JP2005341244A - Imaging device, defective pixel detecting method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device which can raise precision of defective pixel detection, based on an imaging picture signal by solid imaging elements, without increasing the memory capacity. <P>SOLUTION: A defective detector 131 detects a defective pixel candidate based on the imaging picture signal. A data write-in 151 increments the data value of an address on a frame memory 20 for defective discrimination, corresponding to a position of the defective pixel candidate, whenever the defective pixel candidate is detected by the defective detector 131. A defective discriminator 152 extracts the addresses of a predetermined number from a higher order whose data value is large at a point when data value of at least one address on the frame memory 20 for defective detection reaches a predetermined standard value, determines that the pixel corresponding to the address is a defective pixel, and registers it in a defective position information 19a. As a result of this it is possible to carry out defective pixel detection, based on the imaging picture signal of a plurality of frames using one of the frame memory 20 of the defective discrimination. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image pickup apparatus that picks up an image using a solid-state image pickup apparatus, a defective pixel detection method and a program in the image pickup apparatus, and in particular, a frame memory that stores data at an address corresponding to each pixel of one frame of a picked-up image. In addition, the present invention relates to an imaging apparatus, a defective pixel detection method, and a program capable of detecting a defective pixel based on a captured image signal.

  In general, in a solid-state imaging device that is mounted on a digital still camera, a digital video camera, or the like and images a subject, a defect may occur in some of a large number of pixels. Such defective pixels are generated due to, for example, generation of excessive charges due to local crystal defects of the semiconductor constituting the solid-state imaging device. Since such a defective pixel outputs an abnormal level signal, the defective pixel causes deterioration in image quality. For this reason, in a conventional image sensor using a solid-state image sensor, the position of a defective pixel is detected and the output signal is corrected.

  There are various methods for detecting defective pixels. For example, a defective pixel having an abnormally high output level (referred to as a white defect) can be detected by capturing an image with the shutter completely closed. In addition, defective pixels with abnormally low output levels (called black defects) can be detected by irradiating a light receiving surface with a reference light source or the like and imaging.

  There is also a method of detecting the position of a defective pixel based on an image signal at the time of normal imaging without using such a light shielding means or a reference light source. For example, a method of estimating a defective pixel position based on a signal level difference between a predetermined pixel and surrounding pixels is generally used, and further, defect detection by such a method is performed over a plurality of frames, Some detection results for a plurality of frames are stored in a memory, and finally it is determined whether or not the pixel is a defective pixel based on the stored information. 1). Here, in order to store detection results for a plurality of frames, it is desirable to use a so-called frame memory in which data is arranged at an address corresponding to each pixel for one frame, thereby improving processing efficiency. can do.

As a conventional technique using a method of detecting a bright spot (white defect) by shielding a light receiving surface of a solid-state imaging device, one frame is used according to a comparison result between a captured image signal and a reference signal at the time of shielding. By incrementing or decrementing the data at the corresponding address on the memory and repeating this detection operation for a plurality of frames, and determining the pixel corresponding to the address with the large data on the frame memory as a bright spot, the memory capacity is reduced. There has been a bright spot detection apparatus in which the influence of random noise is reduced and detection accuracy is increased without increasing the number (for example, see Patent Document 2).
JP-A-6-284346 (paragraph numbers [0032] to [0038], FIG. 2) JP-A-4-115785 (pages 555-557, FIG. 1)

  As described above, the method of detecting a defective pixel based on the captured image signal does not require the use of a light shielding unit or a reference light source, and can be realized with a relatively simple configuration. In addition, when such a method is used, it is better to detect defects for a larger number of frames and to determine defective pixels based on the detection results as disclosed in Patent Document 1 above. The detection accuracy can be increased.

  However, when performing defect detection for a large number of frames, a frame memory for storing detection results corresponding to the number of frames is necessary, which causes a problem that the circuit scale increases and the manufacturing cost increases. In particular, in recent years, the number of pixels of a solid-state imaging device has been increased, and it is necessary to provide a frame memory having a very large capacity in order to satisfy a certain degree of detection accuracy.

  The present invention has been made in view of such problems, and provides an imaging apparatus capable of increasing the accuracy of defective pixel detection based on a captured image signal from a solid-state imaging device without increasing the memory capacity. The purpose is to do.

  Another object of the present invention is to provide a defective pixel detection method based on a picked-up image signal from a solid-state image pickup device capable of increasing detection accuracy without increasing the memory capacity.

  Furthermore, another object of the present invention is to provide a defective pixel detection program based on a picked-up image signal from a solid-state image pickup device capable of increasing detection accuracy without increasing the memory capacity.

  In the present invention, in order to solve the above-described problem, in an imaging apparatus that captures an image using a solid-state imaging apparatus, a frame memory that stores data at an address corresponding to each pixel of one frame of the captured image, and a captured image signal Defective pixel candidate detecting means for detecting a defective pixel candidate based on the data, and each time the defective pixel candidate is detected by the defective pixel candidate detecting means, the address data on the frame memory corresponding to the position of the defective pixel candidate Data writing means for incrementing the value, and when the data value of at least one address on the frame memory reaches a predetermined reference value, a predetermined number of addresses are extracted from the top in descending order of the data value at that time, Provided is an imaging device having defective pixel determination means for determining a pixel corresponding to the address as a defective pixel It is.

  In such an imaging apparatus, when defective pixel candidates are detected by a defective pixel candidate detection unit for a plurality of frames, the number of times detected as a defective pixel candidate is stored in one frame memory as the data value of the corresponding address of the pixel. To be recorded. Then, when the data value of at least one address on the frame memory reaches a predetermined reference value, only a pixel having a large data value on the frame memory is finally determined as a defective pixel by the defective pixel determination means. .

  Further, according to the present invention, in a defective pixel detection method for detecting a defective pixel in a solid-state imaging device using a frame memory that stores data at an address corresponding to each pixel of one frame of the captured image, Each time a defective pixel candidate is detected, the data writing means increments the data value of the address on the frame memory corresponding to the detected position of the defective pixel candidate; and the defective pixel determination means, When the data value of at least one address on the frame memory reaches a predetermined reference value, a predetermined number of addresses are extracted in descending order of the data value at that time, and the pixel corresponding to the address is defined as a defective pixel. And determining a defective pixel.

  In such a defective pixel detection method, when defective pixel candidates are detected for a plurality of frames by the defective pixel candidate detection means, the number of times detected as defective pixel candidates is one frame as the data value of the corresponding address of the pixel. Recorded in memory. Then, when the data value of at least one address on the frame memory reaches a predetermined reference value, only a pixel having a large data value on the frame memory is finally determined as a defective pixel by the defective pixel determination means. .

  According to the present invention, the number of times detected as a defective pixel candidate is recorded in the frame memory for each pixel, so that the frame memory is 1 while the defective pixel candidate is detected based on the captured image signals of a plurality of frames. Only one is needed. Further, when the number of defective pixels for any pixel reaches a predetermined value, the final defective pixel is determined, and at this time, the predetermined number of pixels is determined as the defective pixel in descending order of the number of times. Therefore, a pixel that is likely to be a defective pixel under the same detection condition is preferentially determined as a defective pixel, so that a defective pixel candidate that can be realized with a relatively simple configuration without using a light shielding unit or a reference light source is used. While performing detection, the detection accuracy can be improved. Therefore, it is possible to detect defective pixels with high accuracy at low cost without increasing the memory capacity.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, taking the case where the present invention is applied to a digital still camera as an example.
<< First Embodiment >>
FIG. 1 is a block diagram showing the overall configuration of the digital still camera according to the first embodiment of the present invention.

  The digital still camera shown in FIG. 1 includes an optical block 11, an analog front end (AFE) processing circuit 12, a camera signal processing circuit 13, an encoder / decoder 14, a system control unit 15, an input unit 16, and a graphic I / F (interface). 17, a display 17 a, and an R / W (reader / writer) 18. Further, an EEPROM (Electronically Erasable and Programmable ROM) 19 and a defect determination frame memory 20 are connected to the system control unit 15. Further, the memory card 18a is detachably connected to the R / W 18.

  The optical block 11 includes an optical low-pass filter (OP−) including a lens mechanism unit 111 including a plurality of lenses and a moving mechanism thereof, an exposure mechanism unit 112 including an iris and a shutter and driving mechanisms thereof, an infrared cut filter, and the like. LPF) 113 and CCD (Charge Coupled Device) 114 as one of the solid-state imaging devices. Further, a lens driver 115, an exposure control driver 116, and a timing generator (TG) 117 are provided for driving the lens mechanism unit 111, the exposure mechanism unit 112, and the CCD 114, respectively.

  In the optical block 11, the reflected light from the subject that has passed through the optical system including the lens mechanism 111, the exposure mechanism 112, and the OP-LPF 113 is received by the CCD 114 and subjected to photoelectric conversion. In addition to the CCD, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor may be used as the solid-state imaging device.

  The lens driver 115 and the exposure control driver 116 respectively control the operations of the lens mechanism unit 111 and the exposure mechanism unit 112 under the control of the system control unit 15. The TG 117 supplies a timing signal to the CCD 114 under the control of the system control unit 15 and controls its driving timing. This timing signal is also supplied to the AFE processing circuit 12.

  The AFE processing circuit 12 samples and holds the analog image signal output from the CCD 114 so as to maintain a good S / N (Signal / Noise) ratio by CDS (Correlated Double Sampling) processing, and further performs AGC (Auto The gain is controlled by gain control), A / D conversion is performed, and a digital image signal is output. The AFE processing circuit 12 operates according to the timing signal from the TG 117, and the gain of the AGC processing is given from the system control unit 15.

  Under the control of the system control unit 15, the camera signal processing circuit 13 performs defective pixel correction processing, white balance adjustment processing, color correction processing, and AF (Auto Focus) processing on the image signal from the AFE processing circuit 12. And camera signal processing such as AE (Auto Exposure) processing. Further, for example, when the power is turned on or at regular intervals, a defective pixel detection process is performed based on the image signal from the AFE processing circuit 12 as described later. In the present embodiment, the defective pixel detected by the camera signal processing circuit 13 is handled as a defective pixel candidate, and the final determination as to whether or not it is a defect is performed by the processing of the system control unit 15, and the pixel. The position is recorded in the EEPROM 19, for example.

  The encoder / decoder 14 performs compression coding processing on the image signal from the camera signal processing circuit 13 in a predetermined still image data format such as JPEG (Joint Photographic Coding Experts Group) method. Further, the encoded data of the still image supplied from the system control unit 15 is decompressed and decoded.

  The system control unit 15 is a microcontroller composed of, for example, a CPU, a ROM, a RAM, and the like, and executes a program stored in the ROM, the EEPROM 19 or the like in accordance with a control signal from the input unit 16, thereby digitally Centrally control each part of the still camera.

  In the present embodiment, in particular, the system control unit 15 performs final defective pixel determination processing based on defective pixel detection by the camera signal processing circuit 13, and for this processing, the system control unit 15 includes A defect determination frame memory 20 configured so that data is sequentially arranged at addresses corresponding to the pixels of one frame of the captured image is connected.

  Each time a defective pixel is detected by the camera signal processing circuit 13, the system control unit 15 increments the data value of the address of the defect determination frame memory 20 corresponding to the pixel, and records in the defect determination frame memory 20. Based on the data, the position of the defective pixel is finally determined, and the position information is recorded in the EEPROM 19. Then, when the defective pixel is corrected by the camera signal processing circuit 13 at the time of capturing an image, the position information of the defective pixel is read from the EEPROM 19 and output to the camera signal processing circuit 13.

  The input unit 16 includes various operation keys such as a shutter release button, a lever, a dial, and the like, for example, and outputs a control signal corresponding to an input operation by the user to the system control unit 15.

  The graphic I / F 17 generates an image signal to be displayed on the display 17a from the image signal supplied from the system control unit 15, supplies the signal to the display 17a, and displays an image. The display 17a is composed of, for example, an LCD (Liquid Crystal Display), and displays a camera-through image being captured, a reproduced image based on data recorded on the memory card 18a, and the like.

  A memory card 18a composed of a portable flash memory is detachably connected to the R / W 18 as a recording medium for recording image data generated by imaging. The R / W 18 writes the data supplied from the system control unit 15 to the memory card 18a, and outputs the data read from the memory card 18a to the system control unit 15. As the recording medium, for example, a writable optical disk or HDD (hard disk drive) may be used.

Here, a basic operation at the time of imaging in the above digital still camera will be described. First, the operation at the time of capturing a still image will be described.
Prior to capturing a still image, signals received by the CCD 114 and subjected to photoelectric conversion are sequentially supplied to the AFE processing circuit 12. The AFE processing circuit 12 performs CDS processing and AGC processing on the input signal, and further converts it into a digital signal. The camera signal processing circuit 13 performs image quality correction processing on the digital image signal supplied from the AFE processing circuit 12 and supplies it as a camera-through image signal to the graphic I / F 17 via the system control unit 15. As a result, the camera-through image is displayed on the display 17a, and the user can adjust the angle of view while viewing the display 17a.

  In this state, when the shutter release button of the input unit 16 is pressed, the system control unit 15 outputs a control signal to the exposure control driver 116 and the TG 117 to operate the shutter. As a result, an image signal for one frame is output from the CCD 114. At this time, the system control unit 15 outputs control signals to the lens driver 115, the exposure control driver 116, and the TG 117 in accordance with the results of the AF processing and AE processing in the camera signal processing circuit 13, and thereby exposure is performed. It is controlled so that the time and the exposure amount are appropriate.

  The camera signal processing circuit 13 performs image quality correction processing on the image signal for one frame supplied from the CCD 114 via the AFE processing circuit 12, and supplies the processed image signal to the encoder / decoder 14. The encoder / decoder 14 compresses and encodes the input image signal, and supplies the generated encoded data to the R / W 18 via the system control unit 15. Thereby, the data file of the captured still image is stored in the memory card 18a.

  On the other hand, when playing back a still image file stored in the memory card 18a, the system control unit 15 sends the selected still image file from the memory card 18a to the R / W 18 in response to an operation input from the input unit 16. And is supplied to the encoder / decoder 14 to execute decompression decoding processing. The decoded image signal is supplied to the graphic I / F 17 via the system control unit 15, and a still image is reproduced and displayed on the display 17a.

Next, detection of defective pixels in this digital still camera will be described in detail.
FIG. 2 is a block diagram showing functions for detecting defective pixels provided in the digital still camera.

  As shown in FIG. 2, the digital still camera includes a defect detection unit 131 and a defect determination processing unit 150 as functions for detecting defective pixels. In addition, a defect correction unit 132 that corrects the defective pixel based on the detected position information of the defective pixel (defect position information 19a) is also provided.

  The defect detection unit 131 is realized as a function of the camera signal processing circuit 13, detects a defective pixel based on the image signal output from the AFE processing circuit 12, and notifies the system control unit 15 of an address indicating the pixel position. . For example, the defect detection unit 131 compares the signal levels of the detection target pixel and surrounding pixels, and determines that the pixel is a defective pixel when the signal level of the detection target pixel is extremely high or low.

  The defect determination processing unit 150 is realized as a function of the system control unit 15 and includes a data writing unit 151 and a defect determination unit 152. The data writing unit 151 is a functional block that writes a data value to the defect determination frame memory 20 in accordance with the detection result of the defect detection unit 131. Specifically, every time a defect pixel candidate is detected by the defect detection unit 131, the data value of the address of the defect determination frame memory 20 corresponding to the pixel position is incremented. As a result of this processing, the number of times detected by the defect detection unit 131 as a defective pixel candidate is recorded in the defect determination frame memory 20 for each pixel.

  In addition, by using the frame memory to record the number of detections as defective pixel candidates, the recording operation of the number of detections can be easily synchronized with the detection operation by the defect detection unit 131, and the processing efficiency is improved.

  The defect determination unit 152 determines a final defective pixel based on the recording data of the defect determination frame memory 20. Specifically, the data value of each pixel recorded in the defect determination frame memory 20 is monitored, and the defect determination is performed when the maximum value of these data values reaches a predetermined threshold value. At this time, a predetermined number of addresses are extracted from the top in descending order of data values, pixels corresponding to these addresses are determined as defective pixels, and are recorded in the EEPROM 19 as defect position information 19a.

  The defect correction unit 132 is realized as a function of the camera signal processing circuit 13. When the image is captured, the defect position information 19 a is read from the EEPROM 19 through the system control unit 15, and based on this information, the image signal from the AFE processing circuit 12 is read out. In contrast, signal correction of defective pixels is performed by interpolation calculation or the like. Part of signal correction processing such as interpolation calculation may be performed by the system control unit 15.

  As described above, since the defect detection unit 131 detects a defective pixel candidate based on the captured image signal, the defect detection unit 131 is realized by a relatively simple device configuration that does not use a light shielding unit or a reference light source. And since the defect determination process part 150 determines the position of the final defective pixel based on the frequency | count made into the defective pixel candidate, it can improve the detection precision of a defective pixel. As a defect detection method in the defect detection unit 131, for example, a general method as shown in FIG. 3 below can be used.

FIG. 3 is a diagram for explaining an example of a defect detection method in the defect detection unit 131.
FIG. 3 shows, as an example, the state of the light receiving surface of the CCD 114 when a Bayer array RGB primary color filter is provided. In this case, filters of the same color are provided every other pixel. If a pixel to be detected as a defect is a target pixel P, signals of the same color pixel existing around the target pixel P are used to detect the target pixel P. Here, as an example, peripheral eight pixels (peripheral pixels P1 to P8) are used as shown in FIG. At this time, the difference between the average value of the signal levels of the peripheral pixels P1 to P8 and the signal level of the target pixel P is taken, and if the absolute value exceeds the threshold value, it is determined as a defective pixel. Thereby, a pixel having an extremely large signal level difference from surrounding pixels is determined as a defect.

  In such a detection method, the detection accuracy can be increased by increasing the number of peripheral pixels to be compared with the target pixel P. Further, for example, by using a statistical calculation method such as calculation of a variance value of signal levels of peripheral pixels, or by correlating with signal levels of peripheral pixels having a color different from the target pixel P, the detection accuracy is further increased. Can do. As described above, in the defect detection based on the captured image signal, the detection accuracy can be increased as the complicated calculation is used.

  However, in the present embodiment, the final defect determination is performed by the defect determination processing unit 150 based on the detection result obtained by executing the defect detection realized by such a relatively simple device configuration for a plurality of frames. Therefore, even when the defect detection unit 131 adopts a relatively simple defect detection method as shown in FIG. 3, for example, the detection accuracy can be increased.

FIG. 4 is a flowchart showing a flow of processing at the time of defect determination in the defect determination processing unit 150.
The process shown in FIG. 4 is executed when the defect detection unit 131 performs defect detection based on the captured image signal for one frame at the time of power-on or at certain time intervals (FIG. 5, which will be described later). The same applies to FIGS. 6 and 7. First, steps S101 to S104 are executed by the data writing unit 151.

[Step S101] The defect detection result for one pixel is received from the defect detection unit 131.
[Step S102] If it is detected that the pixel is defective, the process proceeds to step S103. If not detected, the process proceeds to step S104.

[Step S103] The data value of the address on the defect determination frame memory 20 corresponding to the position of the defective pixel is incremented.
[Step S104] It is determined whether or not the defect detection for one frame has been completed. If not, the process returns to step S101 to receive the detection result for the next pixel. When the process is completed, steps S105 to S108 are subsequently performed by the defect determination unit 152.

  [Step S105] It is determined whether or not the maximum value of the data value recorded in the defect determination frame memory 20 has reached a predetermined threshold value (255 in this case). If so, the process proceeds to step S106. Otherwise, the process is terminated.

  [Step S106] On the defect determination frame memory 20, a predetermined number of addresses (here, 30 addresses) are extracted in descending order of data values. At this time, a lower limit value is set for the data value to be extracted, and if the data value does not reach the lower limit value even if it is within a predetermined number from the top, the corresponding address is not extracted. May be.

[Step S107] A pixel corresponding to the extracted address is determined as a defective pixel, and this address is registered in the EEPROM 19 as defect position information 19a.
[Step S108] The recording data in the defect determination frame memory 20 is reset.

  In the above processing, the defective pixel is determined when the number of defective pixel candidates by the defect detection unit 131 reaches a predetermined value in any pixel, and at this time, a predetermined number of pixels in descending order of the number of times. Are determined to be defective pixels. For this reason, the detection condition is the same for all pixels, and a pixel that is highly likely to be a defective pixel under that condition is preferentially determined as a defective pixel. Therefore, the maximum value in step S105 or the address in step S106 High defect determination accuracy can be obtained by appropriately setting the number of extractions.

  Further, since the defect determination is performed based on the picked-up image signals for a plurality of frames, it is possible to cancel the influence of the detection error caused by the occurrence of random noise or the occurrence of erroneous detection at the pixel edge. And, since the number of times of detection as a defective pixel candidate is recorded in one frame memory, the necessary capacity of the frame memory can be suppressed while performing defect detection for a plurality of frames in this way. The circuit scale can be reduced and the manufacturing cost can be suppressed.

<< Second Embodiment >>
In the first embodiment described above, the defect detection unit 131 is configured to determine whether or not the target pixel is a defective pixel. In addition to this, for example, the defect detection unit 131 may detect when a defect is detected. The defect level may be output for each pixel according to the calculation result. For example, the higher the value of the defect level, the higher the possibility of a defective pixel. For example, in the defect detection method described above with reference to FIG. 3, it is considered that the higher the absolute value of the difference value between the average value of the signal level of the peripheral pixels and the signal level of the target pixel is, the higher the possibility of the defective pixel is. Therefore, the absolute value of this difference value (or a value assigned stepwise according to this value) can be used as the defect level.

  In this way, when the defect level is output from the defect detection unit 131, the defect determination processing unit 150 uniquely determines whether or not to be a defective pixel candidate based on the defect level, and further determines the number of times that the defect pixel candidate is determined. Based on the final defect determination, the determination accuracy can be improved. In this embodiment, when a defect level detected based on a captured image signal for one frame is received, a predetermined number of pixels from the top in the descending order of the defect level are set as defective pixel candidates.

FIG. 5 is a flowchart showing a flow of processing at the time of defect determination in the defect determination processing unit 150 in this case.
First, similarly to FIG. 4, steps S <b> 201 to S <b> 203 are executed by the data writing unit 151.

[Step S201] The defect level of each pixel for one frame is sequentially received from the defect detector 131. The received defect level is temporarily stored in, for example, a RAM.
[Step S202] A predetermined number (30 in this case) of pixels in the descending order of the defect level in one frame is extracted as defective pixel candidates. At this time, a lower limit of the defect level may be provided for the defective pixel candidate.

[Step S203] The data value of the address on the defect determination frame memory 20 corresponding to the position of the pixel determined as the defective pixel candidate is incremented.
The processing in the following steps S204 to S207 corresponds to steps S105 to S108 in FIG. 4 and will not be described here. However, in the above process, the detection accuracy can be increased by determining a predetermined number of pixels from the top in the descending order of the defect level, so that the number of frames required until the final defect determination can be reduced. it can. Therefore, in step S204, the determination reference value for determining a defective pixel can be made lower than that in the first embodiment. At the same time, the number of bits per pixel recorded in the defect determination frame memory 20 can be reduced, so that the memory capacity is suppressed.

<< Third Embodiment >>
By the way, although it is impossible to completely eliminate the false detection by the defect detection in the defect detection unit 131, the occurrence probability of the false detection also changes depending on the exposure condition at the time of imaging. For example, the system control unit 15 controls the shutter speed of the mechanical shutter and the electronic shutter, the gain of the AGC in the AFE processing circuit 12 and the like according to the result of the AE processing by the camera signal processing circuit 13. When the gain of AGC is set high, the noise component included in the image signal increases accordingly, and it becomes difficult to distinguish between defects and noise. Alternatively, with respect to random noise generated on the CCD 114, noise components cancel each other by integration for the exposure time, so that the generation of noise decreases as the shutter speed is slower and the exposure time is longer. On the other hand, since the white defect is caused by the generation of excess charge in the defective pixel, the longer the exposure time is, the more excess charge is accumulated and the white defect is easily detected.

  In consideration of such a property, in the present embodiment, the detection condition of the defective pixel is changed by changing the condition of the defective pixel candidate based on the detection result of the defect detection unit 131 according to the exposure condition. Improve. For this reason, when the detection by the defect detection unit 131 is started, the data writing unit 151 of the defect determination processing unit 150 calculates the shutter speed and AGC gain for imaging the frame calculated in the system control unit 15. And the number of pixels to be extracted as defective pixel candidates is changed.

FIG. 6 is a flowchart showing a flow of processing at the time of defect determination in the defect determination processing unit 150 in this case.
First, steps S301 to S304 are executed by the data writing unit 151.

  [Step S301] An exposure condition at the time of imaging is acquired, and the number of pixels to be extracted as a defective pixel candidate in a subsequent step S303 is set according to this condition. For example, the higher the AGC gain, the smaller the number of pixels to be extracted. Further, the slower the shutter speed, the larger the number of pixels to be extracted.

[Step S302] The defect level of each pixel for one frame is sequentially received from the defect detector 131. The received defect level is temporarily stored in, for example, a RAM.
[Step S303] The number of pixels set in step S301 is extracted as defective pixel candidates in descending order of defect level. At this time, a lower limit of the defect level may be provided for the defective pixel candidate.

[Step S304] The data value of the address on the defect determination frame memory 20 corresponding to the position of the pixel determined as the defective pixel candidate is incremented.
The subsequent processes in steps S305 to S308 correspond to steps S105 to S108 in FIG. In the above processing, the determination accuracy of defective pixel candidates is further increased. Therefore, in order to obtain the same defect detection accuracy, a frame required until the final defect determination is obtained as compared with the second embodiment. The number can be reduced, and the capacity of the defect determination frame memory 20 can be further suppressed.

<< Fourth Embodiment >>
In the third embodiment, the number of defective pixel candidates is changed according to the exposure conditions. For example, the defective pixel candidate is determined according to the value of the defect level. The reference value may be changed according to the exposure conditions.

FIG. 7 is a flowchart showing a flow of processing at the time of defect determination in the defect determination processing unit 150 in this case.
First, steps S401 to S405 are executed by the data writing unit 151.

  [Step S401] An exposure condition at the time of imaging is acquired, and in accordance with this condition, a determination reference value is set for extraction as a defective pixel candidate in a subsequent step S403. For example, the higher the AGC gain, the higher the criterion value, and the slower the shutter speed, the lower the criterion value.

[Step S402] The defect level for one pixel is received from the defect detector 131.
[Step S403] It is determined whether or not the defect level is equal to or higher than the determination reference value set in Step S401. In that case, the process proceeds to step S405.

[Step S404] The data value of the address on the defect determination frame memory 20 corresponding to the position of the pixel determined as the defective pixel candidate is incremented.
[Step S405] It is determined whether or not the defect detection for one frame has been completed. If not, the process returns to step S402 to receive the defect level for the next pixel. When the process is completed, steps S406 to S409 are subsequently executed by the defect determination unit 152. Since these steps S406 to S409 correspond to steps S105 to S108 in FIG. 4, description thereof is omitted here. To do.

  In the above processing, the determination accuracy of the defective pixel candidate can be further improved by changing the determination reference value of the defective pixel candidate in accordance with the exposure condition. Therefore, as in the third embodiment, the second Compared to the embodiment, the number of frames required until the final defect determination can be reduced, and the capacity of the defect determination frame memory 20 can be further suppressed.

<< Fifth Embodiment >>
FIG. 8 is a block diagram illustrating functions for detecting defective pixels included in a digital still camera according to the fifth embodiment of the present invention.

  In the digital still camera shown in FIG. 8, the camera signal processing circuit 13 is provided with defect detection units 131a and 131b for white defect detection and black defect detection, respectively. In such a case, the system control unit 15 is also provided with defect determination processing units 150a and 150b for white defects and black defects, respectively, and dedicated frame memories (white defect determination frame memory 20a, black defect determination defect), respectively. A frame memory 20b) may be provided. Even when the defect determination is performed individually for the white defect and the black defect in this way, only one frame memory is required for each of the white defect and the black defect, so that the defect detection accuracy can be increased without increasing the memory capacity. Can be increased.

  Further, in the defect determination processing units 150a and 150b, any of the above-described processing procedures of FIGS. 4 to 7 may be used as the defective pixel determination process. In addition, different values are set for white defects and black defects for the determination criteria for determining defective pixel candidates and the maximum data value on the frame memory for starting the final defective pixel determination. Also good.

  Furthermore, even when defect detection units 131a and 131b for white defects and black defects are individually provided, only one defect determination frame memory is provided, which simplifies the process and suppresses the memory capacity. Also good. In this case, in the defect determination processing units 150a and 150b, only a function for extracting defective pixel candidates (corresponding to the data writing unit 151) is individually provided, and at this time, each function has a data value for the same frame memory. Is incremented. Therefore, the frame memory records the number of times that the defective pixel candidate is identified without distinguishing between the white defect and the black defect. Further, only one function (corresponding to the defect determination unit 152) for performing defect determination based on the data value on the frame memory may be provided and shared.

  In the above embodiment, the case where the present invention is applied to a digital still camera has been described. However, the present invention can also be applied to other imaging apparatuses using a solid-state imaging device. For example, the present invention can be applied to an imaging function such as a digital video camera, a mobile phone, and a PDA (Personal Digital Assistants).

  Furthermore, the processing functions of the imaging apparatus described above can be realized by a computer. In that case, a program describing the processing contents of the functions that the imaging apparatus should have (particularly, the functions corresponding to the defect determination processing units 150, 150a, 150b, etc.) is provided. And the said processing function is implement | achieved on a computer by running the program with a computer. The program describing the processing contents can be recorded on a computer-readable recording medium. Examples of the computer-readable recording medium include a magnetic recording device, an optical disk, a magneto-optical disk, and a semiconductor memory.

  In order to distribute the program, for example, portable recording media such as an optical disk and a semiconductor memory on which the program is recorded are sold. It is also possible to store the program in a storage device of a server computer and transfer the program from the server computer to another computer via a network.

  The computer that executes the program stores, for example, the program recorded on the portable recording medium or the program transferred from the server computer in its own storage device. Then, the computer reads the program from its own storage device and executes processing according to the program. The computer can also read the program directly from the portable recording medium and execute processing according to the program. Further, each time the program is transferred from the server computer, the computer can sequentially execute processing according to the received program.

1 is a block diagram showing an overall configuration of a digital still camera according to a first embodiment of the present invention. It is a block diagram which shows the function for the defective pixel detection which the digital still camera concerning the 1st Embodiment of this invention comprises. It is a figure for demonstrating an example of the defect detection method in a defect detection part. It is a flowchart which shows the flow of the process at the time of the defect determination in the defect determination process part which concerns on 1st Embodiment. It is a flowchart which shows the flow of the process at the time of the defect determination in the defect determination process part which concerns on 2nd Embodiment. It is a flowchart which shows the flow of the process at the time of the defect determination in the defect determination process part which concerns on 3rd Embodiment. It is a flowchart which shows the flow of the process at the time of the defect determination in the defect determination process part which concerns on 4th Embodiment. It is a block diagram which shows the function for the defective pixel detection which the digital still camera concerning the 5th Embodiment of this invention comprises.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Optical block, 12 ... AFE processing circuit, 13 ... Camera signal processing circuit, 14 ... Encoder / decoder, 15 ... System control part, 16 ... Input part, 17 ... Graphic I / F, 17a ... Display, 18 ... R / W, 18a ... Memory card, 19 ... EEPROM, 20 ... Frame memory for defect determination, 111 ... Lens mechanism, 112 ... Exposure mechanism, 113 ... OP- LPF, 114 ... CCD, 115 ... lens driver, 116 ... exposure control driver, 117 ... TG, 131 ... defect detection unit, 132 ... defect correction unit, 150 ... defect determination processing unit, 151 ... Data writing unit, 152... Defect determination unit

Claims (11)

In an imaging device that captures an image using a solid-state imaging device,
A frame memory for storing data at an address corresponding to each pixel of one frame of the captured image;
A defective pixel candidate detecting means for detecting a defective pixel candidate based on the captured image signal;
Data writing means for incrementing the data value of the address on the frame memory corresponding to the position of the defective pixel candidate each time the defective pixel candidate is detected by the defective pixel candidate detection means;
When the data value of at least one address on the frame memory reaches a predetermined reference value, a predetermined number of addresses are extracted in descending order of the data value at that time, and the pixel corresponding to the address is defined as a defective pixel. Defective pixel determination means for determining
An imaging device comprising: The defective pixel candidate detection means outputs a defect level indicating a high possibility of being a defective pixel for each detected defective pixel candidate,
The data writing means extracts a predetermined number of the defective pixel candidates from the top in descending order of the defect level from the captured image of one frame, and the data value of the address on the frame memory corresponding to the position of the defective pixel candidate The imaging apparatus according to claim 1, wherein:   3. The imaging according to claim 2, wherein the defective pixel candidate detection unit outputs the defect level according to a comparison result between a signal level of a detection target pixel in a captured image signal and a signal level of surrounding pixels. apparatus.   3. The imaging apparatus according to claim 2, wherein the data writing unit changes the number of addresses for incrementing the data value on the frame memory in accordance with an exposure condition at the time of the previous imaging. The defective pixel candidate detection means outputs a defect level indicating a high possibility of being a defective pixel for each detected defective pixel candidate,
When the defect level has reached a predetermined lower limit value, the data writing means increments the data value of the address on the frame memory corresponding to the position of the pixel, and further sets the lower limit value to the immediately preceding imaging value. The imaging apparatus according to claim 1, wherein the imaging apparatus is changed according to exposure conditions at the time. The frame memory is individually provided for white defect determination and black defect determination,
The defective pixel candidate detecting means detects a white defect and a black defect as the defective pixel candidates,
The data writing unit increments the data value of the frame memory corresponding to each of a white defect and a black defect according to a detection result by the defective pixel candidate detection unit,
The imaging apparatus according to claim 1, wherein the defective pixel determination unit determines a white defect and a black defect based on data values of the corresponding frame memories.   The defective pixel determining means determines that a pixel corresponding to one having a data value greater than or equal to a predetermined threshold among defective addresses extracted from the frame memory in descending order of data value is determined as a defective pixel. The imaging apparatus according to claim 1, characterized in that: Defect position storage means for storing position information of the defective pixels determined by the defective pixel determination means;
Defective pixel correction means for correcting the pixel signal of the defective pixel in the captured image signal based on the storage information of the defect position storage means;
Further comprising
2. The imaging according to claim 1, wherein each time the defective pixel determination unit determines a new defective pixel, the position information is written to the defect position storage unit and all data values of the frame memory are reset. apparatus.   The imaging apparatus according to claim 1, wherein the defective pixel candidate detecting unit detects the defective pixel candidate based on a signal level of a detection target pixel in a captured image signal and a signal level of surrounding pixels. In a defective pixel detection method for detecting a defective pixel in a solid-state imaging device using a frame memory that stores data at an address corresponding to each pixel of one frame of a captured image,
Each time a defective pixel candidate is detected based on the captured image signal, the data writing means increments the data value of the address on the frame memory corresponding to the detected position of the defective pixel candidate;
When the data value of at least one address on the frame memory reaches a predetermined reference value, the defective pixel determination unit extracts a predetermined number of addresses from the top in descending order of the data value at that time, Determining a corresponding pixel as a defective pixel;
A defective pixel detection method comprising: In a defective pixel detection program that causes a computer to execute a process of detecting a defective pixel in a solid-state imaging device using a frame memory that stores data at an address corresponding to each pixel of one frame of a captured image.
Data writing means for incrementing the data value of the address on the frame memory corresponding to the position of the defective pixel candidate each time a defective pixel candidate is detected based on the captured image signal;
When the data value of at least one address on the frame memory reaches a predetermined reference value, a predetermined number of addresses are extracted in descending order of the data value at that time, and the pixel corresponding to the address is defined as a defective pixel. Defective pixel determination means for determining
A defective pixel detection program for causing the computer to function as:

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