• Journal of KIISE:Information Networking
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• v.31 no.3
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• pp.298-304
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• 2004

In transmitting a compressed video bit-stream over Internet, a packet loss causes an error propagation in both spatial and temporal domain, which in turn leads to a severe degradation in image quality. In this paper, a new error concealment algorithm is proposed to repair damaged portions of the video frames in the receiver. Conventional BMA(Boundary Matching Algorithm) assumes that the pixels on the boundary of the missing block and its neighboring blocks are very similar, but has no consideration of edges t)r discontinuity across the boundary. In our approach, the edges are detected across the boundary of the lost or erroneous block. Once the edges are detected and the orientation of each edge is found, only the pixel difference along the expected edges across the boundary is measured instead of calculating differences between all adjacent pixels on the boundary. Therefore, the proposed approach needs very few computations and the experiment shows an improvement of the performance over the conventional BMA in terms of both subjective and objective quality of video sequences.

• Journal of Broadcast Engineering
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• v.5 no.2
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• pp.167-175
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• 2000

Compressed bitstreams generated by an MPEG-2 video encoder (or digital TV picture transmission are quite sensitive to channel errors. Due to the coding structure of the MPEG-2 video compression algorithm, a single bit error can affect not only the current Picture frame but also succeeding frames. Error concealment algorithms attempt to repair damaged portions of the picture by exploiting spatial and temporal redundancies in the correctly received and reconstructed video frames. In this paper, we analyze the effect of channel errors in MPEG-2 video bitstreams and estimate lost motion vectors by exploiting temporal redundancies in the video frames. Motion vectors can be estimated from the vertically adjacent extended region of lost macroblocks. Finally, we conceal the damaged macroblocks by compensating the displacement with the estimated motion vectors. Simulation results demonstrate that both the weighted sum algorithm and the extension matching algorithm achieve good performance in terms of PSNR values as well as subjective image quality.

• The Journal of the Korea Contents Association
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• v.8 no.5
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• pp.29-37
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• 2008

To transmit video bit stream over low bandwidth such as wireless channel, high compression algorithm like H.264 codec is exploited. In transmitting high compressed video bit-stream over low bandwidth, packet loss causes severe degradation in image quality. In this paper, a new algorithm for recovery of missing or erroneous motion vector is proposed. Considering that the missing or erroneous motion vectors in blocks are closely correlated with those of neighboring blocks. Motion vector of neighboring blocks are clustered according to average linkage algorithm clustering and a representative value for each cluster is determined to obtain the candidate motion vector sets. As a result, simulation results show that the proposed method dramatically improves processing time compared to existing H.264/AVC. Also the proposed method is similar to existing H.264/AVC in terms of visual quality.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.377-380
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• 2007

본 논문은 에러블록에 대해 인트라 프레임 예측모드를 이용하여 효율적인 공간적 에러 은닉 방법을 제안한다. 먼저, 에러블록내 픽셀값 복원을 위한 에러블록의 에지방향 예측은 주변 블록의 변환영역 예측모드를 이용한다. 예측된 에러블록의 정확한 에지방향은 인접한 두 에지방향과 비교하여 결정한다. 에러블록의 에지방향 예측을 주변블록의 예측모드를 이용함으로써, 기존의 에지방향 계산을 단축시킴으로써 효율적인 에러 은닉을 가능하게 한다

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2006.11a
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• pp.77-80
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• 2006

본 논문에서는 블록 기반의 영상압축에 있어서 선택적 방향성 보간을 이용하는 공간적 에러 은닉 기법을 제안한다. 기존의 공간적 경계 정합 기법은 에지가 단순한 영역에서는 좋은 성능을 보이지만, 손실 블록 내에서 에지의 변화가 큰 영역에서는 좋지 못한 성능을 보인다. 제안된 기법은 이웃한 상하 블록들을 이용하여 에지의 연결성을 추정하고, 이에 따라 공간적 경계정합 기법과 이동 스트라이프 정합 기법을 선택적으로 이용한다. 따라서 에지변화에 적응적으로 대응함으로써 우수한 복원영상을 구할 수 있다. 제안된 기법은 슬라이스 단위의 에러에 대해 적합한 방식으로써, 복잡도가 낮을 뿐만 아니라 객관적 주관적으로 우수한 복원 화질을 얻게 해준다.

• Proceedings of the Korea Information Processing Society Conference
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• 2001.10a
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• pp.793-796
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• 2001

이동 통신 채널과 같이 에러 발생율이 놀은 환경에서 부호화된 비디오 스트림 전송시 발생된 에러는 비디오 화질에 큰 영향을 줄 수 있다. 본 논문에서 현재 널리 사용되고 있는 H.263 복호화기에서 전송도중 에러가 발생했을 경우 추가적인 데이터 삽입 없이 효율적으로 에러를 은닉한 수 있는 기법에 관하여 제안하였다. 특히 인터프레임 영상에서 손상되거나 손실된 움직임벡터에 대해 시간영역에서 관계가 깊은 이전 프레임에서 손실블록(매크로블록)과 같은 위치에 있는 블록의 움직임벡터와 현재 프레임에서 손실블록과 인접한 블록들의 움직임벡터 정보를 이용하여 손상된 블록에 대해 에러를 은폐시키는 방법을 제안한다. 기본적으로 손상된 매크로블록 주변에 인접한 화소값들을 움직임 벡터 추정에 사용한다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.6
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• pp.623-629
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• 2002

In transmitting compressed video bit-stream over Internet, packet losses cause error propagations in both spatial and temporal domains, which in turn leads to severe degradation I image quality. In this paper, a new error concealment algorithm, called EBMA(Edge Detection based Boundary Matching Algorithm), is proposed to repair damaged portions of the video frames in the receiver. Conventional BMA(Boundary Matching Algorithm) assumes that the pixels on the boundary of the missing block and its neighboring blocks are very similar, but has no consideration of edges across the boundary. In our approach, the edges are detected across the boundary of the lost or erroneous block. Once the orientation of each edge is found, only the pixel difference along the expected edges across the boundary is measured instead of the calculation of difference along the expected edges across the boundary is measured instead of the calculation of differences between all adjacent pixels on the boundary Therefore, the proposed approach needs very few computations and the experiment shows and improvement of the performance over the conventional BMA in terms of both subjective and objective quality of video sequences.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.10C
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• pp.950-958
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• 2007

This paper presents an efficient packet loss resilient scheme for real-time video transmission over the Internet. By analyzing the temporal and spatial dependencies in inter- and intra-frames, we assign forward error correction codes (FEC) across video packets for minimizing the effect of error concealment and error propagation from packet loss. To achieve optimal allocation of FEC codes, we formulate the effect of packet loss on video quality degradation as packet distortion model. Then we propose an unequal FEC assignment scheme with low complexity based on packet correction rate, which uses the packet distortion model and includes channel status information. Simulation results show that the proposed FEC assignment scheme gives substantial improvement for the received video quality in packet lossy networks. Furthermore the proposed scheme achieves relatively smaller degradation of video quality with higher packet loss rates.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.39 no.5
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• pp.21-31
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• 2002

As the MPEG streaming traffics are transmitted over the Internet, MPEG packet losses cause error propagation in both spatial and temporal domains which in turn leads to severe degradation in image quality. This image degradation is become worse by the bursty packet loss at the network. In this paper, we propose a new error spreading method to reduce the effects of bursty packet losses over the Internet. The proposed error spreading method spreads out the not utilize packet losses widely, and can be used for videocasting and video-broadcasting that do not utilize the ARQ method. The proposed method can not only reduce the consecutive losses of image blocks, but also improve the performance of error concealment. Experimental results show that the deterioration of MPEG video quality can be reduced by spreading out the MPEG packet losses.

• The KIPS Transactions:PartB
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• v.10B no.2
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• pp.163-168
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• 2003

In transmitting compressed video bit-stream over Internet, packet loss causes error propagation in both spatial and temporal domain, which in turn leads to severe degradation in image quality. In this paper, a new approach for the recovery of lost or erroneous Motion Vector(MV)s by classifying the movements of neighboring blocks by their homogeneity is proposed. MVs of neighboring blocks are classified according to the direction of MVs and a representative value for each class is determined to obtain the candidate MV set. By computing the distortion of the candidates, a MV with the minimum distortion is selected. Experimental results show that the proposed algorithm exhibits better performance in many cases than existing methods.