本研究以1的補數編碼替換方式(One’s Complement Substitution Process, OCSP)為基礎，對灰階影像提出三種資訊隱藏技術。第一種技術結合OCSP與直方圖修改(histogram modification)，將OCSP用來記錄是否需進行1的補數編碼運算的記錄位元(record bit)，以直方圖修改的方式隱藏到直方圖的峰值之中。但實驗結果顯示，藏入秘密資訊後對掩護影像(cover image)造成的失真程度，大於以最不重要位元(Least Significant Bit, LSB) 法的資訊隱藏技術。第二種技術結合OCSP及LSB法，研究結果顯示，平均峰值訊號雜訊比 PSNR (Peak Signal to Noise Ratio) 較LSB法高出19.21%，較最佳像素修正處理 (Optimal Pixel Adjustment Process, OPAP)法高出13.03%。第三種技術則結合整數小波轉換、OCSP法及LSB法。觀察實驗結果發現，藏入秘密資訊後對掩護影像造成的失真程度，會受到原始影像特性的影響，但仍有六成偽裝影像其PSNR高於使用OCSP法，整體結果比LSB法平均PSNR高出20.28%，比OPAP法平均PSNR高出15.51%。除此之外，第二種及第三種技術，將取出秘密資訊時所需的資訊，如k值(每一個像素使用最後k個bit來隱藏資訊)及記錄位元(record bit)的資料長度，也一併嵌入掩護影像中，所以解密時不需再參考其他額外的資訊，即可取出所隱藏的秘密資訊。

This research focuses on keeping low distortion in data hiding for grayscale images. We propose three data hiding methods based on OCSP (One's Complement Substitution Process). First, we combine OCSP and histogram modification for embedding the OCSP’s record bit(s) to the peak value of the histogram. However, the experimental result shows the distortion is more than using LSB (Least Significant Bit) substitution approach. Second, we combine OCSP and LSB. The experiment result shows PSNR (Peak Signal to Noise Ratio) of this method is 19.21% higher than LSB, also 13.03% higher than Optimal Pixel Adjustment Process (OPAP). The third method combines integer wavelet transform, OCSP and LSB. Through experiments we find the distortion after embedded secret data are influenced by the characteristics of the original images. Even so, 60% cover images have higher PSNR than OCSP. Furthermore, the average PSNR is 20.28% higher than LSB, and 15.51% higher than OPAP. Another important advantage is that the second and the third methods do not need extra information for extracting the hidden data, while keeping the low distortion and no extra record bits.

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