臺灣博碩士論文加值系統

色散及色偏現象為造成水下攝影失真最主要的兩個原因，其中色散現象為物
體反射光線經水中粒子吸收與多次漫射所造成，色散現象會對影像產生能見度與
對比降低的影響；色偏現象則是光線於水中傳播時，因不同波長具相異之能量衰
減程度，而令水下環境呈現偏藍色調。
本文針對水下影像之色散與色偏失真提出結合除霧演算法及波長能量補償之
水下影像強化演算法，首先以Dark Channel Prior 估測物體至相機距離並產生物體
至相機距離深度圖(Depth Map)，接著以影像前景與背景之亮度差值來判斷影像拍
攝時是否存在人造光源照射。於移除人造光源的影響後，使用除霧演算法移除色
散造成之霧化效應，再以水下背景光之各波長能量剩餘比率估測拍攝場景之水下
深度，最後根據各波長能量衰減進行逆向補償，以還原影像之色偏失真。此外超
解析度影像(Super-Resolution)可呈現較多的影像細節，此為低解析度水下影像處理
時相當重要且不可或缺的技術之一，本文結合以梯度為基礎的超解析度演算法
(Gradient-Base)及反投影疊代法(IBP)提出雞尾酒式(Cocktail)超解析度演算法，配合
雙邊濾波器消除影像邊緣之棋盤效應及震鈴效應以提升影像品質。
將自 Youtube 網站下載之各種解析度之水下影片分別以WCID、直方圖等化
及傳統除霧演算法處理，比較後發現WCID 演算法具有同時解決色散與色偏之能
力且可有效提高影像能見度與色彩保真度，配合超解析度影像的處理可使水下拍
攝影像及影片均獲得良好視覺效果如呈現於空氣中觀賞之原有色調，清晰度及細
節保真度。

Light scattering and color shift are two major sources of distortion for underwater
photography. Light scattering is caused by light incident on objects reflected and
deflected multiple times by particles present in the water before reaching the camera.
This in turn lowers the visibility and contrast of the image captured. Color shift
corresponds to the varying degrees of attenuation encountered by light traveling in the
water with different wavelengths, rendering ambient underwater environments
dominated by bluish tone.
This paper proposes a novel approach to enhance underwater images by a
dehazing algorithm with wavelength compensation. Once the depth map, i.e., distances
between the objects and the camera, is estimated by dark channel prior, the light
intensities of foreground and background are compared to determine whether an
artificial light source is employed during image capturing process. After compensating
the effect of artifical light, the haze phenomenon from light scattering is removed by the
dehazing algorithm. Next, estimation of the image scene depth according to the residual
energy ratios of different wavelengths in the background is performed. Based on the
amount of attenuation corresponding to each light wavelength, color shift compensation
is conducted to restore color balance. A Super-Rsolution image can offer more details
that must be important and necessary in low resolution underwater image. In this paper
combine Gradient-Base Super Resolution and Iterative Back-Projection (IBP) to
propose Cocktail Super Resolution algorithm, with the bilateral filter to remove the
chessboard effect and ringing effect along image edges, and improve the image quality.
The underwater videos with diversified resolution downloaded from the Youtube
website are processed by employing WCID, histogram equalization, and a traditional
dehazing algorithm, respectively. Test results demonstrate that videos with significantly
enhanced visibility and superior color fidelity are obtained by the WCID proposed.

摘要 ......................................................................................................................iv
Abstract .......................................................................................................................v
目錄.................................................................................................................... vii
圖目錄......................................................................................................................ix
表目錄......................................................................................................................xi
第一章 簡介...............................................................................................................1
1.1 影像霧化...................................................................................................... 2
1.2 色偏現象...................................................................................................... 4
1.3 超解析度...................................................................................................... 6
1.4 研究總述...................................................................................................... 7
第二章 相關研究.......................................................................................................8
2.1 基於光學物理模型之除霧方法.................................................................. 8
2.2 影像除霧技術.............................................................................................. 9
2.3 移除影像色偏現象.................................................................................... 17
2.4 傳統內插放大法與超解析度演算法........................................................ 18
第三章 理論基礎.....................................................................................................24
3.1 Dark Channel Prior..................................................................................... 24
3.2 Image matting............................................................................................. 27
3.3 Connected Component Labeling ................................................................ 31
3.4 Simple Linear Regression........................................................................... 32
3.5 Jacobi Iterative............................................................................................ 33
3.6 YCbCr 色彩空間........................................................................................ 35
3.7 類神經網路(Artificial Neural Network) .................................................... 36
3.8 雙向濾波器(Bilateral Filter) ...................................................................... 39
3.9 最小邊緣路徑法(Minimum Error Boundary Cut) .................................... 40
第四章 研究方法.....................................................................................................41
4.1 Algorithm ................................................................................................... 42
4.2 Distance between the camera and the object: d(x) ..................................... 43
4.3 Laplacian matrix matting using guided filter ............................................. 45
viii
4.4 Removal of the artificial light source L...................................................... 48
4.5 Underwater depth at the top of the photo scene: D .................................... 51
4.6 Image depth range R................................................................................... 53
4.7 Super-Resolution ........................................................................................ 54
第五章 實驗結果.....................................................................................................59
第六章 結論與未來工作.........................................................................................70
參考文獻.....................................................................................................................71

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