Color Zero-Watermarking Algorithm for Medical Images Based on BEMD-Schur Decomposition and Color Visual Cryptography

Table 3

NC values under median, Gaussian, and mean filtering attacks.

Attack type	Attack intensity	Fundus1	Fundus2	Fundus3	Fundus4	Cerebral1	Cerebral2	Cerebral3	Cerebral4
Median filter	3 × 3	0.9993	0.9997	0.9997	0.9996	0.9952	0.9974	0.9971	0.9957
	5 × 5	0.9987	0.9986	0.9993	0.9982	0.9919	0.9954	0.9938	0.9909
	9 × 9	0.9986	0.9977	0.9988	0.9972	0.9858	0.9922	0.9897	0.9864
Gaussian filter	3 × 3	0.9984	0.9991	0.9995	0.9992	0.9992	0.9983	0.9991	0.9993
	5 × 5	0.9982	0.9990	0.9990	0.9991	0.9991	0.9981	0.9991	0.9990
	9 × 9	0.9981	0.9990	0.9990	0.9991	0.9991	0.9980	0.9989	0.9990
Mean filter	3 × 3	0.9993	0.9995	0.9991	0.9993	0.9992	0.9993	0.9991	0.9994
	5 × 5	0.9980	0.9985	0.9983	0.9981	0.9982	0.9985	0.9983	0.9988
	9 × 9	0.9974	0.9977	0.9982	0.9981	0.9979	0.9980	0.9978	0.9981