JP5264318B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus and a control method thereof.

  In a conventional imaging apparatus, exposure control is automated, and even a person who is not familiar with camera operation can take a picture without failure if it is a normal subject. In addition, when using these cameras to shoot still images under low illuminance such as night views and sunset views, shooting using a flash or shooting using a slow shutter is performed. Also, in situations where the flash light does not reach the distance and the background becomes dark, a slow sync photography method is used in which the background is brightened by using a low-speed shutter and the person is brightened by the flash light. It has been.

  In particular, in this slow sync shooting, the method of measuring light by dividing the area was used as a method to improve the situation that the camera recognizes the person as the background when the person is not in the middle of the screen and the person is overexposed. There exists an imaging device (for example, refer patent document 1). In this imaging apparatus, it is disclosed that exposure time control and flash emission control are performed based on photometric data obtained from each area.

  In addition, there is an image pickup apparatus that employs an XY address type image pickup element such as a CMOS sensor as the image pickup element (see, for example, Patent Document 2).

Japanese Patent Laid-Open No. 2002-229094 JP 2003-32556 A

  However, in the conventional slow sync photography method described above, since the entire screen is exposed with the same exposure time, the background may not be photographed with sufficient brightness.

  The present invention has been made in view of the above problems, and an object of the present invention is to enable photographing with more appropriate brightness over the entire screen when photographing under low illuminance.

In order to achieve the above-described object, an imaging device that performs pre-light emission before causing the light- emitting device of the present invention to perform main light emission includes an image sensor having a plurality of two-dimensionally arranged photoelectric conversion elements, and pre-lights the light- emitting device. First luminance information, which is luminance information of image data obtained by imaging with the imaging device, and luminance information of image data obtained by imaging with the imaging device without causing the light- emitting device to emit pre-light. 2 based on the luminance information, and the exposure time calculation means for calculating the exposure time of each of the divided areas of the image sensor is divided into divided regions of several, said respective calculated by pre Symbol exposure time calculating means of it based on the exposure time of the divided regions, and exposure control means for varying the exposure start timing for each of the plurality of divided regions, based on the first and second luminance information, the plurality of divided regions A first divided region that is a region where a subject is present at an effective distance of the light emitted from the light emitting device, and a second divided region that is a region where the subject is present at a distance at which the light emitted from the light emitting device is effective determination means for determining bets, the first divided region have a, and light emission control means for emitting the light emitting device during a period that is exposed, the exposure time calculation means, the first divided area Calculation is performed so that the exposure time of the second divided region becomes longer than the exposure time, and the exposure control means starts the exposure of the first divided region after starting the exposure of the second divided region. Let

Further, according to the control method of the present invention for an imaging apparatus having an imaging element having a plurality of two-dimensionally arranged photoelectric conversion elements that perform pre-emission before the main emission of the light emitting apparatus , the exposure time calculation means includes the light emitting apparatus . First luminance information, which is luminance information of image data obtained by pre-light emission and imaged by the image sensor, and luminance of image data obtained by the image sensor without pre-lighting the light- emitting device a is based on the second luminance information information, and the exposure time calculation step of calculating the exposure time for each of the divided areas of the image sensor is divided into a plurality of divided regions, exposure control means, before Symbol exposure time based on the exposure time of the calculated the respective divided regions in the calculating step, an exposure control step of varying the exposure start timing for each of the plurality of divided regions, a determination unit, wherein the first and second Based on the degree information, among the plurality of divided areas, the first divided area, which is the area where the subject is at a distance where the light emitted from the light emitting device is effective, and the distance where the light emitted from the light emitting apparatus is effective. A determination step of determining a second divided region which is a region where a subject does not exist, a light emission control step of causing the light emission control unit to emit light while the first divided region is exposed; have a, the exposure time calculation step, the first than the exposure time of the divided region is calculated as the exposure time of the second divided area is increased, the exposure control step, the second split After the exposure of the area is started, the exposure of the first divided area is started .

  According to the present invention, it is possible to shoot with more appropriate brightness over the entire screen when shooting with low brightness.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram illustrating a main configuration of the imaging apparatus according to the present embodiment. In the figure, 1 is a lens group (in FIG. 1, a single lens is simply shown), 2 is a diaphragm, 3 is a diaphragm drive motor for driving the diaphragm, and 4 is a diaphragm state for detecting the position of the diaphragm 2. A detection sensor is shown. In the present embodiment, the diaphragm 2 also serves as a mechanical shutter function (light-shielding means), and a mechanical shutter is realized by closing the diaphragm 2 instantaneously during still image shooting. Reference numeral 5 denotes an ND filter, 6 denotes an ND filter driving motor for driving the ND filter 6, 7 denotes an ND filter state detection detection sensor for detecting the position of the ND filter 6, and 8 denotes an image sensor such as a CMOS sensor. The image sensor 8 is not limited to a CMOS sensor, and may be another image sensor as long as it is an XY address type sensor that drives a plurality of two-dimensionally arranged photoelectric conversion elements by the XY address method. Absent.

  9 denotes a CDS / AGC circuit, and 10 denotes an A / D converter. Here, the CDS / AGC circuit 9 and the A / D converter 10 may be incorporated into the image sensor 8 or included in the digital signal processing circuit 11. Reference numeral 11 denotes a digital signal processing circuit that digitally processes the video signal output from the A / D converter 10, and reference numeral 12 receives information such as luminance and color from the digital signal processing circuit 11, performs various calculations, and outputs a control signal. It is a microcomputer. Reference numeral 13 denotes an aperture mechanism drive circuit, and reference numeral 14 denotes an image sensor drive circuit including an electronic shutter function for controlling charge reading of the image sensor 8 and controlling a reset pulse for resetting the charge. The exposure time of the image sensor 8 is controlled by the electronic shutter function of the image sensor drive circuit 14 and the mechanical shutter function of the diaphragm 2. That is, the image sensor driving circuit 14 and the diaphragm 2 constitute an exposure time control means. Reference numeral 15 denotes an ND filter driving circuit for inserting / removing the ND filter into / from the optical path, and 16 denotes an AGC control circuit for controlling the gain.

  Reference numeral 17 denotes a luminance information detection circuit that detects luminance information of the video signal, 18 denotes a luminance information calculation circuit that calculates based on detection information, and 19 denotes an area division circuit that performs area division based on the calculation result of the luminance information calculation circuit 18. is there. An exposure time calculation unit 20 calculates the exposure time of each area based on the detection result of the microcomputer 12 or the luminance information detection circuit 17, the calculation result of the luminance information calculation circuit 18, and the area division result of the area division circuit 19. . Similarly, reference numeral 21 denotes a flash calculation that calculates a light emission amount and a light emission timing when the flash 23 emits light based on information obtained by the microcomputer 12, the luminance information detection circuit 17, the luminance information calculation circuit 18, and the area division circuit 19. Unit (light emission time calculation means). Reference numeral 22 denotes a light emission control circuit, which is a device for controlling actual flash light emission based on the calculation result of the flash calculation unit 21, and sends a signal to the flash light emission tube of the flash 23 to emit light from the flash. Note that the flash 23 may be provided integrally with the imaging apparatus or may be detachable. Reference numeral 24 denotes a recording medium for recording video of the imaging apparatus.

  In normal imaging in the imaging apparatus having the above-described configuration, first, charges accumulated in the imaging device 8 are sampled and amplified by the CDS / AGC circuit 9 and converted into digital image data by the A / D converter 10, and digital signal processing is performed. Send to circuit 11. The luminance information detection circuit 17 extracts the luminance component of the subject from the image data and performs photometry, and the microcomputer 12 obtains the appropriate luminance of the subject. The microcomputer 12 has an aperture mechanism drive circuit 13, an ND filter drive circuit 15, an AGC control circuit 16, and an image sensor drive circuit 14 (electronic shutter) so that an image signal having an appropriate exposure value can be obtained based on the luminance information. Function and read function).

  Next, an exposure control and flash control method in the present embodiment will be described with reference to FIGS. 2 and 3 are diagrams for explaining area division, and FIG. 4 is a timing chart showing drive timings of the image sensor 8 and the diaphragm 2.

  First, the luminance information detection circuit 17 detects luminance information before and after flash pre-emission during still image shooting. Based on the luminance information before and after the flash pre-light emission, the luminance information calculation circuit 18 detects information on the area where the flash light reaches and the background area where the flash light does not reach based on the reflectance and the luminance difference of the luminance information. Based on this information, the area dividing circuit 19 performs area division as a control area at the time of still image shooting.

  For example, when the subject image obtained by flash pre-emission in the case of low illuminance is as shown in FIG. 2, based on the reflectance and luminance difference of luminance information before and after flash pre-emission, two images as shown in FIG. Divide the area into areas (divided areas).

  In the actual photographing, the result of the area division and the result of the luminance information calculation circuit 18 are used to determine the exposure time of each area (each divided area) by the exposure time calculation unit 20 and the flash 23 by the flash calculation unit 21. The main light emission amount is calculated. Here, it is necessary to lengthen the exposure time for the area where the flash is determined not to reach (in the example shown in FIG. 3, area 1). Therefore, based on the calculation result by the exposure time calculation unit 20, in the area (area 1) determined to be an area where the exposure time should be increased, the image sensor is driven earlier in time than the area determined to have a short exposure time. Batch reset is performed by electronic shutter control of the circuit 14 (t1). As described above, the exposure start timing is controlled to be different for each area according to the exposure time. However, since the charge is read out by the read pulse during the read operation, the charge is lost and the same effect as the reset operation can be obtained. Therefore, it is not always necessary to perform the reset operation for the area having the longest exposure time. Thereafter, a batch reset operation is performed for an area with a short exposure time (area 2 in the example of FIG. 3), which is determined that flash light arrives, with an exposure time difference between the areas (t2). Thereafter, during the time until the main photographing is read, the main light emission of the flash 23 is performed according to the main light emission amount calculated by the flash calculating unit 21 (t3). Thereafter, when the end time of the exposure time is reached (after the exposure time has elapsed), the aperture 2 is closed to simultaneously end the exposure of the entire screen and perform the reading operation (t4). By this operation, the simultaneous exposure of the entire screen is maintained.

  Next, the procedure of exposure control of the imaging apparatus in the present embodiment will be described using the flowchart shown in FIG.

  When the process is started, first, in step S101, a condition determination is made as to whether or not the above-described exposure control for each area is performed. Here, for example, when the present control is switched by a button operation or menu setting, whether the present control is started is determined based on a user setting condition. If the user setting is not set in step S101 to perform the above-described control, the process returns to step S101. If it is set to perform this control, the process proceeds to step S102.

  In step S102, luminance information before flash pre-emission is acquired in a series of still image shooting operations, and then the flash calculation unit 21 calculates the light emission amount for pre-emission of the flash 23 (step S103). Based on the pre-emission amount calculated in step S103, pre-emission control of the flash 23 is performed (step S104), and luminance information of the image obtained by pre-emission is acquired (step S105). Based on the luminance information obtained in step S102 and the luminance information obtained in step S105 (luminance information before and after flash pre-emission), luminance information such as reflectance and luminance difference is calculated (step S106).

  Next, in step S107, it is determined whether area division is necessary using the calculation result of step S106. The determination of whether or not area division is necessary can be made by, for example, obtaining a luminance difference between images obtained before and after flash pre-emission and examining whether or not the obtained luminance difference is smaller than a preset threshold value. it can. When the brightness difference is lower than a preset threshold, it is possible to obtain an image with sufficient brightness in each area without changing the exposure time for each area, so it is determined that there is no need for area division (NO in step S107). On the other hand, when the luminance is equal to or higher than a preset threshold, there is a possibility that overexposure occurs in a bright area and blackout occurs in a dark area when shooting is performed on the entire screen with the same exposure time. Therefore, it is determined that area division is necessary to control the exposure time for each area described above (YES in step S107).

  If it is determined that there is no need to divide the area, the process proceeds to step S112, and photographing is performed by a conventional method. After shooting in step S112, the process proceeds to step S113 to end the shooting, and the process returns to step S101.

  On the other hand, if it is determined that area division is necessary (YES in step S107), the process proceeds to step S108 to perform exposure control including area division as described above. In step S108, according to the calculation result of step S106, area division is performed as described above with reference to FIGS. In step S109, after the area division, the exposure time calculation unit 20 calculates the exposure time of each area. Further, in step S110, the main light emission amount and the light emission timing of the flash 23 are controlled on the basis of the luminance information obtained in step S105 by the flash calculation unit 21 for each area. In step S111, as described above with reference to FIG. 4, the main photographing is performed by controlling the exposure time for each area calculated in steps S109 and S110, the main light emission amount and the light emission timing of the flash 23. . In the next step S113, a series of shooting operations is terminated, and the process returns to step S101.

  Here, the exposure time calculation in step S109, the flash light emission amount calculation in step S110, and the photographing control in step S113 are features of the present invention, and will be described in more detail below.

First, the calculation of the exposure time and the flash emission amount will be described. The exposure time and the flash emission amount are calculated separately. As a calculation method of the flash light emission amount, it is calculated for each area based on the following formula (1).
T _Target = (((L _target −L ₂ ) + (L ₂ −L ₁ )) / (L ₂ −L ₁ )) xT _p (1)

In the above equation (1), T _Target is the target flash emission time, L _target is the target luminance value, L ₁ is the luminance value before pre-emission, L ₂ is the luminance value after pre-emission, and T _p pre- Indicates the light emission time.

First, by subtracting the luminance value L ₂ after the pre-light emission from the luminance target value L _target that is set to a predetermined appropriate exposure, the degree of the luminance value L ₂ after the pre-light emission with respect to the luminance target value L _target is determined. It is calculated whether or not there is excess or deficiency. Then by subtracting the luminance value L ₁ prior to preliminary light emission from the luminance value L ₂ after pre-emission, to calculate how affected the extent subject by performing the pre-flash. By adding these two results, it is possible to calculate how much the luminance is increased with respect to the luminance value L ₁ before the pre-light emission in order to obtain the luminance target value L _target . By dividing this result by how much the luminance is increased by the pre-emission, it is possible to calculate how much light should be emitted in the main emission. This series of operations can be calculated by equation (1).

The exposure time is calculated for each area based on the following equation (2).
T _e = (((L _target − ((L ₂ −L ₁ ) × (T _f / T _p ) + L ₁ ) + L ₁ ) / L ₁ ) xT _s (2)

In the above formula (2), _Te represents the exposure time, and T _s represents the electronic shutter time (exposure time) during pre-emission.

First, by subtracting the luminance value of L ₁ before pre-emission from the luminance value L ₂ after pre-emission, and multiplying that value by the ratio of the main emission time T _f to the pre-emission time T _p , how much is the main emission. It is calculated whether it can be expected that the brightness of the will increase. By adding the luminance value L ₁ prior to preliminary light emission on the value, the luminance value that is assumed at the time of main light emission is calculated. By subtracting this from the luminance target value L _target , it is calculated how much the exposure amount is insufficient during the main light emission. This was divided by the pre-emission before the luminance value L _1, by multiplying the electronic shutter time T _s at the time of preliminary light emission, it is possible to calculate the exposure time T _e during the shooting.

  As described above, according to the present embodiment, it is possible to shoot with more appropriate brightness over the entire screen when shooting with low brightness.

1 is a block diagram illustrating a schematic configuration of an imaging apparatus according to an embodiment of the present invention. It is a figure which shows an example of the image obtained by the conventional imaging | photography method. It is a figure of an example which concerns on the area division | segmentation in embodiment of this invention. It is a figure which shows the timing of exposure control of this invention, and flash light emission. It is a flowchart which shows the procedure of exposure control of the imaging device in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens group 2 Aperture 3 Aperture drive motor 4 Aperture state detection sensor 5 ND filter 6 ND filter drive motor 7 ND filter state detection sensor 8 Image sensor 9 CDS / AGC
DESCRIPTION OF SYMBOLS 10 A / D converter 11 Digital signal processing circuit 12 Microcomputer 13 Aperture mechanism drive circuit 14 Image sensor drive circuit 15 ND filter drive circuit 16 AGC control circuit 17 Luminance information detection circuit 18 Luminance information calculation circuit 19 Area division circuit 20 Exposure time Arithmetic Unit 21 Flash Computing Unit 22 Light Emission Control Circuit 23 Flash 24 Recording Medium

Claims (6)

An imaging device that performs pre-light emission before the light emitting device performs main light emission,
An image sensor having a plurality of photoelectric conversion elements arranged two-dimensionally;
Obtained by imaging by the imaging device the light-emitting device wherein the light emitting device and the first luminance information is luminance information of the image data obtained by imaging by the imaging device by pre emit without preflash based on the second luminance information is luminance information of the image data, the exposure time calculation means for calculating the exposure time for each of the divided areas of the image sensor is divided into divided regions of several,
Based on prior Symbol exposure time calculating means the exposure time of each of the divided regions which are calculated by the exposure control means for varying the exposure start timing for each of the plurality of divided areas,
Based on the first and second luminance information, of the plurality of divided regions, a first divided region that is a region where a subject is present at an effective distance of light emitted from the light emitting device and the light emitting device. A determination means for determining a second divided region that is a region where a subject whose irradiation light is at an effective distance does not exist;
Have a, and light emission control means for the first division region to emit the light emitting device during a period that is exposed,
The exposure time calculating means calculates the exposure time of the second divided region to be longer than the exposure time of the first divided region;
The image pickup apparatus , wherein the exposure control means starts exposure of the first divided area after starting exposure of the second divided area . The exposure time calculation means, when the difference between the first luminance information and the second luminance information is less than a preset threshold value, the exposure time of the first divided area and the second divided area 2. The imaging apparatus according to claim 1 , wherein the calculation is performed so that the exposure time is the same . The imaging apparatus according to claim 1, wherein the determination unit determines that a divided area in which a luminance difference is generated between the first luminance information and the second luminance information is the first area. A light-shielding means for shielding the image sensor;
4. The image pickup apparatus according to claim 1 , wherein exposure of the first and second divided regions is terminated by shielding the image sensor by the light shielding unit. 5.   The image pickup apparatus according to claim 1, wherein the image pickup device is an XY address type image pickup device. A method for controlling an imaging apparatus having an imaging element having a plurality of two-dimensionally arranged photoelectric conversion elements that pre-emit light before the main light emission of the light emitting apparatus ,
Exposure time calculation means, by the imaging device the light-emitting device wherein the light emitting device and the first luminance information is luminance information of the image data obtained by imaging by the imaging device by pre emit without preflash An exposure time calculating step for calculating an exposure time of each divided area of the image sensor divided into a plurality of divided areas based on second luminance information that is luminance information of image data obtained by imaging ; ,
Exposure control means, before SL based on the exposure time of the respective divided areas calculated by the exposure time calculation process, an exposure control step of varying the exposure start timing for each of the plurality of divided areas,
A determination unit configured to determine, based on the first and second luminance information, a first divided region that is a region where a subject is present at an effective distance of the light emitted from the light emitting device among the plurality of divided regions; A determination step of determining a second divided region that is a region where no subject is present at an effective distance of irradiation light of the light emitting device;
Emission control means, have a, a light emission control step of emitting the light emitting device while the first divided region is exposed,
The exposure time calculation step calculates the exposure time of the second divided region to be longer than the exposure time of the first divided region,
The method for controlling an imaging apparatus, wherein the exposure control step starts exposure of the first divided region after starting exposure of the second divided region .

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