視覺密碼學的研究者一直以來的目標就是降低像素擴展與提升還原影像的品質。近年來提出的通用存取結構（General Access Structures），都是以像素擴展式機密分享的作法為主。Kafri與Keren 所提出的隨機網格，改善了像素擴展的問題。
本研究提出一個將機密影像依通用存取結構編碼為多張分享投影片，透過隨機編碼與控制分配的概念，產生相似於隨機網格的分享投影片，此模型具備漸進式還原效果的方法，我們稱之漸進式半隨機網格視覺機密分享模型（Progressive Semi-Random Grids Visual Secret Sharing Model；PSRD VSS Model），簡稱為PSRD模型。

The goal of visual cryptography's researchers are reduce the pixel-expansion and enhance the restored image quality. General access structures that proposed in recent years based on pixel-expansion. Kafri and Keren （1987）proposed a random grid, to improve the pixel-expansion problems.
This study proposes a general access structures of the secret image is encoded as multiple share transparencies, through the concept of random and control distribution, make the share transparencies that are similar to the random grid and restore with progressive, we call Progressive Semi-Random Grids Visual Secret Sharing Model referred to as PSRD VSS Model.

目錄
摘要	I
Abstract	II
第一章　前言	1
第二章　視覺機密分享的製作與相關研究	3
2.1	視覺機密分享	3
2.2	隨機網格（Random Grids）	4
2.3	藏密學技術（Steganography）	8
2.4	通用存取結構（General Access Structures）	10
2.5	漸進式還原之機密分享（Progressive secret sharing）	12
第三章　本研究的分享模型	16
第四章　實作與結果分析	23
4.1	PSRD VSS 的實驗結果	23
4.1.1	實驗一	23
4.1.2	實驗二	27
4.1.3	實驗三	31
4.2	實驗結果分析	35
第五章　結論	38
參考文獻	39

 
表目錄
表 2-1：Shyu（2007）的分享模型	6
表 2-2：Ateniese et al.（2001）所提出的編碼模型	9
表 2-3：Hou 與 Quan（2011）的非擴展且漸進式之分享模型	14
表 3-1：5個參與者的視覺機密分享矩陣	22

圖目錄
圖 2-1：Chen and Tsao的編碼程序	7
圖 3-1：PSRD VSS 編碼概念圖	19
圖 3-2：PSRD VSS 編碼演算法	20
圖 4-1：實驗影像	23
圖 4-2：以 Heart 為例的PSRD VSS還原結果	26
圖 4-3：以 Recycle 為例的PSRD VSS還原結果	29
圖 4-4：以 TKU 為例的PSRD VSS還原結果	32

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