臺灣博碩士論文加值系統

現今的數位相機(digital still camera, DSC)由於具有操作簡單、即拍即看的功能而深受消費者的喜愛，故其普及性遠超過傳統相機。通常我們在數位相機中，所指的3A意即三種預處理自動化系統：自動對焦(auto focus)、自動曝光(auto exposure)，以及自動白平衡(auto white balance)，這三種自動化過程不僅為「拍攝簡單化」的幕後功臣，且對最後影像的品質皆有非常重大的影響。本篇論文針對數位相機的其中兩種自動功能—自動對焦以及自動白平衡—做探討與研究，並對其分別提出演算法。
在自動對焦方面，我們提出以離散餘弦轉換(discrete cosine transform)為基礎的對焦值計算方法，其方法能在低對比度情況下表現良好；而在自動對焦中的搜尋演算法方面，我們提出了一個能夠概略的估計出最大對焦值的位置的搜尋方法，不但有效而且快速。在自動白平衡方面，我們以取樣影像邊緣為概念，同時加入對光源色度的限制，以及考慮亮度資訊等技術，發展出一個大部分情況下在視覺上表現皆相當良好的演算法。同時，針對自動對焦以及自動白平衡，我們皆展示一些與前人方法比較的結果。
本論文最後將對我們所提出的演算法做一總結，並加以檢討與改進。

第一章 緒論 1
第一節 數位相機的架構 1
第二節 本篇論文架構 3
第二章 自動對焦 5
第一節 相機的對焦原理 5
2.1.1 薄透鏡方程式 5
2.1.2 光圈 6
2.1.3 景深 6
第二節 自動對焦系統的概論 7
2.2.1 主動式對焦系統 8
2.2.2 被動式對焦系統 8
2.2.3 單點對焦與多點對焦 10
第三節 對焦值的測量 11
2.3.1 Tenengrad方法 11
2.3.2 拉普拉斯遮罩 12
2.3.3 變異數 13
2.3.4 標準化後變異數 13
2.3.5 基於離散小波轉換的對焦值 14
第四節 對焦鏡片位置的搜尋演算法 14
2.4.1 全域搜尋法 15
2.4.2 爬山法 16
2.4.3 費柏納契搜尋法 18
第五節 提出的對焦值以及搜尋演算法 18
2.5.1 對焦值演算法 19
2.5.2 鏡頭位置搜尋演算法 21
第六節 實驗結果與比較 24
2.6.1 對焦值方法之比較 24
2.6.2 搜尋演算法實驗結果 28
第三章 自動白平衡. 31
第一節 色彩恆常性與白平衡 31
3.1.1 色彩恆常性 31
3.1.2 色溫 32
3.1.3 自動白平衡 34
第二節 前人的自動白平衡演算法 36
3.2.1 Grey world方法 37
3.2.2 Grey world資料庫方法 37
3.2.3最大色彩值法 38
3.2.4 ACASDL方法 39
3.2.5 Grey-edge假說 41
第三節 提出的方法 43
3.3.1 光源色度的限制 43
3.3.2 演算法流程 47
第四節 實驗結果與比較 51
3.4.1 SFU提供的影像之測試 52
3.4.2 自行實際拍攝影像之測試 53
第四章 結論與未來展望 61
第一節 自動對焦 61
第二節 自動白平衡 61
參考文獻 63

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