Image processing device and method, imaging device, program, and storage medium

Abstract

To obtain an image which is reduced in saturation and black defects and has a gradation characteristic not for making the image unnatural as a whole image, in a scene having a wide dynamic range.SOLUTION: An image processing device includes: acquisition means for acquiring an image; classifying means for classifying the image acquired by the acquisition means into a plurality of regions on the basis of a predetermined condition; decision means for deciding a correction characteristic for correcting a gradation characteristic for each of the plurality of regions; and correction means for correcting the gradation characteristic of each region by using the correction characteristic corresponding to each region. The decision means sets the correction characteristic corresponding to one region as a reference among the plurality of regions as a reference correction characteristic and decides at least the correction characteristic of a part having luminance lower than predetermined luminance on the basis of the reference correction characteristic for the correction characteristics other than the reference correction characteristic.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image processing apparatus and method, an imaging apparatus, a program, and a storage medium, and more particularly to a method for determining gradation correction characteristics for each area having different characteristics in an image. [Background technology]

[0002] Conventionally, tone correction processes such as high dynamic range compositing (HDR) and dodging are known in which the dynamic range of an input signal is expanded and then the tone is compressed at the output stage. Furthermore, in scenes with a wide dynamic range, this method of performing tone correction for each region is effective, but there is a problem in that it can make the image as a whole look unnatural.

[0003] To address this problem, Patent Document 1 discloses a method of obtaining a representative luminance value and a luminance histogram for each subject region, determining a tone curve for each subject region, and adjusting the amount of compression of the tone curve according to the representative luminance difference between subjects. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-82768 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology disclosed in Patent Document 1 adjusts the amount of compression of the tone curve depending on the representative luminance difference between subjects, which may result in over-correction or under-correction depending on the luminance distribution of each subject.

[0006] The present invention has been made in consideration of the above problems, and aims to obtain an image with gradation characteristics that has little saturation or blackout in scenes with a wide dynamic range, and that does not look unnatural as a whole. [Means for solving the problem]

[0007] In order to achieve the above object, the image processing device of the present invention comprises an acquisition means for acquiring an image, a classification means for classifying the image acquired by the acquisition means into a plurality of regions based on predetermined conditions, a determination means for determining correction characteristics for correcting gradation characteristics for each of the plurality of regions, and a correction means for correcting the gradation characteristics of each of the regions using the correction characteristics corresponding to each of the regions, wherein the determination means sets the correction characteristics corresponding to one region among the plurality of regions as a reference correction characteristic, and determines correction characteristics for at least parts of the region with brightness lower than a predetermined brightness based on the reference correction characteristics for correction characteristics other than the reference correction characteristic. [Effects of the Invention]

[0008] According to the present invention, in a scene with a wide dynamic range, it is possible to obtain an image with gradation characteristics that are less prone to saturation and blackout and that do not appear unnatural as a whole. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a schematic functional configuration of an imaging device according to first and second embodiments of the present invention. [Figure 2] FIG. 2 is a block diagram showing the functional configuration of an image processing unit according to the first embodiment. [Figure 3] 6 is a flowchart showing a region-by-region tone correction process according to the first embodiment. [Figure 4] 6 is a flowchart showing an example of a method for calculating tone compression characteristics of an object region according to the first embodiment. [Figure 5] 5A to 5C are diagrams for explaining a method of calculating a representative luminance value of a face area according to the first embodiment. [Figure 6] 5A and 5B are diagrams for explaining a method for determining a highlight luminance value of a person area according to the first embodiment. [Figure 7] 5A to 5C are diagrams for explaining a method for determining tone compression characteristics of an object region according to the first embodiment. [Figure 8] 6 is a flowchart showing an example of a method for calculating tone compression characteristics of a background region according to the first embodiment. [Figure 9] 5A to 5C are diagrams for explaining a method for determining a dark area representative luminance value of a background region according to the first embodiment. [Figure 10] 5A to 5C are diagrams for explaining a method for calculating tone compression characteristics of a background region according to the first embodiment. [Figure 11] 5A to 5C are diagrams for explaining a method for determining tone compression characteristics of a background region according to the first embodiment. [Figure 12] FIG. 10 is a block diagram showing the functional configuration of an image processing unit according to a second embodiment. [Figure 13] 10 is a flowchart showing an area-by-area tone correction process according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0011] First Embodiment FIG. 1 is a block diagram showing the functional configuration of an imaging apparatus equipped with an image processing apparatus according to a first embodiment of the present invention. 1, the optical system 101 includes a lens group consisting of multiple lenses including a zoom lens and a focus lens, an aperture adjustment device, and a shutter device. The optical system 101 adjusts the magnification, focus position, and light amount of a subject image that reaches the image sensor 102. The optical system 101 may be configured as an integral part of the image sensor, or may be configured as a detachable part.

[0012] The image sensor 102 is a photoelectric conversion element such as a CCD or CMOS sensor that photoelectrically converts the light beam of the subject that has passed through the optical system 101 into an electrical signal. The A / D conversion unit 103 converts the image signal input from the image sensor 102 into a digital image signal. In addition to normal signal processing, the image processing unit 104 also performs regional gradation correction processing. The regional gradation correction processing will be described in detail later. The image processing unit 104 can perform similar processing not only on the image output from the A / D conversion unit 103 but also on the image read out from the recording unit 108.

[0013] The system control unit 105 controls the overall operation and control of the image processing device of this embodiment, and also controls the driving of the optical system 101 and the image sensor 102 based on the luminance value obtained from the image processed by the image processing unit 104 and instructions sent from the operation unit 106.

[0014] The display unit 107 is configured with a liquid crystal display, an organic EL (Electro Luminescence) display, or the like, and displays images generated by the imaging element 102 and images read from the recording unit 108. The recording unit 108 has a function of recording images, and may include an information recording medium such as a memory card equipped with a semiconductor memory or a package containing a rotary recording medium such as a magneto-optical disk, or the information recording medium may be configured to be detachable. The bus 109 is used to exchange images and various information among the image processing unit 104, the system control unit 105, the display unit 107, and the recording unit 108.

[0015] FIG. 2 is a block diagram showing a specific functional configuration related to the area-by-area tone correction process performed by the image processing unit 104. As shown in FIG. As shown in Figure 2, the functional configuration related to the regional gradation correction processing within the image processing unit 104 includes a subject region detection unit 201, a regional histogram generation unit 202, a subject region gradation compression characteristic calculation unit 203, a background region gradation compression characteristic calculation unit 204, and a regional gradation compression processing unit 205.

[0016] 3 is a flowchart showing the regional gradation correction process in this embodiment by the image processing unit 104 having the above configuration. The regional gradation correction process in the first embodiment will be described below with reference to the functional configuration shown in FIG. 2 and the flowchart in FIG.

[0017] In S301, the subject area detection unit 201 detects a subject area, which is a detection target, for an input image using predetermined conditions. In this embodiment, a person area and a face area of ​​a person included in the person area are detected, and the person area is classified as a subject area, and an area other than the person area is classified as a background area. Then, a region map indicating whether each pixel in the image is a subject area or a background area is generated. Note that the person area can be detected using a known method such as object recognition using learning data from a neural network (see, for example, Japanese Patent Application Laid-Open No. 2006-39666). Furthermore, the image used for detection may be a normal image taken with proper exposure, or a so-called HDR image obtained by combining multiple images with different exposures, such as proper exposure, underexposure, and overexposure.

[0018] In S302, the region histogram generation unit 202 generates a histogram (hereinafter referred to as a "luminance histogram") showing the luminance distribution of each luminance signal in the person region, face region, and background region using the result of the subject region detection by the processing in S301. In S303, the object area gradation compression characteristic calculation unit 203 calculates the gradation compression characteristic of the object area using the luminance histograms of the person area and face area calculated in S301.

[0019] Here, an example of a specific method for calculating the gradation compression characteristics of the object region performed by the object region gradation compression characteristics calculation unit 203 will be described with reference to the flowchart of FIG. In S401, a representative luminance value of the face region is calculated. FIG. 5 shows an example of a luminance histogram of the face region, with the shaded area representing the top 50% of the luminance histogram. In this embodiment, the average value of this top 50% region is used as the representative luminance value of the face. The reason for using the top 50% here is that when there is a difference in luminance of the face region, such as in an obliquely lit scene, the luminance value on the brighter side is used as the representative luminance value to prevent the face from being overly brightened. Alternatively, the representative luminance value may be calculated using a different method, such as using the average value of the overall luminance of the face region as the representative luminance value, instead of the top 50%. Note that, although the top 50% is used in the above example, the present invention is not limited to this, and any predetermined ratio may be set.

[0020] In S402, a highlight luminance value of the person region is calculated. Fig. 6 shows an example of a luminance histogram of the person region, and in this embodiment, the luminance value in the top 0.1% of the luminance histogram of the person region is set as the highlight luminance value. Note that, although the above example uses the top 0.1%, the present invention is not limited to this, and any predetermined ratio may be set.

[0021] In S403, the gradation compression characteristics of the person area are determined using the representative luminance value of the face area determined in S401 and the highlight luminance value of the person area determined in S402.

[0022] Here, a method for determining the gradation compression characteristics of the subject area will be explained using FIG. 7. FIG. 7 is a diagram showing an example of tone curve correction, with the horizontal axis representing input luminance and the vertical axis representing output luminance, and the input luminance and output luminance are each expressed as 8-bit numerical values. As shown in FIG. 7, Fp (Face Point) is determined so that the output luminance for the representative luminance value of the face is 180, and HLp (High Light Point) is determined so that the output luminance for the highlight luminance value is 255. The gradation compression characteristics are then determined by connecting the points (0,0) and (255,255) with Fp and HLp.

[0023] If this tone compression characteristic were applied uniformly to the entire image, the output luminance for background areas with a luminance higher than HLp would be 255, resulting in saturation. However, in this embodiment, it is applied only to the subject area, so the output luminance for the luminance range above HLp can be set to 255. On the other hand, since more gradations can be allocated to the luminance range below HLp, the subject area can be corrected while maintaining natural gradations. Furthermore, different parameters may be used for the output luminance of Fp and HLp, and upper limits may be set for the correction amounts of Fp and HLp to prevent noise from worsening due to gain application.

[0024] Once the tone compression characteristics of the object region have been calculated as described above, the process returns to the process shown in FIG.

[0025] Next, in S304, the background region gradation compression characteristic calculation unit 204 calculates the gradation compression characteristic of the background region using the brightness histogram of the background region calculated in S301 and the gradation compression characteristic of the subject region calculated in S303.

[0026] Here, an example of a specific method for calculating the background region tone compression characteristics performed by the background region tone compression characteristics calculation unit 204 will be described with reference to the flowchart of FIG.

[0027] In S801, a representative dark area luminance value of the background region is calculated. In this embodiment, the average value of the bottom 50% of the luminance histogram of the background region is set as the representative dark area luminance value. The reason for using the bottom 50% here is to detect the luminance value of the dark area of ​​the background and correct the luminance of that region to be brighter. Note that in the above example, the bottom 50% is used, but the present invention is not limited to this, and any predetermined ratio may be set.

[0028] In S802, the amount of correction for the dark area representative luminance value calculated in S801 is determined. FIG. 9 is a diagram showing a correction table, which is an example of the amount of correction for the dark area representative luminance value, and is prepared in advance. In this correction table, the amount of correction is reduced when the dark area representative luminance value is smaller than threshold value a, because there is a concern that overcorrection may occur if a large correction is made to an originally small signal value. Also, when the threshold value for the dark area representative luminance value is larger than threshold value b, there is no need to make a brighter correction, so the amount of correction is weakened.

[0029] Next, in S803, a dark area luminance value that is common to the gradation characteristics of the subject area is calculated. This is because if the subject area and the background area have completely different gradation characteristics, it may result in an unnatural image that looks like the subject area and the background area have been combined. By using a common gradation characteristic for the dark areas, this unnaturalness can be alleviated.

[0030] First, based on the gradation compression characteristics of the subject area shown in FIG. 7 calculated in S403, as shown in FIG. 10(a), an output luminance value corresponding to a luminance value that is half the representative luminance value of the face is set as a common point Cp (Common Point) so that it is common to the gradation characteristics of the subject area.

[0031] Next, this common point Cp is corrected to Cp2 shown in FIG. 10(b). In FIG. 10(b), BGp (Background Point) is a point that indicates the value obtained by correcting the representative luminance value of the dark area of ​​the background region calculated in S801 with the correction value determined in S802. If the slope of the line connecting Cp and BGp is ​​smaller than a preset threshold, the output luminance of Cp is reduced so that the slope becomes the threshold, and the resulting point is designated as Cp2. If the slope of the line connecting Cp and BGp is ​​small, the gradation characteristics in this range will be poor, so this processing is performed to maintain a minimum slope. Alternatively, as shown in FIG. 10(c), point BGp2 may be obtained by changing the correction amount to increase BGp without changing Cp, or both Cp and BGp may be changed little by little.

[0032] In S804, the gradation compression characteristics of the background region are determined using Cp or Cp2 determined in S801 to S803 and BGp2 or BGp. Figure 11 shows an example in which the gradation compression characteristics are determined by connecting the points Cp2, BGp, (0,0), (210,210), and (255,255). Note that the point indicated by (210,210) indicates the luminance of a high-luminance region in the background, such as the sky. Since it is often desirable to minimize correction of high-luminance regions, the luminance of high-luminance regions above 210 is not corrected here. Once the tone compression characteristics of the background region have been calculated as described above, the process returns to the process shown in FIG.

[0033] In S305, the regional gradation compression processing unit 205 uses the gradation compression characteristics of each region calculated in S303 and S304 and the region map generated in S301 to perform gradation compression processing using the gradation compression characteristics corresponding to each region, and then ends the processing.

[0034] As described above, according to the first embodiment, in a scene with a wide dynamic range, it is possible to obtain an image with gradation characteristics that are less prone to saturation and blackout and that do not look unnatural as a whole.

[0035] <Second embodiment> A second embodiment of the present invention will now be described. The configuration of the imaging device in the second embodiment is the same as that described in the first embodiment with reference to Fig. 1, and therefore a description thereof will be omitted. However, the functional configuration related to the regional tone correction processing in the image processing unit 104 is different from that shown in Fig. 2, and therefore will be described with reference to Fig. 12.

[0036] Fig. 12 is a block diagram showing a specific functional configuration related to the regional gradation correction processing performed by the image processing unit 104 in the second embodiment. In the configuration shown in Fig. 12, the same components as those shown in Fig. 2 are given the same reference numerals, and their description will be omitted. The image processing unit 104 in the second embodiment does not have the regional gradation compression processing unit 205, but has a configuration further including a gradation compression processing unit 1205 and an image synthesis unit 1206.

[0037] Fig. 13 is a flowchart showing the regional gradation correction process in the second embodiment. The regional gradation correction process in the second embodiment will be described below with reference to the functional configuration shown in Fig. 12 and the flowchart in Fig. 13. In the process shown in Fig. 13, the same steps as those shown in Fig. 3 are assigned the same step numbers, and descriptions thereof will be omitted where appropriate.

[0038] In S1305, the gradation compression processing unit 1205 performs gradation compression processing on the input image using the gradation compression characteristics of the subject area obtained in S303 and the gradation compression characteristics of the background area obtained in S304, respectively, to generate two pieces of image data.

[0039] Then, in S1306, the image synthesis unit 1206 synthesizes the two image data generated in S1305 using the region map generated in S301 to generate a single image in which gradation correction has been performed for each region. Specifically, the image synthesis unit 1206 selects, for the subject region, an image signal that has been gradation corrected using the gradation compression characteristics of the subject region, and selects, for the background region, an image signal that has been gradation corrected using the gradation compression characteristics of the background region, and synthesizes the images.

[0040] As described above, according to the second embodiment, the same effects as those of the first embodiment can be obtained.

[0041] In the first and second embodiments described above, an image is divided into two regions: a person region is detected as the subject region, and the region other than the subject region is defined as the background region. However, the present invention is not limited to this. The image may be divided into multiple regions with different characteristics, and the tone compression characteristics may be calculated based on the brightness histogram of each region. For example, two or more different types of subjects, such as a person, a vehicle, and an animal, may be detected, and the tone compression characteristics of each subject region may be calculated.

[0042] Even when dividing into three or more regions, by using the gradation compression characteristics (reference correction characteristics) corresponding to the reference subject region and generating the gradation compression characteristics corresponding to the other regions, it is possible to obtain an image with gradation characteristics that do not look unnatural as a whole.

[0043] <Other embodiments> The present invention may be applied to a system made up of a plurality of devices, or to an apparatus made up of a single device.

[0044] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the 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 realizes one or more functions.

[0045] <Summary> The disclosure of this embodiment includes the following configuration.

[0046] (Item 1) an acquisition means for acquiring an image; a classification means for classifying the image acquired by the acquisition means into a plurality of regions based on predetermined conditions; a determination means for determining a correction characteristic for correcting a gradation characteristic for each of the plurality of regions; a correction unit that corrects the gradation characteristics of each of the regions using the correction characteristics corresponding to each of the regions; The image processing device is characterized in that the determination means sets the correction characteristic corresponding to one of the multiple areas as a reference correction characteristic, and determines the correction characteristics for at least parts of the image having a brightness lower than a predetermined brightness based on the reference correction characteristic, for correction characteristics other than the reference correction characteristic. (Item 2) The image processing device described in item 1, characterized in that the determination means determines the luminance distribution of each of the regions and determines the reference correction characteristics based on a first representative luminance value obtained from the luminance distribution of one of the regions used as the reference. (Item 3) The image processing device described in item 2 is characterized in that the determination means determines correction characteristics excluding the reference correction characteristics based on a second representative luminance value obtained from the luminance distribution of each area excluding the one area used as the reference and the reference correction characteristics. (Item 4) the classification means classifies the image into a subject region including a predetermined subject and a region excluding the subject region; 4. The image processing device according to item 3, wherein the determining means determines the subject area as one area to be used as the reference. (Item 5) The predetermined subject is a person, Item 5. The image processing device according to item 4, characterized in that the first representative luminance value includes a luminance that constitutes a predetermined first proportion from the high luminance in the luminance distribution of the person's face area or a first average value of the luminance that constitutes the luminance distribution, and a luminance value of a luminance that constitutes a predetermined second proportion from the high luminance in the luminance distribution of the subject area. (Item 6) Each area other than the one reference area is a background area, Item 6. The image processing device according to item 5, characterized in that the second representative luminance value includes a second average value of luminances that constitute a predetermined third proportion from the lowest luminance in the luminance distribution of the background area, and the first average value. (Item 7) 7. The image processing device according to any one of items 1 to 6, wherein the correction characteristics other than the reference correction characteristics have a smaller correction amount of the gradation characteristics in high brightness areas than the reference correction characteristics. (Item 8) the classification means generates a region map indicating the types of the plurality of classified regions in the image; 8. The image processing device according to any one of items 1 to 7, wherein the correction means corrects the gradation characteristics of each of the regions based on the region map using the correction characteristics corresponding to each of the regions. (Item 9) the classification means generates a region map indicating the types of the plurality of classified regions in the image; The image processing device described in any one of items 1 to 7, characterized in that the correction means corrects the gradation characteristics of the image using each of the multiple correction characteristics, and combines the resulting multiple images according to the area map. (Item 10) The image processing device described in item 2 is characterized in that the determination means, for correction characteristics excluding the reference correction characteristics, makes the correction characteristics of brightness parts lower than the predetermined brightness closer to the reference correction characteristics, and the predetermined brightness is lower than the first representative brightness value. (Item 11) 11. The image processing device according to any one of items 1 to 10, wherein the acquisition means acquires an HDR (high dynamic range) image obtained by combining a plurality of images taken with different exposures. (Item 12) An imaging means; An image processing device according to any one of items 1 to 11, An imaging device comprising: (Item 13) an acquisition step of acquiring an image; a classification step of classifying the image acquired in the acquisition step into a plurality of regions based on predetermined conditions; a determining step of determining a correction characteristic for correcting the gradation characteristic for each of the plurality of regions; a correction step of correcting the gradation characteristics of each of the regions using the correction characteristics corresponding to each of the regions; In the determination step, the correction characteristic corresponding to one of the plurality of regions as a reference is set as a reference correction characteristic, and for the correction characteristics other than the reference correction characteristic, the correction characteristics for at least parts of brightness lower than a predetermined brightness are determined based on the reference correction characteristic. (Item 14) 12. A program for causing a computer to function as each of the means of the image processing device according to any one of items 1 to 11. (Item 15) Item 15. A computer-readable storage medium storing the program described in item 14.

[0047] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0048] 101: optical system, 102: image sensor, 103: A / D conversion unit, 104: image processing unit, 105: system control unit, 106: operation unit, 107: display unit, 108: recording unit, 109: bus, 201: subject area detection unit, 202: area-specific histogram generation unit, 203: subject area gradation compression characteristic calculation unit, 204: background area gradation compression characteristic calculation unit, 205: area-specific gradation compression processing unit, 1205: gradation compression processing unit, 1206: image synthesis unit

Claims

1. an acquisition means for acquiring an image; a classification means for classifying the image acquired by the acquisition means into a plurality of regions based on predetermined conditions; a determination means for determining a correction characteristic for correcting a gradation characteristic for each of the plurality of regions; a correction unit that corrects the gradation characteristics of each of the regions using the correction characteristics corresponding to each of the regions; The image processing device is characterized in that the determination means sets the correction characteristic corresponding to one of the multiple areas as a reference correction characteristic, and determines the correction characteristics for at least parts of the image having a brightness lower than a predetermined brightness based on the reference correction characteristic, for correction characteristics other than the reference correction characteristic.

2. 2. The image processing device according to claim 1, wherein the determining means determines a luminance distribution of each of the regions, and determines the reference correction characteristic based on a first representative luminance value determined from the luminance distribution of one of the regions used as the reference.

3. 3. The image processing device according to claim 2, wherein the determination means determines the correction characteristics excluding the reference correction characteristics based on a second representative luminance value obtained from the luminance distribution of each area excluding the one area used as the reference and the reference correction characteristics.

4. the classification means classifies the image into a subject region including a predetermined subject and a region excluding the subject region; 4. The image processing apparatus according to claim 3, wherein the determining means determines the subject area as one area to be used as the reference.

5. The predetermined subject is a person, 5. The image processing device according to claim 4, wherein the first representative luminance value includes a luminance that constitutes a predetermined first proportion from the high luminance side in the luminance distribution of the person's face area or a first average value of the luminance that constitutes the luminance distribution, and a luminance value of a luminance that constitutes a predetermined second proportion from the high luminance side in the luminance distribution of the subject area.

6. Each region other than the one reference region is a background region, 6. The image processing device according to claim 5, wherein the second representative luminance value includes a second average value of luminances that constitute a predetermined third proportion, from the lowest luminance, in the luminance distribution of the background region, and the first average value.

7. 2. The image processing apparatus according to claim 1, wherein the correction characteristics other than the reference correction characteristics have a smaller correction amount of the gradation characteristics in a high-brightness area than the reference correction characteristics.

8. the classification means generates a region map indicating the types of the plurality of classified regions in the image; 2. The image processing apparatus according to claim 1, wherein the correction means corrects the gradation characteristics of each of the regions based on the region map using the correction characteristics corresponding to each of the regions.

9. the classification means generates a region map indicating the types of the plurality of classified regions in the image; 2. The image processing apparatus according to claim 1, wherein the correction means corrects the tone characteristics of the image using a plurality of the correction characteristics, and combines the resulting images in accordance with the region map.

10. The image processing device described in claim 2, characterized in that the determination means, for correction characteristics excluding the standard correction characteristics, makes the correction characteristics of brightness parts lower than the predetermined brightness closer to the standard correction characteristics, and the predetermined brightness is lower than the first representative brightness value.

11. 2. The image processing apparatus according to claim 1, wherein the acquisition means acquires an HDR (High Dynamic Range) image obtained by combining a plurality of images taken with different exposures.

12. An imaging means; The image processing device according to any one of claims 1 to 11, An imaging device comprising:

13. an acquisition step of acquiring an image; a classification step of classifying the image acquired in the acquisition step into a plurality of regions based on predetermined conditions; a determining step of determining a correction characteristic for correcting the gradation characteristic for each of the plurality of regions; a correction step of correcting the gradation characteristics of each of the regions using the correction characteristics corresponding to each of the regions; In the determination step, the correction characteristic corresponding to one of the plurality of regions as a reference is set as a reference correction characteristic, and for the correction characteristics other than the reference correction characteristic, the correction characteristics for at least the brightness parts lower than a predetermined brightness are determined based on the reference correction characteristic.

14. A program for causing a computer to function as each of the means of the image processing apparatus according to any one of claims 1 to 11.

15. A computer-readable storage medium storing the program according to claim 14.

Images