利用隨機位元取代與頻率轉換作影像隱藏

Abstract

「影像隱藏」是一種為保護重要或機密影像所發展的技術。吾人可透 過此種技術將機密影像隱藏於另一張偽裝影像之後, 使得竊取者無法察覺 。本論文提出兩種影像隱藏的方法。第一種方法利用「隨機位元取代」技 術, 將偽裝影像每一點的灰階值中最不重要的數個位元以機密影像資訊取 代, 以達成影像隱藏目的。第二種方法則是利用現今相當熱門的「浮水印 技術」中所使用的頻率轉換方法, 先將兩張影像轉換至頻率值域, 接著利 用機密影像與偽裝影像頻率值的相似性作取代, 以達到影像隱藏目的。所 提出的方法都是依據人眼無法察覺影像灰階值的細微變化的特性。此外, 兩種方法都可以結合保密學上的方法以增加系統的安全性。最後提出實驗 結果來證明所提方法的可行性。 Image Hiding is a technique to protect important or secret images. People canuse this technique to embed a secret image into another, called the counterfeitimage, such that illicit users cannot observe the secret image. In this study,two approaches to image hiding are proposed. The first, called random bit re-placement, is proposed to embed the secret image by replacing the least sig-nificant bits of the pixel gray values in the counterfeit image to achieve thepurpose of image hiding. The second approach is based on frequency transfor- mations of the watermarking technique that is popular nowadays. Firstly, thecounterfeit and the secret images are transformed into the frequency domain.Then, a replacement operation is performed using the similarity of the frequencyvalues of the counterfeit image and the secret image to achieve the purpose of image hiding. The two proposed schemes are based on the characteristic of the human visual system, i.e., a minor modification of image gray levels is diffi-cult perceive. Moreover, two approaches can be combined with cryptosystem to increase system security. Some experiments showing the feasibility of the pro-posed methods are also included.