在影像系統中，失焦是經常且容易產生的一個問題；在不同的物距下，會對應到不同的焦距。拍攝的物體們到透鏡的距離不一定相同。背景距離鏡頭較遠，前景距離鏡頭較近，而在焦距只能有一個的情況下，在其他距離外的物體就會在成像上產生了模糊的現象。
我們的目的在改善傳統透鏡易受失焦干擾，因此我們設計一個相位薄膜，使得使焦對影像的傷害降低進而獲得改善，得到比較好的影像品質。在這個目的下提出了波前理論，波前理論就是在透鏡前面加了一道薄膜，藉此去改變影像的品質。
論文中提出的環狀相位薄膜套用到光學影像系統上，得到了對應的光學轉移函數和模擬的影像。接著，我們模擬在不同的失焦程度下，將其和其他學者已發表的相位薄膜相作比較，我們的環狀相位薄膜在光學轉移函數和模擬影像上都有明顯的效果。

In the imaging system, a blurred defocus image is a common problem.
This is because different objects in the scene need different focus for imaging clearly. Background’s focus distance is different to the objects.
However, we can only have one focus distance in one picture. Therefore, the images of the other objects in different focus distance would be blurred by the faulty focuses.
We solve the above defocus problem by wave front coding. Wave front coding is a technique that adds a phase mask in front of the lens, changing the image performance.
In this thesis, we used a ring phase screen, computed accordingly its optical transfer function and then simulated the resulting images. We compared with other phase screens provided by other researchers for different defocus situations. From our simulated images and OTF results, our ring phase pupil is slightly superior.

第1章 引言...............................................1
第2章 光學影像系統之基礎.................................4
2.1 同調之影像系統.....................................4
2.2 非同調之影像系統...................................6
2.3 同調轉移函數與OTF 之間的關係......................7
第3章 多重焦距與光學轉移函數.............................9
3.1 失焦概論...........................................9
3.2 次方薄膜..........................................11
3.3 二階薄膜..........................................16
3.4 帶狀薄膜.........................................17
3.5 環狀薄膜.........................................25
3.5-1 環狀薄膜I…………………………………………..26
3.5-2 環狀薄膜II………………………………………….28
第4章 模擬結果與分析....................................34
4.1 模擬結果和比較....................................34
4.1.1 光學轉移函數和自相關函數.....................35
4.1.2 影像圖.......................................40
4.2 其他實驗結果......................................41
4.3 環狀薄膜I 與II 的比較............................43
第5章 結論..............................................45
參考文獻.................................................47

圖 2.1-1 影像系統之模型..................................4
圖 3.1-1 平面圖.........................................10
圖 3.2-1 3-D 表示之三次方薄膜相位圖.....................12
圖 3.2-2 灰階表示之三次方薄膜相位圖.....................12
圖 3.2-3 成像示意圖.....................................14
圖 3.3-1 3-D 表示之二階薄膜相位圖.......................16
圖 3.3-2 灰階表示之二階薄膜相位圖.......................16
圖 3.4-1 薄膜上得光學轉移函數示意圖.....................17
圖 3.4-2 OTF計算示意圖.................................19
圖 3.4-3 薄膜示意圖，紅色橫線為蛋形區域，藍色直線為帶狀區域.............................................20
圖 3.4-4 薄膜示意圖......................................21
圖 3.4-5 3-D 表示之新薄膜相位圖，方法II 且引入權重........24
圖 3.4-6 灰階表示之新薄膜相位圖，方法II 且引入權重.......25
圖 3.5-1 環狀薄膜I 設計示意圖...........................26
圖 3.5-1 環狀薄膜II 設計示意圖...........................28
圖 3.5-3 3-D 表示之環狀薄膜II 相位圖.....................33
圖 3.5-4 灰階表示之環狀薄膜II 相位圖.....................33
圖 4.1-1 在無加薄膜下之曲線.............................35
圖 4.1-2 用3 次方薄膜治療失焦之曲線 ....................35
圖 4.1-3 用二階薄膜治療失焦之曲線.......................36
圖 4.1-4 MTF 之比較.................................... .37
圖 4.1-5 在帶狀薄膜下之曲線.............................37
圖 4.1-6 在環狀薄膜II 下之曲線..........................38
圖 4.1-7 在環狀薄膜II 下之曲線..........................38
圖 4.1-8 在各種薄膜下模擬不同失焦狀況之影像圖...........40
圖 4.2-1 帶狀薄膜方法下模擬不同失焦狀況之影像圖….......41
圖 4.2-2 模擬不同失焦狀況之影像圖.......................42
圖 4.2-3 二階薄膜與新薄膜II 之比較......................43
圖 4.3-1 環狀薄膜I 與II 之比較..........................43
圖 4.3-2 模擬不同失焦狀況之影像圖.......................44

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