Research On Auto-Focusing System For Effect Of Athermalization Tester

The Effect of Athermalization Tester was an equipment that used to measure whether the effect of IR optical system's athermalization met the requirement. In this paper, auto-focusing system for the Effect of Athermalization Tester was researched, which was composed by the infrared image detection system, position controlling component, signal processing circuit and controlling software. The controlling software was make up by the image processing module, the motion control module, the auto-focus module and the athermalization testing module.The automatic focusing algorithms on spatial domain, information domain and frequency domain were researched. According to the features of the infrared image, performances of many auto-focusing algorithms were researched, using there groups of infrared images of the Effect of Athermalization Tester that were gathered from different conditions as researching candidates. Auto-focusing algorithms based on Sum Modulus Difference(SMD) operator and Laplacian operator were used as cursory focusing algorithm and accurate focusing algorithm, because of their well real-time performance, high stability and accuracy. Some key technologies and problem in system auto-focusing realization, such as system image preprocessing, focus strategy, focus point searching algorithm, the division of image focusing region, and the focus curve fitting, were researched and solved. An image focusing region divided algorithm was proposed to improve the focusing accuracy and speed, which identified the target of the focus image using region growing at first, then used the identified target region as operating focus region.The software of the Effect of Athermalization Tester was designed. According to the hardware of the tester, the thermo-regulating system and position controlling component controlling, infrared image acquisition and processing, auto-focusing, and effect of athermalization measuring were achieved. During image acquisition and preprocessing, an image enhanced method based on adaptive threshold was proposed according to different responsiveness of the system image, which generated gray scale transferring function based on the image brightness.When system hardware and software were installed completely, experiments of the Effect of Athermalization Tester were conducted with infrared detectors of short wave, medium wave and long wave, and a variety of targets, which the system was required to use. Experiments proved that every module of the tester run properly, and the system implemented auto-focusing and other required functions correctly. Finally the locating accuracy of the motion controlling module, the auto-focusing repeatability accuracy and the auto-focusing accuracy were measured. According to the testing result, all of the there performance parameters were meet to the design requirements.