JP5418553B2 - Imaging apparatus and imaging method using the same - Google Patents

Description

  The present invention relates to an imaging device and a photographing method using the same, and more particularly to an imaging device that performs automatic focus detection according to the luminance of a subject and a photographing method using the same.

An electronic imaging device such as a digital still camera generally includes an autofocus (hereinafter referred to as “AF”) device that automatically focuses on a subject.
Conventionally, so-called hill-climbing AF control is known as a control method of the AF device (for example, see Patent Document 1 below).
This hill-climbing AF control method will be briefly described.
In this method, an integral value of a luminance difference between high frequency components or adjacent pixels is obtained from a video signal obtained for each field or frame, and the integrated value of the luminance difference is used as an AF evaluation value indicating the degree of focus. . In this case, the AF evaluation value increases when the subject is in focus because the edge portion of the subject is clear, and the AF evaluation value decreases when the subject is out of focus. When the AF operation is executed, the AF evaluation values are sequentially acquired while moving the lens, and the lens is stopped at the point where the AF evaluation value is maximized, that is, at the peak position as a focal point. .

  By the way, since an apparatus that captures a still image, such as a digital still camera, generally requires strict focusing as compared with an apparatus that captures moving images such as a video camera, an AF operation is performed every time a shooting operation is performed. Or the focusing operation is always repeated in the recording mode.

  However, when the luminance is low or when shooting a low-contrast subject, the peak of the AF evaluation value is low, or noise is generated in the AF evaluation value data due to low contrast. A plurality of peak peaks may appear, and there is a problem that a good in-focus state cannot be obtained.

In response to such a conventional problem, luminance data corresponding to digital image data is output as an automatic exposure (hereinafter referred to as “AE”) evaluation value, and when the AE evaluation value is smaller than a predetermined value, that is, the subject is dark. In this case, a method has been proposed in which AF control is performed by increasing the area from which the AF evaluation value is acquired (see, for example, Patent Document 2 below).
However, in the method disclosed in Patent Document 2, if the area for acquiring the AF evaluation value is inadvertently enlarged, the shooting background is affected, and for example, without focusing on the subject intended by the photographer, for example, There was a problem that it sometimes focused on the background.

There is also a proposal for a method that enables accurate focusing regardless of the luminance of the image by creating a histogram from the luminance signal of the image, setting a gamma table based on this histogram, and performing gamma correction. (For example, refer to Patent Document 3 below.)
However, in such a method, it is necessary to prepare a plurality of gamma tables suitable for the environment, and the processing operation becomes complicated. Therefore, there is an increasing demand for a method that enables accurate focusing with fewer gamma tables. I came.
In addition, it is known that the gamma correction increases the contrast, but the subject is darkened at low brightness, so it is more desirable to use a method that does not perform gamma correction at low brightness. It was.

Japanese Examined Patent Publication No. 39-5265 Japanese Patent Laid-Open No. 2003-230039 JP 2003-289467 A

  Therefore, in the present invention, in view of the problems of the conventional technology as described above, the AF evaluation value capture timing is changed, particularly when the luminance is low, in accordance with the shooting environment. The present invention proposes an imaging apparatus capable of performing AF widely from high luminance to low luminance, and an imaging method using the same, with a variable filter for acquisition.

In order to solve the above-described problem, an imaging apparatus according to claim 1 is an imaging apparatus that obtains image data by receiving an image of a subject by light from a subject that has passed through a photographing lens, and obtaining image data. An acquisition timing setting means for setting a timing for acquiring an AF evaluation value from image data; and a filter used for acquiring the AF evaluation value from the image data, wherein an arbitrary frequency component of the image data is transmitted. Filter selection means for selecting a filter, automatic focus detection means for detecting a focus based on the AF evaluation value acquired from image data obtained by moving the focus lens to the lens position, and photometry for measuring subject luminance And the acquisition timing setting means is configured such that the subject brightness obtained by the photometry means has a predetermined threshold value. If it is above, the post-gamma correction is set as the timing for obtaining the AF evaluation value, and if the subject brightness obtained by the photometry means is less than a predetermined threshold, the pre-gamma correction is obtained as the timing for obtaining the AF evaluation value. And after the digital clamp, the filter selection means is lower than the filter selected when the post-gamma correction is set as the filter when the acquisition timing setting means is set after the digital clamp. And a detection result judging means for judging whether or not focus detection is possible using a threshold as a result of performing focus detection by the automatic focus detection means and selecting a filter that transmits only the image data. Thus, the threshold value used in the detection result judging means is changed.

According to a second aspect of the present invention, in the imaging apparatus according to the first aspect, when the acquisition timing setting means is set after digital clamping, the threshold used by the detection result determination means is lowered.

The imaging method according to claim 3 , wherein the imaging device obtains image data by receiving a subject image by light from the subject that has passed through the photographing lens, and obtains an AF evaluation value from the image data. An acquisition timing setting step, a filter used for acquiring the AF evaluation value from the image data, a filter selection step for selecting a filter that transmits an arbitrary frequency component of the image data, and a lens An automatic focus detection step for detecting a focus based on the AF evaluation value acquired from image data obtained by moving a focus lens to a position, and a photometry step for measuring subject luminance, and the acquisition timing setting The process determines the AF evaluation value when the subject brightness obtained in the photometry process is equal to or greater than a predetermined threshold. After the gamma correction is set as the timing to perform, and when the subject brightness obtained in the photometry step is less than a predetermined threshold, the timing for obtaining the AF evaluation value is set before the gamma correction and after the digital clamp, When the acquisition timing setting step is set after digital clamping , the filter selection step selects a filter that transmits only a lower band than the filter selected when setting after gamma correction as the filter , and As a result of performing focus detection in the automatic focus detection step, the threshold value used in the detection result determination step according to image data output has a detection result determination step for determining whether or not focus detection is possible using a threshold value. To change.

According to a fourth aspect of the present invention, in the imaging method according to the third aspect , when the acquisition timing setting step is set after digital clamping, the threshold used in the detection result determination step is lowered.

  According to the present invention, it is possible to execute the autofocus function in a wide luminance range from high luminance to low luminance.

  Hereinafter, specific embodiments of an image pickup apparatus and a photographing method using the same according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following examples.

FIG. 1 is a schematic diagram of a digital still camera as an example of an imaging apparatus of the present invention.
1A is a plan view of the digital camera as viewed from above, FIG. 1B is a plan view as viewed from the front, and FIG. 1C is a plan view as viewed from the back.
FIG. 2 is a block diagram illustrating an internal system configuration example of the imaging apparatus according to the present invention.

As shown in FIG. 1A, a release shutter SW1, a mode dial SW2, and a sub liquid crystal display (hereinafter referred to as “LCD”) 1 are arranged on the upper surface side of the digital camera.
As shown in FIG. 1B, on the front side of the digital camera, a lens barrel unit 7 including a taking lens, an optical finder 4, a strobe light emitting unit 3, a distance measuring unit 5, a remote control light receiving unit 6, a memory card loading chamber. A battery loading chamber lid 2 is disposed.
As shown in FIG. 1C, on the back side of the digital camera, there are a power switch 13, an LCD monitor 10, an AF LED 8, a strobe LED 9, an optical viewfinder 4, a wide angle direction zoom switch SW3, a telephoto direction zoom switch SW4, a self-portion. Timer setting and release switch SW5, menu switch SW6, upward movement and strobe set switch SW7, rightward movement switch SW8, display switch SW9, downward movement and macro switch SW10, leftward movement and image confirmation switch SW11, OK switch SW12, quick access A switch SW13 is arranged.

Next, an internal system configuration of the digital camera will be described.
As shown in FIG. 2, each part of the digital still camera is configured to be controlled by a digital still camera processor 104 (hereinafter simply referred to as “processor 104”).
The processor 104 includes a CCD1 signal processing block (104-1), a CCD2 signal processing block (104-2), a CPU block (104-3), a local SRAM (104-4), a USB block (104-5), and a serial block. (104-6), JPEG / CODEC block (104-7), RESIZE block (104-8), TV signal display block (104-9), and memory card controller block (104-10). Are connected to each other by a bus line.
An SDRAM 103 for storing RAW-RGB image data, YUV image data, and JPEG image data is disposed outside the processor 104, and is connected to the processor 104 by a bus line.
Outside the processor 104, a RAM 107, a built-in memory 120, and a ROM 108 storing a control program are arranged, and are connected to the processor 104 by a bus line.

The lens barrel unit 7 includes a zoom optical system (7-1) having a zoom lens (7-1a), a focus optical system (7-2) having a focus lens (7-2a), and a diaphragm (7-3a). It has a mechanical shutter unit (7-4) having a diaphragm unit (7-3) and a mechanism shutter (7-4a).
The zoom optical system (7-1), the focus optical system (7-2), the aperture unit (7-3), and the mechanical shutter unit (7-4) are respectively a zoom motor (7-1b) and a focus motor (7- 2b), a diaphragm motor (7-3b), and a mechanical shutter motor (7-4b). These motors are controlled by a CPU block (104-3) of the processor 104. The operation is controlled by (7-5).

The lens barrel unit 7 has a photographic lens that connects a subject image to a CCD 101 that is an image sensor. The CCD 101 converts the subject image into an image signal and inputs the image signal to the F / E-IC 102.
As is well known, the F / E-IC 102 includes a CDS (102-1), an ADC (102-2), and an A / D conversion unit (102-3), and performs predetermined processing on each of the image signals. The digital signal is converted into a digital signal and input to the CCD1 signal processing block (104-1) of the processor 104. These signal processing operations are controlled via the TG (102-4) by the VD / HD signal output from the CCD1 signal processing block (104-1) of the processor 104.

The CPU block (104-3) of the processor 104 controls the sound recording operation by the sound recording circuit (115-1). The voice recording circuit (115-1) records an amplified signal of the voice signal converted by the microphone (115-3) by the microphone amplifier (115-2) according to the command.
The CPU block (104-3) also controls the operation of the sound reproduction circuit (116-1). The audio reproduction circuit (116-1) reproduces an audio signal recorded in an appropriate memory according to a command, inputs the audio signal to the audio amplifier (116-2), and outputs the audio from the speaker (116-3). It is configured.
The CPU block (104-3) also emits illumination light from the strobe light emitting unit 3 by controlling the operation of the strobe circuit 114.
The CPU block (104-3) also controls the operation of the distance measuring unit 5.

The CPU block (104-3) is connected to a sub CPU 109 arranged outside the processor 104, and the sub CPU 109 controls display by the sub LCD 1 via the LCD driver 111.
The sub CPU 109 is further connected to an AF LED 8, a strobe LED 9, a remote control light receiving unit 6, an operation key unit including the switches SW1 to SW13, and a buzzer 113.

The USB block (104-5) is connected to a USB connector 122, and the serial block (104-6) is connected to an RS-232C connector (123-2) via a serial driver circuit (123-1). ing.
The TV display block (104-9) is connected to the LCD monitor 10 via the LCD driver 117, and is connected to the video jack 119 via the video amplifier 118. The memory card controller block (104-10) is connected to the card contact of the memory card slot 121.

Next, the operation of the digital still camera having the above-described configuration will be described. First, an overall operation outline of the digital still camera will be described.
When the mode dial SW2 shown in FIG. 1 is set to the recording mode, the camera is activated in the recording mode. The mode dial SW2 is set by the CPU detecting that the mode switch included in the operation unit in FIG. 2 is in the recording mode ON, and controlling the motor driver (7-5) to control the lens barrel unit 7. Move to a position where you can shoot. Further, the power is turned on to the respective parts such as the CCD 101, the F / E-IC 102, the LCD display 10 and the like to start the operation. When the power of each part is turned on, the operation in the finder mode is started.

In the finder mode, the light incident on the image sensor (CCD101) through the lens is converted into an electrical signal and converted into analog signals R, G, B as a CDS circuit (102-1) and an A / D converter (102-3). Sent to.
The predetermined signal converted into the digital signal by the A / D converter (102-3) is converted into a YUV signal by the YUV conversion unit in the digital signal processing IC (SDRAM 103), and written into the frame memory by the memory controller. .
This YUV signal is read out by the memory controller and sent to the TV or LCD monitor 10 via the TV signal display block (104-9) for display.
This process is performed at 1/30 second intervals, and a finder mode display updated every 1/30 seconds is obtained.

Also, an AF evaluation value indicating the degree of focusing on the screen and an AE evaluation value indicating the exposure state are calculated from the digital RGB signals captured in the CCD-I / F block of the digital signal processing IC (SDRAM 103).
The AF evaluation value data is detected by the CCD1 signal processing block (104-1) in the digital still camera processor 104 using a certain area section of the CCD 101 as feature data.
The AF evaluation value is generated in the CCD1 signal processing block (104-1).
In the CCD 1 signal processing block (104-1), first, data from the F / EIC is digitally clamped, white balance, and gamma corrected.
The AF evaluation value is detected either after digital clamping or after gamma correction (FIG. 3).
In this camera, means for setting either after digital clamping or after gamma correction in FIG. 3 is provided so that the setting can be changed according to the situation.

Here, the gamma correction is to perform color correction in order to obtain a display close to natural, and to perform a process for bringing the ratio of the change in the voltage conversion value to the change in the brightness of the image close to 1.
By performing this gamma correction, the contrast of the subject tends to increase. Therefore, by default, it is set after gamma correction.
Also, the AF evaluation value is created based on the output integrated value of the frequency component extraction filter and the integrated value of the luminance difference between adjacent pixels when it is detected.

As shown in FIG. 4, there are two types of frequency component extraction filters, a first filter 41 for high frequency and a second filter 42 for low frequency, and an output integrated value of a filter obtained by multiplying these filters. Can also be created (third filter 43 in FIG. 4).
The high frequency first filter 41 and the low frequency second filter 42 are filters in an image processing field.
The first filter 41 for high frequency is a filter (high pass filter) that emphasizes the luminance difference between pixels. The first filter 41 for high frequency is configured to apply coefficients of “−1”, “2”, and “−1” to the luminance data of adjacent pixels.
The low-frequency second filter 42 is a filter (low-pass filter) that removes a noise component by making the outside correlation close by gently approaching. The second filter 42 multiplies the luminance data of adjacent pixels by coefficients of “1”, “2”, and “1”, respectively.
The third filter 43 is a filter that removes noise from the luminance data emphasized by the high frequency filter 41 by the low frequency filter 42. Usually, a filter such as the first filter 41 for high frequency or the third filter 43 is used as a filter for outputting AF evaluation value data.

  When the integral value is close to the adjacent pixel, the high frequency component becomes the highest because the edge portion of the subject is clear. By utilizing this, during the focus detection operation by AF, the AF evaluation value at each focus lens position is acquired, and the point (peak position) at which the maximum is obtained is detected. It is also necessary to take into account that there are multiple points that can be maximized. If there are a plurality of local maximum points, the magnitude of the evaluation value at the peak position and the degree of descending or rising from the surrounding evaluation values are judged, and AF is executed with the most reliable point as the in-focus position.

In the AE evaluation value, the digital RGB signal is divided into several areas and the luminance data in the area is used.
In this case, for pixels in each area, those exceeding a predetermined threshold are set as target pixels, and their luminance values are added and multiplied by the number of target pixels. An appropriate exposure amount is calculated based on the luminance distribution of each area, and correction is performed for capturing the next frame.

When the button of the release shutter SW1 in FIG. 1 is pressed, a still image shooting start signal is taken into the processor 104 via the F / E-IC 102 from the CCD 101 shown in FIG.
Subsequently, the microcomputer (CPU block 104-3) drives the drive motor (7-2b) of the focus lens (7-2a) via the motor driver (7-5) in synchronization with the frame rate, thereby climbing the mountain. Execute AF.
When the in-focus range is the entire region from infinity to close, the focus lens moves from close to infinity, or from infinity to close, and each frame (= focus position) created by the digital signal processing IC. The microcomputer reads out the AF evaluation value at).
The focus lens (7-2a) is moved to the in-focus position with the point at which the AF evaluation value at each focus position is maximized as the in-focus position.

After the AF as described above is completed, the analog RGB signal extracted from the CCD 101 is converted into a digital RGB signal and stored in the SDRAM 109 as a frame memory via the digital signal processing IC.
The digital RGB signal is read again by the digital signal processing circuit, converted into YUV data, and written back to the frame memory.
At the time of capturing a still image, YUV converted image data is sent to a JPEG CODEC block (104-7) as an image compression / decompression circuit in the digital signal processing IC.
The YUV data sent to the image compression / decompression circuit is compressed and written back to the frame memory.
The compressed data in the frame memory is read out through a digital signal processing circuit and stored in a data storage memory, for example, a memory card.

Examples of the imaging apparatus according to the present invention will be described with reference to a flowchart, with reference to the flowchart.
In each illustrated flowchart, the operation steps are displayed as (5-1), (5-2).

[Example 1]
FIG. 5 shows a specific operation flowchart of the imaging apparatus.
The image pickup apparatus in this example obtains image data by receiving a subject image of light from a subject that has passed through a lens by an image sensor, and selects a filter that transmits an arbitrary frequency component of the subject image. And an automatic focus detection means for detecting a focus from image data obtained by moving the focus lens to the lens position, and an acquisition timing setting means for setting the timing for acquiring the image data. The capture timing setting means is used according to conditions, and the filter of the filter selection means is changed according to the capture timing set by the capture timing setting means. Yes.

  First, the release shutter button SW1 shown in FIG. 1 is operated to detect the shooting mode immediately before the release shutter button is pressed (5-1). As the shooting mode, two modes of (a) normal shooting mode and (b) dark shooting mode can be detected, and can be switched as appropriate by the mode dial SW2 shown in FIG. Yes.

Next, the setting of the AF evaluation value capture timing is determined according to the detected shooting mode (5-2).
The evaluation value fetch timing setting process is shown in FIG.
If the shooting mode is the normal shooting mode (a) (6-1), the evaluation value fetch timing is set to (6-2) after gamma correction, and the process proceeds to the next process.
When the shooting mode is the dark shooting mode (b) above, it is often used in the dark, so if gamma correction is performed, the subject may also sink in the dark. After the digital clamp, the subject is prevented from sinking (6-3), and the process proceeds to the next process.

Subsequently, the filter selection process shown in FIG. 5 is performed (5-3).
A flowchart relating to this processing is shown in FIG.
When the evaluation value fetch timing is after the default gamma correction (7-1), the first filter 41 for high frequency is selected for the filter (7-2). In the case of after the digital clamping, the third filter 43 obtained by multiplying the first filter 41 for high frequency and the second filter 42 for low frequency is selected as the filter (7-3). .

  In this way, particularly in the dark shooting mode, the AF evaluation value is acquired after digital clamping and the filter is set to the second filter 2 for low frequency so that black sink due to gamma correction does not occur. It is possible to increase AF accuracy even with luminance.

Subsequently, as shown in FIG. 5, the focus lens (7-2a) is moved to the focus start position (5-4), and an AF evaluation value is acquired (5-5).
After obtaining the AF evaluation value, the peak determination process (5-6) determines whether the evaluation value is a peak, that is, “peak detection NG?” (5-7). As for the threshold used for the peak determination process, when a peak is detected, the process moves to the peak position determination process (5-10). If no peak is detected, the process proceeds to a step (5-8) for determining whether or not the scan has been completed to the final end of the focus position. If the scan has not been completed, the focus position is sequentially moved (5-9). ), Returning to the evaluation value acquisition processing step (5-5), the same processing is repeated.
When the scan is completed, the process moves to the peak position determination process (5-10).

Next, a more reliable peak position is determined from the scanned AF evaluation value, the focus lens is moved to the determined peak position, and the operation ends.
If no reliable peak position is found, the focus lens is moved to a predetermined focus position, for example, a focus position corresponding to about 2.5 m, as AF scan NG, and the operation ends (5-10). ).

  In the above-described example, a simple three-factor high-frequency filter, a low-frequency filter, and a filter obtained by multiplying them are used. It is preferable to use a filter such as 7 coefficients.

  Also, considering that the output of the peak of the AF evaluation value peak differs depending on the setting state of the evaluation value capture timing and the filter selection method, the threshold value used for peak determination in the peak determination process (5-6) It is preferable that the above can be changed according to the state of image data output.

In the above-described embodiments, the AF evaluation value capture timing is selected in two shooting modes. However, the present invention is not limited to the above-described example.
For example, with respect to the macro mode, when shooting a macro subject, the camera itself may become a shadow, which may result in a low brightness state on the screen. In consideration of such a case, in macro mode, it is desirable to prevent the darkening of the subject from occurring after the digital clamping of the AF evaluation value capturing timing.

[Example 2]
FIG. 8 shows an operation flowchart of the second embodiment in the imaging apparatus of the present invention.
The imaging apparatus in this example includes a filter selection unit that selects a filter that transmits an arbitrary frequency component of a subject image, and an automatic focus detection unit that detects a focus from image data obtained by moving the focus lens to a lens position. Suppose that it is provided with a capture timing setting means for setting the timing for capturing the image data and a photometric means for measuring the subject brightness, and the capture timing setting means is used according to the photometric result obtained by the photometric means. It is assumed that the filter of the filter selection unit is changed according to the capture timing set by the capture timing setting unit.

First, the release shutter button SW1 shown in FIG. 1 is operated, and the luminance of the subject is determined from the photometric result immediately before the release shutter button is pressed (8-1).
The subject brightness can be measured from the output of the CCD 101. In accordance with the luminance (LV value) obtained from the measurement result, the setting of the AF evaluation value capture timing is determined (8-2).

FIG. 9 shows the evaluation value fetch timing setting process.
If the subject brightness is LV6 or higher (9-1), the evaluation value capture timing is set to after gamma correction (9-2), and the process proceeds to the next process.
If it is less than LV6, the evaluation value fetch timing is set after digital clamping (9-3), and the process proceeds to the next process.
As a result, the darkening of the subject can be prevented from occurring in the dark case of less than LV6.
The above-described luminance threshold value (LV value) set in each determination step is limited to the case of the second embodiment, and generally depends on the lens aperture value (F value), the performance of the CCD 101, and the like. Make changes as appropriate.

Subsequently, as shown in FIG. 8, filter selection processing is performed (8-3).
A flowchart regarding this processing is as shown in FIG.
That is, when the AF evaluation value capturing timing is after the default gamma correction (7-1), the first filter 41 for high frequency is selected for the filter (7-2). In the case of after the digital clamping, the third filter 43 obtained by multiplying the first filter 41 for high frequency and the second filter 42 for low frequency is selected as the filter (7-3). .
Thus, in the case of a low-luminance environment such as that after digital clamping, the AF accuracy can be increased by setting the filter to the low frequency side.

Subsequently, as shown in FIG. 8, the focus lens (7-2a) is moved to the focus start position (8-4), and an AF evaluation value is acquired (8-5).
After obtaining the AF evaluation value, whether or not the evaluation value is a peak is detected by peak determination processing (8-6). That is, “peak detection NG?” Is judged (8-7). If a peak is detected, the process moves to a peak position determination process (8-10). If no peak is detected, the process proceeds to a step (8-7) for determining whether or not the scan has been completed up to the end of the focus position. If the scan has not been completed, the focus position is sequentially moved (8-9). Returning to the evaluation value acquisition processing step (8-5), the same processing is repeated.
When the scan is completed, the process moves to the peak position determination process (8-10).

Next, a more reliable peak position is determined from the scanned AF evaluation value, the focus lens is moved to the determined peak position, and the operation ends.
If no reliable peak position is found, the focus lens is moved to a predetermined focus position, for example, a focus position corresponding to about 2.5 m as AF scan NG, and the operation is terminated (8-10). .

  In the above-described example, a simple three-factor high-frequency filter, a low-frequency filter, and a filter obtained by multiplying them are used. It is preferable to use a filter such as 7 coefficients.

In the second embodiment described above, the filter is variable according to the evaluation value fetch timing. However, it is more preferable that the filter can be separately changed according to the subject according to the luminance.
Considering that the output of the peak of the AF evaluation value peak varies depending on the setting state of the evaluation value capture timing and the filter selection, the threshold value used for the peak determination in the peak determination processing is the image data output It is desirable to make it variable according to the state.

  As in the first and second embodiments described above, in order to correspond to various subject luminances, the evaluation value capture timing is set after digital clamping when the luminance is low or when photographing a dark subject such as a dark photographing mode. By doing so, it is possible to cope with subjects having various luminances by supplementing the output at that time by selecting a filter. Example 1 is a reference example.

(A) The top view which looked at the digital camera from upper direction is shown. (B) The top view which looked at the digital camera from the front is shown. (C) The top view which looked at the digital camera from the back is shown. The block diagram of the example of an internal system structure of a digital camera is shown. The processing in the CCD1 signal processing block is shown. A frequency extraction filter is shown. The operation | movement flowchart of Example 1 is shown. The flowchart of an evaluation value taking-in timing setting process is shown. The flowchart of the filter selection process by evaluation value taking-in timing is shown. The operation | movement flowchart of Example 2 is shown. The flowchart of the evaluation taking-in timing setting process by luminance is shown.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display 2 Cover of memory card filling room and battery filling room 3 Strobe light emitting part 4 Optical finder 5 Distance measuring unit 6 Remote control light receiving part 7 Lens barrel unit 7-1 Zoom optical system 7-1a Zoom lens 7-2 Focus optical system 7-2a Focus lens 7-3 Aperture unit 7-3a Aperture 7-4 Shutter unit 7-4a Mechanism shutter 7-1b Zoom motor 7-2b Focus motor 7-3b Aperture motor 7-4b Mechanical shutter motor 7-5 Motor driver 8 AF LED
9 Strobe LED
10 LCD monitor 13 Power switch 41 High frequency first filter 42 Low frequency second filter 101 CCD
102 F / E-IC
102-1 CDS
102-2 ADC
102-3 A / D converter 102-4 TG
103 SDRAM
104 Digital still camera processor 104-1 CCD1 signal processing block 104-2 CCD2 signal processing block 104-3 CPU block 104-4 Local SRAM
104-5 USB block 104-6 Serial block 104-7 JPEG / CODEC block 104-8 RESIZE block 104-9 TV signal display block 104-10 Memory card controller block 107 RAM
108 ROM
109 CPU
111 LCD driver 113 Buzzer 115-1 Audio recording circuit 115-2 Microphone amplifier 115-3 Microphone 116-1 Audio reproduction circuit 116-2 Audio amplifier 116-3 Speaker 117 LCD driver 118 Video amplifier 119 Video jack 120 Built-in memory 121 Memory card Slot 122 USB connector 123-1 Serial driver circuit 123-2 RS-232C connector SW1 Release shutter SW2 Mode dial SW3 Wide angle zoom switch SW4 Telephoto zoom switch SW5 Self-timer setting and release switch SW6 Menu switch SW7 Up and strobe set Switch SW8 Move right switch SW9 Display switch SW10 Move down and macro switch SW11 Move left Image confirmation switch SW12 and OK switch SW13 quick access switch

Claims (4)

An imaging device that obtains image data by receiving an image of a subject by light from a subject that has passed through a photographing lens,
Acquisition timing setting means for setting a timing for acquiring an AF evaluation value from the image data;
A filter selection unit that selects a filter that is used to obtain the AF evaluation value from the image data and transmits an arbitrary frequency component of the image data;
Automatic focus detection means for detecting a focus based on the AF evaluation value acquired from image data obtained by moving the focus lens to a lens position;
Photometric means for measuring subject brightness,
The acquisition timing setting unit sets after gamma correction as a timing for acquiring the AF evaluation value when the subject luminance obtained by the photometry unit is equal to or higher than a predetermined threshold, and the subject luminance obtained by the photometry unit is predetermined. If it is less than the threshold value, before the gamma correction is set as the timing for obtaining the AF evaluation value, after the digital clamp,
When the acquisition timing setting unit is set after digital clamping , the filter selection unit selects a filter that transmits only a lower band than the filter selected when setting after gamma correction as the filter ,
And, as a result of performing focus detection by the automatic focus detection means, comprising a detection result determination means for determining whether focus detection is possible using a threshold value,
An imaging apparatus characterized by changing a threshold used by the detection result judging means in accordance with image data output.   The imaging apparatus according to claim 1, wherein when the acquisition timing setting unit is set after digital clamping, the threshold used by the detection result determination unit is lowered. An imaging method for obtaining image data by receiving an image of a subject by light from a subject that has passed through a photographing lens by an imaging device,
An acquisition timing setting step for setting a timing for acquiring an AF evaluation value from the image data;
A filter selection step for selecting a filter that is used to acquire the AF evaluation value from the image data and transmits an arbitrary frequency component of the image data;
An automatic focus detection step of detecting a focus based on the AF evaluation value acquired from image data obtained by moving the focus lens to a lens position;
A photometric process for measuring subject brightness,
The acquisition timing setting step sets post-gamma correction as a timing for acquiring the AF evaluation value when the subject luminance obtained in the photometry step is equal to or higher than a predetermined threshold, and the subject luminance obtained in the photometry step is predetermined. If it is less than the threshold value, before the gamma correction is set as the timing for obtaining the AF evaluation value, after the digital clamp,
In the filter selection step, when the acquisition timing setting step is set after digital clamping, as the filter , a filter that transmits only a low frequency than a filter selected when setting after gamma correction is selected,
And, as a result of performing focus detection in the automatic focus detection step, it has a detection result determination step of determining whether focus detection is possible using a threshold value,
An imaging method, wherein a threshold used in the detection result determination step is changed according to image data output. The imaging method according to claim 3 , wherein when the acquisition timing setting step is set after digital clamping, a threshold used in the detection result determination step is lowered.

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