• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 제13회 신호처리 합동 학술대회 논문집
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• pp.647-650
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• 2000

PACS의 보급으로 인하여 CT, MRI 등의 의료영상이 진료에 광범위하게 사용되고 있고, 또 의사가 좀 더 정량적이거나 사실적인 visualization을 위해서 분할은 필수적으로 수행되어져야 할 과정이라고 할 수 있다. 의료 영상에서 watershed 알고리듬을 이용하여 분할을 하는데 있어 가장 큰 문제가 되는 점은 과분할현상(Oversegmentation)이기 때문에 그 분할된 영역을 의미 있는 영역별로 합치는 영역 병합(merge) 과정을 필요로 하게 된다. 의료영상에서 모호한 경계는 매우 빈번하게 나타나기 때문에 기존의 병합 방법을 적용하는데 어려움이 있다. 본 논문에서는 이런 모호한 경계를 갖는 영상에서도 알맞는 병합을 가질 수 있는 적응적 영역 병합 방법을 제안한다. 제안된 분할 방법을 DICOM 영상의 폐 영상과 다리 뼈 영상에서 실험하였다. 그 결과 뼈와 폐영역을 성공적으로 병합하면서 인접한 장기들과는 구분 지을 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권6호
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• pp.1881-1900
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• 2014

Since 802.11 wireless LANs are so widely used, it has become common for numerous access points (APs) to overlap in a region, where most of those APs are managed individually without any coordinated control. This pattern of wireless LAN usage is called the private OBSS (Overlapping Basic Service Set) environment in this paper. Due to frame collisions across BSSs, each BSS in the private OBSS environment suffers severe performance degradation. This study approaches the problem from the perspective of congestion control rather than noise or collision resolution. The retry limit, one of the 802.11 attributes, could be used for traffic control in conjunction with TCP. Reducing the retry limit causes early discard of a frame, and it has a similar effect of random early drops at a router, well known in the research area of congestion control. It makes the shared link less crowded with frames, and then the benefit of fewer collisions surpasses the penalty of less strict error recovery. As a result, the network-wide performance improves and so does the performance of each BSS eventually. Reducing the retry limit also has positive effects of merging TCP ACKs and reducing HOL-like blocking time at the AP. Extensive experiments have validated the idea that in the OBSS environment, reducing the retry limit provides better performance, which is contrary to the common wisdom. Since our strategy is basically to sacrifice error recovery for congestion control, it could yield side-effects in an environment where the cost of error recovery is high. Therefore, to be useful in general network and traffic environments, adaptability is required. To prove the feasibility of the adaptive scheme, a simple method to dynamically adjust the value of the retry limit has been proposed. Experiments have shown that this approach could provide comparable performance in unfriendly environments.