JP5917142B2 - Imaging apparatus, control method therefor, and program - Google Patents

Description

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

  2. Description of the Related Art Conventionally, an exposure correction function that corrects the flash emission and exposure in the over direction in a scene where the subject becomes dark, such as a backlight scene, has been known to make the brightness of the subject appropriate.

  On the other hand, it is not preferable to perform strobe light emission on a subject sensitive to light stimulation such as an infant. Therefore, the brightness of the subject can be brought close to an appropriate level by setting the exposure correction amount to be larger than that at the time of strobe light emission, by making the strobe non-light-emitting.

  In this case, simply overexposure has a problem that an area where the subject is bright, such as a background portion in a backlight scene, becomes brighter and more likely to be overexposed.

  Therefore, in an imaging device that detects whether or not a shooting scene is backlit from the brightness of the person subject and the background, the background brightness is checked so that the background does not fly out and the person subject is as bright as possible. A method of performing exposure correction is disclosed (for example, see Patent Document 1).

JP 2010-283593 A

  However, when shooting a subject with a white wall as a background, it may not always be necessary to suppress white background blur depending on the shooting scene.

  In the prior art disclosed in Patent Document 1, even in a scene where it is not necessary to suppress overexposure, the exposure correction amount may be reduced so that overexposure does not occur, and the human subject may become darker than desired.

  An object of the present invention is to provide an imaging apparatus capable of appropriate exposure control, a control method thereof, and a program.

To achieve the above object, an imaging apparatus according to claim 1, detects an area indicating an acquisition unit for acquiring an image signal representing a subject, the main object in the image shown in the image signal acquired by the acquisition unit using a detection means, the area detected by the previous SL detecting means, dividing means for dividing the image into the main subject region and one or more background regions, the saturation in the background regions divided by the dividing means or using the luminance, whiteout judging means for judging whether a scene that does not permit, the by determination means, white the dividing means effected even if it is determined that the scene that does not permit skipping said image the when divided into two or more background areas, the brightness of the background region between you adjacent, characterized by comprising determination means for determining the exposure compensation amount to be below the saturation intensity.

  According to the present invention, it is possible to provide an imaging apparatus capable of appropriate exposure control, a control method therefor, and a program.

1 is a diagram illustrating a schematic configuration of an imaging apparatus according to an embodiment of the present invention. It is a flowchart which shows the flow of the exposure correction amount calculation process performed by the exposure correction amount calculation process part in FIG. It is a flowchart which shows the procedure of the white-out permission determination process performed by the white-out permission determination part in FIG. 3 is a flowchart showing a procedure of exposure correction amount changing processing executed when whiteout is not permitted by the exposure correction amount changing unit in FIG. 1.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an imaging apparatus 100 according to an embodiment of the present invention.

  In FIG. 1, an image signal acquisition unit 101 (acquisition means) acquires a digital image signal that is an image signal indicating a subject. This digital image signal is acquired as follows.

  First, an incident light is received through an optical unit (not shown) composed of a lens or the like, and an analog image signal with an electric charge corresponding to the amount of light is output from an image sensor unit (not shown). Then, a digital image signal is obtained by performing sampling, gain adjustment, A / D conversion, and the like on the analog image signal output from the imaging element unit by an A / D conversion unit (not shown). When this digital image signal is input to the image signal acquisition unit 101, the image signal acquisition unit 101 acquires the image signal.

  The digital image signal acquired by the image signal acquisition unit 101 is subjected to various types of image processing by an image processing unit (not shown), and then converted into a YUV image signal and output to the subject detection unit 102. In the following description, a signal output from the image signal acquisition unit 101 is simply expressed as an image signal.

  The subject detection unit 102 (detection means) detects an area indicating the main subject in the image. For example, the face area is detected as an area indicating the main subject based on color information or contrast in the image indicated by the image signal.

  The exposure correction amount calculation unit 103 (calculation unit) calculates the exposure correction amount using the luminance in the image indicated by the image signal acquired by the image signal acquisition unit 101. In calculating the exposure correction amount, the luminance distribution in the image and the luminance value of the subject area detected by the subject detection unit 102 are used.

  For example, the exposure correction amount calculation unit 103 calculates the exposure correction amount so that the face area detected by the face detection function approaches the appropriate luminance. At that time, the exposure correction amount may be calculated according to the size of the main subject in the entire image.

  In this case, the exposure correction amount calculation unit 103 considers the main subject to be taken with priority as the proportion of the main subject in the image increases, and increases the exposure correction amount so that the main subject is more appropriately brought closer.

  Further, the correction amount may be changed depending on the person specified based on the face area image. For example, if the exposure correction amount calculation unit 103 can grasp before photographing that a subject sensitive to light stimulation such as an infant in a backlight scene is taken, the strobe is not emitted and the exposure correction amount is increased instead. .

  On the other hand, if it is determined that the subject is less affected by the flash emission, the flash is emitted and the exposure correction amount is reduced instead.

  The whitening allowance determination unit 104 (dividing unit, determination unit) divides an image into a main subject region and one or more background regions using the region detected by the subject detection unit 102. Then, using the saturation or luminance in the divided background region, it is determined whether or not the image is an image in which whiteout is unacceptable.

  For example, the whitening allowance determination unit 104 makes it easy to allow whiteout in a scene where the subject is dark but there are many achromatic areas such as white walls in the background, and whiteout if there are many chromatic areas in the background. It is difficult to tolerate flying.

  In addition, the whiteout allowance determining unit 104 makes it difficult to allow whiteout if the scene is such that the boundary line between adjacent background regions in the image is not noticeable by exposure correction. The adjacent background area in the image refers to, for example, an outdoor building area and an empty area in contact therewith. For example, the brightness value of the adjacent background region is used to determine whether or not the boundary line becomes inconspicuous.

  When the brightness of the sky area is saturated by correcting the exposure in the backlight scene, if the exposure is further corrected in the over direction, the brightness value is increased only in the building area, and the brightness difference is reduced. Then, the boundary line between the building area and the sky area becomes inconspicuous, and it is difficult to allow overexposure in such a scene.

  The exposure correction amount changing unit 105 (changing unit) adjusts the luminance in the adjacent background region to be lower than the saturation luminance when the whiteout allowable determination unit 104 determines that the image is an image in which whiteout is not allowable. The exposure correction amount calculated by the exposure correction amount calculation unit 103 is changed.

  For example, in a scene in which the boundary line between adjacent background areas is not noticeable due to exposure correction, exposure correction is performed only to a range where the luminance value of a high luminance value area in the adjacent background areas is not saturated.

  The exposure correction amount output unit 106 outputs the exposure correction amount calculated by the exposure correction amount calculation unit 103 and changed as necessary by the exposure correction amount change unit 105. A process for controlling the exposure mechanism is performed in accordance with the output exposure correction amount. With the configuration described above, it is possible to determine an appropriate exposure correction amount according to the scene.

  FIG. 2 is a flowchart showing the flow of exposure correction amount calculation processing executed by the exposure correction amount calculation unit 103 in FIG.

  In FIG. 2, first, a luminance target is set (step S201). This luminance target indicates, for example, the luminance that the face area is considered to have proper luminance or the luminance that the entire screen is considered to have proper luminance.

  Next, it is determined whether or not a face is detected in the image by the subject detection unit 102 (step S202).

  If the result of determination in step S202 is that a face has not been detected (NO in step S202), the process proceeds to step S204. On the other hand, when a face is detected (YES in step S202), the brightness of the face area that is an area including the face is calculated (step S203). This calculation method will be described later.

  Next, the brightness of the entire image is calculated (step S204). This calculation method will be described later. Then, using the brightness of the calculated face area and the entire image, an exposure correction amount is calculated (step S205), and this process ends.

  First, regarding the luminance target in step S201, a luminance target that assumes that the face area has appropriate luminance is YrefFace, and a luminance target that assumes that the entire screen has appropriate luminance is Yref.

  Next, a method of calculating the luminance between the face area and the entire image in step S203 will be described. In this luminance calculation method, an image is divided into a plurality of M × N blocks, and the average luminance Y (m, n) calculated for each block (m = 0 to M−1, n = 0 to N−1). Is used.

  For example, assuming that M = 32 and N = 24, the average luminance value YLFace of the block corresponding to the face area among the blocks is calculated as the luminance of the face area.

  In addition, photometric weights W (m, n) (m = 0 to M−1, n = 0 to N−1) are used as a method for calculating the luminance of the entire image.

Using this photometric weight, the luminance value YLAll of the entire image is calculated by the following equation.
YLAll = (ΣY (m, n) × W (m, n)) / ΣW (m, n)
Σ is the sum of m = 0 to M−1 and n = 0 to N−1. The photometric weight W (m, n) is set to a larger value as it approaches the center of the screen, for example.

  The exposure correction amount is calculated from the brightness YLFace of the face area thus obtained and the brightness YLAAll of the entire image.

  In calculating the exposure correction amount, first, the difference in the number of steps from the luminance target of the face area and the entire image is calculated.

A step number difference DeltaBvFace from the appropriate luminance of the face area and a step number difference DeltaBvAll from the appropriate luminance of the entire image are calculated as follows.
DeltaBvFace = log (YLFace / YrefFace)
DeltaBvAll = log (YrefFace / Yref)
The base of the logarithm of the above formula is 2.

  Next, a correction amount is calculated according to the difference between DeltaBvFace and DeltaBvAll.

  For example, when DeltaBvFace <DeltaBvAll, as in a backlight scene where the background area is brighter than the face area, Delta = | DeltaBvAll-DeltaBvFace | is first calculated.

  When Delta is small, that is, when the difference in brightness between the face and the background is small, the exposure correction amount is set so that the face area is appropriate.

  On the other hand, when Delta is large, if the exposure correction is performed until the face area becomes appropriate, the correction amount increases and the background area may be easily overexposed.

  Therefore, Th_FaceUnder having a proportional relationship that increases as Delta increases is used.

  Then, by calculating the exposure correction amount so that the face area becomes smaller by Th_FaceUnder than appropriate, it becomes possible to make the background difficult to white out while appropriately approaching the face area.

  Further, since Th_FaceUnder is in a proportional relationship with Delta, the face brightness after exposure correction does not become too bright as the face brightness becomes much darker than appropriate, and it is possible to suppress overexposure of the background.

  Even in a scene where DeltaBvFace> DeltaBvAll, the exposure correction amount is calculated so that the face and background are not overexposure and blackout is caused in the same manner as described above.

  An individual may be specified based on the face area image, and the value of Th_FaceUnder may be switched according to the specified result.

  For example, if a subject is equipped with a strobe that illuminates the light, and a person who does not want to emit strobe light such as an infant in a backlit scene is known to be the subject, instead of shooting without the strobe, Th_FaceUnder Decrease the value.

  By doing so, it is possible to increase the exposure correction amount and to bring the subject luminance closer to the subject more appropriately for a subject for which strobe non-emission is preferable.

  As described above, when the image of the region indicating the main subject detected by the subject detection unit 102 is an image showing a predetermined subject (an infant or an infant), irradiation with a strobe is not performed. Then, the exposure correction amount calculation unit 103 calculates the exposure correction amount larger than the exposure correction amount calculated when the subject is not a predetermined subject.

  In addition, when the image of the area indicating the main subject detected by the subject detection unit 102 is an image indicating another predetermined subject, irradiation with a strobe is performed. Then, the exposure correction amount calculation unit 103 may calculate the exposure correction amount smaller than the exposure correction amount calculated in the case of a predetermined subject (infant or infant). It should be noted that the other predetermined subject is a subject that has little influence even when the flash is emitted.

  Further, as the ratio of the face area to the image increases, it is considered that the main subject is preferentially shot, and the value of Th_FaceUnder is decreased so that the main subject is more appropriately brought closer to the exposure correction amount. Good. As described above, the exposure correction amount calculation unit 103 calculates the exposure correction amount according to the size occupied by the area indicating the main subject detected by the subject detection unit 102.

  With the above method, it is possible to determine the exposure correction amount based on the luminance information in the image.

  FIG. 3 is a flowchart showing a procedure of the white-out permission determination process executed by the white-out permission determination unit 104 in FIG.

  In this whiteout allowance determination process, whiteout allowance determination in a backlight scene will be described.

  In FIG. 3, first, the image is divided into M × N blocks (step S301). Next, the loop variables n and m are initialized with 0 (step S302), and the feature amount of each block is calculated (step S303). The calculation of the feature amount will be described later.

  Next, feature quantities of the (n × M + m) -th block, the block above the block, and the left block are compared (step S304).

  It is determined whether or not the absolute value of the difference between the feature value of the (n × M + m) -th block and the feature value of the upper block is within a predetermined threshold Th_same (step S305). This threshold value Th_same is determined by experiments or the like.

  As a result of the determination in step S305, when the absolute value of the difference is not within the predetermined threshold Th_same (NO in step S305), the process proceeds to step S307.

  On the other hand, if the absolute value of the difference is within the predetermined threshold Th_same as a result of the determination in step S305 (YES in step S305), the (n × M + m) th block is set to the same group as the upper block (step S306).

  Next, it is determined whether or not the absolute value of the difference between the feature value of the (n × M + m) th block and the feature value of the left block is within a predetermined threshold Th_same (step S307).

  As a result of the determination in step S307, when the absolute value of the difference is not within the predetermined threshold Th_same (NO in step S307), the process proceeds to step S309.

  On the other hand, as a result of the determination in step S307, when the absolute value of the difference is within a predetermined threshold Th_name (YES in step S307), the (n × M + m) th block is set to the same group as the left block (step S308).

  Next, m is incremented by 1 (step S309), and it is determined whether m is larger than M-1 (step S310).

  If it is determined in step S310 that m is equal to or less than M-1 (NO in step S310), the process proceeds to step S304. On the other hand, when m is larger than M-1 (YES in step S310), m is initialized with 0, n is incremented by 1 (step S311), and it is determined whether n is larger than N-1 (step S312). ).

  As a result of the determination in step S312, when n is N−1 or less (NO in step S312), the process proceeds to step S304. On the other hand, when n is larger than N−1 (YES in step S312), it is determined for each group whether the main subject area or the background area (step S313). This determination method will be described later.

  Next, it is determined whether or not there is a group having an area greater than or equal to Th_Area_1 and an average saturation greater than or equal to Th_Chroma among the groups determined to be the background region (step S314). If the result of determination in step S314 is affirmative (YES in step S314), it is determined that overexposure is not permitted (step S316), and this process ends.

  On the other hand, if the result of determination in step S314 is negative (NO in step S314), the following processing is performed. That is, it is determined whether there is a group having an area of Th_Area_2 or more, an average luminance of Th_Y_1 or more, and an adjacent background group having an average luminance of Th_Y_2 or less among the groups determined as the background region (step S315).

  If the result of determination in step S315 is affirmative (YES in step S315), the process proceeds to step S316. On the other hand, when a negative determination is made (NO in step S315), it is determined that over-exposure is permitted (step S317), and this process ends.

  First, the feature value calculation method in step S303 will be described. As for the feature amount, for example, each block is further divided into a plurality of small regions, a luminance value is calculated for each small region, and the smallest luminance value in the plurality of small regions is used as the feature amount of the block.

  Further, if there is a small area having a luminance value equal to or higher than the threshold Th_HighLevel, the largest luminance value in the plurality of small areas is used as the feature amount. This threshold Th_HighLevel is determined by experiments or the like.

  For example, when only an extremely low luminance region and a high luminance region exist in a block, a value that is neither low luminance nor high luminance may be a feature amount in a method using an average value as a feature amount. However, the luminance value of either low luminance or high luminance existing in the block can be used as the feature amount by the method described above.

  Next, with regard to the processing of steps S304 to S312, processing for grouping each block is performed based on the calculated feature amount.

  In the above steps, the process of determining whether or not they are in the same group based on the feature values of adjacent blocks is performed in order from the upper left block in the image to the right side, and if scanning to the right end is performed, the next lower line This process is repeated such as scanning from the left end to the right side.

  And the block which discriminate | determines whether it is the same group is made into the block located on the target block, and the block located on the left.

  For determining whether or not they are in the same group, for example, the magnitude of the absolute value of the difference between the feature amounts of two adjacent blocks is used. When the absolute value of the difference between the feature amounts is small, the same group is regarded as the same group. Otherwise, it is not regarded as the same group.

  By performing these processes on all blocks in the image, blocks having similar feature amounts are grouped. As described above, the whitening allowance determination unit 104 divides the image into a plurality of blocks, and divides the image into groups by grouping the plurality of blocks using the luminance for each of the divided blocks. Then, the image is divided into a main subject area and one or more background areas for each group. The luminance used when grouping a plurality of blocks is the average luminance of each block in the plurality of blocks.

  Next, the process of determining whether the subject area or the background area for each group in step S313 will be described. First, the average brightness and saturation of each group are calculated. Then, the face area detected by the face detection function and the low luminance area around the face area are set as the main subject area, and all areas other than the main subject area in the image are set as the background area.

  Next, when an affirmative determination is made in step S314, a chromatic background region occupying most of the screen is present. At this time, the appearance of the image may be different if the area is blown out by exposure correction. Therefore, if such a group is found, it is determined that whiteout is not allowed.

  On the other hand, if the determination in step S315 is affirmative, it means that there is a high-luminance region that is equal to or greater than a certain size in the image, and the difference between the luminance values of adjacent background groups is large. In this case, in an actual scene, it is possible to visually determine the boundary between adjacent groups at the time of shooting.

  However, if exposure correction is performed until the high-luminance background area becomes equal to or higher than the saturation luminance, the difference in luminance between groups will be small, and it will be difficult to visually distinguish the boundaries in the captured image. May look different. Therefore, if an affirmative determination is made in step S315, it is determined that whiteout is not allowed.

  If neither step S314 nor S315 is satisfied, it is determined that whiteout is allowed.

  With the above method, it is possible to determine whether or not an image is allowed to be overexposed. Note that the above-described threshold values Th_Area_1, Th_Area_2, Th_Chroma, Th_Y_1, and Th_Y_2 are determined through experiments or the like.

  FIG. 4 is a flowchart showing the procedure of the exposure correction amount changing process executed when the exposure correction amount changing unit 105 in FIG.

  In FIG. 4, in each group determined to be the background region, an exposure correction value Value_1 is calculated so that all of the maximum luminances of the groups having an area of Th_Area_1 or more and an average saturation of Th_Chroma or more are Th_Ylimit_1 or less (step). S401).

  Before the exposure correction, an upper limit of the luminance value that is increased by the exposure correction is set so that the background area that is a chromatic color does not approach an achromatic color by the exposure correction. By doing so, it is possible to change the exposure correction amount in a range in which the background region maintains high saturation.

  The next step S402 is processing that targets groups having an area of Th_Area_2 or more, an average luminance of Th_Y_1 or more, and an adjacent background group having an average luminance of Th_Y_2 or less among the groups determined as background regions. An exposure correction value Value_2 is calculated so that all the maximum luminances in the target group are equal to or less than Th_Ylimit_2 (step S402).

  An upper limit of the luminance value that is increased by exposure correction is set so that both areas are lower than the saturation luminance between adjacent background groups. By doing so, the exposure correction amount can be changed within a range in which the luminance difference between the background groups is maintained.

  Next, the smaller one of Value_1 and Value_2 is clipped to Value (step S403). When the exposure correction amount calculated in the flowchart of FIG. 2 exceeds Value, the exposure correction amount is changed to Value.

  The above-described threshold values Th_Ylimit_1 and Th_Ylimit_2 are determined through experiments or the like.

  By the above method, the exposure correction amount can be changed based on the exposure correction amount calculated based on the image and the determination result of whether or not the image is allowable for overexposure.

  According to the above-described embodiment, the imaging apparatus 100 acquires an image signal indicating a subject, detects an area indicating a main subject in the image, and performs exposure correction using the luminance in the image indicated in the acquired image signal. Calculate the amount.

  The detected area is used to divide the image into a main subject area and one or more background areas, and the saturation or brightness in the divided background area is used to make the image unacceptable for overexposure. It is determined whether or not.

  Next, when it is determined that the image is unacceptable for overexposure, the exposure correction amount calculated so that the brightness in the adjacent background area is lower than the saturation brightness is changed, so that proper exposure control is possible. Become.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

(Other embodiments)
The present invention is also realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program code. It is a process to be executed. In this case, the program and the storage medium storing the program constitute the present invention.

DESCRIPTION OF SYMBOLS 100 Imaging device 101 Image signal acquisition part 102 Subject detection part 103 Exposure correction amount calculation part 104 Overexposure allowance determination part 105 Exposure correction amount change part 106 Exposure correction amount output part

Claims (11)

Obtaining means for obtaining an image signal indicating a subject;
Detecting means for detecting a region showing main object in an image represented by an image signal acquired by the acquisition unit,
Using a region detected by the front Symbol detection means, dividing means for dividing the image into the main subject region and one or more background regions,
Using saturation or brightness in the divided background region by the dividing means, determining means for determining whether a scene that does not permit whiteout,
By the determination unit, when overexposure said dividing means effected even if it is determined that the scene that does not permit it obtained by dividing the image into two or more background areas, the brightness of the background region between you adjacent the imaging apparatus characterized by comprising a determination means for determining the exposure compensation amount to be below the saturation intensity. The determining means determines that adjacent background areas are determined when the determining means determines that the scene does not allow overexposure and the dividing means divides the image into two or more background areas. The image pickup apparatus according to claim 1, wherein the exposure correction amount is determined so that the difference in brightness is equal to or greater than a predetermined difference in brightness. When the divided region divides the image into two or more background regions, the determination unit includes a background region in which the luminance between adjacent background regions is equal to or less than a predetermined threshold, and each of the adjacent backgrounds The imaging apparatus according to claim 1, wherein when the area of the region is equal to or larger than a predetermined area, the scene is determined not to allow the whiteout. Said determining means, to any one of claims 1 to 3 region showing a main subject detected and determines the exposure correction amount according to the size occupied by the image by said detecting means The imaging device described. The dividing unit divides the image into a plurality of blocks, groups the plurality of blocks using the luminance for each of the divided blocks, and divides the image into a main subject region and one or more groups by the group unit. the imaging apparatus according to any one of claims 1 to 4, wherein the dividing of the background area. The imaging apparatus according to claim 5 , wherein the luminance used when grouping the plurality of blocks is an average luminance of each of the plurality of blocks. A strobe for irradiating the subject with light;
Wherein when the main object scene object detected by the detection means is a subject that has been previously determined, without irradiation by the flash, the determining means, said not a predetermined subject If I remote the imaging apparatus according to any one of claims 1 to 6, wherein the magnitude camphor Rukoto the exposure correction amount. Wherein when the main object scene object detected by the detection means is another object other than the object said predetermined performs irradiation by the flash, the determining means, if the subject said predetermined O remote imaging apparatus according to claim 7, wherein the small camphor Rukoto the exposure correction amount. The photographic material, said predetermined imaging apparatus according to claim 7 or 8 characterized in that it is a baby or infant. A method for controlling an imaging apparatus,
An acquisition step of acquiring an image signal indicating a subject;
A detection step of detecting a region showing main object in an image represented by an image signal acquired by the acquisition step,
Using a region detected by the front Symbol detection step, a dividing step of dividing the image into the main subject region and one or more background regions,
The resolved using saturation or brightness in the divided background area in step, a determining step of determining whether a scene that does not permit whiteout,
Wherein the determination step, when the effected even if it is determined that the scene that does not permit whiteout image is divided into two or more background areas, the brightness of the background region between you adjacent, saturated brightness control method characterized by comprising a determination step of determining the exposure compensation amount to below. A program for causing a computer to execute a control method of an imaging apparatus,
The control method is:
An acquisition step of acquiring an image signal indicating a subject;
A detection step of detecting a region showing main object in an image represented by an image signal acquired by the acquisition step,
Using a region detected by the front Symbol detection step, a dividing step of dividing the image into the main subject region and one or more background regions,
The resolved using saturation or brightness in the divided background area in step, a determining step of determining whether a scene that does not permit whiteout,
Wherein the determination step, when the effected even if it is determined that the scene that does not permit whiteout image is divided into two or more background areas, the brightness of the background region between you adjacent, saturated brightness a program characterized by comprising a determination step of determining the exposure compensation amount to below.

Images