同位檢查之易碎式與基於小波轉換之強健式浮水印之研究
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2004
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Abstract
本研究針對數位影像之驗證與所有權歸屬的兩大課題，分別提出易碎式與兩種強健式數位浮水印演算法：
基於同位檢查之易碎式浮水印的部分，乃配合密碼學的機制，產生與影像大小相同的一組亂數。再根據各像素點所對應的亂數值，檢查該點灰階值特定數個位元平面之同位特性，對LSB做第一道的編碼。為了避免某些灰階值造成第一道編碼不可區分的情形，再以XOR運算對LSB做第二道的編碼。整個浮水印技術是公開、安全的，且不需複雜的數學運算。對於影像於傳輸中可能遭遇的各種竄改，在接收端均能有效地偵測出來。並且偵測是以像素點為基礎，能夠達到精確地偵測影像遭竄改的區域。
基於小波轉換之強健式浮水印部分演算法一：在藍、綠、紅三個平面不同的中頻小波係數中，考慮於中間位元平面，分別在不同的空間相對位置，嵌入多個浮水印。其後以投票的機制，萃取浮水印並解密。演算法二的部分：則採用能量相近、空間分佈相關的兩個中頻小波頻帶，以相對的大小關係來嵌入浮水印，並且可以彈性調整嵌入的強度。實驗結果顯示，本研究所提出來的方法其嵌入浮水印的影像，對於亮度調整、對比調整、裁切、濾波、影像失真壓縮等攻擊，具有一定程度的強健性，適合用來作為數位影像版權的保護機制。
In this research, we focus on the issues of the digital image authentication and ownership verification. We proposed a fragile watermarking and two robust watermarking algorithms to solve these problems respectively: A parity-check fragile watermarking technique for color image authentication is proposed. First, we generate a series of random numbers with the number equal to the number of pixels in the image. The random numbers are used to select predefined patterns for parity checking. The LSB of each pixel is encoded according to the result of parity check. To avoid some special cases of gray level, the pixel is encoded further by a simple XOR operation with the same random number. The proposed scheme is simple, secure, and public. In addition, the tamper detection is pixel based. Experimental results show that the proposed technique can accurately indicate the altered areas under many attacks of image processing. Two robust watermarking algorithms based on the property of the multiresolution signal decomposition of the discrete wavelet transform are proposed. In the first algorithm, we embed the encrypted watermarks into the wavelet coefficients of the intermediate frequencies separately correspond to blue, green, and red image planes. The watermarks are embedded repeatedly in different relative locations. After that, extraction of the watermark is based on the voting scheme. In the second algorithm, we embed the encrypted watermark into the wavelet coefficients of the two similar intermediate bands. The embedding procedure is based on the magnitude relation between the related coefficients. By the experimental results, both the proposed watermarks could survive under certain attacks to show the robustness of the watermark and to serve as a basic copyright protection scheme for digital images.
In this research, we focus on the issues of the digital image authentication and ownership verification. We proposed a fragile watermarking and two robust watermarking algorithms to solve these problems respectively: A parity-check fragile watermarking technique for color image authentication is proposed. First, we generate a series of random numbers with the number equal to the number of pixels in the image. The random numbers are used to select predefined patterns for parity checking. The LSB of each pixel is encoded according to the result of parity check. To avoid some special cases of gray level, the pixel is encoded further by a simple XOR operation with the same random number. The proposed scheme is simple, secure, and public. In addition, the tamper detection is pixel based. Experimental results show that the proposed technique can accurately indicate the altered areas under many attacks of image processing. Two robust watermarking algorithms based on the property of the multiresolution signal decomposition of the discrete wavelet transform are proposed. In the first algorithm, we embed the encrypted watermarks into the wavelet coefficients of the intermediate frequencies separately correspond to blue, green, and red image planes. The watermarks are embedded repeatedly in different relative locations. After that, extraction of the watermark is based on the voting scheme. In the second algorithm, we embed the encrypted watermark into the wavelet coefficients of the two similar intermediate bands. The embedding procedure is based on the magnitude relation between the related coefficients. By the experimental results, both the proposed watermarks could survive under certain attacks to show the robustness of the watermark and to serve as a basic copyright protection scheme for digital images.
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Keywords
數位浮水印, 影像驗證, 小波轉換, 同位檢查