JPH10319313A - Automatic focus detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic focus detecting device which can perforfn high-accurate and stable focus detection and for which image evaluation function is used. SOLUTION: The optical image of a sample 1 is fetched in an image sensor 4 through an objective lens 2 and an image formation lens 3, the image data fetched in the sensor 4 are stored in a memory 7, pixel data within the specified range of the memory 7 are read out to a contrast evaluation calculating means 8, the sum of the adjoining plural pixels of the pixel data is defined as one pixel block, the total sum of the difference of the adjoining pixel blocks or the square of the difference is calculated as the contrast value of the image, also the contrast value of the image is found plural times while changing the combination of the pixel data included in the pixel block in the case of each image input, and focusing degree is found while the sum of those is defined as the image evaluation function.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focus detection apparatus using an image evaluation function to calculate a degree of focus.

[0002]

2. Description of the Related Art As is well known, it is known that an optical image formed by a lens has a feature that the amplitude of the brightness level of the image, that is, the contrast is maximized during focusing. I have. This is a phenomenon that occurs because the light intensity (power spectrum) at each spatial frequency of the optical image becomes maximum at the time of focusing, and a method of detecting the focal position using this phenomenon has been considered.

[0003] Conventionally, as an automatic focus detecting device based on such a concept, as disclosed in Japanese Patent Application Laid-Open No. Sho 56-1022, a self-scanning photoelectric device comprising a plurality of micro photoelectric devices has been used. Used, 2 of the micro photoelectric elements
Extract the signal obtained by dividing the photoelectric output difference between the units by the photoelectric output sum,
Japanese Patent Application Laid-Open No. 57-207 discloses a method in which a peak value in a certain scanning cycle of the signal is used as a contrast signal.
As disclosed in Japanese Patent Publication No. 210-210, with respect to the outputs of two groups of light receiving elements positioned before and after a predetermined focal plane of the optical system, two adjacent light receiving elements are set in each group in a predetermined adjacent relationship. The position of the optical system is detected by performing a non-linear operation by taking an output difference of a predetermined combination including a combination that does not exist, and a difference between two sets of these detection signals is obtained. And outputs an analog signal corresponding to the position of the optical system in an out-of-focus area, and outputs a focus signal of a predetermined level in a focused area having a width. As disclosed in Japanese Unexamined Patent Publication No. 6-78112, while the subject image formed by the imaging optical system is sequentially accumulated by the charge transfer clock from each pixel of the CCD image sensor projected on the light receiving surface, Charge transfer A predetermined number of adjacent pixels are added by resetting at a cycle obtained by multiplying a half cycle of the clock by an integer, and the added charges are sampled. The pixel input range when capturing a subject from the CCD image sensor is determined by the reset cycle. It is known that the maximum value of the number of pixels that can be added in between is set to a pixel range obtained by multiplying the integer by an integer, so that the capturing range of the subject image is fixed and the accuracy of image evaluation is improved.

[0004]

By the way, these conventional focus detection methods are for obtaining a contrast value of an image using two non-adjacent pixels, and for obtaining a contrast value of an image using two adjacent pixels. Divided into things.

In the case of using two pixels that are not adjacent to each other, the difference between the signal levels of the pixels that are not adjacent to each other is determined as the contrast value of the image. In this case, each pixel is thinned and used. Since the obtained contrast value does not use all the image information, the reliability of the calculation result of the contrast value is low, and the accuracy of the obtained focus position is low. If the signal levels of the respective pixels within the image evaluation range are S0, S1, S2,..., For example, | S0−
S4 | + | S4-S8 | and | S2-S6 |
In the case of + | S6−S10 |, there is a difference between the respective contrast values even in the case of the same image.

On the other hand, in the case of using two pixels having an adjacent relationship, the sum of a plurality of adjacent pixels is used as a pixel block to determine the output difference of the adjacent pixel block and to obtain the contrast value of the image. , | (S0 + S1
+ S2 + S3)-(S4 + S5 + S6 + S7) | + |
(S8 + S9 + S10 + S11)-(S12 + S13 +
S14 + S15) | +... And | (S2 + S3)
+ S4 + S5)-(S6 + S7 + S8 + S9) | + |
(S10 + S11 + S12 + S13)-(S14 + S1
5 + S16 + S17) | +..., And even in the case of the same image, a difference occurs between the respective contrast values.

When the image evaluation function is applied to the focus adjustment in this manner, in the process of performing the focus adjustment while calculating the contrast value, even if the position of the image captured by the image sensor or the like is slightly shifted, the contrast value is reduced. The combination of pixels to be obtained has changed,
For this reason, there is a problem that the calculation result of the contrast value becomes unstable, and stable and accurate focus detection cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an automatic focus detection apparatus using an image evaluation function capable of performing highly accurate and stable focus detection.

[0009]

According to the first aspect of the present invention,
The sum of a plurality of adjacent pixels of a predetermined range of pixel data in an image captured by an image sensor onto which a light image of a sample is projected is defined as one pixel block, and the difference between adjacent pixel blocks or the square of the difference is calculated. The sum is calculated as the contrast value of the image, the contrast value of the image is obtained a plurality of times by changing the combination of the pixel data included in the pixel block in each image input, and the sum is focused as an image evaluation function. I want to ask for degrees.

According to a second aspect of the present invention, in the first aspect, the number of times that the contrast value of the image is obtained by changing the combination of the pixel data included in the pixel block is the amount of deviation from the focal position and the necessity of the focus adjustment. It is determined on the condition of at least one of the accuracy.

According to a third aspect of the present invention, in the first aspect, the number of pieces of pixel data included in one of the pixel blocks includes a shift amount from a focus position, a required precision of focus adjustment, image brightness and It is determined on the condition that at least one of the optical conditions of the optical system for capturing the optical image of the sample is a condition.

As a result, according to the first aspect of the present invention,
Since the contrast information to be evaluated in the image signal can be evaluated without omission, the contrast evaluation value does not change even when the image projected on the image sensor is slightly shifted during the focus adjustment operation.

According to the second aspect of the present invention, in a region having a large defocus, a relatively simple contrast evaluation function is used as a contrast evaluation function to prioritize a reduction in processing time, and the complexity increases as the focus position is approached. Can be changed to a highly accurate contrast evaluation function.

According to the third aspect of the invention, the size of the pixel block is changed according to optical conditions such as the amount of deviation from the focal position, the required precision of focus adjustment, the brightness of the screen, and the magnification of the objective lens. The user can select an evaluation function of an image that matches the purpose.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows a schematic configuration of an embodiment to which the present invention is applied. In FIG. 1, reference numeral 1 denotes a sample, and an optical image of the sample 1 is converted into an objective lens 2 and an imaging lens 3.
Through the image sensor 4 to project a light image of the sample 1 onto the image sensor 4.
In this case, the imaging lens 3 projects an optical image of the sample 1 at a predetermined focal position of the image sensor 4. When the image sensor 4 projects a light image at or near the planned focal position by the imaging lens 3, the light image is photoelectrically converted for each pixel and output as image data.

An arithmetic circuit 5 is connected to the image sensor 4, a memory 7 is connected to the arithmetic circuit 5 via an A / D converter 6, and a contrast evaluation operation means 8 is connected to the memory 7. In addition, a timing generator 9 is connected to the image sensor 4, the arithmetic circuit 5, and the A / D converter 6.

Here, the arithmetic circuit 5 includes the image sensor 4
Then, a predetermined process such as waveform shaping is performed on the image captured in. The A / D converter 6 converts the image data processed by the arithmetic circuit 5 into a digital signal. The memory 7 temporarily stores the pixel data digitized by the A / D converter 6. The contrast evaluation calculating means 8 reads out only the pixel data corresponding to the preset image evaluation range from the pixel data written into the memory 7 from the image sensor 4, and calculates the sum of a plurality of adjacent pixels of the pixel data as 1 As one pixel block, a difference between adjacent pixel blocks or a sum of squares of the difference is calculated as a contrast value of an image. The timing generator 9 outputs a drive pulse to the image sensor 4 and outputs a timing pulse for performing signal processing to the arithmetic circuit 5 and the A / D converter 6.

Next, the operation of the first embodiment configured as described above will be described. First, when the sample 1 is irradiated with illumination light from a light source (not shown), a light image from the sample 1 is projected on the image sensor 4 via the objective lens 2 and the imaging lens 3, and the timing generator 9 The optical image is photoelectrically converted for each pixel in accordance with the drive pulse output from the pixel, and is output as pixel data.

The pixel data from the image sensor 4 is sent to an arithmetic circuit 5 and subjected to predetermined processing such as waveform shaping. Then, the A / D converter 6 responds to a timing pulse from a timing generator 9. It is converted to a digital signal and written to the memory 7.

In this state, the contrast evaluation calculating means 8
Reads out only the pixel data within the preset image evaluation range from the pixel data written into the memory 7 from the image sensor 4 and sets the sum of a plurality of adjacent pixels as one pixel block; And the sum of the squares of the differences is calculated as the contrast value of the image, and the contrast value of the image is obtained a plurality of times by changing the combination of the pixel data included in the pixel block in one image input. The degree of focus is obtained based on

In this case, as shown in FIG. 2A, the size of one pixel block is 4 pixels, and pixel numbers I (0), I (1), I (2),. Assuming that the respective signal levels are S0, S1, S2,...
As shown in (b), pixel numbers I (0) to I (3) are defined as pixel block BL1 (1), pixel numbers I (4) to I (7) are defined as pixel block BL1 (2),. EF (0) = | (S0 + S1 + S2 + S3)-(S4 +
S5 + S6 + S7) | + | (S8 + S9 + S10 + S1
1) − (S12 + S13 + S14 + S15) | +..., And similarly, pixel numbers I (1) to I
(4) is a pixel block BL2 (1), a pixel number I (5)
To I (8) as a pixel block BL2 (2),..., And the contrast value EF (1) at this time is EF (1) = | (S1 + S2 + S3 + S4)-(S5 +
S6 + S7 + S8) | + | (S9 + S10 + S11 + S
12) − (S13 + S14 + S15 + S16) | +... Further, as shown in FIG. 2C, the pixel numbers I (2) to I (5) are assigned to the pixel block BL3 (1), and the pixel numbers I (6) to I (9) are assigned to the pixel block BL3 (2).
The contrast value EF (2) at this time is expressed as: EF (2) = | (S2 + S3 + S4 + S5)-(S6 +
S7 + S8 + S9) | + | (S10 + S11 + S12 +
S13) − (S14 + S15 + S16 + S17) | +...

In this way, the contrast values EF (3), EF (4),... Are further obtained while shifting the combination of the pixels included in each pixel block by one pixel, and thereafter these contrast values EF ( 0), EF
(1),..., That is, F (0) + EF (1) + F
(2) + EF (3) +,... Are calculated, and the result is used as the contrast evaluation value of the image.

Accordingly, since the contrast information to be evaluated in the image signal captured by the image sensor 4 can be evaluated without leaking, the image is projected onto the image sensor 4 during the focusing operation. Even when the image to be read is slightly displaced in the direction perpendicular to the optical axis of the objective lens 2, the contrast evaluation value does not suddenly change, and stable image evaluation can be performed.

As a result, such a concept is applied to, for example, a so-called optical path difference system in which two images before and after a predetermined focus are projected on the image sensor 4 and the contrast evaluation values of these two images are compared to adjust the focus. When this method is employed, even in the case of such a method, although it is necessary that the image evaluation ranges before and after the expected focal point match each other, when used in combination with various optical elements for microscopic observation, etc. If the image range is shifted by several pixels, there is a difference in the contrast evaluation results as shown in FIGS. 2B and 2C in the related art, regardless of whether the same image is projected. However, by performing the above-described evaluation operation, the operation result of FIG. 2B can be evaluated as an image including the operation result shown in FIG. It is possible to obtain a stable image evaluation.

In the first embodiment described above, 1
Although the size of one pixel block is set to four pixels, the processing can be performed in the same manner as described above even when the number of pixels is other than four. (Second Embodiment) FIG. 3 shows a schematic configuration of a second embodiment of the present invention, and the same parts as those in FIG.

In this case, the CPU 10 is connected to the contrast evaluation calculating means 8. The CPU 10 gives a control command to the timing generator 9 and reads out the contrast evaluation value calculated by the contrast evaluation calculating means 8 to calculate the direction and amount of shift of the focus.

The stage drive circuit 11 is connected to the CPU 10. This stage drive circuit 11
The driving of the stage 12 on which the sample 1 is mounted in the optical axis direction is controlled based on the direction and amount of shift of the focus calculated by the CPU 10.

Next, the operation of the second embodiment configured as described above will be described with reference to the flowchart shown in FIG.
First, in step 401, pixel data is written into the memory 7. Also in this case, as described above, when the light image from the sample 1 is projected onto the image sensor 4 via the objective lens 2 and the imaging lens 3, the image data is photoelectrically converted by the image sensor 4 for each pixel, and the pixel data is converted. Is output as Then, the pixel data is subjected to predetermined processing such as waveform shaping by the arithmetic circuit 5, converted into a digital signal by the A / D converter 6, and written into the memory 7.

Next, at step 402, the contrast evaluation calculating means 8 sequentially reads out pixel data in a preset image evaluation range from the memory 7, sets the sum of a plurality of adjacent pixels as one pixel block, and Is calculated as the contrast value EF (0) of the image. That is, in this case, as shown in FIG. 2A, the size of one pixel block is 4 pixels, and the pixel numbers I (0), I (1), I (2),.
Are defined as S0, S1, S2,..., First, as shown in FIG.
I (3) is a pixel block BL1 (1), a pixel number I
(4) to I (7) are defined as pixel blocks BL1 (2),..., And the contrast value EF (0) at this time is EF (0) = | (S0 + S1 + S2 + S3)-(S4 +
S5 + S6 + S7) | + | (S8 + S9 + S10 + S1
1)-(S12 + S13 + S14 + S15) | +...

Next, in step 403, the CPU 10
The contrast value EF is output from the contrast evaluation calculating means 8.
(0) is read out, and it is determined whether or not the defocus amount is larger than a predetermined level.

Here, if the defocus amount is larger than the predetermined level and the result is Yes, it is determined that it is not necessary to perform high-precision evaluation.
By calculating the stage drive amount and the drive direction based on (0), and giving the results to the stage drive circuit 11,
The drive of the stage 12 in the optical axis direction is controlled. On the other hand, if the defocus amount is smaller than the predetermined level and is No, it is determined that the pixel is located near the focus, and the CPU 10 instructs the contrast evaluation calculation means 8 to change the pixel block configuration of EF (0) different from EF (0). ) Is output.

Thus, the contrast evaluation calculating means 8
Is a contrast value EF according to a command from the CPU 10.
(2) is calculated. In this case, as shown in FIG. 2C, the pixel numbers I (2) to I (5) are assigned to the pixel block BL3.
(1) Pixel numbers I (6) to I (9) are assigned to pixel block B
L3 (2),..., The contrast value EF at this time
EF (2) = | (S2 + S3 + S4 + S5)-(S6 +
S7 + S8 + S9) | + | (S10 + S11 + S12 +
S13) − (S14 + S15 + S16 + S17) | +...

Then, in step 405, the CPU 10
Is the contrast value E from the contrast evaluation calculating means 8.
F (2) is read, and EF (0) + EF (2)
Is calculated, and it is determined in step 406 whether or not it is near the focal position.

Here, too, if it is not near the focal point, and if No, the process proceeds to step 404, where the contrast value EF (0) + EF
By calculating the stage drive amount and the drive direction based on (2), and giving the results to the stage drive circuit 11,
The drive of the stage 12 in the optical axis direction is controlled. On the other hand, if it is near the focal position and the result is Yes, as the final stage of focusing, the CPU 10 instructs the contrast evaluation calculating means 8 to use the EF (1) having a different pixel block configuration from EF (0), EF (2). ) Is output. As a result, the contrast evaluation calculating means 8
The contrast value EF (1) is calculated in accordance with the instruction.

In this case, the pixel numbers I (1) to I (4) are assigned to the pixel block BL2 (1) and the pixel numbers I (5) to I (5).
(8) is a pixel block BL2 (2),..., And the contrast value EF (1) at this time is EF (1) = | (S1 + S2 + S3 + S4)-(S5 +
S6 + S7 + S8) | + | (S9 + S10 + S11 + S
12) − (S13 + S14 + S15 + S16) | +..., And pixel numbers I (3) to I (6) are assigned to pixel block BL4 (1), pixel numbers I (7) to I (1).
0) as the pixel block BL4 (2),..., The contrast value EF (3) at this time is expressed as EF (3) = | (S3 + S4 + S5 + S6)-(S7 +
S8 + S9 + S10) | + | (S11 + S12 + S13
+ S14)-(S15 + S16 + S17 + S18) | +
… Ask more.

Then, in step 407, the CPU 10
Is the contrast value E from the contrast evaluation calculating means 8.
F (1) and EF (3) are read and EF (0)
+ EF (1) + EF (2) + EF (3) is calculated, and in step 408, it is determined whether or not it is within the focusing range.

Here, too, if it is not within the focusing range and No,
Proceeding to step 404, the contrast value EF (0) + E
The stage drive amount and the drive direction are calculated based on F (1) + EF (2) + EF (3), and the results are given to the stage drive circuit 11, whereby the drive of the stage 12 in the optical axis direction is controlled. On the other hand, it is determined that it is within the in-focus range, and if Yes, the focus adjustment operation ends.

Accordingly, in this case, in a region where the defocus is large, EF (0) is used as the contrast evaluation function.
By using a comparatively simple contrast evaluation function as described above, priority is given to shortening the processing time compared to the accuracy, and EF (0) + EF (2) or EF as the focus position is approached.
By changing to a complex and high-precision contrast evaluation function such as (0) + EF (1) + EF (2) + EF (3), high-speed and high-precision focus adjustment can be realized. That is, in the second embodiment, only EF (0) is used as the contrast evaluation function to be used for focus adjustment depending on the amount of shift from the focus, and EF (0) + EF (2).
Or EF (0) + EF (1) + EF (2) + EF
Since (3) is selectable, EF (0) + EF (1) + EF (2) + EF (3) can be used when extremely high-precision focusing is required, for example, in photographing.
If you select a contrast evaluation function for high accuracy consisting of and observe while moving the sample like visual inspection, accuracy is not required compared to photography,
When high-speed tracking performance is required, the contrast evaluation function is selected according to the focus adjustment mode such that the contrast evaluation function of EF (0) or EF (0) + EF (2) is selected. High-speed and highly accurate focus adjustment can be realized. (Third Embodiment) In this case, in the third embodiment, since the configuration is the same as that of FIG. 3 described in the second embodiment, the description is omitted here with reference to FIG. I do.

The operation of the third embodiment will be described with reference to the flowchart shown in FIG. First, in step 501, pixel data is written to the memory 7. Also in this case, as described above, the light image from the sample 1 is
Image sensor 4 via objective lens 2 and imaging lens 3
When projected on the upper side, the image is photoelectrically converted for each pixel by the image sensor 4 and output as pixel data. And
The pixel data is subjected to predetermined processing such as waveform shaping by the arithmetic circuit 5, converted into a digital signal by the A / D converter 6, and written into the memory 7.

Next, at step 502, the CPU 10 determines whether or not the magnification of the objective lens 2 currently in the optical path is high. Here, if the objective lens 2 has a low magnification and is No, at step 503, an output is made to the contrast evaluation calculation means 8 so as to reduce the number of pixels included in one pixel block. If the magnification is high and the result is Yes, in step 504, the contrast evaluation calculation means 8 is output so as to increase the number of pixels included in one pixel block.

Then, in step 505, the contrast evaluation calculating means 8 sequentially reads out the pixel data of the preset image evaluation range from the memory 7, and specifies the pixel data in the CPU 10 in the same manner as described in the first embodiment. The sum of the adjacent pixels is regarded as one pixel block, and the sum of the differences between the adjacent pixel blocks is calculated as the contrast value of the image.
At 6, it is determined whether or not it is within the focusing range. Here, if not within the focusing range, if No, the process returns to step 501 to repeat the above-described operation. If within the focusing range, Yes, the process proceeds to step 507 and ends the focus adjustment operation.

Accordingly, in this case, when the microscope is used to change the magnification of the objective lens 2 from the extremely low magnification to the high magnification for observation, the frequency distribution of the observed image greatly changes. However, even in such a case, since the size of the pixel block can be changed according to the magnification of the objective lens 2, stable focus detection can be performed with high accuracy even in the range from low magnification to high magnification of the objective lens 2. It can be performed.

In the above description, the size of the pixel block can be changed according to the optical conditions such as the magnification of the objective lens 2. However, the present invention is not limited to this.
The evaluation function of the image can be selected by changing the size of the pixel block according to optical conditions such as the required accuracy of the focus adjustment and the brightness of the screen.

[0044]

As described above, according to the present invention, since the contrast information to be evaluated in the image signal can be evaluated without leaking, the image projected on the image sensor in the process of the focus adjustment operation can be evaluated. Is slightly shifted, the contrast evaluation value does not suddenly change, and stable image evaluation can be performed.

In a region where the defocus is large, a relatively simple contrast evaluation function is used as the contrast evaluation function, so that the processing time is prioritized in comparison with the accuracy, and as the focus position is approached, the processing becomes complicated and highly accurate. By changing to the contrast evaluation function of, high-speed and high-accuracy focus adjustment that meets the purpose can be realized.

It is also possible to change the size of the pixel block according to optical conditions such as the amount of deviation from the focal position, the required accuracy of focus adjustment, the brightness of the screen, the magnification of the objective lens, and to select an image evaluation function. Therefore, also in this case, high-speed and high-accuracy focus adjustment that meets the purpose can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the first embodiment.

FIG. 3 is a diagram showing a schematic configuration of a second embodiment of the present invention.

FIG. 4 is a flowchart for explaining a second embodiment;

FIG. 5 is a flowchart for explaining a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... sample, 2 ... objective lens, 3 ... imaging lens, 4 ... image sensor, 5 ... arithmetic circuit, 6 ... A / D converter, 7 ... memory, 8 ... contrast evaluation calculation means, 9 ... timing generator, 10 ... CPU, 11: Stage drive circuit, 12: Stage.

Claims (3)

[Claims] 1. A pixel block, wherein the sum of a plurality of adjacent pixels of a predetermined range of pixel data in an image captured by an image sensor onto which an optical image of a sample is projected is defined as one pixel block, and the difference or The sum of the squares of the differences is calculated as the contrast value of the image.
An automatic focus detection device, wherein a contrast value of an image is obtained a plurality of times by changing a combination of pixel data included in a pixel block in an image input every time, and a sum thereof is obtained as an image evaluation function to obtain a degree of focus. . 2. The method according to claim 1, wherein the number of times of obtaining a contrast value of an image by changing a combination of pixel data included in the pixel block is determined based on at least one of a shift amount from a focus position and a necessary accuracy of focus adjustment. The automatic focus detection device according to claim 1, wherein: 3. The number of pieces of pixel data included in one of the pixel blocks is determined by a shift amount from a focus position, a necessary accuracy of focus adjustment, an image brightness, and an optical condition of an optical system for capturing an optical image of a sample. The automatic focus detection device according to claim 1, wherein the automatic focus detection device is determined based on at least one of the following conditions.