JPH04195110A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To obtain high-accurate automatic focusing without increasing the number of searching lines by providing a movement control means which moves an observing surface to a position where the focusing is attained. CONSTITUTION:An image pickup means 11, a storage means 20 which stores the brightness data of an objective image, which is picked up, by a picture element unit and a movable means 14 where the observing surface is fitted and which can be moved in a direction perpendicular to the observing surface are provided. Besides, the movement control means 22 which calculates the differential value of the brightness data of the picture elements which are closely brought into contact with each other, calculates difference quantity between the maximum value and the minimum value of the differential value and moves the movable means 14 to the position where the focusing is attained based on the difference quantity at the same time is provided. Thus, the effect of noise from the outside and the inside of a camera is reduced without increasing the searching lines and the high-accurate automatic focusing is obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an autofocus device for optical equipment.

[Prior Art] Conventional autofocus devices employ a method of measuring distance using reflected light from an object, or a method of measuring the distance using reflected light from an object, or a method of measuring brightness of an image of the object obtained through an optical system. A method of recognizing the degree of blur in an image itself using the method is widely used.

As the latter method of using luminance information, a method using a histogram distribution of luminance of an image taken by a camera or a differential value is generally known. In the method using this differential value, CC
D (Charge coupled device) Sequentially find the absolute value of the brightness difference (differential value) between a pixel on the search line set on the image captured from the camera and the pixels adjacent to this pixel, and then calculate the value on the search line. The maximum value at is taken as a focus degree parameter representing the focus degree.

This focus degree parameter increases as the image approaches the in-focus image, decreases after passing through the in-focus point, and changes into a mountain shape with the in-focus point as the apex. Therefore, autofocusing using the so-called hill climbing method becomes possible.

Further, as the above-mentioned focusing degree parameter, in addition to the one that uses the absolute value of the maximum value of the brightness difference on the search line, there is also one that uses the absolute value of the minimum value of the brightness difference on the search line.

[Problems to be Solved by the Invention] In the above-mentioned conventional autofocus device, C.
When an image is obtained using a CD camera, there is a problem in that noise from outside and inside the camera causes pixels on the image to have brightness different from the actual brightness.

In other words, if the brightness of this pixel is extremely high or low, the above-mentioned focus degree parameter may show a larger value than the focus degree parameter at the original focus point, and it is difficult to focus on a point other than the focus point. It will be seen as a focal point.

As a solution to this problem, a method is adopted to reduce the influence of noise by increasing the number of search lines and averaging the maximum value of the focus degree parameter on each search line, but this method has the disadvantage of significantly increasing processing time. be.

Therefore, an object of the present invention is to provide an autofocus device that can reduce the influence of noise without increasing the number of search lines, and can obtain highly accurate autofocus.

[Means for solving the problem] The observation surface is attached to an imaging means for imaging an object on the observation surface, a storage means for storing luminance data of the object image captured by the imaging means in pixel units, and an observation surface. A movable means that can be moved in a direction perpendicular to the observation plane, calculates the differential value of the luminance data of adjacent pixels, calculates the difference between the maximum value and the minimum value of this differential value, and calculates the difference between the maximum value and the minimum value of this differential value, and based on this difference and movement control means for moving the movable means to a focused position.

[Operation: The image of the object on the observation surface is captured by the imaging means, and the luminance data of the object image is stored in the storage means pixel by pixel. The movement control means calculates the differential value of the luminance data of adjacent pixels, and further calculates the difference between the maximum value and the minimum value of this differential value, and it is possible to move to the in-focus position based on the calculated difference. As the means moves, the viewing surface moves.

Therefore, the influence of noise can be reduced without increasing the number of search lines, and highly accurate autofocus can be obtained.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

This embodiment is an example in which an autofocus device according to the present invention is used in a microscope.

FIG. 1 is a block diagram of the main parts of an autofocus device according to the present invention.

As shown in the figure, the autofocus device of this embodiment includes a CCDC camera, a lens barrel I2, an eyepiece 13,
Z-axis stage 14, lifting handle 15, drive shaft 16,
pulse motor 17, object 18, A/D conversion circuit 19,
An image memory 20, a drive circuit 2I, and a processing device 22 are provided.

CCD camera 11 used for autofocus
is the two-axis stage I4 and the object 18 via the lens barrel 12.
It is arranged above the image memory 2G and connected to the image memory 2G via the A/D conversion circuit 19. Also, CCD camera 1
1 is fixed to the lens barrel I2 so that when a focused image of the object 18 is obtained by the eyepiece 13, a similar focused image is formed on the lens of the CCD camera 11.

An eyepiece lens 13 is attached to the side of the lens barrel 12.

An object 18 is placed on the top of the Z-axis stage 14, and a lifting handle I5 is attached to the side of the two-pongee stage 14.

The lifting handle I5 is connected to a pulse motor I7 via a drive shaft 16, and the pulse motor 17 is connected to a drive circuit 2.
Connected to 1.

The two-axis stage 14 is configured to be movable in two directions shown in the figure by driving a pulse motor 17.

The image memory 20 and the drive circuit 21 are connected to the processing device 22
It is connected to the.

The CCD camera 11, lens barrel 12, and eyepiece lens 13 are one embodiment of the imaging means of the present invention. Image memory 20 is one embodiment of the storage means of the present invention. Z-axis stage 14 is one embodiment of the movable means of the present invention.

Pulse motor 17, drive circuit 21 and processing device 22
This is an embodiment of the movement control means of the present invention.

FIG. 2(A) is an explanatory diagram showing the configuration of the search line 20c of the image memory 20 of the autofocus device of FIG.
Figure (B) is an enlarged view of the main part of Figure 2 (^).

As shown in FIG. 2(A), the image memory 20 is provided with a plurality of scanning lines 20a and 20b along the vertical and horizontal directions, and as shown in FIG. 2(B),
A pixel unit is formed from one section constituted by these scanning lines 20a and 20b.

The search line 20c is constructed by assigning arbitrary adjacent scanning lines 203 in the horizontal direction.

Note that the search line 20c is any vertically adjacent scanning line 20.
It may be configured by assigning b. Further, the number of search lines 20c may be plural.

FIG. 3 is a block diagram of the processing device 22 of the autofocus device of FIG. 1.

As shown in the figure, the processing device 22 includes an arithmetic logic unit (ALU) 22a and a random access memory (RA).
M) 22b, a central processing unit (CPU) 22c, and a random only memory (ROM) 22d.

The processing device 22 is configured to control the drive of the pulse motor 17 via the drive circuit 21 based on luminance data sent from the image memory 20 and described later.

A control program for performing this control is stored in the ROM 22d.

Next, the operation of the above embodiment will be explained.

With the object 18 placed on the top of the two-axis stage 14, an image of the object 18 is captured by the CCD camera 11, and this image data is converted into an electrical signal, and further converted by the A/D conversion circuit 19. It is A/D converted and temporarily stored in each pixel of the image memory 20 as luminance data.

When the brightness data is stored in each pixel of the image memory 20,
The image memory 20 scans the brightness data of pixels on a predetermined search line 2Oc, and the brightness data of each pixel is sent to the CPU 22c of the processing device 22.

FIG. 4 is a flowchart schematically showing a part of the control program stored in the ROM 22d.

As shown in the flowchart of the figure, autofocus control in the above embodiment is performed as follows.

First, in step Sl, luminance data of each pixel is input from the image memory 20 to the CPU 22c.

Next, in step S2, the CPU 22c
By controlling 22a and RAM 22b, the luminance difference (differential value) between the pixel on the search line 2Oc of the image memory 20 and a neighboring pixel is sequentially determined. After the brightness differences are determined for all pixels on the search line 2Oc, the maximum and minimum values of the brightness differences are determined,
The difference between these maximum and minimum values (focus degree parameter) is determined. That is, in step S2, a focus degree parameter is calculated.

Next, in step S3, the focus degree parameter calculated in this way is applied to the two-axis stage I in this state.
4 is stored in the RAM 22b of the processing device 22 along with the position data in the two directions shown in the figure.

Next, in step S4, the pulse motor 17 is driven by a command to the drive circuit 21 from the CPU 22e, and the position of the Z-axis stage 14 is moved by a predetermined distance in the two directions shown in the figure.

The above processing operation, that is, inputting the luminance data of each pixel from the image memory 20 to the CPU 22c (step Sl)
, calculating the focus degree parameter (step 32), storing the focus degree parameter and the position of the Z-axis stage 14 (step S3), and moving the Z-axis stage 14 a predetermined distance (step 54) are performed in step S5. is repeated until it is determined that the focus degree parameter continues to increase and then decreases.

If it is determined in step S5 that the focus degree parameter increases and then decreases, the next step S
In step 6, the maximum value of the focus degree parameter stored in the RAM 22b is searched, and the position of the Z-axis stage 14 corresponding to when the focus degree parameter is the maximum value is detected.

2-axis stage 1 when the focus parameter takes the maximum value
Since the position No. 4 is the focus position, in the next step S7, the pulse motor 17 is driven to move the Z-axis stage 14 to that position.

Therefore, according to the above embodiment, since it is not affected by sudden changes in brightness difference due to noise, the influence of noise can be reduced without increasing the number of search lines, and highly accurate autofocus can be obtained. .

In addition, since the number of search lines in the image memory 20 is not increased, the influence of noise can be reduced without the problem of increased processing time that would occur when the number of search lines is increased, and the maximum value of the brightness difference Or, rather than using only the absolute value of the minimum value,
It becomes possible to perform highly accurate autofocus and improve the reliability of automation.

Note that the search line 2 when calculating the brightness difference in step S2
The pixels on Oc may be configured to select pixels that are spaced apart from each other at a constant interval, or may be configured to select pixels that are adjacent to each other. Selection of a pixel combination for obtaining such a brightness difference is possible by actually performing focusing and selecting a pixel combination that yields a good result.

Further, in step S4, when the Z-axis stage 14 moves by a predetermined distance in the two directions shown in the figure, if the moving direction of the Z-axis stage 14 becomes, for example, a defocus direction due to the moved distance, the in-focus Since the degree parameter decreases, it may be recognized by the processing device 22 that it is moving in the wrong direction.

Therefore, in such a case, the pulse motor 17 may be driven so that the two-axis stage 14 moves in the opposite direction, that is, fine adjustment may be made.

Furthermore, the predetermined distance by which the position of the Z-axis stage 14 is moved in step S4 is determined by the lens of the COD camera 11 and the direction of movement from the focus direction, even though the position is moved in a fixed direction as described above. It is possible to make a selection taking into account the fact that it will be in the defocus direction.

[Effects of the Invention] As explained above, the present invention includes an imaging means for imaging an object on an observation surface, a storage means for storing luminance data of the object image captured by the imaging means in pixel units, and an imaging means for capturing an image of an object on an observation surface. A movable means that is attached and movable in a direction perpendicular to this observation plane calculates the differential value of the luminance data of adjacent pixels, calculates the difference between the maximum value and the minimum value of this differential value, and calculates the difference between the maximum value and the minimum value of this differential value. and a movement control means for moving the movable means to an in-focus position based on the amount of difference, thus reducing the influence of noise and obtaining highly accurate autofocus without increasing the number of search lines. be able to.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of main parts of an autofocus device according to the present invention, FIG. 2(A) is an explanatory diagram showing the configuration of a search line of an image memory of the autofocus device of FIG. 1, and FIG. 2(B) is an enlarged view of the main part of Fig. 2 (A), Fig. 3 is a configuration diagram of the processing device of the autofocus device of Fig. 1, and Fig. 4 is a ROM
2 is a flowchart schematically representing a part of a control program stored in the computer. 11...CCD camera, 12...lens barrel, 13...eyepiece, 14...Z-axis stage, 15...for lifting Handle, 16...
... Drive shaft, 17 ... Pulse motor, 18
...Object, 19...A/D conversion circuit, 20...Image memory, 21...Drive circuit, 22...Processing Device, 22a ---
---ALU, 22b--RAM, 22c
m...-CPU. 22d...---ROM0 Hesitation 1 Figure 4

Claims (1)

[Claims] an imaging means for capturing an image of an object on an observation surface; a storage means for storing luminance data of the object image captured by the imaging means in pixel units; and a direction perpendicular to the observation surface to which the observation surface is attached. a movable means that is movable to a pixel; and a movable means that calculates a differential value of the luminance data of adjacent pixels, calculates a difference between a maximum value and a minimum value of the differential value, and moves the movable means based on the differential value. An autofocus device comprising a movement control means for moving the device to a focused position.