JP2018014678A - Imaging apparatus, control method therefor, and program - Google Patents

Abstract

An imaging apparatus capable of presenting an effect of changing a dynamic range in an easy-to-understand manner.
An image processing unit includes a gamma correction circuit that performs gamma correction on imaged image data. The system control unit 50 changes the exposure and gamma correction characteristics according to the change amount for changing the current dynamic range related to the image data to the target dynamic range. The image processing unit 24 displays image data corresponding to the current dynamic range and image data corresponding to the target dynamic range on the screen.
[Selection] Figure 5

Description

  The present invention relates to changing the dynamic range of an imaging apparatus.

  As a method of expanding the dynamic range of an image as compared with the case of proper exposure, there is a method of taking a picture with exposure lower than the proper exposure (underexposure) and adjusting luminance by gamma correction (gradation correction). By this method, it is possible to suppress overexposure and underexposure in the captured image. The gamma correction characteristic (also referred to as a gamma curve) is a characteristic that defines a correspondence between an input level range corresponding to a set dynamic range and a predetermined output level range. By changing the gamma correction characteristic (gamma curve shape), it is possible to control how the gradation of the input level is reflected in the output level.

  If not all the brightness values of the shooting subject are included in the dynamic range set by the imaging device, the amount of light of the lighting device that illuminates the shooting subject so that the brightness value of all shooting subjects is included in the dynamic range as much as possible, It is necessary to adjust the irradiation angle. At this time, the luminance value is generally measured using an incident luminance meter that measures the light applied to the subject. However, it is necessary to measure at a plurality of locations for each subject. Moreover, it is necessary to perform measurement many times each time the environment of the lighting device is adjusted. In addition, the specifications of the imaging device to be used and the target value of the luminance meter are often different, and it is necessary to correct the measurement result in order to match the measurement result of the luminance meter to the characteristics of the imaging device to be used.

  Further, when the luminance value of the photographic subject is saturated with respect to the output of the imaging device, how much the light amount of the illumination device and the dynamic range of the imaging device should be set in order to include the saturated luminance value in the dynamic range. I do n’t know.

  Patent Document 1 discloses an imaging apparatus that displays a through image after dynamic range expansion and displays a luminance histogram of the image signal for display.

JP 2009-239637 A

  However, the imaging device described in Patent Document 1 cannot simultaneously compare the image after dynamic range expansion and the image before dynamic range expansion. For this reason, it is difficult for the user to determine how much the dynamic range should be changed, and the intention of the user cannot be reflected.

  An object of the present invention is to provide an imaging apparatus capable of presenting the effect of changing the dynamic range in an easily understandable manner.

  An imaging apparatus according to an embodiment of the present invention is an imaging apparatus including an imaging unit that images a subject through an imaging optical system, and a correction unit that performs gradation correction on image data acquired by the imaging unit; Dynamic range changing means for changing the current dynamic range related to the image data to a target dynamic range, characteristic changing means for changing the characteristics of the exposure and the correction means according to the changed amount of the dynamic range, Display control means for displaying on the screen image data corresponding to the current dynamic range and image data corresponding to the target dynamic range.

  According to the imaging apparatus of the present invention, the effect of changing the dynamic range can be presented in an easily understandable manner.

1 is an external view of an imaging apparatus according to an embodiment of the present invention. It is a block diagram which shows the structure of the imaging device which concerns on embodiment of this invention. It is a figure which shows the gamma correction characteristic example before and behind a dynamic range change. It is a figure which shows the example of a display of the photometry frame with respect to a to-be-photographed object, and a difference value. It is a figure which shows the example of a display of the image before dynamic range expansion and after expansion. It is a flowchart explaining the display control which concerns on a dynamic range setting.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention can be applied to an imaging apparatus such as a digital camera and various information processing apparatuses having an imaging unit.

(First embodiment)
FIG. 1 is an external view showing a digital video camera 100 as an example of an imaging apparatus. Below, the subject side is defined as the front side, and the positional relationship of each part will be described. The display unit 28 is attached to the side surface of the camera body so as to be opened and closed, and displays images and various information on the screen. The recording switch 61 is an operation member for issuing a shooting instruction, and is disposed on the rear surface of the camera body. The mode switch 60 is an operation member for switching various modes, and is disposed on the side surface of the camera body. The operation unit 70 includes operation members such as various buttons that accept various operation instructions from the user and a cross key, and is disposed on the side surface of the camera body or the housing of the display unit 28. The connector 112 is a member that is disposed on a side surface portion of the camera body and connects the connection cable and the digital video camera 100.

  The power switch 72 is disposed on the upper surface of the camera body and is used by the user to switch between a power-on operation and a power-off operation. The recording medium 200 is a recording medium such as a memory card or a hard disk. The recording medium slot 201 is disposed on the rear surface of the camera main body, and stores the recording medium 200. The recording medium 200 stored in the recording medium slot 201 can communicate with the digital video camera 100.

  FIG. 2 is a block diagram illustrating an internal configuration example of the digital video camera 100. The imaging lens 103 is a lens group including a zoom lens and a focus lens, and forms an image of light from a subject. The diaphragm 101 is a light amount adjusting member. The ND filter 104 is an optical filter for dimming. The imaging unit 22 includes an imaging element that photoelectrically converts an optical image into an electrical signal. The imaging device is a CCD (Charge Imaging Element) type image sensor, a CMOS (Complementary Metal Oxide Semiconductor) type image sensor, or the like. The imaging unit 22 also has functions such as control of charge accumulation by a so-called electronic shutter function capable of controlling read-out and reset timing of accumulated charge, and changing analog gain and readout speed. The barrier 102 covers the components of the imaging optical system including the imaging lens 103, thereby preventing the imaging lens 103, the diaphragm 101, the imaging unit 22, and the like from being dirty or damaged. The imaging unit 22 outputs an imaging signal to an A (analog) / D (digital) converter 23.

  The A / D converter 23 converts the analog signal output from the imaging unit 22 into a digital signal and outputs the digital signal to the image processing unit 24 and the memory control unit 15. The image processing unit 24 performs processing such as predetermined pixel interpolation, resizing processing, color conversion processing, gamma correction, and digital gain addition on the data from the A / D converter 23 or the data from the memory control unit 15. I do. The image processing unit 24 performs predetermined calculation processing using the captured image data, and transmits the calculation result to the system control unit 50. The system control unit 50 performs exposure control, focus detection and focus adjustment control, white balance control, and the like based on the calculation result transmitted from the image processing unit 24. As a result, TTL (through-the-lens) AF (autofocus) processing, AE (automatic exposure) processing, AWB (auto white balance) processing, and the like are performed.

  The output data of the A / D converter 23 is directly written into the memory 32 via the image processing unit 24 and the memory control unit 15 or via the memory control unit 15. The memory 32 stores image data captured by the imaging unit 22 and converted into digital data by the A / D converter 23 and image data to be displayed on the display unit 28. The memory 32 has a storage capacity sufficient for storing moving images and sounds over a predetermined time. The memory 32 also serves as an image display memory (video memory). The D / A converter 13 converts the image display data read from the memory 32 into an analog signal and outputs the analog signal to the display unit 28. The display unit 28 includes a display device such as an LCD (Liquid Crystal Display) and displays an image on a screen according to image display data. The digital signal once A / D converted by the A / D converter 23 and stored in the memory 32 is converted into an analog signal by the D / A converter 13 and sequentially transferred to the display unit 28 to display an image. Thus, it is possible to display a through image by the electronic viewfinder function.

  The nonvolatile memory 56 is an electrically erasable and recordable memory. For example, an EEPROM (Electrically Erasable Programmable Read-Only Memory) is used. The nonvolatile memory 56 stores constants, programs and the like for operating the system control unit 50. Here, the program is a program for executing processing of various flowcharts to be described later.

  The system control unit 50 includes a CPU (Central Processing Unit) and controls the entire digital video camera 100. The system control unit 50 performs various processes by executing a program stored in the nonvolatile memory 56. The system memory 52 is a RAM (Random Access Memory). The system memory 52 stores constants and variables for the operation of the system control unit 50, programs read from the nonvolatile memory 56, and the like. In addition, the system control unit 50 performs display control by controlling the memory 32, the D / A converter 13, the display unit 28, and the like. The system timer 53 is a timer unit that measures the time used for various controls.

  The user instructs the system control unit 50 to perform various operations using the mode switch 60, the recording switch 61, and the operation unit 70. The mode switch 60 is an operation member that switches the operation mode of the system control unit 50. For example, the modes are a moving image recording mode, a still image recording mode, a reproduction mode, and the like. As modes included in the moving image recording mode and the still image recording mode, there are an auto shooting mode, an auto scene discrimination mode, a manual mode, various scene modes for setting shooting settings for each shooting scene, a program AE mode, a custom mode, and the like. The user can directly switch to a desired mode by operating the mode switch 60.

  The recording switch 61 is an operation member used by the user when switching between the shooting standby state and the shooting state. When receiving an operation instruction for the recording switch 61, the system control unit 50 starts a series of operations from reading the signal of the imaging unit 22 to writing the moving image data to the recording medium 200.

  The operation unit 70 has function buttons that are used when a user selects and operates various function icons displayed on the display unit 28, for example, and functions are appropriately assigned to each scene. For example, there are an end button, a return button, an image advance button, a jump button, a narrowing button, an attribute change button, and the like. When the user operates the menu button, the display unit 28 displays various settable menu items on the screen. While viewing the menu screen displayed on the display unit 28, the user can make various settings using the up / down / left / right four-way buttons and the SET button.

  The power switch 72 is used by the user to turn on or off the camera. The power control unit 80 includes a battery detection circuit, a DC-DC converter, a switch circuit that switches a block to be energized, and the like. The power supply control unit 80 detects the presence / absence of a battery, the type of battery, and the remaining battery level, controls the DC-DC converter based on the detection result and an instruction from the system control unit 50, and moves to each unit including the recording medium 200. Supply power. The power supply unit 30 includes a primary battery or a secondary battery, an AC adapter, and the like. The recording medium I / F unit 18 is an interface unit with the recording medium 200. The recording medium 200 is a recording medium such as a memory card that records captured image data, and includes a semiconductor memory, a magnetic disk, and the like.

  Next, the operation in this embodiment will be described. In the present embodiment, an input image before dynamic range expansion and an output image after dynamic range expansion can be displayed without switching images. In the present embodiment, a first process for changing the exposure and gamma correction characteristics based on the dynamic range change amount and a second process for calculating the difference value based on the photometric value are executed.

  In this embodiment, the maximum dynamic range that can be set by the imaging apparatus is used as the target value of the dynamic range, but the target dynamic range is not limited to this. The target dynamic range is a D range that can be set within a predetermined range, and may be freely set by the user within the range, or selected by a user from a predetermined value that is held in advance by the imaging apparatus. May be. As described above, when the value set by the user is used as the target value of the dynamic range, the place calculated using “Dmax” (maximum D range) in the following processing is expressed as “target value of dynamic range”. The value may be replaced with the value set as “”.

First, a first process for changing the exposure and gamma correction characteristics based on the change amount of the dynamic range will be described. First, the system control unit 50 calculates a dynamic range change amount. The change amount of the dynamic range is expressed as Dchange, and the current dynamic range is expressed as Dnow. When the maximum dynamic range that can be set by the imaging apparatus is expressed as Dmax, the change amount of the dynamic range is calculated from the following (Equation 1).

Log ₂ () in the formula represents a logarithmic function with 2 as a base. For example, the maximum dynamic range is 800%, and the current dynamic range is 400%. In this case, the change amount of the dynamic range is one stage. Also, assuming that the current dynamic range is 300%, the amount of change in the dynamic range is about 1.52 steps.

  Next, the system control unit 50 changes the exposure and gamma correction characteristics according to the calculated change amount of the dynamic range. For exposure, there is a method of changing the aperture 101, the ND 104, an electronic shutter in the imaging unit 22, an analog gain, and the like. For example, there is a method of changing the shutter speed having a fast response speed by an amount corresponding to the change amount of the dynamic range. When changing with the electronic shutter, if the electronic shutter is 1/60 before the dynamic range is changed and the amount of change of the dynamic range is one step, it is changed to 1/120. Note that the method of changing the exposure is not limited to this, and any method may be used as long as it can be changed before the signal is output from the sensor.

  Simultaneously with such exposure change, the system control unit performs processing for changing gamma correction characteristics set in the gamma correction circuit in the image processing unit 24. The input before the dynamic range change is expressed as X, and the output is displayed as Y. When the dynamic range is changed, the gamma correction characteristic is changed so that the output of “X × Dnow / Dmax” becomes Y. Further, the maximum value of the input before changing the dynamic range is expressed as Xmax, and the maximum value of the output is expressed as Ymax. When the dynamic range is changed, Ymax is set when the input is Xmax × Dnow / Dmax, and Ymax is set for an output corresponding to a larger input. A specific example of the gamma correction characteristics before and after the dynamic range change will be described with reference to FIG.

  FIG. 3 shows an example where Dnow is 400% and Dmax is 800%. The horizontal axis represents input bits of the gamma correction circuit, and the vertical axis represents output bits. A gamma correction characteristic 301 before changing the dynamic range is indicated by a solid line, and a gamma correction characteristic 302 after changing the dynamic range is indicated by a broken line. Since Dnow / Dmax is 1/2 (= 400% / 800%), the output Y with respect to the input X before the dynamic range change is the same as the output Y with respect to the input X / 2 after the dynamic range change. The characteristics are shown. Further, after the dynamic range is changed, the output at Xmax / 2 becomes Ymax, and Ymax is maintained in a range larger than Xmax / 2. The system control unit 50 transmits a setting value based on the gamma correction characteristic determined according to Dnow to the image processing unit 24 and sets it in the gamma correction circuit inside the image processing unit 24. Thereby, the gradation correction characteristic is changed.

  Next, a second process for calculating the difference value based on the photometric value will be described. First, the system control unit 50 acquires a photometric value. The image processing unit 24 calculates a photometric value from the image data before passing through the gamma correction circuit. Any method may be used for obtaining the photometric value, but in the present embodiment, the image data is divided into a plurality of specific sizes, and the respective luminance signals related to the image data in the divided frames. Is calculated as a photometric value. A specific example will be described with reference to FIG.

  FIG. 4 exemplifies a case in which the photometric frame is displayed on the captured image by dividing it into 8 × 8 frames by dividing it into 8 in the vertical direction and 8 in the horizontal direction. 4A illustrates an example image 401 of the subject, and FIG. 4B illustrates the subject image 402 and the photometric frame 403. In this example, the system control unit 50 acquires 64 luminance average values related to image data in each photometric frame. In addition, although the example which uses the average value of a luminance signal as a photometric value was shown, since it is only necessary to know the brightness of each frame, it may be expressed by an integral value, or a value that is an index of brightness such as an EV value is used. May be.

Next, the system control unit 50 determines the maximum photometric value. The system control unit 50 extracts the maximum photometric value from the 64 photometric values and stores it in the memory together with the frame position information. The system control unit 50 calculates a difference value from the current dynamic range (current D range), the maximum dynamic range (maximum D range), the maximum value, and the maximum photometric value. The difference value between the current dynamic range and the maximum photometric value is calculated from the following (Equation 2).

  For example, assuming that the current dynamic range is 400%, the maximum dynamic range is 800%, the maximum value (maximum brightness that can be displayed in the case of 12 bits) is 4095, and the maximum photometric value is 3500, the difference value is about 0.77. It becomes. That is, if the dynamic range is changed by 0.77 steps to a dynamic range of about 680%, the photometric values are within the dynamic range for all frames including the frame of the maximum photometric value. By presenting the calculated difference value to the user, the user can confirm the possibility of a decrease in the S / N ratio for 0.77 steps and the necessity of exposure change. The system control unit 50 performs a process of displaying the difference value on the screen of the display unit 28.

  The system control unit 50 transmits the frame position information and the difference value to the image processing unit 24. The image processing unit 24 creates a photometric frame corresponding to the position of the frame and an image depicting a difference value in the photometric frame, and generates an image superimposed on the image data. The image data is displayed on the display unit 28 via the memory control unit 15 and the D / A converter 13. FIG. 4C shows a display example of the difference value, and is an example when the photometric value of the photometric frame A indicated by reference numeral 404 in FIG. 4B is maximum. Note that the image processing unit 24 creates an image depicting not only the difference value but also the dynamic range of the maximum photometric value obtained based on the difference value, the current dynamic range, and the maximum dynamic range of the imaging device, and image data An image superimposed on the image may be generated.

  The calculated difference value is displayed at a position 406 corresponding to the photometric frame A in the screen 405. The user can grasp that it is necessary to change (increase) the dynamic range of 0.77 levels from the current state in order to keep the subject in the photometric frame A within the range of the dynamic range. At this time, the user can select a difference value using the operation unit. For example, when the user designates the position 406 corresponding to the photometric frame A with a finger on the touch panel attached to the display unit 28, the system control unit 50 accepts a dynamic range change instruction based on the selected difference value, and the user Judge that the dynamic range has been determined. Alternatively, the user can issue an instruction to change and determine the dynamic range corresponding to the difference value by operating an operation button or the like provided on the imaging apparatus.

  The system control unit 50 receives an operation instruction and determines that the user has determined the dynamic range. When the user determines the dynamic range, the image processing unit 24 generates an image in which the image data based on the changed dynamic range and the image data based on the dynamic range before the change are overlapped. The image data is displayed on the display unit 28 via the memory control unit 15 and the D / A converter 13. FIG. 5B shows a display example of superimposed images, and is an example when the photometric value of the photometric frame A indicated by reference numeral 404 in FIG. 4B is maximum.

  FIG. 5 illustrates an image before dynamic range expansion (change) and an image after dynamic range expansion. FIG. 5A shows an image 501 of the subject before the dynamic range expansion, and shows a state where the maximum photometric value in the photometric frame 502 is saturated. A region 503 shows a wave form of the luminance value of the image 501. FIG. 5B shows an image 504 of the subject after dynamic range expansion, and displays an image based on the dynamic range after expansion in an area 505 at a position corresponding to the photometric frame 502. In addition, an image based on the dynamic range before enlargement is displayed in an area outside the photometric frame of the image 504. That is, in FIG. 5B, the image after the dynamic range expansion and the image before the dynamic range expansion are displayed without image switching.

  Note that difference values may be displayed in the photometric frames 502 and 505. Moreover, the display method of a photometry frame and the display place of a numerical value are arbitrary, and are not limited to the example mentioned above. For example, an image based on the expanded dynamic range may be displayed not only in the region 505 corresponding to the maximum photometric value in the screen but also in a region on the high brightness side with respect to the appropriate exposure of the entire screen. Good. Further, the image 504 based on the expanded dynamic range may be configured to be movable not only to the area 505 corresponding to the photometric frame 502 indicating the maximum photometric value of the image 501 but also to an arbitrary position according to the user's designation. .

  In this case, the dynamic range may be automatically changed so that the subject included in the frame moved in accordance with the user's designation is properly displayed in the enlarged dynamic range. In addition, the wave form of the brightness value displayed in the image 504 is configured to display not only the wave form based on the brightness value of the image 504 after enlargement but also the wave form based on the brightness value of the image 501 before enlargement. It may be. At this time, the color and shape of the graph before and after enlargement may be displayed differently. Further, the present invention is not limited to the luminance value wave form, and may be configured to display a luminance value histogram.

  As described above, if the photometric value is within the range of the maximum dynamic range that can be set by the imaging device, even if the photometric value exceeds the current dynamic range, the gradation of the high luminance part is maintained. The relationship between the current dynamic range and the maximum photometric value can be presented to the user. Therefore, it can be used as a guide when the user changes the dynamic range.

  With reference to the flowchart of FIG. 6, processing related to display control in the present embodiment will be described. In the present embodiment, as described above, the maximum dynamic range that can be set by the imaging apparatus is used as the target dynamic range. However, the present invention is not limited to this.

  In step S <b> 101, the user sets a dynamic range to be applied to the imaging apparatus via the operation unit 70. In step S102, the system control unit 50 determines which one of the target dynamic range and the current dynamic range has been set. If the set dynamic range is not the target dynamic range, in step S103, the system control unit 50 sets the current dynamic range as the dynamic range to be applied to the imaging apparatus.

  If the current dynamic range has already been set before step S103 is executed, step S103 is not executed. In step S104, the image processing unit 24 displays an image corrected based on the current dynamic range on the display unit 28 (FIG. 5A). In this embodiment, the wave form of the brightness value of the image is displayed. However, the display is not limited to the wave form as long as the display can correspond to the brightness value and the position in the image.

  On the other hand, when the set dynamic range is the target dynamic range in step S102, in step S105, the system control unit 50 sets the target dynamic range as the dynamic range adapted to the imaging apparatus. Here, changes in exposure are reduced, and changes in the current dynamic range and the target dynamic range are controlled. For this reason, the image based on the target dynamic range displayed on the display unit 28 is substantially the same as the image based on the current dynamic range except for the high luminance portion. In step S106, an image corrected based on the target dynamic range is displayed on the display unit 28 (FIG. 5B).

  Thus, in this embodiment, images before and after the dynamic range change (enlargement) can be displayed simultaneously, and the effect of the dynamic range change can be presented to the user in an easily understandable manner. Further, along with the change of the dynamic range, the output with respect to the incident light is made substantially the same as before the expansion. For this reason, it is possible to acquire a photometric value that has been saturated before the dynamic range is changed, while generally maintaining the gradation of the image of the high luminance portion. Therefore, when images are switched before and after the dynamic range change, it is possible to display a wave form or the like having a different dynamic range without a large change.

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

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

22 Imaging unit 24 Image processing unit 28 Display unit 50 System control unit 100 Digital video camera

Claims (9)

An imaging apparatus comprising imaging means for imaging a subject through an imaging optical system,
Correction means for performing gradation correction on image data acquired by the imaging means;
Dynamic range changing means for changing a current dynamic range related to the image data to a target dynamic range;
Characteristic changing means for changing the exposure and the characteristics of the correcting means according to the changed amount of the dynamic range;
An image pickup apparatus comprising: display control means for displaying image data corresponding to the current dynamic range and image data corresponding to the target dynamic range on a screen.   The display control means displays a frame indicating a specific area on the screen, displays image data corresponding to the target dynamic range in the frame, and corresponds to the current dynamic range outside the frame. The image pickup apparatus according to claim 1, wherein the image data is displayed.   3. The imaging according to claim 2, wherein the display control unit displays the frame in a region where a photometric value acquired from the image data before gradation correction is performed by the correction unit is maximized. apparatus.   The display control means calculates a difference value of a dynamic range with respect to the maximum value of the photometric value using the current dynamic range, the target dynamic range, and the maximum value of the photometric value, and the difference value is calculated on the screen. The imaging device according to claim 3, wherein the imaging device is displayed.   5. The imaging apparatus according to claim 2, wherein the position of the frame can be moved to an arbitrary position in the screen.   6. The imaging according to claim 1, wherein the display control unit displays a histogram or a wave form of a luminance value of image data corresponding to the target dynamic range on the screen. apparatus.   The imaging apparatus according to claim 1, wherein the target dynamic range is a maximum dynamic range that can be set. A method for controlling an imaging apparatus including imaging means for imaging a subject through an imaging optical system,
A correction step in which the correction unit performs gradation correction on the image data acquired by the imaging unit;
A dynamic range changing step of changing a current dynamic range related to the image data to a target dynamic range;
A characteristic changing step of changing the exposure and the characteristics of the correcting means in accordance with the changed amount of the dynamic range;
A control method for an imaging apparatus, comprising: a display control step of displaying image data according to the current dynamic range and image data according to the target dynamic range on a screen.   A program that causes a computer to function as each unit included in the imaging apparatus according to any one of claims 1 to 7.