臺灣博碩士論文加值系統

在此博士論文中主要探討兩大主題。第一個主題是影像隱藏技術，第二個主題則是數位浮水印技術。雖然影像隱藏技術和數位浮水印技術是不同的研究主題，但是影像隱藏技術和數位浮水印技術具有一個共同點，那就是這兩個主題的技術，都必須將資料藏入數位影像中。所不同的是，數位浮水印技術必須能多達一個特性，即是確保藏入資料的強韌性。因此，可以將數位浮水印技術，當作是影像隱藏技術的一個特殊應用。由於影像隱藏技術和數位浮水印技術具有此共同點，在此博士論文中，包含影像隱藏技術和數位浮水印技術這兩種技術。
首先先探討第一個主題，那就是影像隱藏技術。影像隱藏技術又可分成兩大類。第一類是灰階影像影藏技術，第二類是彩色影像隱藏技術。
灰階影像影藏技術是目前熱門的研究主題。再眾多的方法中，最直接的方法，就是將秘密資料藏到原影像中不重要的位置。 然而此種隱藏方法，會對原影像產生比較大的傷害。在2001年，Wang等人將 “一對一取代表” (One-to-one Substitution Table)的技術引入灰階影像影藏技術中。經由 “一對一取代表” 的指引，就可以將秘密資料，轉換成另一個秘密資料。而這轉換後的秘密資料，將會更接近原影像中不重要位置的值。所以將轉換後的秘密資料，藏入原影像中的不重要位置，會降低對原影像的傷害。然而Wang等人所提的方法，並不能保證可以找到最佳的“一對一取代表”。在2003年，Chang等人利用動態程式規劃(Dynamic Programming Strategy)來找到最佳的“一對一取代表”。
為了對灰階影像影藏技術提供貢獻，此博士論文提出三個不同的方法，來做灰階影像隱藏。第一個方法是“多位元參考取代表”(Multi-bit-reference Substitution Table)，第二個方法是“一對二取代表”(One-to-two Substitution Table)，第三個方法是“模數函式取代表(Modulus Function Based Substitution Table)”。
第一個方法，利用在原影像中沒有藏秘密資料的部份，來將原影像分割成不同的影像平面。對每一個的影像平面，分別使用‘動態程式規劃’來找到最佳的“一對一取代表”。而後將每一個平面的“一對一取代表”組合起來，就可以得到“多位元參考取代表”。
第二個方法，介紹如何用產生最佳的“一對二取代表”，並利用它來做秘密資料之隱藏。為了要產生最佳的“一對二取代表”，首先會建立一個三維的陣列，而後利用 ‘動態程式規劃’ 在此三維的陣列上，從而獲得最佳解的“一對二取代表”。
第三個方法，結合Thien and Lin所提的模數函式(Modulus Function)資料隱藏法以及Chang等人所提的“一對一取代表”，來產生的最佳的“模數函式取代表”。經由此表的指引，可得到轉換後的秘密資料。對於這個轉換後的秘密資料，利用 ‘模數函式資料隱藏法’ 藏入原影像，會對原影像的傷害最小。
接著介紹第二類的影像隱藏技術，彩色影像隱藏技術。在彩色影像隱藏技術中，將彩色秘密影像藏入彩色原影像中，來產生彩色偽裝影像。對於彩色秘密影像，先利用調色盤(Palette)將此彩色秘密影像進行量化，而產生索引影像(Indexed Color Image)。然後分別對原彩色影像以及索引影像，計算每一個像素與其鄰近像素的差值。接著再把 ‘索引影像’ 所產生的像素差值，藏入原彩色影像所產生的像素差值中。最後將藏入資料的彩色影像的像素差，反轉回像素值，而得到彩色偽裝影像。
緊接著介紹第二個主題，數位浮水印技術。數位浮水印是用於數位影像的保護。在數位浮水印的嵌入階段，先將原影像切成一個個區塊，並且將這些區塊投影到一個線性空間，而後將這些投影值與數位浮水印產生關連。當要取出數位浮水印時，要對修改過的影像，進行相同的程序。也就是將修改過的影像，切成區塊，並且投影到線性空間，以找到投影點。經由這些投影點，可以將浮水印取出。

There are two topics in this dissertation. One is image steganography and the other is digital watermarking. Although image steganography and digital watermarking are two different topics, there exists one common point. Both image steganography and digital watermarking embed data into images except that digital watermarking has an additional property, the robustness of the embedded data. Therefore, we can treat digital watermarking as a special case of image steganography. Owing to this common point, two topics are studied in this dissertation.
Regarding, image steganography, we consider the problems of gray-level image hiding and color image hiding. For gray-level images, we propose three different methods; a color image hiding technique is also proposed for color images.
Among all related works for gray-level images, least-significant-bit (LSB) substitution is the most straightforward way to embed a secret image into a host image. To avoid the image degradation of the LSB substitution technique, Wang et al. proposed a method using the substitution table to perform image hiding. In 2001, Wang et al. brought up the concept of one-to-one mapping where each secret data value is transformed into another value by applying the table. Nevertheless, Wang et al. have not developed any method to obtain an optimal one-to-one substitution table. In 2003, Chang et al. proposed a way to find an optimal one-to-one substitution table by using the dynamic programming strategy.
In this dissertation, we have proposed three gray-level image hiding techniques by using an optimal multi-bit-reference substitution table, an optimal one-to-two substitution table and an optimal modulus function based substitution table.
In the first method, we use un-embedded bits of host pixels to partition the host pixels into different planes. We can derive an optimal substitution table for each plane. After combining all optimal substitution tables, we can obtain an optimal multi-bit-reference substitution table. The secret data being transformed via the optimal multi-bit-reference substitution table will degrade the host image possibly least.
In the second method, we introduce a new method that uses an optimal one-to-two substitution table. We first built up a square-error matrix with 3-dimension. After applying a dynamic programming strategy on the square-error matrix, we can obtain an optimal one-to-two substitution table.
Combing the modulus function, proposed by Thien and Lin, and the optimal substitution table, we develop a novel method to improve the image quality of the stego-image.
Now, consider the problem of color image embedding. The secret image to be embedded is first color-quantized using a palette previously sorted by the principal component analysis technique to generate the indexed color image. Then, the concept of pixel difference is employed to process both the host image and the indexed color image. After that, the processed indexed color image is embedded into the processed color host image.
Finally, we describe the second topic, digital watermarking, in this dissertation. Digital watermarking is used for the copyright protection of digital images. To embed the watermark, the proposed method partitions an original image into blocks and uses a PCA function to project these blocks to a linear subspace. There is a watermark table, which is computed from projection points, kept in our proposed method. When extracting a watermark, the proposed method projects the blocks of the modified image by using the same PCA function. Both the newly projected points and the watermark table are used to reconstruct the watermark.

ABSTRACT
中文摘要
LIST OF FIGURES
LIST OF TABLES
CHAPTER 1
INTRODUCTION
1.1 MOTIVATION
1.2 IMAGE HIDING TECHNIQUES
1.3 DIGITAL WATERMARKING
1.4 ORGANIZATION
CHAPTER 2
A SURVEY OF RELATED WORKS
2.1 IMAGE HIDING TECHNIQUES
2.1.1 LSB substitution method
2.1.2 Modulus function method
2.1.3 Image differencing method
2.2 CHANG AND TSAI’S WATERMARKING METHOD
2.2.1 Principal Component Analysis (PCA)
2.2.2 Watermarking Techniques with Codebooks
CHAPTER 3
THE PROPOSED METHOD
3.1 GRAY-LEVEL IMAGE HIDING USING SUBSTITUTION TABLE
3.1.1 The Multi-bit-reference Substitution Table
3.1.2 An One-to-two Substitution Table
3.1.3 Combing Modulus Function and Substitution Table
3.2 COLOR IMAGE HIDING USING IMAGE DIFFERENCING
3.3 A NEW WATERMARKING TECHNIQUE
CHAPTER 4
EXPERIMENTAL RESULTS
4.1 GRAY-LEVEL IMAGE HIDING USING SUBSTITUTION TABLE
4.1.1 The Multi-bit-reference Substitution Table
4.1.2 An One-to-two Substitution Table
4.1.3 Combing Modulus Function and Substitution Table
4.2 COLOR IMAGE HIDING USING IMAGE DIFFERENCING METHOD
4.3 A NEW WATERMARKING TECHNIQUE
CHAPTER 5
DISCUSSIONS AND CONCLUSIONS
REFERENCES

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