用小波轉換作彩色影像中之資料隱藏及浮水印

Abstract

資料隱藏是一種保護機密資料的方式，數位浮水印則是用來證明所有權的歸屬。本論文對於彩色影像中資料隱藏和數位浮水印都各提出一種方法。資料隱藏方法是將影像經過小波轉換後，將祕密資訊藏入中、高頻區域的係數中。我們根據人類的視覺系統，建議了一個關係表及位元取代表。利用這些表格，我們可以在不同的頻率區域中藏入不同的位元數，並可以得到跟原圖相似的隱藏結果。數位浮水印方法則是將影像經過小波轉換後，將浮水印嵌入低頻區域的係數中。我們將低頻區域分成 的子影像，利用浮水印和這個區域係數的關係，更改每個子影像中左上角係數的值。所提出的方法都可以結合保密學上的技術，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。

Data hiding is a technique to protect secret data, and digital watermarking is to prove the owner's copyright. In this study, new approaches to data hiding and watermarking in color images are proposed. In the proposed data hiding method, the wavelet transform is performed, and the secret message is embedded by replacing the middle and high frequency coefficients of the transform. Based on the characteristics of the human visual system, a relation table and some replacement tables are proposed for use in the hide process. Different numbers of bits can be embedded in different wavelet decomposition bands and an imperceptive result can be produced. In the proposed watermarking method, the wavelet transform is performed and the watermark is embedded into the low frequency coefficients. The low frequency band is divided into 2 by 2 nonoverlapping sub-images. Each bit of the watermark is embedded into a 2 by 2 sub-image by changing the top-left coefficient value of the sub-image according to a relation among the currently processed bit of the watermark and the other three coefficient values of this sub-image. Moreover, the two approaches can be combined with cryptosystems to increase system security. The experimental results show the feasibility of the proposed methods.