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인간 시각 특성을 고려한 오차 확산 커널의 동적 결정 방법
김춘우(Kim Choon Woo),강승우(Kang Seung Woo),강기민(Kang Ki Min) 한국화상학회 1997 한국화상학회지 Vol.3 No.1
Conversion of the gray level image into the binary equivalent is called as digital halftoning. Error diffusion has been one of the most popular digital halftoning techniques. The quality of binary image obtained by the error diffusion technique is majorly determined by the error diffusion kernel, locations of neighbors for the error propagation, and quantization process. This paper presents an error diffusion method to dynamically calculate the kernel for error propagation based on the input gray level image. The error diffusion kernel is determined by minimizing the predefined error criterion between the input gray level and ouput binary image. The characteristics of human visual system is incorporated into the error criterion for minimization. The results obtained based on the proposed techniques are analyzed and compared with those by the existing error diffusion techniques.
김춘우(Kim Choon Woo),조민기(Cho Min Ki) 한국화상학회 1998 한국화상학회지 Vol.4 No.1
Printed images through color printer often exhibit color distortion due to the nonlinear characteristics of the device. One of the most popular techniques for reducing such color distortions is to employ LUT based color correction. Gray balance should be taken into account during the color correction procedure. Traditionally, it is accomplished by generating additional three 1-D LUTs. This paper presents a 3-D LUT design technique with gray balance correction without the additional 1-D LUTs. The proposed method enables the reduction of the memory size and computational complexity. The traditional way of making 1-D LUTs for the gray balance relies on the operators experience. But, each step of the proposed method depends only on the objective and quantitative criterion. The proposed method is relatively insensitive to the small variations on the uniformity and repeatability of the input devices such as image scanner.
강기민,김춘우,Kang, Ki-Min,Kim, Choon-Woo 대한전자공학회 2000 電子工學會論文誌-SP (Signal processing) Vol.37 No.4
디지털 영상 출력 장치를 위해 연속 계조 영상을 이진 영상으로 변환하는 오차확산 방법은 사람의 시각 특성에 적합한 고주파 성분의 이진 영상을 만들어 내지만 균일하지 못한 점의 분포로 인해 영상의 화질을 저하시키는 패턴이 발생하게 된다. 이러한 단점을 해결하기 위해 다양하게 개선된 오차확산 방법들이 제안되었다. 본 논문에서는 우선 오차확산 방법이 균일한 점의 분포를 발생시키지 못하는 원인을 분석하고 주기함수를 이용하여 이진 문턱값을 조절함으로서 이진 영상의 점의 분포를 균일하게 하여 화질을 향상시키는 방법을 제안한다. 제안하는 방법은 이진 영상의 화질을 결정하는 소수 화소(minor pixels)가 주어진 계조에 따라 일정한 주거리(principal distance)를 갖도록 하여 이진 화소의 뭉침 현상이나 공백 현상을 최소화 하고 균일한 분포를 갖도록 한다. The error diffusion technique is frequently utilized for the digital Imaging output devices to convert continuous level Image into bi-level Image It Yields the binary image with the high frequency emphasis that gives a pleasing perception to human eyes But, due to the non-homogeneous distribution of dots, It exhibits undesirable patterns that degenerate the perceived quality Various techniques have been proposed to Improve the Image quality by the error diffusion techniques In this paper, the cause of non-homogeneity of dot distribution is analyzed first. A threshold modulation technique that employs a simple sinusoidal function is proposed in this paper The proposed method achieves the homogeneous dot distribution by forcing the minor pixels on the binary Image to maintain the principal distance defined according to their gray levels. It also minimizes the void and clusters of minor pixels.
김경태 ( Kyoung Tae Kim ),김춘우 ( Choon Woo Kim ) 한국화상학회 2011 한국화상학회지 Vol.17 No.4
Abstract Colorfulness is one of the most important factors for image quality on displays. This paper proposes a colorfulness evaluation model for natural color images on displays. Images are generated by independently changing the lightness, chroma, and hue. Regression between results of human visual tests and statistical parameters of perceptual attributes is performed. Statistically significant attributes are selected and utilized to construct the proposed colorfulness evaluation model. Correlation coefficient between the results of human visual tests and the calculated metrics from the proposed evaluation model serves as a performance indicator. Experimental results indicate that the proposed evaluation model yields higher accuracy than previous models chosen for comparison.
기준색 고정 색 보정 방법과 칼라 스캐너-프린터에의 응용
한규서(Han Kyu Seo),김춘우(Kim Choon Woo) 한국화상학회 1996 한국화상학회지 Vol.2 No.1
The output images of color imaging devices often exhibit color distortions due to the nonlinear characteristics of their components. Color correction techniques minimizing the color distortion play a key role in obtaining high quality images. This paper presents a linear transformation based color compensation method with a fixed reference color. In the proposed method, the color distortion is modeled as a linear transformation with a constant vector. The proposed method is applied to the imaging chain of color scanner and printer. The experimental results are compared with those from conventional linear transformation based method.