• 한국통신학회논문지
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• 제22권4호
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• pp.675-684
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• 1997

The bit rate control algorithm which is capable of handing scene change is proposed. In MPEG-2 TM5, block variance is used to measure block activity. But block variance is not consistent with human visual system and does not differenciate the distribution of pixel values within the block. In target bit allocation process of TM5, global complexity, obtained by results of previous coded pictures, is used. Since I pictures are spaced relatively far apart, their complexity estimate is not very accurate. In the proposed algorithm local variance is used to measure block activity and detect scene change. Local variance, using deviation from the mean of neighboring pixels, well represents the distribution of pixel values within the block. If scene change is detected, the local variance information is used for target bit allocation process. Allocating target bits for I picture, the average local variance difference between previous and current I picture is considered. The experimental results show that the proposed algorithm can detect scene change very precisely and gives better picture quality and higher PSNR values than MPEG-2 TM5.

• 한국컴퓨터그래픽스학회논문지
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• 제7권1호
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• pp.11-17
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• 2001

프랙탈 이미지 코딩은 높은 압축율을 비롯하여 많은 장점을 가지고 있다. 그러나 압축 과정은 일반적으로 domain 블록 pool에 대한 긴 탐색시간으로 효율이 나빠진다. 본 논문에서는 블록 분류와 분산 기반의 탐색을 병용한 domain 블록 pool 탐색 방법을 소개한다. 이 방법은 블록 분류에 대하여 분류 블록의 분산 값은 독립적이라는 사실을 이용한다. 따라서 이 방법은 단순한 분산 기반의 탐색 방법보다 O(number of classes)에 비례하는 탐색 속도향상이 된다. 실험의 결과는 본 방법이 단순히 분산 값을 적용한 탐색 방법과 비교하여 이미지 품질은 거의 그대로 유지하면서 17배 이상의 속도 향상을 이루었음을 보인다. 또한 이미지 품질의 가시적인 손실 없이 탐색 속도를 더욱 향상시키는 분산 기반의 탐색 방법을 제안한다.

• 한국통신학회논문지
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• 제21권5호
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• pp.1089-1095
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• 1996

가변블록 변환부호화는 변환부호화에 적용되는 블럭의 크기를 다르게 하여 코딩의 효율을 좋게 한다. 변환블록의 크기는 블럭의 활성도에 따라 적응된다. 즉, 블럭의 활성도가 크면 블럭의 크기는 작아지고, 반대로 활성도가 작으면 블럭의 크기가 커진다. 본 논문에서는 블럭의 활성도로서 분산값 대신에 변환계수의 고주파 에너지를 이용하였다. 컴퓨터 시뮬레이션 결과, 제안한 방법이 분산값을 이용한 방법보다는 약 1~5dB, MAD를 이용한 방법보다는 약 0.5~3dB정도의 성능개선을 보여주었다.

• Communications for Statistical Applications and Methods
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• 제7권3호
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• pp.741-757
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• 2000

In may experimental situations, whenever a block design is used, the block effect is usually considered to be fixed. There are, however, experimental situations in which it should be treated as random. The choice of a blocking arrangement for a response surface design can have a considerable effect on estimating the mean response and on the size of he prediction variance even if the experimental runs re the same. Therefore, care should be exercised in the selection of blocks. In this paper, in the presence of a random block effect, we propose a graphical method or evaluating the effect of blocking in response surface designs using cuboidal regions. This graphical method can be used to investigate how the blocking has influence on the prediction variance throughout all experimental regions of interest when this region is cuboidal, and compare the block effects in the cases of the orthogonal and non-orthogonal block designs, respectively.

• 정보처리학회논문지C
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• 제15C권3호
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• pp.149-156
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• 2008

JPEG2000은 차세대 이미지 압축 포맷으로 JPEG에 비하여 우수한 압축률과 화질을 제공할 수 있다. JPEG2000 이미지를 커버 오브젝트로 사용하는 lazy-mode 스테가노그라피는 압축과정에서 발생하는 정보 손실에 의해 메시지가 손실되지 않도록 제안된 알고리즘으로 많은 양의 메시지 삽입이 가능하다. 그러나 이 방법은 메시지 삽입으로 인하여 코드블럭 노이즈 분산의 변화를 발생하게 되고, 이러한 특징을 기반으로 하는 Hilbert-Huang 변환 (HHT) 기반의 스테거낼리시스에 의하여 메시지 삽입여부가 탐지될 수 있다. 본 논문에서는 코드블럭 노이즈 분산의 변화를 예측하고, 이를 최소화하도록 메시지를 삽입하여 HHT 기반 스태거낼리시스에 의해 탐지되지 않는 새로운 JPEG2000 스테가노그라피 알고리즘을 제시한다. 코드블록 노이즈 분산의 변화를 예측하기 위하여 low precision code-block variance와 low precision code-block noise variance를 활용하였다. 또한 메시지 삽입 후의 높은 영상 화질을 유지하기 위하여 JPEG2000의 quality layer 정보를 활용하였다. 제안한 알고리즘의 성능을 보이기 위하여 2048장의 다양한 영상에 대하여 분석을 수행하였고, 이를 통하여 HHT 기반 스태거낼리시스 방법에 안전함을 증명하였다.

• 한국멀티미디어학회논문지
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• 제7권12호
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• pp.1665-1670
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• 2004

The general fractal image compression provides a high compression rate, but it requires a large encoding time. In order to overcome this disadvantage, many researchers have introduced various methods that reduce the total number of domain blocks considering their block similarities or control the number of searching domain block depending on its distribution. In this paper, we propose a method that can reduce the number of searching domain blocks employing the variance coherence of intensity values and also the number of range blocks requiring the domain block search through the classification of range blocks. This proposed method effectively reduces the encoding time and also a negligible drop of the quality as compared with the previous methods requiring the search of all range blocks.

• 건설안전기술
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• 통권43호
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• pp.98-106
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• 2007

In this paper, a ground disturbance effects, strength and consolidation characteristics of soft clay through using the large block samples($\theta$:300mm, H:400mm) and the piston samples, f hose which had been gathered in west coast and south coast. Especially, we have assessed the coefficient of horizontal consolidation when penetrating the mandrel considering the variance of ratio between diameter and height in drainage sample through the experiment of the oedometer test and Rowecell and also investigated the disturbance area in smear zone by interior model test, the strength originated by disturbance, the variance in characteristics of the consolidation. As the result, the large block sample has been investigated that ihe uniaxial compression test(qu) was shown bigger than the piston sample by about 11-19%. Under the size of anistropy in consolidation, the coefficient ratio of consolidation(ch/cv,) perfomed by standard consolidation test(SC) was shown bigger than that of (Cro/Cv) by the Rowecell test. And the coefficient ratio of consolidation(Cro/Cv) perfomed by piston sample was evaluated bigger than that Of (Cro/Cv) by the large block sample by about 0.9-1.9. The coefficient ratio of consolidation along with the variance in ratio of between diameter and height when penetrating the mandrel was shown big difference according to the characteristics of soil of the specimen. In addition, ds/dw of smear zone at the marine clay in west-south was ranged from 1.6 to 4.2. The width of variance in rat io[(qud)/(quud)] of strength n the area between disturbance and undisturbance was shown big as about 72-91% but the principle was judged with the similiar range when the decrease of the strength in smear zone become the zone under 25% in unditurbance area.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 하계종합학술대회논문집
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• pp.677-680
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• 1998

In this paper, we proposed a lwo bit rate subband coding with adaptive vector quantization using the correlation between motion vector and block energy in subband. In this method, the difference between the input signal and the motion compensated interframe prediction signal is decomposed into several narrow bands using quadrature mirror filter (QMF) structure. The subband signals are then quantized by adaptive vector quantizers. In the codebook generating process, each classified region closer to the block value in the same region after the classification of region by the magnitude of motion vector and the variance values of subband block. Because codebook is genrated considering energy distribution of each region classified by motion vector and variance of subband block, this technique gives a very good visual quality at low bit rate coding.

• Communications for Statistical Applications and Methods
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• 제12권1호
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• pp.181-189
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• 2005

This paper suggest a method of inclusion probability proportional to size sampling that provides a non-negative and stable variance estimator. The sampling procedure is quite simple and flexible since a sampling design is easily obtained using mathematical programming. This scheme appears to be preferable to Nigam, Kumar and Gupta's (1984) method which uses a balanced incomplete block designs. A comparison is made with their method through an example in the literature.

• 전자공학회논문지B
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• 제29B권7호
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• pp.62-69
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• 1992

The conventional BMA is performed with the fixed block size. For better performance at low bitrate, the block size is required to be large in relatively stationary area, while small in moving area. Thus, in this paper, a video coding technique using variable block size model is proposed. It decides the block size based on the degree of local motion defined by the local mean and variance of blocks. Computer simulation shows that the proposed method gives comparable performance to the conventional one with less bits required for motion vector coding.