• 한국정보과학회논문지:시스템및이론
• /
• 제36권2호
• /
• pp.68-72
• /
• 2009

접미사 배열은 주어진 문자열 내의 모든 접미사를 사전식 순서로 저장하는 자료 구조로, 많은 저장 공간을 사용하는 접미사 트리를 대체하면서 여러 가지 문자열 관련 문제에 사용되고 있다. 이를 O(n) 시간 내에 생성하는 것과 더불어, 실세계 입력에 대하여 작은 시간과 공간을 사용하여 구성하는 알고리즘들 역시 제안되어 왔다. 본 논문은 Maniscalco와 Puglisi[1]가 제안한 접미사 정렬 알고리즘을 분석하고, 프로그램의 수행 시간을 개선한 새로운 알고리즘을 제안한다.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제11권9호
• /
• pp.4567-4587
• /
• 2017

With the growth of the Internet and the extensive applications of image editing software, it has become easier to manipulate digital images without leaving obvious traces. Copy-move is one of the most common techniques for image forgery. Image blind forensics is an effective technique for detecting tampered images. This paper proposes an improved copy-move forgery detection method based on the discrete cosine transform (DCT). The quantized DCT coefficients, which are feature representations of image blocks, are truncated using a truncation factor to reduce the feature dimensions. A method for judging whether two image blocks are similar is proposed to improve the accuracy of similarity judgments. The main transfer vectors whose frequencies exceed a threshold are found to locate the copied and pasted regions in forged images. Several experiments are conducted to test the practicability of the proposed algorithm using images from copy-move databases and to evaluate its robustness against post-processing methods such as additive white Gaussian noise (AWGN), Gaussian blurring, and JPEG compression. The results of experiments show that the proposed scheme effectively detects both copied region and pasted region of forged images and that it is robust to the post-processing methods mentioned above.