Gradient method,surface fitting and N-R method are 3 main sub-pixel displacement algorithms of digital speckle correlation method to improve the precision of the measuring system. The principles of three kinds of algorithm were studied and numerical simulation was carried out. To compare the different precision from 3 methods under noise,the computer models generate a series of speckle gram whose displacement is 0. 01 pixels and different Gaussian noise was added in generated graphics. The results showed that in the precision requirement in 0. 01 pixels,the upper bounds on noise variance of gradient method and N-R method are respectively 0. 006 and 0. 000 5,and the calculation precision of surface fitting method has huge uncertainty,gradient method is more suitable for engineering application.%梯度法、曲面拟合法和 N-R 法是数字散斑相关方法中提高位移测量精度的3种主要亚像素位移算法。研究了3种算法的原理并进行了数值模拟仿真。首先使用计算机模拟生成一系列位移为0.01 pixel 的散斑图，并在生成的图像中添加方差不同的高斯噪声，对3种算法在噪声条件下的精度进行比较，结果显示在精度要求为0.01 pixel 时，梯度法的噪声方差上限为0.006，N-R 法的噪声方差上限为0.0005，而曲面拟合法的计算精度具有较大不确定性，无法保证精度，梯度法更适用于工程应用。
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