JP2014077976A - Focusing device and imaging apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focusing device capable of executing AF processing in a short time, without being affected by the change of an object during AF.SOLUTION: When a camera-shake amount predicted by camera-shake amount prediction means is larger than a predetermined value, setting means makes the area of each of a plurality of set range-finding areas large and focusing is performed by focusing means, based on an AF evaluation value obtained in the range-finding areas except the range-finding area where the change amount of a signal differential value is determined to be larger than the predetermined value by reliability evaluation value determination means.

Description

  The present invention relates to a focus adjustment device, and more particularly to a focus adjustment device that performs focus adjustment using an image signal acquired by an image sensor that photoelectrically converts a subject image formed by an imaging optical system.

  In digital cameras and video cameras, an autofocus (hereinafter referred to as AF) method is generally used in which an output signal from an image sensor such as a CCD or CMOS is used to detect and focus a signal corresponding to the contrast of a subject. .

  However, in the above method, since it is necessary to sequentially detect the contrast of the subject while the focus lens is scan-driven over a predetermined range, it takes a long time to obtain a contrast detection signal.

  In particular, if the subject moves in or out of the AF evaluation range as the subject moves or blurs, the subject changes during AF, making it difficult to focus accurately.

As a response to changes in the subject during AF,
For example, as disclosed in Patent Document 1, when two evaluation ranges having different sizes are superimposed on the photographing range and there is a large change in evaluation value only in a larger evaluation range, the subject moves. Some of them determine and change the position and size of the distance measurement frame.

Japanese Patent Laid-Open No. 9-018768

  However, in the prior art disclosed in Patent Document 1 described above, since the AF evaluation range is changed after detecting that the subject has changed during AF, it is necessary to perform AF processing again, and AF time Will become longer. In addition, when the subject moves, the AF time becomes longer, and the reliability of the AF result is also impaired.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a focus adjustment apparatus that can execute AF processing in a short time without being affected by changes in a subject during AF.

In order to achieve the above object, the present invention provides an image sensor that receives a light beam that has passed through a photographing optical system and outputs an image signal, and a setting unit that sets a plurality of distance measuring areas divided on the image sensor. A focus evaluation value generating means for generating a focus evaluation value for evaluating a focused state using a high-frequency component of the image signal in the distance measurement area; and a maximum output value of the image signal in at least a part of the distance measurement area. Difference value generation means for generating a signal difference value calculated using the difference between the value and the minimum value, and an AF evaluation value that is the sum of the focus evaluation values in the distance measurement area obtained in a plurality of in-focus states The amount of change in the signal difference value generated by the focus adjustment means that adjusts the in-focus state so as to maximize the difference value generation means obtained in at least two in-focus states of the plurality of in-focus states. Use at least the plurality of ranging areas A focusing device having a reliability evaluation value determining means for determining a distance measuring area used for point regulation, and hand shake prediction means for predicting the amount of hand-shake, the,
When the camera shake amount predicted by the camera shake amount prediction unit is larger than a predetermined value, the setting unit increases the area of each of the set plurality of distance measurement areas,
Based on the AF evaluation value acquired in the distance measurement area excluding the distance measurement area in which the change amount of the signal difference value is determined to be larger than a predetermined value by the reliability evaluation value determination means, the focus adjustment means The focus adjustment is performed.

  According to the present invention, it is possible to provide a focus adjustment apparatus that can execute AF processing in a short time without being affected by a change in a subject during AF.

It is a flowchart which shows the AF operation | movement procedure of the focus adjustment apparatus in a 1st Example. It is a block diagram which shows the example of schematic structure of the imaging device which has a focus adjustment apparatus in 1st Example. A and B are diagrams showing setting of a distance measurement area in the first embodiment. It is a subroutine for reliability evaluation of each ranging area in the first embodiment. FIGS. 4A to 4D are diagrams schematically showing changes in the imaging range during AF scanning in the first embodiment. FIGS. 5A and 5B are diagrams showing a focus evaluation value E and a luminance signal difference value D in a distance measurement area in the situation of FIGS. 5A to 5D in the first embodiment. It is a subroutine of the distance competition determination of each ranging area group in the first embodiment. It is the figure which showed the change of AF evaluation value of each ranging area group in a 1st Example. It is the figure which showed the ranging area which is not selected by step S3 and step S4 in a 1st Example. FIGS. 5A and 5B are diagrams showing a focus evaluation value E and a luminance signal difference value D in a distance measurement area in the situation of FIGS. 5A to 5D in the second embodiment. It is a flowchart which shows the AF operation | movement procedure of the focus adjustment apparatus in a 3rd Example. It is the figure shown about the setting of the ranging area in a 3rd Example. It is a flowchart which shows the AF operation | movement procedure of the focus adjustment apparatus in a 4th Example. FIGS. 7A and 7B are diagrams schematically illustrating changes in the imaging range during AF scanning in the fourth embodiment. FIGS.

Example 1
Hereinafter, a first preferred embodiment of the present invention will be described in detail with reference to FIGS. FIG. 2 is a block diagram illustrating a schematic configuration example of an imaging apparatus having a focus adjustment apparatus according to an embodiment of the present invention. The imaging apparatus includes, for example, a digital still camera and a digital video camera, but is not limited thereto, and an incident optical image is electrically converted by photoelectric conversion using a two-dimensionally arranged solid-state imaging device such as an area sensor. The present invention can be applied if it is acquired as an image.

  In FIG. 2, reference numeral 1 denotes an imaging device. Reference numeral 2 denotes a zoom lens group, and reference numeral 3 denotes a focus lens group, which constitutes a photographing optical system. Reference numeral 4 denotes a light amount adjusting means for controlling the amount of light flux that passes through the photographing optical system, and an aperture that is an exposure means. A lens barrel 31 includes a zoom lens group 2, a focus lens group 3 as a focus adjusting unit, a diaphragm 4, and the like.

  Reference numeral 5 denotes a solid-state imaging device (hereinafter referred to as a CCD) such as a CCD that forms a subject image that has passed through the photographing optical system and photoelectrically converts the image. The solid-state imaging device receives a light beam that has passed through the photographing optical system and outputs an image signal. The solid-state imaging device may be a CMOS.

  Reference numeral 6 denotes an image pickup circuit that receives an electrical signal photoelectrically converted by the CCD 5 and performs various image processing to generate a predetermined image signal. Reference numeral 7 denotes an A / D conversion circuit that changes an analog image signal generated by the imaging circuit 6 into a digital image signal.

  Reference numeral 8 denotes a memory (VRAM) such as a buffer memory for temporarily storing the digital image signal output from the A / D conversion circuit 7. Reference numeral 9 denotes a D / A conversion circuit that reads out an image signal stored in the VRAM 8, converts it into an analog signal, and converts it into an image signal in a form suitable for reproduction output.

  Reference numeral 10 denotes an image display device (hereinafter, LCD) such as a liquid crystal display device (LCD) for displaying image signals. Reference numeral 12 denotes a storage memory that stores image data including a semiconductor memory or the like. Reference numeral 11 denotes a compression / decompression circuit including an expansion circuit that performs a decoding process, an expansion process, and the like. The compression / decompression circuit 11 reads the image signal temporarily stored in the VRAM 8 and stores the image data in the compression circuit and the storage memory 12 that perform compression processing and encoding processing of the image data in order to make it suitable for storage in the storage memory 12. The form is optimal for reproducing and displaying the stored image data.

  Reference numeral 13 denotes an AE processing circuit that receives an output from the A / D conversion circuit 7 and performs automatic exposure (AE) processing. Reference numeral 14 denotes a scan AF processing circuit that receives an output from the A / D conversion circuit 7 and performs autofocus (AF) processing. Reference numeral 15 denotes a CPU with a built-in memory for controlling the image pickup apparatus. Reference numeral 16 denotes a timing generator (hereinafter referred to as TG) that generates a predetermined timing signal.

  The CPU 15 has a function as setting means for setting a plurality of distance measurement areas divided on the solid-state image sensor.

  The CPU 15 has a function as a focus evaluation value generation unit that generates a focus evaluation value for evaluating the in-focus state using a high-frequency component of the image signal in the distance measurement area.

  The CPU 15 has a function as difference value generation means for generating a signal difference value calculated using the difference between the maximum value and the minimum value of the output values of at least a part of the image signal in the distance measurement area.

  The CPU 15 uses at least a change amount of the signal difference value generated by the difference value generation means obtained in at least two in-focus states, and uses a focus detection area for focus adjustment among the plurality of distance measurement areas. There is a function as a reliability evaluation value determination means for determining.

  Reference numeral 17 denotes a CCD driver. Reference numeral 21 denotes an aperture drive motor that drives the aperture 4. Reference numeral 18 denotes a first motor driving circuit for driving and controlling the diaphragm driving motor 21. A focus drive motor 22 drives the focus lens group 3. Reference numeral 19 denotes a second motor drive circuit that drives and controls the focus drive motor 22. A zoom drive motor 23 drives the zoom lens group 2. Reference numeral 20 denotes a third motor drive circuit for driving and controlling the zoom drive motor 23.

  Reference numeral 24 denotes an operation switch composed of various switch groups. An EEPROM 25 is an electrically rewritable read-only memory in which programs for performing various controls, data used for performing various operations, and the like are stored in advance. Reference numeral 26 denotes a battery, 28 denotes a strobe light emitting unit, 27 denotes a switching circuit that controls flash light emission of the strobe light emitting unit 28, and 29 denotes a display element such as an LED for displaying OK / NG of AF operation.

  A storage memory, which is a storage medium for image data or the like, is a fixed semiconductor memory such as a flash memory, and has a card shape or a stick shape. In addition to a semiconductor memory such as a card type flash memory that is detachably formed in the apparatus, various forms such as a magnetic storage medium such as a hard disk and a flexible disk are applied.

  The operation switch 24 includes a main power switch, a release switch, a reproduction switch, a zoom switch, a switch for turning on / off the display of the AF evaluation value signal on the monitor, and the like. The main power switch is for starting up the imaging apparatus 1 and supplying power.

  The release switch starts a shooting operation (storage operation) and the like. The reproduction switch starts a reproduction operation. The zoom switch moves the zoom lens group 2 of the photographing optical system to perform zooming.

  The release switch then performs a first stroke (hereinafter referred to as SW1) for generating an instruction signal for starting an AE process and an AF process performed prior to a photographing operation and a second stroke (hereinafter referred to as an instruction signal for starting an actual exposure operation). SW2) and a two-stage switch.

  Next, a focusing operation (AF operation) according to an embodiment of the present invention of the imaging apparatus having the above configuration will be described with reference to FIG. FIG. 1 is a flowchart showing an AF operation procedure of the imaging apparatus. A control program relating to this operation is executed by the CPU 15.

  When starting the AF operation, the CPU 15 first sets a ranging area and a ranging area group for performing focus adjustment on the subject. In the process of step S1, a plurality of ranging areas consisting of M = m_h × m_v (m_h = 1, 2,..., M_v = 1, 2,...) Are set in the image.

  A plurality of imaging pixels are two-dimensionally arranged in each of the plurality of ranging areas. The number of pixels of the plurality of shooting pixels arranged in each of the distance measurement areas is the same.

  3A and 3B are diagrams showing setting of the ranging area. In FIG. 3A, as an example, an entire distance measurement area 504 divided into M = 5 × 5 is set in the center of the photographing screen 500. The total distance measurement area 504 is an area in which an image signal for focus adjustment is evaluated by AF processing described later. The purpose of the AF operation is focus adjustment on a subject intended by the photographer in the whole distance measurement area 504. Is to do. Later, it is determined whether or not each of these areas is affected by the movement of the subject during the AF operation. Here, the position, size, and number of the distance measurement areas are not limited to the examples in FIGS. 3A and 3B, and may be arbitrarily set.

  FIG. 3B is an enlarged view of the entire ranging area 504 in FIG. 3A. The ranging area A [h, v] (where h = 1, 2,..., M_h, v = 1, 2,..., M_v) divides the entire ranging area 504 and has a smaller area. Is shown.

  In step S1, ranging area groups are set. As an example of the ranging area group, in FIG. 3B, in the center area hatched in a grid pattern with the ranging area group 506 in the outer peripheral area hatched with diagonal lines. Distance measurement area group 507 is set. These distance measurement area groups are used to make a distance conflict determination that determines the presence or absence of a subject having a different distance from the imaging device within the entire distance measurement area 504. Detailed processing will be described later.

  In this embodiment, since there is a high probability that the photographer wants to adjust the focus at the center of all the distance measurement areas 504, the distance measurement area groups are set at the center and the peripheral areas. Not limited to. For example, if the face size is known by subject detection, the distance measurement area group may be set to a position and size corresponding to the face size.

  Returning to FIG. 1, the description of the flowchart will be continued.

  In step S2, AF scanning (focus detection operation) is performed in each distance measurement area set in step S1. In the AF scan, the focus lens group 3 is moved by a predetermined amount from the scan start position to the scan end position, and the focus evaluation value E [n] [h, v] (however, at each focus lens group position is detected by the scan AF processing circuit 14. , N = 0, 1, 2, ..., N-1, h = 1, 2, ..., m_h, v = 1, 2, ..., m_v) and the luminance signal difference value D [n] [h, v] ( However, n = 0, 1, 2,..., N−1, h = 1, 2,..., M_h, v = 1, 2,.

  The focus evaluation value E [n] [h, v] represents the focus evaluation value of the distance measurement area A [h, v] at the nth focus lens position from the AF scan start position.

  Further, the number of scan points is N points from the start to the end of AF scan. The focus evaluation value E is received by the scan AF processing circuit 14 and the high-frequency component of the image signal in the distance measurement area A [h, v] is extracted through a high-pass filter or the like, and further accumulated. Calculated by performing arithmetic processing such as addition. The focus evaluation value calculated in this way corresponds to a state in which the spatial frequency corresponds to the contour component amount in the high region in the image signal in the distance measurement region A [h, v] and decreases when defocused and is in focus. The maximum evaluation value at.

  The focus evaluation value E may be calculated as the direction in which the high-frequency component is extracted as one of the row direction, the column direction, or both.

  As the focus evaluation value E, a value of a representative high-frequency component in one row in the distance measurement area A [h, v] may be used. As a representative one row, for example, the value of the row having the largest high-frequency component value is used. Further, as the focus evaluation value E, an integrated value of high-frequency components in all rows in the distance measurement area A [h, v] may be used.

  The luminance signal difference value D [n] [h, v] represents the luminance signal difference value of the distance measurement area A [h, v] at the nth focus lens position from the AF scan start position. Further, the number of scan points is N points from the start to the end of AF scan. The luminance signal difference value D [n] [h, v] is an evaluation value for detecting the movement of the subject during the AF scan in the distance measurement area A [h, v].

  For example, the luminance signal difference value in the distance measurement area A [h, v] is calculated by the following formula by receiving the input image signal by the scan AF processing circuit 14.

max [h, v] (l) and min [h, v] (l) are the maximum values of the luminance signals in the l-th row in the L-row pixel array constituting the distance measurement area A [h, v]. And the minimum value. In the above mathematical formula, the difference between the maximum value and the minimum value of the luminance signal is calculated for each row, the sum of all the rows in the distance measurement area is calculated, and the luminance signal difference value D [n] is calculated. [H, v]. Here, as the luminance signal, the image signal may be used as it is, or may be used after low-pass filter processing is performed on the image signal to remove high-frequency noise.

  In the present embodiment, the integrated value of the difference between the maximum value and the minimum value of the luminance signal of each row is the luminance signal difference value D, but the calculation method is not limited to this. For example, the maximum value and the minimum value of the luminance signal may be calculated for each row, and the maximum difference value of each row may be used as the luminance signal difference value D. Further, the luminance signal difference value D is also calculated in a direction that matches the direction in which the focus evaluation value E high-frequency component is extracted.

  The luminance signal difference value D calculated using Equation 1 is less affected by a change in the focus state of the contour of the subject, and the minimum and maximum values of the luminance signal in the distance measurement area are newly calculated during AF scanning. Affected when changed. Changes in the minimum value and maximum value of the luminance signal in the distance measurement area occur when the minimum value and maximum value of the luminance signal in the distance measurement area are updated due to movement of the subject or change in the blurring state. That is, the luminance signal difference value D changes due to a change in the luminance signal in the distance measurement area due to the movement of the subject or a change in the blurred state. In addition, as a method of obtaining the focus evaluation value E and the luminance signal difference value D, a method of obtaining the focus evaluation value E while moving the focus lens may be used.

  Next, in step S3, the reliability of each ranging area is evaluated. The reliability evaluation value calculated here has an effect on the AF due to the movement of the subject during the AF scan performed in step S2 and on the AF of the subject outside the distance measurement area due to the image magnification change or the blur change. It is an evaluation value used for exclusion. When the value of the reliability evaluation value is large, it indicates that the above-described event during the AF scan has a large influence on the AF. The details of the method for calculating the reliability evaluation value of the distance measurement area will be described later.

  Next, in step S4, perspective conflict determination for each distance measurement area group is performed. The position of the focus lens group 3 at which the focus evaluation value reaches a peak in each of the distance measurement area groups 506 and 507 described with reference to FIG. 3B, that is, the focus position is calculated. Here, by comparing in-focus positions for each distance measurement area group, it is determined whether or not there is a distance conflict in all the distance measurement areas 504, and the distance measurement area group in which the main subject exists is determined. The details of the distance competition determination method for each distance measurement area group will be described later.

  Subsequently, in step S5, it is determined whether or not there is a ranging area that constitutes a ranging area group that is evaluated to be reliable in step S3 and that is determined to have a main subject in step S4. . Here, the determination may be made based on whether or not it exists, or it may be determined that a ranging area exists when the number of existing objects is larger than a predetermined threshold. When the distance measurement area exists, the process proceeds to step S6, and the AF evaluation value is calculated.

  At this time, the AF evaluation value is calculated using the focus evaluation value E acquired in step S2 without driving the focus lens again. The AF evaluation value AF_V [n] is a value indicating the in-focus state of all the ranging areas 504 at the n-th focus lens position from the AF scan start position, and takes a larger value as it approaches the in-focus state. It is an evaluation value. In the present embodiment, the entire ranging area 504 is divided into a plurality of ranging areas, and the focus evaluation value E is calculated in each ranging area.

  As described above, the focus evaluation value E decreases when defocused and is the maximum evaluation value in focus. Therefore, the AF evaluation value AF_V [n] calculated as the sum of the focus evaluation values E is also Has similar properties.

  Further, the number of scan points is N points from the start to the end of AF scan. For example, when the number of AF-evaluable ranging areas determined in step S5 is AF_Num, the AF evaluation value AF_V [n] is calculated by the following formula.

  In Expression 2, the focus evaluation value E [n] [h, v] is evaluated as having reliability in Step S3, and other than the ranging areas included in the ranging area group usable in Step S4, The operation is performed as 0. Further, the sum of the focus evaluation values is normalized by the number AF_Num of distance measurement areas in which AF evaluation is possible. As a result, a stable AF evaluation value can be obtained regardless of the number AF_Num of distance measurement areas where AF evaluation is possible.

  That is, the AF evaluation value is normalized by dividing the total sum of focus evaluation values by the number of distance measurement areas determined to be used for focus adjustment.

  In this embodiment, the focus evaluation values are integrated in calculating the AF evaluation value, but the calculation method is not limited to this. For example, emphasizing the focus area in the center of all focus areas, weighting the focus evaluation value in the focus area in the center so that the value is greater than the focus evaluation value in other focus areas It may be done. In the present invention, the sum of the focus evaluation values is used as the AF evaluation value, but the sum calculation method includes the sum after the weighting as described above.

  On the other hand, if it is determined in step S5 that there is reliability in step S3, and it is determined in step S5 that there is no ranging area included in the ranging area group in which the main subject exists, the process proceeds to step S7. The AF evaluation value is calculated in a predetermined area within the entire distance measurement area 504. For example, the sum of all the focus evaluation values E [n] [h, v] in the 25 ranging areas in FIG. 3B is calculated as the AF evaluation value. In the case where the center is more important than the peripheral part, the distance measuring area to be used is not limited to this, for example, a total of nine distance measuring areas of 3 × 3 near the center are used.

  After calculating the AF evaluation value in steps S6 and S7, in-focus determination is performed in step S8. Here, the presence / absence of the local maximum value of the AF evaluation value with respect to the focus lens group position is determined, and the focus lens group position when the local maximum value exists is calculated. Furthermore, the reliability of the change curve of the AF evaluation value near the maximum value is evaluated. In this reliability evaluation, it is determined whether the obtained AF evaluation value takes the maximum value because the optical image of the subject is formed on the CCD 5 or takes the maximum value due to other disturbances.

  As a detailed method for determining the focus, for example, a method described in FIGS. 10A and B to FIG. 13 of JP 2010-078810 A may be used.

  That is, whether or not the AF evaluation value indicating the in-focus state is mountain-like is determined by the difference between the maximum value and the minimum value of the AF evaluation value, the length of the portion that is inclined at a certain value (SlopeThr) or more. , And the slope of the inclined portion. Thereby, focus determination can be performed.

  Next, in step S9, as a result of focusing determination, the CPU 15 determines whether focusing is possible. If it is determined that focusing is possible, in step S10, the CPU 15 calculates a peak position based on the AF evaluation value, and drives the focus lens group 3 to the peak position. In step S11, the CPU 15 performs in-focus display and ends the AF operation.

  On the other hand, if it is not determined in step S9 that the in-focus state is possible, in step S12, the CPU 15 drives the focus lens group 3 to a position having a high subject existence probability called a preset fixed point. In step S13, the CPU 15 performs out-of-focus display and ends the AF operation.

  A subroutine for evaluating the reliability of each ranging area performed in step S3 of FIG. 1 according to the first embodiment of the present invention of the imaging apparatus having the above configuration will be described below with reference to FIG. FIG. 4 is a flowchart showing a processing procedure for reliability evaluation of each ranging area. A control program relating to this operation is executed by the CPU 15.

  First, in step S31, the CPU 15 affects the influence of each distance measurement area on the AF due to the movement of the subject during the AF scan, and the influence of the subject outside the distance measurement area due to a change in image magnification or a change in blur. A reliability evaluation value R [h, v] for determining whether or not it is received is calculated. The reliability evaluation value R [h, v] is calculated as the amount of change in the luminance signal difference value D [n] [h, v] of the distance measurement area A [h, v] during AF scanning. expressed.

  The reliability evaluation value R [h, v] obtained by Expression 3 indicates the amount of change in the luminance signal difference value D [n] [h, v] due to the change in the focus lens position during AF scanning.

  The above-described reliability evaluation value R [h, v] is affected by the influence of the movement of the subject during the AF scan on the AF, and the influence of the subject outside the distance measurement area due to the image magnification change and the blur change. The reason for determining whether or not is present will be described with reference to FIGS.

  5A to 5D are diagrams schematically showing changes due to movement of the focus lens during AF scanning in the photographing screen 500 shown in FIGS. 3A and 3B.

  FIG. 5A shows a state where the farthest side is in focus in FIGS. The main subject 501 and the tree 503 are blurred. On the other hand, the person 505 and the tree 502 that are far from the imaging device are generally in focus.

  FIG. 5B shows a state where the focus is closer to the side closer to FIG. 5A. While the persons 501 and 505 and the tree 502 are blurred, the tree 503 is generally in focus. In addition, with respect to FIG. 5A, the person 505 moves in the upper left direction in the shooting screen 500. Furthermore, the person 501 has moved the position of the left arm.

  FIG. 5C shows a state where the focus is closer to the near side than FIG. 5B. While the main subject 501 is generally in focus, the trees 502 and 503 and the person 505 are out of focus. 5B, the person 505 is moving in the upper left direction in the shooting screen 500.

  FIG. 5D shows a state where the focus is closer to the side closer to FIG. 5C. Although the blurred state varies depending on the subject, all the subjects within the shooting range 500 are in a blurred state.

  FIGS. 6A and 6B show the focus evaluation value E and the luminance signal difference value D in the distance measurement area in the situation shown in FIGS. In the present embodiment, as a representative example of the ranging area, focus evaluation values E and luminance signal difference values of A [1,5], A [3,1], A [3,3] shown in FIGS. D is shown.

  6A is a diagram showing the relationship between the position of the focus lens group 3 and the focus evaluation value E. FIG. E [1,5], E [3,1] and E [3,3] in the figure are the distance measurement areas A [1,5], A [3,1] and A [3,3], respectively. 6 is a curve showing a change in a focus evaluation value E. LP1, LP2, LP3, and LP4 indicate focus lens positions, and correspond to the focus lens positions shown in FIGS.

  FIG. 6B is a diagram showing the relationship between the position of the focus lens group 3 and the luminance signal difference value D. D [1,5], D [3,1] and D [3,3] in the figure are the distance measurement areas A [1,5], A [3,1] and A [3,3], respectively. It is a curve which shows the change of the luminance signal difference value D. LP1, LP2, LP3, and LP4 indicate focus lens positions, and correspond to the focus lens positions shown in FIGS.

  In the distance measurement area A [1,5], the person 505 is almost in focus at the focus lens position LP1, so the focus evaluation value E [1,5] takes a maximum value in the vicinity of LP1. The person 505, who is the main subject in the distance measurement area A [1,5], has moved outside the distance measurement area A [1,5] when acquiring the image signal at the focus lens position LP3. . Therefore, the focus evaluation value E [1, 5] is greatly reduced in the vicinity of the focus lens position LP3.

  On the other hand, the luminance signal difference value D [1,5] of the ranging area A [1,5] is the maximum value of the luminance signal while the contour of the person 505 is in the ranging area A [1,5]. Since the minimum value is almost the same in every row, it is a constant value. However, after the focus lens position LP3 where the contour of the person 505 moves to the outside of the distance measurement area A [1,5], there is no main subject in the distance measurement area A [1,5]. The difference between the value and the minimum value decreases, and the luminance signal difference value D [1, 5] also decreases.

  Next, in the distance measurement area A [3, 1], the tree 503 is substantially in focus at the focus lens position LP2, so that the focus evaluation value E [3, 1] increases as it approaches the vicinity of LP2. However, as the in-focus state is reached, the width of the outline of the tree 503 decreases as the blur decreases, and the outline of the tree 503 moves to the outside of the distance measurement area A [3, 1]. In the distance measurement area A [3, 1], there is no subject having contrast other than the tree 503, and therefore the focus evaluation value E [3, 1] decreases near the focus lens position LP2. When the focus lens position LP2 is passed and the outline of the tree 503 enters the distance measurement area A [3, 1] due to blurring, the focus evaluation value E [3, 1] increases again.

  On the other hand, the luminance signal difference value D [3, 1] of the ranging area A [3, 1] is the maximum value of the luminance signal while the outline of the tree 503 is in the ranging area A [3, 1]. Since the minimum value is almost the same in every row, it is a constant value. However, in the vicinity of the focus lens position LP2 where the tree 503 is in focus, there is no main subject in the distance measurement area A [3, 1], so the difference between the maximum value and the minimum value of the luminance signal decreases, and the luminance The signal difference value D [3, 1] also decreases.

  Next, in the distance measurement area A [3, 3], since the person 501 is substantially in focus at the focus lens position LP3, the focus evaluation value E [3, 3] takes a maximum value in the vicinity of LP1.

  On the other hand, in the luminance signal difference value D [3, 3] of the distance measurement area A [3, 3], the contour of the person 501 is always in the distance measurement area A [3, 3] regardless of the focus lens position. For this reason, the maximum value and the minimum value of the luminance signal are constant in each row with little change.

  As described above, the focus evaluation value and the luminance signal difference value vary depending on the distance measurement area. In each of the above-mentioned distance measurement areas A [1,5], A [3,1], A [3,3], the focus evaluation value E has a maximum value, but correctly shows the maximum value as a focus position. Only the distance measurement areas A [1,5] and A [3,3] are present.

  The ranging area A [3, 1] shows maximum values at two focus lens positions, which is because the blur of the outline of the tree 503 has moved in and out of the ranging area. Thus, it is difficult to discriminate the local maximum value indicating the correct focus position from the change curve of the focus evaluation value E.

  Therefore, in this embodiment, the maximum value indicating the correct in-focus position is determined using the change in the luminance signal difference value D. Among the ranging areas A [1,5], A [3,1] and A [3,3], the luminance signal difference value D [1 of the ranging areas A [1,5] and A [3,1]. , 5] and D [3, 1] are greatly changed. This is because the movement of the person 505 is caused in the distance measurement area A [1, 5], and the blur of the outline of the tree 503 has moved in and out of the distance measurement area in the distance measurement area A [3, 1]. Responsible. Using the reliability evaluation value R [h, v] shown in Equation 3 above, the reliability of the maximum value of the focus evaluation value in these distance measurement areas is determined.

  Since the reliability evaluation value R [h, v] is a change amount of the luminance signal difference value D [n] [h, v] due to the change of the focus lens position, the curve of the luminance signal difference value D shown in FIG. 6B. Corresponding to the slope component of. By providing a threshold for this inclination component, the distance measurement area A [3, 3] is determined to be a distance measurement area where the reliability of the maximum value of the focus evaluation value is high.

  On the other hand, the distance measurement areas A [1,5] and A [3,1] are determined to be distance measurement areas where the reliability of the maximum value of the focus evaluation value is low. In Expression 3, the change amount of the luminance signal difference value D at the continuous focus lens position is set as the reliability evaluation value R. However, in order to avoid the influence of high frequency noise of the luminance signal difference value D, the low pass filter process is appropriately performed. The reliability evaluation value R may be calculated using the luminance signal difference value after being performed.

  Returning to the description of the flowchart of FIG.

  In step S32, it is determined whether or not reliability evaluation values have been calculated for all distance measurement areas. If there is still a ranging area for which the reliability evaluation value has not been calculated, the CPU 15 returns to step S31 and repeats the same processing.

  On the other hand, when the reliability evaluation value is calculated in all the distance measurement areas, in step S33, the CPU 15 sets a threshold value for performing the reliability evaluation of the distance measurement area. The threshold is set for each distance measurement area based on the magnitude of the maximum value of the luminance signal in the distance measurement area obtained in step S2. This threshold value may be set based on the sum of the luminance signals in the distance measurement area, or may be set to a predetermined fixed value.

  Next, in step S34, the CPU 15 determines whether or not the reliability evaluation value R calculated in step S31 is smaller than the threshold calculated in step S33. As described above, the smaller the reliability evaluation value R is, the more reliable the ranging area is determined. Therefore, the ranging area whose reliability evaluation value R is smaller than the threshold is determined as the highly reliable ranging area in step S35. Is set.

  On the other hand, a distance measurement area in which the reliability evaluation value R is larger than the threshold is set as a distance measurement area with low reliability in step S36. The signal difference value change amount determining means in the claims corresponds to the CPU 15.

  After setting whether the reliability of the ranging area is high or low, in step S37, it is determined whether or not the determination of all the ranging areas has been completed. If all the distance measurement areas have not been completed, the process returns to step S34 to continue the distance measurement area reliability determination process. On the other hand, when the determination of all the distance measurement areas is completed, the subroutine for reliability evaluation of each distance measurement area ends.

  That is, in this embodiment, based on the AF evaluation value acquired in the distance measurement area excluding the distance measurement area in which the change amount of the signal difference value is determined to be larger than the predetermined value by the CPU 15 as the reliability evaluation value determination means. The focus lens group as the focus adjusting means is moved in the optical axis direction to adjust the focus.

  Next, with reference to FIG. 7, a subroutine for determining the distance competition of each ranging area group performed in step S4 of FIG. 1 according to the first embodiment of the present invention of the imaging apparatus having the above-described configuration will be described. The following processing is executed by the CPU 15.

  First, in step S41, an AF evaluation value for each ranging area group is calculated. In FIG. 3B, a distance measuring area group 506 at the outer peripheral portion and a distance measuring area group 507 at the central portion are set as the distance measuring area groups. The AF evaluation value of each distance measurement area group is calculated as the sum of the focus evaluation values E of the distance measurement areas constituting the distance measurement area group for each focus lens position. FIG. 8 illustrates AF evaluation values of the ranging area group set in FIG. 3B. In FIG. 8, the situation of FIGS. 5A to 5D described above is assumed as the situation of the imaging range during the AF scan.

  The AF evaluation value AF_S of the distance measuring area group 506 in the outer peripheral portion is influenced by the tree 502 and the person 505 in FIGS. 5A to 5D, and takes the maximum maximum value near the focus lens position LP1. This is also influenced by the fact that the tree 503 takes a maximum value in the vicinity of the focus lens position LP1 in the same manner as the change in the focus evaluation value of the distance measurement area A [3, 1] in FIG. 6A. Further, a smaller extreme value is also taken near the focus lens position LP3, but this is also affected by the tree 503.

  The AF evaluation value AF_C of the distance measurement area group 507 at the center portion has a maximum value at the focus lens position LP3 that is the focus position of the person 501 because only the person 501 exists in the distance measurement area group.

  Next, in step S42, focusing determination is performed using the AF evaluation value of each ranging area group. The processing performed here is the same as that performed in step S8 of FIG. 1, and the focus lens position to be focused is calculated and the reliability evaluation of the AF evaluation value curve is performed.

  Next, in step S43, based on the focus determination result, it is determined whether or not the number of focus detection area groups that can be focused is plural. When the number of focus detection area groups is 1 to 0, the process proceeds to step S45.

  In step S45, it is determined whether or not there is only one focus detection area group. If there is one focusing area group that can be focused, the process proceeds to step S47, and the ranging area within the focusing area group that can be focused is set to be usable. On the other hand, if there are no focusable distance measurement area groups, the distance competition area subroutine for each distance measurement area group is terminated without setting any distance measurement area groups as usable distance measurement areas. .

  If it is determined in step S43 that there are a plurality of focus detection area groups, the process proceeds to step S44. In step S44, it is determined whether or not the difference in focus position between each of the plurality of ranging area groups is large. If the difference in focus position between the plurality of distance measurement area groups is small, the process proceeds to step S47, and the distance measurement areas in the plurality of distance measurement area groups are set to be usable.

  On the other hand, if the difference in focus position between each of the plurality of distance measurement area groups is large in step S44, the process proceeds to step S46, and the distance measurement near the focus position between the priority distance measurement area group and the priority distance measurement area group. The distance measurement area included in the area group is set to be usable.

  The above-mentioned priority ranging area group will be described with reference to FIGS. FIG. 8 is a diagram showing a change in AF evaluation value of each ranging area group. 5A to 5D, the AF evaluation values of the center distance measurement area group 507 and the outer periphery distance measurement area group 506 are as shown in FIG. 8 as described above, and the focus lens positions in the in-focus state are different. . However, any ranging area group has a maximum value, and the AF evaluation value shape near the maximum value is reliable.

  Therefore, in the situation of FIGS. 5A to 5D, in step S43 of the flowchart of FIG. 7, it is determined that there are a plurality of two distance measurement area groups 506 and 507 as focusable distance measurement area groups. Next, in step S44, it is determined that the difference in focus position between the two distance measurement area groups 506 and 507 is the difference between the focus lens positions LP3 and LP1, and is large. As a result, in step S46, the central ranging area group 507 having a high main object existence probability generally intended by the photographer is set as the priority ranging area group.

  5A to 5D, there is no other distance measurement area group having a maximum value in the vicinity of the focus lens position LP3 in which the priority distance measurement area group is in focus. Only the distance measurement area constituting the area 507 is set to be usable, and the distance competition determination subroutine for each distance measurement area group is terminated.

  In the present embodiment, for the distance conflict determination, a distance measurement area group in which the distance measurement areas are grouped is created. However, the distance conflict determination method is not limited to this. For example, when sufficient focus position evaluation can be performed in one distance measurement area, the distance conflict determination may be performed in each distance measurement area. Further, although the priority ranging area group is the central portion, it may be configured to give priority to an object detection result in the ranging area or an area having a large focus evaluation value.

  As described above, the reliability of each ranging area is evaluated in step S3 in FIG. 1, so that the influence of the movement of the subject during the AF scan on the AF, the ranging according to the change in the image magnification and the change in the blur is performed. A distance measurement area that has little influence on AF of a subject outside the area is extracted. Further, in step S4, the distance measurement area including the subject intended by the photographer is extracted by eliminating the distance measurement areas in the distance measurement area 504 where the perspective conflict has occurred.

  The distance measurement area extracted in both step S3 and step S4 in the situation of FIGS. 5A to 5D will be described with reference to FIG. FIG. 9 is a diagram showing distance measurement areas that are not selected in steps S3 and S4 with respect to the diagram of FIG. 5A. In FIG. 9, ranging areas not selected in step S3 are indicated by hatching with vertical lines, and ranging areas not selected in step S4 are indicated by hatching with horizontal lines.

  In addition, ranging areas that are not selected in both step S3 and step S4 are hatched in a lattice shape. As a result, in the situation of FIGS. 5A to 5D, processing such as in-focus determination is performed using the focus evaluation values of the eight distance measurement areas that are not hatched.

  By performing the processing after step S6 in FIG. 1 using the focus evaluation value E obtained in the ranging area extracted in both step S3 and step S4, it is not affected by the change of the subject during AF. The AF process can be executed in a short time.

(Example 2)
Hereinafter, a focus adjusting apparatus according to a second embodiment of the present invention will be described with reference to FIGS. 10A and 10B. The main difference from the first embodiment is the difference in the calculation method of the reliability evaluation value R. In the above-described embodiment, only the change amount of the luminance signal difference value D is used as the reliability evaluation value R. Therefore, the change of the luminance signal difference value D at the focus lens position that has little influence on the calculation of the in-focus position. Therefore, it may be determined that the reliability of the distance measurement area is low. In the second embodiment, the reliability evaluation value R is calculated using both the luminance signal difference value D and the focus evaluation value E, and the luminance signal difference is calculated at the focus lens position that has a large influence on calculating the in-focus position. Only when the value D changes, it is determined that the reliability of the ranging area is low. Therefore, the reliability of the distance measurement area can be determined with higher accuracy, and the S / N deterioration of the AF evaluation value due to unnecessary removal of the distance measurement area can be prevented.

  The block diagram (FIG. 2) of the image pickup apparatus having the focus adjustment apparatus in the first embodiment, the diagrams for explaining the AF operation (FIGS. 1, 4, and 7), and the diagram for explaining the setting of the ranging area (FIG. 3A and 3B are the same in the second embodiment and perform the same operation, and thus the description thereof is omitted.

  Step S31 of the subroutine for evaluating the reliability of each ranging area in FIG. 4 in which the processing content performed in the second embodiment is different from that in the first embodiment will be described.

  In step S31, the CPU 15 is affected by the influence of each distance measurement area on the AF due to the movement of the subject during the AF scan, and on the AF of the subject outside the distance measurement area due to the image magnification change or blur change. A reliability evaluation value R [h, v] for determining whether or not there is is calculated. The reliability evaluation value R [h, v] is the amount of change in the luminance signal difference value D [n] [h, v] and the focus evaluation value E [n] of the distance measurement area A [h, v] during AF scanning. It is calculated as the product of the amount of change in [h, v] and is represented by the following equation.

  The reliability evaluation value R [h, v] obtained by Expression 3 is the amount of change in the luminance signal difference value D [n] [h, v] due to the change in the focus lens position during the AF scan and the focus evaluation value E [n. ] [H, v].

  That is, in this embodiment, the CPU 15 as the reliability evaluation value determination means determines that the change amount of the signal difference value is larger than the predetermined value, and determines that the change amount of the signal difference value is larger than the predetermined value. Based on the AF evaluation value acquired in the distance measurement area excluding the distance measurement area in which the amount of change in the focus evaluation value obtained in the in-focus state is determined to be larger than the predetermined value, the focus lens group as the focus adjustment unit is illuminated. Move in the axial direction to adjust the focus.

  Further, it is determined that a value obtained by multiplying the change amount of the signal difference value generated by the CPU 15 as the reliability evaluation value determination means and the change amount of the focus evaluation value generated by the change amount of the signal difference value is larger than a predetermined value. Based on the AF evaluation value acquired in the distance measurement area excluding the measured distance measurement area, focus adjustment is performed by moving a focus lens group as a focus adjustment unit in the optical axis direction.

  The above-described reliability evaluation value R [h, v] is affected by the influence of the movement of the subject during the AF scan on the AF, and the influence of the subject outside the distance measurement area due to the image magnification change and the blur change. The reason why it is determined whether or not is present will be described with reference to FIGS.

  FIGS. 5A to 5D are diagrams simply showing changes due to movement of the focus lens during AF scanning in the photographing screen 500 shown in FIGS. 3A and 3B.

  FIG. 5A shows a state where the farthest side is in focus in FIGS. A person 501 that is a main subject has a left arm portion arranged inside the body.

  FIG. 5B shows a state where the focus is closer to the side closer to FIG. 5A. The left arm of the person 501 is widened and arranged outside the body.

  FIG. 5C shows a state where the focus is closer to the near side than FIG. 5B. The position of the left arm portion of the person 501 has not changed from the state of FIG. 5B.

  FIG. 5D shows a state where the focus is closer to the side closer to FIG. 5C. The position of the left arm portion of the person 501 has not changed from the state of FIG. 5D.

  FIGS. 10A and 10B show the focus evaluation value E and the luminance signal difference value D in the distance measurement area in the situation shown in FIGS. In the present embodiment, the focus evaluation value E and the luminance signal difference value D of A [5, 4] shown in FIGS.

  FIG. 10A is a diagram showing the relationship between the position of the focus lens group 3 and the focus evaluation value E. FIG. E [5, 4] in the figure is a curve showing the change in the focus evaluation value E of the distance measurement area A [5, 4]. LP1, LP2, LP3, and LP4 indicate focus lens positions, and correspond to the focus lens positions shown in FIGS.

  FIG. 10B is a diagram showing the relationship between the position of the focus lens group 3 and the luminance signal difference value D. D [5, 4] in the figure is a curve showing the change in the luminance signal difference value D of the distance measurement area A [5, 4]. LP1, LP2, LP3, and LP4 indicate focus lens positions, and correspond to the focus lens positions shown in FIGS.

  In the distance measurement area A [5, 4], since the person 501 is at the focus lens position LP1 and the left arm portion is arranged inside the body, the focus evaluation value E [5, 4] is small in the vicinity of LP1. The change is small. In addition, when the person 501 who is the main subject in the distance measurement area A [5,4] acquires an image signal at the focus lens position LP2, the left arm portion is widened, and the person 501 is in the distance measurement area A [1,5]. The left arm has entered. Therefore, the focus evaluation value E [5, 4] changes between the focus lens positions LP1 and LP2. However, the focus lens position at which the person 501 is focused is in the vicinity of LP3 and is largely blurred, so the amount of change is small.

  On the other hand, the luminance signal difference value D [5, 4] of the ranging area A [5, 4] indicates that a subject having a change in luminance signal is displayed while the left arm portion of the person 501 is placed inside the body. Since it does not exist in the distance measurement area, the value is small and the change is small. However, when the left arm of the person 501 is spread, a difference between the maximum value and the minimum value of the luminance signal occurs in the distance measurement area, and the luminance signal difference value D [5, 4] increases rapidly.

  In the situation as described above, when the reliability evaluation value R is calculated using only the luminance signal difference value D as in the first embodiment, the ranging area A [5, 4] is determined in step S34 in FIG. It is not selected as a ranging area with low reliability. However, the focus evaluation value E [5, 4] in FIG. 10A has a maximum value in the vicinity of the focus lens position LP3 that is the focus position of the person 504, and the evaluation value curve shape in the vicinity of the maximum value is also highly reliable.

  In order to make use of the focus evaluation value of such a distance measurement area, even if the luminance signal difference value D changes due to a certain focus lens position change by calculating the reliability evaluation value R as shown in Equation 4, When the change in the focus evaluation value E is small, a calculation formula that reduces the reliability evaluation value R is used.

  As described above, when the change in the luminance signal difference value D occurs at the focus lens position having a small influence when the focus position is calculated, it is more appropriate to use the distance measurement area for focus determination. The signal amount of the AF evaluation value indicating the position increases, and the focusing accuracy can be increased.

  In the present embodiment, the case where one distance measurement area is set at the center has been described, but the position and number of distance measurement areas are not limited thereto. For example, a plurality of ranging areas may be set, the reliability of each ranging area may be determined, and the in-focus position may be calculated for each ranging area determined to have high reliability. In such a case, the lens may be driven by selecting a focus position intended by the photographer from a plurality of calculated focus positions.

(Example 3)
A focus adjustment apparatus according to a third embodiment of the present invention will be described below with reference to FIGS. The main difference from the first embodiment is the difference in the number of ranging areas used for focus adjustment. In the above-described embodiment, since the focus adjustment is performed by using a total of 25 distance measuring areas of 5 × 5, a large amount of memory for storing various evaluation values is necessary, and the calculation load is large. There is.

  In the third embodiment, the number of distance measurement areas used for focus adjustment is one, and focusing is impossible when the AF evaluation value is affected by movement of the subject or change in blurring state during AF scanning. To continue processing. Therefore, the possibility of performing inaccurate focus adjustment can be eliminated while reducing the memory capacity for storing the evaluation value and the calculation load.

  Note that the block diagram (FIG. 2) of the image pickup apparatus having the focus adjustment device in the first embodiment and the reliability evaluation subroutine (FIG. 4) of each ranging area are also the first in the third embodiment. Since the configuration is similar to that of the embodiment and performs the same operation, the description thereof is omitted.

  A flowchart of the focusing operation (AF operation) in FIG. 1 in which the processing content performed in the third embodiment is different from that in the first embodiment will be described with reference to FIG.

  FIG. 11 is a flowchart illustrating an AF operation procedure of the imaging apparatus. A control program relating to this operation is executed by the CPU 15.

  When the CPU 15 starts the AF operation, the CPU 15 first sets a distance measurement area for performing focus adjustment on the subject. In the process of step S21, one distance measurement area is set in the image.

  FIG. 12 is a diagram showing setting of the distance measurement area. In FIG. 12, a ranging area 604 is set at the center of the shooting screen 500. The total distance measurement area 604 is a range in which an image signal for performing focus adjustment is evaluated by AF processing described later. The purpose of the AF operation is focus adjustment on a subject intended by the photographer in the whole distance measurement area 604. Is to do. Later, it is determined whether or not each of these areas is affected by the movement of the subject during the AF operation.

  Returning to FIG. 11, the description of the flowchart will be continued.

  In step S22, AF scanning (focus detection operation) is performed in each distance measurement area set in step S21. In the AF scan, the focus lens group 3 is moved by a predetermined amount from the scan start position to the scan end position, and the focus evaluation value E [n] at each focus lens group position (where n = 0, 1, 2,..., N−1) and the luminance signal difference value D [n] (where n = 0, 1, 2,..., N−1) are stored in the CPU 15.

  The focus evaluation value E [n] represents the focus evaluation value of the ranging area 604 at the nth focus lens position from the AF scan start position. Further, the number of scan points is N points from the start to the end of AF scan. The focus evaluation value E is received by the scan AF processing circuit 14 and the high-frequency component of the image signal in the distance measurement area 604 is extracted via a high-pass filter or the like, and further arithmetic processing such as cumulative addition is performed. To calculate. The focus evaluation value calculated in this manner is an evaluation in the image signal in the distance measurement area 604 that corresponds to the contour component amount in the high frequency, decreases when defocused, and becomes the maximum when the focus is achieved. Value.

  The luminance signal difference value D [n] represents the luminance signal difference value of the ranging area 604 at the nth focus lens position from the AF scan start position. Further, the number of scan points is N points from the start to the end of AF scan. The luminance signal difference value D [n] is an evaluation value for detecting the movement of the subject during the AF scan in the distance measurement area 604.

  For example, the luminance signal difference value in the distance measuring area 604 is calculated by the following formula in response to the input image signal by the scan AF processing circuit 14.

max (l) and min (l) indicate the maximum value and the minimum value of the luminance signal of the l-th row in the L-row pixel array constituting the distance measurement area 604. In the above mathematical formula, the difference between the maximum value and the minimum value of the luminance signal is calculated for each row, the sum of all the rows in the distance measurement area is calculated, and the luminance signal difference value D [n] is calculated. It is said. Here, as the luminance signal, the image signal may be used as it is, or may be used after low-pass filter processing is performed on the image signal to remove high-frequency noise.

  The luminance signal difference value D calculated using Equation 1 is less affected by a change in the focus state of the contour of the subject, and the minimum and maximum values of the luminance signal in the distance measurement area are newly calculated during AF scanning. Affected when changed. Changes in the minimum value and maximum value of the luminance signal in the distance measurement area occur when the minimum value and maximum value of the luminance signal in the distance measurement area are updated due to movement of the subject or change in the blurring state. That is, the luminance signal difference value D changes due to a change in the luminance signal in the distance measurement area due to the movement of the subject or a change in the blurred state.

  In addition, as a method of obtaining the focus evaluation value E and the luminance signal difference value D, a method of obtaining the focus evaluation value E while moving the focus lens may be used.

  Next, in step S3, the reliability of each ranging area is evaluated. Since the process performed in step S3 is the same as that of the first embodiment, the description thereof is omitted. The calculation process of the reliability evaluation value performed in step S31 of the distance measurement area reliability evaluation subroutine (FIG. 4) performed in step S3 is performed in either the first embodiment or the second embodiment. It may be the one described.

  Next, in step S23, it is determined whether or not the ranging area 604 has been evaluated to be reliable in step S3. If it is determined that there is reliability, the process proceeds to step S24, and an AF evaluation value is calculated.

  At this time, the focus evaluation value E acquired in step S22 is used as the AF evaluation value without driving the focus lens again. In the third embodiment, since there is only one distance measuring area, the focus evaluation value E is equal to the AF evaluation value. The AF evaluation value AF_V [n] is a value indicating the in-focus state of all the ranging areas 604 at the nth focus lens position from the AF scan start position, and takes a larger value as it approaches the in-focus state. It is an evaluation value. Further, the number of scan points is N points from the start to the end of AF scan. As described above, the AF evaluation value AF_V [n] is calculated by the following equation.

  Since the AF evaluation value AF_V [n] calculated here is a value for which the reliability evaluation has been completed in step S23, there is no influence of subject movement or blur during AF scanning, and high-precision focus adjustment is performed. It is possible evaluation value.

  About the process from step S8 after step S24 to step S13, the process similar to a 1st Example is performed.

  On the other hand, if it is determined in step S23 that the ranging area 604 is not reliable in step S3, it is determined that high-precision focusing is impossible by the ranging area 604, and the process proceeds to step S12. Processes when out of focus. Since the processing content after step S12 at this time is the same as that of the first embodiment, the description thereof is omitted.

(Example 4)
A focus adjustment apparatus according to a fourth embodiment of the present invention will be described below with reference to FIGS. The main difference from the first embodiment is the difference in the method of setting a plurality of distance measurement areas used for focus adjustment. In the above-described embodiment, since the focus adjustment is always performed using a total of 25 distance measuring areas of 5 × 5, all the distance measuring areas are reliable if they are easily affected by the camera shake of the photographer. In some cases, it was determined that the device could not be used.

  In the present embodiment, a camera shake prediction unit (CPU 15) for predicting a camera shake amount is provided, and when the camera shake amount predicted by the camera shake amount prediction unit is larger than a predetermined value, the setting unit (CPU 15) includes a plurality of set distance measuring methods. It is characterized in that the number of ranging areas is reduced while keeping the total area. Therefore, when the camera shake amount predicted by the camera shake amount prediction unit is larger than the predetermined value, the setting unit (CPU 15) increases the area of each of the set plurality of distance measurement areas.

  In the fourth embodiment, the area of each distance measurement area is changed while maintaining the area of the entire distance measurement area depending on whether or not the distance measurement area used for focus adjustment is likely to cause camera shake. In other words, in a situation where camera shake is likely to occur, the number of each ranging area is reduced while maintaining the entire area of the ranging area. Therefore, when the camera is easily affected by the camera shake of the photographer, it is possible to reduce the possibility that each distance measurement area is determined to be unusable by the reliability determination, and to reduce the situation where focus adjustment cannot be performed. Can do.

  The block diagram (FIG. 2) of the image pickup apparatus having the focus adjusting apparatus in the first embodiment, the reliability evaluation subroutine for each ranging area, and the perspective conflict determination subroutine (FIGS. 4 and 7) are the same as those in FIG. The fourth embodiment also has the same configuration as that of the first embodiment and performs the same operation, so that the description thereof is omitted.

  A flowchart of the focusing operation (AF operation) in FIG. 1 in which the processing content performed in the fourth embodiment is different from that in the first embodiment will be described with reference to FIG.

  FIG. 13 is a flowchart illustrating an AF operation procedure of the imaging apparatus. A control program relating to this operation is executed by the CPU 15.

  When starting the AF operation, the CPU 15 first acquires camera shake prediction information in step S31. In this embodiment, as the camera shake prediction information, focal length information of the photographing optical system, hand shake information such as whether the camera shake correction function of the photographing optical system is enabled, whether the imaging device is fixed, or the like is used. .

  The focal length information of the photographing optical system is stored in the EEPROM 25. When the focal length is longer than a predetermined value, it is determined that a camera shake is likely to occur.

  Whether or not the camera shake correction function is enabled is information on whether or not a vibration-proof lens (not shown in FIG. 2) is performing a vibration-proof operation. When the camera shake correction function is invalid, it is determined that camera shake is likely to occur.

  Whether or not the imaging device is fixed is determined by using a camera shake detection sensor (not shown in FIG. 2) or not. As the camera shake detection sensor, for example, a gyro (angular velocity sensor) using a piezoelectric element may be used, and the angular velocity of shake in each direction can be detected. When it is detected that the imaging apparatus is not fixed using the camera shake detection sensor, it is determined that the camera shake is likely to occur. Here, regardless of whether the imaging device is fixed, the output of the camera shake detection sensor is stored, and the output stored immediately before the AF operation is used to determine whether camera shake is likely to occur during AF. May be.

  Next, in step S32, using the information acquired in step S31, it is determined whether or not the camera shake is likely to occur during AF. In the present embodiment, if it is determined that any one of the above-described three pieces of information is likely to cause camera shake, the result of step S32 is Yes, and the process proceeds to step S33. However, the method for determining a situation in which camera shake is likely to occur is not limited to this. Each camera shake prediction information may be weighted, and the total sum may be used to determine whether or not the camera shake is likely to occur.

  In step S33, a smaller distance measurement area and a distance measurement area group are set. If No in step S32, the process proceeds to step S34, where a larger distance measurement area and a distance measurement area group are set.

  The size of the ranging area set in steps S33 and S34 will be described with reference to FIG.

  FIG. 14A shows the ranging area set in step S33. In FIG. 14A, as in FIG. 3A, the entire ranging area 504 divided into M = 5 × 5 is set at the center of the shooting screen 500. The total distance measurement area 504 is an area in which an image signal for focus adjustment is evaluated by AF processing described later. The purpose of the AF operation is focus adjustment on a subject intended by the photographer in the whole distance measurement area 504. Is to do. Later, it is determined whether or not each of these areas is affected by the movement of the subject during the AF operation.

  FIG. 14B shows the ranging area set in step S34. In FIG. 14B, an entire ranging area 704 divided into M = 3 × 3 is set at the center of the shooting screen 500.

  The entire ranging area 504 in FIG. 14A and the entire ranging area 704 in FIG. 14B are areas having substantially the same size. This is because the frequency of occurrence of perspective conflict increases as the size of the entire ranging area increases, so that it is substantially constant regardless of the amount of camera shake. On the other hand, in FIG. 14A and FIG. 14B, since the number of divisions of the distance measurement area is different, the area of each distance measurement area is set larger in FIG. 14B than in FIG. 14A.

  In the present embodiment, when there is a concern that the amount of camera shake during AF is large, the size of all ranging areas is not changed as shown in FIG. 14B, and the number of individual ranging areas is reduced. The change in the luminance signal difference value due to camera shake is suppressed, and the frequency of reliability reduction in the distance measurement area is reduced.

  In Steps S33 and S34, a ranging area group is also set. This is for performing near-far conflict determination as in the first embodiment. In step S33, the same setting as in FIG. In step S34, the central area and the surrounding eight areas may be divided and set as a distance measurement area group.

  When the setting of the distance measurement area and the distance measurement area group is completed in step S33 or S34, the process proceeds to step S2. Since the processing performed after step S2 is the same as that described in the first embodiment, description thereof is omitted. The same step numbers are assigned to the same processes in the flowchart of the AF operation in FIG. 1 and the flowchart of the AF operation in FIG.

  In the above embodiments, the change in the focus state of the subject is realized by moving the focus lens, but the method for realizing the change in the focus state is not limited to this. For example, you may implement | achieve by moving an image pick-up element instead of a focus lens. Further, as in Japanese Patent Application Laid-Open No. 2011-113174, an imaging apparatus that can acquire incident angle information (light field information) of a light beam may realize a change in focus state by reconstruction processing.

  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.

2 Zoom lens group 3 Focus lens group 4 Aperture 5 Solid-state image sensor (CCD)
14 Scan AF processing circuit 15 CPU

Claims (8)

An image sensor that receives a light beam that has passed through the photographing optical system and outputs an image signal; a setting unit that sets a plurality of distance measurement areas divided on the image sensor; and a high-frequency component of the image signal in the distance measurement area And a focus evaluation value generating means for generating a focus evaluation value for evaluating the in-focus state, and a difference between the maximum value and the minimum value of the output values of the image signal in at least a part of the distance measurement area. Difference value generating means for generating a signal difference value, and adjusting the in-focus state so that an AF evaluation value that is a sum of the focus evaluation values in the ranging area obtained in a plurality of in-focus states is maximized Of the plurality of ranging areas using at least a change amount of the signal difference value generated by the focus adjustment means and the difference value generation means obtained in at least two focusing states of the plurality of focusing states. Signal for determining the distance measurement area used for focus adjustment A focusing device having a sexual evaluation value decision means, and the hand shake prediction means for predicting the amount of hand-shake, the,
When the camera shake amount predicted by the camera shake amount prediction unit is larger than a predetermined value, the setting unit increases the area of each of the set plurality of distance measurement areas,
Based on the AF evaluation value acquired in the distance measurement area excluding the distance measurement area in which the change amount of the signal difference value is determined to be larger than a predetermined value by the reliability evaluation value determination means, the focus adjustment means A focus adjustment device that performs focus adjustment. The reliability evaluation value determination means is a change amount of a signal difference value generated by the difference value generation means obtained in at least two focusing states of the plurality of focusing states and at least two of the plurality of focusing states. Determining a distance measurement area to be used for the focus adjustment among the plurality of distance measurement areas using at least a change amount of the focus evaluation value obtained in one in-focus state;
Obtained in an in-focus state in which the reliability evaluation value determining means determines that the amount of change in the signal difference value is greater than a predetermined value and the amount of change in the signal difference value is determined to be greater than the predetermined value. The focus adjustment unit performs focus adjustment based on the AF evaluation value acquired in a distance measurement area excluding a distance measurement area in which a change amount of the focus evaluation value is determined to be larger than a predetermined value. The focus adjustment apparatus according to claim 1.   It is determined that a value obtained by multiplying the change amount of the signal difference value generated by the reliability evaluation value determination means and the change amount of the focus evaluation value generated by the change amount of the signal difference value is larger than a predetermined value. The focus adjustment apparatus according to claim 2, wherein the focus adjustment unit performs focus adjustment based on the AF evaluation value acquired in the distance measurement area excluding the distance measurement area.   The plurality of ranging areas are divided into a plurality of ranging area groups, the in-focus state where the focus evaluation value is maximized for each of the divided ranging area groups is compared, and the focus adjustment unit adjusts the focus. 4. The focus adjustment apparatus according to claim 1, further comprising a perspective conflict determination unit that selects a distance measurement region group for performing the measurement.   5. The AF evaluation value is normalized by dividing the total sum of the focus evaluation values by the number of distance measurement areas determined to be used for the focus adjustment. The focus adjustment apparatus according to any one of the above.   The plurality of in-focus states are realized by at least one of movement of a focus lens position included in the photographing optical system in an optical axis direction and movement of the imaging element in an optical axis direction. 6. The focus adjustment apparatus according to any one of 5 above.   When the camera shake amount predicted by the camera shake amount prediction unit is larger than a predetermined value, the setting unit reduces the number of the distance measurement areas while maintaining the sum of the areas of the plurality of set distance measurement areas. The focus adjusting apparatus according to claim 1.   An imaging apparatus comprising the focus adjustment apparatus according to claim 1.

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