JP2014016570A - Imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high-speed contrast AF control even when a high-luminance subject exists in a shooting screen.
In order to achieve the above object, a peak position of a first contrast evaluation value of the subject image obtained based on a pixel signal output from the image sensor during a first accumulation time and the first There is a difference greater than or equal to a predetermined value in the peak position of the second contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor during the second storage time shorter than the storage time of In this case, it is configured to include a determination unit that determines that the in-focus position cannot be specified.
[Selection] Figure 1

Description

  The present invention relates to an imaging apparatus such as a digital still camera and a digital video camera, and more particularly to an imaging apparatus equipped with a contrast detection type autofocus.

  The conventional contrast detection type autofocus has a drawback that it is difficult to obtain an accurate focus on a specific subject when a high brightness subject such as a night view is scattered. This is because when the luminance level of the point light source reaches the saturation level, the contrast value is low in the original in-focus state and high in the out-of-focus state out of the original in-focus position. In other words, when the brightness level of the point light source is saturated, contrast occurs at the periphery of the point light source, so the larger the image of the point light source due to defocusing, the greater the contrast value, and accurate focusing is obtained. Absent.

  In order to deal with such a problem, there is a known technique in which a high brightness subject in a photographing screen is detected and AF proper exposure is set so that the high brightness subject is not saturated. For example, Patent Document 1 discloses a technique in which an imaging screen is divided into a plurality of areas, the brightness level of each divided area is detected, and AF proper exposure is set for an area having the highest brightness level. ing.

JP 2007-65048 A

  However, the technique disclosed in Patent Document 1 sets AF proper exposure after detecting a high-luminance subject. That is, since the detection operation and the AF operation for the high-brightness subject are performed separately, it takes time to focus, and there may be a problem that high-speed and high-precision contrast AF cannot be performed.

  Therefore, the present invention has been made in view of the above problems, and acquires a plurality of contrast evaluation values with different accumulation times, and determines whether or not a false focus is achieved by a high-intensity light source from the acquired plurality of contrast evaluation values. It is an object to realize high-speed and high-precision contrast AF by making the determination.

In order to achieve the above object, in the present invention, an image sensor that generates a subject image by receiving a light beam that has passed through an exit pupil of a photographing optical system, and the pixel signal output from the image sensor is obtained. A focus adjustment unit that performs focus adjustment using a contrast evaluation value of a subject image,
The peak position of the first contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor during the first accumulation time, and the second accumulation that is shorter than the first accumulation time. If the peak position of the second contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor over time has a difference of a predetermined value or more, it is determined that the in-focus position cannot be specified It has the determination means to do.

  According to the imaging apparatus of the present invention, even when a high-luminance light source is present in the shooting screen, high-speed and high-precision contrast AF control is realized by determining whether or not false in-focus is caused by a high-luminance subject. be able to.

It is a block diagram of an imaging device in an embodiment of the present invention. It is a figure explaining the image acquisition timing of embodiment of this invention. It is an image figure of contrast AF evaluation value when a high-intensity subject exists in a photography screen. It is an image figure explaining the determination means of embodiment of this invention. It is a figure showing the operation | movement after determining by the determination means of embodiment of this invention. It is a flowchart of an embodiment of the present invention. It is a figure showing the operation | movement after determining by the determination means of embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[First embodiment]
1 to 5 are diagrams according to a first embodiment of the present invention. Hereinafter, the operation of the first embodiment will be described with reference to the drawings.

(Configuration of imaging device)
FIG. 1 is a block diagram of an image pickup apparatus according to the present invention. Reference numeral 1 denotes a camera body, 2 denotes a fixed lens 2a, a variable magnification lens 2b, an AF (autofocus) focus lens 2c, an optical low-pass filter 2d, and an image pickup element 2e. This is a photographic optical system configured and held by a lens barrel 3. Reference numeral 8 denotes a rear liquid crystal monitor. The focus lens 2c is driven in the direction of arrow 4 by an actuator (not shown). The shutter 5 guides the light flux from the subject to the image sensor 2e by opening the shutter blade 6 for an appropriate exposure time. The CPU 7 as the control means built in the camera body 1 is shown outside the camera body 1 as a block diagram of only elements related to the present invention.

  Inside the CPU 7 are exposure control means 002, image processing means 003, image temporary storage means 004, AF image selection means 005, evaluation value calculation means 006, determination means 007, AF drive control means 008 as focus adjustment means, AF drive means 009. Have The exposure control unit 002 performs opening / closing drive control of the shutter blade 6 via the shutter drive unit 001. An AF drive control unit 008 serving as a focus adjustment unit drives and controls the focus lens 2c in the direction of arrow 4 via the AF drive unit 009. The exposure control unit 002 sets an exposure time suitable for still image and moving image shooting based on the subject information from the image processing unit 003.

  The AF drive control unit 008 serving as a focus adjustment unit receives the light beam that has passed through the exit pupil of the photographing optical system and obtains the contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor that generates the subject image. It has a function to adjust the focus using.

  The determination unit 007 has a peak position of the first contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor during the first accumulation time and a second accumulation time shorter than the first accumulation time. When the peak position of the second contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor during the accumulation time is greater than or equal to a predetermined value, it is determined that the in-focus position cannot be specified To do.

  Then, at the time of still image shooting, the shutter blade 6 is opened for a time corresponding to the shooting conditions, and the subject light flux is guided to the image pickup device 2e to pick up an image. Record. At the time of moving image shooting, the exposure control means 002 always keeps the shutter blades 6 open during moving image shooting, and controls the electronic shutter function (not shown) of the image sensor to give a frame length of 21 (for example, 1/60 seconds). I will update the image.

  Here, in the present embodiment, the images 22a and 22b in FIG. 2 are acquired by dividing the frame length 21 into, for example, frames of 1/90 seconds and 1/180 seconds. As described above, in this embodiment, as will be described in detail later with reference to FIG. 2, a plurality of images having different shooting periods (different exposure times) are acquired for each frame. The image temporary storage unit 004 temporarily stores the image in the frame 21 of FIG. 2 acquired by the image processing unit 003.

  The AF image selection means selects a plurality of types of images 22a and 22b in FIG. FIG. 2 specifically illustrates how exposure control means 002 updates a plurality of images every one frame length (for example, 1/60 second) by controlling an electronic shutter function (not shown) of the image sensor in moving image shooting. It is a figure to do. In FIG. 2, the horizontal axis indicates the elapsed time, and the vertical axis indicates the height of each image on the screen.

  When an image is acquired with an electronic shutter using a CMOS type imager as the image sensor 2e, the exposure timing is shifted above and below the image for so-called rolling shutter reading. FIG. 2 shows a state in which 1/60 seconds determined to be preferable by the exposure control unit 002 is set to one frame length 21 and a plurality of images are acquired by dividing the frame length 21. Therefore, the 1/90 second image 22a and the 1/180 second image 22b shorter than the image 22a are acquired and stored in one frame length 21. Thereafter, the operation of storing an image for each frame length is similarly repeated.

  Here, each image within one frame length 21 is acquired with an exposure time as a different accumulation time. In FIG. 2, the time is shortened to half, such as 1/90 seconds and 1/180 seconds. However, the number of images, the ratio of exposure times, and the context are not limited thereto. The AF image selection unit 005 selects the image 22a and the image 22b stored in the image primary storage unit 004 after being photographed based on the AF exposure condition set by the exposure control unit 002. The evaluation value calculation unit 006 calculates a first contrast evaluation value and a second contrast evaluation value having a shorter accumulation time than the first contrast evaluation value from the two types of images selected by the AF image selection unit 005. To do.

  Further, the peak positions of the contrast evaluation values of the first contrast evaluation value and the second contrast evaluation value obtained by the determination unit 007 are compared to determine whether or not the in-focus position can be specified.

  Here, the determination unit 007 will be described using the determination unit subflow of FIG.

  In step S101, a first contrast evaluation value is acquired.

  In step S102, a second contrast evaluation value is acquired.

  In step S103, it is determined whether or not the contrast peaks of the first contrast evaluation value and the second contrast evaluation value have been acquired. If it is determined that at least one of the first contrast evaluation value and the second contrast evaluation value has not been acquired, the process returns to step S101 to acquire the contrast evaluation value again. . On the other hand, if it is determined that the contrast peaks of both the first contrast evaluation value and the second contrast evaluation value have been acquired, the process proceeds to step S104.

  In step S104, it is determined using the lens position of the contrast peak acquired in step S103 whether the in-focus position has been detected. First, the lens position difference between the first contrast peak and the second contrast peak is calculated. Then, determination is performed using the calculated lens position difference of the contrast peak and the threshold value. If it is determined that the lens position difference of the contrast peak is larger than the threshold value, it is determined that the in-focus position has not been specified, and the process proceeds to step S105 to calculate the in-focus position. On the other hand, when the lens position difference of the contrast peak is smaller than the threshold value, it is determined that the in-focus position can be specified, and the determination unit subflow is exited.

  If it is determined that the in-focus position can be specified, the AF drive control unit 008 determines the AF drive unit 009 based on the first contrast evaluation value and the second contrast evaluation value calculated by the evaluation value calculation unit 006. Then, the focus lens 2c is driven to adjust the focus in the arrow 4 direction.

  Here, a method of determining whether or not the focus position in step S104 of the determination unit subflow has been identified will be described with reference to FIGS. FIG. 3 shows an image (FIG. 3-1) and a contrast AF evaluation value (FIG. 3-2) at the time of focusing and defocusing when there is a high-luminance subject in the shooting screen.

  FIG. 4 is a diagram for explaining the determination means of the present invention. FIG. 4A is a diagram in which the evaluation value calculation means 006 calculates from the output of the image sensor 2e accumulated during the first accumulation time controlled by the exposure control means 002. FIG. 4B shows the second contrast calculated by the evaluation value calculation means 006 from the output of the image sensor 2e accumulated during the second accumulation time shorter than the first accumulation time. Represents an evaluation value. The contrast detection method of the present invention will be described. The contrast detection method is a focus adjustment method in which a focus position is detected by evaluating the contrast of a subject image captured by an image sensor while driving a focus lens in the optical axis direction.

  The details of the contrast AF detection method are disclosed in various patent documents and are known techniques, and thus the description thereof is omitted. When a high-intensity light source is present in the shooting screen as shown in FIG. 3, the luminance level of the high-intensity light source reaches the saturation level LS not only at the time of focusing but also at the time of defocusing. In such a case, the contrast evaluation value is low at the in-focus position (FIG. 3-a)) and high at the time of defocusing (FIG. 3-b)).

  In other words, when the brightness level of the high-intensity light source is saturated, contrast occurs at the periphery of the light source, so the larger the image of the high-intensity light source by defocusing, the more the contrast evaluation value increases and the more accurate Can't get the right focus position.

  Therefore, in the present invention, whether or not the high-intensity light source is a false focus even if a high-intensity light source exists in the shooting screen using the first contrast evaluation value and the second contrast evaluation value having different accumulation times. And high-speed, high-precision contrast AF is performed.

  FIG. 4B shows a first contrast evaluation value when defocused in the case where a high-intensity light source exists in the photographing screen described with reference to FIG. FIG. 4C shows a second contrast evaluation value having an accumulation time different from that of the first contrast evaluation value. In the present embodiment, the case where an image acquired with a shorter accumulation time is used for the second contrast evaluation value than the first contrast evaluation value is described. However, the accumulation time of the image used is opposite. It is possible.

  As shown in FIG. 4, when a high-luminance light source is present in the shooting screen, the peak positions of the first contrast evaluation value and the second contrast evaluation value are different. It is determined that it cannot be identified.

  FIG. 4B is a graph in which the first contrast evaluation value and the second contrast evaluation value are written together. The horizontal axis represents the defocus amount, and the vertical axis represents the contrast evaluation value at each defocus. A waveform 51 represents the relationship with the defocus amount of the first contrast evaluation value, and a waveform 52 represents the relationship with the defocus amount of the second contrast evaluation value.

  Now, consider a case where the focus lens 2C is scanned in the direction of arrow 4 in FIG. 1 and the defocus amount is changed from left to right in FIG. At this time, in the case of a low-luminance subject, the waveform 51 and the waveform 52 both exceed the peak d of the contrast evaluation value as shown in FIG. 4-3, but in the case of a high-luminance subject, the waveform is first shown in FIG. The peak b of 51 is exceeded, and then the peak c of the waveform 52 is exceeded.

  Therefore, when the state shown in FIG. 4B is reached, it is determined that the in-focus position cannot be specified. As described above, according to the imaging apparatus of the present invention, it is possible to determine whether it is a false focus by a high-intensity light source as well as contrast AF using a plurality of contrast evaluation values having different accumulation times. High-speed and high-precision contrast AF control can be realized.

  Here, a countermeasure when the in-focus position cannot be specified will be described below.

  In the determination means of the present invention, when it is determined that the in-focus position cannot be specified, the acquisition range of the contrast evaluation value is expanded and the in-focus position is calculated using the two obtained contrast evaluation values. .

  As shown in FIG. 5, when two contrast peak positions appear due to saturation of both the first contrast evaluation value and the second contrast evaluation value, the centers of the two obtained contrast peaks are focused. FIG. 5 is a diagram for explaining the above operation. If it is determined in step S104 in FIG. 6 that the in-focus position has not been specified, it is determined that the in-focus position exists at a position that is not the peak position of the current contrast evaluation value. Is extended from the lens position L1 to the lens position L2. By expanding the acquisition range of the contrast evaluation value in this way, two peak positions of the contrast evaluation value appear when a high-intensity light source exists in the shooting screen. And it determines with the intermediate position L3 of the peak of these two contrast evaluation values being a focus position.

  Since L3 is an intermediate position between the two contrast peaks P1 and P2, the calculation method is L3 = (P1 + P2) / 2. Then, either the first contrast evaluation value or the second contrast evaluation value may be used to calculate the in-focus position of the intermediate position L3 between the peaks of the two contrast evaluation values.

The first contrast evaluation value is generated from a subject signal having a good SN because the accumulation time is longer than that of the second contrast evaluation value. Therefore, it is not easily affected by disturbances such as camera shake.
On the other hand, since the second contrast evaluation value has a shorter accumulation time than the second contrast evaluation value, it is possible to obtain an evaluation value that is less affected by saturation than the first contrast evaluation value. Further, when the second contrast evaluation value does not saturate as shown in FIG. 7, the second contrast peak position is focused. FIG. 7 is a diagram for explaining the above operation. If it is determined in step S104 in FIG. 6 that the in-focus position has not been specified, in order to find the in-focus position, the contrast evaluation value acquisition range is from the lens position L1 ′ to the lens position L2 ′ in FIG. spread. By expanding the acquisition range of the contrast evaluation value in this way, two peak positions of the first contrast evaluation value appear when a high-intensity light source is present in the shooting screen.

  However, in the second contrast evaluation value having an accumulation time shorter than that of the first contrast evaluation value, saturation does not occur, and the peak position of the control and evaluation value is L3 ′. From this, it is determined that the peak L3 ′ of the second contrast evaluation value is the in-focus position.

  As described above, according to the imaging apparatus of the present invention, when the determination unit specifies that the position is not the in-focus position, the acquisition range of the contrast evaluation value is expanded, and the peak of the two contrast evaluation values obtained is obtained. Since the center is focused, high-speed contrast AF control can be realized.

  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.

DESCRIPTION OF SYMBOLS 1 Camera body 2a Fixed lens 2b Variable magnification lens 2c Focus lens 2d Optical low-pass filter 2e Image pick-up element 3 Lens barrel 4 Focus lens drive range 5 Shutter 6 Shutter blade 7 CPU
8 Rear LCD monitor

Claims (7)

Focus adjustment is performed using an image sensor that receives a light beam that has passed through an exit pupil of a photographing optical system to generate a subject image, and a contrast evaluation value of the subject image that is obtained based on a pixel signal output from the image sensor. An imaging device having a focus adjustment means for performing,
The peak position of the first contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor during the first accumulation time, and the second accumulation that is shorter than the first accumulation time. If the peak position of the second contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor over time has a difference of a predetermined value or more, it is determined that the in-focus position cannot be specified An image pickup apparatus comprising: a determination unit that performs the determination.   When the determination unit determines that the in-focus position cannot be specified, the second contrast of the subject image obtained based on the pixel signal output from the image sensor during the second accumulation time The imaging apparatus according to claim 1, wherein focusing is performed using the evaluation value.   If the determination unit determines that the in-focus position cannot be specified, the first contrast of the subject image obtained based on the pixel signal output from the image sensor during the first accumulation time The imaging apparatus according to claim 1, wherein a peak position between two peak positions of the evaluation value is set as a focus position.   When the determination unit determines that the in-focus position cannot be specified, the second contrast of the subject image obtained based on the pixel signal output from the image sensor during the second accumulation time The imaging apparatus according to claim 1, wherein a peak position between two peak positions of the evaluation value is set as a focus position.   The imaging apparatus according to claim 3, wherein a peak position located between two peak positions of the first contrast evaluation value of the subject image is set as an in-focus position.   The imaging apparatus according to claim 4, wherein a peak position located between two peak positions of the second contrast evaluation value of the subject image is set as an in-focus position. Focus adjustment is performed using an image sensor that receives a light beam that has passed through an exit pupil of a photographing optical system to generate a subject image, and a contrast evaluation value of the subject image that is obtained based on a pixel signal output from the image sensor. A method of controlling an imaging apparatus having a focus adjustment unit,
The peak position of the first contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor during the first accumulation time, and the second accumulation that is shorter than the first accumulation time. If the peak position of the second contrast evaluation value of the subject image obtained based on the pixel signal output from the image sensor over time has a difference of a predetermined value or more, it is determined that the in-focus position cannot be specified An image pickup apparatus control method comprising: a determination unit that performs the determination.

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