Design&Realization Of Auto-focusing In FPGA-based Infrared Imaging System

Infrared is the most widely distributed nature radiation, congenital advantage decidesthat infrared thermal imaging infrared has significant advantages. Now, infrared thermalimaging technology has been widely used in military and civil aspects of monitoring,detection and so on. In recent years, with the rapid development of the technology ofinfrared thermal imaging, requirement for the imaging effect becomes high, how toquickly obtain the clear imaging results becomes more and more important. As a keytechnology of rapid access to clear imaging results, auto-focusing technique has developedto be more digital and intelligent focusing method based on digital image processing,which is easy to implement in embedded system.Auto-focusing technique based on digital image processing need to establish theimage clarity evaluation function, to complete the evaluation on the quality of imagingand then complete the final focusing process. In this paper, firstly, basic optical defocusblur model is established and the existing algorithm of image clarity evaluation iscompared by using the model. Combining the engineering demand, image clarityevaluation function is selected.The image data output of infrared detector is difficult to directly be used forauto-focusing, image preprocessing is needed. Here, with existing640×512infraredimaging system in laboratory, auto-focusing system is developed. The image data firstlyneed non-uniformity correction and image bad point correction, considering the influenceof noise, a image smoothing filter is also needed.In this paper, the auto-focusing module is fully implemented in FPGA. For the imagedata through the image preprocessing, image clarity evaluation function is used to judgethe clarity of image, at the same time, window selection algorithm is also used to furtherreduce calculation and stepper motor mountain-climb searching algorithm is completed tooutput motor driver control signal. By experimental verification, the auto-focusingfunction module can ensure real-time and practicality and meet the infrared imagingsystem with large noise.