Image processing apparatus, and image processing method

An apparatus includes a first brightness value acquisition unit configured to obtain a first absolute brightness value by converting a representative brightness value of an image obtained using an image pickup unit, into absolute brightness, a first determination unit configured to determine an output value based on an input-output characteristic of an output device, the output value corresponding to the first absolute brightness value obtained by the first brightness value acquisition unit, and a second determination unit configured to determine information about exposure corresponding to the output value.

BACKGROUND OF THE INVENTION

Field of the Invention

The aspect of the embodiments relates to an image processing apparatus, and an image processing method for presenting display of an image in absolute brightness.

Description of the Related Art

Brightness of an input image has conventionally been determined according to a dynamic range of brightness (hereinafter, simply referred to as a dynamic range) displayable in an output device such as a television set and a display. For example, when an image pickup apparatus is used to capture an image of an object, a video signal obtained by capturing an object image is compressed according to the dynamic range of the output device. For example, a face area which is a main object within an angle of view can be displayed in viewable brightness by compressing the brightness of the face area at a predetermined ratio with respect to an upper limit value of the brightness displayable by the output device.

However, in such a case, the face area is displayed in brightness different from the actual object. This reduces a sense of realism of the displayed image compared to the actual object observed by the user during the image capture. The tones of objects which are brighter than the face area within the angle of view are compressed, whereby the tones of the entire image are lost relative to the brightness of the actual object.

Japanese Patent Application Laid-Open No. 2004-286979 discusses a technique in which when a film is used to capture an image of an object, an average density of the entire image is determined from the average density obtained by averaging transmission densities of pixels on the negative to obtain an absolute brightness value of the object, and the absolute brightness value is converted into a predetermined exposure amount.

SUMMARY OF THE INVENTION

According to an aspect of the embodiments, an apparatus comprising circuitry configured to perform first brightness obtaining process to obtain a first absolute brightness value by converting a representative brightness value of an image obtained by capturing an object image, into absolute brightness, first determining process to determine an output value based on an input-output characteristic of an output device, the output value corresponding to the first absolute brightness value obtained by the first brightness obtaining, and second determining process to determine information about exposure corresponding to the output value.

DESCRIPTION OF THE EMBODIMENTS

A first exemplary embodiment will be described below. An exemplary embodiment of the disclosure is described with reference to the accompanying drawings.FIG. 1is a block diagram illustrating a configuration example of a digital video camera (hereinafter, referred to simply as a video)100which is an exemplary embodiment of an image processing apparatus performing the disclosure. One or more functional blocks illustrated inFIG. 1may be implemented by hardware such as an application specific integrated circuit (ASIC) and a programmable logic array (PLA). Alternatively, one or more functional blocks illustrated inFIG. 1may be implemented by executing software by a programmable processor such as a central processing unit (CPU) and a microprocessing unit (MPU). Furthermore, one or more functional blocks illustrated inFIG. 1may be implemented by a combination of software and hardware. In the following description, even if different functional blocks are described as operation subjects, the same piece of hardware can therefore implement the subjects.

As illustrated inFIG. 1, an imaging lens unit101is a lens unit including various imaging lenses such as a zoom lens and a focus lens. The imaging lens unit101is an optical member for forming an object image. A diaphragm102is a first light amount adjustment member for adjusting an amount of a light beam having passed through the imaging lens unit101. An aperture diameter of the diaphragm102is changed to adjust the amount of light entering the inside of the video100. A neutral density (ND) filter103is a second light amount adjustment member for further adjusting the amount of the light beam having passed through the diaphragm102. The ND filter103can be inserted or removed to adjust the amount of light entering the inside of the video100. The ND filter103may be configured to have different transmission densities area by area and control its insertion position to adjust the amount of incident light. A barrier104is a lens barrier that transitions between a protection state in which the barrier104covers a front (object side) of the imaging lens unit101and a retracted state in which the barrier104is retracted from the front of the imaging lens unit101to allow capture of an object image.

An imaging unit105includes a solid-state image sensor of charge accumulation type for converting an optical image into an electrical signal. Examples of the solid-state image sensor include a charge-coupled device (CCD) sensor and a complementary-metal-oxide-semiconductor (CMOS) sensor. The imaging unit105is a unit for photoelectrically converting (capturing an image) the light beam of the object which is incident via the imaging lens unit101, and outputting analog image data (analog image signal).

The imaging unit105can perform various functions. The functions include control of a charge accumulation time by controlling reading or reset timing of accumulated charges, which is an electronic shutter function, and adjustments of an analog gain amount and a reading speed.

An analog-to-digital (A/D) converter106is an A/D conversion unit for converting analog image data into digital image data. An image processing unit107is a unit for performing various types of processing on image data output from the A/D converter106or image data which input is controlled by a memory control unit108. The various types of processing include color conversion processing, tone correction, and an adjustment of a digital gain amount. The image processing unit107performs predetermined calculation processing using image data obtained by capturing the object image, and transmits a result of the calculation to a system control unit111described below. Based on the result of the calculation received from the image processing unit107, the system control unit111performs various controls and adjustments such as exposure control, ranging control, and white balance adjustment. Through-the-lens (TTL) automatic focus (AF) processing, automatic exposure (AE) processing, and automatic white balance (AWB) processing are thereby executed. Details of the processing executed by the image processing unit107will be described below.

The image data output from the A/D converter106is written into a memory112via the image processing unit107and the memory control unit108, or directly via the memory control unit108. The memory112is a first storage unit for storing image data obtained by using the imaging unit105and image data to be displayed on a display unit110. The memory112has a storage capacity sufficient to store a predetermined duration of moving images and sound. The memory112also serves as a memory for image display (video memory).

A digital-to-analog (D/A) converter109is a D/A conversion unit for converting digital image data for display stored in the memory112into analog image data, and supplying the analog image data to the display unit110. The display unit110is a display device such as a liquid crystal display (LCD). The display unit110presents display according to the analog image data output from the D/A converter109. When image data is sequentially transferred to and displayed on the display unit110, the display unit110can function as an electronic viewfinder to present a live view display of the image data.

A nonvolatile memory113is an electrically erasable and recordable, second storage unit. For example, an electrically erasable programmable read-only memory (EEPROM) is used as the nonvolatile memory113. The nonvolatile memory113stores operation constants and programs of the system control unit111. The programs include a program for executing various flowcharts described below in the present exemplary embodiment.

The system control unit111is a control unit for controlling an operation of the video100in a centralized manner. The system control unit111includes a CPU (not illustrated) which is a microprocessor. The system control unit111implements processes described below by executing the programs stored in the nonvolatile memory113. A system memory114is a third storage unit including a RAM area. Operation constants of the system control unit111, variables, and programs read from the nonvolatile memory113can be loaded into the system memory114. The system control unit111can control the memory112, the D/A converter109, and the display unit110to control display of the image data. A system timer115is a real-time clock for measuring time used for various controls and the time of a built-in clock.

A mode change switch120, an imaging switch121, and an operation unit122are units for inputting various operation instructions into the system control unit111. The mode change switch120is a first operation member for switching an operation mode of the system control unit111to any one of a moving image recording mode, a still image recording mode, and a playback mode. The moving image recording mode and the still image recording mode include an automatic imaging mode, an automatic scene determination mode, a manual mode, various scene modes, a program AE mode, and a custom mode. In the scene modes, settings are made individually for each imaging scene. The mode change switch120may be configured to directly switch an operation to any one of the modes included in the moving image recording mode. Alternatively, the mode change switch120may be configured to switch an operation to each mode after it switches the operation to the moving image recording mode.

The imaging switch121is a second operation member for switching an operation between an imaging preparation state and an imaging state. For example, a first stroke (half press) of the imaging switch121switches the video100to the imaging preparation state. A second stroke (full press), in which the imaging switch121is further pressed from the first stroke, switches the video100to the imaging state. If the imaging switch121is not pressed, the video100is in an imaging standby state. In the moving image recording mode, when the imaging switch121is pressed by a predetermined amount, the system control unit111executes a series of operations from the reading of a signal from the imaging unit105to the writing of moving image data to an external recording medium200described below.

Appropriate functions are assigned scene by scene to each operation member of operation unit122when various function icons displayed on the display unit110are selected and operated. The operation members thus function as various function buttons. Examples of the function buttons include an end button, a return button, an image forward button, a jump button, an aperture narrow-down button, and an attribute change button. For example, if a menu button is pressed, a menu screen capable of making various settings is displayed on the display unit110. The user can observe the menu screen displayed on the display unit110while operating the operation unit122to make various settings in an intuitive manner.

A power supply control unit116is a control unit including a battery detection circuit, a direct-current-to-direct-current (DC-DC) converter, and a switch circuit for switching blocks to be energized. The power supply control unit116detects whether a battery (not illustrated) is attached, the type of the battery, and the remaining battery level. The power supply control unit116controls the DC-DC converter (not illustrated) based on the results of detection and instructions from the system control unit111. The power supply control unit116thereby supplies needed voltages to various parts of the video100including the external recording medium200, for a needed period. The supply of power to various parts of the video100is switched on/off by operating a power switch123which is a fourth operation member.

A power supply unit117is a power supply device including a primary battery such as an alkali battery and a lithium battery, a secondary battery such as a NiCd battery, a NiMH battery, and a Li ion battery, and/or an alternating-current (AC) adapter. An interface unit (I/F)118is an interface for performing communication with the external recording medium200such as a memory card and a hard disk, or an external output device (not illustrated). The external recording medium200is a medium such as a memory card for recording image data obtained by capturing an object image. The external recording medium200includes a semiconductor memory and/or a magnetic disk.

(Detailed Configuration of Image Processing Unit107)

Next, an internal configuration of the image processing unit107according to the present exemplary embodiment will be described with reference toFIG. 2.FIG. 2is a block diagram for illustrating the internal configuration and related parts of the image processing unit107according to the present exemplary embodiment. While the image processing unit107executes white balance control and sharpness control, a description thereof is omitted in the present exemplary embodiment. The blocks in the image processing unit107can obtain various types of data through the system control unit111. The various types of data include information about the diaphragm102and the ND filter103, and exposure conditions (parameters) including a shutter speed and various gain amounts in capturing an image of an object.

As illustrated inFIG. 2, a detection unit301is a unit that performs detection processing on image data output from the A/D converter106or image data output by controlling the memory control unit108to determine a representative brightness value of the image data. Details of the detection processing performed by the detection unit301will be described below.

An absolute brightness calculation unit302is an absolute brightness calculation unit for calculating a reference signal corresponding to a reference brightness value and an absolute brightness value (hereinafter, referred to simply as Bv value) which expresses the representative brightness value detected by the detection unit301in absolute brightness. Details of the absolute brightness value will be described below.

An absolute brightness code determination unit303is an output characteristic determination unit for determining an absolute brightness code based on an input-output characteristic of a display device. The absolute brightness code refers to a code about an output characteristic corresponding to the Bv value (absolute brightness value) calculated by the absolute brightness calculation unit302. The input-output characteristic of the display device connected to the video100may be either one that is recorded in the nonvolatile memory113in advance or one that is input by the user and read by the memory control unit108. The absolute brightness code determination unit303may be configured to obtain the input-output characteristic from the display device connected to the video100.

An exposure amount determination unit304is a unit for determining exposure (exposure control amount) for the display device which outputs a display image in absolute brightness, based on a tone conversion characteristic described below and the absolute brightness code determined in advance. Based on the exposure determined by the exposure amount determination unit304, the system control unit (exposure control unit)111can control (change) exposure parameters to perform exposure control according to the absolute brightness.

A tone correction unit305is a tone correction unit for correcting (changing) the tone conversion characteristic which is an input-output characteristic of a video signal. The tone correction unit305performs tone correction on the data from the A/D converter106or the data output under control of the memory control unit108. The configuration of the processing unit107according to the present exemplary embodiment has been described above. Processing and controls to be performed by the foregoing units will be described below with reference toFIG. 3.

The absolute brightness (absolute luminance) mentioned above will be described. Conventional display devices, such as a video display and a projector, display a 100% white video signal at a brightness value of 100 nit (cd/m2). Some display devices are known that can present display with a brightness value higher than 100 nit (100 cd/m2). For example, high dynamic range (HDR) displays capable of presenting display with brightness values of 1000 to 4000 nit (4000 cd/m2) are known. An electro-optical transfer function (EOTF) is a conversion function corresponding to a tone conversion characteristic for an HDR display. As an example of the EOTF, an EOTF to which a perceptual quantizer (PQ) system is applied has been standardized. The PQ system refers to a system in which an EOTF that provides visually optimum quantization precision for a display brightness range of up to 10000 nit is used as a reference. Such EOTFs for HDR displays are defined as quantization values with respect to the absolute brightness of the video output of the display devices.

Conventional image pickup apparatuses such as a video camera have a tone conversion characteristic referred to as an optical-electro transfer function (OETF). The OETF usually has a characteristic approximate to the inverse characteristic of a display EOTF, or a characteristic taking account of the total tone of the system. For example, an OETF defined by BT.709 is one optimized to a monitor that can present the foregoing brightness display at 100 nit.

Such a camera system OETF is expressed in terms of relative brightness instead of the foregoing absolute brightness. For example, a sensor output value varies with the settings of the aperture value, the shutter speed, and the gain amount. The relative brightness OETF assigns a sensor output with respect to an object having a standard reflectance to the sensor output value as a predetermined reference value. According to BT.709, appropriate exposure is typically determined by using the output value of a standard white object or 18% gray object as a reference signal (reference brightness value).

As described above, absolute brightness is expressed by an absolute value (fixed value) determined for a predetermined output characteristic (code) in advance, and enables display at a constant display brightness relative to an output value since the relationship between the tone value and display brightness is defined. On the other hand, in relative brightness, the upper and lower limits of the display brightness vary with the output value. For example, display brightness corresponding to an output value may vary depending on the display device.

For example, suppose that the brightness of image data obtained on image processing apparatus side such as an image pickup apparatus is calculated in relative brightness, and a brightness of 70% is defined to be an appropriate brightness of a main object area while an upper limit value of expressible brightness is 100%. In such a case, if the actual main object has a brightness value of 300 nit in absolute brightness and the upper limit of the expressible brightness values of the display device is 1000 nit, the display device displays the main object at a brightness value of 700 nit. In other words, the brightness of the main object presented on the display device is largely different from the actual brightness. This results in an unnatural image (video image) display with less sense of realism.

Other than the PQ system, a plurality of methods is discussed for absolute brightness display. If an output value is determined on the image processing apparatus side regardless of the input-output characteristic which can be presented by the display device, the display device presents a display image at a brightness value different from that of the actual brightness.

As described above, if the image processing apparatus side is unable to output image data having brightness suited to the characteristic of the display device, it is difficult for the image processing apparatus to determine how much the current exposure deviates from the brightness of the actual object. The image processing apparatus is therefore not able to perform exposure control so that the display image on the display device has the brightness of the actual object. The present exemplary embodiment solves the foregoing situation by determining the absolute brightness value of the image data and performing exposure control based on the absolute brightness value and the characteristic of the display device. Details are described below.

(Details of Exposure Change Processing)

Next, an operation of the exposure change processing of the image processing apparatus according to the present exemplary embodiment will be described with reference toFIG. 3.FIG. 3is a flowchart illustrating an operation of the exposure change processing according to an exemplary embodiment of the disclosure. When the video100is powered on, the system control unit111controls various units of the video100to capture an image of an object and obtain pre-image data for detection (hereinafter, each piece of image data will be referred to simply as an image). During acquisition of a pre-image, the exposure recorded in the nonvolatile memory113in advance is used. In the present exemplary embodiment, the exposure change processing is described which is started when power is turned on. However, this is not restrictive. For example, the exposure change processing may be performed at every predetermined number of frames in obtaining a moving image for recording or a live view (LV) display image. The exposure change processing may be performed in response to detection of a change in the brightness of the object by a conventional method. In other words, any information about the presence or absence of a change in exposure when capturing an object image to obtain an image may be used as a trigger to start the exposure change processing.

In step S301, the detection unit301performs detection on the obtained image, and determines a representative brightness value of the image. In performing the detection, the detection unit301according to the present exemplary embodiment calculates brightness values by multiplying average brightness values in each predetermined area where the image is divided, by coefficients to which weight is assigned to a greater degree regarding the acquisition of a brightness value in substantially center portions of the image. The detection unit301then calculates an average value of the brightness values of each area as a representative brightness value of the image. In the present exemplary embodiment, the representative brightness value is calculated by conversion into a code value based on a predetermined conversion characteristic. Suppose, for example, that the code value of the representative brightness value is 2132. Instead of calculating the representative brightness value by the conversion into a code value, the detection unit301may be configured to obtain a representative brightness value converted into an Additive System of Photographic Exposure (APEX) unit. In such a case, the value in the APEX unit is to be converted into a code value in subsequent processing.

The method for calculating the representative brightness value is not limited to the foregoing. For example, the detection unit301may be configured to calculate the representative brightness value by placing weight on a specific object portion detected by a conventional method. In this case, considering that the dynamic range changes at the time of shooting due to subsequent exposure control, an object that can be detected regardless of a change of the dynamic range is selected as the specific object. In such a case, the detection unit301can set thresholds serving as upper and lower limit values of brightness of an object that can become the specific object, according to the dynamic range of the imaging unit105, and select an object existing between the thresholds.

In step S302, the absolute brightness calculation unit302calculates a Bv value (absolute brightness value) which indicates the representative brightness value expressed in terms of absolute brightness. A method for calculating the Bv value will be described. For example, the Bv value is calculated from a reference brightness value (reference signal), exposure parameters such as the aperture value, the shooting sensitivity, and the shutter speed in obtaining (capturing) the pre-image, and the representative brightness value obtained by the detection unit301. The reference brightness value is a brightness value with reference to an object that provides 18% gray input in the image data (object showing a reflectance of 18%). When the exposure parameters are converted into APEX units, a reference Bv value (reference absolute reference value) which is the reference brightness value expressed in absolute brightness is given by Eq. (1):
ReferenceBvvalue=2(Av+Tv−Sv)×(0.32×k)[cd/m2]   (1)
In Eq. (1), Av is the aperture value, Tv is the shutter speed, and Sv is exposure (exposure control value) in an APEX unit into which the shooting sensitivity is converted. k is a correction coefficient. The correction coefficient k is used in converting the brightness value expressed in the APEX unit into a unit of absolute brightness, cd/m2(or nit) so that the 18% gray input is provided. In the present exemplary embodiment, k=12.5. A brightness value Z expressed in the APEX unit can be converted into an absolute brightness value X based on a relative equation log2(x/0.32×k)=Z, i.e., by X=2Z×(0.32×k). For example, suppose that Av=F4.0, Tv= 1/128, and Sv=International Organization for Standardization (ISO) speed 200. Based on Eq. (1):
ReferenceBvvalue=(2(4(Av)+7(Tv)−6(Sv)))×(0.32×12.5)=128[cd/m2].

The reference brightness value (reference brightness) related to the reference Bv value is converted into code A, which is a code value based on the output characteristic of the video100, by using Eq. (2):
CodeA=(2(number of bits))×(reference brightness value [%]/dynamic range[%])  (2)
For example, suppose that the dynamic range of the signal the imaging unit105can output is 1200%, the reference brightness value is 20% of the upper limit value of the brightness value, and the number of bits of the image data is 14. Then:
CodeA=(214)×(20/1200)
≈273.
The code of the reference signal is thus 273.

Suppose that code B, which is the code value of the representative brightness value calculated above, is 2132. In such a case, code B is expressed as Eq. (3):
CodeB=codeA×α(3)
where α is a ratio about a difference between the representative brightness value and the reference brightness value. For example, applying the foregoing parameters to Eq. (3) yields:
2132=273×α
α≈7.81.
That is, in the present exemplary embodiment, the ratio about the difference between the representative brightness value and the reference brightness value shows a relationship of 7.81:1. The representative Bv value which is the representative brightness value expressed in absolute value is thus given by Eq. (4):
RepresentativeBvvalue=(α×referenceBvvalue)   (4)
=7.81×128[cd/m2]
≈1000[cd/m2]

The foregoing is an example of the method for calculating the representative Bv value. The absolute brightness calculation unit302may be configured to calculate the representative Bv value by using other methods. In other words, in the present exemplary embodiment, the method for calculating the representative Bv value is not limited.

In step S303the absolute brightness code determination unit303determines an absolute brightness code (code C) for display. Code C is a code value for conversion into absolute brightness according to which the image displayed on the display device has the representative Bv value calculated above. In the present exemplary embodiment, the absolute brightness code for display is calculated based on the input-output characteristic of the display device and the representative Bv value calculated in the processing of the foregoing step S302.

FIG. 4is a diagram for illustrating the input-output characteristic of the output device (display device). The vertical axis indicates the output value (output brightness) from the video100. The horizontal axis indicates the absolute brightness code which is the input value (input signal) to the display device. If the display device has an input-output characteristic as illustrated inFIG. 4, the input value (absolute brightness code) serving as the representative Bv value which is the output value calculated by the video100is determined by the graph. In the present exemplary embodiment, the absolute brightness code is determined based on the graph about the input-output characteristic of the display device illustrated inFIG. 4. However, this is not restrictive. For example, the absolute brightness code determination unit303may be configured to use a calculation formula indicating the input-output characteristic of the display device corresponding to the graph. Further, the absolute brightness code determination unit303may be configured to use table data indicating absolute brightness codes corresponding to representative Bv values.

In step S304, after the determination of the absolute brightness code for display based on the input-output characteristic of the display device, the exposure amount determination unit304calculates an exposure control amount β based on the absolute brightness code calculated in step S303. Specifically, the exposure amount determination unit304calculates the exposure control amount β such that the output from the tone correction unit305becomes the absolute brightness code calculated in step S303with respect to the representative brightness value obtained in advance.

For example, the exposure amount determination unit304can obtain the tone conversion characteristic of the video100from the tone correction unit305, and calculate the exposure control amount β based on the tone conversion characteristic.FIG. 5is a diagram for illustrating the tone conversion characteristic of the video100according to an exemplary embodiment of the disclosure.FIG. 5illustrates the absolute brightness code for display (code C) calculated in advance, the code input to the tone correction unit305. More specifically, code Y is a code value for tone correction corresponding to absolute brightness. The code Y refers to the input value input to the tone correction unit305such that the output value becomes the absolute brightness code according to the tone conversion characteristic of the video100. In the present exemplary embodiment, a graph about the relationship between the absolute brightness code and code Y for tone correction as illustrated inFIG. 5, is recorded in the video100in advance, and code Y is determined based on the graph. However, such a configuration is not restrictive. For example, a calculation formula or table data corresponding to the graph may be recorded inside the video100or in an apparatus or cloud data connected to the video100, and code Y may be calculated based on the calculation formula or table data.

If the tone conversion characteristic is inverse (counterbalancing) to the input-output characteristic of the display device, the exposure control amount β is given by Eq. (5) in a case where the absolute brightness code corresponds to the representative brightness value as the output value:
Exposure control amount β=Y/representative brightness value.   (5)
The representative brightness value calculated in step S301is used as the representative brightness value. In the present example, the tone conversion characteristic is described as inverse (counterbalancing) to the input-output characteristic of the display apparatus. However, this is not restrictive.

In step S305, the system control unit111operates various units of the video100to perform exposure control based on the exposure control amount β determined in step S304. For example, if the exposure control amount β determined by the processing of step S304is ½ (i.e., 0.5), the system control unit111performs exposure control by changing one or more of the exposure parameters to reduce exposure in the APEX unit by one stop. That is, the exposure control amount β is calculated as a change rate (change amount) relative to the current exposure set in the video100.

A method for the exposure control will be described. The exposure control is performed by changing at least one of the exposure parameters, i.e., the aperture value, the shutter speed, and the shooting sensitivity. In addition to the foregoing three exposure parameters, a light attenuation ratio of the amount of light entering the inside of the video100by the ND filter (not illustrated) may be changed for exposure control.

Based on the calculated exposure control amount β the system control unit111may change time needed to complete a change of exposure from the current exposure condition. Specifically, if the exposure change amount β is greater than or equal to a predetermined value, the system control unit111changes the exposure to a target value of exposure stepwise by a plurality of frames. In the present exemplary embodiment, the predetermined value is a value equivalent to two steps of exposure in the APEX unit. On the other hand, if the exposure change amount β is smaller than the predetermined value, the system control unit111changes the exposure within the duration of one frame. With such a configuration, exposure changeable within a predetermined period can be controlled, so that a video image can be output in which brightness changes smoothly between images.

In step S306, the tone correction unit305corrects the tone conversion characteristic applied to the obtained image according to the exposure control performed in advance. The exposure change processing according to the present exemplary embodiment has been described above. As described above, the video100according to the present exemplary embodiment is configured to convert the representative brightness value of the obtained image into absolute brightness in view of the input-output characteristic of the output device such as a display device, and perform exposure control based on the absolute brightness. With such a configuration, exposure control in view of the input-output characteristic of the output device can be performed to display an image having a sense of realism by preventing reduction in the reproducibility of the brightness of the actual object. The video100according to the present exemplary embodiment can thus present video display adjusted to the actual brightness of the object in view of the input-output characteristic of the output device.

The exemplary embodiment of the disclosure has been described above. The disclosure is not limited thereto, and various changes and modifications may be made without departing from the gist of the disclosure. For example, in the foregoing exemplary embodiment, only a case where the representative brightness value is converted into absolute brightness to calculate the value has been described. However, this is not restrictive. For example, the video100may be able to switch between an absolute brightness mode (first mode) in which absolute brightness is calculated as the representative brightness value, and a relative brightness mode (second mode) in which, unlike the first mode, relative brightness is calculated as the representative brightness value.

In such a case, the system control unit111serving as a detection (determination) unit for detecting (determining) the output device detects the display device connected to the video100. The system control unit111serving as a mode change unit for switching between the foregoing two modes may be configured to automatically switch the foregoing modes based on the result of detection. For example, the system control unit111controls each unit of the video100to enter the absolute brightness mode if the upper limit of the display brightness of the display device exceeds 1000 nit, and enter the relative brightness mode if the upper limit of the display brightness is lower than or equal to 1000 nit. An arbitrary value may be employed as the upper limit (threshold) of the display brightness, whereas the value allows a distinction between an HDR display and a standard dynamic range (SDR) display having a narrow dynamic range of display brightness. Further, the video100may be configured such that the first and second modes can be switched when the user inputs an operation.

If the representative brightness value is calculated in terms of relative brightness (second mode), the processing corresponding to steps S302and S303ofFIG. 3can be omitted. In the processing of step S304, the exposure amount determination unit304calculates an exposure control value to reach the target value based on the representative brightness value. For example, if the representative brightness value is calculated by adding weight to a great degree to a face area that is a main object in the image, as the target value the brightness of the face area is approximately 70% of the upper limit value of the brightness values expressed in terms of relative brightness. Suppose that the tone (gamma) correction characteristic is inverse to the input-output characteristic of the display device (output device), and the number of bits of the image is 14. The exposure control value is given by Eq. (6):
Exposure control value=(0.7×(214))/representative brightness value  (6)
The subsequent processing is similar to step S305and the subsequent steps described above.

In the foregoing exemplary embodiment, the image processing apparatus including the imaging unit105is the digital video camera100which is an image pickup apparatus. However, this is not restrictive. For example, an image pickup apparatus and an image processing apparatus may be configured as separate members, and the image processing apparatus may be configured to perform the foregoing exposure change processing based on image data obtained from the image pickup apparatus. In such a case, the image processing apparatus calculates the exposure change amount β inside the apparatus, and transmits information about the exposure change amount β to the image pickup apparatus side. The image pickup apparatus side may be configured to control exposure when capturing and obtaining an object image, based on the information about the exposure change amount β obtained from the image processing apparatus. The connection between the image pickup apparatus and the image processing apparatus is not limited to a wired connection. A wireless connection or a connection via another host apparatus may also be used.

In the foregoing exemplary embodiment, the units constituting the video100such as the image processing unit107and the system control unit111, operate in cooperation with each other to control the operation of the video100. However, such a configuration is not restrictive. For example, a (computer) program according to the flow illustrated inFIG. 3described above may be recorded in the nonvolatile memory113in advance. The system control unit111including a microcomputer may be configured to execute the program to control the operation of the video100. The program may be in any form as long as the functions of the program are provided. Examples include object code, a program executed by an interpreter, and script data supplied to an operating system (OS). Examples of a recording medium for supplying the program may include magnetic recording media such as a hard disk and a magnetic tape, and optical/magnetooptical recording media.

In the foregoing exemplary embodiment, the digital video camera100is described as an example of the image pickup apparatus carrying out an exemplary embodiment of the disclosure. However, this is not restrictive. For example, an image pickup apparatus other than a digital camera may be employed. For example, portable devices such as a digital camera and a smartphone, a wearable terminal, and a security camera may be employed.

Other Exemplary Embodiments

An exemplary embodiment of the disclosure may be carried out by processing for supplying a program for implementing one or more functions of the foregoing exemplary embodiment to a system or an apparatus via a network or a storage medium, and reading and executing the program with one or more processors of a computer of the system or apparatus. Further, an exemplary embodiment of the disclosure may be carried out by using a circuit (for example, ASIC) that implements one or more of the functions.

Other Embodiments

This application claims the benefit of Japanese Patent Application No. 2016-188327, filed Sep. 27, 2016, which is hereby incorporated by reference herein in its entirety.