新型態的影像分享技術

Abstract

本論文提出四種新型的影像分享方法。在翻轉型影像分享，我們產生出兩張投影片。直接將這兩張投影片相疊會看到一張機密影像﹔而如果將其中一張翻轉後再相疊，則可以看到另一機密影像。在兩層型影像分享，我們也產生出兩張投影片。如果直接對齊相疊, 則可以看到機密影像，如果將某一張偏移到特定位置後再將兩張投影片相疊， 則可以看到驗證用的更進一層資訊。在通用型影像分享，我們設計出一張由公司召集人持有的特殊分存。此特殊分存可以通用於任意多張機密影像之分享，召集人可持此特殊分存參加任一張機密影像之解碼會議。這可以解決公司有太多機密影像要分享時，召集人手上的分存數量日益增加的問題。最後，在快速解碼型影像分享，我們用位元平面的分解法去分享灰階影像。在影像的解碼會議上，解碼可快速達成。

This dissertation proposes four new types of image sharing: turnover, two-level, universalizing, and fast decoding. In the turnover type, for any two given secret images, two corresponding transparencies are produced. Both transparencies look noisy. If we stack the front view of both transparencies, then we can see the first secret image. On the other hand, if we stack the front view of Transparency 1 with the back view (the turnover) of Transparency 2, then the second secret image is unveiled. In the two-level type, we present a two-in-one visual cryptography scheme, which not only shares an image of moderate confidentiality between two noisy transparencies, but also hides in these two transparencies a more confidential text file, which is either the information for authentication purpose or the information describing the image. More specifically, if we stack the two transparencies without any shift, then we can see the secret image. On the other hand, if we shift Transparency 1 to a predefined amount before stacking with Transparency 2, then we can see some other information of more confidential level in the shifted stacking. In the third type, we design a so-called universal share. A company’s organizer can hold this special share to attend any unveiling meeting of any secret image shared in his company. No matter how many secret images are shared in his company, the organizer only have to hold this special share, rather than thousands or millions of shares. Finally, in the forth type, we use bit-plane decomposition to design a scheme to share gray-value secret images. The decoding speed is fast. The method is particularly useful if the threshold r in the (r,n) sharing scheme equals n. In this case, not only the decoding speed, but also the encoding speed, is very fast