CN103529543A - Automatic microscope focusing method - Google Patents

Abstract

The invention provides an automatic microscope focusing method, comprising the steps of utilizing a liquid lens of which the focal length is capable of being controlled by voltage in a microscope optical path to be used as a zooming element, capturing a video stream while performing continuous stepping changing on the driving voltage of the liquid lens, performing focusing evaluation on each captured image, utilizing a focal point searching method to find the liquid lens voltage, positioned at the optimal focusing state, of the microscopic image, and then driving the liquid lens voltage to such a position to finish the automatic focusing. The automatic microscope focusing method fully utilizes the advantages of fast responding speed and small delaying of the liquid lens and solves the problems of slow and inaccurate focusing during the automatic focusing process by using a traditional mobile lifting table.

Description

A Microscope Automatic Focusing Method

technical field

The invention relates to the field of microscopic vision in photoelectric detection technology, and more particularly relates to a method for automatic focusing of microscopic vision.

Background technique

Autofocus system is a key component of automatic video microscope observation, measurement and depth information reconstruction. Research on microscope autofocus system has always been a hot spot in microscope research, especially for automatic video microscopes with large numerical aperture, high magnification and small depth of field.

Currently proposed autofocus systems mainly include active autofocus systems based on external auxiliary measurement equipment and passive autofocus systems based on image quality evaluation. The active autofocus system based on external auxiliary measurement equipment adjusts the distance between the optical imaging system and the imaged target measured by the external measurement equipment to achieve autofocus, but this method is complicated to install and debug, and the system structure is also relatively complicated , and are therefore less used. At present, the passive auto-focus system based on image quality evaluation is widely used, and the focus position is searched by using the auto-focus evaluation function to evaluate the quality of the collected images. The passive autofocus system is simple to implement and easy to use. The current passive autofocus system mainly uses motor-driven platform movement and the use of electric zoom lenses, and uses focus evaluation to feedback the movement, so that the observed object is adjusted to the working distance of the microscope. The method is limited by motor precision, vibration, response speed and hysteresis error in the process of motor movement, which causes the limitation of focusing accuracy.

Liquid lens is a new type of optical lens based on the principle of electro-wetting effect. By changing the voltage applied to the electrodes at both ends of the lens, its focal length can be changed quickly and accurately. Therefore, it can be used to replace the electric zoom lens in the microscopic optical path. Because The liquid lens is fast and stable in response, which improves the speed and precision of the autofocus system.

Contents of the invention

The technology of the present invention solves the problem: the variable-focus liquid lens is used to realize automatic focusing of the microscopic system, so as to ensure that the microscopic imaging system can quickly and accurately acquire high-definition images.

The technical scheme of the present invention is: the device that realizes the method of the present invention is made of optical microscope, camera, liquid lens and its driving part and automatic focusing system software, and liquid lens is fixed on the rear end surface of microscope objective lens by specially designed adapter , the automatic focusing system software can realize the comprehensive control of the liquid lens, the precision electric lifting platform and the camera, and can realize the one-button automatic focusing function at the same time. The automatic focusing software realizes the step change of liquid lens driving voltage and the synchronization of video stream capture and image focus evaluation. Through the maximum value search algorithm, the liquid lens driving voltage when the image focus evaluation value is maximum is obtained, and the liquid lens driving voltage is adjusted. Up to this value, the auto focus is completed.

Description of drawings

By describing the embodiments of the present invention in detail in conjunction with the accompanying drawings, the above-mentioned and other objects, features and advantages of the present invention will become more clear, wherein:

Fig. 1 is a flow chart of an automatic focusing method according to an embodiment of the present invention.

Fig. 2 is an optical path diagram of a microscope system according to an embodiment of the present invention.

Fig. 3 is a liquid lens adapter according to an embodiment of the present invention.

Fig. 4 is a schematic block diagram of a liquid lens according to an embodiment of the present invention.

Detailed ways

Embodiments according to the present invention will be described below with reference to the drawings. In the drawings, like reference numerals denote like elements throughout.

The optical path of the microscope imaging system according to the embodiment of the present invention is described with reference to the accompanying drawings.

Fig. 1 shows a flow chart of an automatic focusing method according to an embodiment of the present invention. In the autofocus process, the liquid lens is used as the zoom element, the focus evaluation operator is used to evaluate the focus state of the microscopic image in real time, and the focus search algorithm is used to servo-control the driving voltage of the liquid lens until the microscopic image has the highest focus evaluation value, and the microscopic image Focusing is complete when the sharpest state is reached.

Fig. 2 shows an optical path diagram of a microscope system according to an embodiment of the present invention. As shown in FIG. 2 , the optical path 20 of the microscope system includes a measured object 21 , an objective lens 22 , a liquid lens 23 , an adapter mirror 24 and a detector CCD25 . The liquid lens 23 is placed between the objective lens 22 and the adapter lens 24 .

FIG. 3 shows a liquid lens adapter 30 according to an embodiment of the present invention. As shown in Figure 3, the adapter is composed of two parts 31, 32. The lower thread of 31 can be connected with the upper thread of 32, and the liquid lens can be fixed inside it. The upper part of 31 can be connected with the adapter mirror through the thread, and the lower part of 32 can be It is connected with the objective lens through threads, and the groove on the side of 32 can place the driving wire of the liquid lens.

Next, the principle of the present invention is briefly explained.

Firstly, the principle and characteristics of liquid lens are briefly introduced. Liquid zoom lens is a new type of optical lens based on the principle of electrowetting effect. Fig. 4 shows the working principle diagram of the liquid lens. The liquid lens contains two liquids, one is a conductive liquid and the other is an insulating liquid. The two liquids are mutually non-wetting and have a certain difference in refractive index. The two liquids are placed in a container whose inner wall is coated with transparent electrodes, and a layer of hydrophobic dielectric layer is deposited on the surface of the transparent electrodes, so that two contact angles and contact surfaces are formed between the two layers of liquids. When a voltage is applied between the conductive liquid and the transparent electrode on the inner wall, the electric field between the conductive liquid and the electrode changes, so that the contact angle and the shape of the contact surface change, and the focal length of the liquid lens also changes. The liquid zoom lens technology is basically mature now, there are already market-oriented products, there are agents in China, and the price is relatively low, a liquid zoom lens is about several hundred yuan. Utilizing the variable focus characteristics of the liquid lens, it is added to the digital microscope imaging system. When the driving voltage of the liquid lens changes, its focal length also changes. According to the double-lens focal length synthesis formula, the synthetic focal length of the entire microscopic system can be known Therefore, the distance of the object plane that can be clearly imaged by the microscopic imaging system also changes. Therefore, there is a one-to-one correspondence between the driving voltage of the liquid lens and the digital microscopic system that is added to the liquid lens. This characteristic of the liquid lens makes It becomes possible as a passive distance measuring element.

Then, the focus evaluation function for quantitatively examining the sharpness of captured images in the present invention will be introduced. Compared with the out-of-focus image, the in-focus image has clearer edges, more details in the spatial domain, and more high-frequency components in the frequency domain, so many evaluations are performed in the spatial domain and frequency The focus evaluation algorithm of is proposed. In the invention, we use the Tenegrad function in the space domain (as shown in formula 1) to judge the focus and defocus state of the image.

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; TEN</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; Height</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}\underset{\mathrm{<span\; class="notranslate">\; Width</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; G</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, G _x (x, y) and G _y (x, y) are the convolution results of the original image and Sobel operators S _x and S _y . The Sobel operator is as follows:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\left(\begin{array}{ccc}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 2</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right)<span\; class="notranslate">\; ,</span>$ ${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; =</span>\left(\begin{array}{ccc}\mathrm{<span\; class="notranslate">\; 1</span>}& \mathrm{<span\; class="notranslate">\; 2</span>}& \mathrm{<span\; class="notranslate">\; 1</span>}\\ \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}& \mathrm{<span\; class="notranslate">\; 0</span>}\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}& <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right)$

Then introduce the maximum value search algorithm in this automatic focusing software, the present invention adopts hill-climbing method, and its basic steps are:

1) Set the initial focusing direction, fine-tune one step along the initial focusing direction, and change the focusing direction if the value of the focusing function drops by more than a threshold.

2) Adjust the focus in large steps along the focusing direction, find the drop point of the focus function and return to the maximum point recorded during the focusing process.

3) Fine-tune a small step along the large-step focusing direction. If the focus function value increases, the small-step fine-tuning direction is correct. Otherwise, change the small-step focusing direction.

4) Find the descending point along the small-step focusing direction, find the descending point of the focus function, and return to the maximum value recorded during the focusing process, which is the correct focus point.

During the experiment, after changing the driving voltage of the liquid lens once, the camera is used to capture the current image, and at the same time, the focus evaluation function mentioned above is used to evaluate the focus. When the driving voltage of the liquid lens is reached, the automatic focusing is completed.

While example embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that changes may be made to these example embodiments without departing from the scope and spirit of the invention as defined in the claims and their equivalents. Variations in various forms and details.

Claims (3)

1. A microscope automatic focusing method, the method device is made of optical microscope, liquid lens and drive module thereof, digital camera, computer and autofocus software, it is characterized in that: liquid lens is introduced in optical microscope light path, utilizes liquid lens As a zoom element, changing its diopter by controlling the electrode voltage at its two ends causes the focal length of the entire optical system to change. The change of the driving voltage of the liquid lens is servo-controlled by performing focus evaluation on the video image until the focus evaluation value of the video image is the highest and the image reaches the clearest state. 2. The microscope automatic focusing method according to claim 1, characterized in that: the focal length of the entire microscope optical system is controlled by the liquid lens drive voltage, and when the liquid lens drive voltage is changed, its diopter change causes the entire micro-optic system to change, Unlike fixed objects, when the driving voltage of the liquid lens is continuously changed and the voltage of the liquid lens is optimally focused, the microscopic image presents a change process from blurred to clear and then to blurred. 3. the microscope automatic focusing method according to claim 1, is characterized in that: automatic focusing software realizes the comprehensive control function to liquid lens focal length, camera image capturing, image quality evaluation, adopts automatic focusing evaluation function to carry out real-time evaluation to image , and use the focus search algorithm to perform servo control on the driving voltage of the liquid lens in real time, so that it converges to the driving voltage of the liquid lens that can present the best focused image.

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