半色調影像是為只能輸出有限色彩的裝置而設計的，如印表機和非全彩顯示器。半色調影像已經被廣泛使用於印刷應用上，如報紙、書籍、雜誌等等。這篇論文提出了半色調影像的回復與浮水印演算法.
半色調影像回復演算法是用於將半色調影像重建回灰階影像。基植於查表演算法，一種提升回復影像品質的以邊為基礎之半色調影像回復查表演算法被提出。實驗結果顯示我們所提出演算法比 Meşe 和Vaidyanathan 擁有更好的回復影像品質。
基植於以邊為基礎之半色調影像查表演算法，我們將其擴充到彩色半色調影像空間使其能重建彩色影像。彩色半色調影像回復演算法是設計用於將彩色半色調影像回復成全彩影像。Meşe 和Vaidyanathan 於過去提出了一個基植於計算不同色彩平面關聯度之查表法的彩色半色調影像回復演算法，可以提升回復彩色影像品質。我們首先會說明 Meşe 和Vaidyanathan 的演算法只有在非平滑區域有較好的回復影像品質，但在平滑區域也許會產生較差的回復影像品質。因此，一個基植於查表法之適應性色彩關聯度的彩色半色調影像回復法被提出用於提升回復的彩色影像品質。實驗結果顯示我們的演算法比 Meşe 和Vaidyanathan 的演算法有更好的回復影像品質。
由於網際網路與數位媒體的大量成長，如何在數位影像上達成資料隱藏變得越來越重要，其應用有驗證、鑑定、及智慧財產權的保護等。在廣大的數位影像中，文字影像、半色調影像及文字/半色調混合影像最常用於二元文件影像中。我們提出了一個基植於 unified min-max transition (MMT) 資料隱藏演算法，可以嵌入文字/半色調混合的影像資料於中而不造成影像視覺上的失真。實驗結果顯示我們的演算法優於先前相關的演算法；此外，我們的演算法與先前針對文字或半色調影像的演算法相比, 依舊可以擁有同樣的效果。

Halftones are dedicated for output devices, such as halftone printers
and palette-based displays that are capable of producing only a
limited number of colors. Halftones have been widely used in the
publishing applications, such as newspapers, books, magazines, etc.
In this thesis, inverse halftoning and watermarking of halftone
images are presented.

Inverse halftoning algorithm is used to reconstruct the gray image
from the input halftone image. Based on the recently published lookup
table (LUT) technique, a novel edge-based LUT method for inverse
halftoning is proposed for increasing the quality of the
reconstructed gray image. The experimental results demonstrate the
better image quality of the proposed edge-based LUT method when
compared to the Mese and Vaidyanathan algorithm.

Based on the proposed edge-based LUT inverse halftoning algorithm, a
color inverse halftoning algorithm is proposed. Color inverse
halftoning algorithm can transform color halfotnes to full color
image. Previously, Mese and Vaidyanathan proposed an efficient
LUT-based color inverse halftoning algorithm using the color
correlations among different color planes to improve the quality of
the reconstructed color images. The proposed algorithm first
demonstrates that although the Mese and Vaidyanathan algorithm
produces good quality reconstruction of color pixels in non-smooth
regions, the quality of reconstructed color pixels in smooth regions
may be degraded. Therefore, a new LUT color inverse halftoning
algorithm using an adaptive color correlation scheme is presented to
improve the quality of reconstructed color images. The experimental
results demonstrate the proposed algorithm achieves better
reconstructed image quality than that of the Mese and
Vaidyanathan algorithm.

Due to the growth of internet and digital media, the issue of data
hiding becomes more and more important since hiding data into
digitized images has many applications, such as authentication,
identification, annotation, and copyright protection, etc. Among
these digitized images, halftone images, text images, and mixed
text/halftone (MTH) images are three widely used binary document
images. A unified min-max transition (MMT)-based data hiding
algorithm for mixed text/halftone images is proposed to embed data
into MTH images without visual degradation. The experimental results
demonstrate that for MTH images, our proposed algorithm outperforms
the previous relevant algorithms. In addition, for embedding data
into halftone images or text images, our proposed algorithm is quite
competitive to the previously algorithms.

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