• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.665-668
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• 2012

멀티미디어 콘텐츠는 디지털 데이터의 특성상 수정과 복제가 쉽고, 이에 따라 불법 유통과 위 변조 등의 문제가 발생할 수 있으므로 콘텐츠 보안의 중요성이 높아지고 있고 가역 워터마킹 방법은 하나의 솔루션이다. 본 논문에서는 JPEG 압축 표준에서 사용할 수 있는 가역 워터마킹 기법을 제안한다. JPEG 압축 과정 중 비손실 과정에서 유지되는 양자화 DCT 블록 데이터에 대하여 인접 블록의 계수간 차이값의 히스토그램을 계산하고, 히스토그램 쉬프팅을 통하여 가역 워터마크를 삽입한다. 디코딩 과정에서 영상에 삽입된 워터마크를 추출함과 동시에 원본 JPEG 표준 영상의 품질을 복원한다. 제안 알고리즘의 성능 평가를 위해 다양한 영상을 대상으로 영상 품질과 압축률을 평가하였다. 삽입된 영상의 PSNR과 압축률은 32.33dB과 89.69%로, 표준 JPEG 압축된 영상 대비 각 3.24dB의 PSNR 차이와 2.58%의 압축률 차이를 보였다.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.43 no.5 s.311
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• pp.57-67
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• 2006

Intellectual property rights are gathering strength theses days. Because digital contents are easily reproduced and distributed by advanced computers and networks. Digital watermarking is one of the best solutions for this problem. Generally, frequency-domain watermarking algorithms are preferred since they are more robust than spatial-domain algorithms. However, coefficients in the frequency domain are floating-point numbers. Thus, it is not easy to manipulate those floating-point coefficients and frequency-domain watermarking algorithms have some limitations in their applications. In order to overcome this difficulty, we employ an integer transform in this paper. In addition, our proposed algerian can extract the watermark from both the spatial and frequency domains. We embed the watermark into a specific bit-plane of mid-frequency coefficients. This is equivalent to the differential energy watermarking (DEW) in the spatial domain. Our simulation results show that the proposed algorithm is imperceptible, good for the watermark payload, and robustness against various attacks. Moreover, it is more efficient than any other algorithm working in only one domain.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4B
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• pp.771-782
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• 2000

In this paper, an H.263 video codec is implemented by adopting the concept of hardware and software co-design. Each module of the codec is investigated to find which approach between hardware and software is better to achieve real-time processing speed as well as flexibility. The hardware portion includes motion-related engines, such as motion estimation and compensation, and a memory control part. The remaining portion of theH.263 video codec is implemented in software using a RISC processor. This paper also introduces efficient design methods for hardware and software modules. In hardware, an area-efficient architecture for the motion estimator of a multi-resolution block matching algorithm using multiple candidates and spatial correlation in motion vector fields (MRMCS), is suggested to reduce the chip size. Software optimization techniques are also explored by using the statistics of transformed coefficients and the minimum sum of absolute difference (SAD)obtained from the motion estimator.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.4
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• pp.833-839
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• 2016

In this paper, we propose a selective feature extraction algorithm between Markov transition probability and co-occurrence probability for an effective image splicing detection. The Features used in our method are composed of the difference values between DCT coefficients in the adjacent blocks and the value of Kullback-Leibler divergence(KLD) is calculated to evaluate the differences between the distribution of original image features and spliced image features. KLD value is an efficient measure for selecting Markov feature or Co-occurrence feature because KLD shows non-similarity of the two distributions. After training the extracted feature vectors using the SVM classifier, we determine whether the presence of the image splicing forgery. To verify our algorithm we used grid search and 6-folds cross-validation. Based on the experimental results it shows that the proposed method has good detection performance with a limited number of features compared to conventional methods.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.11
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• pp.2543-2551
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• 1997

This paper proposes a compression technique of image data, a variable length PN code and channel models which are required in CDMA communication system. It also analyzes their performances. Original images is compressed by 2-D DCT and its coefficients are quantized by optimal quantizer at compression rate 0.84bit/pel. Channel model 1 and 2 which are composed of 5 and 4 channels respectively are employed to be used in CDMA. Such a situation forces us to empoly variable length PN code, such as Chebyshev map for spread spectrum system. When average PN code length of model 1 and 2 is 44.4 and 26.7 chips respectively, the received image through these models under Gaussian noise with variance 1.75 is visually of the same quality as the transmitting image. Thus, the model 2 appears to be better in channel efficiency, comparing with channel model 1 and channel model which uses fixed length PN code.

• Journal of IKEEE
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• v.5 no.2 s.9
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• pp.221-231
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• 2001

In this paper, we propose an efficient requantization method for INTRA frames in heterogeneous transcoding from MPEG-1 to MPEG-4 simple profile. The quantizer for MPEG-1 INTRA MB usually uses a quantization weighting matrix while the quantizer for MPEG-4 simple profile doesn't. As a result, the quantization step sizes of the two quantizers may not be the same even for the same quantization parameter. Due to this mismatch in the quantization step site, the transcoded MPEG-4 sequence suffers from serious quality degradation and the number of bits produced by transcoding increases from the original MPEG-1 video sequence. To solve these problems, we propose an efficient method to find a near-optimum reconstruction level in the transcoder. We also present a PDF (probability distribution function) estimation method for the original DCT coefficients of MPEG-1 video sequence, which is required for the proposed requantization. Experimental results show that the proposed method gives $0.3{\sim}0.6dB$ improvement in PSNR over the conventional method, even at the reduced bit-rate about $5{\sim}7%$ from the conventional method.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.4
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• pp.399-407
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• 2002

In this paper, a novel algorithm is proposed to reduce the blocking artifacts of block-based coded images by using block classification and MLP. In the proposed algorithm, we classify the block into four classes based on a characteristic of DCT coefficients. And then, according to the class information of neighborhood block, adaptive neural network filter is performed in horizontal and vertical block boundary. That is, for smooth region, horizontal edge region, vertical edge region, and complex region, we use a different two-layer neural network filter to remove blocking artifacts. Experimental results show that the proposed algorithm gives better results than the conventional algorithms both subjectively and objectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6A
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• pp.584-591
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• 2002

In this paper, we proposed a b1ocking artifact reduction algorithm using similarity and linear combination between blocks. In the proposed method, all of the blocks are classified into low frequency block and high frequency block according to the their DCT coefficients. And we defined range block which shows blocking artifacts, as block centered to block boundary and defied domain block as similar block with range block within search range. In the search procedure, we used sub-block's property of range block and similarity for more accurate searching. Finally blocking artifact reduction algorithm is performed using linear combination between searched domain block and blocky range block. The performance of the proposed method is investigated by computer simulation in comparison with the traditional methods. In the experimental results, Ire confirmed the better performance in the subjective by 0.04∼0.4 dB and objective image quality.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.1
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• pp.79-86
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• 2003

A new quantization constraint set based on the theory of Projection onto Convex Set(POCS) is proposed to reduce blocking artifact appearing in block-coded images. POCS-based postprocessing for alleviating the blocking artifact consists of iterative projections onto smoothness constraint set and quantization constraint set, respectively. In general, the conventional quantization constraint set has the maximum size of range where original image data can be included, therefore over-blurring of restored image is unavoidable as iteration proceeds. The projection onto the proposed quantization constraint set can reduce blocking artifact as well as maintain the clearness of the decoded image, since it controls adaptively the size of quantization constraint set according to the DCT coefficients. Simulation results using the proposed quantization constraint set as a substitute for conventional quantization constraint set show that the blocking artifact of the decoded image can be reduced by the small number of iterations, and we know that the postprocessed image maintains the distinction of the decoded image.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.41 no.4
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• pp.113-123
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• 2004

This paper presents a new collusion-secure fingerprinting scheme to embed fingerprints into three-dimensional(3-D) mesh models efficiently. In the proposed scheme, we make the same number of fingerprints as the number of customers based on the finite projective geometry, partition a 3-D mesh model related to the number of bits assigned to each fingerprint and then embed a watermark representing copyright information into each submesh to be marked. Considering imperceptibility and robustness of the watermarking algorithm we embed the watermark signal into mid-frequency DCT coefficients obtained by transforming vertex coordinates in the triangle strips which are generated from the submeshes to be marked. Experimental results show that our scheme is robust to additive random noises, MPEG-4 SNHC 3-D mesh coding, geometrical transformations, and fingerprint attacks by two traitors' collusion. In addition, we can reduce the number of bits assigned to each fingerprint significantly.