臺灣博碩士論文加值系統

不同於傳統密碼學，視覺秘密分享技術不需要透過複雜的演算法，而是直接利用人類視覺感官來進行解密。大多數的視覺秘密分享技術會先對機密影像的像素進行擴展，而後將擴展的機密影像分解成數張黑白偽裝影像，所分解出的偽裝影像皆為雜亂無章，且為不具任何意義的影像。
本碩士論文裡，我們提出兩種分享方法，針對像素擴展與無意義的偽裝影像來提出改善，第一是像素不擴展之灰階視覺秘密分享技術，我們先調整機密影像色階範圍值，再配合半色調影像技術將調整過之灰階影像轉換成黑白二元圖，而後對於某些區塊黑點個數進行調整，使所有區塊的黑點個數，介於固定範圍內。最後將調整過後之二元圖以不擴展方式分解成兩張不具任何意義偽裝影像。第二是像素不擴展以產生多張有意義偽裝影像，首先將機密影像與多張偽裝影像，透過影像色階的調整，調整至不同的色階範圍。而後，運用半色調技術，將機密影像與偽裝影像轉換成黑白二元圖。針對轉換過的半色調影像，調整每個區塊中黑點與白點個數。最後，根據半色調機密影像，來調整替換半色調偽裝影像之黑點與白點位置，讓所有半色調偽裝影像疊合之後，能顯示出半色調機密影像。
由我們的實驗結果顯示，在實驗中我們知道一般人並無法從任意一張偽裝影像中觀察出機密二元圖的相關資訊，同時我們的方法可達到一定的安全水準。另外最重要的是偽裝影像疊合之後的機密影像品質都相當良好。

Unlike traditional cryptography, visual secret sharing technology decodes a ciphertext by using human’s eyes. The traditional visual secret sharing technology must go through pixel expansion and decomposition to produce some meaningless images.
In this thesis, we propose two kinds of visual secret sharing method. The first method is proposed to overcome the drawback of pixel expansion. Applying the first method, the second method goes further to produce meaningful images. For the first method, Visual Secret Sharing Techniques for Gray-level Image without Pixel Expansion, we adjust the range of the pixel value, and then a halftoning technique is performed to obtain the secret halftone image. After that, the numbers of black pixels in some blocks shall be adjusted so that those numbers are in a fixed range. Finally, we decompose the secret halftone image into two meaningless images. For the second method, Visual Secret Sharing Techniques for Multiple Counterfeit Images, we adjust different ranges of pixel values for the secret image and counterfeit images. Then, the halftoning technique is performed to obtain the secret halftone image and counterfeit halftone images. For each halftone image, we modify the number of black pixels in a block to a pre-determined range. Finally, according to the secret halftone image, we arrange the positions of black pixels in counterfeit halftone images so that the secret halftone image can be revealed after stacking all counterfeit halftone images.
According to our experimental results, no information can be revealed through observing any camouflaged image. Besides, we can obtain the secret image with high quality after overlapping camouflaged images.

中文摘要 i
Abstract ii
致謝 iii
目錄 iv
圖目錄 vi
表目錄 viii
第一章、 緒論 1
1.1 研究動機 1
1.2 研究目的 4
1.3 論文架構 5
第二章、 相關文獻探討 6
2.1 視覺密碼技術 6
2.2 視覺密碼基本原理 7
2.3 像素擴展型視覺秘密分享技術相關研究 9
2.3.1　彩色型像素擴展分享技術 9
2.3.2　灰階型有意義圖像擴展分享技術 12
2.4 像素不擴展型視覺秘密分享相關研究 14
2.4.1　Ito等人提出的像素不擴展方法 14
2.4.2　Yang等人提出的像素不擴展方法 15
2.5 機密影像分享技術 17
2.6 半色調影像技術(Halftone) 20
第三章、 像素不擴展之灰階視覺秘密分享技術 21
3.1 研究方法與分析 21
3.2 灰階影像轉換半色調 22
3.3 機密二元圖分解動作 23
3.4 實驗結果 26
3.5 實驗結果分析 30
第四章、 像素不擴展以產生多張具有意義偽裝影像 31
4.1 研究方法與分析 31
4.2 灰階影像轉換半色調 32
4.2.1 機密影像調整 32
4.2.2 偽裝影像調整 33
4.3 偽裝影像疊合 33
4.4 偽裝圖像素的重新排列 35
4.5 實驗結果 39
4.6 實驗結果分析 42
第五章、 結論 43
5.1 研究貢獻與未來研究方向 43
參考文獻 44
個人履歷 47

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