以邊緣角度為基礎之頻率域影像增強方法

A Method of Edge-based Image Enhancement in the Compressed Domain

林耿屹(Geng-Yi Lin)

指導教授 ： 林啟芳

元智大學/資訊學院/資訊工程學系/碩士(2012年)

https://doi.org/10.6838/YZU.2012.00198

摘要

由於數位影像的應用情境越來越廣泛，因此影像增強技術的應用也隨之普遍起來。其中，針對影像裡若細節存在於過暗或過亮的區域裡，則會造成細節辨識度不佳。為了能將影像裡辨識度不佳的細節增強以利人眼觀看，現今所常使用的演算為動態範圍壓縮(dynamic range compression)及增強影像對比(contrast enhancement)這兩種方法。其運用方式為，利用動態範圍壓縮來帶出影像細節，而利用增強影像對比來提高因執行動態範圍壓縮所損失的影像對比。因此需同時使用這兩種方法，來達到影像增強的目的。
目前在頻率域底下進行這兩種影像增強的演算法，大部份都以高頻和低頻能量的比值，作為調整增強係數之依據，並沒有利用到區塊本身的邊緣(edge)屬性。而本論文所提出的方法，是一個以邊緣角度為基礎之頻率域影像增強方法。其特點在於利用邊緣偵測演算法，先將DCT區塊分類成為邊緣區塊(edge block)和平滑區塊(non-edge block)，再針對各區塊依其特性進行不同的強化方式，以增進影像增強的效果。這樣子的好處是可以針對不同屬性的DCT區塊，來使用針對該屬性有最佳效果的方法，以進一步提升影像品質。
而在經過實驗與統計分析後，本論文所提出之演算法確實可使影像的邊緣品質變的更好。由其在前背景交界的地方，變得更加銳利，且細節上也變得更加清晰，使得整體的影像品質更為提升。

關鍵字

增強影像對比 ； 頻率域 ； 邊緣區塊

並列摘要

The process of generating digital images is likely to be affected by certain factors leading to image quality reduction. In order to solve this problem, image enhancement techniques are often utilized for improving image quality. Image enhancement methods can be classified into two types in general: spatial domain and compressed domain. In the type of compressed domain algorithm, mostly the ratio between high and low frequency energy is used as the basis for adjusting enhancement coefficient without utilizing the attributes of edges. This paper proposes an image enhanced method based on edge angles in the DCT block. The feature is utilizing the edge detection algorithm to divide DCT blocks into edge blocks and non-edge blocks, and then further focusing on edge blocks in particular direction to enhance the original image, so as to achieve the purpose of improving image quality. Finally, through experiment verification, our proposed algorithm actually enhances image edges and further improves overall image quality.

並列關鍵字

Contrast Enhancement ； Compressed Domain ； Edge Block

參考文獻

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