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    Please use this identifier to cite or link to this item: http://tkuir.lib.tku.edu.tw:8080/dspace/handle/987654321/21044


    Title: 像素不擴展之灰階視覺密碼方法
    Other Titles: An Unexpanded Visual Cryptography Method for Gray-level Images
    Authors: 侯永昌;Hou, Young-chang;許慶昇
    Contributors: 淡江大學資訊管理學系
    Keywords: 視覺密碼;視覺式秘密分享;半色調技術;灰階影像;visual cryptography;visual secret sharing;halftoning;gray-level images
    Date: 2004-12-01
    Issue Date: 2009-11-30 13:11:54 (UTC+8)
    Publisher: 政治大學資訊管理學系
    Abstract: 視覺密碼的方法將一張機密影像加密成n張分享影像,參與機密分享的每個人都可以持有一張分享影像。一群被授權的人將他們所持有的分享影像重疊後,就可以在重疊的影像上看到機密訊息;而不被授權的一群人便無法利用分享影像獲得任何機密訊息。視覺密碼學的主要精神在於解密的方法是透過人類視覺系統,而不需使用任何密碼學的知識與計算機資源;因此,在一些無法使用電腦解密的情況下,視覺式的秘密分享方法是一個很好的解決方案。許多視覺密碼方法都使用像素擴展的技巧來進行加密,因此使得分享影像被擴展為機密影像的好幾倍;如此不但造成儲存空間的浪費,也使攜帶更為不方便。此外,大部分的視覺密碼研究都是關於黑白影像的,而較少關於灰階影像的研究。在本文中,我們提出一個可以應用在單一機密影像之任意使用結構,且不需要像素擴展的灰階視覺密碼方法。我們的方法結合機率的觀念來達成分享影像不擴展的目標;同時,我們利用半色調技術,使得黑白視覺密碼技術能夠很容易地被應用在灰階影像上。此外,我們也考量對比損失的問題,提出一個適用於半色調影像的對比補償方法,使重疊影像能達到更好的視覺效果。實驗結果顯示,我們的方法不但有可能達到更好的對比,同時透過對比補償的方法,我們也能獲得更好的重疊影像視覺效果。
    Visual cryptography is a method to encrypt a secret image into n shares so that any qualified set of shares can recover the secret, whereas any forbidden set of shares cannot leak out any secret information. Since visual cryptography uses human visual system to decrypt the secret, it becomes an appropriate scheme while computers or other decryption devices are not available. Most visual cryptographic methods use the concept of pixel expansion; therefore, the size of shares is larger than that of the secret image. Pixel expansion not only results in distortion of shares, but also consumes more storage space. In addition, most studies of visual cryptography were about black-and-white images, whereas few studies were made on gray-level images. In this paper, we proposed an unexpanded visual cryptography method for gray-level images. Our method used the concept of probability to achieve the goal of non-pixel-expansion. Moreover, we employed digital image halftoning to deal with gray-level images. Finally, we also proposed a method to cope with the problem of loss of contrast in visual cryptography. Experimental results showed that our method might get better contrast and better visual effect of the stacked images.
    Relation: 資管評論13,頁107-124
    Appears in Collections:[資訊管理學系暨研究所] 期刊論文

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