April 2014
Beginner to intermediate
830 pages
15h 21m
Chinese
Content preview from Mathematica 錦囊妙計
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8.4 使用直方圖規格化（Histogram Specification）處理影像
|
347
1. 以訣竅 8.3 的方式，將輸入影像轉換為均勻分布。
2. 將目標影像均衡化轉換的反轉換，作用於步驟 1 的輸出。
這個做法的關鍵在於找出反轉換，因為在離散數學的領域進行數學運算，也許無法找出
精確的反轉換，但可以下列方式取得近似反轉換：將
targetMap
的索引址與元素進行翻
轉互換，取最小的獨特元素值作為索引址，若有缺漏值則使用下一個最接近的數值。
以下的
inverseEqualizationMap
函數可從輸入的影像建立反轉換，但如果你仔細檢查
histogramSpecification
的程式碼，會發現為了效率考量，並未建立反轉換，而是直接
從輸入與目標影像的均衡化轉換，使用規格化映射函數
specificationMap
計算反轉換。
350]
使用
histogramSpecificationPlot
指令可繪出輸入及目標均衡化轉換、目標均衡化反轉
換及最終的直方圖規格化轉換，藉此獲得更進一步的理解，這些圖形顯示輸入灰階影像
如何映射至輸出。如果你還沒有被說服
specificationMap
即為所需轉換，試著將上圖的
specMap
的圖形取代為
inverseMap[#]&/@inputMap
，仍可輸出完全相同的圖形。
計算目標影像的直方圖映射
計算輸入影像的直方圖映射
計算
targetMap的 反映射
mathemaca 6 以前的版本才需載入此套件
ch08.indd 347 2014/4/7 下午 12:29:39 ...
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