利用Otsu門檻化與格雷碼改良式鈍化遮罩偵測於影像竄改辨識之應用

Abstract

近幾年來，科技快速地發展使得行動裝置普及，拍攝數位照片變得越來越容易，再加上數位影像的技術愈來愈成熟，影像編輯軟體也因此盛行。由於數位影像的內容資訊容易被修改，衍生數位影像鑑識的議題。因此該如何確認其攝影內容的真實性變得越來越重要。本研究的目的在於快速偵測經過鈍化遮罩處理後的影像，也就是將銳化後的影像偵測出來，以垂直邊緣二進位編碼演算法為基礎加以改良，利用格雷碼對稱的特性，降低特徵的運算量，改善其執行時間。再加上使用Otsu門檻化方法搭配Canny邊緣偵測，保留對比明顯的邊緣，增加辨識的成功率。最後，比較兩種編碼方式並且觀察原始影像與銳化後影像的特徵對分類結果的影響。 經由實驗結果顯示，本論文之改良式鈍化遮罩偵測系統，對於一般拍攝環境下，經過鈍化遮罩處理過的影像具有快速且較佳的檢測效果。

In recent years, the development of the wireless technologies is growing rapidly. People generally have more than one mobile device such as smart phones or tablet PCs. Therefore, taking a picture becomes a simple thing in our live. Due to the fact that digital image processing software is easy to use, the research of digital image forensics becomes popular in the world. In this study, we focus on Unsharp Masking (USM) detection. The proposed detecting system is based on Edge Perpendicular Binary Coding (EPBC). We use Otsu thresholding to enhance the performance of Canny edge detection, so that the accuracy of USM detection is increased. Moreover, the symmetric property of Gray encoding is used to reduce the number of feature points. This improves the execution time of the detecting system. Experimental results show that our proposed method has faster execution and better accuracy of USM detection for the normal shooting environment.