為了研究和觀察照片，圖片增強常常用來改善低品質圖片的方法。圖片增強的目的是希望能夠讓圖片中觀察者比較感興趣的部分變的比較清晰，同時讓不感興趣的部分能夠減弱甚至直接去除。其最終目的是使處理過後的圖片，能夠更適合讓人類的視覺系統去做辨識。因此，圖片增強技術是圖片應用中最基礎的一個步驟，也是圖片處理中最重要的一個部分。

在這篇論文中，我們使用基於Retinex理論的人類視覺系統和曝光融合去增強圖片的對比度。我們可以降低光暈、色彩失真和噪度的問題，而且也能夠保留住圖片的自然性。在所提出的方法中，我們只處理HSV色彩空間的V通道，以儘量保持顏色不變。我們分別估算局部和整體的入射光，並根據Retinex理論的運算，得到局部細節和整體細節的圖片。再進一步利用原圖及具局部和整體細節的三張圖片，使用曝光融合的方式，產生影像增強的結果圖。實驗結果顯示，我們的方法可以極度提升局部和整體的細節，和有效率的改善亮度和光暈及色彩失真與噪度的問題;並且能達到圖片增強的目的，讓人類視覺系統能夠更容易地去辨識和分析圖片。

In order to study and observe images, image enhancement methods are often used to improve low quality images. The purpose of image enhancement is to make the region of interest become clearer, and to weaken or even delete the uninterested region. The ultimate goal of image enhancement is to make image be clearly identified by human visual systems. Therefore, image enhancement methods are the basic step in image applications, and play an important part in image processing.

In this thesis, we use the retinex theory and exposure fusion to enhance the contrast of images. In the proposed method, we only manipulate the V channel of the HSV color space to maintain color consistency as far as possible. First, we estimate the local and the global incident lights respectively, and use the retinex theory to get images with local and global details. Following exposure fusion, the two images and the original image are used to generate the enhanced image. Experiments show that the proposed method can strengthen both the local and global details, and effectively reduce halo, color distortion, and noise problems. In short, the result images look quite nature. In summary, the proposed method can enhance the image quality, and make images easier to be analyzed and understood.

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