First we construct a covariance matrix from sample images , then compute the eigenvalues and corresponding eigenvectors of the covariance matrix , construct a feature matrix with the eigenvectors . then every images in database can be projected into the feature matrix and gain a projection vector , so does the input image . then we can judge the resemblance between input image with each image in database by computing the distance between their projection vectors 我们首先根据采集的样本图像构造一个协方差矩阵，然后求取该矩阵的特征值，以这些矩阵特征值对应的特征向量构造出一个特征空间，然后将输入图像向该特征空间映射，将获取的映射系数与样本库中图像的映射系数进行距离计算，根据计算出的距离判定输入图像与样本图像间的匹配程度。
