[Retracted] Robust and Secure Zero-Watermarking Algorithm for Medical Images Based on Harris-SURF-DCT and Chaotic Map

Table 3

The test data under conventional attacks.

Conventional attacks	Intensity	PSNR (dB)	NC
Gaussian noise	1%	21.52	0.92
	5%	14.98	0.83
	15%	10.89	0.75
	30%	8.80	0.61
JPEG compression	75%	48.80	1.00
	35%	28.63	0.90
	10%	24.34	0.79
	5%	22.39	0.90
Median filter (3 × 3)	5 times	22.50	0.79
	10 times	21.80	0.79
	20 times	21.29	0.71
Median filter (5 × 5)	5 times	19.02	0.74
	10 times	18.41	0.58
	20 times	17.86	0.63
Median filter (7 × 7)	5 times	17.26	0.58
	10 times	17.06	0.63
	20 times	16.97	0.63