| As one of the critical technologies of microscope imaging system,autofocus technology has significance influence to the efficiency of microscopic slide scanning.At present,off-line autofocus methods are mainly adopted inmicroscopic slide scanning technology in industrial applications field,however,those kind of methods can't get the defocus value quickly in any position,therefore the focal plane modeling of the whole tissue sample is needed before scanning,it results in low efficiency of slide scanning.Some of on-line autofocus methods could achieve high speed of acquisition of defocus value in any position,and the scanning efficiency was improved at some extent.However,some problems still remains,such as the delay time gap of signal acquisition,and the costly of the complexity of the system structure,etc.In order to solve these problems,an autofocus method based on tilt camera and ordinary camera is presented in this paper,which has the advantages of fast and without delay,simplicity of system structure.In this paper,the theory of the autofocus principle of tilt camera focusing was introduced,the focusing system was realized with the modular design,and the performance of the dual cameras focusing system was tested.The main studies as follows:Firstly,in order to enhance the speed of the focusing system,a novel method of obtaining the eigenvalue of the tilt camera was proposed.And the theoretical relationship of the tilt focusing principle is obtained.Three key technical problems were also analyzed and determined,including the selection of tilt angle,the position relation of dual cameras and the mapping relationship between eigenvalue and defocus.The method of selecting tilt angle theory were studied,and the factors influence of the principle of tilting autofocus system were discussed.By choosing system parameters,the influence of depth of field,the resolution and the uniformity towards system could be reduced.The illumination system of single lens aspherical condenser is designed and accomplished.Secondly,according to the theory of tilt focusing discussed above,the fixed structures were designed.The evaluation functions of the feature image wereanalyzed,and the five kinds of image definition functions were compared.The Tenengrad function with best efficiency and unimodality and sensitivity were adopted.The reasonable region of interest was designed after research,which improved the computational efficiency of the algorithm.The design of motion control system is based on STM32 microprocessor.Phased controlling algorithm was designed and analyzed,which could compress the influence of electrical shock and threshold selection towards the stability of imaging.Thirdly,in order to obtain ideal feature image,position of two cameras was calibrated with the Motic Calibration Slide.Through the experiment,the curve of the mapping relationship was determinated,and the slope error and the truncation error of curve was analyzed.The feasibility of tilt focusing system was verified.The Man-machine interface of system was designed,and the integrated function of focusing system was realized.Finally,the performance of tilt focusing system was tested.The system can achieve autofocus function in 1.08 s,and the efficiency of microscopic slide scanning was improved to higher level.The sensitivity of the system is measured as12pixels/?m,slightly lower than the theoretical value.With the 10 X,20X objective lens,working range was measured,which can respectively reach 105.2?m and48.8?m,this could fullfill the demand of tissue samples measurements. |
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