Aiming at the characteristics that the contrast of schlieren sphere image is weak, the color of spheretarget is black, and the sphere target is surrounded by background area in the fast collimation process ofintegrated diagnostic system, a method for calculating the schlieren sphere center based on gray stretchingand digital morphology is proposed in this paper. Firstly, the original image is transformed by linear grayscale to enhance the contrast between the schlieren sphere target and the background area, and then the lineargray scale image is binarized by using the OTSU method. Secondly, the background area is transformed into acontinuous connected region by using digital morphological operations such as corrosion and expansion, andsearch for the maximal connected area is the background area. Thirdly, the image of using digital morphologymethod and the image of background area are processed NOR operation to obtain the schlieren sphere target.Finally, on the basis of edge detection by sobel operation, the least square method is used to fit the center andradius of the schlieren sphere. The experimental results show that the algorithm can calculate the center of theschlieren sphere whose gray level difference between the sphere area and the background area is greater than10( the max gray level is 4095). The error between the center coordinate obtained by circle fitting method andthe real center coordinate is less than 2 pixels, which meets the requirement of the integrated diagnostic beamfast automatic collimation system that the accuracy of the schlieren sphere center is less than 3 pixels.
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