JP2014022992A - Imaging apparatus and imaging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a sudden change of an image plane brightness that occurs during a live view or moving image capturing.SOLUTION: An analog gain adjustment part 29 sets a setting ISO sensitivity to be set at an imaging device 13 on the basis of an instruction of a CPU 28. A gain correction part 35 of the CPU 28 successively switches over the setting ISO sensitivities to be set at the imaging device 13 so that exposure that is determined on the basis of object brightness acquired right after power activation becomes constant, identifies a setting ISO sensitivity that requires correction on the basis of an output of the imaging data acquired from the imaging device for each of the switched over setting ISO sensitivities, and calculates data for correction so that an output value corresponding to the identified setting ISO sensitivity approaches a reference output value. The calculated correction data is associated with a setting ISO sensitivity that is a target for correction and memorized in a RAM 21 in advance. A digital gain adjustment part 31 performs corrects by using the correction data memorized in the RAM 21 the digital image data acquired from the imaging device 13 during a normal imaging.

Description

  The present invention relates to an imaging device and an imaging method.

  A digital camera generally includes an AGC (Automatic Gain Control). AGC refers to control that automatically adjusts the gain of the video signal amplification unit (AGC circuit) of the camera in accordance with the brightness of the subject to keep the signal output constant.

  In the digital camera, an AGC adjustment value is obtained by performing AGC adjustment before shipment from a factory, and a reference AGC gain is calculated from the obtained AGC adjustment value. The reference AGC gain is a gain given to the AGC circuit so that the output of the AGC circuit corresponding to a predetermined reference light amount has a predetermined reference sensitivity. At the time of AGC adjustment, an AGC adjustment value is obtained based on an average value of outputs of a plurality of pixels existing in a predetermined area of a solid-state imaging device (hereinafter referred to as “imaging device”) such as a CMOS or a CCD. In the digital camera, a reference ISO sensitivity (reference ISO sensitivity) is determined based on the output characteristics of the AGC circuit with respect to the incident light amount after AGC adjustment.

  By the way, the sensitivity characteristics of the image sensor vary, and the image sensor output at the reference light amount varies for each digital camera incorporating the image sensor as shown in FIG. In a digital camera, an optimal target ISO sensitivity is set according to subject brightness, shutter speed, aperture, and the like, and the gain of the AGC circuit is controlled so that the actual ISO sensitivity approaches the target ISO sensitivity. When the AGC gain is increased in proportion to the ratio of the target ISO sensitivity to the reference ISO sensitivity as the target ISO sensitivity increases (subject brightness decreases), the output of the AGC circuit is linear due to the aforementioned variation. It does not change, and the actual ISO sensitivity becomes larger than the target ISO sensitivity.

  Therefore, the magnification (ISO sensitivity correction gain) to be multiplied by the AGC adjustment reference gain is corrected according to the target ISO sensitivity so that the relationship between the target ISO sensitivity and the actual ISO sensitivity changes to a linear relationship. (Patent Document 1).

Japanese Patent Application No. 2006-157777

  By the way, since the adjustment work for obtaining the ISO sensitivity correction gain is performed for all the ISO sensitivities that can be set in the AGC circuit before shipment from the factory, it takes too much time and is complicated. For this reason, in the adjustment process, adjustment work for obtaining ISO sensitivity correction gains is performed only for specific ISO sensitivities determined in advance, for example ISO sensitivities for two ISO sensitivities such as ISO 100 and ISO 3200, and other ISO sensitivities are gained by interpolation. I try to decide.

  However, in a digital camera incorporating an image sensor with a large variation in sensitivity characteristics, when the ISO sensitivity adjusted by interpolation is set for the image sensor, the exposure is not constant due to the variation, and thus a still image In this case, fluctuations in screen brightness (flickering) that were not a problem may occur during live view or moving image shooting. Such a phenomenon is prominent when the subject brightness fluctuates at the gain switching point of the AGC circuit and the ISO sensitivity set in the image sensor is frequently changed.

  In view of the above problems, an object of the present invention is to provide an imaging apparatus and an imaging method capable of suppressing a rapid change in screen brightness that occurs during live view or moving image shooting.

  In one aspect of an imaging apparatus illustrating the present invention, an imaging element that converts an optical image into an electrical signal, luminance information acquisition means that acquires information on subject luminance, and a plurality of set ISO sensitivities that can be set for the imaging element ISO sensitivity setting means for setting one ISO sensitivity so that the actual ISO sensitivity becomes a target ISO sensitivity determined based on the subject brightness, and an exposure determined based on the subject brightness acquired by the pre-imaging. ISO sensitivity switching means for switching the set ISO sensitivity while keeping constant, and setting ISO sensitivity that needs to be corrected based on the output value of the imaging data acquired from the image sensor for each setting ISO sensitivity switched by the ISO sensitivity switching means The correction data is calculated so that the output value corresponding to the specifying means and the set ISO sensitivity specified by the specifying means approaches the reference output value. Calculation means, storage means for storing the correction data calculated by the calculation means in association with the set ISO sensitivity of the correction target, and correction data in which the imaging data acquired from the image sensor during normal imaging is stored in the storage means And a correcting means for correcting using.

  According to one aspect of the imaging method of the present invention, the set ISO sensitivity set in the image sensor is switched while the exposure determined based on the subject luminance acquired by the pre-imaging is kept constant, and imaging is performed for each switched set ISO sensitivity. The set ISO sensitivity that needs to be corrected is identified based on the output value of the imaging data acquired from the element, the correction data is calculated so that the output value of the identified set ISO sensitivity approaches the reference output value, and the calculated correction Data is stored in association with the set ISO sensitivity to be corrected, and the imaging data acquired from the imaging device during normal imaging is corrected using the correction data stored in the storage means. .

  In the present invention, flickering of the screen can be suppressed, and the image quality of live view and moving image shooting can be improved.

It is a block diagram which shows the electrical outline of the digital camera which is one Embodiment of this invention. It is explanatory drawing which shows the outline of the 1st correction table which memorize | stores the ISO sensitivity correction gain obtained by adjusting with respect to a specific setting ISO sensitivity in ROM before factory shipment. It is a block diagram which shows the outline of a gain correction | amendment part. It is a flowchart which shows the operation | movement procedure which calculates the ISO sensitivity correction gain adjusted before factory shipment. It is a flowchart which shows the operation | movement procedure of a digital camera. It is a flowchart which shows the procedure of the gain correction operation | movement performed at the time of prior imaging. It is explanatory drawing which shows the ISO sensitivity correction gain calculated with respect to the setting ISO sensitivity identified as the need for correction | amendment by prior imaging. It is a graph which shows the measurement output value of the imaging data acquired by prior imaging with respect to the switched setting ISO sensitivity. It is a graph which shows the output value of the imaging data calculated for every setting ISO sensitivity in consideration of the ISO sensitivity correction gain of the 1st time. It is explanatory drawing which shows the ISO sensitivity correction gain computed for the 2nd time. It is a graph which shows the output value of the imaging data calculated again for every set ISO sensitivity using the ISO sensitivity correction gain calculated for the second time. It is a graph which shows that the reference | standard sensitivity with respect to the reference | standard incident light quantity has variation according to the sensitivity characteristic of an image pick-up element.

  A digital camera 10, which is an embodiment of an imaging apparatus of the present invention, includes a photographing lens 11, an aperture mechanism 12, an imaging element 13, an AFE (Analog Front End) 14, a signal processing unit 15, an element driving unit 16, and a motor driving unit 17. , D / A converter (Digital to Analog Converter) 18, video encoder 19, display unit 20, RAM 21, ROM 22, card control unit 23, card memory 24, AE / AF circuit 25, compression / decompression processing unit 26, operation unit 27, and a CPU 28 that controls them centrally.

  The taking lens 11 forms an optical image of the subject incident through the aperture mechanism 12 on the image pickup surface of the image pickup device 13. The focus driving of the photographing lens 11 and the diaphragm driving of the diaphragm mechanism 12 are controlled by a motor driving unit 17. The imaging device 13 drives vertical / horizontal registers and the like by the drive pulse generated by the device driving unit 16 and outputs an electrical signal obtained by photoelectrically converting the optical image to the AFE 14 as an analog image signal.

  The AFE 14 includes a CDS circuit (not shown), an analog gain adjustment unit (AGC circuit) 29, and an A / D converter (Analog to Digital Converter) 30. The CDS circuit removes reset noise from an analog image signal. The analog gain adjustment unit 29 adjusts the gain for amplifying the analog image signal before A / D conversion in response to the CPU 28 setting the ISO sensitivity determined based on the amount of incident light on the image sensor 13. To do. The analog gain adjustment unit 29 is an example of an ISO sensitivity setting unit. Note that an image sensor in which the AFE 14 is incorporated in the image sensor 13 may be used. When proper exposure cannot be obtained with the set ISO sensitivity, the CPU 28 automatically changes the set ISO sensitivity based on the subject brightness.

  The A / D converter 30 converts the analog image signal output from the analog gain adjustment unit 29 into a digital image signal. The digital image signal output from the A / D converter 30 is sent to the signal processing unit 15. The signal processing unit 15 includes a digital gain adjustment unit 31 that performs processes such as level correction and gamma adjustment, and includes a YC process and an encoder (not shown). The signal processing unit 15 is an example of a calculation unit that calculates correction data for correcting variations in sensitivity characteristics of the image sensor 13 by measuring input / output characteristics of each pixel of the image sensor 13 in advance. The digital gain adjustment unit 31 includes a multiplier for sensitizing the digital value of the image signal, and corrects the exposure level for the image signal after A / D conversion based on a command from the CPU 28.

  Specifically, as the subject brightness changes, the CPU 28 changes the actual ISO sensitivity to the target ISO sensitivity until the analog gain adjustment unit 29 changes to the set ISO sensitivity of the next step. The digital gain adjustment unit 31 performs control so that fine gain adjustment is performed on the image signal. The exposure correction by this digital gain adjustment is performed, for example, in 1/48 steps. The actual ISO sensitivity here is the ISO sensitivity obtained by performing gain adjustment in both the analog gain adjustment unit 29 and the digital gain adjustment unit 31, that is, the ISO sensitivity of the entire digital camera 10.

  A control signal indicating an ISO sensitivity correction gain for correcting the set ISO sensitivity set in the analog gain adjustment unit 29 is applied from the CPU 28 to the multiplier of the digital gain adjustment unit 31. The ISO sensitivity correction gain adjusts variations in sensitivity characteristics of the image sensor 13 before shipment from the factory with respect to one or a plurality of set ISO sensitivities that can be set in the analog gain adjustment unit 29. And is described in the first correction table 33 in association with the adjusted set ISO sensitivity. The first correction table 33 is stored in the ROM 22.

  The digital gain adjustment unit 31 corrects a digital image signal obtained from the image sensor 13 during normal imaging using an ISO sensitivity correction gain (first correction data), thereby obtaining a saturation curve of the image sensor 13. It is an example of the correction | amendment means approximated to an ideal curve. Note that the pre-imaging means imaging performed after the power is turned on until the first regular imaging. Regular imaging refers to imaging for acquiring an image signal for a through image or an image signal accompanying a moving image shooting instruction.

  An operation unit 27 is connected to the CPU 28. The operation unit 27 includes various operation units such as a power selection button, a shutter button, a moving image recording button, a mode selection switch for selecting any one of a moving image mode, a shooting mode, and a reproduction mode.

  The CPU 28 has a gain correction unit 35. The gain correction unit 35 calculates an ISO sensitivity correction gain based on image data acquired after the power button is turned on for a set ISO sensitivity that has not been adjusted before shipment from the factory, and calculates the calculated ISO sensitivity correction. The gain is described in the second correction table 36 in association with the corresponding set ISO sensitivity. The second correction table 36 is stored in the RAM 21. Note that the ISO sensitivity correction gain described in the second correction table 36 is deleted in response to an operation of turning off the power button, and is newly created in response to the next operation of turning on the power button.

  Note that the ISO sensitivity correction gain described in the second correction table 36 is generated every time in response to the half-pressing operation of the shutter button (before performing normal imaging) instead of creating the power button in response to the ON operation. Alternatively, a correction button may be provided, and the correction button may be provided in response to the photographer operating the correction button.

  The image signal that has been subjected to gain correction and exposure correction by the digital gain adjustment unit 31 is sequentially sent to the YC processing and the encoder, and is subjected to predetermined signal processing to include a luminance signal and a color difference signal, for example, a YUV signal. The generated YUV signal is stored in the RAM 21 as image data.

  A signal processing unit 15, an AE / AF circuit 25, a compression / decompression processing unit 26, a RAM 21, a ROM 22, a card control unit 23, and a D / A converter 18 are connected to the CPU 28 via a data bus 32. These units are controlled by the CPU 28 and exchange data with each other.

The AE / AF circuit 25 is a photometric means for measuring the subject luminance, calculates a photometric value representing the subject luminance based on the image data stored in the RAM 21, and outputs the photometric value to the CPU 28. The CPU 28 has exposure determining means, and automatically sets an optimal exposure based on a predetermined program diagram based on the photometric value acquired from the AE / AF circuit 25. The exposure includes a target ISO sensitivity, an aperture value, and a shutter speed.
The CPU 28 controls the aperture mechanism 12 via the motor driving unit 17 based on the aperture value, thereby changing the aperture diameter of the aperture, and further controls the electronic shutter speed of the image sensor 13 based on the shutter speed.

  The AE / AF circuit 25 calculates an AF evaluation value (amplitude value of high frequency component) representing the contrast of the image based on the image data read from the RAM 21 and outputs the AF evaluation value to the CPU 28. The CPU 28 acquires the AF evaluation value while moving the focus lens constituting the photographing lens 11 in the direction of the optical axis 11a via the motor driving unit 17, and moves the focus lens to a position where the AF evaluation value reaches a peak. The motor drive unit 17 is controlled. In place of the AE / AF circuit 25, a distance measuring sensor and a photometric sensor are connected to the CPU 28, and the object distance and the subject luminance are directly measured by the distance measuring sensor and the photometric sensor. Also good.

  In response to a shooting command from the CPU 28, the compression / decompression processing unit 26 reads the image data stored at that time from the RAM 21, compresses the read image data into a predetermined image format such as JEPG, and outputs the data. It sends out to the control unit 23. The card control unit 23 records the compressed image data in the card memory 24. In the card memory 24, moving image data is recorded in addition to still image data. Further, the compression / decompression processing unit 26 decompresses the compressed image data read from the card memory 24 to the original image data in the reproduction mode.

  The D / A converter 18 converts the image data read from the RAM 21 into an analog image signal and sends it to the video encoder 19. The video encoder 19 converts it into an NTSC composite image signal. The converted composite image signal is output to the display unit 20. The display unit 20 displays live view images (through images) and images during moving image shooting in real time.

  The RAM 21 is used as a temporary storage area for image data and a work area for the CPU 28, and also stores a second correction table 36 created every time the power button is turned on. The RAM 21 is an example of a second storage unit that stores correction data calculated by the calculation unit before the start of imaging. In the ROM 22, various programs, a first correction table 33, a program diagram for determining exposure, and the like are stored in advance.

  In the first correction table 33, the output (exposure) of the analog gain adjustment unit 29 becomes constant in association with at least two set ISO sensitivities among a plurality of set ISO sensitivities that can be set in the analog gain adjustment unit 29. In this way, the table stores the magnification (ISO sensitivity correction gain) for correcting the set ISO sensitivity, and is created before factory shipment and stored in the ROM 22. The ROM 22 is an example of a first storage unit that stores first correction data (ISO sensitivity correction gain) calculated by the calculation unit before shipment from the factory.

  In the present embodiment, the plurality of set ISO sensitivities that can be set in the analog gain adjusting unit 29 are set in advance in steps of “ISO 100, 200, 400, 800, 1600, 3200”, for example, as shown in FIG. Of these, only the two ISO settings “ISO 100, 3200” are set ISO sensitivities adjusted before shipment from the factory. For example, when the set ISO sensitivity set in the analog gain adjustment unit 29 is “ISO100”, the CPU 28 sets the digital gain adjustment unit 31 to a magnification of “1.09 (109%)” and the set ISO sensitivity is, for example, In the case of “ISO3200”, for example, a magnification of “1.05 (105%)” is set, and the digital gain adjustment unit 31 performs gain correction.

  As shown in FIG. 3, the gain correction unit 35 includes a setting ISO sensitivity switching unit 40, an output value calculation unit 41, an output value determination unit 42, and a correction calculation unit 43, and performs pre-imaging after turning on the power button. A process for creating the second correction table 36 is performed based on the acquired image data. The setting ISO sensitivity switching unit 40 changes one or both of the shutter speed and the aperture value in order to keep the exposure determined based on the subject brightness acquired after the power button is turned on constant. Change the set ISO sensitivity. The output value calculation unit 41 measures the output value (luminance value) of the image data output from the digital gain adjustment unit 31 for each set ISO sensitivity to be switched. Note that the output value may be an average output value obtained by capturing a predetermined number of images for each set ISO sensitivity and averaging the output values of the respective image data.

  The output value determination unit 42 compares the output values measured for each set ISO sensitivity with output values having adjacent set ISO sensitivities, and determines whether the difference between the output values to be compared exceeds a predetermined threshold. Go. When the difference exceeds the threshold value, the correction calculation unit 43 obtains ISO sensitivity correction gains for correcting the comparison target output value so that the comparison target output value approaches the reference output value.

  The output value calculation unit 41, the output value determination unit 42, and the correction calculation unit 43 correct the output value measured at the first time using the obtained ISO sensitivity correction gain, and use the corrected output value again. Adjacent ones of the set ISO sensitivities are compared, it is determined whether the difference between the output values to be compared exceeds the threshold value, and the processing for obtaining the ISO sensitivity correction gain based on the output value exceeding is performed. Iterate until the difference in output values does not exceed the threshold.

  Next, the operation of the above configuration will be briefly described. The digital camera 10 corrects variations in sensitivity characteristics of the image sensor 13 with respect to a specific set ISO sensitivity among a plurality of set ISO sensitivities that can be set in the image sensor 13 in an adjustment process before factory shipment. An ISO sensitivity correction gain is obtained. In the adjustment step, as shown in FIG. 4, the reference light source is imaged by the image sensor 13, and the actual ISO sensitivity is measured with respect to the sensitivity at two locations (S-1). For example, this measurement is performed by adjusting the sensitivity at both ends of a plurality of set ISO sensitivities (inspection ranges), that is, the two set ISO sensitivities of “ISO 100” and “ISO 3200” as described in FIG. It is desirable to do it.

  Note that the specific set ISO sensitivity is not limited to the sensitivity at both ends of the inspection range, and may be at least one sensitivity. It is preferable to make adjustments for the sensitivities at two distant locations in the inspection range.

  Thereafter, an ISO sensitivity correction gain is obtained so that the measured ISO sensitivity measurement value becomes the target ISO sensitivity (S-2). Then, the calculated ISO sensitivity correction gain is described in the first correction table 33 in association with the corresponding set ISO sensitivity, and the first correction table 33 describing the ISO sensitivity correction gain is stored in the ROM 22 (S-3). ).

  As shown in FIG. 5, the digital camera 10 after factory shipment turns on the power button (S-4), and then operates the mode selection operation unit to select a mode (S-4 to S-6). The shooting mode includes three modes: a moving image mode (S-4), a still image mode (S-5), and a playback mode (S-6).

  When the moving image mode (S-4) is selected, the AE / AF circuit 25 obtains the subject brightness based on the image data obtained by the pre-imaging after turning on the power button, and the gain correction unit 35 obtains the obtained subject. Based on the brightness, a gain correction operation is performed to obtain an ISO sensitivity correction gain for the set ISO sensitivity that has not been adjusted to create the second correction table 36 (S-8). Here, a detailed description of the gain correction operation performed before the pre-imaging will be described later.

  Through the gain correction operation, ISO sensitivity correction gains are obtained for all set ISO sensitivities that can be set in the image sensor 13. The ISO sensitivity correction gain obtained by the pre-imaging is stored in the RAM 21 in the format stored in the second correction table 36.

  Thereafter, the image signal acquired from the image sensor 13 is sequentially processed by the AFE 14 and the signal processing unit 15 and stored in the RAM 21 as digital image data. The AE / AF circuit 25 reads the image signal stored in the RAM 21, calculates a photometric value representing the subject brightness, and outputs the photometric value to the CPU 28. Based on the photometric value acquired from the AE / AF circuit 25, the CPU 28 automatically sets the target ISO sensitivity, aperture value, and shutter speed based on the program diagram read from the ROM 22 so that the optimum exposure is obtained. Decide. The CPU 28 then performs ISO sensitivity exposure control (set ISO sensitivity adjustment to the analog gain adjustment unit 29 and gain correction to the digital gain adjustment unit 31 so that the actual ISO sensitivity becomes the target ISO sensitivity. S-9) is executed. Based on the target ISO sensitivity, the CPU 28 selects a set ISO sensitivity to be set in the analog gain adjustment unit 29 from among a plurality of set ISO sensitivity that can be set, and further, the target ISO sensitivity approaches the actual ISO sensitivity. The digital gain adjustment unit 31 is controlled so as to correct the exposure level. Further, the CPU 28 sets the ISO sensitivity correction gain in the digital gain adjustment unit 31 as gain correction.

  The CPU 28 refers to the first correction table 33 stored in the ROM 22 or the second correction table 36 stored in the RAM 21, reads the ISO sensitivity correction gain corresponding to the set ISO sensitivity set at that time, and reads the read ISO. The sensitivity correction gain is set in the digital gain adjustment unit 31.

  Thus, the actual ISO sensitivity is determined by the gain adjustment according to the set ISO sensitivity set in the analog gain adjustment unit 29, the gain correction by the digital gain adjustment unit 31, and the exposure level correction.

  Thereby, the image data controlled to a constant exposure from the next imaging is stored in the RAM 21. The CPU 28 controls the D / A converter 18 and the video encoder 19 to display the image signal stored in the RAM 21 on the display unit 20 as a through image (S-10).

  In moving image shooting, recording recording is started by the first full pressing operation of the moving image recording button (S-11), and recording recording is ended by the second full pressing operation of the moving image recording button (S-12). The image signal captured in the RAM 21 during this time is subjected to compression processing by the compression / decompression processing unit 26 and stored in the card memory 24 as moving image data in a compressed format (S-13). As described above, the ISO sensitivity correction gain is obtained for all of the plurality of set ISO sensitivities that can be set in the analog gain adjustment unit 29, and thus flickering of the screen is suppressed in the through image and the recorded image.

Next, the gain correction operation will be described with reference to FIG. The operation for obtaining the ISO sensitivity correction gain for the set ISO sensitivity that has not been adjusted is performed before the through image is displayed.
Immediately after the power button is turned on, the image sensor 13 is driven (S-14), and an image signal is acquired from the image sensor 13. The acquired image signal is sequentially processed by the AFE 14 and the signal processing unit 15 and stored in the RAM 21 as digital image data. The AE / AF circuit 25 reads the image data stored in the RAM 21, calculates a photometric value representing the subject luminance, and outputs this photometric value to the CPU 28. The CPU 28 calculates the optimum exposure based on the photometric value acquired from the AE / AF circuit 25 (S-15), and sets the target ISO sensitivity, aperture value, and shutter speed to the program line so as to obtain the optimum exposure. It is automatically determined based on the figure (S-16).

  The setting ISO sensitivity switching unit 40 switches the setting ISO sensitivity while changing either one or both of the shutter speed and the aperture so that the calculated exposure becomes constant. The setting ISO sensitivity is switched in order from the low sensitivity side to the high sensitivity side of the inspection range (S-17). That is, the setting ISO sensitivity switching unit 40 first sets the setting ISO sensitivity to “ISO100” in the analog gain adjustment unit 29. It may be switched from the high sensitivity side.

The CPU 28 reads the first correction table 33 from the ROM 22 and refers to the read first correction table 33. Then, the corresponding ISO sensitivity correction gain is set in the digital gain adjustment unit 31 for the set ISO sensitivity that has been adjusted according to the switching of the set ISO sensitivity.
In response to switching the set ISO sensitivity, the CPU 28 changes either or both of the shutter speed and the aperture value in order to keep the exposure constant (S-18).

  The output value calculation unit 41 measures the output value (luminance value) of the image data output from the digital gain adjustment unit 31 for each set ISO sensitivity to be switched. In this example, the output value calculation unit 41 acquires a plurality of image signals for each set ISO sensitivity, calculates an average value of the output values of the plurality of image signals, and stores them in the RAM 21 (S-19).

  As the measured output value, for example, in the example shown in FIG. 7, when the set ISO sensitivity is set to “ISO100”, the measured output value (8-bit system) is set to “100”, and the set ISO sensitivity is set to “ISO200”. The measured output value is “101”, the set ISO sensitivity is set to “ISO400”, the measured output value is “105”, and the set ISO sensitivity is set to “ISO800”. It is assumed that the measured output value when the set ISO sensitivity is set to “ISO1600” is “97”, and the measured output value when the set ISO sensitivity is set to “ISO3200” is “100”.

  Here, the measured output value when the set ISO sensitivity is set to “ISO100” and “ISO3200” is the output value after correction with the ISO sensitivity correction gain adjusted before shipment from the factory. Is a reference output value based on (reference output value).

  After obtaining the average output value for all the set ISO sensitivities (S-20), the output value determination unit 42 compares the output values measured for each set ISO sensitivity between adjacent set ISO sensitivities, Based on the comparison result, it is determined whether the output difference exceeds a predetermined threshold (S-21), and the correction calculation unit 43 calculates an ISO sensitivity correction gain for an output value exceeding the threshold (S-). 22).

  FIG. 8 is a graph showing the relationship between the output (measurement output value) described in FIG. 7 and the gain (set ISO sensitivity). In the example illustrated in FIG. 8, the output value determination unit 42 compares the output “100” when the adjacent gain is “ISO100” with the output “101” when the gain is “ISO200”. Next, the output “101” when the gain is “ISO200” and the output “105” when the gain is “ISO400” are compared. Thereafter, the output “105” when the gain is “ISO400” is compared with the output “103” when the gain is “ISO800”, and then the output “103” and the gain “ISO1600” when the gain is “ISO800” are compared. The output “97” of the hour is compared. Finally, the output “97” when the gain is “ISO1600” and the output “100” when the gain is “ISO3200” are compared. And it is determined whether the difference compared by each exceeds the threshold value. In this example, the threshold value is predetermined to 4% of the reference output value “100”, that is, “4”. In the first comparison result, as shown in FIG. 8, the output difference A between the gains “ISO800” and “ISO1600” exceeds the threshold “4”.

  The correction calculation unit 43 obtains an ISO sensitivity correction gain for the corresponding gain so that the output values (“103” and “97”) to be compared whose difference exceeds the threshold value approaches the reference output value “100”. That is, as shown in FIG. 7, the ISO sensitivity correction gain is calculated as “97%” and “103%” for the set ISO sensitivities “ISO800” and “ISO1600” (items indicated by hatching in FIG. 7). The obtained ISO sensitivity correction gain is described in the second correction table 36 stored in the RAM 21 in association with the corresponding set ISO sensitivity (S-23).

  The output value calculation unit 41 and the output value determination unit 42 use the obtained ISO sensitivity correction gain to correct the output value measured at the first time to calculate a new output value (S-24), and then gain again. Compare adjacent output values, determine whether the difference between the output values to be compared exceeds the threshold value, and obtain the ISO sensitivity correction gain until the difference does not exceed the threshold value.

  9, the output value calculation unit 41 uses the ISO sensitivity correction gains “97%” and “103%” that are first corrected by the correction calculation unit 43 for the output of the gain whose difference exceeds the threshold based on the first comparison result. It is a graph which shows the result calculated again. As shown in FIG. 9, the output values of the gains “ISO800” and “ISO1600” are both replaced with “100” as compared to FIG. 8. The output value calculation unit 41 calculates the second output value using the ISO sensitivity correction gain corrected by the correction calculation unit 43 for the first time.

In this way, the output value calculation unit 41 does not acquire image data newly from the second time and measure the output value for the gain determined to be corrected, but instead determines the ISO sensitivity obtained at the first time. Since the output value is calculated and compared using the correction gain, the subsequent comparison determination can be performed quickly.
The output value determination unit 42 performs the second comparison determination on the output value shown in FIG. In the second comparison determination, as shown in the figure, it is determined that the output difference B between the set ISO sensitivities “ISO400” and “ISO800” exceeds the threshold “4”.

  The correction calculation unit 43 compares the output value to be compared (“150” and “100”) whose difference exceeds the threshold value by the second determination so as to approach the reference output value “100”. An ISO sensitivity correction gain is obtained. That is, as shown in FIG. 10, the ISO sensitivity correction gain is set to “95%” with respect to the set ISO sensitivity “400” (items indicated by hatching in FIG. 10). Here, since the output is the reference output value for the set ISO sensitivity “ISO800”, it is not necessary to obtain the ISO sensitivity correction gain, and the ISO sensitivity correction gain obtained at the first time is used as it is.

  As shown in FIG. 11, the output value calculation unit 41 calculates the new output as “100” by multiplying the output of the gain “ISO400” that needs to be corrected by the second comparison result by the ISO sensitivity correction gain. To do. For the output shown in FIG. 11, the output value determination unit 42 performs the third comparison determination. In the example illustrated in FIG. 11, there is no output to be compared in which the difference between the outputs having adjacent gains exceeds the threshold value. If the output value determination unit 42 determines that there is no output in which the difference in output between adjacent gains exceeds the threshold value, the gain correction operation ends.

  Accordingly, the ISO sensitivity correction gain obtained for the set ISO sensitivity that needs to be corrected among the set ISO sensitivities that have not been adjusted before shipment from the factory is stored in the RAM 21 in the form described in the second correction table 36. Saved. In FIG. 10, the ISO sensitivity correction gain is described as “100%” (1 time) for the set ISO sensitivity that is determined not to require correction.

  In this way, by specifying the set ISO sensitivity that needs to be corrected based on the difference between adjacent output values of the set ISO sensitivity, the output value corrected by the calculated ISO sensitivity correction gain becomes the reference output value “ It falls within the range of “98 to 102” within the threshold value centering on “100”.

  In the second correction table 36 stored in the RAM 21, the value of the ISO sensitivity correction gain is cleared in response to an operation of turning off the power button (S-25 shown in FIG. 5). Then, in response to the next power-on operation, the ISO sensitivity correction gain is obtained again for the set ISO sensitivity adjusted by interpolation based on the subject brightness at that time.

  When the still image mode described with reference to FIG. 5 is selected (S-6), the still image operation (S-25) is executed. The exposure control of the ISO sensitivity in this still image operation is also performed by the same exposure control (S-9) as described above, but the fluctuation of the screen brightness (flicker) is not noticeable during the display of the through image. So desirable.

  In the embodiment described above, the set ISO sensitivity is specified based on the difference between adjacent output values as the condition of the output value determination unit 42 that specifies the set ISO sensitivity that needs to be corrected. However, the present invention is not limited to this. Alternatively, the determination may be made based on whether or not a threshold range centering on the reference output value is exceeded. For example, as indicated by the alternate long and short dash line in FIG. 8, FIG. 9, and FIG. It may be determined whether or not the range “98 to 102” (100 ± 2 range) is exceeded, and the output value exceeding the range may be corrected. In this case, as compared with the method of determining based on the output difference described above, the number of times of correcting the output is increased and the determination becomes severe, and the accuracy of correcting the set ISO sensitivity is improved. On the other hand, when the judgment is loosened, it may be configured to correct the output value exceeding the range of ± threshold (96 to 104) centering on the reference output “100”.

  In the above embodiment, the digital camera 10 is described, but the present invention can also be applied to camera-equipped mobile phones, camera-equipped electronic devices such as smartphones, and the like.

  The present invention has been specifically described above based on the preferred embodiments. However, the present invention is not limited to the above-described numerical values such as the set ISO sensitivity, and may be variously modified without departing from the gist thereof. Needless to say, it can be changed.

DESCRIPTION OF SYMBOLS 10 Digital camera 29 Analog gain adjustment part 31 Digital gain adjustment part 33 1st correction table 35 Gain correction part 36 2nd correction table

Claims (7)

An image sensor that converts an optical image into an electrical signal;
Luminance information acquisition means for acquiring subject luminance information;
ISO sensitivity setting means for setting one set ISO sensitivity so that the actual ISO sensitivity becomes a target ISO sensitivity determined based on the subject brightness among a plurality of set ISO sensitivities that can be set for the image sensor. When,
ISO sensitivity switching means for switching the set ISO sensitivity while keeping the exposure determined based on the subject brightness acquired by pre-imaging constant,
A specifying unit that specifies a set ISO sensitivity that needs to be corrected based on an output value of imaging data acquired from the imaging element for each setting ISO sensitivity switched by the ISO sensitivity switching unit;
Calculating means for calculating correction data so that the output value corresponding to the set ISO sensitivity specified by the specifying means approaches a reference output value;
Storage means for storing the correction data calculated by the calculation means in association with the set ISO sensitivity to be corrected;
Correction means for correcting imaging data acquired from the imaging element by regular imaging using correction data stored in the storage means;
An imaging apparatus comprising: The imaging device according to claim 1,
The imaging apparatus according to claim 1, wherein the ISO sensitivity setting means is an analog adjustment means for adjusting an AGC gain in accordance with the set ISO sensitivity. The imaging device according to claim 2,
The calculation means is means for calculating, as the correction data, a correction magnification to be multiplied by the AGC gain according to the set ISO sensitivity in order to linearly interpolate the actual ISO sensitivity with respect to the target ISO sensitivity. An imaging apparatus characterized by being configured. The imaging device according to any one of claims 1 to 3,
The specifying means is:
Output value calculating means for calculating an output value of imaging data acquired from the imaging element for each set ISO sensitivity switched by the ISO sensitivity switching means;
Output for determining whether to correct the output value to be compared based on the comparison result by comparing the difference between output values adjacent to each other with the set ISO sensitivity among the output values calculated by the output value calculating means. Value judging means;
An imaging apparatus comprising: The imaging device according to any one of claims 1 to 4,
Prior to factory shipment, first correction data for correcting an output value obtained by imaging a reference light source with the image sensor so as to approach an output value of the reference sensitivity is included in the plurality of set ISO sensitivities. First storage means for obtaining for each specific set ISO sensitivity and storing the obtained first correction data in association with the specific set ISO sensitivity,
The ISO sensitivity switching means switches to the remaining set ISO sensitivity other than the specific set ISO sensitivity,
The storage means is second storage means for storing correction data calculated by the calculation means as second correction data,
The correction means selects, from the first correction data or the second correction data, correction data corresponding to a set ISO sensitivity set according to the subject brightness at that time, and uses the selected correction data To correct the imaging data,
An imaging apparatus characterized by that. In the imaging device according to any one of claims 1 to 5,
The imaging apparatus according to claim 1, wherein the preliminary imaging is imaging performed prior to the regular imaging for acquiring imaging data for a through image or imaging data associated with a moving image imaging instruction.   The setting ISO sensitivity set in the image sensor is switched while keeping the exposure determined based on the subject brightness acquired by the pre-imaging, and the image data acquired from the image sensor is output for each switched setting ISO sensitivity. The set ISO sensitivity that needs to be corrected is specified, correction data is calculated so that the output value of the specified set ISO sensitivity approaches the reference output value, and the calculated correction data corresponds to the set ISO sensitivity to be corrected An image capturing method that stores the image data acquired from the image sensor at the time of normal image capturing using the correction data stored in the storage unit.

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