在Bitmap 圖檔中藏入訊息之實作與應用

Implementations and Applications for Hiding Information in Bitmap Files

本論文的目的在提供一應用程式的實作，能將額外的訊息藏在任意給定的bitmap 影像檔中，藉由bitmap 檔案格式不會進行失真壓縮的特性，來確保能將原先藏入的訊息正確無誤地自該合成後的bitmap 圖檔中取出或回復。透過這樣的程序可以經由傳送一個外顯影像 （apparent image） 並將希望傳遞的訊息化成二進位的資訊，任選地加碼藏入該外顯影像中各像素點顏色分量的較低位元中，如此不但視覺上幾乎無損該外顯影像的呈現品質，而且可以把各式相關的資料訊息諸如影像、文字與應用程式等檔案藏入該選定的外顯影像檔中並加以儲存。此外我們同時也提供一個全新的影像位元反轉 （inverse-bit） 藏入法能夠將一張訊息影像 （information image） 的主要位元部分經由位元反轉放入外顯影像中，將這兩張影像融合成一個bitmap 影像，而彼此可以透過位元反轉來切換顯示，在取得最佳訊息影像藏入結果的同時，也讓原外顯影像有最小的視覺失真，將它應用在執行期間電腦繪圖的貼圖內容記憶體儲存上，可最多節省一半的容量。一個利用前述位元反轉合成的問與答 （questions and answers,Q&As） 有趣教學應用也在本文中提出。

In this paper, a novel method for hiding information in bitmap files,called the inverse-bit method, is introduced. With this method, any typeof information can be hidden in an apparent image, in bitmap format, andthe merged image, saved as a bitmap file, can be sent anywhere as aninformation carrier. For security, the method adds key codes duringprocessing, so the hidden information can exactly and safely be retrieved. The information is saved in the lower bits of pixel color components,therefore, there is almost no degradation of images. The informationimage is merged with the apparent image. Pixel pairs are merged usingthe inverse-bit method. An information image pixel is inverted and thenmerged with an apparent image pixel. Thus, the merged image is actuallytwo images and there is no loss from higher bits. The two images can beshown alternately. When the method is applied to the texturing ofgraphics, it can save as much as half of the memory storage needed andprocessing time also. Other applications of the inverse-bit method, suchas Q and A quizzes, are also demonstrated.