The Journal of Korean Institute of Communications and Information Sciences (한국통신학회논문지)

The Korean Institute of Commucations and Information Sciences (한국통신학회)
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Hybrid Watermarking Technique using DWT Subband Structure and Spatial Edge Information

DWT 부대역구조와 공간 윤곽선정보를 이용한 하이브리드 워터마킹 기술

  • 서영호 (광운대학교 전자재료공학과) ;
  • 김동욱 (광운대학교 전자재료공학과)
  • Published : 2004.05.01
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Abstract

In this paper, to decide the watermark embedding positions and embed the watermark we use the subband tee structure which is presented in the wavelet domain and the edge information in the spatial domain. The significant frequency region is estimated by the subband searching from the higher frequency subband to the lower frequency subband. LH1 subband which has the higher frequency in tree structure of the wavelet domain is divided into 4${\times}$4 submatrices, and the threshold which is used in the watermark embedding is obtained by the blockmatrix which is consists by the average of 4${\times}$4 submatrices. Also the watermark embedding position, Keymap is generated by the blockmatrix for the energy distribution in the frequency domain and the edge information in the spatial domain. The watermark is embedded into the wavelet coefficients using the Keymap and the random sequence generated by LFSR(Linear feedback shift register). Finally after the inverse wavelet transform the watermark embedded image is obtained. the proposed watermarking algorithm showed PSNR over 2㏈ and had the higher results from 2％ to 8％ in the comparison with the previous research for the attack such as the JPEG compression and the general image processing just like blurring, sharpening and gaussian noise.

본 논문에서 제안되는 워터마크(Watermark) 삽입 알고리즘은 웨이블릿 변환 영역에서 구성되는 부대역간의 트리구조(Tree structure)와 공간 영역에서의 윤곽선 정보를 이용하여 워터마크를 삽입할 영역을 결정하고 삽입한다. 먼저 생성되는 고주파 성분의 부대역으로부터 저주파 부대역으로 중요 주파수 영역을 예측하게 되는데 웨이블릿 변환영역에서 구성된 트리구조에서 높은 주파수를 가지는 LHI 부대역을 4${\times}$4의 부행렬(Submatrix)로 나누고 행렬에 대한 평균과 이들에 의해 구성되는 블록 행렬(Block matrix)로부터 전체 평균 및 워터마크 삽입에 이용될 임계값을 얻는다. 또한 주파수 영역에서 구해진 에너지 특성에 대한 블록 행렬과 공간 영역에서 얻어진 영상의 윤곽선 정보에 의해 워터마크가 삽입될 위치인 키맵(Keymap)이 구해진다. 구해진 키맵에 따라서 LFSR(Linear feedback shift register)을 이용하여 발생된 무작위 순열(Random sequence)를 웨이블릿 도메인에서 이웃 웨이블릿 계수간의 관계를 이용하여 삽입한다. 최종적으로 역 웨이블릿 변환을 취함으로써 워터마크가 삽입된 영상을 생성한다. 제안된 워터마킹 알고리즘은 JPEG과 같은 압축과 Blurring, Sharpening, 그리고 가우시안(Gaussian) 잡음 등의 공격에 대해서도 기존의 방식에 비해 약 2㏈ 절도 높은 PSNR(Peak signal to noise ratio)를 보이면서 2%에서 8% 정도 높은 NR(Normalized correlation)를 가져서 좋은 특성을 나타냈다.

Keywords

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