结构相似性，是一种衡量两幅图像相似度的指标。该指标首先由德州大学奥斯丁分校的图像和视频工程实验室(Laboratory for Image and Video Engineering)提出。SSIM使用的两张图像中，一张为未经压缩的无失真图像，另一张为失真后的图像。(Structural similarity is a measure of the similarity between two images. The target was first presented by the Laboratory for Image and Video Engineering at the University of Dezhou, Austen. One of the two images used by SSIM is an uncompressed and undistorted image, and the other is a distorted image.)