Mr. Ki-Youn Lee Profile

Ki-Youn Lee

at Samsung Electronics Co Ltd

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Publications (3)

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Proceedings Article | 24 January 2011 Paper

Quantification of perceived macro-uniformity

Ki-Youn Lee, Yousun Bang, Heui-Keun Choh

Proceedings Volume 7867, 786704 (2011) https://doi.org/10.1117/12.877633

KEYWORDS: Printing, Scanners, Visualization, Linear filtering, Image filtering, Calibration, Smoothing, Information technology, Electronics, Image quality standards

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Macro-uniformity refers to the subjective impression of overall uniformity in the print sample. By the efforts of INCITS W1.1 team, macro-uniformity is categorized into five types of attributes: banding, streaks, mottle, gradients, and moiré patterns, and the ruler samples are generated with perceptual scales. W1.1 macro-uniformity ruler is useful for judging the levels of print defect, but it is not an easy task to reproduce the samples having the same perceptual scales at different times in different places. An objective quantification method is more helpful and convenient for developers to analyze print quality and design printing system components. In this paper, we propose a method for measuring perceived macro-uniformity for a given print using a flat-bed scanner. First, banding, 2D noise, and gradients are separately measured, and they are converted to the perceptual scales based on subjective results of each attribute. The correlation coefficients between the measured values of the attributes and the perceptual scales are 0.92, 0.97, and 0.86, respectively. Another subjective test is performed to find the relationship between the overall macro-uniformity and the three attributes. The weighting factors are obtained by the experimental result, and the final macro-uniformity grade is determined by the weighted sums of each attribute.

Proceedings Article | 18 January 2010 Paper

New measurement method of banding using spatial features for laser printers

Ki-Youn Lee, Yousun Bang, Heui-Keun Choh

Proceedings Volume 7529, 75290H (2010) https://doi.org/10.1117/12.840480

KEYWORDS: Nonimpact printing, Linear filtering, Printing, Spatial filters, Visualization, Optical filters, Signal attenuation, Colorimetry, Contrast sensitivity, Halftones

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The techniques of one-dimensional projection in the spatial domain and contrast sensitivity function (CSF) are generally used to measure banding. Due to the complex printing process of laser printers, hardcopy prints contain other 2D nonuniformities such as graininess and mottle besides banding. The method of 1D projection is useful for extracting banding, but it induces the confounding effect of graininess or mottle on the measurement of perceived banding. The appearance of banding in laser printers is more similar to the sum of various rectangular signals having different amplitudes and frequencies. However, in many cases banding is modeled as a simple sinusoidal signal and the CSF is frequently applied. In this paper, we propose new measurement method of banding well correlated with human perception. Two kinds of spatial features give a good performance to banding measurement. First the correlation factor between two adjacent 1D signals is considered to obtain banding power which reduces the confounding effect of graininess and mottle. Secondly, a spatial smoothing filter is designed and applied to reduce the less perceptible low frequency components instead of using the CSF. By using moving window and subtracting the local mean values, the imperceptible low frequency components are removed while the perceptible low frequency components like the sharp edge of rectangular waves are preserved. To validate the proposed method, psychophysical tests are performed. The results show that the correlations between the proposed method and the perceived scales are 0.96, 0.90, and 0.95 for black, cyan, and magenta, respectively.

Proceedings Article | 19 January 2009 Paper

Characterization of '2D noise' print defect

Ki-Youn Lee, Yousun Bang, Heui-Keun Choh

Proceedings Volume 7242, 72420M (2009) https://doi.org/10.1117/12.805791

KEYWORDS: Printing, Wavelets, Image filtering, Optical filters, Imaging systems, Scanners, Image quality, RGB color model, Image quality standards, Spatial frequencies

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Graininess and mottle described by ISO 13660 standard are two image quality attributes which are widely used to evaluate area uniformity in digital prints. In an engineering aspect, it is convenient to classify and analyze high frequency noise and low frequency noise separately. However, it is continuously reported in previous literature that the ISO methods do not properly correlate with our perception. Since area quality is evaluated by observing all the characteristics with a wide range of spectral frequencies in a printed page, it is almost impossible to differentiate between graininess and mottle separately in our percept. In this paper, we characterize '2D noise' print defect based on psychophysical experiments which appear as two dimensional aperiodic fluctuations in digital prints. For each channel of cyan, magenta, and black, our approach is to use two steps of hybrid filtering to remove invisible image components in the printed area. '2D noise' is computed as the weighted sum of the graininess and mottle, which two weighting factors are determined by subjective evaluation experiment. By conducting psychophysical validation experiments, the strong correlation is obtained between the proposed metric and the perceived scales. The correlation coefficients r2 are 0.90, 0.86, and 0.78 for cyan, magenta and black, respectively.

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