• Journal of Broadcast Engineering
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• v.17 no.2
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• pp.316-324
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• 2012

In this paper, a novel descreening method using HOG(histogram of gradient)-based adaptive smoothing filter is proposed. Conventional edge-oriented smoothing methods does not provide enough smoothing to the halftone image due to the edge-like characteristic of the halftone noise. Moreover, clustered-dot halftoning method, which is commonly used in printing tends to create Moire pattern because of the intereference in color channels. Therefore, the proposed method uses HOG to distinguish edges and the amount of smoothing to be performed on the halftone image is then calculated according to the magnitude of the HOG in the edge and edge normal orientation. The proposed method was tested on various scanned halftone materials, and the results show that it effectively removes halftone noises as well as Moire pattern while preserving image details.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.41 no.3
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• pp.111-120
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• 2004

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.

• Journal of Korea Multimedia Society
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• v.4 no.2
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• pp.116-129
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• 2001

To improve the performance of the inverse halftoning, smoothing masks should be designed optimally by using the accurate information of halftone cells. In this thesis, the method of energy minimization is so defined as to determine the exact information of halftone cell. A heuristic search method is proposed to obtain efficiently the parameters of halftone cells which determine the minimum energy. A halftone-peak modeling method with several functions is proposed and used to get initial values of the parameters. The dimension decomposition technique is also adopted to speed up the search process of energy minimization. Several experiments show that the proposed method extracts correct location of the seed pixel of the halftone cell and the extracted information of the halftone cell can be used to get more exactly smoothed color images. The proposed method can be applied to extract the texture patterns, to separate channel images of a scanned color halftone image, and to extract the moire area in an image.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.4 s.304
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• pp.49-59
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• 2005

This paper proposed a six-color separation using additional colorants and quantitative granularity metric to reduce color difference and graininess. In the conventional method, light magenta and light cyan are used in the bright region instead of magenta and cyan. However, the hue value of liBht magenta and light cyan is different from the one of magenta and cyan in CIELAB space, so that this makes the colorimetric reproduction more or less inaccurate. To improve this inaccuracy, the proposed method uses yellow and light magenta colorants as the additional colorants. In the bright region, magenta is replaced with light magenta and yellow, while cyan is replaced with light cyan and light magenta. This selection reduces hue difference because it creates the color of similar hue to magenta and cyan. In addition, smooth image can be simultaneously obtained by the less dot visibility of additional colorants. In the middle region, magenta is replaced with light magenta and magenta, while cyan is replaced with light cyan and cyan. The use of two colorants having a different concentration makes the dot Pattern coarse. To reflect this Phenomenon, quantitative granularity metric is used. In the dark region, only magenta and cyan colorant is used as usual. Through experiments, it is shown that the proposed method improves both colorimetric and smooth tone reproductions.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.40 no.1
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• pp.1-9
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• 2003

In this paper, we propose a new method dispersing spatially C(Cyan), M(Magenta), Y(Yellow) instead of K(black) in the bright region. The overlapping of black dots decreases brightness in the dark region, and black dots are very sensitive to human visual system in the bright region. Therefore, to avoid this problem, bright and dark gray region in the color image is considered in the proposed approach. A new method which uses CMY simultaneously in single mask is proposed, and CMY dots are used dispersing spatially for the bright region instead of black dot by this method. And tone curve connection is used to consider the gray level of dark region. In previous method, BNM (Blue Noise Mask) has high granularity and a narrow dynamic range. But the proposed method has the low granularity, wide dynamic range, and high contrast properties. Because the proposed method uses three times dots spatially in the different position than a conventional BNM, it can express more spatial information and a similar gray level compared with BNM.