94 IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE JUNE 2022 12 3 k-2 k-1 k n-2 n-1 n (a) Construction Median 12 3 k k-2-1 k-3 n n-1-2 n Median Median 12 3 k k-2-1 k-3 n n-1-2 n Segmentation Reconstruction Algorithm 12 3 k k-2-1 k-3 n n-1-2 n Reconstruction (b) Median Median Median (c) (d) FIGURE 5. The subspace structure-based infrared small-target detection methods. (a) The original image. (b) The original patch image (PI). (c) The target PI (top) and background PI (bottom). (d) The detection map (top), target image (center), and background image (bottom).