Fig. 1. L2,1-norm based on collaborative sparse representations

Fig. 2. Test images

Fig. 3. (a) Convergence of objective function Eq. (5) along with the increasing of iteration number; (b) average PSNR with different clustering number K; (c) average PSNR with different dictionary size M; (d) average PSNR with different λ

Fig. 4. Visual comparisons of different SR results on No. 1 image using different methods.(a) Original HR image; (b) Bicubic algorithm; (c) NE + LLE algorithm; (d) SCSR algorithm; (e) Zeyde algorithm; (f) ANR algorithm; (g) A+ algorithm; (h) SRCNN algorithm; (i) proposed algorithm

Fig. 5. Visual comparisons of different SR results on No. 3 image using different methods.(a) Original HR image; (b) Bicubic algorithm; (c) NE + LLE algorithm; (d) SCSR algorithm; (e) Zeyde algorithm;(f) ANR algorithm; (g) A+ algorithm; (h) SRCNN algorithm; (i) proposed algorithm