• Title/Summary/Keyword: AC and DC in DCT Coefficients

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A Image Search Algorithm using Coefficients of The Cosine Transform (여현변환 계수를 이용한 이미지 탐색 알고리즘)

  • Lee, Seok-Han
    • The Journal of Korea Institute of Information, Electronics, and Communication Technology
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    • v.12 no.1
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    • pp.13-21
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    • 2019
  • The content based on image retrieval makes use of features of information within image such as color, texture and share for Retrieval data. we present a novel approach for improving retrieval accuracy based on DCT Filter-Bank. First, we perform DCT on a given image, and generate a Filter-Bank using the DCT coefficients for each color channel. In this step, DC and the limited number of AC coefficients are used. Next, a feature vector is obtained from the histogram of the quantized DC coefficients. Then, AC coefficients in the Filter-Bank are separated into three main groups indicating horizontal, vertical, and diagonal edge directions, respectively, according to their spatial-frequency properties. Each directional group creates its histogram after employing Otsu binarization technique. Finally, we project each histogram on the horizontal and vertical axes, and generate a feature vector for each group. The computed DC and AC feature vectors bins are concatenated, and it is used in the similarity checking procedure. We experimented using 1,000 databases, and as a result, this approach outperformed the old retrieval method which used color information.

Image Compression with Edge Directions based on DCT-VQ (DCT-VQ를 기반으로 한 에지의 방향성을 갖는 영상압축)

  • 김진태;김동욱;임한규
    • Journal of Korea Multimedia Society
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    • v.1 no.2
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    • pp.194-203
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    • 1998
  • In this paper, a new DCT-VQ method is proposed which can solve the problems of VQ such as the degradation of edge and enormous calculations. VQ is carried in DCT domain but spatial domain in order to protect the degradation of edge. DCT makes high correlated image data decorrelated and the energy concentrated on a few coefficients. In DCT domain, the DC coefficient is quantized with 8 bits uniform scalar quantizer and the AC coefficients are divided to three regions and coded with vector qiantizer for considering edge components. For the decrease of the calculation and memory, the vectors for three region have small dimension of $1{\times}7$ and use the same codebook. Thus, the proposed method can fully express the edge components by considering AC coefficients in DCT domain and decrease the calculation and memory be reducing the dimension of vectors.

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Fast Detection of Copy-Move Forgery Image using DCT

  • Shin, Yong-Dal
    • Journal of Korea Multimedia Society
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    • v.16 no.4
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    • pp.411-417
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    • 2013
  • In this paper, we proposed a fast detection method of copy-move forgery image based on low frequency coefficients of the DCT coefficients. We proposed a new matching criterion of copy-moved forgery image detection (MCD) using discrete cosine transform. For each $8{\times}8$ pixel block, the DCT transform is calculated. Our algorithm uses low frequency four (DC, 3 AC coefficient) and six coefficients (DC, 5 AC coefficients) of DCT per $8{\times}8$ pixel block. Our algorithm worked block matching for DCT coefficients of the $8{\times}8$ pixel block is slid by one pixel along the image from the upper left corner to the lower right corner. Our algorithm can reduce computational complexity more than conventional copy moved forgery detection algorithms.

Embedding DC Digital Watermarking in the DCT (DCT의 DC 계수에 워터마크 삽입하는 디지털 워터마킹)

  • 신용달;권성근
    • Journal of Korea Multimedia Society
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    • v.6 no.6
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    • pp.962-967
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    • 2003
  • In this paper, we proposed DC term embedding digital watermarking in the DCT domain. We computed a 8${\times}$8 block DCT The watermark signal is composed of a random number sequence of length 1000, which obeys normal distribution with zero mean and unit variance N(0,1). We embedded watermark signal in DC term for small watermark signal, the other watermark signal embedded in the largest AC coefficients. Experiment show that the invisibility and robust of the proposed method better than those of the conventional methods.

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Predictive Coding Methods in DCT Domain for Image Data Compression (영상 압축 부호화를 위한 DCT영역에서의 예측 부호화 방법)

  • Lee, Sang-Hee;Kim, Jae-Kyoon
    • Journal of the Korean Institute of Telematics and Electronics S
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    • v.35S no.8
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    • pp.86-95
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    • 1998
  • Intra-frame video compression, which cannot make use of temporal predictions, requires much higher bit rates compared with inter-frame schemes. In order to reduce bit rates, intra-frame predictive coding methods in DCT domain have been studied especially within the framework of the MPEG-4 video coding standard currently being developed. In this paper, we propose novel intra-frame predictive coding methods in DCT domain with the marginal complexity increase over the conventional methods . The proposed methods consist of a DC coefficient prediction method and two AC coefficient prediction methods. The proposed methods consist of a DC coefficient prediction method and two AC coefficient prediction methods. The proposed DC coefficient prediction method makes it possible to adaptively select the prediction directions without overhead bits, by comparing gradients of DC coefficients from neighboring blocks. As the AC coefficient prediction methods, first, we present an effective method which can improve the prediction directions of the MPEG-4 scheme by considering the DC coefficient of the current block to be coded. And, we present another effective method that decision on the prediction is carried out for each AC coefficient. Simulation results show that substantial bit savings can be achieved by the proposed methods.

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An Adaptive Image Enhancement of the DCT Compressed Image using the Spatial Frequency Property (공간주파수 특성을 이용한 DCT 압축영상의 적응 영상 향상)

  • Jeon, Seon-Dong;Kim, Sang-Hee
    • Journal of the Institute of Convergence Signal Processing
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    • v.11 no.2
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    • pp.104-111
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    • 2010
  • This paper presents an adaptive image enhancement method using the spatial frequency property in the DCT(discrete cosine transform) compressed domain. The dc coefficients, the illumination components of image, are adjusted to compress the dynamic range of image, and the ac coefficients are modified to enhance the contrast by using the human visual system(HVS) and the spatial frequency property. The ac coefficients are separated into vertical direction, horizontal direction, and mixed spatial frequency components, and adaptively modified to minimize the block artifacts that possibly occur in the image enhancement. The proposed method using dynamic range compression and adaptive contrast enhancement shows the advanced performance without the block artifact compared with existing method.

DCT-Based Energy-Ratio Measure for Autofocus in Digital Camera (이산 코사인 변환 계수의 에너지 비를 사용한 디지털 카메라용 초점 간 연산자)

  • Lee, Sang-Yong
    • Journal of the Institute of Electronics Engineers of Korea SP
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    • v.45 no.6
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    • pp.88-94
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    • 2008
  • A DCT-based energy-ratio measure for autofocus in digital camera is proposed in this paper. This measure, namely AC2DC1 and AC5DC1, determines the sharpness of an image using a ratio between AC and DC energy in the DCT domain. This method is derived from energy analysis of DCT coefficients. Autofocus score calculation method is used to assess the performance of the proposed measure and to compare it with other measures. Experimental results under various conditions verify the robustness of the proposed focus measure for the Gaussian as well as impulsive noises.

A Robust Watermark System for MPEG-2 Video Against Geometric and Bitrate Varying Attacks (기하학적 공격 및 비트율 변화 공격에 강한 MPEG-2 동영상 워터마크 시스템 개발)

  • Hwang, Seon-Cheol
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.59 no.3
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    • pp.258-262
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    • 2010
  • This paper describes a watermarking system that has the robust characteristics against the geometric attacks of resizing and the bitrate varying attacks. While the existing watermark methods of marking on AC in DCT coefficients are weak against the geometric attacks, the methods of tiny increasing the DC in DCT coefficients and the system implementations are suggested in this paper. We measure the differences between the original images and the watermarked images and the detecting rate from the geometric and bitrate attacked images. Results of experiments show that our method is robust against that attacks.

DCT Domain Zero-Watermarking based on CRT (CRT 기반의 DCT 영역 제로-워터마킹)

  • Kim, Hyoung-Do;Sohn, Kyu-Seek
    • The Journal of the Korea Contents Association
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    • v.11 no.1
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    • pp.9-15
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    • 2011
  • Zero-watermarking is a digital watermarking technique that can escape from data distortion and quality degradation by no watermark insertion into digital images to be watermarked. This paper proposes DCT0CRT, a CRT-based zero-watermarking technique in the domain of DCT. One of the DC and low-frequency AC coefficients of each DCT block chosen in chaotic way from an image is selected by testing whether it satisfies the CRT-based condition matching with the watermark bit to be embedded. Such selection information forms a key to extract the watermark from the watermarked image. Experimental results show that the image quality watermarked by DCT0CRT is better than that watermarked by any other CRT-based watermarking techniques and the inserted watermark is robust against some common attacks such as sharpening, blurring, and JPEG lossy compression.

Effective scene change detection methods using characteristics of MPEG video (MPEG 비디오의 특성 추출을 이용한 효과적인 장면 전환 검출 기법)

  • 곽영경;최윤석;고성제
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.24 no.8B
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    • pp.1567-1576
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    • 1999
  • In this paper, we propose new methods to detect a scene cut and a dissolve region in compressed MPEG video sequences. The scene cut detection method uses edge images obtained using DCT AC coefficients and the dissolve detection method utilizes the macroblock type information of the MPEG stream. The proposed scene cut detection method is insensitive to brightness and can detect scene changes more precisely than the methods using DC coefficients since AC edge images can express original images more exactly than DC edge images do. The proposed dissolve detection method using the number of intra macroblocks(MBs) computationally efficient since it does not require the decoding process. Experimental results show that the proposed methods perform better in detection scene changes than conventional other methods.

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