JP2011253099A - Focus detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform an autofocus control.SOLUTION: A focus detector includes: extraction means which extracts a high luminance region from an image in an evaluation area set in an imaging screen; excluding means which excludes the image in the high luminance region extracted from the image in the evaluation area by the extraction means; and focus detection means which performs a focus detection based on the image in the evaluation area after the image in the high luminance region is excluded by the exclusion means. The extraction means specifies a high luminance pixel of the image in the evaluation area and groups the specified high luminance pixel by adding hue, or adds a ratio of the area of the high luminance region, to extract the high luminance region from the image in the evaluation area.

Description

  The present invention relates to a focus detection apparatus.

  The following autofocus control devices are known. This autofocus control device performs automatic focus adjustment by hill-climbing control based on contrast evaluation values (for example, Patent Document 1).

Japanese Patent No. 3697745

  However, in hill-climbing control using the contrast evaluation value, control is often performed so that the front subject is focused as much as possible. For this reason, when a high-luminance subject exists around (mainly behind) the main subject, the contrast evaluation value for the high-luminance subject becomes large, and the focal length unintended by the user is focused. there is a possibility.

  A focus detection apparatus according to the present invention includes an extraction unit that extracts a high luminance area from an image in an evaluation area set in a shooting screen, and an image in the high luminance area that is extracted from the image in the evaluation area by the extraction unit. An exclusion means to be excluded and a focus detection means for performing focus detection based on an image in the evaluation area after being excluded by the exclusion means.

  According to the present invention, it is possible to focus on the focal length intended by the user.

1 is a block diagram illustrating a configuration of an embodiment of a camera 100. FIG. It is a figure which shows the specific example of an image. It is a 1st figure which shows the example of calculation of a contrast evaluation value. It is a flowchart figure which shows the flow of AF control. It is the figure which showed the specific example of the change of the brightness | luminance in a horizontal line. It is a 2nd figure which shows the example of calculation of a contrast evaluation value. It is a figure which shows the specific example at the time of dividing | segmenting the AF evaluation area into several detailed area.

  FIG. 1 is a block diagram illustrating a configuration of an embodiment of a camera according to the present embodiment. The camera 100 includes an operation member 101, a lens 102, an image sensor 103, a control device 104, a memory card slot 105, and a monitor 106. The operation member 101 includes various input members operated by the user, such as a power button, a release button, a zoom button, a cross key, an enter button, a play button, and a delete button.

  The lens 102 is composed of a plurality of optical lenses, but is representatively represented by one lens in FIG. The lenses constituting the lens 102 include an AF lens (focus adjustment lens) for AF (Auto Focus / automatic focus adjustment) described later. The image sensor 103 is an image sensor such as a CCD or a CMOS, for example, and captures a subject image formed by the lens 102. Then, an image signal obtained by imaging is output to the control device 104.

  The control device 104 includes a CPU, a memory, and other peripheral circuits, and controls the camera 100. Note that the memory constituting the control device 104 includes SDRAM and flash memory. The SDRAM is a volatile memory, and is used as a work memory for the CPU to develop a program when the program is executed or as a buffer memory for temporarily recording data. The flash memory is a non-volatile memory in which data of a program executed by the control device 104, various parameters read during program execution, and the like are recorded.

  In the present embodiment, the control device 104 generates image data in a predetermined image format, for example, JPEG format (hereinafter referred to as “main image data”) based on the image signal input from the image sensor 103. Further, the control device 104 generates display image data, for example, thumbnail image data, based on the generated image data. The control device 104 generates an image file that includes the generated main image data and thumbnail image data, and further includes header information, and outputs the image file to the memory card slot 105.

  The memory card slot 105 is a slot for inserting a memory card as a storage medium, and the image file output from the control device 104 is written and recorded on the memory card. The memory card slot 105 reads an image file stored in the memory card based on an instruction from the control device 104.

  The monitor 106 is a liquid crystal monitor (rear monitor) mounted on the back surface of the camera 100, and the monitor 106 displays an image stored in a memory card, a setting menu for setting the camera 100, and the like. . Further, when the user sets the mode of the camera 100 to the shooting mode, the control device 104 outputs image data for display of images acquired from the image sensor 103 in time series to the monitor 106. As a result, a through image is displayed on the monitor 106.

  In the present embodiment, the control device 104 performs focus adjustment by executing AF (autofocus / automatic focus adjustment) processing during shooting. For example, the control device 104 executes AF processing when the release button is half-pressed by the user, and performs AF control during single shooting. In addition, it is possible to perform continuous AF control during live view shooting, AF control during subject tracking operation, AF control during moving image shooting, and the like.

  Here, the AF method includes, for example, a contrast method and a phase difference method. In this embodiment, a case where AF processing is performed by the contrast method will be described. In contrast, the focus adjustment by the contrast method calculates a contrast evaluation value while moving the focus adjustment AF lens for a plurality of autofocus areas (AF evaluation areas) set in the shooting screen, and evaluates the contrast. This is a method of performing focus adjustment by detecting the position of the AF lens having a peak value as the focus position. Since the focus adjustment process using the contrast method is a known process, a detailed description thereof will be omitted.

  In this focus adjustment by the contrast method, the first contrast evaluation value peak in the AF evaluation area is detected as an in-focus position while moving the AF lens from the closest side to the infinity side, so that an object that is present as close as possible In many cases, control is performed so as to focus on. This is to avoid focusing behind the main subject. However, if there is a high-brightness subject such as a light source around the main subject (mainly behind), the peak of the contrast evaluation value may be calculated from the high-brightness subject and focus on the high-brightness subject. In some cases, the user may focus on a focal length that is not intended by the user. Note that examples of the high brightness subject include a light source such as a spotlight and a reflective object such as a window glass.

  For example, as shown in FIG. 2, when it is desired to photograph the main subject 2a on the close side illuminated by the rear high-intensity light source 2b, it is necessary to focus on the main subject 2a. When focus adjustment is performed, there is a possibility that the high-intensity light source 2b located behind is in focus and the main subject 2a cannot be focused. In the example shown in FIG. 2, when the entire area scan is performed while moving the AF lens from the closest side to the infinity side, for example, a contrast evaluation value is calculated as shown in FIG. In this case, according to the above-described focus adjustment by the contrast method, the evaluation value 3b calculated from the high-intensity light source 2b is larger than the evaluation value 3a calculated from the main subject 2a that is originally intended to be focused, so The high-intensity light source 2b is in focus. In the present embodiment, in order to solve such a problem, the control device 104 performs AF control as follows.

  FIG. 4 is a flowchart showing the flow of AF control in the present embodiment. The process shown in FIG. 4 is started when the above-described AF control such as AF control during single shooting, continuous AF control during through image shooting, AF control during subject tracking operation, AF control during movie shooting, or the like is started. The program is executed by the control device 104 as a program.

  In step S10, the control device 104 sets a predetermined value (for example, 200) for the luminance of the image of the horizontal line in the AF evaluation area of the image captured from the image sensor 103 in the electronic shutter mode, for example, the horizontal line of one pixel. (8 bits)) The above pixels are detected, and the coordinate value of the detection area constituted by the detected pixels is specified. For example, in the example shown in FIG. 2, the horizontal line 2d is set in the AF evaluation area 2c, and the coordinate value of the detection area is specified for the horizontal line 2d. FIG. 5 is a diagram showing a change in luminance in the horizontal line 2d set in the image shown in FIG. In FIG. 5, the horizontal axis indicates the horizontal pixel position in the horizontal line 2d, and the vertical axis indicates the luminance value. In the horizontal line 2d, the luminance value is changed as shown in FIG. 5, and an example in which the region 5a, the region 5b, and the region 5c are detected as the regions between the horizontal edges is shown. The control device 104 specifies the coordinate value of the detection area while moving the horizontal line 2d upward or downward one pixel at a time within the AF evaluation area 2c, and the detection area of the entire AF evaluation area 2c is identified. Specify coordinate values. Then, it progresses to step S20.

In step S20, the control device 104 acquires an image in the AF evaluation area, converts the color space of the acquired image in the AF evaluation area from RGB to XYZ, and further converts it to Lab. Thereafter, the control device 104 calculates a hue angle by performing a hue calculation according to the following equation (1) based on the image in each AF evaluation area after the color space is converted to Lab.
h = tan ⁻¹ (b ^* / a ^* ) (1)

  Thereafter, the process proceeds to step S30, and the control device 104 detects the edge of the hue component in the horizontal direction in the detection region detected in step S10 based on the hue angle calculated in step S20, and detects the detected edge. Register coordinates. Then, when the detected hue between the edges is uniform within a predetermined range, the control device 104 adds an identification number as the horizontal inter-edge region and registers it in association with the above-described edge coordinates. That is, the control device 104 compares the hues of two edges whose edge coordinates are adjacent to each other, and if the difference in hue is within a predetermined range, for example, the hue angle is within 15 degrees, the hue between the edges is determined. Are determined to be substantially uniform and are grouped as regions between horizontal edges, and an identification number is added to each region between horizontal edges.

  Thereafter, the process proceeds to step S40, and the control device 104 determines whether or not the processes in steps S10 to S30 have been completed for all horizontal lines of the image in the AF evaluation area. If a negative determination is made in step S40, the process returns to step S10 and is repeated. On the other hand, if a positive determination is made in step S40, the process proceeds to step S50.

  In step S50, the control device 104 calculates a vertical shift amount between the upper and lower sides for each horizontal edge region extracted in step S30. Thereafter, the process proceeds to step S60, and the control device 104 determines whether or not the vertical shift amount calculated in step S50 is within a predetermined threshold, for example, within 5 pixels. When an affirmative determination is made in step S60, the process proceeds to step S70, and the control device 104 performs grouping so that the identification numbers added to the regions between the horizontal edges whose deviation amount is within a predetermined threshold value are in the same group. To do. This makes it possible to group high-luminance subjects that have a small hue difference in the horizontal direction and a small amount of deviation in the vertical direction existing in the AF evaluation area. Thereafter, the process proceeds to step S80. On the other hand, if a negative determination is made in step S60, the process proceeds to step S80.

  In step S80, the control device 104 determines whether or not the vertical shift amount determination and the identification number grouping for all horizontal lines in the AF evaluation area have been completed. If a negative determination is made in step S80, the process returns to step S50. On the other hand, if a positive determination is made in step S80, the process proceeds to step S90.

  In step S90, the control device 104 calculates the ratio of the group area grouped in step S70 in the AF evaluation area, that is, the ratio of the area of the group area to the area of the AF evaluation area. Thereafter, the process proceeds to step S100, and the control device 104 determines whether or not the proportion of the group area calculated in step S90 is within a predetermined threshold. The threshold value used at this time may be a value within a range of 1/50 to 1/4 with respect to the size of the AF evaluation area, for example, and may be changed according to the type of the high brightness subject. If a positive determination is made in step S100, the process proceeds to step S110. In step S110, the control apparatus 104 excludes the image in the group area from the images in the AF evaluation area, and proceeds to step S120.

  Thereby, when the grouped group area is small with respect to the size of the AF evaluation area, the group area may be a high-luminance area based on edges detected from high-luminance subjects other than the main subject. Therefore, the images in such a group area can be excluded from the AF evaluation target with high accuracy. On the other hand, when the group area detected with respect to the size of the AF evaluation area is large, the group area is not likely to be an area based on edges detected from high-luminance subjects other than the main subject. Such an image in the group area can be left as an AF evaluation target to improve AF accuracy.

  On the other hand, if a negative determination is made in step S100, the process proceeds to step S120. In step S120, the control device 104 calculates a contrast evaluation value for an image in the AF evaluation area other than the group area excluded in step S110. Thereafter, the process proceeds to step S130, and the control device 104 moves the AF lens to the next focal length and returns to step S10. The control device 104 calculates the AF evaluation value at each focal length, that is, the contrast evaluation value by repeating the above-described processing from step S10 to step S130 until the AF lens reaches the infinity end. The position of the AF lens that becomes the maximum is specified as the in-focus position.

  As described above, the contrast evaluation value is calculated by excluding the image in the range (high luminance area) in which the possibility that the high luminance subject exists is high from the image in the AF evaluation area in advance, as shown in FIG. The illustrated contrast evaluation value calculation example changes as shown in FIG. That is, as shown in FIG. 6, the evaluation value 3b calculated from the high-intensity light source 2b detected in FIG. 3 is removed, and the evaluation value 6a calculated from the main subject 2a is calculated as the peak of the contrast evaluation value. Will be. Thereby, when the focus adjustment is performed while the AF lens is moved from the closest side to the infinity side, it is possible to prevent the user from focusing on an unexpected high-brightness subject.

According to the present embodiment described above, the following operational effects can be obtained.
(1) The control device 104 calculates contrast evaluation values by excluding images in a range (high luminance region) where there is a high possibility that a high luminance subject exists from within the AF evaluation area, and performs AF processing. I made it. Thus, it is possible to prevent the user from focusing on an unexpected high brightness subject.

(2) The control device 104 identifies a detection area for each horizontal line in the AF evaluation area, and groups the detection areas based on the amount of deviation in the vertical direction, so that there is a possibility that a high-luminance subject exists. The high range was specified. As a result, it is possible to specify with high accuracy a range in which a high-luminance subject is highly likely to exist.

(3) When the ratio of the group area calculated in step S90 in FIG. 4 is within a predetermined threshold, the control device 104 excludes the image in the group area from the image in the AF evaluation area. . Accordingly, when the grouped group area is small with respect to the size of the AF evaluation area, the group area may be an area based on an edge detected from a high-intensity subject other than the main subject. In consideration of the high level, it is possible to accurately exclude a range in which a high-luminance subject is highly likely to exist.

-Modification-
The camera according to the above-described embodiment can be modified as follows.
(1) In the above-described embodiment, the control device 104 calculates a contrast evaluation value for an image in the AF evaluation area other than the group area excluded in step S110 in step S120 of FIG. Thus, an example has been described in which the contrast evaluation value is calculated by excluding an image in a range where a high-luminance subject is highly likely to exist from an image in the AF evaluation area. However, when a large number of high-luminance areas are detected from the AF evaluation area, the control device 104 excludes an isolated area from a detailed evaluation area obtained by subdividing the AF evaluation area from the target for calculating the contrast evaluation value. It may be.

  Specifically, the control device 104 divides the AF evaluation area 7a in the image shown in FIG. 7A into a plurality of detailed areas as shown in FIG. Subdivide the inside. Then, the control device 104 specifies an isolated high-brightness detailed area as an isolated point from the detailed areas set in the AF evaluation area 7a, and excludes the isolated point from the contrast evaluation value calculation target. Here, a method for determining whether or not the detailed area k0 is an isolated point will be described.

Based on the contrast evaluation values of the detailed areas k0 to k8, the control device 104 determines whether or not the detailed area k0 is isolated from the surrounding detailed areas k1 to k8. Specifically, when the contrast evaluation value of the detailed area k0 satisfies the condition expressed by the following equation (2), the control device 104 is isolated from the surrounding detailed areas k1 to k8. That is, it is determined that the detailed area k0 is an isolated point. In this case, the detailed area k0 is excluded from the contrast evaluation value calculation target. Note that a in the following equation (2) takes a value of 1 or more, and may be a fixed value or a variable that varies depending on the luminance level of the entire image.
Contrast evaluation value of detailed area k0> max (contrast evaluation value of detailed area k1 to contrast evaluation value of detailed area k9) × a (2)

  The control device 104 performs the above processing for all the detailed areas in the AF evaluation area 7a to identify isolated points, excludes the isolated points from the AF evaluation area 7a, and sets the remaining detailed areas. The sum of the contrast evaluation values is calculated as the contrast evaluation value of the AF evaluation area 7a. As a result, when there are a plurality of high-luminance areas in the AF evaluation area 7a, an area that is highly likely to be a high-luminance subject such as a light source is detected with high accuracy, and the area is detected from the calculation target of the contrast evaluation value. Can be excluded.

  If the detailed area specified as an isolated point is excluded from the AF evaluation area 7a and the sum of the contrast evaluation values of the remaining detailed areas is calculated as the contrast evaluation value of the AF evaluation area 7a, it is used for calculating the contrast evaluation value. The number of detail areas changes for each focal length. That is, the reference (parameter) for each focal length changes. Therefore, it is desirable that the control device 104 calculates the contrast evaluation value on the basis of the unit area in consideration of the number of effective detailed areas after the isolated points are excluded.

(2) In the above-described embodiment, the AF evaluation area set in the shooting screen is used as an evaluation area for focus adjustment, and an image within a range in which there is a high possibility that a high-luminance subject is included from the image in the AF evaluation area. An example in which the focus adjustment is performed without the above has been described. However, the present invention can also be applied to a case where an evaluation area other than the AF evaluation area is excluded from the evaluation target. For example, the present invention can be applied to a case where an image in a range where a high-luminance subject is likely to be included is excluded from images in an evaluation area for performing AE (automatic exposure) and AWB (auto white balance). is there.

(3) In the above-described embodiment, the example in which the control device 104 automatically excludes an image within a range that is likely to include a high-luminance subject has been described. However, the control device 104 highlights on the screen a range that is likely to include a high-luminance subject in the AF evaluation area, notifies the user, and excludes the range from the calculation target of the contrast evaluation value. The user may select whether or not.

(4) In the above-described embodiment, the case where the present invention is applied to the camera 100 has been described. However, the present invention can also be applied to other imaging devices having a photographing function, such as a mobile phone with a camera and a video camera.

  Note that the present invention is not limited to the configurations in the above-described embodiments as long as the characteristic functions of the present invention are not impaired. Moreover, it is good also as a structure which combined the above-mentioned embodiment and a some modification.

100 Camera, 101 Operation member, 102 Lens, 103 Image sensor, 104 Control device, 105 Memory card slot, 106 Monitor

Claims (4)

An extraction means for extracting a high brightness area from an image in the evaluation area set in the shooting screen;
Excluding means for excluding images in the high brightness area extracted by the extracting means from images in the evaluation area;
A focus detection apparatus comprising: focus detection means for performing focus detection based on an image in the evaluation area after being excluded by the exclusion means. The focus detection apparatus according to claim 1,
The extraction unit extracts the high-brightness region from the image in the evaluation area by specifying the high-brightness pixel of the image in the evaluation area and grouping the specified high-brightness pixel in consideration of the hue. A focus detection device. The focus detection apparatus according to claim 1 or 2,
The focus detection apparatus, wherein the excluding unit excludes the image in the high luminance area from the image in the evaluation area, taking into account the ratio of the area of the high luminance area to the area of the evaluation area. In the focus detection apparatus according to any one of claims 1 to 3,
The exclusion means divides the evaluation area into a plurality of detailed areas, and excludes a detailed area isolated from the surrounding detailed areas from the plurality of detailed areas. .

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