| Abstract: | 由於網際網路的蓬勃發展，使得數位化電子資料(如：數位影像、數位音訊、數位視訊)的取得及傳送極為便利。但也由於網際網路具有開放性，且數位化電子媒體具有易於複製及修改的特性，使得數位資料易於被他人擷取、盜拷及竄改。因此，數位資料的智慧財產權保護是目前極為熱門的課題。而數位浮水印即是為了解決上述問題而發展出來的技術。 在本論文中我們藉由人類視覺系統中的正好視覺扭曲度模型(just noticeable distortion, JND)在不影響影像品質的情形下，計算各像素所能修改的灰階值。為了能夠得到更好之強健性，各像素之最小視覺扭曲度(minimally noticeable distortion, MND)值作為可修改的最大範圍，藉此增強隱藏浮水印的資訊量。為了增加浮水印之強健性，我們也運用影像區塊分類的概念，將影像各個區塊分類，依據各區塊的特性來決定其隱藏資訊量的多寡。若區塊性質屬於高頻，人眼不易察覺其變化，故隱藏較多的資訊量，以增加浮水印的強健性。反之，若區塊性質屬於低頻，人眼較易察覺其變化，故隱藏適當的資訊量，以保持影像的視覺品質。為了增加浮水印的隱蔽性及安全性，在浮水印隱藏的過程中通常藉由虛擬亂數產生器(pseudo random number generator)來將浮水印資訊打散至原影像，使得浮水印類似散亂之訊號，具有不易察覺之特性。但藉由虛擬亂數產生其無法提供足夠的安全機制，且無法適當地產生散亂效果。因此，本論文也針對這點提出新方法，文中我們以灰色累加生成數列(accumulated generating operation, AGO)產生散亂訊號，將此訊號與浮水印作運算來達到打散浮水印之效果，並使用一安全編碼模組來提供個人金鑰(personal key)的安全機制，達到良好的散亂程度及使用的安全性。 本論文針對網路上多媒體的保護機制，採用無需原始影像輔助的擷取策略，以探討浮水印技術的改進空間。藉由人類視覺系統中的特性來對影像品質及浮水印強健性之間作良好的取捨，能在不影響影像視覺品質的情形下得到較佳之強健性。並且藉由影像區塊分類，能夠依據各區塊之特性來決定隱藏的資訊量，使得浮水印的強健性提昇。此外，藉由灰色累加生成數列來打散浮水印，使得浮水印有較佳的安全性。由實驗結果得知，我們所提出的影像浮水印技術能夠有效抵抗JPEG壓縮、雜訊攻擊、銳利化攻擊，且其強健性有相當的提昇。 關鍵字: 影像浮水印、最小視覺扭曲度、正好視覺扭曲度、影像區塊分類、灰色理論
The characteristic of Internet is easy to get, to copy and to modify media, so it is easy for anyone to get the digital multimedia without via the legal way. The protection of the intellectual property for digital media is very necessary. The digital watermarking can provide a good solution for protecting the intellectual property of digital multimedia. The general watermarking techniques can not make good decision between the quality of image and the robustness of the watermark. In order to solve the problem, we employ the just noticeable distortion (JND) of the human visual system (HVS) to calculate the embedded information of each pixel of the image. The minimally noticeable distortion (MND) of each pixel is used to increase the capacity of information of the embedded watermark. To increase the robustness, we also use the image block classification scheme to classify the original image, and decide the embedded information according to content feature of the block. If the content feature of block is belongs to high frequency, that are met sensitive to human vision, more information is embedded. On the other hand, if the content feature of block is belongs to low frequency, that is sensitive to human vision, the appropriate information is embedded to hold the quality of the image. To increase the invisibility and the security, the pseudo random number generator is used to spread the watermark. However, the pseudo random number generator does not provide enough security and spreading effect. In this paper, we use the accumulated generating operation to produce the spreading function, and add it to the watermark to spread watermark. Besides, the security of personal key, which gets good spreading effect and the security of operation is provided. In this paper, the protection of multimedia in the Internet, and deal with the improvement of watermarking techniques is focused. We rely on the characteristics of HVS to make good decision between the quality of image and robustness of watermark, and get the better robustness without affecting the visual quality of image. Besides, we use the accumulated generating operation of Grey system theory to spread watermark, and the security of watermark is then increasing. From several experiment results, our image watermarking technique can resist the JPEG compression, noise attack, sharpen attack, and increase the robustness. Keywords：Image watermarking, Minimally noticeable distortion, Just noticeable distortion, image block classification, Grey system theory |
