後向直方圖等化、後向直方圖指定和其它後向變形

Backward Histogram Equalization, Backward Histogram Specification, and Other Backward Variants

直方圖等化是一種簡單且有效的增強影像對比的演算法。它廣泛被使用在許多影像處理應用上。傳統上，直方圖等化是從最低灰階到最高的灰階的前向（forward）方向被執行。這種思維模式也被其他直方圖相關的技術所繼承，但是這種思考模式也限制直方圖的可能用途。在本論文中，我們利用後向操作觀念以提出後向直方圖等化，後向直方圖指定的演算法，以及將後向的觀念延伸到直方圖重分布上。我們的實驗結果顯示前向和後向直方圖相關等化的方法可以彼此互補，並且在前後方向上選擇一個適當的途徑有助於使用者獲得更加宜人的對比效果和更佳的亮度保持。

Histogram equalization (HE), a simple and effective algorithm to enhance the contrast of an image, is used in a wide range of image processing applications. Traditionally, it is implemented in the forward direction of the histogram of an image, i.e., from the lowest to the highest gray level. This pattern of thinking is also inherited by other histogram-related techniques. However, it limits possible uses for histograms. In this paper, the backward-operating concept is utilized to propose algorithms for backward histogram equalization (BHE), backward histogram specification, and their extension to histogram redistribution. Our experimental results showed that methods of forward and backward histogramrelated equalization can complement each other and that choosing properly between the two can help users obtain more agreeable contrast effects and better brightness preservation.