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지각적 동영상 부호화를 위한 선형 부대역 분해 기반 전처리 기법
최광연(Kwang Yeon Choi),송병철(Byung Cheol Song) 대한전자공학회 2017 전자공학회논문지 Vol.54 No.1
본 논문에서는 선형 부 대역 분해를 이용하여 입력 영상을 분해하고 시각적 민감도가 낮은 고주파 영역만을 효과적으로 억제하여 지각적 동영상 부호화의 효율을 향상시킬 수 있는 전처리 기법을 제안한다. 먼저 소정의 선형 부 대역 분해로 각 입력영상을 여러 주파수 대역들로 나눈다. 그런 다음 인간의 시각적 구조에서 거의 인지가 되지 않는 고주파 대역들에만 1보다 작은 이득 값들을 적용하여 해당 주파수 대역 정보를 억제시킨다. 이와 같이 고주파가 억제된 영상들을 소정의 비디오 인코더로 압축한다. 모의 실험을 통해 제안 기법의 적용 전후 압축 결과를 비교하여 시각적 차이 없음을 확인하였다. 또한, 제안 기법을 H.264 인코더의 전처리로 적용하였을 때 적용 전 대비 평균 13.12%의 데이터 감소 효과를 얻었다. This paper proposes a pre-processing algorithm to improve perceptual video coding efficiency which decomposes an input frame via a sub-band decomposition, and suppresses only high frequency band(s) having low visual sensitivity. First, we decompose the input frame into several frequency subbands by a linear sub-band decomposition. Next, high frequency subband(s) which is rarely recognized by human visual system (HVS) is suppressed by applying relatively small gain(s). Finally, the high frequency suppressed frame is compressed by a specific video encoder. We can find from the experimental results that if comparing before-use and after-use of the proposed pre-processing prior to the encoder, no visual difference is shown. Also, the proposed algorithm achieves bit-saving of 13.12% on average in a H.264 video encoder.
최광연(Kwang Yeon Choi),송병철(Byung Cheol Song) 대한전자공학회 2015 전자공학회논문지 Vol.52 No.10
자연 영상들을 위한 전형적인 지역적 대비 개선 기법을 X-ray 영상에 적용할 경우, X-ray 고유의 특성을 고려하지 않기 때문에 과도한 개선이 이루어지거나 부자연스러운 화질을 생성하는 화상의 결함이 발생할 수 있다. 이러한 문제를 해결하기 위해 본 논문은 지역적으로 X-ray 영상을 위한 블록 기반 대비 개선 기법을 제안한다. 먼저 블록 단위로 가중치 누적 분포 변환 함수를 도출하고, 이를 이용한 블록 단위 대비 개선을 수행한다. 다음으로, 블록 기반 중첩을 적용하여 블록화 현상이 제거된 영상을 획득한다. 후처리로 고주파 성분을 강조하여 최종 영상을 획득한다. 모의실험을 통해 제안한 블록 기반 대비 개선기법이 일반적인 대비 개선 기법보다 정량적인 대비 개선 척도에서 최대 5배 우수함을 확인하였다. If typical contrast enhancement algorithms for natural images are applied to X-ray images, they may cause artifacts such as overshooting or produce unnatural visual quality because they do not consider inherent characteristics of X-ray images. In order to overcome such problems, we propose a locally adaptive block-based contrast enhancement algorithm for X-ray images. After we derive a weighted cumulative distribution function for each block, we apply it to each block for contrast enhancement. Then, we obtain images that are removed from block effect by adopting block-based overlapping. In post-processing, we obtain the final image by emphasizing high frequency components. Experimental results show that the proposed block-based contrast enhancement algorithm provides at maximum 5-times higher visual quality than the exiting algorithm in terms of quantitative contrast metric.
최광연,Choi, Kwang-Yeon 대한생물정신의학회 2011 생물정신의학 Vol.18 No.2
Pavlovian fear conditioning has been extensively studied for the understanding of neurobiological basis of memory and emotion. Pavlovian fear conditioning is an associative memory which forms when conditioned stimulus (CS) is paired with unconditioned stimulus (US) once or repeatedly. This behavioral model is also important for the understanding of anxiety disorders such as posttraumatic stress disorder. Here we describe the neural circuitry involved in fear conditioning and the molecular mechanisms underlying fear memory formation. During consolidation some memories fade out but other memories become stable and concrete. Emotion plays an important role in determining which memories will survive. Memory becomes unstable and editable again immediately after retrieval. It opens the possibility for us of modulating the established fear memory. It provides us with very efficient tools to improve the efficacy of cognitive-behavior therapy and other exposure-based therapy treating anxiety disorders.
급성 조증 환자에서 혈소판 BDNF 농도에 대한 예비 연구
최광연,김용구,이분희,Choi, Kwang-Yeon,Kim, Yong-Ku,Lee, Bun-Hee 대한생물정신의학회 2009 생물정신의학 Vol.16 No.3
Objectives : Serum and plasma BDNF levels have been shown to be decreased in patients with mood disorder such as major depressive disorder and bipolar disorder. We investigated whether platelet BDNF levels would be lower in patients with acute bipolar manic episode compared with those of normal controls. Methods : BDNF levels were examined in platelet-rich plasma(PRP) and platelet-poor plasma(PPP) in 20 healthy controls and 20 hospitalized patients who were diagnosed as bipolar I disorder, most recent episode manic using a Structured Clinical Interview for DSM-IV. And severity of manic symptoms was measured using Young Mania Rating Scale(YMRS). Platelet BDNF level was calculated by subtracting PPP BDNF from PRP BDNF level, and dividing the result by the total platelet count, and it was expressed as pg/$10^6$ platelet. Results : Platelet BDNF levels were significantly lower in patients with acute bipolar manic episode(4.55${\pm}$3.36pg/$10^6$ platelet) than in normal controls(6.84${\pm}$2.32pg/$10^6$ platelet)(p=0.008). However we failed to reveal the significant negative correlation between platelet BDNF levels and YMRS scores in patients with acute bipolar episode. Conclusion : Our finding suggests that there is a decrease in the platelet BDNF of patients with acute bipolar manic episode.