針對彩色影像的對比增強的邊緣保留演算法與針對色彩慮波陣列之去馬賽克及隨意比例尺寸調整演算法

Edge Preserving Algorithm for Color Image Enhancement and Demosaicing and Arbitrary-Ratio Resizing Algorithm for Color Filter Array

楊偉楨(Wei-Jen Yang)

指導教授 ： 傅楸善

共同指導教授 ： 顏文明

國立臺灣大學/電機資訊學院/資訊工程學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.00364

摘要

由於彩色影像可以提供更豐富的資訊，因此在近年來彩色影像處理已經廣泛的成為了非常重要的研究議題。在眾多彩色影像相關的研究中，以針對色彩對比增強的邊緣訊息保留、彩色去馬賽克與馬賽克影像的尺寸調整為相當熱門的研究議題。因此，本論文將針對色彩對比增強的提出一個邊緣訊息保留演算法與探討其在影像分割上的應用，以及針對Bayer色彩濾波陣列，提出一個透過梯度測邊器與適應性的異質估計的去馬賽克演算法。而後再利用與離散餘弦轉換結合，設計一個結合去馬賽克與隨意尺寸調整演算法。

在針對色彩對比增強的邊緣訊息保留的研究議題上，在CIE Lu'v'色彩空間下，我們提出了一個針對色彩對比增強的邊緣訊息保留演算法。該演算法不僅可以如同以往的色彩增強方法一般地增強影像的色彩對比，亦有邊緣訊息保留的效果。此外，所提出之演算法也會部份抑制因色彩對比增強而產生的邊點。該演算法是第一個針對色彩對比增強所提出之邊緣訊息保留技術。為了驗證所提出的演算法在邊緣訊保留上的優勢，我們又提出一個新的彩色影像分割演算法作為驗證之應用。實驗結果顯示所提出之演算法在對比增強、邊訊息保留及彩色影像分割上，都有著相當顯著的效果。

在彩色影像去馬賽克的議題上，在不需事先解馬賽克的情形下，我們首先針對馬賽克影像提出一個能有效地擷取其梯度及邊資訊的方法。之後，基植在頻譜空間的相關性上，決定馬賽克影像中每個像素之適應性異質估計遮罩的大小。最後再結合由每個像素中所擷取出的梯度及邊資訊與適應性異質估計值，提出一個邊緣感測之去馬賽克演算法。實驗結果顯示，所提出之去馬賽克演算法比起過去數種去馬賽克演算法，有著較佳的去馬賽克的影像品質與效果。

在馬賽克影像的尺寸調整的議題上，我們提出了一個結合去馬賽克與隨意尺寸調整演算法。透過邊緣感測與色差的方式，首先將綠色平面回復。為了降低估計的誤差，我們透過內插色差平面的方式取代直接將紅色及藍色平面回復。之後，再透過離散餘弦轉換的技術，將三個平面分別做隨意倍率的尺寸調整。最後透過三個調整過的平面作用之後，就可以得到尺寸調整過後的紅、藍平面，而後便可以得到隨意倍率的尺寸調整後的去馬賽克影像。具我們所知，這是第一個被提出的去馬賽克與隨意尺寸調整演算法。實驗結果顯示，所提出之馬賽克與隨意尺寸調整演算法比起透過直接單獨去馬賽克後又再做隨意尺寸調整的方式，有著較佳的品質與效果。

關鍵字

適應性的異質估計 ； CIE色彩空間 ； 彩色影像的對比增強 ； 彩色影像測邊 ； 色彩濾波陣列 ； 彩色直方圖動差 ； 彩色影像處理 ； 彩色訊號雜訊比 ； 彩色影像切割 ； 色彩飽和及反飽和 ； 去馬賽克演算法 ； 數位相機 ； 離散餘弦轉換 ； 邊訊息保留 ； 亮度估計 ； 馬賽克影像 ； 尺寸調整演算法 ； 索貝爾算子

並列摘要

Recently, color image processing is extensively becoming a very important research area since color images provide more fruitful information. Among the color image processing research issues, the edge-preserving for color contrast enhancement issue, the color demosaicing issue, and the mosaic image resizing issue are three popular research issues. Thus, this thesis presents an efficient edge-preserving algorithm for color contrast enhancement with application to color image segmentation, a demosaicing algorithm for color filter array using gradient edge detection masks and adaptive heterogeneity-projection, and a joint demosaicing and arbitrary-ratio resizing algorithm for mosaic images.

In the edge-preserving for color contrast enhancement issue, a new and efficient edge-preserving algorithm is presented for color contrast enhancement in CIE Lu'v' color space. The proposed algorithm not only can enhance the color contrast as the previous algorithm does, but also has an edge-preservation effect. In addition, the spurious edge points occurred due to the color contrast enhancement can be well reduced using the proposed algorithm. This is the first edge-preserving algorithm for color contrast enhancement in color space. Furthermore, a novel color image segmentation algorithm is presented to justify the edge-preservation benefit of the proposed color contrast enhancement algorithm. Experimental results demonstrate the advantages of color contrast enhancement, edge-preservation effect, and segmentation result in our proposed algorithm.

In the color demosaicing issue, without demosaicing processing, a new approach is first proposed to extract more accurate gradient/edge information on mosaic images directly. Next, based on spectral-spatial correlation, a novel adaptive heterogeneity-projection with proper mask size for each pixel is presented. Combining the extracted gradient/edge information and the adaptive heterogeneity-projection values, a new edge-sensing demosaicing algorithm is presented. Experimental results demonstrated that our proposed high-quality demosaicing algorithm has the best image quality performance when compared with several recently published algorithms.

In the mosaic image resizing issue, a joint demosaicing and arbitrary-ratio resizing algorithm for mosaic images is presented. First, the fully populated green color plane is constructed by using the edge-sensing approach and color difference idea. Instead of interpolating the R and B color planes directly, the green-red color difference plane and green-blue color difference plane are therefore interpolated in order to reduce the estimation error. Next, based on the discrete cosine transform technique, the above three constructed planes are resized to the arbitrary sized ones. Finally, the resized red and blue color planes are constructed by using the three resized planes, and then the arbitrary sized full color image is obtained. To the best of our knowledge, this is the first time that such a joint demosaicing and arbitrary-ratio resizing algorithm for mosaic images is presented. Based on twenty-four popular testing mosaic images, the proposed resizing algorithm has better image quality performance when compared with three native algorithms which are the combinations of three well-know demosaicing methods and one existing resizing method.

並列關鍵字

Adaptive heterogeneity projection ； CIE color model ； Color contrast enhancement ； Color edge detection ； Color filter array (CFA) ； Color histogram moment ； Color image processing ； Color peak signal-to-noise ratio (CPSNR) ； Color image segmentation ； Color saturation and desaturation ； Demosaicing algorithm ； Digital cameras ； Discrete cosine transform (DCT) ； Edge-preservation effect ； Luminance estimation ； Mosaic images ； Resizing algorithm ； Sobel operator.

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