Table 6 Pixel correlation coefficients in three directions: horizontal (H), diagonal (D) and vertical (V) for encrypted images.

From: A secure and efficient image encryption scheme based on chaotic systems and nonlinear transformations

Encrypted image

H

D

V

Mandrill

0.00307613

0.000809074

− 0.00521955

Peppers

− 0.00329259

− 0.00567403

0.000306954

F16

0.00046871

− 0.00129673

− 0.0015519

Sailboat

− 0.00579529

0.00357263

0.00601578

Tree

0.00122393

− 0.00043615

− 0.00441973

Apples

− 0.00213933

0.00248506

− 0.010287

Average

− 0.00107641

− 0.00009002

− 0.00025259

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