realized. For example, the system control unit 113 executes a (computer) program stored in the memory unit 114, thereby realizing functions such as an address detection unit, a leakage amount detection unit, and a pixel detection unit.

  Reference numeral 115 denotes an operation unit for operating the digital still camera according to the present embodiment. Reference numeral 116 denotes a temperature detection unit that detects the ambient temperature of the image sensor 102. In the present embodiment, the temperature detection unit 116 is a thermistor, for example.

FIG. 2 is a circuit diagram illustrating a configuration example of the substrate voltage control unit 104 that controls the substrate voltage of the imaging device (CCD) 102.
The substrate voltage control unit 104 illustrated in FIG. 2 has four substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4, and can set five substrate voltages as the substrate voltages of the image sensor 102. For example, in this embodiment, a substrate voltage setting table as shown in FIG. 3 is provided. Then, based on the substrate voltage setting table, the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4 are turned on (ON) / off (OFF) from the port of the system control unit 113. Accordingly, the substrate voltage control unit 104 selectively supplies five substrate voltages (4.0 V, 4.5 V, 5.0 V, 5, 5 V, 6.0 V) to the image sensor 102.

  In the example of the substrate voltage setting table shown in FIG. 3, 4.0 V is supplied as the substrate voltage to the image sensor 102 by turning on only the substrate voltage control terminal VSUB1, and imaging is performed by turning on only the substrate voltage control terminal VSUB2. 4.5 V is supplied to the element 102 as the substrate voltage. Similarly, by turning on only the substrate voltage control terminal VSUB3, 5.0 V is supplied as the substrate voltage to the image sensor 102, and by turning on only the substrate voltage control terminal VSUB4, 5.5 V is supplied as the substrate voltage to the image sensor 102. Supplied. Further, by turning off all of the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4, 6.0 V is supplied as the substrate voltage to the image sensor 102.

  The configuration of the substrate voltage control unit 104 described above is an example, and the present invention is not limited to this. For example, the voltage that can be set as the substrate voltage of the image sensor 102 is not limited to the five described above, and is arbitrary.

Next, the operation of the digital still camera in this embodiment will be described.
Here, regarding the deterioration of the color change (how to bend the color) characteristics of the high luminance part and the high chromatic part due to the leakage of electric charge to the adjacent pixels in the image sensor, and the occurrence of cross-shaped white scratches, the image sensor There is variation by individual. Therefore, adjustments according to individual imaging elements, that is, individual imaging devices (here, digital still cameras) are required.

  As a first factory adjustment, a process of adjusting a saturation charge amount, that is, a saturation voltage, related to the image sensor 102 will be described with reference to FIG. The saturation voltage is related to the minimum ISO sensitivity specification of the digital still camera, and there is a saturation voltage necessary for the set minimum ISO sensitivity. Therefore, the setting of the substrate voltage is adjusted according to the flowchart shown in FIG.

FIG. 4 is a flowchart showing the flow of the saturation voltage adjustment process in the present embodiment.
When the saturation voltage adjustment process as the first factory adjustment is started (S201), the digital still camera according to the present embodiment first performs uniform luminance light source photographing (S202). In step S202, the digital still camera performs uniform luminance light source photographing under an exposure condition in which at least one signal output is saturated among signal outputs of each color of the image sensor 102. In the present embodiment, as an example, the photographing condition at the time of photographing with the uniform luminance light source in step S202 is an exposure condition in which the Gr signal and Gb signal of the image sensor 102 are saturated (hereinafter referred to as “exposure condition A”).

  Next, the system control unit 113 and the substrate voltage control unit 104 change the substrate voltage of the image sensor 102 (S203). Here, when the substrate voltage of the image sensor 102 is changed, the saturation voltage and sensitivity change in principle. FIG. 5 is a graph showing an example of the relationship between the substrate voltage of the image sensor and the saturation voltage / sensitivity. As shown in FIG. 5, when the substrate voltage of the image sensor is lowered, the saturation voltage and sensitivity characteristics are improved, and when the substrate voltage of the image sensor is raised, the saturation voltage and sensitivity characteristics are deteriorated.

  In step S203, the system control unit 113 switches on / off the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4 in the substrate voltage control unit 104. The substrate voltage control unit 104 supplies a predetermined voltage to the image sensor 102 as a substrate voltage according to the switching. In the present embodiment, in the change of the substrate voltage in step S203 immediately after starting the saturation voltage adjustment process (first time), the system control unit 113 turns off all the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4. Thereby, the substrate voltage of the image sensor 102 supplied from the substrate voltage control unit 104 is switched to the substrate voltage (6.0 V in this embodiment) at which the saturation voltage is lowest.

  Next, the system control unit 113 determines that the saturation voltage of the image sensor 102 at the changed substrate voltage reaches the saturation voltage necessary for the minimum ISO sensitivity set in the specification or the like based on the output of the image sensor 102. It is determined whether or not there is (S204). If the result of determination in step S204 is that the saturation voltage of the image sensor 102 has not reached the saturation voltage required for the minimum ISO sensitivity, the system control unit 113 returns to step S203 again and sets the substrate voltage of the image sensor 102. Make a change.

  Then, the system control unit 113 repeats the processes of steps S203 and S204 described above until it determines that the saturation voltage of the image sensor 102 has reached the saturation voltage necessary for the minimum ISO sensitivity. Specifically, the system control unit 113 appropriately switches on / off the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4 every time the process returns to step S203, and changes the substrate voltage of the image sensor 102 from 5.5V → 5.0V → Change in the order of 4.5V → 4.0V. In step S204, the system control unit 113 determines whether or not the saturation voltage of the image sensor 102 at the changed substrate voltage has reached the saturation voltage necessary for the minimum ISO sensitivity. Thus, the substrate voltage Vsub-sat reaching the saturation voltage necessary for the minimum ISO sensitivity is calculated.

If the result of determination in step S204 is that the saturation voltage of the image sensor 102 has reached the saturation voltage required for the minimum ISO sensitivity, processing proceeds to step S205. Next, the system control unit 113 records the substrate voltage Vsub-sat at that time as an adjustment value in the memory unit 114 (S205), and ends the process (S206).
As described above, the saturation voltage adjustment as the first factory adjustment is completed.

  Next, as a second factory adjustment, FIG. 6 shows a step of detecting a color mixture ratio obtained by quantifying the high-luminance portion linearity collapse (the amount of change in color of the high-luminance portion and the high-color portion) related to the image sensor 102. The description will be given with reference.

First, an outline of a method for calculating the color mixture ratio will be described with reference to FIG.
In FIG. 7, an exposure condition A is an exposure condition in which the Gr output signal and the Gb output signal of the image sensor are saturated and the R output signal and the B output signal are not saturated in the uniform luminance light source photographing (for example, in FIG. 4 described above). (Shooting conditions in step S202 shown). The exposure condition B is an exposure condition in which all of the R output signal, the Gr output signal, the Gb output signal, and the B output signal of the image sensor are not saturated in the uniform luminance light source photographing. α is the output level of the B output signal of the image pickup device under the exposure condition B, β is the output level of the B output signal of the image pickup device under the exposure condition A, and γ is when there is no problem with the linearity characteristic (there is no charge leakage) The output level of the B output signal of the image sensor.

  As shown in FIG. 7, when the high luminance portion linearity characteristic deteriorates in the image sensor, the actual output level indicated by the solid line has a larger slope than the ideal curve indicated by the dotted line. In the present embodiment, the amount of change in inclination is defined as a color mixing ratio Rc, and Rc = β / γ.

FIG. 6 is a flowchart showing the flow of the color mixture rate detection process in the present embodiment.
When the color mixing rate detection process as the second factory adjustment is started (S301), the digital still camera according to the present embodiment first performs uniform luminance light source photographing (S302). In step S <b> 302, the digital still camera performs uniform luminance light source photographing under an exposure condition that does not saturate all the signal outputs of each color of the image sensor 102. That is, the shooting condition at the time of shooting with the uniform luminance light source in step S302 is an exposure condition in which the R signal, the Gr signal, the Gb signal, and the B signal of the image sensor 102 are not saturated (hereinafter referred to as “exposure condition B”).

  Next, the system control unit 113 and the substrate voltage control unit 104 change the substrate voltage of the image sensor 102 (S303). The system control unit 113 switches on / off the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4 in the substrate voltage control unit 104, and the substrate voltage control unit 104 uses a predetermined voltage as the substrate voltage in accordance with the switching. This is supplied to the image sensor 102.

  In the present embodiment, in the change of the substrate voltage in step S303 immediately after the start of the color mixture rate detection process (first time), the system control unit 113 sets the substrate voltage control terminal among the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4. Turn on only VSUB1. As a result, the substrate voltage of the image sensor 102 supplied from the substrate voltage control unit 104 is switched to a substrate voltage (4.0 V in this embodiment) in which the high-luminance portion linearity is likely to be lost.

  Next, the system control unit 113 calculates the color mixing ratio Rc of the image sensor 102 at the changed substrate voltage (S304). The color mixing ratio Rc is calculated by, for example, the output level (β) of the B signal of the image sensor 102 under the exposure condition A photographed in step S202 shown in FIG. 4 and the image sensor 102 under the exposure condition B photographed in step S302. Based on the output level (α) of the B signal. Specifically, the system control unit 113 calculates the ideal output level (γ) under the exposure condition A from the difference between the inclination calculated based on the output level (β) under the exposure condition A and the exposure condition AB. To do. Further, the system control unit 113 calculates the color mixture ratio Rc = β / γ from the output level (α) under the exposure condition B and the ideal output level (γ) under the calculated exposure condition A.

  Next, the system control unit 113 compares the color mixture rate Rc calculated in step S304 with a preset color mixture rate allowable value Rc-st, and the calculated color mixture rate Rc is equal to or less than the allowable value Rc-st. Whether or not (S305). If the result of determination in step S305 is Rc> Rc-st (when the calculated color mixture ratio Rc exceeds the allowable value Rc-st), the system control unit 113 determines that the substrate voltage needs to be changed. Then, the process returns to step S303 again to change the substrate voltage of the image sensor 102.

  Then, the system control unit 113 repeats the processes in steps S303 to S305 described above until it is determined that the color mixture ratio Rc calculated in step S304 is equal to or less than the allowable value Rc-st. Specifically, every time the process returns to step S303, the system control unit 113 switches on / off of the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4 as appropriate, and changes the substrate voltage of the image sensor 102 from 4.5V → 5.0V → Change in order of 5.5V → 6.0V. In step S305, the system control unit 113 determines whether the color mixing ratio Rc of the image sensor 102 at the changed substrate voltage is equal to or less than the allowable value Rc-st. As a result, the substrate voltage Vsub-col at which the color mixing ratio Rc of the image sensor 102 is equal to or less than the allowable value Rc-st is obtained.

As a result of the determination in step S305, if Rc ≦ Rc-st (when the calculated color mixture ratio Rc is equal to or smaller than the allowable value Rc-st), the process proceeds to step S306. Next, the system control unit 113 records the substrate voltage Vsub-col at that time in the memory unit 114 as an adjustment value (S306), and ends the process (S307).
As described above, the color mixing rate detection as the second factory adjustment is completed.

  Next, as a third factory adjustment, a step of detecting the maximum white defect address in the chip of the image sensor 102 will be described with reference to FIG. The maximum white scratch address is an address of a defective pixel having the maximum output level of the output signal among the defective pixels of the image sensor 102 (the worst pixel having a cross-shaped white scratch).

FIG. 8 is a flowchart showing the flow of the maximum white scratch address detection process in the present embodiment.
When the detection process of the maximum white scratch address as the third factory adjustment is started (S401), first, the system control unit 113 and the substrate voltage control unit 104 change the substrate voltage of the image sensor 102 (S402). The system control unit 113 switches on / off the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4 in the substrate voltage control unit 104, and the substrate voltage control unit 104 uses the predetermined voltage corresponding to the substrate voltage as an imaging element. 102.

  In the present embodiment, the system control unit 113 turns off all the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4. As a result, the substrate voltage of the image sensor 102 supplied from the substrate voltage control unit 104 is switched to a substrate voltage (6.0 V in this embodiment) that has a low frequency of charge leakage to adjacent pixels.

  Next, the digital still camera performs black image shooting under predetermined shooting conditions (S403). The shooting conditions relating to black image shooting in step S403 are desirably sensitivity setting, shutter speed, and temperature, which facilitates detection of white spot scratches.

Next, the system control unit 113 uses the output signal of the image sensor 102 obtained by photographing in step S403 to search all pixels for the white spot scratch with the highest level in the image sensor chip, and the largest white scratch. The address of a pixel (defective pixel) in which is present is detected (S404). Subsequently, the system control unit 113 records the address of the target white scratch detected in step S404 as an adjustment value in the memory unit 114 (S405), and ends the process.
As described above, the maximum white scratch address detection as the third factory adjustment is completed.

  By the first factory adjustment, the second factory adjustment, and the third factory adjustment described above, the adjustment according to each digital still camera is completed.

Next, the operation at the time of actual photographing in the present embodiment will be described with reference to FIG.
FIG. 9 is a flowchart showing a flow of processing in an actual photographing operation in the present embodiment. As shown in FIG. 9, by controlling the substrate voltage of the image sensor 102 to an optimum voltage, the color change (color color) of the high luminance part and the high color part due to the leakage of electric charge to adjacent pixels in the image sensor. It is possible to reduce the deterioration of characteristics and the occurrence of cross-shaped white scratches.

  When the user (photographer) determines a subject and enters a photographing operation (S501), the system control unit 113 sets the shutter speed in the main exposure and the ambient temperature of the image sensor 102 with the user pressing the shutter button halfway. It is detected and recorded in the memory unit 114 (S502).

  Next, the system control unit 113 and the substrate voltage control unit 104 turn on / off the substrate voltage control terminals VSUB1, VSUB2, VSUB3, and VSUB4, and obtain the substrate voltage of the image sensor 102 by the second factory adjustment. Vsub-col is set (S503). However, since the saturation voltage at the substrate voltage Vsub-col needs to be equal to or higher than the saturation voltage necessary for the minimum ISO sensitivity of the digital still camera obtained by the first factory adjustment, Vsub-col <Vsub-sat is established. There must be. Therefore, if Vsub-col ≧ Vsub-sat, in step S503, the substrate voltage of the image sensor 102 is set to the substrate voltage Vsub-sat acquired by the first factory adjustment.

  Next, the system control unit 113 determines whether or not black image shooting is necessary based on the shutter speed detected in step S502 and the ambient temperature of the image sensor 102 (S504). Here, in black image shooting, it is confirmed whether or not charge leakage to the adjacent pixel of the maximum white scratch address detected in the third factory adjustment occurs, that is, whether or not a cross-shaped white scratch has occurred. It is an operation for. Therefore, it is not necessary to shoot a black image when the shooting conditions (shutter speed, ambient temperature of the image sensor 102) do not clearly cause a cross-shaped scratch.

  FIG. 10 is a black image shooting determination table for determining whether black image shooting is necessary or not from two parameters of the shutter speed and the ambient temperature of the image sensor 102. The black image photographing determination table is created, for example, by collecting data in advance with a cross-shaped white scratch limit product. The system control unit 113 determines whether it is necessary to perform black image shooting (◯) or not (×) according to the black image shooting determination table. A black image shooting determination table may be provided for each ISO sensitivity.

  If it is determined in step S504 that it is necessary to perform black image shooting, black image shooting is performed under the same conditions as the main exposure conditions (S505). Then, the system control unit 113 calculates how much charge leaks to the adjacent pixel of the maximum white defect address acquired in the third factory adjustment (S506).

FIG. 11 is a diagram for explaining an example of a method of calculating how much charge leaks to the adjacent pixel of the maximum white defect address, that is, the amount of charge leakage to the adjacent pixel.
As shown in FIG. 11, when the maximum white scratch address in the chip of the image sensor 102 is x ₂ y ₂ , the adjacent pixels x ₂ y ₁ , x ₁ y ₂ , x ₃ y ₂ , and x ₂ The average output level of a total of 4 pixels of ₂ y ₃ pixels is calculated as the charge leakage amount of the adjacent pixels.

Here, the output of the pixel x ₂ y ₂ is Vx ₂ y _2, and the outputs of the pixels x ₂ y ₁ , x ₁ y ₂ , x ₃ y ₂ , x ₂ y ₃ are Vx ₂ y ₁ and Vx ₁ , respectively. Let y ₂ , Vx ₃ y ₂ , and Vx ₂ y ₃ . At this time, the leak amount Dave of charge to the adjacent pixel is calculated as Dave = ((Vx ₂ y ₁ + Vx ₁ y ₂ + Vx ₃ y ₂ + Vx ₂ y ₃ ) / 4) / Vx ₂ y ₂ . In the example shown in FIG. 17, the leak amount Dave of charge to the adjacent pixel is Dave = ((20 mV + 20 mV + 18 mV + 22 mV) / 4) / 100 mV = 20%.

  Next, the system control unit 113 determines whether or not the charge leakage amount Dave to the adjacent pixel calculated in step S506 is less than the charge leakage amount Dst to the adjacent pixel that is allowable as a preset image. Determination is made (S507).

  When Dave <Dst (when the calculated charge leakage amount Dave is less than the permissible value Dst), the cross-shaped white scratch is at an acceptable level even in the main exposure. Therefore, if the result of determination in step S507 is Dave <Dst, the system control unit 113 does not change the substrate voltage of the image sensor 102, and the digital still camera starts shooting for main exposure (S509). ). Then, an image obtained by photographing in the main exposure is recorded in the recording medium unit 110 (S510), and the photographing operation is finished (S511).

  On the other hand, when Dave ≧ Dst (when the calculated charge leakage amount Dave is equal to or greater than the allowable value Dst), the system control unit 113 refers to the substrate voltage change table and determines the substrate voltage of the image sensor 102. The voltage is changed to reduce the leakage of electric charge to the adjacent pixels. FIG. 12 is a diagram illustrating an example of the substrate voltage change table. The substrate voltage change table is created, for example, by previously collecting data on the relationship between the amount Dave of charge leakage into adjacent pixels and the substrate voltage. The substrate voltage change table may be provided for each ISO sensitivity. Then, the digital still camera starts photographing for the main exposure (S509), records an image obtained by photographing for the main exposure in the recording media unit 110 (S510), and ends the photographing operation (S511).

  According to the present embodiment, imaging is performed according to detection results relating to charge leakage to adjacent pixels in the image sensor 102 such as, for example, the color mixture ratio of the image sensor 102 and the amount of charge leakage to adjacent pixels due to defective pixels. The substrate voltage of the element 102 is controlled. As a result, the occurrence of charge leakage to adjacent pixels in the image sensor 102 can be suppressed, and a good image can be obtained.

(Other embodiments of the present invention)
For realizing the functions of the above-described embodiment with respect to an apparatus or a computer (CPU or MPU) in the system connected to the various devices so as to operate various devices to realize the functions of the above-described embodiments. Supply software programs. And what was implemented by operating the said various devices according to the program stored in the computer of the system or the apparatus is also contained under the category of this invention.
In this case, the software program itself realizes the functions of the above-described embodiments, and the program itself constitutes the present invention. Further, means for supplying the program to the computer, for example, a recording medium storing the program constitutes the present invention. As a recording medium for storing such a program, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.
In addition, such a program is also included in the embodiment of the present invention when the function of the above-described embodiment is realized in cooperation with an operating system or other application software running on a computer. Needless to say.
Further, after the supplied program is stored in a memory provided in a function expansion board or a function expansion unit related to the computer, a CPU or the like provided in the function expansion board or the like based on an instruction of the program may be a part of actual processing or Do everything. Needless to say, the present invention includes the case where the functions of the above-described embodiments are realized by the processing.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  DESCRIPTION OF SYMBOLS 101 Imaging optical system, 102 Imaging device, 103 Imaging drive part, 104 Substrate voltage control part, 113 System control part, 114 Memory part, 115 Operation part, 116 Temperature detection part

Claims (14)

An imaging device having a plurality of pixels;
A color mixing rate detecting means for detecting a color mixing rate between pixels of the image sensor;
An image pickup apparatus comprising: a substrate voltage control unit that controls a substrate voltage of the image pickup device in accordance with the color mixture rate detected by the color mixture rate detection unit. The color mixing rate detecting means includes
First level detection means for performing uniform luminance light source photographing under an exposure condition that does not saturate all the output signals of each color of the image sensor, and detecting the output level of the output signal of the image sensor;
Second level detection means for performing uniform luminance light source photographing under an exposure condition in which at least one of the output signals of each color of the image sensor is saturated and detecting the output level of the output signal of the image sensor; Have
The image pickup apparatus according to claim 1, wherein the color mixing ratio is detected based on output levels detected by the first level detection unit and the second level detection unit.   The color mixture ratio detected by the color mixture ratio detection means is compared with a preset allowable value of the color mixture ratio, and if the detected color mixture ratio exceeds the allowable value, the substrate voltage of the image sensor is changed. The imaging apparatus according to claim 1 or 2, wherein An imaging device having a plurality of pixels;
Address detecting means for detecting an address of a defective pixel having a maximum output level of an output signal among defective pixels of the image sensor;
A leakage amount detection means for detecting a leakage amount of electric charge to an adjacent pixel of an address detected by the address detection means;
An image pickup apparatus comprising: a substrate voltage control unit that controls a substrate voltage of the image pickup device according to a leak amount detected by the leak amount detection unit. A light shielding means for blocking the incidence of subject light on the image sensor;
The imaging apparatus according to claim 4, wherein the leakage amount detection unit detects the leakage amount based on an output signal of the imaging element obtained by imaging in a state where the leakage is shielded by the light shielding unit. .   The image pickup apparatus according to claim 5, further comprising: a pixel detection unit that detects a defective pixel having an output level of an output signal that is the highest among the defective pixels among all the pixels of the image pickup element.   The pixel detection unit detects a defective pixel having a maximum output level of the output signal based on an output signal of the imaging element obtained by photographing in a state where the light is shielded by the light shielding unit. 6. The imaging device according to 6.   8. The substrate voltage of the image pickup device is controlled according to a leak amount detected by the leak amount detection unit and a shooting condition at the time of shooting. Imaging device.   The imaging apparatus according to claim 8, wherein the photographing condition includes a temperature or a shutter speed related to the imaging element.   The imaging apparatus according to claim 1, wherein the substrate voltage of the imaging element is changed according to an ISO sensitivity of the imaging apparatus. Of the output level of the output signal of the image sensor detected by uniform luminance light source photographing under an exposure condition in which all of the output signals of each color of the image sensor having a plurality of pixels are not saturated, and the output signal of each color of the image sensor A color mixing rate detecting step of detecting a color mixing rate between pixels of the image sensor based on an output level of the output signal of the image sensor detected by uniform luminance light source photographing under an exposure condition in which at least one output signal is saturated; ,
And a substrate voltage control step of controlling a substrate voltage of the image sensor in accordance with the color mixture rate detected in the color mixture rate detection step. An address detection step of detecting an address of a defective pixel having a maximum output level of an output signal among defective pixels of an imaging device having a plurality of pixels;
A leakage amount detection step of detecting a leakage amount of charge to an adjacent pixel of the address detected in the address detection step;
And a substrate voltage control step of controlling a substrate voltage of the image pickup device in accordance with the leakage amount detected in the leakage amount detection step. Of the output level of the output signal of the image sensor detected by uniform luminance light source photographing under an exposure condition in which all of the output signals of each color of the image sensor having a plurality of pixels are not saturated, and the output signal of each color of the image sensor A color mixing rate detection step of detecting a color mixing rate between pixels of the image sensor based on an output level of the output signal of the image sensor detected by uniform luminance light source photographing under an exposure condition in which at least one output signal is saturated; ,
A program for causing a computer to execute a substrate voltage control step of controlling a substrate voltage of the image pickup device in accordance with the color mixture rate detected in the color mixture rate detection step. An address detecting step for detecting an address of a defective pixel having a maximum output level of an output signal among defective pixels of an imaging device having a plurality of pixels;
A leakage amount detection step of detecting a leakage amount of charge to an adjacent pixel of the address detected in the address detection step;
A program for causing a computer to execute a substrate voltage control step of controlling a substrate voltage of the image sensor in accordance with a leakage amount detected in the leakage amount detection step.

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