• Journal of Korea Multimedia Society
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• v.8 no.6
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• pp.783-789
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• 2005

This paper is proposed a watermarking technique for copyright protection of multimedia contents. We proposed adaptive watermark detection algorithm using stochastic perceptual model and statistical decision method in DMWT(discrete multi wavelet transform) domain. The stochastic perceptual model calculates NVF(noise visibility function) based on statistical characteristic in the DMWT. Watermark detection algorithm used the likelihood ratio depend on Bayes' decision theory by reliable detection measure and Neyman-Pearson criterion. To reduce visual artifact of image, in this paper, adaptively decide the embedding number of watermark based on DMWT, and then the watermark embedding strength differently at edge and texture region and flat region embedded when watermark embedding minimize distortion of image. In experiment results, the proposed statistical decision method based on multiwavelet domain could decide watermark detection.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.7
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• pp.119-124
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• 2015

Speech enhancement has been required as a preprocessor for a noise robust speech recognition system. Codebook-based Speech Enhancement (CBSE) is highly robust in nonstationary noise environments compared with conventional noise estimation algorithms. However, its performance is severely degraded for the codevector combinations that have lower correlation with the input signal since CBSE depends on the trained codebook information. To overcome this problem, only the reliable codevector combinations are selected to be used to remove the codevector combinations that have lower correlation with input signal. The proposed method produces the improved performance compared to the conventional CBSE in terms of Log-Spectral Distortion (LSD) and Perceptual Evaluation of Speech Quality (PESQ).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.822-832
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• 1994

DSC-HDTV image compression algorithm removes spatial, temporal, and amplitude redundancies of an image by using transform coding, motion-compensated predictive coding, and adaptive quantization, respectively. In this paper, leak processing method which is used to recover image quality quickly from scene change and transmission error and adaptive quantization using perceptual weighting factor obtained by HVS are proposed. Perceptual weighting factor is calculated by contrast sensitivity, spatio-temporal masking and frequency sensitivity. Adaptive quantization uses the perceptual weighting factor and global distortion level from buffer history state. Redundant bits according to adaptation of HVS are used for the next image coding. In the case of scene change, DFD using motion compensated predictive coding has high value, large bit rate and unstabilized buffer states since reconstructed image has large quantization noise. Thus, leak factor is set to 0 for scene change frame and leak factor to 15/16 for next frame, and global distortion level is calculated by using standard deviation. Experimental results show that image quality of the proposed method is recovered after several frames and then buffer status is stabilized.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2016.11a
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• pp.100-102
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• 2016

본 논문에서는 기존의 인지 영상 부호화에 사용되던 Just Noticeable Distortion(JND) 보다 더 압축에 적합한 모델인 Just Noticeable Quantization Distortion(JNQD) 모델을 제시하고, 이를 사용한 인지적 영상 압축 방법을 제안한다. 제안하는 인지적 영상 압축 방식은 영상 코덱 내부의 Rate-Distortion Optimization(RDO)을 수정하지 않고 입력되는 영상의 불필요한 정보들을 미리 제거하는 전처리 과정으로서, JNQD 모델을 사용하여 보다 간단하면서 압축 효율을 크게 증가 시킬 수 있다. 기존 영상 압축의 전처리 방법들은 부호화기의 양자화 값을 전처리 과정에서 고려하지 못하여 부정확한 인지 중복성 제거 결과를 초래하였으나, 제안하는 방법은 영상의 특성뿐만 아니라 양자화 크기 값을 고려하여 적응적으로 인지 왜곡이 발생하지 않는 주관적 인지 중복성 제거를 전처리 과정에서 수행할 수 있다. 거의 유사한 주관적 품질 수준을 유지하면서 HEVC 참조 소프트웨어 대비 약 15%의 압축효율 향상을 보인다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2014.06a
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• pp.203-205
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• 2014

본 논문에서는 HEVC 기반 비디오 부호화에 있어 CTU 단위의 시각 민감도에 따라 CTU 별로 QP 를 조절하여 주관적 화질을 향상시키는 방법을 제안한다. 시각 민감도를 측정하는 방법으로서 화소 영역에서의 최소가지차(JND, just noticeable distortion)를 계산하여 이용하였고, 이를 HM 12.0 참조 소프트웨어에서 이용되는 $R-{\lambda}$ 모델 기반의 율 제어 모듈에 결합하여 시각 민감도에 따라 QP 를 제어할 수 있도록 하였다. 시각 민감도가 큰 영상의 영역에 대해서는 상대적으로 작은 QP 값을, 시각민감도가 작은 영역에 대해서는 큰 QP 값을 양자화 과정에 적용함으로써, 시각 민감도가 작은 영역에 대해서는 사용 비트양을 절약하고, 절약된 비트를 상대적으로 시각 민감도가 큰 영역을 위해 사용함으로써 비디오의 주관적 화질을 향상시킬 수 있었다. 뿐만 아니라 이를 하드웨어에 적용 가능하게 하기 위해 HM 12.0 기반 하드웨어 구현을 위한 소프트웨어 플랫폼에 구현하여 실험한 결과, $R-{\lambda}$ 모델 율 제어 알고리즘으로 율 제어 하여 부호화 한 경우 Y-PSPNR(peak signal to perceptual noise ratio)에 대한 BD-rate 는 평균 9.4%의 이득이 있었음을 확인하였다.

• The Journal of the Acoustical Society of Korea
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• v.29 no.1
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• pp.62-68
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• 2010

This paper proposes a new masking threshold adjustment strategy to improve the performance for speech signals in low bit-rate audio coding. After determining formant regions, the masking threshold is adjusted by using the energy ratio of each sub-band to the average energy of each formant. More quantization noises are added to the bands that have relatively large energy, but less distortion is allowed in spectral valley regions by allocating more bits, which reflects the concept of perceptual weighting widely used in speech coding. From the results of objective speech quality measure, we verified that the proposed method improves quality for the speech input signals compared to the conventional one.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.172-175
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• 2002

This paper presents perceptual model with a stochastic rnultiresolution characteristic that can be applied with watermark embedding in the biorthogonal wavelet domain. The perceptual model with adaptive watermarking algorithm embed at the texture and edge region for more strongly embedded watermark by the SSQ(successive subband quantization). The watermark embedding is based on the computation of a NVF(noise visibility function) that have local image properties. This method uses non-stationary Gaussian model stationary Generalized Gaussian model because watermark has noise properties. In order to determine the optimal NVF, we consider the watermark as noise. The particularities of embedding in the stationary GG model use shape parameter and variance of each subband regions in multiresolution. To estimate the shape parameter, we use a moment matching method. Non-stationary Gaussian model use the local mean and variance of each subband. The experiment results of simulation were found to be excellent invisibility and robustness. Experiments of such distortion are executed by Stirmark benchmark test.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.33B no.4
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• pp.156-163
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• 1996

In this paper, we described the implementation and the sound quality assessment of a real-time stereo audio codec using TMS320C40 DSP (digital signal processing) chip for low bitrte and high quality audio. We implemented hardware and software in order to overcome a real-time processing problem of audio compression algorithm that can be produced by largely recursive computing and complexity of the process. We have studied five types of distortion that can be produced by perceptual coding and the codec was evaluated by eight test musics that are selected in SQAM (sound quality assessment material) 422-2-4-2 produced by EBU (european broadcast union). The subjective listening tests were carried out on the codec quality and preformance by double blind method in a listening room with eleven listeners. As a result, 5 grade-impairment scale was scored under minus one and the codec quality was evaluated to be perceptible, but not annoying.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.5 no.1
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• pp.37-42
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• 2006

A reversible audio watermarking algorithm is presented in this paper. This algorithm transforms the audio signal with the integer wavelet transform first in order to enhance the correlation between neighbor audio samples. Audio signal has low correlation between neighbor samples, which makes it difficult to apply difference expansion scheme. Second, a novel difference expansion scheme is used to embed more data by reducing the size of location map. Therefore, the difference expansion scheme used in this paper theoretically secures high embedding capacity under low perceptual distortion. Experiments show that this scheme can hide large number of information bits and keeps high perceptual quality.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.5
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• pp.1388-1399
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• 2012

This paper proposes a quality metric based on a No-Reference Bitstream (NR-B) having least computational complexity for the assessment of the human-perceptual quality of H.264 encoded video. The proposed NR-B method performs a modeling of encoding distortion with three bit-stream information (i.e. frame-rate, motion-vector, and quantization-parameter) that can be directly extractable from the encoded bitstream and does not require additional complex processing of final pictures. From performance evaluation using 165 compressed video sequences, the experiment results show that the proposed metric has a higher correlation with subjective quality than is achieved with other comparable methods.