JP5188171B2 - Imaging device - Google Patents

Description

  The present invention relates to an imaging device that reduces noise in an image signal output from an imaging device.

  In a conventional imaging apparatus, in particular, a digital camera that performs a clamp process on an image signal output from, for example, an image sensor and performs recording and display based on the image signal after the clamp process, the temperature of the image sensor included in the digital camera When the sensitivity changes, a large difference may appear in the dark current (noise) level between the clamp area and the effective area in the image sensor. For example, the dark current level in the clamp area may be larger than the dark current level in the effective area. When the clamping process is performed in a state where there is a difference in dark current level between the two, the level of the image signal after the clamping process may be different from the level of the original image signal.

When the image pickup device is a Bayer array CCD imager and generates a video signal to be displayed on a monitor from an output image signal, more G components are used from the image signal compared to the R component and the B component. There is a technique for generating video signals. In the clamping process, the image signals of the R, G, and B components of the effective area are clamped at the average clamping level of the clamping area in one line. When a video signal is generated by this method, the clamped image signal in a state where there is a difference in dark current level between the two is the G in the R, G, and B components in the clamped image signal. The ratio of the component is larger than the ratio of the G component in the R, G, and B components in the image signal after the clamping process in the state where there is no difference in the dark current level. Since the G component is used, the video signal tends to be green.
JP 2006-94447 A [H04N 5/335]

  In the imaging device of the prior art 1 described in Patent Document 1, image data for one frame is obtained by dividing it into a plurality of fields, and one field is captured from a photoelectric conversion element before still image capturing. The signal charge is read out without being read out, and AGC and A / D conversion are performed as a dummy signal, which is recorded as a correction signal. The noise is reduced by subtracting the correction signal from a plurality of fields for still image capturing. In this imaging apparatus, if random noise is included in the clamp level used in the clamp process, but the image signal does not include random noise, and the image signal is subjected to the clamp process, noise is inherently generated. This is effective in preventing a state in which random noise is subtracted from an image signal that does not contain noise, and new noise is generated by the subtraction.

  However, since the correction signal is generated only once before imaging in the related art 1, the correction signal before shooting is displayed when the environment of the image sensor changes when displaying a through image or capturing a moving image for a long time. There is a possibility that proper image data cannot be obtained by the subtraction based on.

  In the prior art 1, noise is reduced by uniformly subtracting the correction signal from the image data. However, taking into account the difference in dark current (noise) level between the clamp area and the effective area. There is no disclosure regarding the correction of the image signal.

  The present invention solves the above-described problems, and provides an imaging apparatus capable of performing more appropriate noise correction on continuous image signals.

  The imaging apparatus according to claim 1 receives a photoelectric conversion element arranged over a plurality of columns, a photoelectric conversion output from the photoelectric conversion element arranged adjacent to the photoelectric conversion element, and charges including the photoelectric conversion output in a vertical direction. A vertical transfer register for transferring, a horizontal transfer register connected to an end of the vertical transfer register, for transferring the charge transferred from the vertical transfer register in the horizontal direction, and outputting the charge as an imaging signal; Drive control for controlling the transfer of the photoelectric conversion output from the conversion element to the vertical transfer register and the transfer of the charge in the vertical and horizontal registers to drive the image pickup signal so as to sequentially output the image pickup signal at a predetermined frame rate. In a state where transfer of photoelectric conversion output to the vertical transfer register is prohibited, charge transfer is performed in the vertical and horizontal registers, and the horizontal shift is performed as a dark signal detection value. A dark signal detection unit that periodically executes a dark signal detection process output from a register to update a dark signal detection value, and a correction unit that performs a correction process on the video signal based on the imaging signal using the dark signal detection value. It is characterized by that.

  According to the imaging apparatus of the first aspect of the present invention, the dark signal existing in the vertical transfer register is periodically updated, and the updated dark signal, that is, the latest dark signal is used for the video signal obtained continuously. Therefore, even when the environment of the image sensor changes, appropriate video signals can be continuously acquired.

  According to another aspect of the present invention, there is provided an imaging apparatus that sequentially exposes an imaging signal at a predetermined frame rate, an exposure control unit that controls exposure of the photoelectric conversion element, an imaging unit that outputs a photoelectric conversion output from the photoelectric conversion element as an imaging signal The drive control means for driving and controlling the image pickup means, and the dark signal detection processing for outputting the image pickup signal in a state where exposure is prohibited in the exposure control means and outputting from the image pickup means as the dark signal detection value is periodically executed. A dark signal detection unit that updates a dark signal detection value and a correction unit that performs correction processing on the video signal based on the imaging signal using the dark signal detection value are provided.

  According to the imaging device of the second aspect of the present invention, the dark signal existing in both the photoelectric conversion element and the vertical transfer register is periodically updated, and the dark signal that is updated with respect to the continuously obtained video signal, that is, Since correction is performed using the latest dark signal, an appropriate video signal can be continuously acquired even when the environment of the image sensor changes.

  An imaging device according to a third aspect is dependent on the imaging device according to any one of the first to second aspects, wherein the imaging means is formed of a plurality of pixels in which an optical black area and an effective area are adjacent to each other. Clamp means for detecting a clamp level based on the optical black area of the image signal output from the image signal and performing a clamp process on the image signal using the clamp level as a reference black level, and the image signal is subjected to the clamp process. It is a signal based on the imaging signal after being performed.

  An imaging apparatus according to a fourth aspect is dependent on the imaging apparatus according to any one of the first to third aspects, wherein a dark signal detection value is assigned to the first dark signal detection value corresponding to an optical black area and the effective area. Comparing means for comparing the first dark signal detection value corresponding to the optical black area divided into the corresponding second dark signal detection value and the second dark signal detection value corresponding to the effective area, the correction means comprises a comparison If the first dark signal detection value is larger than the second dark signal detection value as a result of the comparison by the means, a subtraction process is performed to subtract the dark signal detection value from the video signal. When the second dark signal detection value is larger than the detection value, an addition process for adding the dark signal detection value to the video signal is performed.

  An image pickup apparatus according to a fifth aspect is dependent on any one of the image pickup apparatuses according to the first to fourth aspects, and includes a detecting unit that compares a plurality of video signals output in succession and detects the amount of motion before and after. A comparison means for comparing whether or not the amount of movement exceeds a threshold value, and a first control means for performing control so as not to operate the prohibition means when the amount of movement exceeds the threshold value as a result of comparison by the comparison means. It is characterized by.

  An imaging device according to a sixth aspect is dependent on any one of the imaging devices according to the first to fifth aspects, and compares luminance detection means for detecting luminance based on a video signal with whether the luminance exceeds a threshold value. And a second control means for performing control so as not to operate the prohibiting means when the luminance is higher as a result of the comparison by the comparing means.

  According to another aspect of the present invention, there is provided an imaging method in which a photoelectric conversion element arranged over a plurality of columns and a photoelectric conversion output from the photoelectric conversion element arranged adjacent to the photoelectric conversion element are received and charges including the photoelectric conversion output are transferred in the vertical direction. An image pickup method having a horizontal transfer register connected to an end of a vertical transfer register and a vertical transfer register for transferring the charge transferred from the vertical transfer register in a horizontal direction and outputting the charge as an image pickup signal, from a photoelectric conversion element Controlling the transfer of the photoelectric conversion output to the vertical transfer register and the transfer of the charges in the vertical and horizontal registers to drive the image pickup signal so as to sequentially output the image pickup signal at a predetermined frame rate; and to the vertical transfer register In the state where transfer of the photoelectric conversion output is prohibited, charge transfer is performed in the vertical and horizontal registers, and the dark signal detection value is output from the horizontal transfer register. And updating the dark signal value detected by performing the dark signal detection process periodically, characterized in that it comprises the step of performing a correction process using the dark signal detection value to the video signal based on the imaging signal.

  The imaging method according to claim 8 is a method of controlling exposure to the photoelectric conversion element, outputting a photoelectric conversion output from the photoelectric conversion element as an imaging signal, and imaging so as to sequentially output the imaging signal at a predetermined frame rate. The step of controlling the drive of the signal and the imaging signal are output in a state where exposure is prohibited, and the dark signal detection value is updated by periodically executing dark signal detection processing using the signal for one frame as the dark signal detection value. And a step of correcting the video signal based on the imaging signal using a dark signal detection value.

  According to the imaging apparatus and imaging method of the present invention, more appropriate noise correction can be performed on continuous imaging signals.

  Hereinafter, the embodiment implemented in the digital camera 10 will be specifically described with reference to the drawings as an embodiment of the imaging apparatus and imaging method of the present invention.

  FIG. 1 is a block diagram of a digital camera 10 according to the first embodiment. The digital camera 10 includes an optical lens 12 and a diaphragm 14. The movement of the optical lens 12 and the diaphragm 14 and the adjustment of the diaphragm 14 are performed by a motor drive unit 16. However, the motor drive unit 16 is composed of two motors (not shown) that adjust the optical lens 12 and the diaphragm 14 separately.

  An optical image of a subject is formed on a light receiving surface of a CCD imager 18 that is an image pickup device via an optical lens 12 and a diaphragm 14. As shown in FIG. 3, the CCD imager 18 includes a plurality of photodiodes 100, a vertical transfer register 102, and a horizontal transfer register 104. R, G, and B primary color filters are attached to the light receiving surface of these photodiodes 100, and light having any one primary color component is irradiated. The photodiode 100 performs photoelectric conversion, and a charge signal accumulated according to light intensity and time is transferred to the vertical transfer register, then transferred to the horizontal transfer register, and output as an analog imaging signal. This transfer operation is performed in accordance with charge readout pulses, vertical transfer pulses, and horizontal transfer pulses, which are various pulse waveforms necessary for driving the CCD imager 18 generated by the signal generator (SG) 20. When recording a still image, when an operation by the operation unit 48, for example, a release button is pressed, the CPU 32 controls the SG 20 and causes the CCD imager 18 to output an analog imaging signal for one frame. When recording a moving image or outputting a through image to the display 46, the CPU 32 controls the SG 20 so that an analog imaging signal is output from the CCD imager 18 at a predetermined frame rate. The output analog imaging signal is input to the CDS / AGC circuit 21, subjected to correlated double sampling processing, and gain adjustment is performed.

  The analog imaging signal output from the CDS / AGC circuit 21 is input to the clamp circuit 22. In the clamp circuit 22, as shown in FIG. 4, the inside of the image sensor is assigned to an effective area and a clamp area that is an optical black area, and the analog image signal is clamped based on the black signal obtained from the clamp area. . The clamped analog image signal is output to the A / D converter 24, converted into a digital image signal, and output to the correction processing circuit 26. In the correction processing circuit 26, the digital imaging signal is corrected by a digital dark signal described later.

  This correction process is a correction for removing the noise of the digital image pickup signal containing noise existing in the CCD imager 18 as an image pickup device. The corrected digital image pickup signal is temporarily stored in the SDRAM 34 via the bus 28, color-separated by the signal processing circuit 27, converted into Y, U, and V signals, and stored again in the SDRAM 34 as a digital image signal. Is done. When recording a still image, the digital image signal stored in the SDRAM 34 is subjected to JPEG compression processing by the image compression / expansion processing unit 36 under the control of the CPU 32 and converted into compressed image data. Under the control of the CPU 32, the card control unit 38 controls the external memory card 40 to record compressed image data.

  When displaying a through image on the display 46, the digital image signal stored in the SDRAM 34 is converted into an analog video signal by the D / A converter 42 under the control of the CPU 32, and converted into an NTSC signal by the video encoder 44. The CPU 32 controls the display 46 to display an analog video signal as a through image at a predetermined frame rate.

  Further, when displaying a through image on the display 46 while recording a moving image, the digital image signal stored in the SDRAM 34 is subjected to MPEG compression processing by the image compression / decompression processing unit 36 under the control of the CPU 32. After being converted into compressed image data, the card control unit 38 controls the external memory card 40 to record the compressed image data under the control of the CPU 32, and the digital image signal stored in the SDRAM 34 is converted by the D / A converter 42. After being converted into an analog video signal and converted into an NTSC signal by the video encoder 44, the analog video signal is displayed on the display 46 as a through image at a predetermined frame rate.

  In the first embodiment, processing for correcting the A / D converted digital image pickup signal by the CPU 32 and the correction processing circuit 26 is executed. This correction processing will be described with reference to the block diagram of the correction processing circuit 26 in FIG. 2 and FIG.

  When the digital camera 10 is turned on, the CPU 32 controls the SG 20 to display an analog imaging signal from the CCD imager 18 at a predetermined frame rate in order to display a through image on the display unit 46. Here, the predetermined frame rate is defined as a first frame rate, and in the first embodiment, the first frame rate is set to 30 fps (first frame rate = 30 fps). In this correction process, one frame is allocated once per second in order to acquire a digital dark signal for correcting a digital imaging signal. That is, since the first frame rate is 30 fps, one frame out of 30 frames output from the CCD imager 18 per second is allocated to acquire a digital dark signal, and 29 frames are displayed on the display unit 46 as a through image. Assigned to acquire a digital imaging signal for display. In this way, the digital imaging signal to be displayed on the display unit 46 as a through image is corrected using the digital dark signal.

  FIG. 5 shows the exposure timing when the analog image signal is output from the CCD imager 18 at the first frame rate and the pulses output from the SG 20 to the CCD imager 18. (A) shows an exposure period, (b) shows a charge readout pulse for transferring charges from the photodiode 100 to the vertical transfer register 102, and (c) shows an output of an analog imaging signal from the CCD imager 18. Indicates the state.

  Specifically, when the first frame exposure is performed, the SG 20 does not output a charge readout pulse to the CCD imager 18, and the charge from the photodiode 100 is not transferred to the vertical transfer register 102. The analog imaging signal of the first frame is output. During the output, the SG 20 gives a sub pulse to the CCD imager 18 and discharges the electric charge held by the photodiode 100. That is, without reading out the charge accumulated in the photodiode 100, the charge held in the vertical transfer register 102, that is, the dark current as noise is transferred to the horizontal transfer register 104 and output as an analog imaging signal from the CCD imager 18. Become. Here, an analog imaging signal based on the dark current output from the CCD imager 18 without reading out the charge of the photodiode 100 is referred to as a dark signal.

  Next, the dark signal is subjected to a series of similar processes until it is output to the analog imaging signal and the correction processing circuit 26 as described above. Here, the digital imaging signal output from the A / D converter 24 is referred to as a digital dark signal.

  While the CPU 32 outputs a digital dark signal for one frame from the A / D converter 24, that is, while the CPU 32 controls to output a dark signal from the CCD imager 18, T1 and T2 are set in the switch SW1. Control to be connected. While T1 and T2 are connected, the digital dark signal for one frame output from the A / D converter 24 is input to the SRAM 26b and to the integration / comparison circuit 26a. The SRAM 26b includes a register F for holding the state of the flag F, and stores the input digital dark signal for one frame. Further, the integration / comparison circuit 26a averages the levels of the digital dark signal in the effective area and the digital dark signal in the clamp area for one frame, and compares them with each other. When the level of the effective area is high, the reset signal for resetting the flag F stored in the register F in the SRAM 26b (F = 0) is output to the SRAM 26b. When the level is lower than the clamp area level, the flag F is set (F = 1) and an ON signal is output to the SRAM 26b.

  Then, exposure of the second frame is performed in parallel with the analog image signal of the first frame, that is, the output of the CCD imager 18 of the analog dark signal. SG 20 gives a charge read pulse to CCD imager 18 to transfer the charge from photodiode 100 to vertical transfer register 102. The charge transferred to the vertical transfer register 102 is transferred to the horizontal transfer register 104 and is output from the CCD imager 18 as an analog imaging signal of the second frame. Then, the CDS / AGC circuit 21, the clamp circuit 22, and the A / D conversion circuit 24 perform the above-described processing, and the digital image signal is output to the correction processing circuit 26. Then, the CPU 32 controls the switch SW1 so that T1 is output while the A / D converter 24 outputs the digital image pickup signal for the second and subsequent frames, that is, while the CCD imager 18 controls to output the analog image pickup signal. Control is performed so that T3 is connected, and the state of the flag F stored in the register F is detected.

  As a result of detection, when the flag F is set (F = 1), the CPU 32 connects T4 and T6 in the switch SW2, supplies the digital imaging signal of the second frame to the adder 26d, and controls the SRAM 26b. The digital dark signal stored in the SRAM 26b is output to the adder 26d. In the adder 26 d, the digital imaging signal and the digital dark signal are added and stored in the SDRAM 34 via the bus 28. On the other hand, when the flag F is not set (F = 0), the CPU 32 connects T4 and T5 in the switch SW2, supplies the digital imaging signal of the second frame to the subtractor 26c, controls the SRAM 26b, and controls the SRAM 26b. The stored digital dark signal is output to the subtractor 26c. In the subtractor 26 c, the digital dark signal is subtracted from the digital imaging signal and stored in the SDRAM 34 via the bus 28.

  The added or subtracted digital image signal stored in the SDRAM 34 is subjected to color separation processing in the signal processing circuit 27 as described above and converted into Y, U, and V signals, and the D / A converter 42 and the video encoder 44 are supplied. Then, it is output to the display 46. At this time, if the frame rate of the analog video signal output to the display 46 is the second frame rate, the second frame rate is a frame rate lower than the first frame rate. That is, if the first frame rate is 30 fps, the second frame rate is 29 fps. By doing so, the user who sees the through image displayed on the display 46 does not feel uncomfortable.

  Next, exposure of the third frame is performed in parallel with the output of the CCD imager 18 of the analog imaging signal of the second frame. The processing from the third frame to the 30th frame is the same as the processing of the second frame described above. The process of the 31st frame is the same as the process of the 1st frame described above. The digital dark signal of the 1st frame is updated to the digital dark signal of the 31st frame, and the flag F is also updated. The digital image pickup signal of the 32nd frame is corrected by the digital dark signal of the 31st frame, and the digital image pickup signals of the 33rd to 60th frames are similarly corrected by the digital dark signal of the 31st frame. The corrected digital image signal is sequentially displayed on the display 46 at the second frame rate = 29 fps.

  Next, the procedure of correction processing in the digital camera 10, particularly the CPU 32 and the correction processing circuit 26 when displaying a through image having a first frame rate of 30 fps will be described with reference to the flowcharts of FIGS. 6 and 7.

  When shifting to the mode for displaying a through image, the CPU 32 sets a variable P to 1 in step S1 (P = 1), and proceeds to step S3. The variable P is stored in a register (not shown) in the CPU 32. In step S3, charge transfer from the photodiode 100 of the P frame to the vertical transfer register 102 is stopped, an analog dark signal is output from the CCD imager 18, and the switch SW1 is controlled to connect T1 and T2. In step S7, the correction processing circuit 26 records / updates the digital dark signal level N in the SRAM 26b. In step S9, the integration / comparison circuit 26a averages the digital dark signal level E in the effective area for one frame and the digital dark signal level C in the clamp area, and compares them.

  In step S11, the integration / comparison circuit 26a determines whether or not the digital dark signal level C is higher than the digital dark signal level E. If YES is determined in step S11, the integration / comparison circuit 26a outputs an ON signal to the SRAM 26b, proceeds to step S13, sets a flag of the register F in the SRAM 26b (F = 1), and if NO is determined, the step S15. Then, a reset signal is output to the SRAM 26b, and the flag of the register F is reset (F = 0).

  After the processing of step S13 and step S15, the process proceeds to step S17, and the CPU 32 increments the variable P by 1 (P = P + 1). In step S19, an analog image signal for the Pth frame is output from the CCD imager 18, and the switch SW1 is controlled to connect T1 and T3. Next, proceeding to step S21, the CPU 32 detects the state of the flag F.

  In the next step S23, the CPU 32 determines whether or not the flag F is set. If YES is determined in the step S23, the process proceeds to a step S25, in which the CPU 32 controls the switch SW2 to connect T4 and T5, and controls to output the digital dark signal stored in the SRAM 26b to the subtractor 26c. The subtractor 26c subtracts the digital dark signal N from the digital image signal of the Pth frame. If NO is determined in step S23, the process proceeds to step S27, in which the CPU 32 controls the switch SW2 to connect T4 and T6 and to control the digital dark signal stored in the SRAM 26b to be output to the adder 26d. The adder 26d adds the digital dark signal N to the digital image signal of the Pth frame.

  After the processing of step S25 and step S27, the process proceeds to step S29, and the CPU 32 determines whether or not the Pth frame is the 30th frame. If NO is determined in step S29, the process returns to step S17. If YES is determined, the process returns to step S1.

  For the sake of convenience, it has been described that steps S9, S11, S13, and S15 are sequentially processed after step S7. However, steps S7 and S9 to S15 are performed in parallel.

  As described above, when displaying the through image, the digital dark signal of one frame recorded in the SRAM 26b is converted into a predetermined frame rate based on the difference in the level of the digital dark signal between the clamp area and the effective area. Thus, appropriate correction for removing noise can be performed by performing correction processing for adding or subtracting the digital image pickup signal based on the analog image pickup signal sequentially output from the CCD imager 18.

  In addition, since the digital dark signal used for the correction process is periodically updated, it is possible to perform an appropriate correction process even when the environment of the image sensor changes.

  FIG. 8 is a block diagram of the digital camera 50 according to the second embodiment. The digital camera 50 according to the second embodiment is a digital camera 10 according to the first embodiment further including a motion amount detection circuit 52. Each function of the digital camera 10 described in the first embodiment is also applied in the second embodiment. Therefore, only functions different from those in the first embodiment will be described in the second embodiment.

  The motion amount detection circuit 52 operates according to an instruction from the CPU 32. In this operation, a digital image signal output from the signal processing circuit 27 is sequentially captured for a predetermined number of frames to detect a motion amount V between the previous and subsequent frames.

  In the digital camera 10 of the first embodiment, an analog imaging signal is output from the CCD imager 18 at the first frame rate = 30 fps, and when the through image is displayed on the display unit 46 at the second frame rate = 29 fps, One frame is allocated once per second, that is, one frame out of 30 frames in order to acquire a digital dark signal for correcting the digital imaging signal. On the other hand, in the digital camera 50 according to the second embodiment, when it is determined that there is a strong movement based on the output of the movement amount detection circuit 52, the above-described correction process is not performed for one second. That is, the process of assigning one frame out of 30 frames per second to obtain a digital dark signal for correcting the digital imaging signal for 29 frames is not performed. The first frame rate of the analog imaging signal output from the CCD imager 18 is equal to the second frame rate of the analog video signal output to the display 46.

  The reason why such correction processing is not performed is that if one frame out of 30 frames output from the CCD imager 18 is allocated to acquire a digital dark signal when the subject moves strongly, the display 46 This is because the user who sees the video displayed on the screen may feel uncomfortable with the lack of one frame.

  Hereinafter, the procedure of the correction process in the digital camera 50, particularly the CPU 32 and the correction processing circuit 26 based on the motion amount V when displaying the through image having the first frame rate of 30 fps will be described with reference to the flowcharts of FIGS. explain.

  When shifting to the mode for displaying the through image, the CPU 32 sets the variable R to 1 in step S51 (R = 1), and proceeds to step S53. In step 53, the analog image signal of the R frame is output from the CCD imager 18. In step S 54, the CPU 32 transfers the digital image signal of the R frame to the motion amount detection circuit 52, detects the motion amount V of the previous and subsequent frames output from the motion amount detection circuit 52, and stores it in the SDRAM 34.

  In step S55, it is determined whether or not the variable R is 3. If NO is determined in step S55, the process proceeds to step S57, 1 is incremented to R (R = R + 1), and the process returns to step S53. If YES is determined in the step S55, the process proceeds to a step S59 so as to calculate a motion amount V13 between the first frame and the third frame from a plurality of motion amounts V stored in the SDRAM 34.

  Next, it progresses to step S61, and it is discriminate | determined whether the motion amount V13 is larger than threshold value Tha, and when YES, it progresses to step S65, and when NO, it progresses to step S63. In step S65, the analog image signal of the R frame is output from the CCD imager 18. In step S67, it is determined whether or not the variable R is 30. If NO is determined in step S67, the process proceeds to step S69, 1 is incremented to the variable R (R = R + 1), and the process returns to step S65. If YES is determined in the step S67, the process returns to the step S51 and the variable R is set to 1.

  In step S63, the process shown in the flowchart of FIG. 10 is performed. After step S61, the process proceeds to step S71, where the variable P is set to R (P = R). And it progresses to step S73 and performs the same process as step S3-step S27 shown to the flowchart of FIG. 6 and FIG. 7 of Example 1. FIG. After step S73, the process proceeds to step S75, where it is determined whether the variable P is 30 or not. If NO is determined in step S75, the process returns to step 73, and steps S3 to S27 of the first embodiment are repeated again. If YES is determined, the process returns to step S51 and the variable R is set to 1 (R = 1).

  As described above, the digital camera 50 according to the second embodiment does not execute the correction process when the movement amount of the analog imaging signal sequentially output from the CCD imager 18 is large, that is, when the movement of the subject is intense, and the first frame rate is set. Since the analog video signal can be output to the display 46 at the same second frame rate, the user can watch the through image without feeling uncomfortable.

  FIG. 11 is a block diagram of the digital camera 80 according to the third embodiment. The digital camera 80 according to the third embodiment is a digital camera 10 according to the first embodiment further including a luminance detection circuit 82. Therefore, the functions of the digital camera 10 described in the first embodiment are also applied in the third embodiment. In the third embodiment, only functions different from the first embodiment will be described.

  The luminance detection circuit 82 operates according to an instruction from the CPU 32. In this operation, the average luminance for one frame is detected from the digital image signal for each frame sequentially output from the signal processing circuit 27.

  In the digital camera 10 of the first embodiment, when the analog image pickup signal is output from the CCD imager 18 at the first frame rate = 30 fps and the through image is displayed on the display 46 at the second frame rate = 29 fps, One frame per second, that is, one frame out of 30 frames is allocated to acquire a digital dark signal for correcting the digital imaging signal. In the digital camera 50 of the second embodiment, the amount of motion is If it is determined that there has been intense movement based on the output of the detection circuit 52, the above-described correction processing is not performed for 1 second. That is, the process of assigning one frame out of 30 frames per second to obtain a digital dark signal for correcting the digital imaging signal for 29 frames is not performed. The first frame rate of the analog imaging signal output from the CCD imager 18 is equal to the second frame rate of the analog video signal output to the display 46.

  The reason for not performing such correction processing is that when the user views the analog video signal displayed on the display 46 based on the analog imaging signal output from the CCD imager 18 of a bright subject, the imaging device It is difficult to feel the influence of noise existing in a certain CCD imager 18. Therefore, in the second embodiment, priority is given to setting the second frame rate of the analog video signal output to the display unit 46 to the first frame rate over the correction process.

  Further, when a user views an analog video signal based on an analog imaging signal output from the CCD imager 18 of a dark subject, the CDS / AGC circuit 21 often performs an adjustment to increase the gain. Since the analog dark signal is also gained up, the user can easily feel the influence of noise. Therefore, when an analog image signal of a dark subject is output from the CCD imager 18, it is better to perform correction processing.

  Hereinafter, the procedure of correction processing in the digital camera 80, particularly the CPU 32 and the correction processing circuit 26 when displaying a through image with a first frame rate of 30 fps will be described with reference to the flowcharts of FIGS.

  When shifting to the mode for displaying the through image, the CPU 32 sets the variable U to 1 in step S81 (U = 1), and proceeds to step S83. In step 83, the analog image signal of the U frame is output from the CCD imager 18. In step S85, the average luminance B of the U frame is detected and stored in the SDRAM 34. Here, when U = 1, average brightness B is stored as brightness B1, when U = 2, average brightness B is stored as brightness B2, and when U = 3, average brightness B is stored as brightness B3. .

  Then, the process proceeds to step S87 to determine whether or not the variable U is 3. If NO is determined in the step S87, the process proceeds to a step S91 to increment the variable U by 1 (U = U + 1), and the process returns to the step S83. If YES is determined in the step S87, the process proceeds to a step S89 so as to compare the brightness B1, B2, B3 with the threshold Thb.

  Next, the process proceeds to step S95, and it is determined whether or not each of the luminances B1, B2, and B3 is greater than the threshold value Thb. If YES is determined in the step S95, the process proceeds to a step S97 so as to output the analog image signal of the U frame from the CCD imager 18. Then, the process proceeds to step S99 to determine whether or not the variable U is 30. If YES is determined in the step S99, the process returns to the step S81. If NO is determined, the variable U is incremented by 1 (U = U + 1) in a step S101, and the process returns to the step S97.

If NO is determined in step S95, the process proceeds to step S103. In step S103, the process shown in the flowchart of FIG. 13 is performed. After step S95, the process proceeds to step S105, and the variable P is set to U (P = U). Then, the process proceeds to step S107.
The same processing as steps S3 to S27 shown in the flowcharts of FIGS. 6 and 7 of the first embodiment is executed. After step 107, the process proceeds to step S109, where it is determined whether or not the variable P is 30. If YES is determined, the process returns to step S81, and if NO is determined, the process returns to step S107.

  As described above, in the digital camera 80 according to the third embodiment, when the average luminance of the analog imaging signal of each frame that is sequentially output from the CCD imager 18 is high, the second frame equal to the first frame rate is not performed without performing the correction process. Since the analog video signal can be output to the display 46 at the frame rate, the user can watch the through image without feeling much influence of noise.

  In the above description of the first to third embodiments, correction processing when displaying a through image on the display device 4 has been described. However, the correction processing can also be applied to recording a moving image on the external memory card 40. When the frame rate of the moving image is 60 fps, one frame out of 60 frames output from the CCD imager 18 per second is allocated to acquire a digital dark signal, and 59 frames are recorded on the external memory card 40. Allocate to acquire digital imaging signal. When the digital image signal recorded on the external memory card 40 is reproduced, the CPU 32 controls to display 59 images on the display 46 per second. Instead of allocating and updating one frame every second to acquire a digital dark signal, one frame may be allocated and updated to acquire a digital dark signal per minute. In the latter case, the number of frames allocated for acquiring a digital dark signal is reduced, so that more moving image data can be recorded. When reproducing the moving image data recorded in the external memory card 40, the CPU 32 performs an expansion process on the digital compressed image in the image compression / decompression processing unit 36, and a D / A converter 42, a video. Analog video data is displayed on the display 46 through the encoder 44. When one frame is allocated to acquire a digital dark signal per minute and the digital compressed image signal subjected to the correction process is displayed on the display 46, the CPU 32 displays 3599 images per minute. Take control.

  As described above, according to the first embodiment, when displaying a through image or capturing a long-time moving image, the dark signal level of the image sensor is periodically detected, and the clamp area of the image sensor is effective. Since correction processing is performed with different correction methods based on the dark signal level of the area, an image signal that is not affected by the dark signal can be obtained even if the environment of the image sensor changes.

  In the digital camera of this embodiment, a CCD imager is used as an image pickup element for outputting an analog image pickup signal. However, a CMOS imager is also applicable.

  Further, in the digital camera 50 of the second embodiment and the digital camera 80 of the third embodiment, as a condition for not performing the correction process, in the second embodiment, there is a case where there is a severe movement between sequentially output frames. In this case, all the subjects in the frames that are sequentially output are bright, but the conditions for performing the correction process and not performing the correction process may be designed by combining these conditions.

  Further, in the digital camera 50 of the second embodiment, the plurality of frames used for detecting intense motion is three frames, but any number of frames may be used. Similarly, in the digital camera 80 of the third embodiment, the plurality of frames used for determining that the subject is bright is three frames, but any number of frames may be used.

  In the digital camera of this embodiment, the digital dark signal is generated by reading the vertical transfer register 102 without reading the charge of the photodiode 100 in the CCD imager 18, but the diaphragm 14 is closed or illustrated. By closing the mechanical shutter, photoelectric conversion is performed without causing the photodiode 100 to receive light, and the charge of the photodiode 100 is transferred to the vertical transfer register 102 by the readout pulse of SG20, and is output as an analog dark signal from the CCD imager 18. A dark signal may be generated. In this case, since not only the dark signal present in the vertical transfer register 102 but also the dark signal present in the photodiode 100 can be taken into account, further appropriate correction processing can be performed.

  In this embodiment, the first frame rate is set to 30 fps and the second frame rate is set to 29 fps. However, the present invention is not limited to this.

  In this embodiment, the correction process is performed by the CPU 32 and the correction processing circuit 26. However, the CPU 32 may execute all the processes. In this case, the correction processing circuit 26, which is a component of the digital camera, is not necessary, and the CPU 32 executes all the correction processing executed by the CPU 32 and the correction processing circuit 26 shown in FIGS. Explaining the case where the CPU 32 performs the processing executed in the correction processing circuit 26, the digital dark signal for one frame output from the A / D converter 24 includes a register F separately connected to the bus 28. Stored in SRAM. The CPU 32 detects and compares the average dark signal level from the digital dark signal in the clamp area and the digital dark signal in the effective area from the digital dark signal for one frame. If the dark signal level in the clamp area is high as a result of the comparison, the flag of the register F in the SRAM is set (F = 1). If the dark signal level in the effective area is high, the flag of the register F in the SRAM is set. Reset (F = 0). Then, the CPU 32 subtracts the digital dark signal from the digital image pickup signals of the second and subsequent frames when F = 1, and adds the digital dark signal to the digital image pickup signals of the second and subsequent frames when F = 0.

1 is a block diagram illustrating a digital camera according to a first embodiment. FIG. 3 is a block diagram illustrating a correction processing circuit included in the digital camera according to the first embodiment. It is an illustration figure which shows pixel arrangement | positioning of the CCD imager which concerns on a present Example. It is an illustration figure which shows the inside of the CCD imager which concerns on a present Example. FIG. 5 is an illustrative view showing exposure timing when outputting an analog imaging signal from the CCD imager 18 at a frame rate of 30 fps in the digital camera according to the present embodiment and pulses output from the signal generator to the CCD imager 18. 3 is a flowchart illustrating a part of correction processing of the digital camera according to the first embodiment. 6 is a flowchart showing a part of a correction process following the flowchart shown in FIG. 5. FIG. 6 is a block diagram illustrating a digital camera according to a second embodiment. 10 is a flowchart illustrating a part of correction processing of the digital camera according to the second embodiment. FIG. 9 is a flowchart showing a part of a correction process following the flowchart shown in FIG. 8. FIG. FIG. 6 is a block diagram illustrating a digital camera according to a third embodiment. 10 is a flowchart illustrating a part of correction processing of the digital camera according to the third embodiment. 12 is a flowchart showing a part of a correction process following the flowchart shown in FIG. 11.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Digital camera 14 ... Aperture 16 ... Motor drive part 18 ... CCD imager 20 ... Signal generator (SG)
22 ... Clamp circuit 24 ... A / D converter 26 ... Correction processing circuit 26a ... Integration / comparison circuit 26b ... SRAM
26c ... Subtractor 26d ... Adder 28 ... Bus 32 ... CPU
34 ... SDRAM
36: Image compression / processing unit 42: D / A converter 44: Video encoder 44
46 ... Display device 50 ... Digital camera 52 ... Motion detection circuit 80 ... Digital camera 82 ... Luminance detection circuit SW1 ... Switch SW2 ... Switch

Claims (8)

An optical black area and an effective area are formed adjacent to each other, and a photoelectric conversion element arranged over a plurality of rows for both areas and a photoelectric conversion output from the photoelectric conversion element arranged adjacent to the photoelectric conversion element are received. A vertical transfer register for transferring charges including the photoelectric conversion output in the vertical direction; and a horizontal transfer register connected to an end of the vertical transfer register for transferring charges transferred from the vertical transfer register in the horizontal direction. Imaging means for outputting as an imaging signal;
Driving the imaging signal so as to sequentially output the imaging signal at a predetermined frame rate by controlling the transfer of the photoelectric conversion output from the photoelectric conversion element to the vertical transfer register and the transfer of the charge in the vertical and horizontal registers. Drive control means for controlling;
In a state in which transfer of photoelectric conversion output to the vertical transfer register is prohibited, charge transfer is performed in the vertical and horizontal registers, and dark signal detection processing that is output from the horizontal transfer register as a dark signal detection value is periodically executed. Dark signal detection means for updating the dark signal detection value;
The dark signal detection value is divided into a first dark signal detection value corresponding to the optical black area and a second dark signal detection value corresponding to the effective area, and the first dark signal detection value and the second dark signal detection are divided. A comparison means for comparing values;
An image pickup apparatus comprising: a correction unit that performs a correction process according to a result of comparison by the comparison unit using the dark signal detection value for a video signal based on the image pickup signal. Exposure control means for controlling exposure of the photoelectric conversion element;
An imaging means for outputting an optical black conversion area and an effective area adjacent to each other, and outputting a photoelectric conversion output from the photoelectric conversion element arranged for both areas as an imaging signal;
Drive control means for driving and controlling the imaging means so as to sequentially output the imaging signals at a predetermined frame rate;
Dark signal detection means for periodically executing a dark signal detection process for outputting the imaging signal in a state where exposure is prohibited in the exposure control means and outputting from the imaging means as a dark signal detection value to update the dark signal detection value When,
The dark signal detection value is divided into a first dark signal detection value corresponding to the optical black area and a second dark signal detection value corresponding to the effective area, and the first dark signal detection value and the second dark signal detection are divided. A comparison means for comparing values;
An image pickup apparatus comprising: a correction unit that performs a correction process according to a result of comparison by the comparison unit using the dark signal detection value for a video signal based on the image pickup signal. A clamp means for detecting a clamp level based on the optical black area of the image pickup signal output from the image pickup means and performing a clamp process on the image pickup signal with the clamp level as a reference black level;
The imaging apparatus according to claim 1, wherein the video signal is a signal based on an imaging signal after the clamp processing is performed.   The correction means performs a subtraction process to subtract the dark signal detection value from the video signal when the first dark signal detection value is larger than the second dark signal detection value as a result of comparison by the comparison means, and the comparison 2. An addition process for adding the dark signal detection value to the video signal when the second dark signal detection value is larger than the first dark signal detection value as a result of the comparison by the means. The imaging device according to claim 3. Detecting means for comparing a plurality of video signals output in succession to detect the amount of motion before and after;
Comparison means for comparing whether the amount of movement exceeds a threshold;
5. The apparatus according to claim 1, further comprising first control means for performing control so that the dark signal detection processing is not executed when the amount of motion exceeds a threshold value as a result of comparison by the comparison means. The imaging device according to any one of the above. Luminance detection means for detecting luminance based on the video signal;
A comparison means for comparing whether the luminance exceeds a threshold;
6. The apparatus according to any one of claims 1 to 5, further comprising second control means for performing control so that the dark signal detection processing is not executed when the luminance exceeds as a result of comparison by the comparison means. Any imaging device. An optical black area and an effective area are formed adjacent to each other, and a photoelectric conversion element arranged over a plurality of rows for both areas and a photoelectric conversion output from the photoelectric conversion element arranged adjacent to the photoelectric conversion element are received. A vertical transfer register for transferring charges including the photoelectric conversion output in the vertical direction; and a horizontal transfer register connected to an end of the vertical transfer register for transferring charges transferred from the vertical transfer register in the horizontal direction. An imaging method comprising imaging means for outputting as an imaging signal,
Driving the imaging means to sequentially output the imaging signals at a predetermined frame rate by controlling the transfer of photoelectric conversion output from the photoelectric conversion element to the vertical transfer register and the transfer of the charge in the vertical and horizontal registers. Controlling step;
In a state in which transfer of photoelectric conversion output to the vertical transfer register is prohibited, charge transfer is performed in the vertical and horizontal registers, and dark signal detection processing that is output from the horizontal transfer register as a dark signal detection value is periodically executed. Updating the dark signal detection value,
The dark signal detection value is divided into a first dark signal detection value corresponding to the optical black area and a second dark signal detection value corresponding to the effective area, and the first dark signal detection value and the second dark signal detection are divided. A comparison step for comparing values;
An imaging method comprising a step of performing a correction process according to a comparison result by the comparison step on the video signal based on the imaging signal using the dark signal detection value. An exposure control means for controlling exposure of the photoelectric conversion element, an optical black area and an effective area are formed adjacent to each other, and a photoelectric conversion output from the photoelectric conversion element arranged for both areas is output as an imaging signal. An imaging method comprising an imaging means,
Drive control to sequentially output the imaging signal at a predetermined frame rate;
Outputting the imaging signal in a state where exposure is prohibited and periodically performing dark signal detection processing as a dark signal detection value to update the dark signal detection value;
The dark signal detection value is divided into a first dark signal detection value corresponding to the optical black area and a second dark signal detection value corresponding to the effective area, and the first dark signal detection value and the second dark signal detection are divided. An imaging method comprising a comparison step of comparing values and a step of performing a correction process according to a result of the comparison in the comparison step using the dark signal detection value on the video signal based on the imaging signal.