• Journal of Korea Multimedia Society
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• v.24 no.8
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• pp.1059-1067
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• 2021

In this paper, a HDR algorithm for a single image is proposed using the exposure fusion, that adaptively calculates gamma correction coefficients according to the image distribution. Since typical HDR methods should use at least three images with different exposure values at the same scene, the main problem was that they could not be applied at the single shot image. Thus, HDR enhancements based on a single image using tone mapping and histogram modifications were recently presented, but these created some location-specific noises due to improper corrections. Therefore, the proposed algorithm calculates proper gamma coefficients according to the distribution of the input image and generates different exposure images which are corrected by the dark and the bright region stretching. A HDR image reproduction controlling exposure fusion weights among the gamma corrected and the original pixels is presented. As the result, the proposed algorithm can reduce certain noises at both the flat and the edge areas and obtain subjectively superior image quality to that of conventional methods.

• Journal of Broadcast Engineering
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• v.22 no.1
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• pp.42-50
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• 2017

A Bit-depth expansion is a method to increase the number of bit. It is getting important as the needs of HDR (High Dynamic Range) display or resolution of display have been increased because the level of luminance or expressiveness of color is proportional to the number of bit in the display. In this paper, we present effective bit-depth expansion algorithm for conventional standard 8 bit-depth content to display in high bit-depth device (10 bits). Proposed method shows better result comparing with recently developed methods in quantitative (PSNR) with low complexity. The proposed method shows 1db higher in PSNR measurement with 40 times faster in computational time.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2016.06a
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• pp.211-214
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• 2016

본 논문에서는 하나의 넓은 동적 영역(High Dynamic Range: HDR)을 갖는 이미지를 Earth Mover's Distance(EMD)값을 이용한 이미지 분할 기법을 적용한 유사 지역 그룹화를 통해, 각 그룹별로 톤 매핑을 수행하는 기법을 제안하고자 한다. 기존의 EMD 값을 통한 이미지 분할 알고리듬은 이미지 내의 같은 그룹으로 분류된 지역에서 휘도(luminance)의 변화가 클 때 후광 현상(halo artifact)이 발생하는 문제점을 보였다. 본 논문에서는 기존의 알고리듬으로 분할된 이미지를 처리할 때 휘도 변화량(gradient)의 정보를 활용하여 후광 현상 제거함으로써 주관적 화질을 향상시켰다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2017.06a
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• pp.55-58
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• 2017

본 논문에서는 넓은 동적 영역(High Dynamic Range: HDR) 이미지에 지역 엣지 보존 필터를 적용한 개선된 다중 스케일 톤 매핑 기법을 제안하고자 한다. 기존 알고리듬의 다중 스케일 분해 과정에서는 과도하게 많은 정보를 보존하여 결과 이미지가 비현실적으로 표현되고 일부 테스트 이미지에서는 화소 값 변화량이 큰 엣지 영역에서 후광 효과가 발생하는 단점이 있다. 본 논문에서는 기존 알고리듬의 다중 스케일 분해 과정을 개선하여 엣지를 적절히 보존함으로써 후광 효과를 제거함과 동시에 주관적 화질을 향상시켰다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.8
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• pp.669-679
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• 2013

When an image is converted from HDR (high dynamic range) to LDR (low dynamic range), a tone mapping process is the essential component. Many TMOs (tone mapping operators) have been motivated by human vision which has lower physical luminance range than that in real scene. The representative of human vision properties which motivate TMOs is the local adaptation. However, TMOs are ultimately compressing image information such as contrast, saturation, etc. and the compression causes defects in image quality. In this paper, in order to compensate the degradation of the image which is caused by TMOs, the visual acuity-based edge stop function is proposed for applying the property of human vision to base-detail separation. In addition, using CSF (contrast sensitivity function) which represents the relationship among spatial frequency, contrast sensitivity, and luminance, the sharpness filter is designed and adaptively applied to the detail layer in regard to surround luminance.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2018.06a
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• pp.55-58
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• 2018

본 논문에서는 넓은 동적 영역 (High Dynamic Range: HDR) 영상의 실시간 처리 방법을 제안한다. HDR 영상은 사람의 눈으로 볼 수 있는 자연 영상과 가깝지만 대부분의 디스플레이 기기들은 좁은 동적 영역 (Standard Dynamic Range: SDR)의 영상 출력만을 지원한다. 이러한 동적 영역의 차이를 사람의 시각 특성을 고려하여 축소하기 위해서는 톤 매핑 기법 (Tone Mapping Operator: TMO)을 수행하여야 한다. 하지만 기존의 이미지 톤 매핑 기법을 실시간 영상에 적용할 경우 영상의 실시간 처리, 플리커링 현상을 해결하는데 어려움이 있다. 본 논문에서는 k-means 클러스터링 기법을 사용하여 플리커 현상에 강인하고 실시간 비디오 톤 매핑이 가능한 알고리듬을 제안한다. 제안하는 알고리듬은 동적 계획법 (Dynamic Programming)을 통해 빠른 전역 해를 찾는 것이 가능하고 세부영상 향상 (Detail Enhancement)의 실시간 처리가 가능함을 보였다.

• Journal of Korea Multimedia Society
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• v.18 no.9
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• pp.1027-1038
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• 2015

For last several decades, the color correction methods have been proposed for HDR(high dynamic range) images. However, color distortion problems take place after correcting the colors such as halos, dominant color as well known. Accordingly, this article presents a novel approach in which the method consists of tone-mapping method and cone response function. In the proposed method, the tone mapping method is used to improve the contrast in the given HDR image based on chromatic and achromatic based on the CIEXYZ tristimulus value, expressed in c/m². The cone response function is used to deal with mismatch between corrected image and displayed image as well as to estimate various human visual effects based on the CMCAT2000 color appearance model. The experimental results show that the proposed method yields better performance of color correction over the conventional method in subjective and quantitative quality, and color reproduction.

• Journal of Korea Multimedia Society
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• v.19 no.5
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• pp.837-847
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• 2016

Tone mapping for High Dynamic Range(HDR) image provides matching human visual perception between real world scene and displayable devices. Recently, a tone mapping algorithm based on localized gamma correction is proposed. This algorithm is using human visual properties of contrast and colorfulness with background intensity, generating a weight map for gamma correction. However, this method have limitations of controlling enhancement region as well as generating halo artifacts caused by the weight map construction. To overcome aforementioned limitations, proposed algorithm in this paper modifies previous weight map, considering base layer intensity of input luminance channel. By determining enhancement region locally and globally based on base layer intensity, gamma values are corrected accordingly. Therefore, proposed algorithm selectively enhances local brightness and controls strength of edges. Subjective evaluation using z-score shows that our proposed algorithm outperforms the conventional methods.

• Annual Conference of KIPS
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• 2024.05a
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• pp.860-861
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• 2024

본 연구는 ISP(Image Signal Processing) 모듈에 적용 가능한 HDR(High Dynamic Range)을 위한 Log Histogram Equalization 기법을 제안한다. 기존의 HDR 기술은 다양한 노출로 찍은 사진들을 합쳐서 한 장의 사진에서 더 넓은 동적 범위를 담아내는 방식에 집중해 왔다. 이 연구에서는 단일 노출 이미지에서도 향상된 HDR 을 구현하기 위해, 로그 함수를 이용한 히스토그램 평준화 방법을 탐구한다. 이 기법은 로그 함수의 특성을 활용하여 이미지의 대비를 증가시킨다. 또한, 룩업 테이블과 선형 근사를 도입하여 연산량을 줄이고, ISP 모듈 내에서의 실시간 처리 가능성을 높인다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.01a
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• pp.154-157
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• 2009

High dynamic range image can describe the real world scenes that have a wide range of luminance intensity. To display high dynamic range (HDR) image into conventional displayable devices such as monitors and printers, we proposed the logarithmic based global mapping algorithm that consider the features of image using mapping parameters. Based on characteristics of image, we first modify input luminance values for reproducing perceptually tuned images and then displayable output values are obtained directly. The experimental results show that the proposed algorithm achieves good subjective results while preserving details of image, furthermore proposed algorithm has fast simple and practical structure for implementation.