JP2013058856A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance correction accuracy of image deterioration by a dark current, while suppressing the increase of power consumption.SOLUTION: A temperature sensor 13 obtains a detection temperature according to the temperature of an imaging device 4. Signals stored in a plurality of pixels of the imaging device 4 during a first storage period in an exposure state are read out as first image signals. Signals stored in the plurality of pixels during a second storage period in a light-shielding state after the first storage period are read out as second image signals. Based on the detection temperature from the temperature sensor 13, a CPU 6 obtains a first estimation value as an estimation value of a total dark current amount in the first storage period, and a second estimation value as an estimation value of a total dark current amount in a period from the start of the second storage period to the present. The CPU 6 terminates the second storage period when the second estimation value becomes a value having predetermined relationship to the first estimation value. Based on the second image signals, the CPU 6 corrects the first image signals.

Description

  The present invention relates to an imaging apparatus.

  In an imaging device such as a digital camera or a video camera, a CCD or a CMOS image sensor is generally used as an imaging device. As a characteristic of the image pickup device, it is well known that dark current becomes fixed pattern noise and deteriorates the image quality of the picked up image.

  The following methods are known as methods for correcting image degradation due to dark current. In other words, since the dark current increases or decreases according to the temperature of the image sensor and the signal accumulation time, immediately after the actual shooting operation, the dark current is darkened by performing the accumulation operation for the same time as the actual shooting with the entire image sensor shielded from light. An image of only current components (dark image) is obtained. Then, by subtracting the image signal of only the dark current component from the actual photographed image signal (actual image), it is possible to reduce the deterioration of the image quality due to the fixed pattern noise due to the dark current including the temperature change and the accumulation time.

  However, the image sensor temperature rises due to, for example, live view or movie shooting. However, when still image shooting is performed immediately thereafter, the image sensor temperature is drastically lowered because the image sensor is generally driven with low power consumption. . Even if it is not immediately after live view or moving image shooting, the temperature of the imaging element may be lowered due to a change in environmental temperature. In these cases, if the storage time of the actual photographing operation (the storage time of the exposure state) and the storage time of the light shielding state are the same as in the above method, compared to the total dark current amount during the storage time of the exposure state, The total dark current amount during the accumulation time in the light-shielded state decreases, and the dark current component indicated by the image signal obtained in the light-shielded state decreases with respect to the dark current component in the image signal obtained in the actual shooting operation. As a result, the accuracy of correcting image degradation due to dark current is reduced.

  Therefore, in the imaging device disclosed in Patent Document 1 below, during still image shooting after live view or moving image shooting, after the actual shooting operation, driving similar to the live view or moving image shooting is performed, and the accumulation operation in the light shielding state is performed. By making the image sensor temperature at the start of the image sensor temperature substantially the same as the actual image capturing operation (exposure state accumulation operation), the dark current component in the image signal obtained by the actual image capturing operation is The correlation of the dark current component indicated by the image signal obtained in the light-shielded state is increased, and the correction accuracy of the image deterioration due to the dark current is increased.

JP 2010-118963 A

  However, in the imaging apparatus disclosed in Patent Document 1, driving for making the imaging element temperature at the start of the light-shielding state accumulation operation substantially the same as the imaging element temperature at the start of the actual imaging operation after the actual imaging operation. Since (driving for temperature adjustment) is performed, there is a problem that power consumption increases accordingly.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an imaging apparatus capable of improving the correction accuracy of image degradation due to dark current while suppressing an increase in power consumption.

  The following aspects are presented as means for solving the problems. An imaging device according to a first aspect includes an imaging element having a plurality of pixels, temperature detection means for obtaining a detection temperature corresponding to the temperature of the imaging element, and accumulation in the plurality of pixels in a first accumulation period of an exposure state. The read signal is read out as the first image signal, and the signals accumulated in the plurality of pixels in the second accumulation period in the light-shielded state after the first accumulation period are read out as the second image signal. As described above, a first estimated value that is an estimated value of the total dark current amount in the first accumulation period is obtained based on the control unit that controls the image sensor and the detected temperature from the temperature detecting unit. And obtaining a second estimated value that is an estimated value of the total dark current amount in the period from the start of the second accumulation period to the present based on the detected temperature from the temperature detecting means. 2 estimated value acquisition And an end means for ending the second accumulation period when the second estimated value becomes a value having a predetermined relationship with the first estimated value, and based on the second image signal. And correcting means for correcting the first image signal so that a dark current component in the first image signal is reduced.

  In the imaging device according to a second aspect, in the first aspect, the first estimated value acquisition unit sequentially acquires detected temperatures from the temperature detection unit in the first accumulation period, and these acquired The first estimated value is acquired based on the detected temperature, and the second estimated value acquiring means sequentially acquires the detected temperature from the temperature detecting means in the second accumulation period, and the second accumulation period. Each time the detected temperature is acquired after the start of, the second estimated value is acquired based on the detected temperature acquired so far in the second accumulation period.

  In the imaging device according to a third aspect, in the second aspect, the first and second estimated value acquisition means use a reference table or a calculation formula indicating a relationship between the detected temperature and the dark current amount, The first or second estimated value is obtained by obtaining the dark current amount corresponding to the detected temperature and integrating the dark current amount corresponding to each detected temperature.

  The imaging device according to a fourth aspect has the predetermined relationship with respect to the first estimated value when a is a value greater than 0 and equal to or less than 1 in any of the first to third aspects. The value is within a predetermined range based on a value a times the first estimated value, a value not less than a value a times the first estimated value, or a value a times the first estimated value. Is the value of.

  Note that a may be, for example, 0.25 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.75 or more, or 1 .

  The imaging device according to a fifth aspect is the imaging device according to the fourth aspect, wherein the correction unit subtracts a signal obtained by multiplying the second image signal by 1 / a from the first image signal. The image signal is corrected.

  In the imaging device according to a sixth aspect, in any one of the first to fifth aspects, the control unit reads the second image signal when the first estimated value is equal to or less than a predetermined value. While stopping, the second estimated value acquisition means, the end means, and the correction means stop operating.

  In the imaging device according to a seventh aspect, in any one of the first to sixth aspects, the ending unit is a value in which the second estimated value has the predetermined relationship with respect to the first estimated value. If the second accumulation period is not less than a predetermined time, the second accumulation period is terminated.

  In the imaging device according to an eighth aspect, in the seventh aspect, when the first estimated value is A and the latest second estimated value is B, the correcting means is the first The first image signal is corrected by subtracting a signal obtained by multiplying the second image signal by A / B from the image signal.

  ADVANTAGE OF THE INVENTION According to this invention, the imaging device which can raise the correction precision of the image degradation by dark current can be provided, suppressing the increase in power consumption.

1 is a schematic block diagram illustrating an imaging apparatus according to an embodiment of the present invention. It is a figure which shows typically the general temperature dependence of the dark current amount per unit time of an image pick-up element. It is a figure which shows an example of the reference table which shows the correspondence of imaging element temperature and the amount of dark current per unit time. It is a figure which shows typically an example of transition of image sensor temperature and the amount of dark current per unit time when performing still image photography immediately after live view or moving image photography. It is a figure which shows typically an example of transition of image pick-up element temperature and the amount of dark current per unit time when environmental temperature changes during still image photography which is not immediately after live view or video recording. 3 is a schematic flowchart showing still image shooting operation of the imaging apparatus shown in FIG. 1. 6 is another schematic flowchart showing still image shooting operation of the imaging apparatus shown in FIG. 1. 7 is still another schematic flowchart showing still image shooting operation of the imaging apparatus shown in FIG. 1.

  Hereinafter, an imaging device according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic block diagram showing an imaging apparatus 1 according to an embodiment of the present invention. The imaging device 1 according to the present embodiment is configured as a so-called digital camera, but may be another imaging device.

  The imaging apparatus 1 according to the present embodiment includes a photographic lens 2, a mechanical shutter 3, an imaging element 4, an A / D conversion unit 5, a CPU 6, an imaging control unit 7, a memory 8, and a recording medium 9. A recording unit 10 that is detachably mounted, a display unit 11 such as a rear liquid crystal panel, an operation unit 12 such as a release button, and a temperature sensor 13 serving as a temperature detection unit that obtains a detection temperature according to the temperature of the image sensor 4. And.

  The photographic lens 2 is driven by a lens control unit (not shown) to focus and stop under the control of the CPU 6. In the image space of the photographic lens 2, the imaging surface of the imaging element 4 is arranged. The mechanical shutter 3 is provided between the photographic lens 2 and the image sensor 4 and performs exposure control of the image sensor 4 under the control of the CPU 6.

  The imaging element 4 has a plurality of pixels (not shown) arranged in a two-dimensional shape, is driven by a control signal output from the imaging control unit 7, and outputs a signal. As the imaging device 4, for example, a CMOS image sensor or a CCD image sensor is used. Under the control of the CPU 6, the imaging control unit 7 uses signals accumulated in a plurality of pixels of the imaging device 4 in the first accumulation period (main image accumulation period) in the exposure state as first image signals (main images). Signals that are read out and accumulated in a plurality of pixels of the image sensor 4 in the second accumulation period (dark image accumulation period) in a light-shielded state after the first accumulation period (main image accumulation period) The image sensor 4 is controlled so as to be read out as an image signal (dark image). In the present embodiment, each image signal read out and output from the image sensor 4 is an analog signal and is converted into a digital signal by the A / D conversion unit 5. The main image and the dark image converted into digital signals are temporarily stored in the memory 8 under the control of the CPU 6. The A / D converter 5 may be mounted on the image sensor 4.

  In the following description, the accumulation operation of the main image (the accumulation operation in the exposure state) may be referred to as the main exposure, and the accumulation operation of the dark image (the accumulation operation in the light shielding state) may be referred to as the dark exposure. In addition, the main image accumulation period may be referred to as a main exposure period, and the dark image accumulation period may be referred to as a dark exposure period.

  The temperature sensor 13 directly or indirectly detects the temperature of the image sensor 4 and outputs detected temperature data indicating a detected temperature corresponding to the temperature of the image sensor 4. This detected temperature data is supplied to the CPU 6. The temperature sensor 13 may be disposed in the vicinity of the image sensor 4 or may be built in the image sensor 4.

  FIG. 2 is a diagram schematically showing a general temperature dependency of the dark current amount per unit time of the image sensor 4. As shown in FIG. 2, the amount of dark current generated in the unit time of the image sensor 4 tends to increase exponentially as the element temperature increases. In the present embodiment, a reference table showing a correspondence relationship between detected temperature data from the temperature sensor 13 and dark current amount per unit time of the image sensor 4 according to the characteristics of the image sensor 4 as shown in FIG. Lookup table) is stored in the memory 8 in advance. FIG. 3 shows an example of the reference table.

  Although the temperature dependence of the dark current amount per unit time as shown in FIG. 2 varies for each pixel of the image sensor 4, the reference table may be created from data actually measured for one pixel, for example. Alternatively, it may be created by an average value of data actually measured for a predetermined number of pixels. The reference table does not necessarily have to be created from data actually measured for the image sensor 4 actually used, but may be created from data actually measured for the same kind of image sensor as the image sensor 4 actually used. You may create from a value etc. Since the reference table is used to estimate the total dark current amount for determining the dark exposure period, as will be described later, the accuracy of the dark current amount per unit time with respect to the temperature detected by the temperature sensor 13 is: High accuracy is not necessarily required.

  Instead of the reference table, a calculation formula indicating the correspondence between the detected temperature data from the temperature sensor 13 and the dark current amount per unit time of the image sensor 4 is prepared in advance. The amount of dark current per unit time corresponding to the detected temperature data may be obtained by calculating using the above formula.

  The imaging device 1 according to the present embodiment is capable of performing live view and moving image shooting in the same manner as a known imaging device, in addition to still image shooting described later. The live view is an operation mode in which an image repeatedly captured by the image sensor 4 is displayed on the display unit 11 as a moving image in real time. Movie shooting is an operation mode in which an image repeatedly captured by the image sensor 4 is recorded on the recording medium 9 by the recording unit 10 as a moving image.

  FIG. 4 is a schematic diagram illustrating an example of the transition of the temperature of the image sensor 4 and the amount of dark current per unit time when still image shooting is performed immediately after live view or moving image shooting in the imaging device 1 according to the present embodiment. FIG. The broken line in FIG. 4 shows the transition of the temperature of the image sensor 4, and the solid line in FIG. 4 shows the transition of the dark current amount per unit time.

  As shown in FIG. 4, during live view or moving image shooting, the image sensor 4 generates a large amount of heat, so the temperature of the image sensor 4 rises with time. Therefore, the amount of dark current generated in the unit time of the image sensor 4 increases as the temperature of the image sensor 4 increases due to the characteristics shown in FIG. When still image shooting is started immediately after live view or moving image shooting, the power consumption of the image sensor 4 shifts to a low state, so that the temperature of the image sensor 4 decreases toward the environmental temperature and the unit time per unit time. The amount of dark current also decreases sharply.

  FIG. 5 shows the temperature of the image sensor 4 and the dark current amount per unit time when the environmental temperature changes during still image shooting that is not immediately after live view or moving image shooting in the imaging device 1 according to the present embodiment. It is a figure which shows an example of transition typically. In FIG. 5, since the still image shooting is started not after the live view or the moving image shooting but after the state where the power consumption of the image sensor 4 is low continues for a relatively long time, the still image shooting is started from the start of the still image shooting. Even during shooting, the temperature of the image sensor 4 is a temperature corresponding to the environmental temperature. In FIG. 5, the environmental temperature decreases from the middle of dark exposure for still image shooting, and the temperature of the image sensor 4 decreases accordingly from the middle of dark exposure for still image shooting. Note that the vertical scale in FIG. 5 is an enlargement of the vertical scale in FIG.

  4 and 5, in still image shooting, dark exposure is performed after main exposure. 4 and 5, the area RA of the main exposure period (main image accumulation period) corresponds to the total dark current amount in the main exposure period, and the area RB of the dark exposure period (dark image storage period). The area corresponds to the total dark current amount during the dark exposure period.

  In the situation shown in FIG. 4 and the situation shown in FIG. 5, if the dark exposure period is made the same as the main exposure period as in the conventional technique described above, the area of the region RB (that is, the total dark current amount in the dark exposure period). Is smaller than the area of the region RA (that is, the total dark current amount in the main exposure period), the dark current component in the main image (dark current component in the image signal obtained by the actual photographing operation) The correlation of the dark current component indicated by the dark image (dark current component indicated by the image signal obtained in the light-shielded state) is lowered, and as a result, the correction accuracy of the image deterioration due to the dark current is lowered.

  On the other hand, in the present embodiment, as shown in FIGS. 6 to 8 described later, the CPU 6 performs the total dark current amount (area of the region RA) in the main exposure period based on the detected temperature data from the temperature sensor 13. Is obtained (first estimated value) A, and based on the detected temperature data from the temperature sensor 13, the estimated value (second estimated value) of the total dark current amount in the period from the start of the dark exposure period to the present ) B is acquired, and the dark exposure period is terminated when the estimated value B becomes a value having a predetermined relationship with the estimated value A. Therefore, according to the present embodiment, even in the situation shown in FIG. 4 or the situation shown in FIG. 5, the dark current component in the main image (the dark current component in the image signal obtained by the actual photographing operation). ) With respect to the dark current component (dark current component indicated by the image signal obtained in the light-shielded state) indicated by the dark image increases, and thus the correction accuracy of the image deterioration due to the dark current increases.

  6 to 8 are schematic flowcharts showing still image shooting operations of the imaging apparatus 1 according to the present embodiment.

  When the still image shooting mode is started, the CPU 6 first determines whether or not a release button (not shown) in the operation unit 12 is half-pressed (step S1). Wait until. When the release button is half-pressed, the CPU 6 performs automatic focus adjustment, automatic exposure control, etc., and sets shooting conditions (including the length of the main exposure period) used for shooting the main image (step S2). Subsequently, the CPU 6 determines whether or not the release button is fully pressed (step S3), and waits until the release button is fully pressed.

  When the release button is fully pressed, the CPU 6 determines whether or not dark current correction (correction of the main image based on the dark image) is performed (step S4). For example, it is determined that dark current correction is performed when the length of the main exposure period set in step S2 is longer than a predetermined length (that is, when the set shooting condition is long exposure), and when not so It may be determined that dark current correction is not performed. This is greatly affected by dark current and dark current unevenness in the case of long exposure, but is hardly affected by dark current and dark current unevenness in the case of short exposure, so dark current correction is not necessarily required. This is because it is possible to shoot as it is. The determination in step S4 is not limited to this, and it may be determined whether or not dark current correction is performed according to a user setting (setting whether or not dark current correction is performed) by the operation unit 12. Whether or not the dark current correction is automatically performed may be determined from the various determination data.

  If it is determined in step S4 that dark current correction is not performed, the CPU 6 opens the shutter 3 to place the image sensor 4 in an exposure state, and once resets the image sensor 4 via the image capture controller 7, The accumulation operation (main exposure) of the main image is started (step S5). Next, the CPU 6 determines whether or not the length of the main exposure period (the set accumulation time of the main image) set in step S2 has elapsed since the start of the main exposure in step S5 (step S2). S6) If it has not passed, wait until it passes.

  If it is determined in step S6 that the storage time of the main image set in step S2 has elapsed, the CPU 6 closes the shutter 3 to end the storage of the main image (main exposure) (step S7), and the imaging control. The main image is output from the image sensor 4 via the unit 7 (step S8). The main image read out as an analog signal is converted into a digital signal by the A / D converter 5 and then temporarily stored in the memory 8 under the control of the CPU 6.

  Next, the CPU 6 causes the recording unit 10 to record the main image read in step S8 and stored in the memory 8 on the recording medium 9 (step S9), and ends still image shooting.

  Thus, if it is determined in step S4 that dark current correction is not performed, only the main image is acquired and the main image is recorded on the recording medium 9.

  If it is determined in step S4 that dark current correction is to be performed, the CPU 6 resets the estimated value A stored in advance in the memory 8 to 0 (step S11).

  Next, the CPU 6 opens the shutter 3 to place the image pickup device 4 in an exposure state, and once resets the image pickup device 4 via the image pickup control unit 7 to start the accumulation operation (main exposure) of the main image. (Step S12).

  Next, the CPU 6 determines whether or not the present time is the timing (detected temperature acquisition timing) for acquiring the detected temperature data from the temperature sensor 13 (step S13). Wait until In the present embodiment, the detected temperature acquisition timing comes at a constant time period from the time when the main exposure is started in step S12. The cycle of the detected temperature acquisition timing may be fixed or arbitrarily settable.

  If it is determined in step S13 that it is the detected temperature acquisition timing, the CPU 6 acquires detected temperature data from the temperature sensor 13 (step S14). Next, the CPU 6 refers to a reference table as shown in FIG. 3 stored in advance in the memory 8 and acquires the dark current amount per unit time corresponding to the detected temperature data acquired in Step S14 (Step S14). S15) A value obtained by adding the dark current amount to the current estimated value A is set as a new value of the estimated value A (step S16).

  Next, the CPU 6 determines whether or not the length of the main exposure period (the set accumulation time of the main image) set in step S2 has elapsed since the start of the main exposure in step S12 (step S12). S17) If it has not elapsed, the process returns to step S13, and steps S13 to S17 are repeated.

  If it is determined in step S17 that the storage time of the main image set in step S2 has elapsed, the CPU 6 closes the shutter 3 to end the storage (main exposure) of the main image (step S18), and the imaging control. The main image is output from the image sensor 4 via the unit 7 (step S19). The main image read out as an analog signal is converted into a digital signal by the A / D converter 5 and then temporarily stored in the memory 8 under the control of the CPU 6.

  If it is determined in step S17 that the accumulation time of the main image has elapsed, step S16 is no longer repeated, so that the value of the estimated value A is determined, and this determined estimated value A is the total dark current in the main exposure period. This is an estimated value of the amount (corresponding to the area of the region RA in the main exposure period in FIGS. 4 and 5).

  After step S19, the CPU 6 determines whether or not the current estimated value A is less than or equal to a predetermined value (step S20). If it is equal to or smaller than the predetermined value, the CPU 6 causes the recording unit 10 to record the main image read in step S19 and stored in the memory 8 on the recording medium 9 (step S21), and ends still image shooting. If it is determined in step S20 that the current estimated value A is less than or equal to the predetermined value, the dark current component in the main image is small and dark current correction is not necessarily required. The dark current correction is discontinued and the actual image is recorded without obtaining the image. However, in the present invention, steps S20 and S21 may be removed, and after step S19, the process may always be shifted to step S31.

  If it is determined in step S20 that it is not less than the predetermined value, the CPU 6 resets the estimated value B stored in the memory 8 in advance to 0 (step S31).

  Next, the CPU 6 starts the dark image accumulation operation (dark exposure) by temporarily resetting the imaging device 4 via the imaging control unit 7 while keeping the shutter 3 in the closed light-shielding state (step S32). .

  Next, the CPU 6 determines whether or not the present time is the timing (detected temperature acquisition timing) for acquiring the detected temperature data from the temperature sensor 13 (step S33). Wait until In the present embodiment, the detected temperature acquisition timing comes at a constant time period from the time when the main exposure is started in step S32. In the present embodiment, the cycle of the detected temperature acquisition timing is set to be the same as the cycle of the detected temperature acquisition timing in step S13.

  If it is determined in step S33 that it is the detected temperature acquisition timing, the CPU 6 acquires detected temperature data from the temperature sensor 13 (step S34). Next, the CPU 6 acquires a dark current amount per unit time corresponding to the detected temperature data acquired in step S34 by referring to a reference table as shown in FIG. S35) A value obtained by adding the dark current amount to the current estimated value B is set as a new value of the estimated value B (step S36).

  The estimated value B after step S36 is an estimated value of the total dark current amount in the period from the start of the dark exposure period (dark image accumulation period) to the present.

  After step S36, the CPU 6 determines whether or not the current estimated value B is a value having a predetermined relationship with the determined estimated value A (step S37). In the present embodiment, specifically, as this determination, when a is set to a value greater than 0 and less than or equal to 1, the current estimated value B is a value greater than or equal to a value a times larger than the determined estimated value A. It is determined whether or not. However, in the present invention, the determination in step S37 is not limited to this. For example, it may be determined whether or not the current estimated value B is a value a times larger than the determined estimated value A. The current estimated value B is a predetermined range based on a value a times the determined estimated value A (for example, a range of ± 5% with respect to a value a times the determined estimated value A). It may be determined whether or not. Here, a may be 0.25 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.75 or more, or 1, for example. Good.

  In step S37, the current estimated value B is not a value having a predetermined relationship with the determined estimated value A (in this embodiment, the current estimated value B is changed to the determined estimated value A If it is determined that the value is not equal to or greater than the value of a times (a), the process proceeds to step S42.

  In step S42, the CPU 6 determines whether or not the dark image accumulation time (dark exposure time), that is, the elapsed time from the start of dark exposure in step S32 to the present is equal to or longer than a predetermined time. If it is not longer than the predetermined time, the process returns to step S33, and steps S33 to S37 are repeated.

  If it is determined in step S42 that the time is equal to or longer than the predetermined time, the CPU 6 determines in step S37 that the current estimated value B is not a value having a predetermined relationship with the determined estimated value A. Nevertheless, dark image accumulation (dark exposure) is terminated (step S43), and the dark image is output from the image sensor 4 via the imaging control unit 7 (step S44). This dark image read out as an analog signal is converted into a digital signal by the A / D converter 5 and then temporarily stored in the memory 8 under the control of the CPU 6.

  In this way, the dark image accumulation time is cut off at a predetermined time (that is, timed out) because it takes a considerable time until an affirmative determination is made in step S37 because the temperature of the image sensor 4 at the time of dark exposure is low. As a result, the dark exposure time becomes unnecessarily long and the still image capturing operation is delayed unnecessarily, or the process is stopped without affirmative determination in step S37, and more reliably. This is to prevent it. However, in the present invention, steps S42 to S46 may be removed, and if NO in step S37, the process may return to step S33.

  After step S44, the CPU 6 determines that the dark current component in the main image read in step S19 and stored in the memory 8 is based on the dark image read in step S44 and stored in the memory 8. The main image is corrected so as to be reduced, and the corrected image is temporarily stored in the memory 8 (step S45). In the present embodiment, specifically, in step S45, the CPU 6 is read in step S44 and stored in the memory 8 from the main image read in step S19 and stored in the memory 8. An image obtained by subtracting an image obtained by multiplying the dark image by [current estimated value A / current estimated value B] is obtained as a corrected image. Here, the dark image is multiplied by [current estimated value A / current estimated value B] by adjusting the level of the dark current component indicated by the dark image to the level of the dark current component in the main image. This is because the dark current component in the corrected image is further reduced. However, the specific content of the correction process in step S45 is not limited to this. For example, in step S45, the CPU 6 reads in step S44 from the main image read in step S19 and stored in the memory 8. The dark image stored in the memory 8 and subtracted as it is may be obtained as the corrected image. Even in this case, the dark current component in the corrected image can be reduced.

  After step S45, the CPU 6 causes the recording unit 10 to record the corrected image acquired in step S45 and stored in the memory 8 on the recording medium 9 (step S46), and the still image shooting ends.

  In step S37, the current estimated value B becomes a value having a predetermined relationship with the determined estimated value A (in the present embodiment, the current estimated value B is the determined estimated value A If it is determined that the value is equal to or larger than the value of a, the accumulation (dark exposure) of the dark image is terminated (step S38), and the dark image is output from the image sensor 4 via the imaging control unit 7. (Step S39). This dark image read out as an analog signal is converted into a digital signal by the A / D converter 5 and then temporarily stored in the memory 8 under the control of the CPU 6.

  In the present embodiment, if a is set to 1, the dark exposure period is ended when the current estimated value B is equal to the determined estimated value A, and the total dark current in the dark exposure period is reached. The amount is almost the same as the total dark current amount during the main exposure period. 4 and 5 show this example, and the area of the region RB in the dark exposure period (corresponding to the total dark current amount in the dark exposure period) is the area of the region RA in the main exposure period (total in the main exposure period). This corresponds to the amount of dark current). In the present embodiment, if a is set to 0.5, for example, the dark exposure period is ended when the current estimated value B is half of the determined estimated value A, and dark exposure is performed. The total dark current amount in the period is almost half of the total dark current amount in the main exposure period. If a is set to be smaller than 1, the dark exposure period can be shortened as compared with the case where a is set to 1, and as a result, the time required for still image shooting can be shortened.

  After step S39, the CPU 6 determines that the dark current component in the main image read in step S19 and stored in the memory 8 is based on the dark image read in step S39 and stored in the memory 8. The main image is corrected so as to be reduced, and the corrected image is temporarily stored in the memory 8 (step S40). In the present embodiment, specifically, in step S40, the CPU 6 is read in step S39 and stored in the memory 8 from the main image read in step S19 and stored in the memory 8. An image obtained by subtracting an image obtained by multiplying the dark image by 1 / a is obtained as a corrected image. Here, the dark image is multiplied by 1 / a because the dark current component in the corrected image is adjusted by matching the level of the dark current component indicated by the dark image with the level of the dark current component in the main image. This is to further reduce. Of course, the specific content of the correction process in step S40 is not limited to this. Even if a ≠ 1, for example, in step S40, the CPU 6 reads the book read in step S19 and stored in the memory 8. An image obtained by subtracting the dark image read out in step S44 and stored in the memory 8 as it is from the image may be obtained as the corrected image. Even in this case, the dark current component in the corrected image can be reduced.

  After step S40, the CPU 6 causes the recording unit 10 to record the corrected image acquired in step S40 and stored in the memory 8 on the recording medium 9 (step S41), and the still image shooting ends.

  According to the present embodiment, as described above, even in the situation shown in FIG. 4 and the situation shown in FIG. The dark current component indicated by the dark image (the dark current component indicated by the image signal obtained in the light-shielded state) increases in correlation with the dark current component in the dark, and the correction accuracy of the image degradation due to the dark current increases.

  And since the drive for temperature matching performed with the imaging device disclosed by patent document 1 is not performed in this Embodiment, according to this Embodiment, the increase in power consumption can be suppressed. .

  Thus, according to the present embodiment, it is possible to improve the accuracy of correcting image degradation due to dark current while suppressing an increase in power consumption.

  As mentioned above, although embodiment of this invention and its modification were demonstrated, this invention is not limited to these.

  For example, in the above embodiment, when still image shooting is performed immediately after live view or moving image shooting (as shown in FIG. 4), the power consumption of the image sensor 4 is not immediately after live view or moving image shooting. The same process is performed when still image shooting is performed after a small number of states continue for a relatively long time (as shown in FIG. 5). However, the processing content may be appropriately changed between the former case and the latter case. For example, in the latter case, the amount of change in the ambient environment temperature is often relatively small, so that the dark exposure time is unlikely to be long. Accordingly, the “predetermined time” serving as the time-out determination criterion in step S42 in the latter case is set shorter than the “predetermined time” serving as the time-out determination criterion in step S42 in the former case, and step S45 in the former case is employed. Then, while performing the correction process “main image− [A / B] * dark image”, the correction process “main image−dark image” may be performed in step S45 in the latter case.

DESCRIPTION OF SYMBOLS 1 Imaging device 4 Imaging element 6 CPU
13 Temperature sensor

Claims (8)

An imaging device having a plurality of pixels;
Temperature detection means for obtaining a detection temperature according to the temperature of the image sensor;
Signals accumulated in the plurality of pixels in the first accumulation period in the exposure state are read out as a first image signal, and the plurality of pieces in the second accumulation period in the light shielding state after the first accumulation period. A control unit that controls the image sensor so that a signal accumulated in the pixel is read out as a second image signal;
First estimated value acquisition means for obtaining a first estimated value, which is an estimated value of the total dark current amount in the first accumulation period, based on the detected temperature from the temperature detecting means;
Second estimated value acquisition means for obtaining a second estimated value that is an estimated value of the total dark current amount in a period from the start of the second accumulation period to the present based on the detected temperature from the temperature detecting means; ,
Ending means for ending the second accumulation period when the second estimated value becomes a value having a predetermined relationship with the first estimated value;
Correction means for correcting the first image signal based on the second image signal so that a dark current component in the first image signal is reduced;
An imaging apparatus comprising: The first estimated value acquisition means sequentially acquires detection temperatures from the temperature detection means in the first accumulation period, acquires the first estimated value based on these acquired detection temperatures,
The second estimated value acquisition unit sequentially acquires the detection temperature from the temperature detection unit in the second accumulation period, and whenever the detection temperature is acquired after the start of the second accumulation period, Obtaining the second estimated value based on the detected temperature obtained so far in the accumulation period;
The imaging apparatus according to claim 1.   The first and second estimated value acquisition means obtain a dark current amount corresponding to each detected temperature using a reference table or a calculation formula indicating a relationship between the detected temperature and the dark current amount, and according to each detected temperature. The imaging apparatus according to claim 2, wherein the first or second estimated value is obtained by integrating the dark current amount.   When a is greater than 0 and less than or equal to 1, the value having the predetermined relationship with respect to the first estimated value is a value of a times the first estimated value, the first estimated value being The imaging apparatus according to any one of claims 1 to 3, wherein the imaging apparatus is a value that is a value greater than or equal to a or a value within a predetermined range based on a value that is a times the first estimated value. .   5. The correction unit according to claim 4, wherein the correction unit corrects the first image signal by subtracting a signal obtained by multiplying the second image signal by 1 / a from the first image signal. Imaging device.   When the first estimated value is less than or equal to a predetermined value, the control means stops reading the second image signal, and the second estimated value acquisition means, the end means, and the correction means are activated. The imaging apparatus according to claim 1, wherein the imaging apparatus is stopped.   The ending means is configured such that when the second estimated value is not a value having the predetermined relationship with respect to the first estimated value and the second accumulation period is equal to or longer than a predetermined time, The imaging apparatus according to claim 1, wherein the accumulation period of 2 is terminated.   When the first estimated value is A and the latest second estimated value is B, the correction unit multiplies the second image signal by A / B from the first image signal. The imaging apparatus according to claim 7, wherein the first image signal is corrected by subtracting the signal.

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