• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.6C
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• pp.842-847
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• 2004

We present a new video coding technique to tradeoff frame rate and picture quality for low bit rate video coding. We show a model equation for selecting the optimal frame rate from the motion content of the source video. We can determine DCT quantization parameter (QP) using the frame rate and bit rate. For objective video quality measurement we propose a simple and effective error measure for skipped frames. The proposed method enhances the video quality up to 2 ㏈ over the H.263 TMN5 encoder.

• Journal of Internet Computing and Services
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• v.6 no.4
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• pp.103-114
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• 2005

In this paper, we propose a new trnascoding method for improving picture's visual quality when frames are skipped. the proposed method utilizes the relationships of motion vectors between successive frames, and 4 motion vectors a macroblock are considered in transcoding. Since the proposed method does not require any decoding process of encoded bit stream, the computational complexity for estimating motion vectors can be eliminated. Experimental results illustrated that as transcoded frames are getting far from I pictures and as the degree of motions in video sequences are getting higher, the picture quality by using our proposed method shows better performances than existing schemes.

• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.445-447
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• 2004

본 논문에서는 H.263과 같은 MC-DCT방법을 사용하는 코덱에서 IDCT와 MC(Motion Compensation, 움직임보상)방법을 부분적으로 수정하여 제한된 비율의 축소영상을 디코딩 과정에서 직접 얻을 수 있는 방법을 제안한다. 제안한 방법에서는 8$\times$8 DCT 블록에 대하여 약간의 연산을 가하여 k$\times$k IDCT를 수행하고, 시간적 중복성을 제거하는 과정에서 근사적 움직임벡터를 이용한 2k$\times$2k MC 를 수행하였다. 기존의 코덱을 사용하고 후처리로 축소를 하는 경우와 비교하였을 때에 추가적인 오버헤드가 매우 경미하고 디코딩 과정이 많이 축소되어 계산효율에 있어서 대략 32%의 개선된 실험결과를 얻었고, 화질저하 현상이 개선됨을 실험적으로 보였다.

• The Transactions of the Korea Information Processing Society
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• v.7 no.2S
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• pp.701-710
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• 2000

This paper presents a new method for an efficient coding of very low bit-rate color video based on adaptive wavelet transform. Our approach reveals that the coding process works more efficiently if the quantized wavelet coefficients are preprocessed by a mechanism exploiting the redundancies in the wavelet subband structure. Thus, we focuses optimized activity of coding part, and exhaustive overlapped block motion compensation is utilized to ensure coherency in motion compensated error frames, and raised cosine window is applied. The horizontal and vertical components of motion vectors are encoded separately using adaptive arithmetic coding while significant wavelet coefficients are encoded in bit-plane order using adaptive arithmetic coding. On average the proposed codec exceeds H.263 and ZTE in peak signal-to-noise ratio by as much as 2.07 and 1.38dB at 28 kbits, respectively. Fore entire sequence coding, 3DWCVC method is superior to H.263 and ZTE by 0.35 and 0.71dB on average, respectively.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.319-322
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• 2001

최근 몇 년간 멀티미디어의 응용이 활발해지면서 H.261, H263을 이용한 영상회의 MPEG-1, MPEG-2등을 이용한 디지털 저장 미디어와 방송이 주요 관심분야로 발전해왔다. 이러한 기술을 바탕으로 이제는 무선망을 이용한 3세대 이동 통신이 새로운 이슈로 등장하고 있다. 그러나 무선 환경에서는 채널 상에서 데이터를 전송할 때 에러가 많이 발생하기 때문에 에러에 강인한 방법이 반드시 필요하게 된다. 본 논문에서는 특히 향후 많은 응용분야에 쓰일 MPEG-4 데이터를 무선망으로 전송함에 있어 MPEG-4 표준에서 규정하는 에러 내성 방법과 여기에 채널 코딩 기법을 도입하여 오류에 강인한 특성을 지니도록 하는 방법을 제안한다. 실험결과는 단순히 기존의 에러 내성 기법을 활용할 때 보다 에러에 대한 강인성과 에러 검출에 있어 향상된 성능을 보여준다.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.550-552
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• 2002

표준 비디오 압축 기법은 프레임 간의 시간적, 공간적 중복성을 이용하여 데이터를 압축한다. 압축된 프레임이 인터넷을 통하여 전송되는 중에 네트워크의 상태에 따라 패킷의 손실이 발생할 수 있다. 이러한 오류가 발생하면 손실된 블록을 포함하는 프레임의 화질 뿐 아니라, 이 프레임을 참조하여 압축된 이후의 프레임에도 영향을 미친다. 본 논문에서는 전송오류가 발생한 경우, 디코더에서의 오류전파를 최소화하기 위해 보조 모션벡터를 이용한 압축 기법을 제안한다. 즉, 여러 개의 후보 프레임 중 현재 압축하려는 매크로블록과 가장 가까운 값을 가진 두 개의 매크로 블록을 선택하여 그 위치를 기본 모션벡터와 보조 모션벡터로 지정한다. 이때, 두 모션벡터는 서로 다른 프레임에 속한다. 디코더에서 압축해제를 위해 참조하는 기본 모션벡터의 프레임이 손실된 경우, 보조모션 벡터를 이용하여 원래의 화질에 가깝게 디코딩 할 수 있다. 이 기법은 오류제어를 위한 피드백 채널이 필요하지 않으며, 네트워크상의 전송오류 발생시 표준 H.263 압축보다 높은 성능을 보인다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.5
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• pp.1132-1140
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• 1996

In video coding systems, an effective rate control method is one of the most improtant issues for the good video quality. This paper presents an adaptive rate control scheme based on the buffer fullness, quantization, and buffer utilization for very low bit rate communication lines, such as 16kbit/s, 24bit/s, and so on. The strategy is implemented on H.263, whichis a vide coding algorithm for narrow band telecommunication channels up to 64kbit/s recommended by ITU-T SG15, to show the effectiveness. The simulation result shows that the suggested rate control scheme has better SNR performance and buffer utilization of source coder than those of linear and non-linear[9] buffer control strategies.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.4
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• pp.822-833
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• 1996

The video coding for very low bit rate has recently received considerable attention, but conventional block based transform coding schemes suffer from the blocking effect for the constraints of bit rates. In this paper, we present a video coding sysem suing multi-resolution motion estimation/compensation with variable size block(VMRME/C) and multi-resolution vector quantization(MRVQ) in wavelet transform domain for very low bit rate coding. It is shown that the presented scheme has better performance in the peak signal-to-nose ratio(RSNR) by 0.2-0.6 dB as well as subjective quality than that of conventional block based transform video coding techniques(especially, H. 263 which is DCT based video coding).

• The KIPS Transactions:PartB
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• v.13B no.6 s.109
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• pp.607-614
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• 2006

In this paper, we propose an error resilience video coder which uses a hybrid error concealment algorithm. Firstly, the algorithm uses the error concealment with data hiding. If the hiding information is lost, the motion vector of lost macroblock is computed with adaptive selection of adjacent motion vectors and OBMC (Overlapped Block Motion Compensation) is applied with this motion vector. We know our algorithm is more effective in case of continuous GOB. The results show more significant improvement than many temporal concealment methods such as MVRI (Motion Vector Rational Interpolation) or existing error concealment using data hiding.

• The KIPS Transactions:PartB
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• v.11B no.6
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• pp.661-666
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• 2004

In the wireless communication systems, transmission errors degrade the reconstructed image quality severely. Error concealment in video communication is becoming increasingly important because transmission errors can cause single or multiple loss of macroblocks in video delivery over unreliable channels such as wireless networks and internet. Among various techniques which can reduce the degradation of video quality, the error concealment techniques yield good performance without overheads and the modification of the encoder. In this paper, lost image blocks can be concealed with the OBMC(Overlapped Block Motion Compensation) after new motion vectors of the lost image blocks are allocated by median values using the adaptive selection with motion vectors of adjacent blocks. We know our algorithm is more effective in case of continuous GOB loss. The results show a significant improvement over the zero motion error concealment and other temporal concealment methods such as Motion Vector Rational Interpolation or Median＋OBMC by 3dB gain in PSNR.