JP6514577B2 - IMAGE PROCESSING APPARATUS, IMAGE PROCESSING METHOD, AND IMAGING APPARATUS - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, and an imaging apparatus.

  2. Description of the Related Art Conventionally, there have been proposed a technique for performing appropriate exposure amount control at the time of shooting an image and a technique for performing gradation processing optimal for a shot image. However, in a scene such as an oblique person with a wide dynamic range (hereinafter referred to as D range) within the subject area, it is difficult to properly determine the brightness of the subject, and appropriate exposure control and appropriate gradation processing are required. It was difficult to realize. For example, Patent Document 1 proposes using a first exposure correction value calculated as a result of block integration of a captured image and a second exposure correction value calculated using a histogram. In Patent Document 1, the smaller one of the first and second exposure correction values is selected if the average luminance of the entire screen is equal to or less than the threshold value, and the larger one of them is finally determined if the average luminance value is equal to or more It is proposed to set as an exposure correction value.

JP, 2011-259226, A

  However, in the prior art disclosed in the above-mentioned patent documents, the subject position in the photographed image is not taken into consideration, and in particular, when the D range of the subject is wide, the exposure amount to make the subject appropriate brightness. It is difficult to realize settings and gradation processing. In addition, since the exposure correction value is switched according to the average brightness of the entire screen, there is a problem that it is difficult to perform appropriate correction in a scene where the subject is small.

  The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to appropriately determine the brightness of a subject even when the D range of the subject is wide.

In order to achieve the above object, an image processing apparatus according to an aspect of the present invention has the following configuration. That is,
Generation means for generating a luminance image of the input image;
First calculating means for calculating a first luminance value based on the luminance value of a pixel selected from the luminance image in relation to the position of a specific subject region in the luminance image;
A second calculation unit that calculates a second luminance value based on a frequency distribution of luminance values in the specific subject area in the luminance image and the first luminance value;
Determining means for determining a representative luminance value representing the brightness of the specific subject area based on the first luminance value and the second luminance value.

  According to the present invention, it is possible to appropriately determine the brightness of the subject even when the D range of the subject is wide.

FIG. 1 is a block diagram showing an example of the configuration of an imaging device according to an embodiment. FIG. 2 is a block diagram showing an example of the configuration of an image processing apparatus included in the imaging apparatus. FIG. 3 is a block diagram showing an example of the configuration of a representative luminance value calculation unit included in the image processing apparatus. The flowchart which showed the processing of the image processing part. The flowchart which showed the flow of processing of a representative luminance value calculation part. The figure explaining the block integral by embodiment. The figure explaining weighting to a face detection frame and a block. The figure explaining the histogram in a face detection frame. The figure explaining accumulation addition of a histogram, and a luminance point. The figure explaining the weight with respect to the luminance point. The figure explaining the adjustment amount required in order to calculate the last representative luminance value. FIG. 7 is a diagram for explaining adjustment of gradation characteristics.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. In the embodiment described below, the brightness (representative luminance value) of an image of a subject with a wide D range (for example, an image of a person in oblique light state) is appropriately determined, and the image of the subject has suitable brightness. The amount of exposure to be obtained and the gradation characteristics for gradation processing are adjusted. In the following embodiments, a scene in which a person in oblique light is shown is described as an example, but the present invention is not limited to this. The present invention can be applied to a scene other than a person as long as it is a scene in which a subject in which a contrast has occurred due to oblique light or the like is captured.

  FIG. 1 is a block diagram showing an example of the configuration of an imaging apparatus to which the image processing apparatus of the present embodiment is applied. In FIG. 1, an optical system 101 includes a lens unit configured of a zoom lens and a focus lens, an aperture adjustment device, and a shutter device. The optical system 101 adjusts the magnification, the focus position, or the light amount of the subject image reaching the imaging unit 102. The imaging unit 102 is a photoelectric conversion element such as a CCD or a CMOS sensor that converts a light flux of an object having passed through the optical system 101 into an electric signal by photoelectric conversion.

  The A / D converter 103 converts the input video signal into a digital image. The image processing unit 104 performs exposure amount calculation processing and gradation processing, which will be described later, in addition to normal signal processing. The image processing unit 104 can perform similar image 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 109. The exposure control unit 105 controls the exposure of the optical system 101 (for example, controls the aperture and shutter speed) in order to realize imaging with the exposure amount calculated by the image processing unit 104, and controls the imaging unit 102. (Eg, control of the sensor's analog gain).

  A system control unit 106 is a control function unit that controls and controls the overall operation of the apparatus of this embodiment. The system control unit 106 also performs drive control of the optical system 101 and the imaging unit 102 based on a luminance value obtained from the image processed by the image processing unit 104 and an instruction transmitted from the operation unit 107. The operation unit 107 provides a user interface, and outputs an instruction corresponding to a user operation to the system control unit 106. The display unit 108 is configured by a liquid crystal display or an organic EL (Electro Luminescence) display, and displays an image generated by the imaging unit 102 and an image read out from the recording unit 109. The recording unit 109 has a function of recording an image, and may include, for example, an information recording medium using a package containing a rotary recording medium such as a memory card or a magneto-optical disk mounted with a semiconductor memory. Moreover, in the recording unit 109, such an information recording medium may be detachable. The bus 110 connects the image processing unit 104, the system control unit 106, the display unit 108, and the recording unit 109, and enables data (for example, an image) to be exchanged between them.

  Next, the operation and processing of the image processing unit 104 will be described. FIG. 2 is a block diagram showing a configuration example for realizing the exposure amount calculation processing and gradation processing of the image processing unit 104. As shown in FIG. The image processing unit 104 includes an image input unit 201, a representative luminance value calculation unit 202, a gradation characteristic generation unit 203, an exposure amount calculation unit 204, a development processing unit 205, and a face detection unit 206. The image processing unit 104 receives a photographed image obtained in the photographing standby state before the main photographing and a photographed image at the time of the main photographing. These photographed images are both input from the image input unit 201 of the image processing unit 104. When the image input unit 201 inputs a photographed image before main photographing, the photographed image is used for calculation of the exposure amount by the exposure amount calculation unit 204, and the obtained exposure amount calculation result is output to the exposure control unit 105. Be done. On the other hand, when the photographed image at the time of main photographing is input, it is used for generation of the gradation characteristic by the gradation characteristic generation unit 203, and the gradation of the photographed image is used using the gradation characteristic generated by the development processing unit 205. Process and get an output image.

  FIG. 4 is a flowchart showing processing and functions of each block of the image processing unit 104 in FIG. Hereinafter, the flow of the exposure amount calculation processing and the gradation processing of the image processing unit 104 will be described in detail with reference to the flowchart of FIG. 4. In FIG. 4, the processes of steps S401 to S402 are processes for determining a representative luminance value, and are processes common to the exposure amount calculation process and the gradation process. In step S403, the process branches in order to execute the exposure amount calculation process or the gradation process according to, for example, the input shot image and the shot image formation on standby for the shot image formation for the main shooting. If the input image is a photographed image on standby for photographing, the processing of steps S404 to S405 is executed to execute the exposure amount calculation processing. If the input image is a photographed image in the main photographing, the processing of steps S406 to S408 is executed to determine the gradation characteristic and execute the development processing. Each step will be described in detail below.

  In step S401, the image input unit 201 inputs a captured image to be processed. In step S402, the representative luminance value calculation unit 202 calculates a representative luminance value for determining the exposure amount and gradation characteristics. In the case of the scene assumed in this embodiment, the representative luminance value of the person in the oblique state is calculated. Therefore, the representative luminance value calculation unit 202 calculates the representative luminance value using the position of the face of the person detected from the photographed image input by the face detection unit 206. A well-known technique can be applied to the face detection process from the captured image by the face detection unit 206. The method of calculating the representative luminance value will be described later.

  Next, in step S403, the image processing unit 104 determines which of exposure amount calculation processing before main photographing and gradation processing after main photographing is to be performed. For example, the image processing unit 104 determines whether the photographed image input by the image input unit 201 is a photographed image (in the photographing standby state) before the main photographing or a photographed image obtained by the main photographing, It is determined which of the amount calculation processing and the gradation processing is to be performed. If it is determined that the exposure amount calculation process before the main shooting is to be performed, the process proceeds to step S404. If it is determined that tone processing after main shooting is to be performed, the process proceeds to step S406.

  In step S404, the exposure amount calculation unit 204 calculates an exposure amount that is determined to be optimal for photographing based on the representative luminance value calculated in step S402. The method of calculating the exposure amount by the exposure amount calculation unit 204 will be described later. In step S405, the exposure amount calculation unit 204 outputs the exposure amount calculated in step S404 as output data of the image processing unit 104, and ends the processing of the image processing unit 104. This output data is input data of the exposure control unit 105.

  On the other hand, when performing gradation processing, in step S406, the gradation characteristic generation unit 203 calculates gradation characteristics for performing gradation processing based on the representative luminance value calculated in step S402. The calculation method of the gradation characteristic will be described later. Next, in step S407, the development processing unit 205 performs development processing on the captured image input in step S401. In the development processing, not only tone processing is performed on the captured image based on the tone characteristics calculated in step S406, but also processing such as white balance processing, noise reduction processing, and edge enhancement processing is performed. In step S408, the development processing unit 205 outputs the image obtained by performing the development processing in step S407 as output data of the image processing unit 104, and the processing of the image processing unit 104 ends. The above is the processing of the image processing unit 104.

  Next, a method of calculating a representative luminance value by the representative luminance value calculation unit 202 (step S402) will be described. FIG. 3 is a block diagram showing a configuration example of the representative luminance value calculation unit 202. As shown in FIG. The representative luminance value calculation unit 202 includes a luminance image generation unit 301, a block processing unit 302, a first luminance value calculation unit 303, a histogram calculation unit 304, a luminance point calculation unit 305, a second luminance value calculation unit 306, and a third luminance value. A calculation unit 307 is included.

FIG. 5 is a flowchart showing a process of calculating a representative luminance value by the representative luminance value calculation unit 202. The operation of each component of the representative luminance value calculation unit 202 shown in FIG. 4 will be described with reference to the flowchart of FIG. The main processing flow of the representative luminance value calculation unit 202 of this embodiment is as follows:
The first luminance value is calculated based on the luminance value of the pixel selected from the luminance image in relation to the position of the specific subject region (the region of the face in this embodiment) in the luminance image of the photographed image.
A second luminance value is calculated based on the frequency distribution (histogram) of luminance values in a specific subject region in the luminance image and the first luminance value.
Based on the first luminance value and the second luminance value, a representative luminance value representing the brightness of a specific subject area is determined and output.

First, in step S501, the luminance image generation unit 301 generates a luminance image composed of only luminance signals from the input captured image. A known method can be applied to the generation of the luminance signal Y. For example, R, G, and B signals are mixed (MIX) as shown in the following (Expression 1) to create. In Equation (1), k, l and m are MIX coefficients for creating a luminance signal.

  Next, the first luminance value is calculated in steps S502 to S503. In the present embodiment, the weighted average of the luminance values is calculated as the first luminance value, using the weights according to the positional relationship between the pixels of the luminance image and the specific subject region. In the present embodiment, the following processing is performed as a method of obtaining a weighted average by weighting according to the positional relationship between pixels of a luminance image and a specific subject region. That is, the luminance image is divided into a plurality of partial areas (blocks in the present embodiment), and an average luminance value is acquired for each partial area. Then, the weight for each partial area is determined based on the positional relationship between the specific subject area and the partial area, and the average luminance value for each partial area is weighted and averaged by using the determined weight, and the first luminance is obtained. Calculate the value. The following more specifically describes.

  First, in step S502, the block processing unit 302 performs block integration processing on the luminance image created in step S501. In the block integration process of the present embodiment, first, the luminance image 601 generated by the luminance image generation unit 301 as shown in FIG. 6A by the block processing unit 302 is divided into rectangles as shown in FIG. 6B. Get multiple rectangles. In the following description, a frame obtained by the rectangular division is referred to as a block integration frame 602. Then, the block processing unit 302 integrates the luminance values of the pixels in the block integration frame 602, and averages the integration result by the number of pixels in the block integration frame 602. Thus, block integration results of each block integration frame are obtained.

In step S503, the first luminance value calculation unit 303 calculates a first luminance value from the block integration result generated in step S502. The first luminance value calculation unit 303 calculates the first luminance value repY1 by adding a weight to the block integration result and performing weighted averaging, as shown in the following (Expression 2). In Equation (2), the total number of blocks is B_NUM, the ith block integration result is BY (i), and the weight w _i corresponding to the i th block.

In the present embodiment, the weight w _i corresponding to the block is generated based on the face detection frame of the person detected in the photographed image. The face detection frame is provided by the face detection unit 206 that detects a face from the captured image. The image used to generate the face detection frame (the image used to detect the face) may be a photographed image input by the image input unit 201, or the luminance image generated by the luminance image generation unit 301. It may be As shown in FIG. 7A, the face detection frame 701 is arranged in the luminance image 601. FIG. 7B shows the positional relationship between each block integration frame and the face detection frame 701. The block processing unit 302 determines the weight of each block detection frame according to the area in which the face detection frame 701 is included in the block integration frame. As shown in FIG. 7D, the weight of the block detection frame that does not include the face detection frame 701 at all is 0, and the weight increases as the area including the face detection frame 701 increases. Set the value Due to the nature of such weighting, a representative luminance value is calculated which places emphasis on a block integral value including a large amount of luminance of the face area of the subject. FIG. 7C shows a state of weighting values set for each block integration frame when the block integration frame and the face detection frame 701 have the positional relationship as shown in FIG. 7B. There is. In FIG. 7C, the black block integration frame has a weight value of 0, the white block integration frame has a weight value of 1, and the closer to white, the larger the weight value.

  As described above, one of the features of the first luminance value is that the brightness of the subject is determined by the weight according to the subject position in the photographed image. In addition, since the block integration result of the block integration frame including the luminance of the peripheral region of the subject is also used, there is also a feature that the dependence of the spectral reflectance of the subject is reduced to some extent to enhance the robustness.

Next, the second luminance value is calculated by steps S504 to S506. As described above, the second luminance value is calculated based on the frequency distribution (histogram) of the luminance value in the specific subject area (face detection frame) in the luminance image and the first luminance value. In the present embodiment,
A plurality of luminance values are calculated based on the difference between each of the plurality of luminance values and the first luminance value when the cumulative addition value obtained by accumulating the frequencies in the order of luminance reaches a plurality of preset threshold values. Set weights on each of the luminance values of
A weighted average of a plurality of luminance values using the set weight is calculated as a second luminance value. Hereinafter, the calculation process of the second luminance value will be described more specifically.

  First, in step S504, the histogram calculation unit 304 generates a histogram using the luminance image generated in step S501 as an input. The histogram calculation unit 304 calculates the frequency distribution (brightness histogram) of the brightness in the face detection frame 701 as shown in FIG. 8A. An example of such a luminance histogram is shown in FIG. Next, in step S505, the luminance point calculation unit 305 calculates luminance points from the histogram created in step S504. The luminance point is used to calculate a second luminance value in step S506 described later.

  FIG. 9 is a diagram for explaining the process of calculating the luminance point in the present embodiment. The luminance point calculation unit 305 cumulatively adds the histogram (FIG. 9A) of the face detection frame 701 created in step S 504 from the low luminance side, and the luminance at the point when the cumulative addition value reaches a certain threshold Calculate the value as the luminance point. Here, the threshold value is the area of the face detection frame 701, that is, the ratio of the cumulative addition value to the total value of the frequencies of the histogram. In the present embodiment, the luminance value at which the cumulative addition value reaches 20, 40, 60, 80% with respect to the total value of the frequencies is calculated as the luminance point [4] from the luminance point [1]. As shown in FIGS. 9A and 9B, the luminance points calculated from the histogram created from the face detection frame 701 of the person in the oblique state tend to be distributed at distant positions. On the contrary, as shown in FIG. 9 (c), the luminance points calculated from the histogram created from the face detection frame of the person who is not in the oblique state tend to be distributed close to each other as shown in FIG. 9 (d). It is characterized by

Returning to FIG. 5, in step S506, the second luminance value calculation unit 306 calculates a second luminance value with the luminance point calculated in step S505 and the first luminance value calculated in step S503 as inputs. The method of calculating the second luminance value will be described in detail with reference to FIG. The second luminance value calculation unit 306 calculates the second luminance value repY2 by performing weighted averaging with two types of weights W1 and W2 using the value of each luminance point using (Expression 3). In Equation (3), Y_1 to Y_4 indicate the luminance values of the respective luminance points, W1_1 to W1_4 indicate the first weights, and W2_1 to W2_4 indicate the second weights.

  The first weight W1 of (Equation 3) is a weight that increases the weight as the luminance point is different from the first luminance value. The second luminance value calculation unit 306 obtains the difference absolute value (dist1 to dist4) of the luminance point and the first luminance value as shown in FIG. The weight W1 is determined according to the value W1 is proportional to the value of dist). In addition, although the relationship of direct proportion was shown in FIG.10 (b), it is not restricted to this. As described above, the weight W1 may be increased as the luminance point is farther from the first luminance value.

  On the other hand, as shown in FIG. 10C, the second weight W2 is a fixed weight preset for each luminance point. The second weight W2 determines whether to emphasize the luminance point on the low luminance side or to emphasize the luminance point on the high luminance side. For example, if the weights W2_1 and W2_2 of the luminance points [1] and [2] are increased, the low luminance side is emphasized, and if the weights W2_3 and W2_4 of the luminance points [3] and [4] are increased, the high luminance side is emphasized. The specific weight value may be set by the user via a predetermined user interface, or may be fixed to the device.

  As described above, in the present embodiment, by referring to the histogram in the subject region, it is determined whether or not the luminance distribution has a bias from low luminance to high luminance, and the brightness in consideration of the bias is second It is calculated as the luminance value of. This is one of the features of the present embodiment. One of the features is that the bias is calculated using the first luminance value in the second luminance value calculation. Although W1 and W2 are used as weight values for calculating the second luminance value in the above, the second luminance value may be calculated using only W1.

Returning to FIG. 5, in step S507, the third luminance value calculator 307 determines the final representative luminance based on the first luminance value repY1 calculated in step S503 and the second luminance value repY2 calculated in step S506. Determine the value rep_Y. The representative luminance value rep_Y is calculated by adding the adjustment amount ADJ to the first luminance value rep_Y1 as in the following (Expression 4).

In Equation (4), as shown in FIG. 11, the adjustment amount ADJ is calculated by the luminance step between the second luminance value repY2 and the first luminance value repY1. By doing as described above, the brightness of the subject in the input photographed image is determined. In the present embodiment, the binary logarithm (LOG ₂ (repY2 / repY1)) of the ratio of the second luminance value repY2 to the first luminance value repY1 is used as the luminance step, and is proportional to such a luminance step. The value is taken as the adjustment amount ADJ (FIG. 11). Then, a representative luminance value is determined by multiplying the first luminance value by a value obtained by raising the adjustment amount ADJ to a power of 2 as an index.

  The process of calculating the representative luminance value (step S402) by the representative luminance value calculation unit 202 has been described above.

Next, the exposure amount calculation method of step S404 of FIG. 4 will be described. In the exposure amount calculation, the representative luminance value rep_Y calculated by the representative luminance value calculation unit 202 is used. Assuming that the calculated exposure amount is target_bv, the exposure amount of the current input image is capture_bv, and the target luminance value of the object is target_Y, the exposure amount calculation unit 204 calculates the exposure amount as shown in equation 5, for example. By calculating the amount of exposure in this manner, it is possible to control the amount of exposure so that a subject (person) in a state of oblique light can be photographed with an appropriate brightness.

Next, the gradation characteristic calculation method of step S406 will be described. The gradation characteristic of the present embodiment refers to the characteristic of gradation compression based on a γ curve, and there are a luminance range for maintaining the gradation and a luminance range for compressing the gradation. As shown in FIG. 12A, the gradation characteristic generation unit 203 moves the POINT, which is the boundary separating the luminance range, to the left and right, so that the floor adjusted so as to have appropriate brightness even for a person in an oblique state. Create key characteristics. The adjustment of POINT is calculated using the above-described representative luminance value rep_Y and the first luminance value repY1. Assuming that POINT after adjustment is OUT_POINT, POINT as a reference before adjustment is IN_POINT, and the adjustment amount of POINT is POINT_ADJ, adjustment is made as shown in the following (Equation 6).

The adjustment amount POINT_ADJ of POINT is determined based on the luminance step between the first luminance value repY1 and the representative luminance value rep_Y as shown in FIG. 12 (b). On the horizontal axis of FIG. 12B, the binary logarithm (LOG ₂ (repY2 / rep_Y)) of the ratio of the first luminance value repY1 to the representative luminance value rep_Y is used as the luminance step. According to such adjustment of gradation characteristics, when the first luminance value rep_Y1 is higher than the representative luminance value rep_Y, POINT_ADJ is a value smaller than 1 in order to expand the luminance range in which the gradation on the high luminance side is compressed. It becomes. On the other hand, when the representative luminance value rep_Y is higher than the first luminance value rep_Y1, the POINT_ADJ has a value larger than 1 in order to expand the luminance range for maintaining the gradation on the low luminance side. As described above, by adjusting the gradation characteristic, it is possible to control the gradation in each of the bright part and the dark part of the person in the oblique light state and to calculate the gradation characteristic to be appropriate brightness.

  As mentioned above, although the preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary. For example, the application of the image processing apparatus is not limited to an imaging apparatus such as a digital camera or a video camera, and can be applied to various electronic devices such as a portable terminal and a PC.

(Other embodiments)
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. Can also be realized. It can also be implemented by a circuit (eg, an ASIC) that implements one or more functions.

101: optical system, 102: imaging unit, 103: A / D conversion unit, 104: image processing unit, 105: exposure control unit, 106: system control unit, 107: operation unit, 108: display unit, 109: recording unit 110: system bus 202: representative luminance value calculation unit 301: luminance image generation unit 302: block processing unit 303: first luminance value calculation unit 304: histogram calculation unit 305: luminance point calculation unit 306 : Second luminance value calculation unit, 307: Third luminance value calculation unit

Claims (17)

Generation means for generating a luminance image of the input image;
First calculating means for calculating a first luminance value based on the luminance value of a pixel selected from the luminance image in relation to the position of a specific subject region in the luminance image;
A second calculation unit that calculates a second luminance value based on a frequency distribution of luminance values in the specific subject area in the luminance image and the first luminance value;
An image processing apparatus comprising: determining means for determining a representative luminance value representing the brightness of the specific subject area based on the first luminance value and the second luminance value.   The first calculation means is characterized in that a weighted average of luminance values is calculated as the first luminance value using a weight corresponding to a positional relationship between pixels of the luminance image and the specific subject area. The image processing apparatus according to claim 1. The first calculation means is
Dividing the luminance image into a plurality of partial areas;
Get the average luminance value for each partial area,
The weight for each partial area is determined based on the positional relationship between the specific subject area and the partial area,
3. The image processing apparatus according to claim 1, wherein the first luminance value is obtained by performing weighted averaging on average luminance values acquired for each partial area by using the determined weight. .   The image processing apparatus according to claim 3, wherein the weight for each partial area is set in accordance with a ratio of the specific subject area occupied by the partial area. The second calculation means is
Based on the difference between each of the plurality of luminance values and the first luminance value when the cumulative addition value obtained by accumulating the frequencies in the order of luminance for the frequency distribution of the luminance values reaches a plurality of preset threshold values, Set a weight for each of the luminance values,
The image processing apparatus according to any one of claims 1 to 4, wherein a weighted average of a plurality of luminance values using the set weight is calculated as a second luminance value.   The image processing apparatus according to claim 5, wherein a larger weight is set to each of the plurality of luminance values as the difference with the first luminance value is larger. The second calculation means weights each of the plurality of luminance values by further using a weight preset corresponding to each of the plurality of thresholds.
7. The image processing apparatus according to claim 5, wherein the weight set in advance is a larger value on the lower luminance side or a larger value on the higher luminance side.   The determination means determines the representative luminance value by adjusting the first luminance value based on a first ratio of the first luminance value and the second luminance value. The image processing apparatus according to any one of claims 1 to 7.   The determination means sets a value obtained by raising 2 as a exponent to a value proportional to the binary logarithm of the first ratio as an adjustment amount, and subtracting the adjustment amount from the first luminance value to calculate the representative luminance value. The image processing apparatus according to claim 8, wherein the image processing apparatus determines the image.   The image according to any one of claims 1 to 9, further comprising third calculation means for calculating an exposure amount for photographing based on the representative luminance value determined by the determination means. Processing unit.   The image processing according to any one of claims 1 to 10, further comprising: adjustment means for adjusting gradation characteristics used for gradation processing of the input image based on the representative luminance value. apparatus.   The image processing apparatus according to claim 11, wherein the adjustment unit adjusts the gradation characteristic based on a ratio of the representative luminance value to the first luminance value.   The adjustment means uses a value proportional to the binary logarithm of the ratio as an adjustment amount, and uses the adjustment amount as a boundary between a luminance range for maintaining the gradation in the gradation characteristic and a luminance range for compressing the gradation. The image processing apparatus according to claim 12, wherein the image processing apparatus is changed. Imaging means,
An image processing apparatus according to claim 10;
The exposure amount for imaging is acquired by inputting an image captured during imaging standby by the imaging unit to the image processing apparatus, and the exposure of the imaging unit is controlled using the acquired exposure amount. An image pickup apparatus comprising: Imaging means,
An image processing apparatus according to any one of claims 11 to 13.
The gradation characteristic adjusted by the adjustment unit is acquired by inputting the image photographed in the main photographing by the imaging unit into the image processing apparatus, and the image is photographed using the acquired gradation characteristic An imaging device comprising: processing means for processing an image. An image processing method by an image processing apparatus
Generating a luminance image of the input image;
A first calculation step of calculating a first luminance value based on the luminance value of a pixel selected from the luminance image in relation to the position of a specific subject region in the luminance image;
A second calculation step of calculating a second luminance value based on the first luminance value and the frequency distribution of luminance values in the specific subject area in the luminance image;
A determining step of determining a representative luminance value representing the brightness of the specific subject area based on the first luminance value and the second luminance value.   The program for making a computer perform each process of the image processing method of Claim 16.