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研究生:廖姿雯
研究生(外文):Tzu-WenLiao
論文名稱:一個透過RGB均值匹配與直方圖伸展的自動白平衡演算法
論文名稱(外文):An Automatic White Balance Algorithm by RGB Mean Matching and Histogram Stretching
指導教授:戴顯權戴顯權引用關係
指導教授(外文):Shen-Chuan Tai
學位類別:碩士
校院名稱:國立成功大學
系所名稱:電腦與通信工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2012
畢業學年度:100
語文別:英文
論文頁數:55
中文關鍵詞:白平衡色彩一致色偏校正
外文關鍵詞:white balancecolor correlationcolor cast correlation
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自動白平衡是數位攝影機中一項重要的功能,其目的是為了移除所拍攝影像在不同色溫環境下所造成的色偏現象。色偏影像的色彩對比度和色彩變異性資訊經常被色偏所遮蓋,在強烈色偏的影像中尤其嚴重。其色彩對比度和變異性的資訊遺失,經常導致一般常見的白平衡演算法無法正確取得該有的資訊以重建色彩,而造成結果影像的不正確色偏移除或對比度不足等問題。在本文中,我們提出一種利用RGB均值匹配與直方圖伸展為基礎的新白平衡演算法(Mean Matching and Histogram Stretching algorithm, MMHS)。此演算法修改原始的灰階世界理論(Gray World method, GW),以滿足其假說並維持三色通道資訊分布狀態;同時修改原始的色彩直方圖伸展演算法(Color Histogram Stretching algorithm, CHS)以限制其輸出影像的色彩廣度。最後,透過由RGB和YCbCr色彩空間共同定義出的色偏嚴重程度來進行兩修改後之演算法合併。
由實驗結果可得知,本文所提出的自動白平衡演算法不但可以達成灰階世界理論(GW)中三通道平均值相等的目的,也具備色彩直方圖伸展演算法(CHS)有效提升色彩變異性的特質,達到正確校正色偏影像的效果。

Automatic White Balance (AWB) is one of the most important functions of digital cameras. Its purpose is removing the unwanted color from a color cast image that was taken under the un-canonical illumination. Images with color cast always lose color contrast and variation, especially those with heavy color cast. For traditional white balance algorithms, loss of color contrast and variation would probably bring incorrect color temperature predictions and lacks of contrast in output images. In this thesis, a new automatic white balance algorithm, combining RGB mean matching with histogram stretching (MMHS), is proposed. The proposed algorithm modified the original Gray World method for keeping the assumption and maintaining the channel distributions; it also modified the original Color Histogram Stretching algorithm for getting wide color range and limiting the range of distributions. Finally, we use the level of color cast, which is calculated from YCbCr and RGB color model, to combine the modified Gray World theory and the modified Color Histogram Stretching algorithm. In the experimental results, the proposed algorithm, MMHS, keeps the advantages of these two white balance algorithms and avoid the shortcomings of theirs. For our test images, MMHS gets the processed images not only look as taken under canonical illumination but also keep the correct color variation.

List of Contents......................................i
List of Tables......................................iii
List of Figures......................................iv
Chapter 1 Introduction................................1
Chapter 2 Background..................................4
2.1 Color System......................................4
2.2 Color Temperature.................................7
2.3 Color Constancy...................................8
2.4 Color Cast Detection..............................8
2.4.1 Standard Deviations of R, G, B Channel..........9
2.4.2 YCbCr Color Model..............................11
2.5 White Balance Technique..........................14
2.5.1 Color Temperature Estimation...................15
2.5.2 Color Adjustment...............................16
2.6 White Balancing Algorithms.......................17
2.6.1 Gray World Method..............................17
2.6.2 Perfect Reflector Algorithm....................18
2.6.3 Retinex Theory.................................18
2.6.4 Color Histogram Stretching Algorithm...........19
Chapter 3 The Proposed Algorithm.....................20
3.1 Improved Algorithms..............................21
3.1.1 Improved Gray World Method.....................21
3.1.2 Improved Color Histogram Stretching............26
3.2 Weight Decision..................................29
3.3 RGB Mean Matching and Histogram Stretching.......32
Chapter 4 Experimental Results.......................34
4.1 Comparisons with Other Approaches................34
4.1.1 Color Checker Images...........................34
4.1.2 Natural Images.................................41
4.2 More Results.....................................45
Chapter 5 Conclusion and Future Work.................50
5.1 Conclusion.......................................50
5.2 Future Work......................................51
Bibliography.........................................52


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