• Imaging Science in Dentistry
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• 제35권3호
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• pp.157-165
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• 2005

Purpose : To find out the proper compression ratios without degrading image quality and affecting lesion detectability on diagnostic images used in dentistry compressed with JPEG 2000 algorithm. Materials and Methods : Sixty Digora periapical images, sixty panoramic computed radiographic (CR) images, sixty computed tomographic (CT) images, and sixty magnetic resonance (MR) images were compressed into JPEG 2000 with ratios of 10 levels from 5:1 to 50:1. To evaluate the lesion detectability, the images were graded with 5 levels (1 : definitely absent; 2: probably absent; 3: equivocal; 4: probably present; 5: definitely present), and then receiver operating characteristic analysis was performed using the original image as a gold standard. Also to evaluate subjectively the image quality, the images were graded with 5 levels (1 definitely unacceptable; 2: probably unacceptable; 3: equivocal, 4: probably acceptable; 5· definitely acceptable), and then paired t-test was performed. Results : In Digora, CR panoramic and CT images, compressed images up to ratios of 15 : 1 showed nearly the same lesion detectability as original images, and in MR images, compressed images did up to ratios of 25 : 1. In Digora and CR panoramic Images, compressed images up to ratios of 5 : 1 showed little difference between the original and reconstructed images in subjective assessment of image quality In CT images, compressed images did up to ratios of 10: 1 and in MR images up to ratios of 15 : 1 Conclusion : We considered compression ratios up to 5 : 1 in Digora and CR panoramic images, up to 10 : 1 in CT images, up to 15 : 1 in MR images as clinically applicable compression ratios.

• Imaging Science in Dentistry
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• 제34권3호
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• pp.117-122
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• 2004

Purpose : To determine the proper image compression method and ratio without image quality degradation in intraoral digital radiographic images, comparing the discrete cosine transform (DCT)-based JPEG with the wavelet-based JPEG 2000 algorithm. Materials and Methods : Thirty extracted sound teeth and thirty extracted teeth with occlusal caries were used for this study. Twenty plaster blocks were made with three teeth each. They were radiographically exposed using CDR sensors (Schick Inc., Long Island, USA). Digital images were compressed to JPEG format, using Adobe Photoshop v.7.0 and JPEG 2000 format using Jasper program with compression ratios of 5 : 1,9 : 1, 14 : 1,28 : 1 each. To evaluate the lesion detectability, receiver operating characteristic (ROC) analysis was performed by the three oral and maxillofacial radiologists. To evaluate the image quality, all the compressed images were assessed subjectively using 5 grades, in comparison to the original uncompressed images. Results: Compressed images up to compression ratio of 14 : 1 in JPEG and 28 : 1 in JPEG 2000 showed nearly the same the lesion detectability as the original images. In the subjective assessment of image quality, images up to compression ratio of 9 : 1 in JPEG and 14 : 1 in JPEG 2000 showed minute mean paired differences from the original Images. Conclusion : The results showed that the clinically acceptable compression ratios were up to 9 : 1 for JPEG and 14 : 1 for JPEG 2000. The wavelet-based JPEG 2000 is a better compression method, comparing to DCT-based JPEG for intraoral digital radiographic images.

• 대한원격탐사학회지
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• 제28권2호
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• pp.181-189
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• 2012

최근 수질추정을 위한 고해상도 위성영상의 활용 가능성에 대한 관심이 증대되고 있다. 그러나 고해상도 위성영상에서의 수면지역의 낮은 SNR(Signal to Noise Ratio)과 밝기값 비선형성과 같은 방사학적 오차는 수질추정 정확도를 감소시키는 원인이 된다. 이에 따라 위성영상을 이용한 정확한 수질추정을 위해서는 방사학적 보정이 반드시 수행되어져야 하나 KOMPSAT-2 위성영상의 경우 밝기값과 입사광량간 변환관계식이 제공되지 않기 때문에 이러한 방사학적 보정에 어려움이 존재한다. 따라서 수질모니터링에 KOMPSAT-2 영상을 활용하기 위해서는 밝기값 비선형성과 내륙 수면지역의 잡음현상을 실험적으로 파악할 필요가 있다. 본 논문에서는 충분한 검보정을 통해 선형성이 보장되고 있는 IKONOS와 GeoEye-1 영상을 기준영상으로 사용하여 동일시기에 동일지역을 촬영한 KOMPSAT-2 영상과의 밝기값 상호비교를 수행하였다. 상호비교 결과, 기준영상에 비해 KOMPSAT-2 영상의 잡음은 다소 높게 나타나나 밝기값의 경향 및 잡음의 크고 작은 패턴은 정확하게 일치하였고 KOMPSAT-2 영상 내 잡음의 영향이 최소화되는 적절한 영역의 크기는 $5{\times}5$로 나타났다. 또한 모든 실험 영상에서 밝기값의 비선형성은 존재하지 않는 것으로 확인되었다. 실험결과는 KOMPSAT-2 영상이 클로로필 농도와 같은 수질인자 추정을 위해 사용될 수 있는 가능성을 보여준다.

• International Journal of Automotive Technology
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• 제6권1호
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• pp.53-63
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• 2005

We propose a fuzzy neural network (FNN) theory capable of deciding the quality of a road image prior to extracting lane-related information. The accuracy of lane-related information obtained by image processing depends on the quality of the raw images, which can be classified as good or bad according to how visible the lane marks on the images are. Enhancing the accuracy of the information by an image-processing algorithm is limited due to noise corruption which makes image processing difficult. The FNN, on the other hand, decides whether road images are good or bad with respect to the degree of noise corruption. A cumulative distribution function (CDF), a function of edge histogram, is utilized to extract input parameters from the FNN according to the fact that the shape of the CDF is deeply correlated to the road image quality. A suitability analysis shows that this deep correlation exists between the parameters and the image quality. The input pattern vector of the FNN consists of nine parameters in which eight parameters are from the CDF and one is from the intensity distribution of raw images. Experimental results showed that the proposed FNN system was quite successful. We carried out simulations with real images taken in various lighting and weather conditions, and obtained successful decision-making about $99\%$ of the time.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.1227-1229
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• 2003

Kojima Lake in Okayama prefecture is a freshing reservoir constructed adjacent to the oldest reclaimed land in Japan. This lake has a serious water quality problem because two urban rivers are flowing into it. In the present study, unsupervised classification was performed at intervals of several years using Landsat MSS data in the past 15 years. After geometric correction of these data, MSS data corresponding geographically to the field observation data were extracted and subjected to the multivariate analysis. Water quality distribution in the lake was estimated using the regression equation obtained as a result. In addition, two - dimensional and three-dimensional numerical simulations were performed and compared with the distribution obtained from the satellite images. Behavior of the reservoir flows is complicated and water quality distribution varies greatly with the flows. Here, I report the results of analysis on three factors, field observation, numerical simulation and satellite images.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 신호처리소사이어티 추계학술대회 논문집
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• pp.381-384
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• 2003

Among digital halftoning methods, error diffusion is a procedure for generating high quality bilevel images from continuous-tone images but blurs the edge information in the bilevel images. To solve the problem, we propose the edge enhanced error diffusion using the edge information of the original images. The edge enchanted weights is computed by adding local characteristic weights and input pixels multiplied a constant. Also, we combined the edge enhanced method with the adaptive error diffusion using human spatial and frequency perception characteristic. The performance of the proposed method is compared with conventional method by measuring the edge correlation. The halftoned images applied the proposed method get more fine quality due to the enchanced edge and better quality in halftoned image. And the detailed edge is preserved in the halftoned images by the proposed method.

• 한국방사선학회논문지
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• 제3권4호
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• pp.13-21
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• 2009

MRI System은 각종 여러 가지 Parameter들로 구성되어 있다. 그중 MRI 영상의 화질을 빼놓고 MRI를 논한다는 것은 어려운 일이다. 각종 Parameter들이 개발되고 발전되어오면서 MRI영상에서도 예전 System에서 보여지는 영상과는 비교 할 수 없을 정도의 고화질을 출력하고 있다. 그리고 방사선 영상 System이 고식적인 Film방식에서 digital방식으로 전환되어가고 있고 그에 따른 병원의 모든 시스템이 전산화가 되어가고 있다. 방사선 영상의 관리에 있어서 저장 이라는 부분이 아주 중요한 ��을 차지하고 있다. 그 방대한 자료를 Server에 저장하는 방법으로는 압축을 이용 하여 저장하는 방법을 사용하게 된다. 이 때 발생한 문제점은 원본 영상에 비해 압축시 영상의 화질 저하가 발생한다는 것이다. 의료 영상에서는 조그마한 화질저하도 오진의 우려가 있으므로 각별히 주의해야할 사항이다. 본 논문에서는 병원에서 진료중인 영상을 대상으로 각각의 파일 변환과 원본과의 비교, 원본 영상과 진료에 사용되어지는 모니터에서의 MRI 영상의 화질을 PSNR을 이용한 평가와 영상 평가방법에 의한 평가를 하였다. 실험결과 원본과 각종 영상 압축방법을 이용하여 압축한 영상을 비교 분석 하였는데 화질저하가 거의 나타나지 않았다. 하지만 원본영상을 display하는 모니터의 화질 에서 상당한 문제점이 드러났다. 판독용 모니터 와 의료용 모니터에서는 손색없는 고해상도의 영상을 출력해 냈는가 반면 일반 CRT, LCD 모니터에서는 각종 노이즈, 영상왜곡등 많은 문제점들이 나타났다.

• 대한디지털의료영상학회논문지
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• 제13권3호
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• pp.111-115
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• 2011

PET/CT(Positron Emission Tomography/Computed Tomography) is an examination combining morphological and functional information in one examination. The purpose of this study is to see the lowest CT dose for attenuation correction in the PET/CT maintaining good image quality when considering CT scan dose to the patients. We injected $^{18}F$-FDG and water into the cylinder shaped phantom, and obtained emission images for 3 mins and transmission images(140 kVp, 8 sec, 10~200 mA for transmission images), and reconstructed the images to PET/CT images with Iterative method. Data(Maximum, Minimum, Average, Standard Deviation) were obtained by drawing a circular ROI(Region Of Interest) on each sphere in each image set with Image J program. And then described SD according to the CT and PEC/CT images as graphes. Through the graphes, we got the relationships of mA and quality of images. SDs according to CT graph were 16.25 at 10 mA, 7.26 at 50 mA, 5.5 at 100 mA, 4.29 at 150 mA, and 3.83 at 200 mA, i.e. the higer mA, the better image quality was presented. SDs according to PET/CT graph were 1823.2 at 10 mA, 1825.1 at 50 mA, 1828.4 at 100 mA, 1813.8 at 150 mA, and 1811.3 at 200 mA. Calculated SDs at PET/CT images were maintained. This means images quality is maintained having nothing to do with mA of high and low.

• Biomedical Engineering Letters
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• 제8권4호
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• pp.355-364
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• 2018

When focusing using an ultrasonic transducer array, a main lobe is formed in the focal region of an ultrasound field, but side lobes also arise around the focal region due to the leakage. Since the side lobes cannot be completely eliminated in the focusing process, they are responsible for subsequent ultrasound image quality degradation. To improve ultrasound image quality, a signal processing strategy to reduce side lobes is definitely in demand. To this end, quantitative determination of main and side lobes is necessary. We propose a theoretically and actually error-free method of exactly discriminating and separately computing the main lobe and side lobe parts in ultrasound image by computer simulation. We refer to images constructed using the main and side lobe signals as the main and side lobe images, respectively. Since the main and side lobe images exactly represent their main and side lobe components, respectively, they can be used to evaluate ultrasound image quality. Defining the average brightness of the main and side lobe images, the conventional to side lobe image ratio, and the main to side lobe image ratio as image quality metrics, we can evaluate image characteristics in speckle images. The proposed method is also applied in assessing the performance of side lobe suppression filtering. We show that the proposed method may greatly aid in the evaluation of medical ultrasonic images using computer simulations, albeit lacking the use of actual experimental data.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.1011-1012
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• 2008

Image quality analysis has been carried out for both monochrome and colour print images obtained by a calibrated low-end scanner. The analysis method is based upon ISO13660 for monochrome images and additional criteria for colour quality that we have defined. We have compared performance of the calibrated scanner with that of a high-end spectrophotometer in terms of several aspects such as line and large area. They have provided similar results without significant discrepancy.