Imaging apparatus and control method of imaging apparatus

Abstract

To provide a technique which expresses a high luminance region with luminance along with the intent of a user while performing gradation correction according to a target luminance of highlight-weighted photometry.SOLUTION: An imaging apparatus comprises: exposure control means for performing exposure control such that the representative luminance of a high luminance region of an image becomes the target luminance set by a user; and gradation correction means for performing gradation correction on the basis of the luminance of a dark part being a region which has lower luminance than the high luminance region with respect to the photographed image captured after the exposure control is performed. The gradation correction means corrects a correction amount of the gradation correction such that the representative luminance of the high luminance region corrected to be higher than the target luminance by the gradation correction gets close to the target luminance.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an imaging device and a control method for an imaging device. [Background technology]

[0002] Imaging devices such as digital cameras perform a process of automatically correcting the brightness of a captured image. For example, Patent Document 1 proposes a technique for controlling gradation based on a target luminance value and a photometry evaluation value of imaging data. Also, as a photometry method for imaging devices, a highlight-weighted photometry method that focuses on measuring the high-luminance areas of an image is known. In the highlight-weighted photometry method, the imaging device automatically measures the high-luminance areas of the screen and can reduce blown-out highlights. Patent Document 2 proposes a technique in which a user sets a target luminance for a highlight area, and when an area with a higher luminance than the highlight area exists, the influence of the area is reduced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-359773 A [Patent Document 2] JP 2015-166767 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a photograph is taken with exposure adjusted to a target brightness set by the user using highlight-weighted metering and the gradation of dark areas, which are areas with lower brightness than high-brightness areas, is corrected, the brightness of the high-brightness areas also changes, which may result in the brightness of the high-brightness areas deviating from the target brightness set by the user.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a technology that expresses high-brightness areas at a brightness that meets the user's intentions while performing gradation correction according to the target brightness of highlight-weighted metering. [Means for solving the problem]

[0006] The imaging device of the present invention comprises an exposure control means for performing exposure control so that a representative luminance of a high-luminance area of ​​an image becomes a target luminance set by a user, and a gradation correction means for performing gradation correction on an image captured after the exposure control has been performed, based on the luminance of dark areas which are areas with a lower luminance than the high-luminance areas, and the gradation correction means is characterized in that it modifies the amount of correction for the gradation correction so that the representative luminance of the high-luminance area, which is corrected to be higher than the target luminance by the gradation correction, approaches the target luminance. Effect of the Invention

[0007] According to the present invention, it is possible to perform gradation correction according to the target luminance of highlight-weighted metering, while expressing high luminance areas with luminance that meets the user's intention. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram illustrating a configuration of a digital camera. [Diagram 2] 13 is an example of a screen on which a user selects a target luminance of a high luminance area. [Diagram 3] 11 is a flowchart illustrating a tone correction process. [Figure 4] FIG. 2 is a diagram illustrating an example of block division of an image. [Diagram 5] FIG. 2 is a diagram showing an example of a scene to which the first embodiment of tone correction is applied. [Figure 6] 11 is a flowchart illustrating a modification process of tone correction. [Figure 7] FIG. 13 is a diagram illustrating an example of a histogram. [Figure 8] 1 is an example of a correspondence table showing output luminance corresponding to average dark area luminance. [Figure 9] FIG. 1 is a diagram for explaining Example 1 of gradation correction in a tone curve. [Figure 10]13 is an example of a correspondence table showing the weakening amount of gradation correction corresponding to a target luminance. [Figure 11] FIG. 11 is a diagram for explaining Example 2 of gradation correction in a tone curve. [Figure 12] FIG. 13 is a diagram showing an example of a scene to which the third embodiment of the tone correction is applied. [Figure 13] 13 is a flowchart illustrating a correction process according to a third embodiment of the tone correction. [Figure 14] 1A and 1B are diagrams showing an example of a highlight overall portion and a main subject portion. [Figure 15] 13A and 13B are diagrams showing other examples of the overall highlight portion and the main subject portion. [Figure 16] 13 is an example of a correspondence table showing the weakening amount of tone correction corresponding to the degree of coincidence. [Figure 17] 13A to 13C are diagrams illustrating Example 3 of gradation correction in a tone curve. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is one example of a method for realizing the present invention, and may be appropriately modified or changed depending on the configuration of the device to which the present invention is applied and various conditions. In addition, each embodiment may be appropriately combined.

[0010] <Digital camera configuration> 1 is a block diagram illustrating the configuration of a digital camera 100 as an imaging device according to an embodiment of the present invention. The digital camera 100 includes a photographing lens 101 as an imaging mechanism, an aperture and shutter 102, an automatic exposure (AE) processor 103, a focus lens 104, an autofocus (AF) processor 105, an image sensor 106, and an A / D converter 107.

[0011] The photographing lens 101 has a zoom mechanism. The aperture and shutter 102 controls the amount of incident light, which is reflected light from a subject, on the image sensor 106 and the charge accumulation time according to instructions from the AE processing unit 103. The AE processing unit 103 controls the operation of the aperture and shutter 102 to control exposure. The AE processing unit 103 also controls an A / D conversion unit 107. The focus lens 104 focuses on the light receiving surface of the image sensor 106 and forms an optical image according to a control signal from the AF processing unit 105. The AF processing unit 105 also calculates distance information from the digital camera 100 to the subject.

[0012] The imaging element 106 converts the optical image formed on the light receiving surface into an electrical signal by photoelectric conversion means such as a CCD element or a CMOS element, and outputs the electrical signal to the A / D conversion unit 107. The A / D conversion unit 107 converts the received electrical signal (analog signal) into a digital signal (RAW signal). The A / D conversion unit 107 includes a CDS circuit that removes noise from the received electrical signal, and a nonlinear amplification circuit that nonlinearly amplifies the received electrical signal before converting it into a RAW signal.

[0013] The digital camera 100 also includes an image processing unit 108, an image recognition unit 109, a format conversion unit 110, and a DRAM (Dynamic RAM) 111. The image processing unit 108 performs predetermined pixel interpolation, resizing processing such as image reduction, and color conversion processing on the RAW signal input from the A / D conversion unit 107, and performs development processing to output image data.

[0014] The image processing unit 108 adjusts the white balance (WB) of the RAW signal input from the A / D conversion unit 107. The image processing unit 108 also adjusts the image quality of the captured image by performing gradation correction by increasing or decreasing the luminance level of the image.

[0015] For example, the image processing unit 108 has a function of increasing or decreasing the signal level of image data by a uniform amplification factor for the entire image. Also, the image processing unit 108 converts the signal level of the RAW signal input from the A / D conversion unit 107 according to the magnitude of the original signal level. The A / D converter 107 can also convert the analog signal converted by the gamma function into a RAW signal. The image processor 108 can perform gradation correction according to the scene based on the recognition result by the image recognition unit 109.

[0016] The image recognition unit 109 can accept input of image data processed by the image processing unit 108. The image recognition unit 109 can recognize the brightness of the input image by photometry processing. For example, the image recognition unit 109 divides the image into a plurality of regions and measures the light for each region. By measuring the light for each divided region, the image recognition unit 109 can also determine high-luminance regions and obtain photometry results for each divided region. The photometry results recognized by the image recognition unit 109 are output to the AE processing unit 103.

[0017] In addition, when an image is divided into a plurality of blocks, the high luminance region can be the block with the highest luminance among the blocks. The luminance of a block is, for example, the average value, maximum value, minimum value, median value, or mode value of the luminance in the block.

[0018] Furthermore, the image recognition unit 109 can recognize a scene by using a known technique. The image recognition unit 109 can detect the upper body or the whole body of a person, animals such as a dog, a cat, or a bird, or a vehicle such as a car or a motorcycle, and recognize a scene based on the detected subject. For example, when the image recognition unit 109 detects the face of a person who is a subject, it can recognize that the scene is a scene in which a person is to be photographed. Furthermore, when the image recognition unit 109 detects a plurality of cars running side by side, it can recognize that the scene is a motorsports scene. Information on the scene recognized by the image recognition unit 109 is output to the AE processing unit 103.

[0019] The user can select a photometry mode using the operation unit 116. The operation unit 116 outputs the photometry mode selected by the user to the AE processing unit 103. The AE processing unit 103 performs automatic exposure based on the photometry result recognized by the image recognition unit 109, the scene information identified by the image recognition unit 109, and the photometry mode selected by the user.

[0020] Furthermore, the image recognition unit 109 can recognize the focus state of the input image. Based on the recognition result of the focus state by the image recognition unit 109, the AF processing unit 105 realizes AF control. Furthermore, the image recognition unit 109 can generate a luminance histogram of the input image. The image processing unit 108 performs gradation correction according to the scene based on the generated luminance histogram.

[0021] A format conversion unit 110 converts the format of the image data generated by the image processing unit 108 in order to store the image data in a DRAM 111. The DRAM 111 is an internal memory and is used as a buffer for temporarily storing image data, or as a working memory for compressing / decompressing the image data.

[0022] Digital camera 100 includes an image recording unit 112, a system control unit 113, a VRAM (Video RAM) 114, a display unit 115, an operation unit 116, a main switch (main SW) 117, and a shooting switch (shooting SW) 118. Image recording unit 112 has a recording medium such as a memory card for recording shot images (still images, videos) and an interface therefor.

[0023] The system control unit 113 has a CPU (processor), ROM, and RAM. The CPU controls the overall operation of the digital camera 100 by expanding a program stored in the ROM into a working area of ​​the RAM and executing it. The system control unit 113 can realize the processing of each component of the digital camera 100 by executing a program stored in the ROM. The system control unit 113 controls which of a plurality of imaging drive modes of the image sensor 106 is to be used. The VRAM 114 is a memory for displaying images.

[0024] The display unit 115 is, for example, an LCD (Liquid Crystal Display) or the like. The display unit 115 displays images, displays for operational assistance, and displays the state of the digital camera 100, and also displays the shooting screen and the distance measurement area during shooting. As shown in FIG. 2, the display unit 115 also displays a screen for the user to select a target luminance for the luminance of the high-luminance area. The target luminance is a target value or an upper threshold value that determines the luminance of the high-luminance area. The AE processing unit 103 controls the exposure based on the difference between the luminance of the high-luminance area (for example, the average luminance in the high-luminance area) and the target luminance.

[0025] The operation unit 116 is a member that allows the user to externally operate the digital camera 100. The user can use the operation unit 116 to perform various settings, such as exposure compensation, aperture setting, and image playback setting. The operation unit 116 has a menu switch, a zoom lever that instructs the zoom operation of the shooting lens, an operation mode changeover switch for switching between shooting mode and playback mode, and the like.

[0026] The user can select a metering mode by operating the operation unit 116. The metering modes that the user can select are, for example, an evaluative metering mode, a partial metering mode, and a highlight-weighted metering mode.

[0027] The evaluative metering mode is a mode in which the light is measured for each of a plurality of areas set on the screen, and the final exposure is determined based on information such as the brightness distribution, color, distance, and composition of the subject. The evaluative metering mode is suitable for general photography, including backlit photography. The partial metering mode is a mode in which the light is measured in the range at the center of the screen. The partial metering mode is effective when there is strong light around the subject due to backlighting, etc. The highlight-weighted metering mode is a mode in which the exposure is determined so that the high-luminance areas in the screen are mainly at the appropriate brightness. The highlight-weighted metering mode is a mode in which the light is metered with an emphasis on the high-luminance areas as the metering areas. In general, when the exposure is controlled so that the high-luminance areas in the screen are at the appropriate brightness, the exposure is darker in the highlight-weighted metering mode than in the evaluative metering mode.

[0028] The user can select the target luminance of the high-luminance area by operating the operation unit 116 on the screen shown in Fig. 2. The target luminance of the high-luminance area selected by the user is output to the AE processing unit 103 and used for controlling the exposure, and is output to the image processing unit 108 and used for controlling the image processing.

[0029] The main switch 117 is a switch for turning on the power to the digital camera 100. The shooting switch 118 is a switch for performing two-stage operation according to how deeply the switch is pressed. When the shooting switch 118 is pressed halfway (SW1 operation), the system control unit 113 executes shooting preparation operations such as AE processing and AF processing. When the shooting switch 118 is pressed all the way (SW2 operation), the system control unit 113 executes shooting processing.

[0030] The following describes a series of processes executed by the digital camera 100. When the main switch 117 is pressed to turn on the power, the system control unit 113 of the digital camera 100 executes imaging processing at a predetermined cycle (for example, 33 ms cycle) using the image sensor 106. The digital camera 100 enters an actual shooting standby state in which it sequentially displays captured images on the display unit 115.

[0031] When a shooting instruction is received by pressing the shooting switch 118 (SW2 operation), the system control unit 113 executes the actual shooting process by the image sensor 106. The system control unit 113 executes image processing on the captured image by the image processing unit 108, and records the image data after the image processing in the image recording unit 112. The digital camera 100 returns to the actual shooting standby state again. When the in-switch 117 is pressed again, the digital camera 100 is powered off.

[0032] <Gradation correction processing> Fig. 3 is a flowchart illustrating the gradation correction process. The gradation correction process shown in Fig. 3 is a process that controls exposure based on the metering result of highlight-weighted metering and target luminance, and performs gradation correction to express high luminance areas with luminance that meets the user's intention. The gradation correction process in Fig. 3 is started, for example, when the power of the digital camera 100 is turned on and the camera is in a standby state for actual shooting.

[0033] In step S301, the system control unit 113 sets a target luminance according to a user's specification. For example, the user can specify the target luminance of a high luminance region by selecting from among options TH1, TH2, and TH3 through a user interface as shown in FIG.

[0034] TH1, TH2, and TH3 may be preset brightness values ​​or may be changeable by the user. The user interface for setting the target brightness is not limited to the example in Fig. 2. The target brightness may be set by, for example, inputting a brightness value by the user.

[0035] In step S301, the target luminance is set to 200 in JPEG image gradation value. By specifying the target luminance, the user can adjust the luminance of the high luminance area in the captured image to the intended luminance. Note that the luminance of the high luminance area (hereinafter also referred to as the representative luminance) is the average value, maximum value, minimum value, median value, or mode value of the luminance in the high luminance area.

[0036] In step S302, the system control unit 113 determines whether or not a shooting instruction has been received from the shooting switch 118. If a shooting instruction has not been received, the system control unit 113 repeats the process of step S302 at predetermined time intervals until a shooting instruction is received. If a shooting instruction has been received, the process proceeds to step S303.

[0037] In step S303, the system control unit 113 performs exposure control. Here, an example of exposure control in the highlight-weighted metering method will be described. First, the system control unit 113 divides an image (so-called a through image) obtained by periodic imaging processing in the actual shooting standby state into a plurality of blocks by the image recognition unit 109, and obtains an average luminance for each block.

[0038] Fig. 4 shows an example of block division of an image. As shown in Fig. 4, the system control unit 113 may divide the image into a plurality of blocks excluding the peripheral area. The size and number of blocks after division are not limited to the example in Fig. 4, and may be changed based on the scene recognized by the image recognition unit 109, for example.

[0039] The system control unit 113 selects the block with the highest luminance among the divided blocks as the high luminance region. The luminance of the block is, for example, the average value, maximum value, minimum value, median value, or mode of the luminance in the block. Note that the system control unit 113 may select, as the high luminance region, a plurality of blocks including a block whose difference from the luminance of the block with the highest luminance is equal to or less than a threshold value. The high luminance region is also called a highlight portion.

[0040] Here, a case will be described where the target luminance is set to 200 and the luminance of the highlight part is 240. The system control unit 113 converts the target luminance and the luminance of the highlight part into a signal value after A / D conversion processing before gamma processing based on the setting value of the gamma function. The system control unit 113 calculates the APEX (Additive Synchronization Exponential) between the target luminance and the luminance of the highlight part. If the linear signal values ​​before gamma processing of the target luminance and the luminance of the highlight area are Ya and Yb, respectively, the difference in exposure steps in the APEX value can be obtained by Log(Ya / Yb).

[0041] If the signal value Ya for the target luminance of 200 is 5000 and the signal value Yb for the luminance of the highlight part is 10000, then Log(Ya / Yb)=-1. Since the target luminance is lower than the luminance of the highlight part, the system control unit 113 can bring the luminance of the highlight part closer to the target luminance by setting the aperture and shutter 102 to a value one step higher than the current setting value and capturing the image. In this way, the system control unit 113 can control the exposure based on the difference in the number of exposure steps between the target luminance and the luminance of the highlight part so that the luminance of the highlight part substantially matches the target luminance specified by the user in step S301.

[0042] In step S304, the system control unit 113 performs the exposure control determined in step S303 by the AE processing unit 103 to capture a still image. In step S305, the image recognition unit 109 acquires a histogram (brightness histogram) of the still image captured in step S304 (a captured image captured after the exposure control in step S304 has been performed).

[0043] In step S306, the image processing unit 108 acquires the amount of gradation correction based on the histogram obtained in step S305. In highlight-weighted metering, exposure control is performed so that the luminance of the highlight area (high luminance area) becomes the target luminance. In this case, the dark area, which is an area with a lower luminance than the highlight area, becomes dark and is prone to being blocked up in black. For this reason, the image processing unit 108 determines the amount of gradation correction based on the luminance of the dark area in order to brighten the dark area.

[0044] When tone correction is performed based on the luminance of dark areas, the luminance of highlight areas may be corrected to be higher than the target luminance. When the luminance of highlight areas is corrected to be higher than the target luminance, the image processing unit 108 corrects the amount of correction for tone correction so that the luminance of highlight areas approaches the target luminance. The amount of correction corrected so that the luminance of highlight areas approaches the target luminance is the amount of correction acquired in step S306. In step S307, the image processing unit 108 performs tone correction using the amount of correction acquired in step S306.

[0045] (Example 1 of tone correction) A first embodiment of the gradation correction executed in steps S305 and S306 in Fig. 3 will be described with reference to Fig. 5 to Fig. 8. In the first embodiment of the gradation correction, the system control unit 113 corrects the gradation correction by suppressing the overall correction amount of the tone curve so that the luminance of the highlight part approaches the target luminance. Fig. 5 shows an example of a scene to which the first embodiment is applied, which includes the sky and a backlit tree in the angle of view.

[0046] In the scene in FIG. 5, the highlight portion is a block 501 that corresponds to the sky. A still image is captured with a target brightness (after gamma processing) of 200 as specified by the user, and the brightness of the highlight portion of the captured image is as intended by the user. However, the tree in the foreground is backlit and appears dark. The image processing unit 108 can use tone correction to change the tree portion that is darkened by the backlight to a brighter, more pleasing appearance.

[0047] A process of correcting the gradation correction so as to brighten the dark areas and prevent the luminance of the highlight areas from becoming too brighter than the target luminance will be described with reference to Fig. 6. Fig. 6 is a flowchart illustrating an example of the gradation correction correction process.

[0048] In highlight-weighted metering mode, the exposure is controlled so that the highlights are the target brightness. Therefore, the gradation is compressed, and dark areas may become darker than in other metering modes. For this reason, in highlight-weighted metering, the image processing unit 108 performs gradation correction so that dark areas become brighter. However, by performing gradation correction according to the brightness of the dark areas, the brightness of the highlight areas ends up being corrected to be brighter than the target brightness. Therefore, in the highlight-weighted metering mode, the image processing unit 108 modifies the amount of correction so as to weaken the strength of the gradation correction.

[0049] In step S601, as described in step S305 of Fig. 3, the system control unit 113 acquires a histogram of the captured still image. Fig. 7 illustrates an example of a histogram acquired in the scene of Fig. 5. In the scene of Fig. 5, a histogram having two peaks corresponding to the sky area and the tree area is formed. The peak on the high-luminance side corresponds to the sky, and the peak on the low-luminance side corresponds to the tree. The peak corresponding to the sky including the highlight part is formed near 200, which is the target luminance designated by the user.

[0050] In step S602, the system control unit 113 acquires the luminance of the dark area of ​​the histogram acquired in step S601. The dark area is an area with a lower luminance than the highlight area, and may be, for example, a luminance range in which the luminance is equal to or less than a dark area threshold Dth=128. The luminance of the dark area is, for example, the average luminance of the dark area, and may be an average value weighted by the frequency of each bin of the histogram corresponding to the dark area. In the scene of FIG. 5 (example of FIG. 7), the average luminance of the dark area is Dave=50.

[0051] The dark area threshold Dth may be set to a value other than 128 in accordance with the shape of the histogram, as long as it is set to a value lower than the luminance range of the highlight area. In addition, in step S602, an example is shown in which an average luminance is acquired as the luminance of the dark area, but the system control unit 113 may take the luminance at the peak of the histogram corresponding to the dark area as the luminance of the dark area. In the following description, the luminance of the dark area is assumed to be the average luminance of the dark area.

[0052] In step S603, the system control unit 113 determines a dark correction point. The gradation correction in this embodiment is performed based on a tone curve that expresses the correspondence between the input luminance and the output luminance of the correction by a curve or a broken line. The dark correction point is one of the control points of the tone curve. The system control unit 113 can correct the correction amount of the gradation correction by increasing or decreasing the output luminance at the control point.

[0053] FIG. 8 is an example of a correspondence table (lookup table) showing output luminance corresponding to the average luminance of the dark area. The system control unit 113 determines the dark area correction point by referring to a lookup table that is determined in advance by associating output luminance values ​​with values ​​of the average luminance of the dark area. In the example of FIG. 8, the output luminance corresponding to the average luminance of the dark area Dave=50 is 90. The system control unit 113 determines the position where the input luminance is 50 and the output luminance is 90 as the dark area correction point. Note that the output luminance corresponding to the average luminance of the dark area is not limited to the method of being determined in the lookup table, and may be obtained, for example, by using a calculation formula for calculating the output luminance from the average luminance of the dark area.

[0054] A first embodiment of gradation correction in a tone curve will be described with reference to Fig. 9. Fig. 9(A) illustrates a tone curve formed based on the dark area correction point determined in step S603. By forming a tone curve so that the output luminance is 90 for the average luminance Dave=50 in the dark area, the tree part that was in a blocked-up state in the scene in Fig. 5 is corrected to be brighter.

[0055] On the other hand, by correcting the tone curve based on the dark correction point, the output luminance corresponding to the target luminance of 200 specified by the user is increased to 220. If the output luminance for the target luminance of 200 is kept at 220 and gradation correction is performed using the tone curve of FIG. 9(A), the dark area will be Since the highlight portion is corrected to 220, which is higher than the target brightness of 200, there is a possibility that an image with the brightness intended by the user will not be obtained. Therefore, in step S604, the amount of gradation correction is modified so that the brightness of the highlight portion approaches the target brightness of 200.

[0056] In step S604, the system control unit 113 corrects the correction amount of the gradation correction according to the target luminance. Fig. 10 shows an example of a correspondence table (lookup table) showing the weakening amount of the gradation correction corresponding to the target luminance. When the target luminance is TH1=200, TH2=220, and TH3=250, the weakening amounts corresponding to the respective target luminance are 70%, 90%, and 100%. The system control unit 113 corrects the output luminance of the dark correction point determined in step S603 using the weakening amount corresponding to the target luminance.

[0057] For example, the weakening amount corresponding to the target luminance TH1 (=200) is 70%, and the system control unit 113 multiplies the output luminance 90 corresponding to the average luminance Dave=50 of the dark areas by a correction coefficient (first correction coefficient) 0.7 equivalent to the weakening amount to correct the output luminance to 63. By correcting the correction amount of the gradation correction, the strength of the gradation correction is weakened. Note that the weakening amount corresponding to the target luminance is not limited to the method defined in the lookup table, and may be obtained, for example, using a calculation formula for calculating the weakening amount from the target luminance.

[0058] Fig. 9(B) illustrates a tone curve with weakened intensity of gradation correction. The output luminance corresponding to the average luminance Dave=50 in the dark areas is corrected from 90 to 63. By weakening the intensity of gradation correction according to the target luminance, the output luminance for the target luminance 200 becomes 205, which is closer to the target luminance than 220 in Fig. 9(A). By suppressing the overall correction amount of the tone curve and weakening the intensity of gradation correction, the system control unit 113 can bring the luminance of the highlight areas closer to the target luminance intended by the user.

[0059] Since the tone curve does not change the dynamic range of the image, the input luminance and the output luminance coincide at the minimum and maximum signal value points. Therefore, the tone curve is formed by connecting the dark correction point with the minimum signal value point and the maximum signal value point. When gradation correction is performed according to the dark correction point determined in step S603, the lower the target luminance, the greater the change in output luminance of the highlight part. Therefore, as illustrated in FIG. 10, it is more preferable to set the weakening amount of gradation correction lower as the target luminance is lower.

[0060] The weakening amount corresponding to the target luminance is not limited to the lookup table, and may be obtained by defining a calculation formula such that the lower the target luminance, the lower the weakening amount.

[0061] (Example 2 of tone correction) A second embodiment of the gradation correction executed in steps S305 and S306 in Fig. 3 will now be described. In the first embodiment of the gradation correction, the system control unit 113 corrects the gradation correction by suppressing the overall correction amount of the tone curve so that the luminance of the highlight portion approaches the target luminance. In contrast, in the second embodiment of the gradation correction, the system control unit 113 corrects the amount of correction of the gradation correction so that the strength of the gradation correction is weaker for a high luminance range (first luminance range) equal to or greater than the target luminance than for a luminance range (second luminance range) below the target luminance.

[0062] When the overall correction amount of the tone curve is suppressed as in the first embodiment of the gradation correction, the effect of the gradation correction that brightens the dark areas is also weakened. In the second embodiment of the gradation correction, the system control unit 113 modifies the correction amount so that the gradation correction in the first luminance range equal to or greater than the target luminance is weaker than the gradation correction in the second luminance range below the target luminance. In this way, the system control unit 113 can obtain the effect of the dark area correction and also realize the gradation correction that makes the luminance of the highlight areas as intended by the user.

[0063] In the second embodiment of the gradation correction, among the processes in step S306 in Fig. 3, the process in step S604 shown in Fig. 6 is different from the first embodiment of the gradation correction. The other processes are the same as those in the first embodiment of the gradation correction, so detailed descriptions are omitted. The following describes the points that are different from the first embodiment of the gradation correction.

[0064] In step S604, the system control unit 113 modifies the amount of correction so that the gradation correction in the first luminance range equal to or greater than the target luminance is weakened below the tone curve of FIG. 9A formed based on the dark area correction point determined in step S603.

[0065] A second embodiment of tone correction in a tone curve will be described with reference to Fig. 11. In the second embodiment of tone correction, the system control unit 113 modifies the amount of correction so as to weaken the strength of tone correction in a first luminance range by placing a control point of the tone curve at a position where the input luminance is close to the target luminance. In the example of Fig. 11, a control point 1101 is set at a position where the input luminance is the target luminance 200 so that the output luminance of the tone curve is 200, the same value as the input luminance.

[0066] A straight line connects the control point 1101 to the coordinate (255, 255) that is the maximum output value. In the high luminance range (first luminance range) above the target luminance, the luminance of the first luminance range does not change due to tone correction, so the user can obtain an image with the luminance that he or she intends.

[0067] The control point 1101 is not limited to being set at a position where the input luminance and output luminance at the target luminance match. The control point 1101 may be set so that the gradation correction in the first luminance range is weaker than the gradation correction in the second luminance range, and the position may be changed based on the position of the dark correction point or the state of contrast in the second luminance range.

[0068] Specifically, when the slope of the line connecting the dark correction point and the control point 1101 is smaller than the threshold, the contrast becomes too low, so the system control unit 113 may increase the output luminance of the control point 1101. Also, the system control unit 113 may decrease the output luminance of the dark correction point so that the slope of the line connecting the dark correction point and the control point 1101 is equal to or greater than the threshold.

[0069] In the second embodiment of the gradation correction, the amount of correction is modified so that the strength of the gradation correction is weaker for the first luminance range than for the second luminance range, allowing the user to obtain an image in which the effect of gradation correction in dark areas has been achieved and the luminance of highlight areas meets the user's intention.

[0070] (Example 3 of tone correction) 12 to 17, a third embodiment of the gradation correction executed in steps S305 and S306 in Fig. 3 will be described. In the third embodiment of the gradation correction, the system control unit 113 modifies the amount of gradation correction based on the degree of coincidence between an area including a highlight part and an area including a main subject. Fig. 12 shows an example of a scene to which the third embodiment of the gradation correction is applied, in which a spot light source 1201 illuminates from the top of the image to the bottom where an animal 1202, which is a subject, is present.

[0071] In the scene shown in Fig. 5, the tree, which is the main subject, is backlit and appears dark. In contrast, in the scene shown in Fig. 12, the animal 1202, which is the main subject, is brightened by the light from the light source 1201.

[0072] The area including the main subject, an animal 1202, is highlighted when illuminated by a light source 1201. The highlight portion may include a light portion, and the user can specify a target brightness for the highlight portion to bring the area including the main subject closer to the target brightness. For example, the highlight portion of the image in Fig. 12 is assumed to be block 1203 located approximately in the center of the face of the animal 1202. In this case, by controlling the exposure so that the brightness of the highlight portion approaches the target brightness, the area of ​​the main subject including the highlight portion can be made as intended by the user.

[0073] In the scene shown in Figure 12, if the dark areas in the areas other than the area including the main subject are brightened by tone correction, the highlight areas are also brightened, and the brightness of the image may not be as intended by the user. In addition, if tone correction is performed to brighten the dark areas, there is a possibility that adverse effects such as a decrease in the contrast of the entire image and an increase in image noise may occur.

[0074] In the scene in Fig. 5, the tree, which is the main subject, is not a highlighted area, so priority is given to brightening the area including the tree, but in the scene in Fig. 12, it is preferable to weaken the strength of the gradation correction to suppress the adverse effects of brightening the dark areas. That is, when the main subject and the highlighted area overlap, or when the difference in luminance between the main subject and the highlighted area is equal to or less than a threshold, it is preferable to weaken the gradation correction.

[0075] 13 is a flowchart illustrating the correction process of the third embodiment of the gradation correction. The processes of steps S1301 to S1303 are the same as the processes of steps S601 to S603 in FIG. 6, respectively, and therefore detailed explanations are omitted. In step S1302, the system control unit 113 acquires 50 as the average luminance Dave of the dark areas, similar to step S602 in FIG. 6. Furthermore, in step S1303, the system control unit 113 determines a dark area correction point with an output luminance of 90, similar to step S603.

[0076] In step S1304, the image recognition unit 109 acquires the entire highlight portion (first region). The entire highlight portion is a region that combines the highlight portion with blocks whose luminance difference from the highlight portion is equal to or less than a threshold value. For example, when the luminance of the highlight portion is Ymax and the threshold value is (Ymax×0.1), the entire highlight portion can be a region that combines blocks (including blocks of the highlight portion) whose luminance is equal to or more than (Ymax×0.9).

[0077] In Fig. 5, block 501, which is part of the sky, is determined to be a highlight area, and the difference in luminance between the background sky block and block 501 is considered to be equal to or less than a predetermined threshold. Therefore, the entire highlight area of ​​the scene in Fig. 5 is the area that combines the blocks that correspond to the sky.

[0078] 12, on the other hand, the difference in luminance between the block illuminated by the light of the spot light source 1201 and the block corresponding to the animal 1202 and the block 1203 determined to be a highlight portion is considered to be equal to or less than a predetermined threshold value. Therefore, the entire highlight portion of the scene in FIG. 12 is the combined area of ​​the blocks illuminated by the light of the spot light source 1201 (including the block corresponding to the animal 1202).

[0079] In step S1305, the image recognition unit 109 acquires a main subject part (second region). The image recognition unit 109 recognizes a scene by a known technique, and detects a region of a subject such as a person, an animal, or a car that is of interest in the recognized scene as the main subject part.

[0080] Furthermore, the system control unit 113 may acquire the area focused on by the AF processing unit 105 as the main subject area. The area focused on by the AF processing unit 105 is the area of ​​the subject on which the user focuses by performing an AF operation. The area of ​​the subject on which the user focuses is the area surrounded by a frame displayed on the display unit 115. The user may change the focus by Since the focused subject is considered to be recognized as the main subject, the main subject portion can be regarded as the area focused on by the AF processing unit 105.

[0081] In this way, the system control unit 113 can acquire a block including a subject detected by scene recognition or a block including a subject focused on by the user as the main subject part. Note that the system control unit 113 may acquire an area obtained by combining a block including a subject detected by scene recognition and a block including a subject focused on by the user as the main subject part.

[0082] In step S1306, the image recognition unit 109 acquires the degree of match between the entire highlight portion and the main subject portion. The degree of match between the entire highlight portion and the main subject portion will be described with reference to Figs.

[0083] Fig. 14(A) shows an overall highlight portion 1401 including six blocks. Fig. 14(B) shows a main subject portion 1402 including six blocks different from the overall highlight portion 1401. Fig. 14(C) shows a state in which the overall highlight portion 1401 in Fig. 14(A) and the main subject portion 1402 in Fig. 14(B) overlap at block 1403.

[0084] The degree of coincidence between the highlight overall part 1401 and the main subject part 1402 can be calculated, for example, as (the number of blocks where the highlight overall part and the main subject part overlap)÷(the number of blocks occupied by the highlight overall part and the main subject part).

[0085] 14(C), the total number of blocks occupied by the highlight overall portion 1401 and the main subject portion 1402 is 11. The total number of blocks where the highlight overall portion 1401 and the main subject portion 1402 overlap is one block, block 1403. The degree of coincidence between the highlight overall portion 1401 and the main subject portion 1402 is 1÷11=0.1 (rounded to the nearest tenth).

[0086] Fig. 15 shows another example of the overall highlight portion and the main subject portion. In the example of Fig. 15, the number of blocks occupied by the overall highlight portion 1501 and the main subject portion 1502 is 58 blocks. The number of blocks where the overall highlight portion 1501 and the main subject portion 1502 overlap is 32 blocks. The degree of coincidence between the overall highlight portion 1501 and the main subject portion 1502 is 32÷58=0.6 (rounded to the nearest tenth).

[0087] The degree of coincidence between the highlight overall part and the main subject part is not limited to being obtained based on the overlap of blocks (overlap of areas), but may be obtained based on the degree of coincidence of the luminance of each area. For example, the system control unit 113 calculates the average luminance of the highlight overall part 1401 in FIG. 14(A) from the image, and sets it as Yave_a. The system control unit 113 also calculates the average luminance of the main subject part 1402 in FIG. 14(B) from the image, and sets it as Yave_b. The degree of coincidence of the luminance between the highlight overall part 1401 and the main subject part 1402 can be calculated as, for example, 1-(|Yave_b-Yave_a|÷255).

[0088] The average luminance Yave_a of the entire highlight portion 1401 is not limited to being calculated from an image, but may be substituted with a value obtained by converting a target luminance designated by a user into a signal value immediately after A / D conversion before gamma processing. This is because in highlight-weighted metering, the average luminance Yave_a of the entire highlight portion is close to the target luminance. The target luminance can be converted into a signal before gamma processing using the inverse function of the function used for gamma correction. Also, although Yave_a and Yave_b have been described as the average luminance of the entire highlight portion and the main subject portion, respectively, they are not limited to the average luminance, and may be the maximum, minimum, median, or mode of the luminance in each region.

[0089] In step S1307, the system control unit 113 corrects the amount of gradation correction based on the degree of coincidence acquired in step S1306. Fig. 16 shows an example of a correspondence table (lookup table) showing the weakening amount of gradation correction corresponding to the degree of coincidence. The system control unit 113 corrects the output luminance of the dark area correction point determined in step S1303 using the weakening amount corresponding to the degree of coincidence between the entire highlight area and the main subject area.

[0090] The higher the degree of agreement between the entire highlight area and the main subject area, the closer the brightness of the main subject area before tone correction becomes to the target brightness. Therefore, it is preferable that the system control unit 113 weakens the strength of tone correction so that the brightness of the entire highlight area is not corrected to be brighter as the degree of agreement between the entire highlight area and the main subject area increases. In other words, it is preferable to set the weakening amount (the ratio of output brightness after weakening tone correction) lower as the degree of agreement between the entire highlight area and the main subject area increases.

[0091] A specific example of correcting the amount of gradation correction according to the degree of coincidence between the entire highlight area and the main subject area will be described with reference to Fig. 17. Fig. 17(A) shows an example of correction of the tone curve when the degree of coincidence is 0.1. When the degree of coincidence is 0.1, the weakening amount is 95%. The system control unit 113 corrects the output luminance of the dark area correction point to 86 by multiplying the output luminance of 90 for the average luminance Dave=50 of the dark areas by a correction coefficient (second correction coefficient) of 0.95 corresponding to the weakening amount of 95%.

[0092] Moreover, when the degree of coincidence is 0.6, the weakening amount is 70%. The system control unit 113 multiplies the output luminance 90 for the average luminance Dave=50 of the dark area by the correction coefficient 0.7 corresponding to the weakening amount of 70%, thereby correcting the output luminance of the dark area correction point to 63.

[0093] If the output luminance after correction falls below the average luminance Dave of the dark area, the system control unit 113 sets the average luminance Dave as the lower limit, and sets the output luminance of the dark area to the same value as the average luminance Dave. For example, if the degree of agreement is 0.9, the weakening amount is 55%. If the output luminance of 90 for the average luminance Dave=50 of the dark area is multiplied by the correction coefficient 0.55 corresponding to the weakening amount of 55%, the output luminance becomes 49.5. Since the output luminance after correction falls below the average luminance Dave of the dark area, the system control unit 113 leaves the output luminance of the dark area at 50, which is the lower limit, and does not correct the output luminance. Therefore, the output luminance becomes 50 for the average luminance Dave=50 of the dark area, and the tone curve is not substantially corrected as shown in FIG. 17(B).

[0094] As the degree of coincidence between the entire highlight area and the main subject area decreases, the main subject area is a darker area than the entire highlight area, so it is preferable not to weaken the strength of the gradation correction. Therefore, the lower the degree of coincidence, the higher the weakening amount is set. By weakening the strength of the gradation correction by setting the weakening amount lower as the degree of coincidence between the entire highlight area and the main subject area increases, the system control unit 113 can perform gradation correction while reducing the adverse effects of gradation correction in dark areas.

[0095] <Other embodiments> The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0096] The disclosure of this embodiment includes the following configuration, method, and program. (Configuration 1) Exposure control so that the representative luminance of the high-luminance area of ​​the image becomes the target luminance set by the user An exposure control means for performing the above-mentioned a gradation correction means for performing gradation correction on the captured image captured after the exposure control based on the luminance of a dark area, which is an area with a lower luminance than the high luminance area; having The gradation correction means corrects a correction amount of the gradation correction so that the representative luminance of the high luminance area, which is corrected to be higher than the target luminance by the gradation correction, approaches the target luminance. 1. An imaging device comprising: (Configuration 2) The gradation correction means corrects an output luminance corresponding to the luminance of the dark area of ​​the gradation correction using a first correction coefficient corresponding to the target luminance, and corrects each output luminance corresponding to each luminance of the captured image, thereby correcting a correction amount of the gradation correction. 2. The imaging device according to configuration 1, (Configuration 3) The first correction coefficient is determined so that the lower the target luminance, the smaller the output luminance becomes. 3. The imaging device according to configuration 2. (Configuration 4) The gradation correction means modifies the amount of gradation correction so that the intensity of the gradation correction is weaker for a first luminance range equal to or greater than the target luminance than for a second luminance range less than the target luminance. 2. The imaging device according to configuration 1, (Configuration 5) The gradation correction means In the first luminance range, the gradation correction is not performed, In the second luminance range, the gradation correction is performed using an output luminance corresponding to the luminance of the dark area of ​​the gradation correction. 5. The imaging device according to configuration 4. (Configuration 6) The gradation correction means corrects a correction amount of the gradation correction based on an output luminance corresponding to the luminance of the dark part of the gradation correction or a contrast state in the second luminance range. 5. The imaging device according to configuration 4. (Configuration 7) The method further includes acquiring a degree of coincidence between a first region including the high luminance region and a second region including a main subject, The gradation correction means corrects an output luminance corresponding to the luminance of the dark area of ​​the gradation correction using a second correction coefficient according to the degree of coincidence, and corrects each output luminance corresponding to each luminance of the captured image, thereby correcting a correction amount of the gradation correction. 2. The imaging device according to configuration 1, (Configuration 8) The acquiring means acquires the degree of coincidence based on a size of an overlapping area between the first area and the second area or a difference in luminance between the first area and the second area. 8. The imaging device according to configuration 7. (Configuration 9) The second correction coefficient is determined such that the lower the degree of match, the greater the output luminance. 9. The imaging device according to configuration 7 or 8. (Configuration 10) When the output luminance corrected using the second correction coefficient falls below the luminance of the dark area, the gradation correction means does not correct the output luminance. 10. The imaging device according to any one of configurations 7 to 9, wherein: (Configuration 11) The representative luminance of the high luminance region is an average value, a maximum value, a minimum value, a median value, or a mode value of the luminance in the high luminance region. 11. The imaging device according to any one of configurations 1 to 10, (method) an exposure control step of performing exposure control so that a representative luminance of a high luminance area of ​​the image becomes a target luminance set by a user; a gradation correction step of performing gradation correction on the captured image captured after the exposure control based on the luminance of a dark area, which is an area with a lower luminance than the high luminance area; having In the gradation correction step, a correction amount of the gradation correction is corrected so that the representative luminance of the high luminance area, which is corrected to be higher than the target luminance by the gradation correction, approaches the target luminance. 23. A method for controlling an imaging apparatus comprising the steps of: (program) A program for causing a computer to execute each step of the method for controlling an imaging apparatus described in the method. [Explanation of symbols]

[0097] 100: imaging device (digital camera), 103: AE processing unit, 108: image processing unit, 109: image recognition unit, 113: system control unit

Claims

1. Exposure control means for performing exposure control so that the representative luminance of the high-luminance region of the image becomes the target luminance set by the user, tone correction means for performing tone correction on the captured image captured after the exposure control is performed, based on the luminance of the dark part, which is a region having a lower luminance than the high-luminance region having The tone correction means multiplies the output luminance corresponding to the luminance of the dark part by a first correction coefficient corresponding to the target luminance to correct the output luminance corresponding to the luminance of the dark part, and corrects each output luminance corresponding to each luminance of the captured image based on the output luminance corresponding to the corrected luminance of the dark part, so that the representative luminance of the high-luminance region, which is corrected to be higher than the target luminance by the tone correction, approaches the target luminance, and corrects the correction amount of the tone correction The imaging device is characterized by the above.

2. The first correction coefficient is determined such that the lower the target luminance, the smaller the output luminance The imaging device according to claim 1, characterized by the above.

3. Exposure control means for performing exposure control so that the representative luminance of the high-luminance region of the image becomes the target luminance set by the user, tone correction means for performing tone correction on the captured image captured after the exposure control is performed, based on the luminance of the dark part, which is a region having a lower luminance than the high-luminance region having The tone correction means corrects the correction amount of the tone correction so that the intensity of the tone correction becomes weaker for the first luminance range equal to or higher than the control point than for the second luminance range less than the control point, and the representative luminance of the high-luminance region, which is corrected to be higher than the target luminance by the tone correction, approaches the target luminance The imaging device is characterized by the above.

4. The tone correction means does not perform the tone correction in the first luminance range, and performs the tone correction in the second luminance range using the output luminance corresponding to the luminance of the dark part of the tone correction The imaging device according to claim 3, characterized by the above.

5. The tone correction means corrects the correction amount of the tone correction based on the output luminance corresponding to the luminance of the dark part of the tone correction or the contrast state in the second luminance range The imaging device according to claim 3, characterized by the above.

6. Exposure control means for performing exposure control so that the representative luminance of the high-luminance region of the image becomes the target luminance set by the user, ​ Tone correction means for performing tone correction on the captured image captured after the exposure control is performed, based on the luminance of a dark part which is a region having a lower luminance than the high luminance region; Acquisition means for acquiring the degree of coincidence between a first region including the high luminance region and a second region including the main subject and having The tone correction means corrects the output luminance corresponding to the luminance of the dark part of the tone correction using a second correction coefficient corresponding to the degree of coincidence, and corrects each output luminance corresponding to each luminance of the captured image, thereby making the representative luminance of the high luminance region corrected to be higher than the target luminance by the tone correction approach the target luminance, and corrects the correction amount of the tone correction. An imaging device characterized by the above.

7. The acquisition means acquires the degree of coincidence based on the size of the region where the first region and the second region overlap, or the difference in luminance between the first region and the second region. The imaging device according to claim 6, characterized by the above.

8. The second correction coefficient is determined such that the lower the degree of coincidence, the larger the output luminance. The imaging device according to claim 6, characterized by the above.

9. When the output luminance corrected using the second correction coefficient is lower than the luminance of the dark part, the tone correction means does not correct the output luminance. The imaging device according to claim 6, characterized by the above.

10. The representative luminance of the high luminance region is the average value, maximum value, minimum value, median value, or mode value of the luminance within the high luminance region. The imaging device according to any one of claims 1 to 9, characterized by the above.

11. An exposure control step for performing exposure control so that the representative luminance of the high luminance region of the image becomes the target luminance set by the user; A tone correction step for performing tone correction on the captured image captured after the exposure control is performed, based on the luminance of a dark part which is a region having a lower luminance than the high luminance region and having In the tone correction step, the output luminance corresponding to the luminance of the dark part is corrected by multiplying the first correction coefficient corresponding to the target luminance by the output luminance corresponding to the luminance of the dark part, and each output luminance corresponding to each luminance of the captured image is corrected based on the corrected output luminance corresponding to the luminance of the dark part, thereby making the representative luminance of the high luminance region corrected to be higher than the target luminance by the tone correction approach the target luminance, and corrects the correction amount of the tone correction. A control method for an imaging device, characterized by the above. Exposure control is performed such that the representative luminance of the high-luminance region of the image becomes the target luminance set by the user. An exposure control step for performing the exposure control; A gradation correction step for performing gradation correction on the captured image captured after the exposure control, based on the luminance of a dark region which is a region having a lower luminance than the high-luminance region; The method includes: In the gradation correction step, for a first luminance range equal to or higher than a control point, the intensity of the gradation correction is weaker than that for a second luminance range lower than the control point, and the correction amount of the gradation correction is corrected so that the representative luminance of the high-luminance region, which is corrected to be higher than the target luminance by the gradation correction, approaches the target luminance. A control method for an imaging device, characterized by the above. Exposure control is performed such that the representative luminance of the high-luminance region of the image becomes the target luminance set by the user. An exposure control step for performing the exposure control; An acquisition step for acquiring a degree of coincidence between a first region including the high-luminance region and a second region including a main subject; The method includes: In the gradation correction step, the output luminance corresponding to the luminance of the dark region of the gradation correction is corrected using a second correction coefficient corresponding to the degree of coincidence, and by correcting each output luminance corresponding to each luminance of the captured image, the correction amount of the gradation correction is corrected so that the representative luminance of the high-luminance region, which is corrected to be higher than the target luminance by the gradation correction, approaches the target luminance. A control method for an imaging device, characterized by the above.

14. A program for causing a computer to execute each step of the control method for an imaging device according to any one of Claims 11 to 13.

Images