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This paper proposes a method for calculating the multi-exposure times fast and accurately when the scene has a high dynamic range, minimizing the pictures needed to take and improving the dynamic range of the CCD system. The proposed method first measures the camera's response function referring. After that the median value of the output picture is adjusted to be in the middle range of the system output by changing the exposure time. It can be inferred from the histogram of the current picture whether it's a high dynamic range scene by calculating the number of pixels under exposed and over exposed. Once again the under and over exposed pixels are adjusted to be in the middle according to the camera's response function. Finally different exposed pictures (2 or 3) are fused together by Gaussian function and the dynamic range is compressed by γ correction. Experimental results on UNIQ-UM400 analog camera and a digital acquisition system show that the algorithm works well and solve the problem of low dynamic range of CCD camera.