• Title/Summary/Keyword: 문턱 값

Search Result 471, Processing Time 0.022 seconds

Denoising of Infrared Images by an Adaptive Threshold Method in the Wavelet Transformed Domain (웨이브렛 변환 영역에서 적응문턱값을 이용한 적외선영상의 잡음제거)

  • Cho, Chang-Ho;Lee, Sang-Hyo;Lee, Jong-Yong;Cho, Do-Hyeon;Lee, Sang-Chuel
    • 전자공학회논문지 IE
    • /
    • v.43 no.4
    • /
    • pp.65-75
    • /
    • 2006
  • This thesis deals with a wavelet-based method of denoising of infrared images contaminated with impulse noise and Gaussian noise, he method of thresholding the wavelet coefficients using derivatives and median absolute deviations of the wavelet coefficients of the detail subbands was proposed to effectively denoise infrared images with noises. Particularly, in order to eliminate the impulse noise the method of generating binary masks indicating locations of the impulse noise was selected. By this method, the threshold values dividing edges and noises were obtained more effectively proving the validity of the denoising method compared with the conventional wavelet shrinkage method.

Robust Outlier-Object Detection in Image Pairs Based on Variable Threshold Using Empirical Correction Constant (실험적 교정상수를 사용한 가변문턱값에 기초한 영상 쌍에서의 강인한 이상 물체 검출)

  • Kim, Dong-Sik
    • Journal of the Institute of Electronics Engineers of Korea SP
    • /
    • v.46 no.1
    • /
    • pp.14-22
    • /
    • 2009
  • By calculating the differences between two images, which are captured with the same scene at different time, we can detect a set of outliers, such as occluding objects due to moving vehicles. To reduce the influence from the different intensity properties of the images, a simple technique that reruns the regression, which is based on the polynomial regression model, is employed. For a robust detection of outliers, the image difference is normalized by the noise variance. Hence, an accurate estimate of the noise variance is very important. In this paper, using an empirically obtained correction constant is proposed. Numerical analysis using both synthetic and real images are also shown in this paper to show the robust performance of the detection algorithm.

Performance analysis of adaptive turbo coded modulation over mobile communication channel (이동통신 채널에서 적응터보부호화 변조방식의 성능분석)

  • Kim, Yeon-Su;Lee, Sang-Hoon;Joo, Eon-Kyeong
    • Journal of the Institute of Electronics Engineers of Korea TC
    • /
    • v.43 no.10 s.352
    • /
    • pp.69-78
    • /
    • 2006
  • High spectral efficiency can be obtained by adaptive modulation in which the modulation scheme is changed according to the channel environment. Thus it is especially suitable to mobile channel which is a typical example of time-varying channel. It is required to determine the optimum thresholds of signal-to-noise ratio(SNR) to change the modulation scheme effectively according to mobile speeds. Thus the optimum thresholds for specific mobile speeds to get the required bit error rate(BER) of $10^{-6}$ are obtained with the powerful turbo code in this paper. In addition, the optimum thresholds for the continuous mobile speed are proposed by interpolation of the obtained results. And the error performance and average spectral efficiency are investigated at various mobile speeds and channel environments.

Wavelet-based Digital Watermarking Using Human Visual System and Subband Adaptive Threshold (인간 시각 시스템과 부대역 적응적 문턱값을 이용한 웨이브릿 기반의 디지털 워터마킹)

  • Ha, Min-Seong;Gwon, Seong-Gon;Lee, Jong-Won;Ban, Seong-Won;Lee, Seung-Jin;Gwon, Gi-Yong;Lee, Geon-Il
    • Journal of the Institute of Electronics Engineers of Korea CI
    • /
    • v.37 no.6
    • /
    • pp.32-40
    • /
    • 2000
  • In this paper, we proposed a wavelet-based digital watermarking algorithm using human visual system and subband-adaptive threshold. After the original image is transformed by discrete wavelet transform, the perceptually significant coefficients of the each subband excluding the lowest level subbands are utilized to embed the watermark. To select perceptually significant coefficients for each subband, we use subband-adaptive threshold. For the selected coefficients in the high frequency subbands, the watermark is embedded using HVS. For those of the baseband, the watermark is embedded by conventional embedding method. We tested the performance of the proposed algorithm compared with conventional watermarking algorithm by computer simulation. The experimental results show that the proposed watermarking algorithm is less visible to human eyes and more robust to image compressions, image processings, and geometric transformations than the conventional algorithm.

  • PDF

Performance Improvement of Channel Estimation based on Time-domain Threshold for OFDM Systems (시간영역 문턱값을 이용한 OFDM 시스템의 채널 추정 성능 향상)

  • Lee, You-Seok;Kim, Hyoung-Nam
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.33 no.9C
    • /
    • pp.720-724
    • /
    • 2008
  • Channel estimation in OFDM systems is usually carried out in frequency domain based on the least-squares (LS) method and the minimum mean-square error (MMSE) method with known pilot symbols. The LS estimator has a merit of low complexity but may suffer from the noise because it does not consider any noise effect in obtaining its solution. To enhance the noise immunity of the LS estimator, we consider estimation noise in time domain. Residual noise existing at the estimated channel coefficients in time domain could be reduced by reasonable selection of a threshold value. To achieve this, we propose a channel-estimation method based on a time-domain threshold which is a standard deviation of noise obtained by wavelet decomposition. Computer simulation shows that the estimation performance of the proposed method approaches to that of the known-channel case in terms of bit-error rates after the Viterbi decoder in overall SNRs.

Visual Voice Activity Detection and Adaptive Threshold Estimation for Speech Recognition (음성인식기 성능 향상을 위한 영상기반 음성구간 검출 및 적응적 문턱값 추정)

  • Song, Taeyup;Lee, Kyungsun;Kim, Sung Soo;Lee, Jae-Won;Ko, Hanseok
    • The Journal of the Acoustical Society of Korea
    • /
    • v.34 no.4
    • /
    • pp.321-327
    • /
    • 2015
  • In this paper, we propose an algorithm for achieving robust Visual Voice Activity Detection (VVAD) for enhanced speech recognition. In conventional VVAD algorithms, the motion of lip region is found by applying an optical flow or Chaos inspired measures for detecting visual speech frames. The optical flow-based VVAD is difficult to be adopted to driving scenarios due to its computational complexity. While invariant to illumination changes, Chaos theory based VVAD method is sensitive to motion translations caused by driver's head movements. The proposed Local Variance Histogram (LVH) is robust to the pixel intensity changes from both illumination change and translation change. Hence, for improved performance in environmental changes, we adopt the novel threshold estimation using total variance change. In the experimental results, the proposed VVAD algorithm achieves robustness in various driving situations.

A Threshold Optimization Method for Decentralized Cooperative Spectrum Sensing in Cognitive Radio Networks (인지 무선 네트워크 내 분산 협력 대역 검출을 위한 문턱값 최적화 방법)

  • Kim, Nak-Kyun;Byun, Youn-Shik
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.40 no.2
    • /
    • pp.253-263
    • /
    • 2015
  • Lately, spectrum sensing performance has been improved by using cooperate spectrum sensing which each results of sensing of several secondary users are reported to the fusion center. Using Cognitive Radio, secondary user is able to share a bandwidth allocated to primary user. In this paper, we propose a new decentralized cooperative spectrum sensing scheme which compensates the performance degradation of existing decentralized cooperative spectrum sensing considering the error probability of the channel which sensed result of the secondary user is delivered to the fusion center in decentralized cooperative spectrum sensing. In addition, a sensing threshold optimization of minimizing the error probability of decentralized cooperative spectrum sensing is introduced by deriving the equation and the optimal sensing threshold has been confirmed to maximize the decentralized cooperative spectrum sensing performance.

Performance Optimization of Tandem Source-Channel Coding Systems Employing Unequal Error Protection Under Complexity Constraints (복잡도 제한 하에서 비균등 오류 보호 기법을 사용하는 탠덤 소스-채널 코딩 시스템의 성능 최적화)

  • Lim, Jongtae
    • Journal of the Korea Institute of Information and Communication Engineering
    • /
    • v.18 no.10
    • /
    • pp.2537-2543
    • /
    • 2014
  • Between tandem source-channel coding systems and joint source-channel coding systems, it has been known that there is a complexity threshold in complexity versus performance. In this paper, by expanding the previous analysis for equal error protection systems, we analyze and compare the performance under complexity constrains for tandem source-channel coding systems which employ unequal error protection. Under a given complexity constraint, the optimization is performed to minimize the end-to-end distortion of each representative tandem and joint source-channel coding system. The results show that the complexity threshold for unequal error protection systems becomes smaller and the performance enhancement of unequal error protection systems over equal error protection systems gets smaller as the system complexity gets larger.

Automatic Liver Segmentation of a Contrast Enhanced CT Image Using a Partial Histogram Threshold Algorithm (부분 히스토그램 문턱치 알고리즘을 사용한 조영증강 CT영상의 자동 간 분할)

  • Kyung-Sik Seo;Seung-Jin Park;Jong An Park
    • Journal of Biomedical Engineering Research
    • /
    • v.25 no.3
    • /
    • pp.189-194
    • /
    • 2004
  • Pixel values of contrast enhanced computed tomography (CE-CT) images are randomly changed. Also, the middle liver part has a problem to segregate the liver structure because of similar gray-level values of a pancreas in the abdomen. In this paper, an automatic liver segmentation method using a partial histogram threshold (PHT) algorithm is proposed for overcoming randomness of CE-CT images and removing the pancreas. After histogram transformation, adaptive multi-modal threshold is used to find the range of gray-level values of the liver structure. Also, the PHT algorithm is performed for removing the pancreas. Then, morphological filtering is processed for removing of unnecessary objects and smoothing of the boundary. Four CE-CT slices of eight patients were selected to evaluate the proposed method. As the average of normalized average area of the automatic segmented method II (ASM II) using the PHT and manual segmented method (MSM) are 0.1671 and 0.1711, these two method shows very small differences. Also, the average area error rate between the ASM II and MSM is 6.8339 %. From the results of experiments, the proposed method has similar performance as the MSM by medical Doctor.

Effects of the strain on the threshold current density in InGaAs/InGaAsP multiple quantum well lasers (InGaAs/InGaAsP 다중양자우물 레이저에서 변형이 문턱전류밀도에 미치는 효과)

  • 김동철;유건호;주흥로;김형문;김태환
    • Korean Journal of Optics and Photonics
    • /
    • v.9 no.2
    • /
    • pp.111-116
    • /
    • 1998
  • Thirteen InGaAs/InGaAsP separate-confinement heterostructure multiple quantum well lasers were designed such that the strain in the active layer from 0.9% compressive strain to 1.4% tensile, and their threshold current density was caluculated to see the effects of strain on the threshold current density. The well width was adjusted such that the bandgap of the quantum well is 1.55 ${\mu}{\textrm}{m}$, For the calculation of the band structure and transition matrix element needed for the gain calculation, a block diagonalized 8$\times$8 second-order $\to{k}.\to{p}$ Hamiltonian was used to incorporate the conduction band nonparabolicity and the valence band mixing. The threshold current density shows discontinuity at 0.4% tensile strain where the first heavy-hole subband and the first light-hole subband cross and at 0.5% tensile strain where the second conduction subband begins to exist. The threshold current density at room temperature has a maximum around these 0.4-0.5% tensile strains, and as strain varies in either direction it decreases first and then increases a little after a local minimum. This calculated trend is consistent with the other reported experimental results. We discussed the results of this calculation in comparison with other theoretical or experimental papers on the effect of strain.

  • PDF