粗糙表面产生的多波长远场散斑图案的散斑延长现象可以用来进行表面粗糙度测量。以抛喷丸表面为研究对象，具体介绍了多波长散斑自相关表面粗糙度测量方法。根据多波长散斑图案的各向同性径向辐射的特征，提出了适用的数字图像处理方法。探讨了局部自相关函数特征长度的选取、数字图像处理过程中的局部窗口尺寸和散斑图像的饱和曝光比等因素对散斑延长效应的影响。通过拍摄和处理每一样品表面多个位置的多波长远场散斑图像，计算了R_{a分别为0.4,0.8,1.6和3.2 μm的表面样块的光学粗糙度指标值。结果表明，该光学粗糙度指标能很好反映被测表面的粗糙程度。}

The speckle elongation effect of speckle pattern produced at the farfield diffraction plane by roughness surface under illumination of polychromatic light can be utilized to measure surface roughness. A roughness measurement of a shotblasted surface by means of polychromatic speckle autocorrelation is introduced. In consideration of the isotropic radial structure of polychromatic speckle pattern, an appropriate digital image processing algorithm is poposed. Several factors affecting the characteristics of the speckle elongation are discussed, which include the determination of characteristic length of local autocorrelation function, the size of local window for digital image processing, and the exposal saturation ratio of speckle image. By capturing and processing polychromatic farfield speckle images obtained from many points on each sample surface, optical roughness index values of sample surfaces with roughness parameter R_{a of 0.4, 0.8, 1.6 and 3.2 μm are calculated, respectively. It is shown that the optical roughness index can be used in scaling well the roughness degree of sample surfaces.}