Study Of Auto-focus Algorithm Base On Athermal Assessing System

Athermal assessing system is an infrared optical system which is used to detect theoptical system’s performance at different temperature environment. This paper studies theautofocus algorithm that base on the athermal assessing system. And the ultimate goal is todesign a program of autofocus for this system to achieve auto-focus function.In order to achieve auto-focus function，the focus criterion functions have been in-depthresearch and experimental include the intensity difference analysis,image statistics andfrequency domain analysis in this paper. And it has been described in detail that thecharacteristics and application conditions of every focus criterion function. It found that somefocus criterion functions of intensity difference are contrary to the principle in the experimentwhen compute the spot image of the athermal assessing system. The detail analysis andreasonable explanation have been given in this paper.The search method of automatically focus is also the necessary step to achieveauto-focus function. It can find the peak position of the autofocus evaluation curve, which isthe positive focal position in the shortest time. So here are four search algorithms have beenproposed in this paper that are always widely used in some studies. Energy concentration israised according to the image of the athermal assessing system. It found that energyconcentration has good effect and is suitable for fine focusing according to the experiments.To achieve auto-focus function of the athermal assessing system, a software ofauto-focus is developed in this paper by writer himself. The software can complete theexperiments of the focus criterion functions and the auto-focus search algorithm. And it cancontrol all the hardware of the system and also can capture images, store images, compute andanalysis.After finishing of the necessary auto-focus theories and the development of thesoftware,an auto-focus program is designed for the athermal assessing system according tothe results of studies. And some tests has been taken with this system. The test result showthat this program of auto-focus can complete autofocus function stable, and has goodrepeatability and high accuracy.