earticle

영어

Watermarking techniques are mandatory to secure digital communication. For optimal technique, a high signal to noise ratio and normalized correctional is required. In this paper, a method that belongs to digital watermarking is proposed based on chaotic map through image gradient and least significant bit. The image is segmented into un-correlated blocks and calculate the gradient of each block. The gradient of the image expresses the rapid changes in an image. When watermark used chaotic substitution box (S-Box), it scrambled based on piecewise linear chaotic map (PWLCM). PWLCM has positive Lyapunov exponent and better balance property as compare to other chaotic map. This suggested s-box technique is capable to produce dispersive sequence with high nonlinearity in the generated sequence. By modifying the least significant bits of the original image the watermark signal is embedded based on the image gradient. Image block gradient ,direction and magnitude decide how much embeding can be done. The embedding payload compromises between robustness and imperceptibility. By the reverse operation, a watermarked image is obtained. In comparison with other methods, experimental results show satisfactory progress in robustness against several image processing and geometrical attacks while maintaining the imperceptibility of the watermark signal.