Figure 6.

Key sensitivity tests: (a,e): plain-image and its histogram; (b,f): $E1$ and its histogram; (c,g): $E2$ and its histograms; (d,h): $|E1-E2|$ and its histogram; (i): decrypted image of $E1$ using key set $k_{ey}\left(1\right)$ ; (j–n): decrypted image of $E1$ using security key set $k_{ey}\left(2\right)$, $k_{ey}\left(3\right)$, $k_{ey}\left(4\right)$, $k_{ey}\left(5\right)$ or $k_{ey}\left(6\right)$.