靜態影像的壓縮、加密與隱像術

Abstract

摘要本論文提出了一個新的影像表示方法：基底轉換式 (Base- Switching) 演算法。在此演算法中，我們藉由不同的數字進位系統 (基 底) 之互換，分別發展出兩種靜態影像壓縮的版本：無失真壓縮及失真壓 縮。我們的方法除了能達到不錯的壓縮率，也具備了計算量低的優點。另 外，我們將我們所提出的無失真壓縮版本加以應用，而發展出一套新的靜 態影像加密技術。在這套技術中，我們不但可達到很高的保密性，同時也 具備了無失真壓縮的功能。此外，為了擁有漸進性(multiresolution or progressive) 的傳輸功能，我們結合了wavelet transformation另外發 展出一套影像加密技術。這套技術除了具備高保密性及可在任意區域做防 竊(scrambling)處理之外，也具備有漸進性傳輸的功能。最後，我們藉著 不同的數位系統轉換，發展了一套簡單又有效率的隱像技術 (steganography (or data hiding) for for image)。在這套新技術中， 我們不但擁有無需做偽造影像 (counterfeit image)的前置處理、無需建 造參照表 (lookup table) 及很高的隱藏品質外，亦結合了一些既有的影 像加密技術，進一步提高了欲隱藏影像 (main image) 的保密性。 AbstractIn this dissertation, we propose a new image representation scheme called Base-Switching (BS) algorithm. By using the base-switching techniqueback and forth among several number-systems, two image compression versions,lossless compression and lossy compression, are developed. Our methodsnot only achieve acceptable compression ratios but also own the advantage of low computation cost. Furthermore, the proposed lossless compression versioncan be applied to the still image encryption, and we can thus obtain a newstill image encryption method which has the properties of both high securitylevel and lossless compression. In addition, we combine the concept of wavelettransformation with still image encryption to develop a new image encryptionmethod. In this method, some functions such as multiresolution transmission,scrambling arbitrary regions, and high security level are all obtained simultaneously. Finally, using digit number transformation, we also develop a simple and efficient new method for image hiding. The proposed method has theadvantages of no counterfeit image preprocessing, no lookup table establishing,and high quality of the embedding results. To increase the security of the main image, we also combine certain encryption techniques with the proposed method.