JP2008185603A - Automatic focusing device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic focusing device and method, wherein focusing on a subject is made possible without detecting the position of a subject within an image plane and without providing a distance measuring means either even when the subject to be focused and various other subjects are mixed within the image plane. <P>SOLUTION: An image signal corresponding to a predetermined area including a subject is obtained while a focusing position N is updated in one direction. By subjecting the image signal to an operation for enhancing an image characteristic of the subject, a focus evaluation value C<SB>N</SB>for evaluating the sharpness of the image is calculated. The focus evaluation values C<SB>N</SB>at corresponding focusing positions are compared and the maximum value C<SB>max</SB>and focusing position N<SB>max</SB>at that time are stored. If it is judged that the C<SB>max</SB>is not updated even after the focusing position N is changed, this focusing position is set to the position N<SB>max</SB>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an autofocus apparatus and method for adjusting a focus position on a subject surface on which an image pattern is formed.

Conventionally, a contrast method is known as a method of performing autofocus based on an image signal.
The contrast method uses the fact that the contrast of the subject image increases during focusing, and the focus evaluation value is a value obtained by integrating the high-frequency components of the image signal within a specific range of the captured image (hereinafter referred to as a focus area). The focus evaluation value is calculated every time the focus position is changed, and automatically adjusted to the focus position where the focus evaluation value is maximized.
On the other hand, in order to focus accurately on a desired subject, an autofocus method is known in which a subject position is detected and focus adjustment is performed using a focus area at the desired subject position.
For example, in Patent Document 1, a plurality of moving bodies are detected by taking the difference between image signals for each frame, and a moving body having a hue similar to the subject to be focused is selected from among the moving bodies. Describes an autofocus system that can always focus on a moving subject by setting a focus area.
In Patent Document 2, the object distance is obtained in a wide area on the screen, and the distance measurement result is selected by the spatial frequency or amplitude pattern of the image signals of a plurality of distance measurement points on the screen, and the main object is selected. An autofocus camera is described in which a subject is distinguished from a miscellaneous subject and focused.
Japanese Patent Laying-Open No. 2003-241065 (FIG. 3) JP 2003-035861 A (page 3-6)

However, the conventional autofocus apparatus and method as described above have the following problems.
First, the contrast method tries to identify the subject only with the contrast information, so the main subject that you want to focus on occupies a part of the screen, and if there are miscellaneous subjects other than the main subject in the screen, If the object is high in contrast, there is a problem that a miscellaneous subject is in focus.
In the technique described in Patent Document 1, a moving object is extracted and a position is detected, and then an object is selected from the moving objects. Therefore, when the main object is moving, the main object is detected and focused. However, when the subject is stationary, there is a problem that the main subject cannot be focused.
In the technique described in Patent Document 2, the main subject is focused by combining the distance measurement of the subject and the pattern determination based on the image signal, but there is a problem in that it is necessary to provide distance measurement means for this purpose. .
In addition, since the steps of ranging, pattern discrimination, and combination thereof are required for each ranging point, there is a problem that rapid focus adjustment may not be possible when the number of ranging points increases.

  The present invention has been made in view of the above-described problems. Even when a subject to be focused on and other miscellaneous subjects are mixed in the screen, the position of the subject in the screen is not detected. It is another object of the present invention to provide an autofocus apparatus and method that can focus on a subject without providing a distance measuring means.

In order to solve the above-described problem, in the invention according to claim 1, an autofocus device for adjusting a focus position on a subject, an imaging unit that acquires an image signal of a predetermined region including the subject, An imaging control unit that varies the focus position of the imaging unit, calculates an image signal of the predetermined area obtained by the imaging unit, calculates a focus evaluation value corresponding to the sharpness of the image, and at each focus position A calculation unit that compares the focus evaluation values, and the focus evaluation value gives a relatively high evaluation value with respect to a sharpness of an image having an image feature of the subject.
According to the present invention, since the focus evaluation value that is an evaluation value with a relatively high sharpness of the image having the image feature of the subject is calculated, a miscellaneous subject having an image feature different from the subject is mixed in the predetermined region. Even in this case, it is possible to detect the focus position where the sharpness of the image of the subject is the highest, and it is possible to prevent focusing on the miscellaneous subject.

According to a second aspect of the present invention, in the autofocus device according to the first aspect, the focus evaluation value is calculated by a calculation that emphasizes the image feature of the subject.
According to the present invention, since the focus evaluation value is calculated by performing the calculation that emphasizes the image feature of the subject, the focus evaluation value becomes higher with respect to the image signal including the image feature of the subject. Accordingly, it is possible to obtain the focus evaluation value by a simple calculation as compared with the case of performing calculation such as image feature extraction or pattern comparison.

According to a third aspect of the present invention, in the autofocus device according to the first or second aspect, the calculation for enhancing the image feature of the subject is performed by a calculation using a spatial filter.
According to the present invention, since the focus evaluation value is obtained by calculation using a spatial filter, simple and high-speed calculation processing can be achieved.
Also, it is possible to deal with subjects having different image characteristics by simply changing the setting of the spatial filter, so that highly versatile processing can be performed.

According to a fourth aspect of the present invention, there is provided an autofocus method for adjusting a focus position on a subject, wherein an image signal of a predetermined area including the subject is obtained by varying a focus position, and the image signal of the predetermined area is acquired. A focus evaluation value for evaluating the sharpness of the image is calculated from the image signal subjected to the calculation, and the focus evaluation values at the respective focus positions are compared. The focus position is adjusted based on the comparison result.
According to the present invention, the focus position is moved to acquire an image signal of a predetermined area including the subject, and the image sharpness of the image is evaluated by performing an operation for enhancing the image feature of the subject in the image signal. The focus evaluation value is calculated, the focus evaluation values at the respective focus positions are compared, and the focus position is adjusted based on the comparison result.
For this reason, even when a miscellaneous subject having an image characteristic different from that of the subject is mixed in the predetermined area, the focus position is adjusted to correspond to the sharpness of the subject image, and the subject can be focused.

  According to the auto-force device and method of the present invention, a focus evaluation value, which is an evaluation value with a relatively high sharpness of an image having an image feature of a subject, is calculated from an image signal of a predetermined region, and at each focus position. Focus evaluation values can be compared and the focus position can be adjusted. Therefore, even if a miscellaneous subject having image characteristics different from that of the subject is present, the subject position is not detected and the distance measuring means is provided. There is also an effect that the subject can be focused.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
An autofocus device according to an embodiment of the present invention will be described.
FIG. 1 is a functional block diagram for explaining a schematic configuration of an autofocus device according to an embodiment of the present invention. FIG. 2A is a schematic plan view for explaining an example of a subject and a miscellaneous subject of the autofocus device according to the embodiment of the present invention. The XY coordinate system is a coordinate axis for referring to the illustrated upper and lower sides (Y-axis direction) and left and right (X-axis direction). FIG.2 (b) is a graph which shows the height in the longitudinal cross-section of Fig.2 (a). FIG. 2C is a graph showing the differential value of the image signal for explaining the images of the surface of the subject and the miscellaneous subject in FIG. 2B and 2C, the vertical axis represents the height and the differential value of the image signal, and the horizontal axis represents the pixel position.

  The autofocus device 1 according to the present embodiment is a device for adjusting a focus position on a subject having an image from which a feature can be extracted. Therefore, any imaging system that captures such a subject can be used in various optical systems such as a camera, a video, and a microscope. However, in the following, regular systems such as a semiconductor wafer and a liquid crystal glass substrate are used. An example of imaging a subject having an image pattern will be described.

As shown in FIG. 1, the schematic configuration of the autofocus device 1 includes an imaging unit 2, an imaging control unit 3, an image capture unit 5, a calculation unit 7, a storage unit 6, a monitor 8, a setting unit 9, and an overall control unit 4. Consists of.
The subject 11 is, for example, a flat plate shape such as a semiconductor wafer or a liquid crystal glass substrate, and a regular image pattern such as a substrate pattern is formed on the surface. Then, it is placed on the sample stage 12.

The imaging unit 2 is for acquiring an image signal of a predetermined region including a subject, and includes an imaging optical system having an appropriate lens configuration and an imaging element such as a CCD area sensor, although not shown.
Then, an image of a predetermined area including the subject 11 is formed on the imaging surface of the image sensor by the imaging optical system, and photoelectric conversion is performed to obtain an image signal 100 having the predetermined area as a frame range.
The imaging unit 2 in the present embodiment shows an example in which the imaging unit 2 is applied to a microscope including an objective lens that magnifies and observes a part of the subject 11 at a predetermined magnification.
The imaging unit 2 can be moved relative to the sample stage 12 by a moving mechanism (not shown), and can be moved to an appropriate position on the subject 11.

  The imaging control unit 3 is a control mechanism for changing the focus position of the imaging unit 2. The focus position can be varied by moving the objective lens position of the imaging optical system of the imaging unit 2 based on a control signal from the overall control unit 4.

The image capturing unit 5 captures the image signal 100 for one frame acquired by the imaging unit 2 as image data together with focus position information.
The arithmetic unit 7 is for calculating a focus evaluation value corresponding to the sharpness of the image in the image feature portion of the image pattern of the subject 11 with respect to the image signal 100 captured by the image capturing unit 5.
The image capturing unit 5 and the arithmetic unit 7 may be configured by hardware each having a dedicated processing circuit. In this embodiment, a computer having a CPU, a memory, an image data input / output interface, and the like is used. This is realized by executing a program corresponding to each processing.

The storage unit 6 is for storing the setting data of the processing of the arithmetic unit 7, the image signal 100 captured by the image capturing unit 5, and the like. For example, a hard disk or the like can be employed.
The monitor 8 displays the image signal 100 captured by the image capturing unit 5 and an operation screen for performing operation input by the setting unit 9.
The setting unit 9 is used to perform an operation input necessary for operating the autofocus device 1. For example, a keyboard for inputting characters and a pointing device such as a mouse can be employed.
Based on the operation input of the setting unit 9, the overall control unit 4 sends necessary control signals to the imaging control unit 3, the image capture unit 5, the calculation unit 7, the storage unit 6, and the monitor 8 to control these operations. Is for doing.

Next, the operation principle of the autofocus device 1 will be described.
For example, as shown in FIG. 2A, the image pattern of the surface of the subject 11 is extended along the Y-axis direction shown in the figure, and is provided on the relatively low-luminance background portion 16 at an equal pitch in the X-axis direction. For example, a foreign object 13 (miscellaneous object) different from the vertical line pattern 15 is attached on the subject 11, and the foreign object 13 is enlarged and observed with a high-magnification objective lens. Think about what to do.
The foreign matter 13 may be any type, and examples thereof include manufacturing defects and dust adhesion.
The range of the image acquired by the imaging unit 2 is an imaging range captured in the field of view of the objective lens as shown in FIG. 2A, and a focus area 14 is set at the center of the field of view.
In the focus area 14, a subject area A ₁ , a foreign substance area B, and a subject area A ₂ are displayed in this order in the longitudinal direction. Then, as shown in FIG. 2B, the foreign material 13 is at a height H1 from an appropriate reference position, and the subject 11 is at a height H2 lower than that.

In such a case, for example, when a differential value of the image luminance is adopted as the focus evaluation value, the pitch of the unevenness on the surface of the foreign material 13 is narrower than the vertical line pattern 15, and as shown in FIG. Since the number of changes in luminance is greater in the foreign substance area B than in the specimen areas A ₁ and A ₂ , the focus evaluation value is highly evaluated. Therefore, the focus position is determined to be a position where the contrast of the differential value of the luminance of the foreign object region B is maximized, and the focus position is focused on the upper surface of the foreign object 13 having the height H1, and may be focused on the subject 11. Can not. For example, in magnifying observation using a 50 × high-power objective lens, the depth of field is shallow, so that if the subject 11 is desired to be observed, defocusing will cause trouble in observing the subject 11.

In the present embodiment, in order to avoid such a problem, it is possible to calculate a focus evaluation value in which the weight is changed with respect to the actual image sharpness between the vertical line pattern 15 of the subject 11 and the foreign object 13. To do.
For this purpose, a spatial filter calculation process that emphasizes the feature of the vertical line pattern 15 is performed on the image signal 100 in the imaging range 14, and a focus evaluation value is calculated as an integrated value of the image data after the calculation process.
FIG. 3A shows an example of a coefficient matrix of, for example, a 3 × 3 spatial filter f for calculating a focus evaluation value according to the embodiment of the present invention. Note that the illustrated XY coordinate system is for indicating the adjacent direction of the pixels and coincides with the XY coordinate system of FIG.

The coefficient matrix of this spatial filter f is represented by a 3 × 3 matrix in which the row direction coincides with the X-axis direction, and each coefficient f _ij is expressed as f ₁₁ = f ₂₁ = f ₃₁ = f ₁₃ = f ₂₃ = f ₃₃ = −1, f ₁₂ = f ₂₂ = f ₃₂ = 2. With such a coefficient matrix, a 3 × 3 spatial filter operation (spatial filter processing) is performed on the image signal in units of pixels of the image signal 100, and processing for enhancing the edge in the Y-axis direction is performed. In the edge enhancement, the brightness of the edge of the vertical line pattern 15 is enhanced, and the brightness of the surface of the foreign material 13 is lost.
Therefore, the focus evaluation value, which is the integrated value, becomes higher as the sharpness of the image pattern of the subject 11 increases substantially, and the focus position at which the subject 11 is in focus can be obtained.

At this time, the positions of the subject 11 and the foreign object 13 are not detected in the focus area 14, but the same result is obtained when the foreign object 13 is automatically removed from the image data by the spatial filter calculation. It is done.
As described above, in this embodiment, the focus evaluation value from which the foreign matter 13 is removed can be obtained by a simple calculation process of spatial filter calculation and integration calculation for image data, so that quick focus position adjustment can be performed.

Here, when performing the focus detection of another subject having a different image pattern, the coefficient of the spatial filter may be changed. As another example of the spatial filter, FIGS. 3B and 3C show coefficient matrices of the spatial filters g and h.
The spatial filter g (see FIG. 3B) is for emphasizing a horizontal line extending in the X-axis direction, and each coefficient is g ₁₁ = g ₁₂ = g ₁₃ = g ₃₁ = g ₃₂ = g ₃₃ = −. 1, g ₂₁ = g ₂₂ = g ₂₃ = 2.
The spatial filter h (see FIG. 3C) is for emphasizing the foreign substance 13 in FIG. 2A, and the coefficients are h ₂₂ = 4, h ₁₁ = h ₁₃ = h ₃₁ = h ₃₃ = −1, h ₁₂ = h ₂₁ = h ₂₃ = h ₃₂ = 0.
Since the spatial filter h is a spatial filter that emphasizes the image characteristics of the foreign matter 13 compared to the subject 11 of the present embodiment, the spatial filter h can be used when focusing on the foreign matter 13. .

  These are a part of examples of the spatial filter, and the arrangement of the coefficients and the size of the coefficient matrix can be appropriately set according to the characteristics of the image to be emphasized.

Next, the autofocus method according to the embodiment of the present invention will be described together with the operation of the autofocus device.
FIG. 4 is a schematic explanatory diagram for explaining a setting screen of the autofocus device according to the embodiment of the present invention. FIG. 5 is a flowchart for explaining each step of the autofocus method according to the embodiment of the present invention. FIG. 6 is a schematic graph for explaining an example of a focus evaluation value obtained by the autofocus method of the present embodiment. The vertical axis represents the focus evaluation value C, and the horizontal axis represents the focus position N.

In the autofocus method of this embodiment, a process for obtaining a focus evaluation value is selected according to the image pattern of the subject 11. FIG. 4 shows an example of a setting screen displayed on the monitor 8.
The setting screen includes a subject image sample display unit 20, a foreign object image sample display unit 21, a process list display unit 22, a process selection display unit 23, an evaluation result display unit 24, an automatic selection button 25, and the like.
The subject image sample display unit 20 and the foreign object image sample display unit 21 are screens for calling and displaying images α and β, which are representative subject and foreign object image samples stored in the storage unit 6 in advance.
These images α and β can be added to the storage unit 6 as necessary, and the operator can perform intuitive and simple operations. Further, these image data are also trial data for trying a process for obtaining a focus evaluation value and confirming its validity.

The process list display unit 22 displays a list of all executable image processes as, for example, process a, process b,. Here, for convenience, “processing a” is used, but it is needless to say that a name, description, icon, or the like that indicates the processing content may be displayed.
An operator can manually select a process in the process list display unit 22.

In the process selection display unit 23, the process selected from the process list display unit 22 is displayed. For example, the processes a, k, and p are selected. Of these, processing a is vertical edge enhancement processing for setting a spatial filter for obtaining a focus evaluation value.
Processes k and p are other image processes, for example, image processing such as horizontal edge enhancement processing, oblique edge enhancement processing, binarization processing, and isolated point removal processing.
The evaluation result display unit 24 indicates the magnitude of the focus evaluation value when the selected processes a, k, and p are executed on the image samples of the subject image sample display unit 20 and the foreign object image sample display unit 21. is there.
In this embodiment, this value is obtained by calculating the processing selected by the processing selection display unit 23 on the image data of the images α and β.
However, for example, all the processes may be calculated in advance at the time of registration of the image sample, and the result may be stored in the storage unit 6 and displayed by calling as necessary.

  For example, when the focus evaluation value is 300 for the image α and the image β is 50, the ratio of the focus evaluation values is as large as 6: 1. Therefore, even if the image β is mixed in the image α, the image α It is understood that the subject is in focus. When the ratio of the focus evaluation values is small, the process selection is performed again.

The automatic selection button 25 is an operation button for automatically performing the process selection process as described above.
When the automatic selection button 25 is pressed, for example, the processing a, b,... Is automatically tried by brute force processing or optimization processing such as a genetic algorithm, and the focus evaluation values of the images α and β are determined. A process that maximizes the ratio is selected.

Next, the focusing operation will be described with reference to FIGS.
In the present embodiment, focus position information when the objective lens of the imaging unit 2 moves in the optical axis direction is detected at predetermined pitches, and each corresponds to a height distance that increases as the distance from the subject 11 of the sample stage 12 increases. Each focus position is described by the number N.
In step S1, an initial value of number N is initially set to N ₀ at a lower limit position where the objective lens does not contact the subject 11.
Also, the counter M is initialized as M = 0.

In step S2, the objective lens position is moved to the position corresponding to the number N by the control signal of the imaging control unit 3.
In step S <b> 3, the image capturing unit 2 captures an image at the moving position of the objective lens, and the image signal 100 is captured by the image capturing unit 5.
In step S4, it executes the selected processing, calculates a focus evaluation value C _N.

In step S5, compared with the maximum value _{C max} and _{C N} of focus evaluation values calculated so far, _{C N} is if the _maximum, and _{N max = N, C max =} C N.
If C _N <C _max , the counter M is updated.
Then, Step S6 is executed.

In step S6, it is determined whether or not the counter M has reached a predetermined value m. If M = m, N is determined to be an end position, and step S7 is executed.
If M <m, it is determined that N is not the end position, and step S8 is executed.
Here, the counter M is for determining whether or not the peak value of the focus evaluation value has been reliably exceeded, and the predetermined value m is set to 1 or more.

In step S7, a control signal is sent from the imaging control unit 3, and the objective lens position of the imaging unit 2 is set to the position of number _Nmax . This completes focusing.
In step S8, N = N + 1 is set, step S2 is executed, and the above process is repeated.

By such an operation, the focus evaluation value C with respect to the focus position N is expressed as an upward convex chevron graph such as a curve 26 indicated by a thick solid line in FIG. Here, by adopting an appropriate spatial filter in the process a, the focus position N _max giving the peak value C _max of the curve 26 becomes an accurate in-focus position with respect to the subject 11.

For example, a curve 27 indicated by a broken line is a graph of the focus evaluation value C for the foreign material 13 when the spatial filter h is used.
Since the spatial filter h calculates the focus evaluation value C of the foreign material 13 having an edge portion with no directivity, the spatial filter h becomes the maximum focus evaluation value C _F at a position of N _F (where N _F > N _max ). A Yamagata graph is obtained.
However, the spatial filter h is not selected because the focus evaluation value of the image β exceeds the image α at the time of setting.

  As described above, according to the autofocus device and method of the present embodiment, by setting the focus evaluation value of the subject to be focused to be highly evaluated compared to other miscellaneous subjects (foreign matter 13), You can focus on the subject accurately.

In the above description, in step S7 in FIG. 5 it has been described in the example so as to move the focus position N _max corresponding to the maximum value C _max of the focus evaluation values, before and after the vicinity of the focus evaluation value C _max A step of calculating the focus position from the three objective lens positions by an appropriate interpolation method may be provided. In this way, the accuracy of the focus position is improved, so that highly accurate focusing can be performed. Also, focusing can be speeded up by increasing the pitch setting of the moving position N of the objective lens. Further, when focusing on the foreign object 13 that is a miscellaneous subject, the process is selected from the process list display unit 22 such that the focus evaluation value of the evaluation result display unit 24 on the setting screen satisfies image α <image β. In this case, focus evaluation for the foreign material 13 is performed using the spatial filter h, and a curve 27 shown in FIG. 6 is created. The moving position of the objective lens corresponding to the maximum focus evaluation value _CF that is the maximum value of the curve 27 is set to the focus.

In the above description, an example in which a plurality of in-focus positions are generated due to the presence of the foreign object 13 as a miscellaneous subject on the subject has been described. For example, as illustrated in FIG. In the case where the subject 28 has transparency, the present invention is also suitable when the front surface 28a and the back surface 28b have different patterns 29 (see FIG. 7B) and patterns 30 (see FIG. 7C), respectively. Can be applied.
That is, the focus position can be adjusted to one of the front surface and the back surface by setting a focus evaluation value by a spatial filter process for emphasizing one of the patterns 29 and 30.
In addition, the present invention is also suitable in the case where irregularities are formed on the surface of the subject and the concave and convex portions have different image patterns.

  In the above description, the focus evaluation value is calculated by performing an operation that emphasizes the image feature of the subject. However, the focus evaluation value has a sufficient difference in the image feature between the subject and the miscellaneous subject. For example, the focus evaluation value may be obtained by performing a process of operating the luminance signal so as to remove the image feature of the subject or the miscellaneous subject. For example, when the miscellaneous subject is a minute dust or the like, examples such as an isolated point removal process or a process of removing a miscellaneous subject by a binarization process can be given.

  In the above description, an example using a spatial filter for obtaining a focus evaluation value has been described. However, other arithmetic processing may be used as long as it is arithmetic processing on an image signal. For example, a large defect image and a binarized image obtained by processing a binarized image multiple times to create a large defect image by removing a thin pattern and then processing the same number of times of shrinkage processing. Can be calculated between the images of the exclusive OR, and a pattern-only image can be created, and the focal position can be adjusted to this pattern. As described above, by specifying the image feature by the spatial frequency component, the focus evaluation value may be calculated by appropriately weighting the spatial spectrum of the image.

It is a functional block diagram for demonstrating schematic structure of the auto-focus apparatus which concerns on embodiment of this invention. FIG. 1 is a schematic plan view for explaining an example of a subject and a rough subject of an autofocus device according to an embodiment of the present invention, a graph showing the height in a vertical section thereof, and a surface image of the subject and the rough subject. It is a graph which shows the differential value of image signal of. It is an example of the coefficient matrix of the spatial filter for calculating the focus evaluation value which concerns on embodiment of this invention. It is a schematic explanatory diagram for explaining a setting screen of the autofocus device according to the embodiment of the present invention. It is a flowchart for demonstrating each process of the autofocus method which concerns on embodiment of this invention. It is a schematic graph for demonstrating an example of the focus evaluation value by the autofocus method of embodiment of this invention. It is the perspective view explaining the other example of a suitable subject for the autofocus method of the embodiment of the present invention, the front view and the back view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Autofocus apparatus 2 Imaging part 3 Imaging control part 4 Overall control part 5 Image capture part 6 Storage part 7 Calculation part 11, 28 Subject 12 Sample stand 13 Foreign object 14 Focus area (predetermined area)
15 Vertical line pattern (image)
29, 30 pattern (image)
100 image signal

Claims (4)

An autofocus device for adjusting the focus position on a subject,
An imaging unit for acquiring an image signal of a predetermined region including the subject;
An imaging control unit that varies a focus position of the imaging unit;
A calculation unit for calculating the focus evaluation value corresponding to the sharpness of the image by calculating the image signal of the predetermined area obtained by the imaging unit, and for comparing the focus evaluation value at each focus position;
The autofocus device, wherein the focus evaluation value gives a relatively high evaluation value with respect to a sharpness of an image having image characteristics of the subject.   The autofocus apparatus according to claim 1, wherein the focus evaluation value is calculated by a calculation that emphasizes an image feature of the subject.   The autofocus apparatus according to claim 1, wherein the calculation for enhancing the image feature of the subject is performed by a calculation using a spatial filter. An autofocus method for adjusting the focus position on a subject,
An image signal of a predetermined area including the subject is acquired by changing a focus position,
Performing an operation to enhance the image characteristics of the subject on the image signal of the predetermined area;
From the image signal subjected to the calculation, a focus evaluation value for evaluating the sharpness of the image is calculated,
Compare the focus evaluation values at each focus position,
An autofocus method comprising adjusting a focus position based on the comparison result.

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