• The Journal of the Acoustical Society of Korea
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• v.15 no.2
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• pp.95-100
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• 1996

In this paper, we present an image coder using variable quantizer for newly proposed JPEG extensions which has been standardized as ISO/IEC 10918-3(ITU-T Rec. T.84). It is necessary to alleviate the blocking artifact which is more sensitive to human eye in view of the spatial frequency sensitivity. The blocking artifact arises in the lower activity area rather than in the higher area. Therefore variable quantizer use the horizontal and vertical derivatives for calculating the $8{\times}8$ block activity. We classified nonlinear quantizer parameter into 5 categories in order to finely quantize in the lower active region. As a result of simulation for various images, the proposed coder increases subjective and objective quality at a given bit rate.

• The Journal of the Korea Contents Association
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• v.5 no.3
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• pp.123-131
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• 2005

Among the digital halftoning, the error diffusion halftoning gives better subjective quality than other halftoning techniques. But it also makes edges of objects blurred. To overcome the defect, this paper proposes the modified error diffusion halftoning algorithm to enhance the edges using the spatial perceptual properties of the human visual system. Using the properties that the human eyes perceive not the pixel's luminance itself but the local average luminance and the information that human eyes perceive spatial variation, the proposed method computes information of edge enhancement(IEE). The IEE is added to the quantizer's input pixel and feeds into the halftoning quantizer. The quantizer produces the halftone image having the enhanced edge. Also this paper proposes the technique that the coefficients of the error diffusion filter are adapted according to the correlation among color components. The computer simulation results show that the proposed method produces finer halftoning images than conventional methods due to the enhanced edges. And the proposed method also preserves similar in edges to original image and reduces some defects such as color impulse and false contours.

• The Journal of the Korea Contents Association
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• v.5 no.2
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• pp.221-228
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• 2005

The paper proposes the improved error diffusion halftoning system to enhance the edges using the spatial perceptual characteristics of the human visual system. The proposed method computes a spatial variation(SV), which is the difference between a pixel luminance and the average of its $3{\times}3$ neighborhood pixels' luminances weighted according to the spatial positioning. Information of edge enhancement(IEE) Is computed using the SV and the local average luminance. The IEE is added to the quantizer's input pixel and feeds into the halftoning quantizer. The quantizer produces the halftone image having the enhanced edge. The performance of the proposed method is compared with conventional methods by measuring the edge correlation. The halftone images by using the proposed method show better quality due to the enhanced edge. And the detailed edge is preserved in the halftone images by using the proposed method.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2013.06a
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• pp.1-2
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• 2013

KLT-AECQ 는 지각적인 성능 향상을 위하여 formant weighting 필터를 사용한다.Code Excited Linear Prediction(CELP) 코더는 사람의 음성신호를 압축하는 대표적인 방식이다. CELP 의 Rate-Distortion 성능을 향상 시키기 위해서 Karhunen-Loeve-Transform (KLT) 기반의 Classified Vector Quantization (KLT-CVQ) 방식이 제안되었으며, 이는 KLT 기반의 Adaptive Entropy-Constrained Quantization (KLT-AECQ) 방식으로 확장되었다. 기존의 KLT-AECQ 에서는 지각적인 성능 향상을 위하여 formant weighting 필터를 사용한다. 본 논문에서는 이 필터 대신에 Spectral Amplitude Warping (SAW) 필터를 적용함으로써, KLT-AECQ 코더의 지각적인 성능을 향상하였다.

• Journal of Broadcast Engineering
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• v.23 no.2
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• pp.302-315
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• 2018

Highly non-linear electro-optical transfer function of the Perceptual Quantizer was approximated by a truncated Taylor series, resulting in a closed form solution for luma adjustment. This previous solution is fast and quite suitable for the hardware implementation of luma adjustment, but the approximation error becomes relatively large in the range of 600~3,900 cd/m2 linear light. In order to reduce such approximation error, we propose a new linear model, for which a correction is performed on the position and the slope of line based on the scope of approximation. In order to verify the approximation capability of the proposed linear model, a comparative study on the luma adjustment schemes was conducted using various high dynamic range test video sequences. Via the comparative study, we identified a significant performance enhancement over the previous fast luma adjustment scheme, where a 4.65dB of adjusted luma t-PSNR gain was obtained for a test sequence having a large portion of saturated color pixels.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.32B no.1
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• pp.64-72
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• 1995

We propose a new image coding method which takes into account both statistical redundancy and perceptual irrelevancy of the DCT coefficients so as to provide a high quality of the reconstructed images with a reduced transmission bit rate First, a block of DCT coefficients are decomposed into 16 subvectors so as for a subvector to convey key information about one of the low-pass or the dirctional filtered images. Then, the most significant subvector is selected as the principal edge of the block and then vector quantized. After that, the residuals of the block are computed and then sequentially quantized through aforementioned procedure until the quantization distortion is smaller than the target distortion. The proposed scheme is good at encoding images with a variety of transmission bit rates, especially at very low bit rate coding. In addition, it is another benifit of the proposed scheme that an image can be quantized with a wide range of the transmission bit rates by simply adapting the stopping criterion of the sequential vector quantizer according to the target distortion of the reconstructed image.

• The Journal of the Acoustical Society of Korea
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• v.22 no.3E
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• pp.101-109
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• 2003

A multi-mode harmonic transform coding (MMHTC) for speech and music signals is proposed. Its structure is organized as a linear prediction model with an input of harmonic and transform-based excitation. The proposed coder also utilizes harmonic prediction and an improved quantizer of excitation signal. To efficiently quantize the excitation of music signals, the modulated lapped transform(MLT) is introduced. In other words, the coder combines both the time domain (linear prediction) and the frequency domain technique to achieve the best perceptual quality. The proposed coder showed better speech quality than that of the 8 kbps QCELP coder at a bit-rate of 4 kbps.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.345-346
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• 2007

In this paper, we propose a Pyramid VQ(PVQ) to quantize the transform coefficients of TCX module for the music improvement of AMR-WB+ codec. The proposed PVQ is compared to the $RE_8$ Lattice VQ used in the AHR-WB+ standard codec, demonstrating improvement 4% and 5.7%, respectively, in Mean Squared Error(MSE) and 3.3% and 4.7%, respectively, in Perceptual Evaluation of Audio Quality(PEAQ) by 8-dimensional and 16-dimensional Pyramid VQ.

• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.76-82
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• 2001

In this paper, a novel quantization method for wideband signal codec with 7 kHz bandwidth is proposed. In the transform-based wideband signal codecs, the signal is transformed to frequency domain and the spectral coefficients in each frequency band are quantized based on human perceptual model, followed by Huffman coding. However, the property of each band varies with frequency, and the codec has poor performance when all bands are quantized with the same method. Therefore, a selective quantization method is proposed, which analyzes the band property and selects the quantization domain between frequency domain and time domain based on the quantization efficiency. It is confirmed that the proposed method has better performance than the quantizer of G722.1 codec.