采用普通减法获取的数字减影效果不太理想，DA影象的优点无法充分体现和利用，根据X光机系统成象原理，提出了运用对数预处理和非线性灰度映射方法对目前普通减影算法进行改进。与普通算法相比，这个改进算法最终获取令人满意的高清晰度和高对比度血管图象序列。

The effect of DSA(Digital Subtraction Angiography) images acquired with general subtraction algorithm is not satisfied, the merit of DSA images cannot be expressed and used extensively. According to the principle of formation of X ray image, this paper described an improved subtraction algorithm called the logarithm non linear grey mapping. In comparison with general subtraction algorithm, this improved subtraction algorithm finally acquired a satisfactory sequence of DSA vascular images with high contrast and high definition.