JP2013016905A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus in which even when images for recording has to be taken continuously with underexposure, an image for monitoring, for example, never become underexposure.SOLUTION: An imaging apparatus 1 is provided with: an imaging part 23 which takes an image of a subject and outputs an image signal; a display part 14 which successively displays a reproduced image based on the image signal outputted from the imaging part 23; a recording part 17 which records on a recording medium 30 an image for recording based on the image signal outputted from the imaging part 23; an exposure control part 11 which sets the imaging part 23 to underexposure; and a correction processing part 11 which performs underexposure correction processing which is different between the reproduced image displayed by the display part 14 and the image for recording recorded by the recording part 17.

Description

  The present invention relates to an imaging apparatus.

  A function of adjusting a highlight portion, a shadow portion, and a halftone so that the gradation of an image represents an appropriate brightness change is known (see Patent Document 1). In order not to saturate the image data in the highlight portion, a still image is captured below the appropriate exposure, and gradation adjustment is performed later on the captured data.

JP 2010-39423 A

  In the conventional technology, the function of capturing a still image under appropriate exposure and adjusting the gradation of the captured data later is applied to the case of continuous image capturing such as pre-capture shooting and movie shooting. That was not noticed. In general, a monitor image is displayed when continuous imaging is performed, but if the gradation adjustment described above is performed later, the monitor display is not in time, and if the monitor display is performed without gradation adjustment, it is dark due to underexposure. It becomes a monitor display image. Here, the pre-capture shooting is intended to acquire a frame image before the release operation time in consideration of the delay of the shutter timing. For example, a still image is captured at a predetermined frame rate before the release operation and temporarily stored in the memory, and when the release operation is performed, the still image captured after the shooting instruction and the still image stored in the memory are stored. The image is stored in a recording medium (or only the selected still image is stored).

  An imaging apparatus according to the present invention includes an imaging unit that captures a subject image and outputs an image signal, a display unit that sequentially displays a reproduction image based on the image signal output from the imaging unit, and an image signal output from the imaging unit A recording unit that records a recorded image on a recording medium, an exposure control unit that sets the imaging unit to underexposure, and an underexposure correction that differs between a reproduced image displayed on the display unit and a recorded image recorded on the recording unit And a correction processing unit that performs processing.

  According to the present invention, it is possible to prevent the monitor image from being underexposed even when it is necessary to continuously capture the recording image underexposed.

It is a block diagram explaining the principal part structure of the electronic camera by one embodiment of this invention. It is a figure explaining the acquisition timing of the image in pre capture photography mode. It is a flowchart explaining the flow of the pre-capture imaging process performed by the main CPU.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram for explaining a main configuration of an electronic camera 1 according to an embodiment of the present invention. The electronic camera 1 is controlled by the main CPU 11.

  The imaging lens 21 forms a subject image on the imaging surface of the image sensor 23. The diaphragm 22 limits the subject light flux that has passed through the imaging lens 21. The image pickup device 23 is configured by, for example, a CMOS image sensor, picks up a subject image on the image pickup surface, and outputs a photoelectric conversion signal to the image pickup circuit 24. The imaging circuit 24 performs analog processing (such as gain control) on the photoelectric conversion signal output from the imaging element 23, and converts the analog image signal into a digital image signal using a built-in A / D conversion circuit.

  The diaphragm drive mechanism 25 controls the aperture diameter of the diaphragm 22 in accordance with an instruction from the main CPU 11. The main CPU 11 inputs a signal output from each block, performs a predetermined calculation, and outputs a control signal based on the calculation result to each block. The image processing circuit 12 is configured as an ASIC, for example, and performs image processing on the digital image signal input from the imaging circuit 24. The image processing includes, for example, contour enhancement, color temperature adjustment (white balance adjustment) processing, gradation correction processing, format conversion processing, and the like.

  The display image creation circuit 13 generates a display signal for reproducing and displaying the captured image on the liquid crystal monitor 14. The liquid crystal monitor 14 includes a liquid crystal panel, and displays an image, an operation menu screen, and the like based on a display signal input from the display image creation circuit 13. The video output circuit 19 generates and outputs a video signal for displaying an image, an operation menu screen, or the like on an external display device based on the display signal input from the display image creation circuit 13.

  The buffer memory 15 temporarily stores data before image processing, after image processing, and during image processing, and also stores an image file before being recorded on the recording medium 30 and an image file read from the recording medium 30. Used to remember. In the present embodiment, it is also used when a pre-capture image acquired by the image sensor 23 at a predetermined frame rate is temporarily stored before a shooting instruction (before the release button is fully pressed). The pre-capture image will be described later.

  The flash memory 16 stores programs executed by the main CPU 11, data necessary for processing performed by the main CPU 11, and the like. The contents of the program and data stored in the flash memory 16 can be added or changed by an instruction from the main CPU 11.

  The card interface (I / F) 17 has a connector (not shown), and a recording medium 30 such as a memory card is connected to the connector. The card interface 17 writes data to the connected recording medium 30 and reads data from the recording medium 30 in accordance with an instruction from the main CPU 11. The recording medium 30 is configured by a memory card incorporating a semiconductor memory, a hard disk drive, or the like.

  The operation member 18 includes various buttons and switches of the electronic camera 1 and outputs an operation signal corresponding to the operation content of each operation member, such as a switching operation of the mode change switch, to the main CPU 11. The half-press switch 18a and the full-press switch 18b each output an ON signal to the main CPU 11 in conjunction with a pressing operation of a release button (not shown). The ON signal (half-press operation signal) from the half-push switch 18a is output when the release button is pushed down to about half of the normal stroke, and the output is released when the half-stroke push-down operation is released. The ON signal (full push operation signal) from the full push switch 18b is output when the release button is pushed down to the normal stroke, and the output is released when the normal stroke push down operation is released. The half-press operation signal instructs the main CPU 11 to start shooting preparation. The full-press operation signal instructs the main CPU 11 to start acquiring a recording image.

<Shooting mode>
In response to the full-pressing operation signal, the electronic camera 1 receives a normal still image shooting mode in which captured images are acquired frame by frame and recorded on the recording medium 30, and when the half-pressing operation signal is received, a predetermined frame rate (for example, Images continuously taken at 10 frames / second (10 fps) are stored in the buffer memory 15 and when the full-press operation signal is received, a predetermined number of images taken before and after the full-press operation signal is received. Pre-capture shooting mode in which frame images are recorded on the recording medium 30 respectively, and moving image shooting in which moving images are acquired and recorded on the recording medium 30 at a predetermined frame rate (for example, 30 frames / second (30 fps)) according to a recording instruction. Mode. Each photographing mode is configured to be switchable according to an operation signal from the operation member 18.

<Playback mode>
The electronic camera 1 in the reproduction mode reproduces and displays on the liquid crystal monitor 19 the images recorded in the respective photographing modes for each frame or for each predetermined number of frames.

  Since this embodiment is characterized by the operation in the pre-capture shooting mode, the following description will be focused on the pre-capture shooting mode. FIG. 2 is a diagram for explaining image acquisition timing in the pre-capture shooting mode.

<Pre-capture shooting>
In FIG. 2, when a half-press operation signal is input at time t0, the main CPU 11 starts a release standby process. In the release standby process, for example, a subject image is captured at a frame rate of 10 frames / second (10 fps), and the acquired image data is sequentially stored in the buffer memory 15.

  A sufficient memory capacity of the buffer memory 15 used for pre-capture photography is secured in advance. When the number of frame images stored in the buffer memory 15 after time t0 reaches a predetermined number (for example, A), the main CPU 11 overwrites and erases the oldest frame images in order. Thereby, the memory capacity of the buffer memory 15 used for pre-capture photography can be limited.

  When the full press operation signal is input at time t1, the main CPU 11 starts the release process. In the release process, (A + B) frame images, which are a combination of A frame images captured before time t 1 and B frame images captured after time t 1, are recorded on the recording medium 30. A black band in FIG. 2 represents a section in which (A + B) frame images that are recorded images are acquired. The hatched band represents a section in which a frame image that has been temporarily stored in the buffer memory 15 but has been overwritten and erased is acquired.

  In the present embodiment, as the recording method, the first recording method for recording all (A + B) frame images on the recording medium 30 and the C selected from the (A + B) frame images according to the selection operation by the user. (C <(A + B)) sheets or the second recording method for recording the C frame images automatically selected by the main CPU 11 on the recording medium 30 can be switched in accordance with an operation signal from the operation member 18. Has been. In this description, it is assumed that the first recording method is selected. The values of A, B, and C can be changed by user operations.

  FIG. 3 is a flowchart for explaining the flow of the pre-capture photographing process executed by the main CPU 11. When the pre-capture shooting mode is set, the main CPU 11 starts the processing illustrated in FIG. 3 when a half-press operation signal is input.

  In step S1 of FIG. 3, the main CPU 11 causes the image sensor 23 to acquire a photometric image and proceeds to step S2. In step S2, the main CPU 11 calculates a proper exposure by a predetermined exposure calculation based on a signal value from a pixel included in a predetermined area (for example, the screen center area) of the photometric image, and proceeds to step S3.

  In step S3, the main CPU 11 calculates the saturation suppression exposure under amount as follows. For example, the shutter time Tv and the aperture value Av are controlled so as to obtain the appropriate exposure so that a photometric image is obtained again, and a luminance histogram is generated based on signal values from all pixels of the obtained photometric image. . Based on this luminance histogram, a pixel region (called a saturation region amount) composed of a highlight portion where the signal value is equal to or greater than a predetermined value, and a pixel region in which the signal value is classified for each predetermined level (region of each brightness) (Referred to as quantity). The main CPU 11 calculates an exposure under amount (referred to as saturation suppression exposure under amount) necessary to suppress the saturation of the saturation region amount, and proceeds to step S4.

  In step S4, the main CPU 11 starts image accumulation. That is, the shutter time Tv and the aperture value Av are controlled so as to obtain the saturation suppression exposure under amount, and the image sensor 23 starts the release standby process described above. Thus, a subject image is captured at a frame rate of 10 frames / second (10 fps), and the acquired image data is sequentially stored in the buffer memory 15. Since all the acquired images are under the proper exposure, the pixel signal value is not saturated even when a high-luminance subject exists. In this embodiment, the shutter time Tv and the aperture value Av are maintained until the image storage in the buffer memory 15 is completed.

  In step S5, the main CPU 11 sends an instruction to the image processing circuit 12 to perform a gain-up process on the display image. In this embodiment, an image acquired during the release standby is sequentially displayed on the liquid crystal monitor 14 as a monitor image. Since the acquired image is underexposed, the display screen will be dark and difficult to see if played back as it is. Therefore, the main CPU 11 instructs to increase the gain so as to compensate for the underexposure described above (to reproduce and display the monitor image on the liquid crystal monitor 14 with the same brightness as when the image is acquired with appropriate exposure).

  For example, the image processing circuit 12 increases the adjustment gain for adjusting the white balance gain uniformly for each of the RGB colors so as to brighten the display image while maintaining the set white balance. Increase the gain. In step S <b> 6, the main CPU 11 sends an instruction to the display image creation circuit 13 to cause the liquid crystal monitor 14 to sequentially reproduce and display the monitor image (through image) after the gain increase.

  In step S7, the main CPU 11 determines whether or not the release button has been fully pressed. When the full-press operation signal is input, the main CPU 11 makes a positive determination in step S7 and proceeds to step S8. When the full-press operation signal is not input, the main CPU 11 makes a negative determination in step S7 and returns to step S5. When returning to step S5, image storage in the buffer memory 15 is repeated while sequentially overwriting and erasing old frame images.

  In step S <b> 8, the main CPU 11 sends an instruction to the image processing circuit 12 to start gradation correction processing for the image group stored in the buffer memory 15. Since the acquired image is underexposed, the gradation is inappropriate. Therefore, the main CPU 11 compensates for the above-described underexposure (obtains the same brightness as when the image is acquired with appropriate exposure), and highlights and shadows so that the gradation of the image represents an appropriate brightness change. Instructs gradation correction to adjust the color and halftone respectively.

  For example, for each stored image, the image processing circuit 12 associates the brightest pixel signal value with the maximum value of the dynamic range and associates the darkest pixel signal value with the minimum value of the dynamic range. The pixel signal values constituting the image are expanded within the dynamic range, so that gradation correction is performed so that the gradation of the image represents an appropriate brightness change.

  In step S <b> 9, the main CPU 11 continues to store images in the buffer memory 15 even after the full press operation signal is input. Accumulating an image after inputting a full-press operation signal is called post-capture. The number of frames to be accumulated is the B number described with reference to FIG. In step S10, the main CPU 11 sends an instruction to the image processing circuit 12, and continues the gain-up process for the display image similar to step S5. In step S11, the main CPU 11 sends an instruction to the display image creation circuit 13 to cause the liquid crystal monitor 14 to sequentially reproduce and display the monitor image after the gain increase.

  In step S <b> 12, the main CPU 11 determines whether or not the gradation correction processing for all accumulated images stored in the buffer memory 15 has been completed. When the image processing circuit 12 completes the gradation correction processing for all accumulated images, the main CPU 11 makes a positive determination in step S12 and proceeds to step S13. When the image processing circuit 12 does not complete the gradation correction processing In step S12, a negative determination is made and the determination process is repeated. When the determination process is repeated, the image processing circuit 12 is caused to continue the gradation correction process.

  In step S13, the main CPU 11 sends an instruction to the card interface 17 to record the image data after the above-described (A + B) gradation correction processing stored in the buffer memory 15 on the recording medium 30 and perform the processing in step S3. finish.

According to the embodiment described above, the following operational effects can be obtained.
(1) The electronic camera 1 includes an image sensor 23 that captures a subject image and outputs an image signal, a liquid crystal monitor 14 that sequentially displays a monitor display image based on the image signal output from the image sensor 23, and the image sensor 23. The card interface 17 that records a recording image based on the image signal output from the recording medium 30, the main CPU 11 that sets the image sensor 23 to be underexposed, the monitor image displayed on the liquid crystal monitor 14, and the card interface 17. Since the main CPU 11 that performs under-exposure correction processing that differs depending on the recorded image to be recorded is provided, even when the recorded image needs to be imaged under-exposed, for example, the monitor image does not become under-exposed. Can be.

(2) In the electronic camera 1 of the above (1), the main CPU 11 performs a gain-up process that compensates for the underexposure on the monitor image, and performs a gradation correction process that compensates for the underexposure on the recorded image. Therefore, the monitor image can be displayed easily and brightly, and for the recorded image, for example, gradation correction can be performed so that the gradation of the image represents an appropriate brightness change.

(3) In the electronic camera 1 of the above (2), the main CPU 11 is configured to perform the gain-up process by controlling the white balance gain, so that an existing gain control circuit (process) is not added. The monitor image can be displayed brightly using the gain control circuit (processing). Further, since white balance gain adjustment is often performed before other processing (noise reduction or the like), the same processing as the conventional processing can be applied to other processing for the monitor display image.

(4) In the electronic camera 1 of the above (3), the main CPU 11 is configured to start the gain-up process for the monitor image before the shooting instruction, and thus is suitable for observing the monitor image before the shooting instruction. It is.

(5) The electronic camera 1 of (4) above includes a buffer memory 15 that accumulates image signals captured every predetermined time, and the main CPU 11 captures images that have been captured and stored in the buffer memory 15 before the shooting instruction. Since the tone correction processing is started after the shooting instruction for the signal, the tone correction processing can be performed after the shooting instruction separately from the monitor image.

(6) In the electronic camera 1 of the above (5), the main CPU 11 is configured to perform gain-up processing with the same gain on all the monitor images, so that the brightness of the monitor image changes by one frame. And a monitor image with good connection before and after the frame can be obtained.

(Modification 1)
In the above description, an example has been described in which the appropriate exposure is calculated based on the photometric image acquired by the image sensor 23 (step S1) and the saturation suppression under amount is calculated (step S3). Instead of this, a photometric sensor may be provided separately from the image sensor 23, and a proper exposure and saturation suppression under amount may be obtained using the photometric sensor.

(Modification 2)
In the above-described embodiment, the example in which the shutter time Tv and the aperture value Av at the start of image storage (at the start of the release standby process) are maintained until the image storage in the buffer memory 15 ends. Instead, the brightness of the image acquired after the start of image accumulation may be detected, and the shutter time Tv and the aperture value Av during image accumulation may be changed according to the detected brightness. The main CPU 11 of Modification 2 sends an instruction to the display image creation circuit 13 to reproduce and display the monitor image on the liquid crystal monitor 14 when the saturation suppression exposure under amount changes compared to when the image accumulation starts. By changing the gain increase amount with respect to the display signal, the brightness of the display screen is maintained substantially constant.

  According to the second modification, the brightness of the monitor image to be reproduced and displayed is appropriately maintained and can be easily observed.

(Modification 3)
In the above description, the processing performed in the pre-capture shooting mode has been described as an example. However, the present invention may also be applied in the moving image shooting mode. That is, the gain is increased so that the monitor image is reproduced and displayed on the liquid crystal monitor 14 with the same brightness as when the moving image is acquired with proper exposure while the moving image is acquired with underexposure than the appropriate exposure. Specifically, a gain-up process for compensating for underexposure is performed by uniformly increasing the adjustment gain for adjusting the white balance gain for each color of RGB.

(Modification 4)
Further, the present invention may be applied during continuous shooting. That is, the gain is increased so that the monitor image is reproduced and displayed on the liquid crystal monitor 14 with the same brightness as when the continuous shot image is acquired with the proper exposure while the continuous shot image is acquired with the underexposure from the appropriate exposure. Also in the case of the modified example 4, the gain increase process for compensating for the underexposure is performed by uniformly increasing the adjustment gain for adjusting the white balance gain for each of the RGB colors.

(Modification 5)
Although an example has been described in which the gain-up process to compensate for underexposure is performed by increasing the adjustment gain for adjusting the white balance gain, the gain is changed by, for example, increasing the gain at the time of gradation conversion. You may comprise. The image processing circuit 12 in the modification 5 compensates for underexposure when the monitor image is reproduced and displayed on the liquid crystal monitor 14 (to obtain the same brightness as when the image is acquired with appropriate exposure). Is performed by controlling the gain at the time of gradation conversion to compensate for the underexposure of the stored image stored in the buffer memory 15 (to obtain the same brightness as when the image is acquired with proper exposure). Then, the gradation part, the shadow part, and the halftone are respectively corrected for gradation by controlling the gradation conversion gain so that the gradation of the image represents an appropriate brightness change.

(Modification 6)
In the above description, the present invention is applied to a lens-integrated digital camera. However, the present invention is not limited to this. For example, the present invention can be applied to a digital camera having a configuration in which an interchangeable lens is attached to a camera body.

  The above description is merely an example, and is not limited to the configuration of the above embodiment. Moreover, you may combine the structure of each modification suitably with the said embodiment.

1 ... Electronic camera 11 ... Main CPU
DESCRIPTION OF SYMBOLS 12 ... Image processing circuit 13 ... Display image creation circuit 14 ... Liquid crystal monitor 15 ... Buffer memory 17 ... Card interface 22 ... Diaphragm 23 ... Imaging element 24 ... Imaging circuit 25 ... Diaphragm drive mechanism 30 ... Recording medium

Claims (6)

An imaging unit that captures a subject image and outputs an image signal;
A display unit for sequentially displaying reproduced images based on the image signals output from the imaging unit;
A recording unit that records a recording image based on the image signal output from the imaging unit on a recording medium;
An exposure control unit for setting the imaging unit to underexposure;
A correction processing unit that performs underexposure correction processing different between a reproduced image displayed on the display unit and a recorded image recorded on the recording unit;
An imaging apparatus comprising: The imaging device according to claim 1,
The imaging apparatus, wherein the correction processing unit performs a gain-up process for compensating for the underexposure on the reproduced image, and performs a gradation correction process for compensating for the underexposure on the recorded image. The imaging device according to claim 2,
The imaging apparatus according to claim 1, wherein the correction processing unit performs a gain-up process by controlling a white balance gain. The imaging device according to claim 3.
The image pickup apparatus, wherein the correction processing unit starts the gain-up process for the reproduced image before a shooting instruction. The imaging apparatus according to claim 4,
An image storage unit that stores image signals captured every predetermined time;
The imaging apparatus, wherein the correction processing unit starts the gradation correction processing after the shooting instruction is performed on an image signal that is captured before the shooting instruction and is stored in the storage unit. The imaging apparatus according to claim 5,
The image pickup apparatus, wherein the correction processing unit performs the gain-up process with the same gain on all of the reproduced images.

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