臺灣博碩士論文加值系統

彩色轉灰階(color to gray)方法必須能夠保留原始彩色影像的視覺外貌與特
徵辨別特性。現有的演算方法在這兩方面之表現仍顯不足。本論文提出兩個彩色
轉灰階方法。一個是基於全域映射機制，另一個是基於整合區域與全域的映射機
制。這兩個方法皆能精確的將各類彩色影像轉換成灰階影像，如自然影像，電腦
合成影像及繪畫影像等。全域映射方法簡單而快速，但仍能保持彩色特徵之辨別
特性與適當的顏色排序(color order)，而整合區域與全域的映射方法不僅可保留
原始彩色影像之外貌並可補償全域映射法之不足。實驗結果顯示，本論文方法所
產生的灰階影像在感知的精確性與喜好度皆優於其他方法。

Color-to-gray conversion in many applications requires preserving the visual
appearance and feature discrimination of color images. The existing methods are still
need of improvement in this aspect. We propose two color-to-gray conversion
algorithms. One is the global mapping based and the other is the local-global mapping
based. The proposed methods convert accurately various categories of color images to
grayscale images, including natural images, computational images, and painting images.
The global mapping scheme is simple and fast, yet it preserves feature discrimination
and appropriate color order of color images. The local-global mapping scheme not only
retains the visual appearance of the color image but also compensates the global
mapping method for possible loss of color information. Experimental results show that
the proposed methods produced perceptually accurate and preferred images when they
were compared with other schemes.

Acknowledgement............................................................................................................ i
摘要................................................................................................................................. ii
Abstract .......................................................................................................................... iii
Table of Contents ........................................................................................................... iv
List of Figures ................................................................................................................ vi
Chapter 1 Introduction 1
1.1 Motivation .......................................................................................................... 1
1.2 Thesis Objectives................................................................................................ 3
1.3 Thesis Organization ............................................................................................ 3
Chapter 2 Previous work 5
2.1 Introduction ........................................................................................................ 5
2.2 Color models ...................................................................................................... 7
2.2.1 RGB color model..................................................................................... 7
2.2.2 CIE L*a*b*color model ............................................................................ 9
2.2.3 HSI color model .....................................................................................11
2.3 Overview of previous work .............................................................................. 13
2.3.1 Local mapping methods......................................................................... 13
2.3.2 Global mapping methods....................................................................... 19
2.3.3 Global and Local combined methods .................................................... 23
Chapter 3 Proposed method 25
3.1 The global mapping scheme ............................................................................. 25
3.2 The local-global mapping scheme.................................................................... 43
Chapter 4 Experimental results 47
4.1 Experimental results and discussions ............................................................... 47
4.1.1 Accuracy ................................................................................................ 49
4.1.2 Preference .............................................................................................. 60
Chapter 5 Conclusions 66
References 68

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