Steganographic Technique in Z-Domain for Image Authentication (STZ-DIA)

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Nabin Ghoshal


This paper deals with a novel technique for image authentication in Z-domain based on the Discrete two dimensional Z-Transform. The Z-Transform is exploits on sub-image block called mask of size 2 x 2 for frequency components of the corresponding spatial component in row major order. Multimedia Image authentication is done by hiding secret message/image into the real part of the component obtained by discrete two dimensional Z-Transform of the carrier image. A single bit from the authenticating image/message is embedded in middle and low quantum value of carrier image mask. Robustness is achieved through embedding bits in variable positions of carrier image determined by the decimal value of sum of higher three bits of frequency values (i.e. b7+b6+b5). After embedding, a delicate re-adjust phase is incorporated in all frequency components of each mask, to keep the pixel values positive and non-fractional in the spatial domain. The invisibility is conformed by using delicate re-adjust phase. This technique is also applicable for secrete data transmission through carrier color image by hiding secrete data. Experimental results show the robustness and performance of the proposed watermarking technique.

Keywords: Z-Transform, Inverse Z-Transform, DFT, QFT, DCT


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