“…p, , ∈ (1) Only in this way, can we make pixel vector p became a square, its border length and width is n. Suppose that N input training sample images of size isn × n are given, and the patch size is k × k . First of all ,the local features are selected for each training image by using the patch, then subtract patch mean from each and obtain [3] : = ̅ , , ̅ , , … , ̅ , (2) Where, x , is a mean-removed patch, Constructing the same matrix for all input images and putting them together to get: = , , … , ∈ ℝ , ×…”