• Korean Journal of Radiology
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• 제21권4호
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• pp.462-470
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• 2020

Objective: To demonstrate that human visual illusion can contribute to sub-endocardial dark rim artifact in contrast-enhanced myocardial perfusion magnetic resonance images. Materials and Methods: Numerical phantoms were generated to simulate the first-passage of contrast agent in the heart, and rendered in conventional gray scale as well as in color scale with reduced luminance variation. Cardiac perfusion images were acquired from two healthy volunteers, and were displayed by the same gray and color scales used in the numerical study. Before and after k-space windowing, the left ventricle (LV)-myocardium boarders were analyzed visually and quantitatively through intensity profiles perpendicular the boarders. Results: k-space windowing yielded monotonically decreasing signal intensity near the LV-myocardium boarder in the phantom images, as confirmed by negative finite difference values near the board ranging -1.07 to -0.14. However, the dark band still appears, which is perceived by visual illusion. Dark rim is perceived in the in-vivo images after k-space windowing that removed the quantitative signal dip, suggesting that the perceived dark rim is a visual illusion. The perceived dark rim is stronger at peak LV enhancement than the peak myocardial enhancement, due to the larger intensity difference between LV and myocardium. In both numerical phantom and in-vivo images, the illusory dark band is not visible in the color map due to reduced luminance variation. Conclusion: Visual illusion is another potential cause of dark rim artifact in contrast-enhanced myocardial perfusion MRI as demonstrated by illusory rim perceived in the absence of quantitative intensity undershoot.

• Korean Journal of Radiology
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• 제25권4호
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• pp.384-394
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• 2024

Objective: To evaluate the image quality of novel dark-blood computed tomography angiography (CTA) imaging combined with deep learning reconstruction (DLR) compared to delayed-phase CTA images with hybrid iterative reconstruction (HIR), to visualize the cervical artery wall in patients with Takayasu arteritis (TAK). Materials and Methods: This prospective study continuously recruited 53 patients with TAK (mean age: 33.8 ± 10.2 years; 49 females) between January and July 2022 who underwent head-neck CTA scans. The arterial- and delayed-phase images were reconstructed using HIR and DLR. Subtracted images of the arterial-phase from the delayed-phase were then added to the original delayed-phase using a denoising filter to generate the final-dark-blood images. Qualitative image quality scores and quantitative parameters were obtained and compared among the three groups of images: Delayed-HIR, Dark-blood-HIR, and Dark-blood-DLR. Results: Compared to Delayed-HIR, Dark-blood-HIR images demonstrated higher qualitative scores in terms of vascular wall visualization and diagnostic confidence index (all P < 0.001). These qualitative scores further improved after applying DLR (Dark-blood-DLR compared to Dark-blood-HIR, all P < 0.001). Dark-blood DLR also showed higher scores for overall image noise than Dark-blood-HIR (P < 0.001). In the quantitative analysis, the contrast-to-noise ratio (CNR) values between the vessel wall and lumen for the bilateral common carotid arteries and brachiocephalic trunk were significantly higher on Dark-blood-HIR images than on Delayed-HIR images (all P < 0.05). The CNR values were significantly higher for Dark-blood-DLR than for Dark-blood-HIR in all cervical arteries (all P < 0.001). Conclusion: Compared with Delayed-HIR CTA, the dark-blood method combined with DLR improved CTA image quality and enhanced visualization of the cervical artery wall in patients with TAK.

• 융합신호처리학회논문지
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• 제15권3호
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• pp.80-84
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• 2014

Dark channel prior는 열화되지 않은 실외 영상의 경우 각 픽셀과 이웃 픽셀의 컬러 채널 중에 하나는 0에 가까운 값을 가진다는 것으로, 열화된 영상의 열화 정도를 추정하는 데 활용될 수 있다. 즉, 영상이 블러에 의해 열화되면 dark channel 값이 주변 픽셀과의 평균을 통해 증가하게 된다. 본 논문에서는 이러한 dark channel의 변화를 이용하여 영상블러의 세기를 측정하는 방법을 제안한다. 주어진 크기의 가우시안 블러와 수평 모션 블러를 삽입한 영상에 대한 실험을 통해 제안된 방법의 유용성을 검증한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2529-2543
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• 2019

Scanning electron microscopy (SEM) image can link with the microscopic world through reflecting interaction between electrons and materials. The SEM images are easily subject to blurring distortions during the imaging process. Inspired by the fact that dark channel prior captures the changes to blurred SEM images caused by the blur process, we propose a method to evaluate the SEM images sharpness based on the dark channel prior. A SEM image database is first established with mean opinion score collected as ground truth. For the quality assessment of the SEM image, the dark channel map is generated. Since blurring is typically characterized by the spread of edge, edge of dark channel map is extracted. Then noise is removed by an edge-preserving filter. Finally, the maximum gradient and the average gradient of image are combined to generate the final sharpness score. The experimental results on the SEM blurred image database show that the proposed algorithm outperforms both the existing state-of-the-art image sharpness metrics and the general-purpose no-reference quality metrics.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 1999년도 Proceedings of International Symposium on Remote Sensing
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• pp.310-315
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• 1999

We extracted narrow open water streams from JERS-1 SAR images of the Amazon rain forest. The extracted range of these streams were almost comparable to a high level extraction of the same streams from near-IR images of JERS-1 VNIR data notwithstanding that these features in SAR images show the strong dependence of the observation angle. Large water bodies are relatively easy to extract from JERS-1 SAR images, as they tend to appear as very dark areas; but streams whose width is nearly equal to or less than the spatial resolution no longer appear as very dark features. By using strong scatterers distributed sparsely along the radar facing sides of the streams, we can successfully estimate approximate ranges of waterways and then extract relatively dark line-like features within these ranges.

• International Journal of Advanced Culture Technology
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• 제8권4호
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• pp.229-234
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• 2020

Dehazing significantly improves image quality by restoring the loss of contrast and color saturation for images taken in the presence. However, when applied to images not taken according to the prior information, dehazing can cause unintended degradation of image quality. To avoid unintended degradations, we present a hazy scene detection algorithm using a single image based on the distributions of hue, saturation, and dark channel. Through a heuristic approach, we find out statistical characteristics of the distribution of hue, saturation, and dark channels in the hazy scene and make a detection model using them. The proposed method can precede the dehazing to prevent unintended degradation. The detection performance evaluated with a set of test images shows a high hit rate with a low false alarm ratio. Ultimately the proposed method can be used to control the effect of dehazing so that the dehazing can be applied to wide variety of images without unintended degradation of image quality.

• 디자인학연구
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• 제15권4호
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• pp.327-336
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• 2002

본 논문의 목적은 찬피부색을 지닌 사람들이 자신의 이미지를 긍정적인 이미지로 관리하고 자신감 있는 의복색을 선택하여 의상연출에 도움을 주고자 하였다. 찬피부색을 지닌 사람들이 의복색에 따라 어떠한 시각적 이미지 평가가 나타나는지를 준 실험 방법으로 분석한 결과는 다음과 같다. 1. Red계열의 의복색에서는 vivid 톤에서 긍정적인 이미지를, dull과 dark 톤에서 부정적인 이미지를 보여주었다. 2. Yellow계열의 의복색은 vivid, bright 톤에서 긍정적인 이미지를, dull, dark 톤에서 부정적인 이미지를, cool Yellow의 light 톤에서도 긍정적인 이미지 보여주는 것으로 나타났다. 3. warm Green의 의복색은 vivid, deep 톤에서, cool Green의 vivid 톤에서 긍정적인 이미지를 나타내었다. 4. warm Blue의 의복색은 vivid, deep 톤에서 긍정적인 이미지를, cool Blue의 vivid, bright 톤에서 긍정적인 이미지를 지니며, dull 톤에서 부정적인 이미지를 보여주는 것으로 나타났다. 5. Purple계열의 의복색은 vivid, deep, light 톤에서 긍정적인 이미지를, dull 톤에서 부정적인 이미지를 보여주는 것으로 나타났다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권8호
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• pp.2749-2763
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• 2021

The desirable result of infrared (IR) and visible (VIS) image fusion should have textural details from VIS images and salient targets from IR images. However, detail information in the dark regions of VIS image has low contrast and blurry edges, resulting in performance degradation in image fusion. To resolve the troubles of fuzzy details in dark regions of VIS image fusion, we have proposed a method of reflectance estimation for IR and VIS image fusion. In order to maintain and enhance details in these dark regions, dark region approximation (DRA) is proposed to optimize the Retinex model. With the improved Retinex model based on DRA, quasi-Newton method is adopted to estimate the reflectance of a VIS image. The final fusion outcome is obtained by fusing the DRA-based reflectance of VIS image with IR image. Our method could simultaneously retain the low visibility details in VIS images and the high contrast targets in IR images. Experiment statistic shows that compared to some advanced approaches, the proposed method has superiority on detail preservation and visual quality.

• 한국항공우주학회지
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• 제44권1호
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• pp.33-39
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• 2016

칼라 영상의 안개제거 기술이 다양하게 연구되어 왔으며 이 중 칼라 안개 영상의 특성을 토대로 도출한 Dark Channel Prior(DCP) 모델을 이용한 방법이 가장 활발하게 이용되고 있다. 한편 근적외선 영상을 이용한 응용이 널리 사용되고 있으며 근적외선 영상에 존재하는 안개를 제거할 필요가 있음에도 불구하고 기존에 근적외선 영상을 대상으로 하는 안개 제거 기술이 제안되지 않았다. 본 논문에서는 칼라 영상과 근적외선 영상을 안개 제거 측면에서 비교 분석을 수행하며 적외선 영상에 기존의 칼라 안개 제거 알고리즘 기법을 적용했을 때 나타나는 결과를 분석한다. 또한 근적외선 영상에서의 특징에 맞게 기존 칼라 안개 제거 기법을 수정한 기법을 제안하고 그 결과를 분석한다.

• Investigative Magnetic Resonance Imaging
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• 제6권1호
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• pp.21-27
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• 2002

목적: 뇌실질내 혈종의 시기별 확산강조영상 소견을 알아보고자 하였다. 대상 및 방법: 임상적으로 뇌출혈의 시기가 분명한 환자 17명을 대상으로 하였다. 확산강조영상은 1.5 tesla 자기공명영상 기기를 이용하였으며, b 값은 세 방향 모두 $1000{\;}sec/\textrm{mm}^2$으로 하였다. 출혈 시기는 12시간 이하인 초급성기 5예, 3일 이하인 급성기 4예, 3주이하의 아급성기 4예, 3주 이후의 만성기 4예였다. 확산강조영상에서 혈종의 중심부와 주변부의 신호강도를 뇌실질 신호와 비교하여 bright, high, iso, low, dark 신호로 분류하여 분석하였으며, 각 시기의 T2강조영상과 T1강조영상에서의 신호강도와 비교 관찰하였다. 결과: 확산강조영상에서 초급성기 혈종의 중심부와 주면부는 각각 high와 dark신호를 보였고, 급성기는 중심부와 주변부가 각각 dark와 high-bright 신호강도를 보였다. 아급성기와 만성기는 중심부와 주변부가 high-bright와 dark 신호강도를 보였다. 시간 경과에 따른 혈종의 신호 변화는 전체적으로 T2강조영상에서의 신호 변화와 비슷하나, T2강조영상에 비해 빠르고 현저한 신호 변화를 보였다. 결론: 뇌실질내 혈종은 확산강조 자기공명영상에서 중심부와 주변부의 신호강도가 시기별로 특징적으로 변하며 중심부는 초급성기, 아급성기와 만성기에 high-bright신호를, 급성기에는 dark 신호를 보였고, 주변부는 초급성기, 아급성기와 만성기에 dark 신호를, 급성기에는 high-bright 신호를 보였다.