• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.840-866
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• 2014

Visibility in underwater images is usually poor because of the attenuation of light in the water that causes low contrast and color variation. In this paper, a new approach for underwater image quality improvement is presented. The proposed method aims to improve underwater image contrast, increase image details, and reduce noise by applying a new method of using contrast stretching to produce two different images with different contrasts. The proposed method integrates the modification of the image histogram in two main color models, RGB and HSV. The histograms of the color channel in the RGB color model are modified and remapped to follow the Rayleigh distribution within certain ranges. The image is then converted to the HSV color model, and the S and V components are modified within a certain limit. Qualitative and quantitative analyses indicate that the proposed method outperforms other state-of-the-art methods in terms of contrast, details, and noise reduction. The image color also shows much improvement.

• 한국멀티미디어학회논문지
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• 제25권8호
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• pp.991-998
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• 2022

Recently, object recognition using image/video signals is rapidly spreading on autonomous driving and mobile phones. However, the actual input image/video signals are easily exposed to a poor illuminance environment. A recent researches for improving illumination enable to estimate and compensate the illumination parameters. In this study, we propose VE-DCE (video enhancement zero-reference deep curve estimation) to improve the illumination of low-light images. The proposed VE-DCE uses unsupervised learning-based zero-reference deep curve, which is one of the latest among learning based estimation techniques. Experimental results show that the proposed method can achieve the quality of low-light video as well as images compared to the previous method. In addition, it can reduce the computational complexity with respect to the existing method.

• 한국멀티미디어학회논문지
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• 제16권10호
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• pp.1180-1188
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• 2013

영상의 다양한 변환 후에 나타나는 화질의 열화를 복원하기 위한 방법으로 보간법이나 초해상도 기술 등이 사용된다. 낮은 계산복잡도를 가지면서도 주관적 및 객관적 영상 향상을 위한 연구는 현재까지도 다양하게 이루어지고 있다. 본 논문에서는 개선된 자가 열화 복원 기법을 이용한 영상 향상 방법을 제안한다. 제안하는 방법에서는 개선된 자가 열화 복원 기법을 사용하여 영상의 크기 변환에서 소실된 정보를 유추하고, 유추한 정보를 영상 보간 기법과 결합하여 개선된 결과 영상을 생성한다. 실험을 통하여 제안한 방법이 비교 방법들보다 객관적 화질 지표인 PSNR에서 최대 1.8dB 향상된 결과를 나타내며, 주관적 화질에서도 우위에 있음을 확인할 수 있었다. 제안한 방법은 영상의 크기 변환이 요구되는 다양한 응용 환경에서 기반기술로 사용될 수 있다.

• Imaging Science in Dentistry
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• 제32권4호
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• pp.213-219
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• 2002

Purpose : Computed radiography (CR) has been used in cephalometric radiography and many studies have been carried out to improve image quality using various digital enhancement and filtering techniques, During CR image acquisition, the frequency rank and type affect to the image quality. The aim of this study was to compare the diagnostic quality of conventional cephalometric radiographs to those of computed radiography. Materials and Methods : The diagnostic quality of conventional cephalometric radiographs (MO) and their digital image counterparts were compared, and at the same time, six modalities (M1-M6) of spatial frequency-processed digital images were compared by evaluating the reproducibility of 23 cephalometric landmark locations. Reproducibility was defined as an observer's deviation (in mm) from the mean between all observers. Results and Conclusion: In comparison with the conventional cephalometric radiograph (MO), Ml showed statistically significant differences in 8 locations, M2 in 9, M3 12, M4 in 7, M5 in 12, and M6 showed significant differences in 14 of 23 landmark locations (p < 0.05). The number of reproducible landmarks that each modality possesses were 7 in M6, 6 in M5, 5 in M3, 4 in M4, 3 in M2, 2 in Ml, and 1 location in MO. The image modality that observers selected as having the best image quality was M5.

• Journal of Multimedia Information System
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• 제4권2호
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• pp.65-73
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• 2017

This paper proposes a method to improve the image quality by designing Unsharp Mask Filter (UMF) based on Retinex theory which controls the frequency pass characteristics adaptively. Conventional unsharp masking technique uses blurring image to emphasize sharpness of image. Unsharp Masking(UM) adjusts the original image and sigma to obtain a high frequency component to be emphasized by the difference between the blurred image and the high frequency component to the original image, thereby improving the contrast ratio of the image. In this paper, we design a Unsharp Mask Filter(UMF) that can process the contrast ratio improvement method of Unsharp Masking(UM) technique with one filtering. We adaptively process the contrast ratio improvement using Unsharp Mask Filter(UMF). We propose a method based on Retinex theory for adaptive processing. For adaptive filtering, we control the weights of Unsharp Mask Filter(UMF) based on the human visual system and output more effective results.

• 전자공학회논문지 IE
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• 제48권2호
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• pp.32-39
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• 2011

비냉각형 적외선 검출기를 사용한 적외선 열상 카메라의 영상은 다이나믹 레인지가 좁고 신호 증폭에 의한 노이즈로 인하여 피사체를 식별하기 어려운 단점이 있다. 인간의 시각모델을 기반으로 한 레티넥스 알고리즘은 콘트라스트 향상 및 컬러 재현성에 있어서 매우 효과적인 방법으로 알려져 있다. 하지만, 적외선 열상 이미지와 같이 다이나믹 레인지가 좁은 영상에 레티넥스 알고리즘을 적용할 경우 오히려 콘트라스트가 감소하고 이미지 품질이 저하된다. 본 논문에서는 적외선 열상 이미지의 특성에 적합한 레티넥스 알고리즘 기반의 화질 개선 방법을 제안한다. 콘트라스트 개선 성능을 향상시키기 위해 새로운 다이나믹 레인지 압축 함수를 사용하였고, 국부적인 윤곽과 노이즈를 개선하기 위해 콘트라스트 보상 처리를 영상의 합성 과정에 적용하였다. 실험 결과 영상의 비교와 분석을 통해 제안한 알고리즘이 기존의 알고리즘보다 적외선 열상 이미지의 화질 개선에 더 효과적인 방법임을 확인하였다.

• Journal of Information Processing Systems
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• 제18권4호
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• pp.575-586
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• 2022

Uneven light in real-world causes visual degradation for underexposed regions. For these regions, insufficient consideration during enhancement procedure will result in over-/under-exposure, loss of details and color distortion. Confronting such challenges, an unsupervised low-light image enhancement network is proposed in this paper based on the guidance of the unpaired low-/normal-light images. The key components in our network include super-resolution module (SRM), a GAN-based low-light image enhancement network (LLIEN), and denoising-scaling module (DSM). The SRM improves the resolution of the low-light input images before illumination enhancement. Such design philosophy improves the effectiveness of texture details preservation by operating in high-resolution space. Subsequently, local lightness attention module in LLIEN effectively distinguishes unevenly illuminated areas and puts emphasis on low-light areas, ensuring the spatial consistency of illumination for locally underexposed images. Then, multiple discriminators, i.e., global discriminator, local region discriminator, and color discriminator performs assessment from different perspectives to avoid over-/under-exposure and color distortion, which guides the network to generate images that in line with human aesthetic perception. Finally, the DSM performs noise removal and obtains high-quality enhanced images. Both qualitative and quantitative experiments demonstrate that our approach achieves favorable results, which indicates its superior capacity on illumination and texture details restoration.

• 대한전자공학회논문지
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• 제25권6호
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• pp.694-699
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• 1988

Optical phase conjugate mechanism and edge enhancement by degenerate four wave mixing (DFWM) in photorefractive material are described, and image reconstruction is perfromed sucessfully in BaTiO3 single crystal. Also, the edge enhancement is carried out in the crystal by the same DFWM geometry. But the intensities of three incident beams are inverted. Good quality of edge enhancement is observed in real-time (processing time 10 sec) with low incident light intensity (5.38mW/cm\ulcorner.

• 방송공학회논문지
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• 제19권1호
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• pp.118-121
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• 2014

영상 보간법은 영상의 크기 변환에서 나타나는 새로운 좌표의 화소의 값을 결정하는 방법이다. 영상 콘텐츠가 대용량화되면서 고속으로 개선된 결과 영상을 생성할 수 있는 영상 보간법이 요구된다. 따라서 본 논문에서는 영상 해상도 개선을 위한 고속 다중 혼합영상 보간법을 제안한다. 제안하는 방법은 입력 영상의 4개의 부영상으로부터 12개의 예상되는 부족분을 추정하고, 추정된 부족분과 입력 영상을 결합한 후 보간 함수를 거쳐서 결과 영상을 생성한다. 제안하는 방법은 비교 방법들보다 PSNR에서 최대 1.9dB, SSIM에서 최대 0.052 개선된 결과를 나타내었으며, 주관적 화질 비교에서도 우위에 있음을 실험을 통해서 알 수 있었다. 알고리즘의 동작속도 비교를 통해서 기존의 방법들보다 최소 3배 이상 빠르게 동작하는 것을 알 수 있었다. 제안하는 방법은 영상 해상도 개선을 위한 응용 환경에서 유용하게 사용될 수 있다.

• 한국멀티미디어학회논문지
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• 제15권5호
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• pp.569-576
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• 2012

This paper presents an x-ray medical image panorama system which can overcome the smallness of the images that exist on a source computer during remote medical processing. In the system, after the standard medical image format DICOM is converted to the PC standard image format, a MSR algorithm is used to enhance X-ray images of low quality. Then SURF and Multi-band blending are applied to generate a panoramic image. Also, this paper evaluates the proposed SURF based system through the average gray value error and image quality criterion with X-ray image data by comparing with a SIFT based system. The results show that the proposed system is superior to SIFT based system in image quality.