Showing papers by "Yeong-Ho Ha published in 2003"

Multi-carrier PAP reduction method using sub-optimal PTS with threshold

Abstract: This paper presents an orthogonal frequency division multiplexing (OFDM) system, which through the use of sub-optimal PTS combined with a preset threshold, achieves low computational complexity to find optimum weighting factors. A specific bit in weighting factor that leads to a smaller peak-to-average power ratio (PAP) is identified from the sub-optimum method. And a specific threshold, which found from the OFDM frame probability, is also applied to reduce computational complexity. The performance of the proposed method was slightly degraded compared to that of optimum method, PTS. However, the complexity of the proposed method was remarkably lower than that of the optimum method.

Spatial color descriptor for image retrieval and video segmentation

Abstract: An important problem in color-based image retrieval and video segmentation is to lack information about how color is spatially distributed. To solve this problem and enhance the performance of image and video analyses, a spatial color descriptor is proposed involving a color adjacency histogram and color vector angle histogram. The color adjacency histogram represents the spatial distribution of color pairs at color edges in an image, thereby incorporating spatial information into the proposed color descriptor. Meanwhile, the color vector angle histogram represents the global color distribution of smooth pixels in an image. Since the proposed color descriptor includes spatial adjacency information between colors, it can robustly reduce the effect of a significant change in appearance and shape in image and video analyses. Moreover, since the color adjacency histogram is simply represented by binary streams, the storage space required for the image histogram values can be effectively reduced. Experimental results show that even with significant appearance changes, the proposed color descriptor could produce a high image retrieval rate and accurately detect abrupt scene-cuts in a video analysis.

Six-color separation for improving graininess in a middle tone region

Abstract: This paper proposes an improved six-color separation method that reduces the graininess in middle tone regions based on the standard deviation of lightness and chrominance in SCIELAB space. Graininess is regarded as the visual perception of the fluctuation of the lightness of light cyan and cyan or light magenta and magenta. In conventional methods, granularity is extremely heuristic and inaccurate due to the use of a visual examination score. Accordingly, this paper proposes an objective method for calculating granularity for six-color separation. First, the lightness, redness-greenness, and yellowness-blueness of SCIELAB space is calculated, reflecting the spatial-color sensitivity of the human eye and the sum of the three standard deviations normalized. Finally, after assigning the proposed granularity to a lookup table, the objective granularity is applied to six-color separation , thereby reducing the graininess in middle tone regions.

Estimation of spectral distribution of scene illumination from a single image with chromatic illuminant

Abstract: The current paper proposes an illuminant estimation algorithm that estimates the spectral power distribution of an incident light source using its chromaticity determined based on the perceived illumination and highlight method. The proposed algorithm is composed of three steps. First, the illuminant chromaticity of the global incident light is estimated using a hybrid method that combines the perceived illumination and highlight region. Second, the surface spectral reflectance is then recovered from the image after decoupling the global incident illuminant for each channel. The surface spectral reflectance calculation is limited to the maximum achromatic region (MAR), which is the most achromatic and brightest region in the image, and estimated using the principal component analysis (PCA) method along with a set of given Munsell samples. Third, the closest colors are selected from a spectral database composed of reflected-lights generated by the given Munsell samples and a set of illuminants. Finally, the illuminant of the image is calculated using the average spectral distributions of the reflected-lights selected for the MAR region and its average surface reflectance. Simulations were performed using artificial color-biased images and the results confirmed the accuracy of the estimates produced by the proposed method for various illuminants.

Fast multilevel vector error diffusion based on adaptive primary color selection

Abstract: This paper proposes multi-level vector error diffusion based on adaptive primary color selection for fast and accurate color reproduction. Conventional bi-level vector error diffusion uses eight primary colors(R, G, B, C, M, Y, W, K). However, multi-level vector error diffusion uses more primary colors (this paper uses 64 primary colors) depending on the printing device, thereby significantly increasing the time complexity due to the additional increment of computation. Moreover, the output image can also include color artifacts that have a noticeable primary color under the influence of large quantization error and increased primary color. Accordingly, to reduce these problems, we proposed the quantization process to decide a candidate primary among the 64 primary colors using lightness difference. First, we classified the 64 primary colors into 60 chromatic colors and 4 achromatic colors and then we exclude primary colors with the large lightness difference against the input color from a set of 60 chromatic primary colors. Using both 4 achromatic primary colors and a candidate primary colors, we calculated the vector norm to select output color. Also this paper determine optimal threshold experimentally to remove smear artifacts resulting from the diffusion of large quantization error. As a result, this paper archives fast multi-level vector error diffusion by avoiding additional computation and produces visually pleasing halftone pattern by excluding noticeable primary colors.

Disparity space image-based stereo matching using optimal path searching

Abstract: The current paper proposes a fast stereo matching algorithm based on a pixel-wise matching strategy that can produce a stable and accurate disparity map. Since the differences between a pair of stereo images are only small and such differences are just caused by horizontal shifts in a certain order, matching using a large window is not required within a given search range. Therefore, the current study adopts a disparity space image(DSI) for efficient pixel-wise matching. In a DSI, each disparity value is derived from the matching path. As such, when the matching path in a DSI innately satisfies the ordering constraint, continuous matching is possible. In addition, since this continuous matching also considers neighbor pixels, it assumes the characteristics of region-based matching, similar to window-based matching, yet with a lower computational load. To avoid the unstable characteristic of the pixel-based matching, we modified the directions in the cost array in the dynamic programming(DP). Experimental results demonstrate that the proposed method can remove almost all disparity noise and produce a good quality disparity map within a very short time.

Improved shading model in spectral-based ray tracing method

Abstract: This paper proposes an improved ray tracing technique that can reproduce a realistic image based on the spectral characteristic of real lights and objects The proposed algorithm is able to generate a realistic image that simulates the physical quantity of light energy incoming toward a viewer First, an accurate image is reproduced using the backward ray tracing method and by tracing the spectral transformation procedures of the rays using the spectral characteristic of objects and illuminants Next, the shading model of the reproduction algorithm of a realistic image is improved by applying Bouguer-Beer's law to consider the optical absorptive property of transparent objects Finally, a new ambient light term that considers the diffuse reflection of neighboring objects is defined instead of a constant ambient light term

Digital ready TV platform with synchronization shaping circuit

Abstract: This paper proposes an improved digital ready TV platform that can support a signal input with various resolutions Due to the inadequate performance of the built-in digital PLL (phase-locked loop) of an ADC (analog to digital converter) and poor tolerance of ADC ICs, there are problems in the stable processing of synchronization signals with various input signals Accordingly, the proposed synchronization shaping technique regenerates the horizontal synchronization signal in the vertical blanking interval based on the regularity of the synchronization signal, ie the timing of the signal falling edge remains constant, thereby solving the above problem and minimizing the interference of the system As a result, the proposed system can stabilize various synchronization signals with different resolution modes

Color image enhancement technique using gamut mapping based on color space division

Abstract: This paper proposes a gamut mapping algorithm based on color space division for color reproduction of cross media. As each color device has a limited range of producible colors, the reproduced colors on a destination device are different from those of the original device. In order to reduce the color difference between those devices, the proposed method divides the whole gamut into parabolic shapes based on intersecting lightness by the “just noticeable difference” (JND) and the boundary of original gamut. By dividing the gamut with parabolic shapes and piecewise mapping of each region, it not only considers gamut characteristics but also provides for mapping uniformity. The lightness variations are more sensitive to the human visual system and by using lightness JND it can restrict lightness mapping variations that are unperceivable. As a result, the proposed algorithm is able to reproduce high quality color images using low-cost color devices.

Test based on a normal score for efficient edge detection in image

Abstract: The current paper proposes an efficient method for edge detection in original and noisy images using Waerden's statistic. Edges represent a significant amount of information on an image. For example, edges reveal the location of objects, their shape and size, and something about their texture. Since edges represent where the intensity of an image moves from a low value to a high value or vice versa, edge detection is often the first step in image segmentation. As a field of image analysis, image segmentation groups pixels into regions to determine the image composition. Therefore, the current paper describes the nonparametric Wilcoxon test and parametric T test based on statistical hypothesis testing for edge detection. Here, the threshold is determined by specifying a significance level, whereas Bovik, Huang, and Munson considered a range of possible test statistic values for the threshold. In the current study, the test statistic is calculated based on pixel gray levels obtained using an edge-height parameter and compared with the threshold determined by a significance level. Experiments were conducted to evaluate the performance of these methods in both original and noisy images. As a result, the Wilcoxon and T test was found to be sensitive to a noisy image, whereas the proposed Waerden test was robust in both noisy and noise-free images under α=0.0005. Furthermore, when compared with Sobel, LoG, and Canny operators, the proposed Waerden test was also more effective in both noisy and noise-free images.

Hierarchical spatiotemporal moving object segmentation based on a binary split algorithm

Abstract: To segment moving objects in head-and-shoulder image sequences, a new morphological image segmentation algorithm is proposed using a hierarchical structure based on a binary split algorithm. The split method is performed using the combination of spatial and temporal similarities to reduce the residual errors between the original and segmented image. Spatial similarity is used to split those regions with the most different intensity values, while temporal similarity, based on the displacement vectors between two images, is used to split those regions with different motions. As a result, the proposed hierarchical segmentation method, based on a binary split algorithm, can increase the subjective image quality with only a small number of regions. Furthermore, a new contour simplification technique composed of three filtering steps is repeatedly applied to the segmented image, thereby eliminating any noisy contours of segmented regions.

Stereo sequence transmission via conventional transmission channel

Abstract: This paper proposes a new stereo sequence transmission technique using digital watermarking for compatibility with conventional 2D digital TV. We, generally, compress and transmit image sequence using temporal-spatial redundancy between stereo images. It is difficult for users with conventional digital TV to watch the transmitted 3D image sequence because many 3D image compression methods are different. To solve such a problem, in this paper, we perceive the concealment of new information of digital watermarking and conceal information of the other stereo image into three channels of the reference image. The main target of the technique presented is to let the people who have conventional DTV watch stereo movies at the same time. This goal is reached by considering the response of human eyes to color information and by using digital watermarking. To hide right images into left images effectively, bit-change in 3 color channels and disparity estimation according to the value of estimated disparity are performed. The proposed method assigns the displacement information of right image to each channel of YCbCr on DCT domain. Each LSB bit on YCbCr channels is changed according to the bits of disparity information. The performance of the presented methods is confirmed by several computer experiments.

Improved Vector Error Diffusion for Reduction of Smear Artifact in the Boundary Regions

Abstract: This paper proposes a vector error diffusion method for smear artifact reduction in the boundary region. This artifact mainly results from a large accumulation of quantization errors. In particular, color bands with a smear artifact the width of a few pixels appear along the edges. Accordingly, to reduce this artifact, the proposed halftoning process excludes the large accumulated quantization error by comparing the vector norms and vector angles between the error-corrected vector and eight primary color patches. When the vector norm of the error corrected vector is larger than those of eight primary color patches, the quantization error vector is excluded from the quantization error distribution process. In addition, the quantization error is also excluded when the angle between eight primary color patches and error-corrected vector is large. As a result, the proposed method enables a visually pleasing halftone pattern to be generated by all three color separations into account in a device-independent color space and reduces smear artifact in the boundary regions.