• 한국정보시스템학회지:정보시스템연구
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• 제14권3호
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• pp.117-122
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• 2005

This paper presents a method for detecting scene changes in video sequences, in which the $chi^{2}$-test is modified by imposing weights according to NTSC standard. To automatically determine threshold values for scene change detection, the proposed method utilizes the frame differences that are obtained by the weighted $chi^{2}$-test. In the first step, the mean and the standard deviation of the difference values are calculated, and then, we subtract the mean difference value from each difference value. In the next step, the same process is performed on the remained difference values, mean-subtracted frame differences, until the stopping criterion is satisfied. Finally, the threshold value for scene change detection is determined by the proposed automatic threshold estimation algorithm. The proposed method is tested on various video sources and, in the experimental results, it is shown that the proposed method is reliably estimates the thresholds and detects scene changes.

• Journal of Information Processing Systems
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• 제13권3호
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• pp.491-499
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• 2017

In this study, we proposed a new approach to segment ground and nonground points gained from a 3D laser range sensor. The primary aim of this research was to provide a fast and effective method for ground segmentation. In each frame, we divide the point cloud into small groups. All threshold points and start-ground points in each group are then analyzed. To determine threshold points we depend on three features: gradient, lost threshold points, and abnormalities in the distance between the sensor and a particular threshold point. After a threshold point is determined, a start-ground point is then identified by considering the height difference between two consecutive points. All points from a start-ground point to the next threshold point are ground points. Other points are nonground. This process is then repeated until all points are labelled.

• 융합신호처리학회논문지
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• 제22권4호
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• pp.213-219
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• 2021

잠수함의 방수펄스탐지는 적 수상함 및 잠수함, 어뢰 등에서 방사하는 펄스를 탐지하여 자함의 기동 및 생존성을 제공하는 중요한 기능을 수행한다. 방수펄스탐지 여부는 수신한 펄스의 크기와 운용자가 설정한 문턱값의 비교를 통해 결정된다. 방수펄스는 다양한 해양 환경요인의 영향으로 펄스의 세기가 작아지는 경우가 빈번하게 발생한다. 이런 상황에서 고정 문턱값으로 탐지를 수행할 경우 미탐지 문제가 발생되며 운용자가 낮은 문턱값을 설정하기 전까지 지속된다. 본 논문은 고정 문턱값으로 발생하는 미탐지 문제를 줄이기 위한 문턱값 자동 조절 방법을 제안하였다. 펄스 레벨 변동 폭이 다른 4가지 케이스로 시뮬레이션을 수행하였고 모든 케이스에서 문턱값 자동 조절 방법을 적용했을 때 탐지 개수가 증가하여 탐지 성능이 향상됨을 확인하였다. 제안한 방법을 통해 향후 펄스 레벨의 변동이 큰 해양환경에서 방수펄스탐지 성능 향상을 기대해본다.

• Journal of information and communication convergence engineering
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• 제9권6호
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• pp.763-768
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• 2011

Image denoising is a lively research field. Today the researches are focus on the wavelet domain especially using wavelet threshold method. We proposed an adaptive threshold method which considering the characteristic of different sub-band, the method is adaptive to each sub-band. Experiment results show that the proposed method extracts white Gaussian noise from original signals in each step scale and eliminates the noise effectively. In addition, the method also preserves the detail information of the original image, obtaining superior quality image with higher peak signal to noise ratio(PSNR).

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2003년도 춘계종합학술대회논문집
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• pp.426-429
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• 2003

본 논문에서는 3차원 물체의 인식을 위한 표면 분류시 그 임계치를 선정하는 방법에 대해 제안하고자 한다. 특히 보다 세밀하고 복잡한 물체의 표현을 위해 사용하여 왔던 평균 곡률과 가우스곡률이 가지고 있던 문제점인 임계치 선정 문제를 통계적 방법에 의해 해결하는 방법을 제안하고자 한다. 끝으로 본 논문의 유용성을 실험에 의해 입증하였다.

• 전자공학회논문지S
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• 제34S권10호
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• pp.112-119
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• 1997

Zerotreeimage coding is known as a simple and effective image comprssion algorithm. It has the property that the compression is generated in order of improtance. Conventionally, a fixed threshold is applied to the entire wavelet coefficients regardless of frequency and local features of an image. In this paper, we propose a new zerotree coding scheme with adaptive threshold. The adaptive threshold is determined by human visual characteristics. It is shown that the image quality of the proposed method is better than that of the conventional method.

• 한국통신학회논문지
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• 제27권4A호
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• pp.356-363
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• 2002

컷 검출은 내용기반 검색에 필요한 인덱싱을 위해 수행되어야 하는 기초 작업으로 이를 위한 매우 다양한 기법들이 제안된바 있다. 그러나 기존의 연구에서는 대부분 고정된 하나의 임계값을 사용하기 때문에 통영상의 종류나 내용에 따라 최적의 임계값을 정해야만 하는 문제점을 갖는다. 본 논문에서는 컷 검출 간격의 확률적인 분포에 따라 임계값을 조절하며 컷이 발생하면 이전 컷과의 간격과 특징값 차이를 다음 컷 검출을 위한 임계값 설정에 반영하는 가변형 동적 임계값 방법을 제안한다. 이를 위해 임계값 조절에 필요한 인자 값들을 실행시간에 구하는 방법과 이를 사용한 컷 검출 알고리즘을 제시한다. 또한 실험을 통해 제안하는 방법이 기존의 방법에 비해 오 검출율을 줄일 수 있어 효율적임을 보인다.

• 한국통신학회논문지
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• 제36권7B호
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• pp.892-896
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• 2011

본 논문에서는 IEEE 802.15.4a 시스템에 적합한 직렬 검색 비동기 상호 상관(serial search non-coherent correlator)을 이용한 두 단계(two-stage) 방식의 동기 방식(synchronization scheme)을 제안한다. 제안된 방식에서는 다중펄스 신호를 사용하여 단일펄스 신호를 이용하는 기존 방식보다 동기성능을 개선하였고, 적응 임계값(adaptive threshold) 기법을 적용하여 고정 임계값(fixed threshold)을 사용함으로써 생기는 낮은 SNR에서의 성능 열화를 보상하였다. 제안된 기법은 IEEE 802.15.4a 채널 모델에서 기존의 기법과 비교하여 약 0.2~0.3우수한 검출 확률(Detection Probability)을 보였다.

• 대한원격탐사학회지
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• 제15권3호
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• pp.239-251
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• 1999

The elimination process of cloud-contaminated pixels is one of important steps before obtaining the accurate parameters of land and ocean surface from AVHRR imagery. We developed a 6step threshold method to detect the cloud-contaminated pixels from NOAA-14/AVHRR datime imagery over land using different combination of channels. This algorithm has two phases : the first is to make a cloud-free characteristic data of land surface using compositing techniques from channel 1 and 5 imagery and a dynamic threshold of brightness temperature, and the second is to identify the each pixel as a cloud-free or cloudy one through 4-step threshold tests. The merits of this method are its simplicity in input data and automation in determining threshold values. The threshold of infrared data is calculated through the combination of brightness temperature of land surface obtained from AVHRR imagery, spatial variance of them and temporal variance of observed land surface temperature. The method detected the could-comtaminated pixels successfully embedded inthe NOAA-14/AVHRR daytime imagery for the August 1 to November 30, 1996 and March 1 to July 30, 1997. This method was evaluated through the comparison with ground-based cloud observations and with the enhanced visible and infrared imagery.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2651-2673
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• 2019

In order to detect Denial of Service (DoS) attacks, victim-side detection methods are used popularly such as static threshold-based method and machine learning-based method. However, as DoS attacking methods become more sophisticated, these methods reveal some natural disadvantages such as the late detection and the difficulty of tracing back attackers. Recently, in order to mitigate these drawbacks, source-side DoS detection methods have been researched. But, the source-side DoS detection methods have limitations if the volume of attack traffic is relatively very small and it is blended into legitimate traffic. Especially, with the subtle attack traffic, DoS detection methods may suffer from high false positive, considering legitimate traffic as attack traffic. In this paper, we propose an effective source-side DoS detection method with traffic seasonality aware adaptive threshold. The threshold of detecting DoS attack is adjusted adaptively to the fluctuated legitimate traffic in order to detect subtle attack traffic. Moreover, by understanding the seasonality of legitimate traffic, the threshold can be updated more carefully even though subtle attack happens and it helps to achieve low false positive. The extensive evaluation with the real traffic logs presents that the proposed method achieves very high detection rate over 90% with low false positive rate down to 5%.