Kyu-Ik Sohng

Kyungpook National University, Daikyū, Daegu, South Korea

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Publications (101)23.58 Total impact

  • Geun-Young Lee · Hyuk-Ju Kwon · Sung-Hak Lee · Kyu-Ik Sohng

    No preview · Article · Nov 2015
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    Geun-Young Lee · Sung-Hak Lee · Hyuk-Ju Kwon · Kyu-Ik Sohng
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    ABSTRACT: An image appearance model is extremely useful for high-dynamic-range image (HDRI) rendering. However, the base-detail separation and the tone compression process for tonal control cause degradations in image quality. This study focuses on the de-saturation, reduced contrast, and noise problems in dark regions that occur through HDRI-rendering. First, we discuss de-saturation compensation using a bilateral filter that is based on the visual acuity characteristics of various illuminant levels. The edge stop function of the bilateral filter in iCAM06 is adaptively modified according to the illuminant information. Second, to reduce the magnified noise in the dark regions caused by tone mapping, the shadow regions are detected by an object’s intensity and illuminant level, and then the noise of the detected regions is reduced using a luminance-adaptive coring function. Finally, we confirmed the enhanced color saturation, image contrast, and reduced noise in shadow regions through the application of the proposed methods.
    Full-text · Article · Apr 2015 · Optical Review
  • Soo-Young Ha · Uitae Jeong · Il Choi · Kyu-Ik Sohng
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    ABSTRACT: This paper proposes a new planar calibrator, which is suitable for calibrating the fisheye camera in a vehicle around view monitoring system. To facilitate easy feature point detection using the proposed calibrator, we ensure that the shapes of the features and the distances between the adjacent feature points on the calibrator’s image acquired by the fisheye camera are identical squares and equal, respectively, unlike those on the conventional chessboard calibrator. Further, the optimum number and locations of feature points on the proposed calibrator are experimentally determined for ensuring the best camera calibration performance. Compared with the conventional chessboard calibrator and the H-pattern calibrator, the proposed calibrator shows superior performance in terms of feature point detection and camera calibration.
    No preview · Article · Apr 2015 · Optical Review
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    Hyuk-Ju Kwon · Sung-Hak Lee · Geun-Young Lee · Kyu-Ik Sohng

    Full-text · Article · Jan 2015
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    Geun-Young Lee · Sung-Hak Lee · Hyuk-Ju Kwon · Kyu-Ik Sohng
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    ABSTRACT: An image toning method for low dynamic range image compression is presented. The proposed method inserts tone mapping into JPEG baseline instead of postprocessing. First, an image is decomposed into detail, base, and surrounding components in terms of the discrete cosine transform coefficients. Subsequently, a luminance-adaptive tone mapping based on the human visual sensitivity properties is applied. In addition, compensation modules are added to enhance the visually sensitive factors, such as saturation, sharpness, and gamma. A comparative study confirms that the transmitted compression images have good image quality.
    Full-text · Article · Nov 2014 · Optical Engineering
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    Hyuk-Ju Kwon · Sung-Hak Lee · Geun-Young Lee · Kyu-Ik Sohng
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    ABSTRACT: Tone mapping algorithms are used for image processing to reduce the dynamic range of an image to be displayed on low dynamic range (LDR) devices. The Retinex, which was developed using multi-scale and luminance-based methods, is one of the tone mapping algorithms for dynamic range compression, color constancy and color rendition. Retinex algorithms still have drawbacks, such as lower contrast and desaturation. This paper proposes a multi-scale luminance adaptation transform (MLAT) based on visual brightness functions for the enhancement of contrast and saturation of rendered images. In addition, the proposed algorithm was used to estimate the minimum and maximum luminance and a visual gamma function for local adapted viewing conditions. MLAT showed enhanced contrast and better color representation than the conventional methods in the objective evaluations (CIEDE200 and VCM).
    Full-text · Article · Jul 2014 · Digital Signal Processing
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    Sung-Hak Lee · Hyuk-Ju Kwon · Kyu-Ik Sohng
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    ABSTRACT: A low-dynamic tone-compression technique is developed for realistic image rendering that can make three-dimensional (3D) images similar to realistic scenes by overcoming brightness dimming in the 3D display mode. The 3D surround provides varying conditions for image quality, illuminant adaptation, contrast, gamma, color, sharpness, and so on. In general, gain/offset adjustment, gamma compensation, and histogram equalization have performed well in contrast compression; however, as a result of signal saturation and clipping effects, image details are removed and information is lost on bright and dark areas. Thus, an enhanced image mapping technique is proposed based on space-varying image compression. The performance of contrast compression is enhanced with complex adaptation in a 3D viewing surround combining global and local adaptation. Evaluating local image rendering in view of tone and color expression, noise reduction, and edge compensation confirms that the proposed 3D image-mapping model can compensate for the loss of image quality in the 3D mode.
    Full-text · Article · Jul 2014 · Optical Review
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    ABSTRACT: Infrared (IR) imaging systems obtain thermal images by converting surface temperature into two-dimensional images by measuring IR radiation from an object's surface. This research proposes a wavelength-band transformation method to convert an IR image of an arbitrary wavelength-bandwidth into an IR image of another wavelength-bandwidth. We estimate the temperature of an arbitrary wavelength by obtaining the radiance from the black body radiation theory and the linear transformation function of the gray level from the radiance. We generate an IR image for another wavelength-bandwidth by calculating the radiance of another wavelength-bandwidth using the estimated temperature. The validity of the proposed method was verified through simulations. The IR target image was generated using RadThermIR software, and images, acquired from a thermal observation device, were used as IR background image.
    No preview · Article · Dec 2013 · International Journal of Control and Automation
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    Seok-Min Chae · Sung-Hak Lee · Kyu-Ik Sohng
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    ABSTRACT: The iCAM06 has been used as an image appearance model for HDR image rendering. iCAM06 goes through the color space conversions of the several steps to present HDR images. The dynamic range of a HDR image needs to be mapped onto the range of output devices, which is called the tone mapping. However, tone compression process of iCAM06 causes white point shift and color distortion because of colorclipping and cross-stimulus. Therefore, we proposed a modified whitebalanced method in low-chromatic region and a color adjustment method in IPT space to compensate the color distortion during in tone compression process. Through the experimental results, we confirmed the proposed compatible color adjustment method had better performance than iCAM06 and enhanced models.
    Full-text · Article · Nov 2013 · IEICE Transactions on Electronics
  • Geun-Young Lee · Sung-Hak Lee · Kyu-Ik Sohng
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    ABSTRACT: In pursuance of the tone mapping for LDR images, the proposed method inserts the tone mapping into JPEG baseline not as post-processing. First, an image is decomposed in detail, base, surround images in term of DCT coefficients. Then, a surround-adaptive tone mapping is applied to the base image. In addition, a compensation module is added for the defects such as desaturation and sharpness falling resulted by tone mapping. As a result, it is confirmed that transmitted JPEG images are enhanced in term of image quality.
    No preview · Conference Paper · Oct 2013
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    Geun-Young Lee · Sung-Hak Lee · Hyuk-Ju Kwon · Kyu-Ik Sohng
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    ABSTRACT: 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.
    Full-text · Article · Aug 2013
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    Hyuk-Ju Kwon · Sung-Hak Lee · Tae-Wuk Bae · Kyu-Ik Sohng
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    ABSTRACT: The iCAM06, a high dynamic range rendering process, contains chromatic adaptation method based on the CIECAM02 model. The D factor, degree of adaptation, in the chromatic adaptation of the iCAM06 is the function of the adapting luminance level, but it does not consider the visual white point shift according to the variation of luminance level. The iCAM06 acquires a blurred illuminant image. So, each pixel has a different illuminant color. When some of the colors cover the entire image, a de-saturation effect appears around these colors. The simply modified D factor to reduce the de-saturation effect causes unsuitable changes in the degree of adaptation. Therefore, we propose a new method to find the global illuminant information and the D factor for the illuminant in the HDR image rendering process. Comparing the proposed with the conventional method, we confirm that the proposed method provides better illuminant estimation and color representation.
    Full-text · Article · Aug 2013 · Journal of Visual Communication and Image Representation
  • Byeong-No Kim · Chan-Ho Han · Kyu-Ik Sohng
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    ABSTRACT: We propose a composite DCT basis line test signal to evaluate the video quality of a DTV encoder. The proposed composite test signal contains a frame index, a calibration square wave, and 7-field basis signals. The results show that the proposed method may be useful for an in-service video quality verifier, using an ordinary oscilloscope instead of special equipment. Copyright © 2013 The Institute of Electronics, Information and Communication Engineers.
    No preview · Article · Jul 2013 · IEICE Transactions on Electronics
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    Seok-Min Chae · Sung-Hak Lee · Kyu-Ik Sohng
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    ABSTRACT: The iCAM06 has been used as an image appearance model for HDR image rendering. The iCAM06 goes through the color space conversions and scale conversions of the several steps to present HDR images. The dynamic range of an HDR image needs to be mapped on the range of output devices, which is called the tone mapping. However, tone compression process of the iCAM06 causes color distortion because of color-clipping and cross-stimulus. Therefore, we proposed that a color correction method in IPT space which compensates the color distortion in tone compression process. Through the experimental results, we conformed that proposed color correction method had better performance than the iCAM06 and enhanced models.
    Full-text · Article · Mar 2013
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    Hyuk-Ju Kwon · Sung-Hak Lee · Seok-Min Chae · Kyu-Ik Sohng
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    ABSTRACT: HDR (high dynamic range) tone mapping algorithms are used in image processing that reduces the dynamic range of an image to be displayed on LDR (low dynamic range) devices properly. The retinex is one of the tone mapping algorithms to provide dynamic range compression, color constancy, and color rendition. It has been developed through multi-scale methods and luminance-based methods. Retinex algorithms still have drawbacks such as the emphasized noise and desaturation. In this paper, we propose a multi scale tone mapping algorithm for enhancement of contrast, saturation, and noise of HDR rendered images based on visual brightness functions. In the proposed algorithm, HSV color space has been used for preserving the hue and saturation of images. And the algorithm includes the estimation of minimum and maximum luminance level and a visual gamma function for the variation of viewing conditions. And subjective and objective evaluations show that proposed algorithm is better than existing algorithms. The proposed algorithm is expected to image quality enhancement in some fields that require a improvement of the dynamic range due to the changes in the viewing condition.
    Full-text · Article · Dec 2012
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    Seok-Min Chae · In-Ho Song · Sung-Hak Lee · Kyu-Ik Sohng
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    ABSTRACT: In this study, we show that the motion blur is caused by exposure time of video camera as well as the characteristics of LCD system. Also, we suggest that evaluation method of motion picture quality according to the frequency response of video camera and LCD systems of hold and scanning backlight type.
    Full-text · Article · Jul 2012 · IEICE Transactions on Information and Systems
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    ABSTRACT: Recently, a new image appearance model, designated iCAM06, was developed for High-Dynamic-Range (HDR) image rendering. The dynamic range of a HDR image needs to be mapped on the range of output devices, which is called the tone reproduction or tone mapping. The iCAM06, the representative HDR rendering algorithm also uses the tone compression for image reproduction on the dynamic range of output devices, however occurs white point shift during its tone compression process. Therefore, we propose compensation method for white point shift using the corrected channel gain. Experiment results show that the proposed method has better performance than the iCAM06.
    Full-text · Article · Apr 2012
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    ABSTRACT: Chromatic adaptation transform is used to many color appearance models. Also, the iCAM06 model, a high-dynamic range (HDR) rendering process contains chromatic adaptation and is based on the CIECAM02 model. The D factor or degree of adaptation in chromatic adaptation of the iCAM06 model is the function of surround luminance or adapting luminance level, but does not consider visual white point shift according to the variation of luminance level. The iCAM06 model acquires a white image from the Gaussian low-passed image. So, each pixel has different white value, and when some of colors cover the whole image, de-saturation effect appears around these colors. In addition, the scale factor used to reduce de-saturation effect causes unsuitable change of adaptation degree. Therefore, we propose the new method to find global illuminant information and degree of adaptation in the HDR image rendering process. By comparing the proposed with the conventional method, we confirm that the proposed method has better performance in illuminant estimation and color representation.
    Full-text · Article · Apr 2012
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    Seok-Min Chae · Sung-Hak Lee · Hyuk-Ju Kwon · Kyu-Ik Sohng
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    ABSTRACT: Recently, a new image appearance model, named iCAM06, was developed for High-Dynamic-Range (HDR) image rendering. The dynamic range of a HDR image needs to be mapped onto the range of the output device where it will be displayed, this is called tone reproduction or tone mapping. iCAM06, a representative HDR rendering algorithm also uses tone compression for image reproduction on the dynamic range of output devices. However, iCAM06 causes a white point shift during its tone compression process. Therefore, we propose a compensation method for white point shifts using corrected channel gain. Experiment results show that the proposed method has better performance than iCAM06.
    Full-text · Article · Jan 2012 · IEICE Transactions on Fundamentals of Electronics Communications and Computer Sciences
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    Sung-Hak Lee · Kyu-Ik Sohng
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    ABSTRACT: The color appearance model gives us the proper brightness information and optimized display conditions for various viewing surroundings. However on conditions of low-level illumination or low background reflectivity, the performance of brightness estimation is relatively poor. Therefore, through our psychophysical experiments, we investigated the state of visual luminance adaptation for comparing single adaptations and mixed adaptations under a complex viewing field, and we also investigated background adaptation degrees and exponential nonlinearity factors for mixed adaptation models. It provides more accurate brightness predictions according to different adapting luminance, which is decided from object and background luminance.
    Full-text · Article · Nov 2011 · IEICE Transactions on Electronics