JP2014216832A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device capable of suppressing a rapid change in an exposure value even when a main subject is temporarily undetectable.SOLUTION: An imaging device includes: subject detection means for repeatedly detecting a main subject in a subject image consisting of imaging elements; first luminance value detection means for detecting a first luminance value in the region of the main subject each time the main subject is detected by the subject detection means; storage means for storing the first luminance value each time the first luminance value is detected by the first luminance value detection means; second luminance value detection means for repeatedly detecting a second luminance value in a region wider than the region of the main subject; and calculation means for calculating a third luminance value for exposure control on the basis of the first luminance value detected by the first luminance value detection means and the second luminance value detected by the second luminance value detection means, and for, when the main subject is not detected by the subject detection means, calculating the third luminance value on the basis of the stored first luminance value and the second luminance value detected by the second luminance value detection means.

Description

  The present invention relates to an imaging apparatus.

  Conventionally, there has been known a control in which a luminance value (photometric value) acquired from a face photometric frame is weighted larger than the luminance value of the entire screen so that the luminance value of the face is appropriately exposed (for example, patent) Reference 1).

JP 2011-49737 A

  The prior art has a problem that the exposure changes abruptly when the face cannot be detected temporarily.

  The image pickup apparatus according to claim 1, an image pickup device that picks up a subject, a subject detection unit that repeatedly detects a main subject in a subject image by the image pickup device, and each time the subject detection unit detects the main subject. First brightness value detection means for detecting a first brightness value in the area of the main subject; and storage means for storing the first brightness value each time the first brightness value detection means detects the first brightness value; , Second luminance value detecting means for repeatedly detecting a second luminance value in an area wider than the area of the main subject, the first luminance value detected by the first luminance value detecting means, and the second luminance value Calculation means for calculating a third luminance value for exposure control based on the second luminance value detected by the detection means, and the calculation means was unable to detect the main subject by the subject detection means. Expediently, characterized by calculating the third luminance value based on the detected second intensity value by the stored the first luminance value second luminance value detecting means.

  According to the present invention, a sudden change in exposure can be suppressed even when the main subject cannot be detected temporarily.

1 is a block diagram illustrating a configuration of an imaging apparatus according to a first embodiment of the present invention. 6 is a flowchart of a through image display process executed by the control device 4; It is a flowchart of the face luminance value continuation determination process called in step S220 of FIG.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the imaging apparatus according to the first embodiment of the present invention. The imaging device 1 is a so-called lens-integrated digital camera. The control device 4 captures a subject image formed by the photographing optical system 2 with an image pickup device 3 such as a CCD or CMOS to create digital image data and displays it on the rear monitor 5 or a storage medium (not shown). Or remember.

  The control device 4 is a device including a microcomputer (not shown) and its peripheral circuits, and controls the entire image pickup device 1 by reading and executing a control program stored in advance in a ROM 6 that is a nonvolatile storage medium. To do. This control program uses the RAM 7 which is a volatile storage medium as a temporary work area. The rear monitor 5 is a display device having a liquid crystal panel or the like, for example, and is provided on the rear surface of the housing of the imaging device 1.

  Next, a live view function (through image display function) by the imaging apparatus 1 will be described. The imaging device 1 has a so-called live view function. The control device 4 captures images every predetermined period (for example, 1/60 second) to create a through image, and displays the created through image on the rear monitor 5. The control device 4 performs exposure control when creating a through image, and keeps the through image at an appropriate exposure following the change in ambient light.

  FIG. 2 is a flowchart of a through image display process executed by the control device 4. The through image display process is included in a control program that the control device 4 reads from the ROM 6 and executes. First, in step S100, the control device 4 initializes a face detection flag used in the through image display process to 0.

  In step S <b> 110, the control device 4 captures a subject image with the image sensor 3, creates a through image from the image signal, and displays the through image on the rear monitor 5. In subsequent step S120, the control device 4 measures the amount of light of the entire photographing screen based on the imaging signal acquired in step S110. The light amount (luminance) of the entire screen measured here is referred to as an overall luminance value.

  Next, in step S130, the control device 4 detects the position and range of the person's face included in the shooting screen based on the imaging signal acquired in step S110. The control device 4 detects the face using a known technique such as pattern matching. In step S140, the control device 4 determines whether or not the face has been successfully detected in step S130.

  If the face detection is successful, the process proceeds to step S150, and the face detection flag is set to 1. In step S160, the amount of light is measured in the detected face range in the entire shooting screen. Here, the “face range” may be, for example, a rectangular area circumscribing the detected face, or may be an area represented by the detected face outline. The amount of light in the face range measured here is referred to as a face luminance value. In step S170, the control device 4 causes the RAM 7 to store the face luminance value acquired in step S160. If the face luminance value is already stored in the RAM 7, the control device 4 updates the old face luminance value with the latest face luminance value acquired in step S160.

  In step S180, the control device 4 calculates a control luminance value for exposure control based on the latest overall luminance value acquired in the latest step S120 and the latest face luminance value acquired in the latest step S160. To do. The control brightness value is, for example, a weighted average of the overall brightness value and the face brightness value, and is weighted so that the influence of the face brightness value is greater than the overall brightness value. This is to prevent at least the face from becoming difficult to visually recognize due to whiteout or blackout when a face is included in the shooting range.

  In step S190, the control device 4 performs exposure control based on the control luminance value calculated in step S180, and proceeds to step S200. The exposure control is control for setting an aperture value, a shutter speed, a gain of the image sensor 3 and the like so that an appropriate exposure with respect to a control luminance value can be obtained.

  On the other hand, if the control device 4 determines in step S140 that face detection has failed, the control device 4 advances the process to step S210. In step S210, the control device 4 determines whether or not the face detection flag is 1. If the face detection flag is 1, the control device 4 advances the process to step S220.

  In step S220, the control device 4 executes a face luminance value continuation determination process described later. In the face luminance value continuation determination process, the control device 4 determines whether or not to continue exposure control based on the face luminance value. When it determines with continuing exposure control based on a face brightness value, affirmation determination is made by step S230, and the control apparatus 4 advances a process to step S240.

  In step S240, the control device 4 calculates a control brightness value for exposure control based on the latest overall brightness value acquired in the latest step S120 and the face brightness value stored in the RAM 7. The specific calculation contents are the same as in step S180. Then, the process proceeds to step S190, exposure control is performed based on the control luminance value calculated in step S240, and the process proceeds to step S200.

  If the face detection flag is 0 in step S210, the control device 4 advances the process to step S260. In step S260, the control device 4 performs exposure control based only on the latest overall luminance value acquired in the latest step S120, and proceeds to step S200. The exposure control performed here is based only on the light amount of the entire shooting screen measured in step S120, and the presence of a face on the shooting screen is not considered.

  In the face luminance value continuation determination process, when it is determined not to continue the exposure control based on the face luminance value, a negative determination is made in step S230, and the control device 4 advances the process to step S250. In step S250, the control device 4 sets the face detection flag to 0, and clears the face luminance value if the face luminance value is stored in the RAM 7. Then, the process proceeds to step S260, where the control device 4 performs exposure control based only on the latest overall luminance value acquired in the most recent step S120, and proceeds to step S200.

  In step S200, the control device 4 determines whether or not to end the display of the through image. For example, when the live view display is terminated, such as when the power of the imaging apparatus 1 is turned off or when the display device transitions to a playback mode for playing back a captured image, the live view display process illustrated in FIG. In other cases, the control device 4 advances the process to step S110 and repeatedly executes the processes of steps S110 to S200.

  FIG. 3 is a flowchart of the face luminance value continuation determination process called in step S220 of FIG. First, in step S300, the control device 4 determines whether or not the difference between the latest overall luminance value and the previous overall luminance value (that is, the difference between the overall luminance values between frames) exceeds a predetermined threshold value. In other words, the control device 4 determines whether or not the amount of change in the overall luminance value between frames exceeds a predetermined threshold value. When the amount of change exceeds a predetermined threshold value, the control device 4 advances the process to step S340 and determines that the use of the face luminance value should not be continued. On the other hand, when the amount of change is not more than the predetermined threshold value, the control device 4 advances the process to step S310.

  In step S310, the control device 4 determines whether or not a predetermined period (for example, 3 seconds) has elapsed since the last face detection. In other words, the control device 4 determines whether or not a predetermined period has elapsed since the face could not be detected. If the predetermined period has elapsed, the control device 4 advances the process to step S340, and determines that the use of the face luminance value should not be continued. On the other hand, when the predetermined period has not elapsed, the control device 4 advances the process to step S320.

  In step S320, the control device 4 determines the difference (that is, between frames) between the amount of motion in the shooting screen of the imaging signal obtained by the latest imaging and the amount of motion in the shooting screen of the imaging signal obtained by the previous imaging. It is determined whether or not the difference in motion amount exceeds a predetermined threshold value. In other words, the control device 4 determines whether or not the amount of change in the overall luminance value between frames exceeds a predetermined threshold value. Although not explicitly shown in FIG. 2, the control device 4 repeatedly detects the amount of movement in the shooting screen every time shooting is performed in step S <b> 110. When the change amount of the motion amount exceeds the predetermined threshold value, the control device 4 advances the process to step S340 and determines that the use of the face luminance value should not be continued. On the other hand, if the change amount is equal to or less than the predetermined threshold value, the control device 4 advances the process to step S330. In step S330, the control device 4 determines that exposure control based on the face luminance value should be continued.

  Next, a specific operation example of the imaging apparatus 1 when the through image display process described above is executed will be described.

(1) When the face is not included in the shooting screen When the face is not included in the shooting screen, for example, when shooting a landscape, the face detection in step S130 always fails. Accordingly, a negative determination is always made in step S140. Further, since the face detection flag remains 0, the negative determination is always made in step S210, which is the next step after step S140. Thereby, the control apparatus 4 repeats a process in order of step S110-S140, S210, S260, S200. That is, the imaging and live view display and the exposure control based on the entire luminance value that is the photometric result of the entire screen are repeatedly executed.

(2) When a face is included in the shooting screen and the detection is always successful Assuming that face detection does not fail, an affirmative determination is always made in step S140. In this case, the control device 4 repeats the processing in the order of steps S110 to S200. That is, the imaging and live view display and the exposure control based on the control brightness value calculated from the overall brightness value that is the photometric result of the entire screen and the face brightness value that is the photometric result of the face area are repeatedly executed.

(3) When a face is included in the shooting screen and the detection temporarily fails The face included in the shooting screen is, for example, a face that faces sideways or the amount of light from the light source changes suddenly. If whiteout or blackout occurs, detection may not be possible. If the cause of the face detection failure is due to such a temporary problem, for example, the face orientation may be restored or the face may be over-exposured or eliminated by exposure control. Can be detected. For example, when a through image is displayed at 60 frames per second, there is a high possibility that a face can be detected immediately even if only a few frames to a few dozen frames are not detected.

  Therefore, when the face cannot be detected despite the fact that the face has been successfully detected until recently (the face detection flag is 1), the control device 4 is temporarily unable to detect the face. It is checked in steps S310 and S320 (FIG. 3) whether there is any. If it is determined that the cause of the face detection failure is temporary, the latest face photometry result (the face luminance value stored in the RAM 7) is used as if the face detection was successful. The same exposure control as when the face detection is successful is performed (steps S230, S240, S190).

  Further, when it is determined that the face detection failure is not temporary (steps S310 and S320), or when it is determined that it is not appropriate to use the past face luminance value due to a significant change in the luminance of the entire screen (step S310). In step S300, the face detection flag is set to 0 and the face luminance value stored in the RAM 7 is cleared, and exposure control based on the entire luminance value, which is the photometric result of the entire screen, is performed without considering the face area and the like. To come.

According to the imaging apparatus according to the first embodiment described above, the following operational effects can be obtained.
(1) The control device 4 repeatedly detects the face in the subject image by the image sensor 3 and detects the face luminance value in the face area and stores it in the RAM 7 each time a face is detected. The control device 4 calculates the control brightness value for exposure control based on the face brightness value and the overall brightness value in the entire shooting screen area that is wider than the area of the main subject, but the face cannot be detected. In this case, the control brightness value is calculated based on the face brightness value stored in the RAM 7 and the latest overall brightness value. Since it did in this way, even when it becomes impossible to detect a face temporarily, the rapid change of exposure can be suppressed.

(2) The control device 4 clears the face luminance value stored in the RAM 7 when a predetermined condition is satisfied. When the face luminance value stored in the RAM 7 has not been detected and the face luminance value stored in the RAM 7 has been cleared, the control device 4 performs exposure control based on the overall luminance value. Since it did in this way, when it becomes impossible to detect a face for a long time, not temporarily, it can transfer to exposure control based on a whole luminance value rapidly, and the followability of exposure control improves.

(3) As a predetermined condition, the control device 4 clears the face luminance value stored in the RAM 7 when the difference between the latest total luminance value and the previous total luminance value exceeds a predetermined threshold value. Since it did in this way, it can respond rapidly also to the big change of the luminance value of the whole screen, and the followability of exposure control improves.

(4) As the predetermined condition, the control device 4 clears the face luminance value stored in the RAM 7 when a predetermined period elapses after the face cannot be detected. Since it did in this way, the followability of exposure control improves.

(5) The controller 4 stores the face stored in the RAM 7 as a predetermined condition when the difference between the most recent motion amount in the subject image by the image sensor 3 and the previously detected motion amount exceeds a predetermined threshold value. Clear the brightness value. Since it did in this way, the followability of exposure control improves.

  The following modifications are also within the scope of the present invention, and one or a plurality of modifications can be combined with the above-described embodiment.

(Modification 1)
In the embodiment described above, the imaging apparatus is configured to detect a human face as a main subject and perform exposure control using the luminance value of the face and the luminance value of the entire screen. Other than the face may be detected. Further, instead of the brightness value of the entire screen, a brightness value in a wider range than the face including the face may be used. For example, a rectangle circumscribing the face may be expanded vertically and horizontally by a predetermined length, and the luminance value in the expanded rectangular range may be used as the overall luminance value described above.

(Modification 2)
In the embodiment described above, the exposure control based on the face brightness value is not continued when any of the three conditions (steps S300, S310, S320) is satisfied in the face brightness value continuation determination process. That is, when none of the three conditions is satisfied, the exposure control based on the face luminance value is continued. The content of the face luminance value continuation determination process is not limited to this. For example, in the face luminance value continuation determination process, only one of the three conditions described above may be examined, or another condition different from these three conditions may be examined.

  As an example of conditions different from the above three conditions, a condition of whether or not the target subject (face) has left the shooting screen can be considered. If the person to be photographed is out of the photographing range (angle of view) of the image sensor 3, it is considered that the face detection will not succeed again even if waiting. Therefore, in the face luminance value continuation determination process, it is determined whether or not the main subject is out of the imaging range of the image sensor 3, and when it is determined that the main subject is out of the imaging range of the image sensor, the face luminance value is determined. What is necessary is just to determine that the use of should not be continued.

  As a method for determining whether or not the main subject is out of the imaging range of the image sensor 3, for example, a face movement history is tracked by keeping a history of face positions detected in the past, and the face is within the imaging range. What is necessary is just to use the method of detecting that it faces outside, and the method of estimating that the face came out of the imaging | photography range when the detection of a face failed in the edge part of the imaging | photography range.

(Modification 3)
In the above-described embodiment, the through image is displayed on the rear monitor 5, but the through image may be displayed on another display device such as an electronic viewfinder. In addition, although photometry is performed using the image pickup signal output from the image pickup device 3, a photometry sensor may be provided separately from the image pickup device 3 and the photometry sensor may be used for photometry.

(Modification 4)
In the above-described embodiment, the exposure control in displaying a through image has been described, but the present invention is not limited to such an embodiment. For example, exposure control as described with reference to FIG. 2 can be performed during moving image shooting or continuous shooting of still images.

(Modification 5)
In the embodiment described above, an example in which the present invention is applied to a lens-integrated digital camera has been described. It can also be applied.

  As long as the characteristics of the present invention are not impaired, the present invention is not limited to the above-described embodiments, and other forms conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention. .

DESCRIPTION OF SYMBOLS 1 ... Imaging device, 2 ... Imaging optical system, 3 ... Imaging element, 4 ... Control apparatus, 5 ... Back monitor, 6 ... ROM, 7 ... RAM

Claims (7)

An image sensor for imaging a subject;
Subject detection means for repeatedly detecting a main subject in a subject image by the image sensor;
A first luminance value detecting means for detecting a first luminance value in a main subject area each time the subject detecting means detects the main subject;
Storage means for storing the first luminance value each time the first luminance value detecting means detects the first luminance value;
Second luminance value detecting means for repeatedly detecting a second luminance value in an area wider than the area of the main subject;
A third luminance value for exposure control is calculated based on the first luminance value detected by the first luminance value detecting means and the second luminance value detected by the second luminance value detecting means. An arithmetic means,
When the subject detection means cannot detect the main subject, the calculation means is based on the stored first brightness value and the second brightness value detected by the second brightness value detection means. An image pickup apparatus that calculates the third luminance value. The imaging device according to claim 1,
The storage means clears the stored first luminance value when a predetermined condition is satisfied,
The computing means is configured to detect the second luminance value detected by the second luminance value detecting means when the subject detecting means cannot detect the main subject and the stored first luminance value is cleared. An image pickup apparatus that calculates the third luminance value based on a luminance value. The imaging device according to claim 2,
When the difference between the latest second luminance value detected by the second luminance value detecting unit and the previous second luminance value exceeds a predetermined threshold as the predetermined condition, An image pickup apparatus that clears the stored first luminance value. In the imaging device according to claim 2 or 3,
The storage device clears the stored first luminance value as the predetermined condition when a predetermined period elapses after the subject detection unit cannot detect the main subject. In the imaging device according to any one of claims 2 to 4,
A motion amount detecting means for repeatedly detecting a motion amount in the subject image by the image sensor;
When the difference between the most recent motion amount detected by the motion amount detection unit and the previous motion amount exceeds a predetermined threshold as the predetermined condition, the storage means stores the first stored An imaging device characterized by clearing a luminance value. In the imaging device according to any one of claims 2 to 5,
Determining means for determining whether or not the main subject is out of the imaging range of the image sensor;
The storage device clears the stored first luminance value when the determination unit determines that the main subject is out of the imaging range of the imaging device as the predetermined condition. In the imaging device according to any one of claims 1 to 6,
The imaging device characterized in that the subject detection means detects a face as a main subject.

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