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안석출(Ahn Suk Chul),이철희(Lee Cheol Hee),이채수(Lee Chae Soo),하영호(Ha Yeong Ho) 한국화상학회 1999 한국화상학회지 Vol.5 No.1
Print quality depends on so many factors such as mechanical attributes of printers, ink and substrate interaction, registration between different inks, and halftoning techniques etc. thus characteristics of printers are multi-parametric and nonlinear. Currently, a variety of methods have been studied to calibrate these complicated characteristics of printers by modeling with neural network. In this study, we propose a printer tone-reproduction algorithm which linearizes outputs of printers using neural network. Here, objective of the printer tone-reproduction is defined as equi-visual tone-reproduction in terms of lightness and color difference of CIELAB color system which is used as the device-independent color space then, the printer controller which has a inverse transfer function for the four inks of CMYK of unknown printer system is modeled by neural netwrok. Therefore, we could obtain linear printer outputs by adding the controller to input of the printer as a preprocessor and calibrating input images. To evaluate performance of proposed algorithms, we simulated for artificial images and natural images and estimated the linearity of the proposed algorithm by measuring for the calibrated sample patches.
프린터 색역에 균등한 분포를 갖는 색표본 생성 및 색재현
이철희,김희수,안석출,하영호,Lee, Cheol-Hee,Kim, Hee-Soo,Ahn, Suk-Chul,Ha, Yeong-Ho 대한전자공학회 2000 電子工學會論文誌-SP (Signal processing) Vol.37 No.5
본 논문에서는 출력 장치의 색역에 대하여 균일한 분포를 갖는 색표본(color sample) 생성 방법을 제안하고, 이를 이용한 색재현 방법을 소개한다. 즉 기존의 방법인 RGB(red, green, and blue) 혹은 CMY(cyan, magenta, yellow) 등 장치 의존형 색공간에서 균일한 색표본을 선택하는 것이 아니라 장치 독립형 균등 색공간인 CIELAB공간에서 균등 색표본을 선택하는 방법을 제안한다 또한 제안된 색표본의 성능을 평가하기 위하여 회귀 모델과 신경망을 이용한 색공간 변환을 수행하였다 동일한 크기의 색표본의 경우, 제안된 색표본을 이용한 색공간 변환 방법이 신경망, 회귀 모델 모두에서 색차를 줄일 수 있었다. This paper proposes a color sample selection method that produces a uniform distribution in the display gamut plus a color reproduction method for using a uniform color sample In contrast to the conventional method, the proposed uniform color samples are selected m CIELAB, a device-independent color space, instead of RGB (red, green, and yellow) or CMY (cyan, magenta, and yellow) space, device-dependent color spaces To evaluate the performance of the proposed color samples, they were applied to color space conversion using both a regression model and neural network As a result, in the case of a color sample of the same size, the color space conversion method using the proposed samples showed a lower color difference for color conversions using either neural or regression.
시각특성기반 FM 스크린에 의한 잉크젯 프린터의 측색적 색재현
이상남(Lee Sang Nam),이을환(Lee Eul Hwan),김종필(Kim Jong Pil),안석출(Ahn Suk Chul),박희윤(Park Hee Youn),최환언(Choi Hwan Eon) 한국화상학회 1998 한국화상학회지 Vol.4 No.1
There are several methods to halftone continuous image. The widespread methods are dithering and error-diffusion. Non-linear color transform by using neural network depends on halftoning methods. Error diffusion has jump of tone in the middle tone area. This affects teaming of neural network and results in increasing color difference. In this paper, we apply FM screen based on visual characteristic to color image. Tone density curve of FM screen is better than that of error diffusion. As a result, using FM screen as halftoning method affects colorimetric color reproduction by neural network and results in decreasing color difference.
분광 분포에 근거한 주성분 분석과 신경망을 이용한 정확한 색 재현
이을환(Lee Eul Hwan),김재호(Kim Jae Ho),안석출(Ahn Suk Chul) 한국화상학회 1999 한국화상학회지 Vol.5 No.1
The spectral reflectance of the object color can be represented as a linear combination of a set of basis functions. We measure the reflectance spectra of 729 color patches of inkjet printing. The basis functions are extracted from the patch data using principal component analysis by Karhunen-Loeve expansion. The spectral reflectance of the patch data that is reproduced with an inkjet printer can be reconstructed as 99.97% by only seven basis functions. Neural network approach is used to transform the coefficients of principal component analysis to CMY colorants. We also introduce the design of the color patches where the sample points are not equally spaced. This new patch design increases the accuracy of the conversion of the neural network. The mean square error is compared and the color difference is obtained under various illuminants. This approach can be used for the accurate color reproduction, which is not relevant to illuminants.
동일색상 분류와 RGB 색 신호를 이용한 물체의 분광반사추정
유미옥(Mee Ok Yoo),조석제(Seok Je Cho),안석출(Suk Chul Ahn) 한국화상학회 2000 한국화상학회지 Vol.6 No.1
This paper propose a new spectral reflectance estimation algorithm that can estimate the spectral reflectance of object from 3 band digital color image values. To estimate the spectral reflectance of object, the conventional estimation methods are required 5 bands or 9 bands digital color values. The 5 band or 9 band image acquisition systems are required 3 or 5 times same work for color image acquisition process. To solve the above problems, we propose a new method that spectral reflectance estimation of object. Proposed method has two steps, the one step is the classification of similar color and the other step is estimation of the reflectance ratio corresponding to a color stimulus. In order to classification of similar color corresponding to a color stimulus, we use hue angle and chroma vector of a color stimulus. The classified similar colors are used the population corresponding to a color stimulus. The estimation of spectra] reflectance is performed with 3 band color image using the population of similar color classification.
김종필(Kim Jong Pil),문영득(Moon Young Deuk),안석출(Ahn Suk Chul) 한국화상학회 1997 한국화상학회지 Vol.3 No.1
In digital printing, most halftoning techniques assume that the printed color dots are square and dot gain is zero. However, most ink jet printers produce roughly circular dots and dot gain is not zero. Thu′s, dots are overlapped by adjacent dots, and they occupy adjacent space that should be empty space. These facts cause the significant image distortion on the reproduced image. In this paper, we proposed a new ink jet printer calibration method based on visual perception characteristic. Experimental results show that the proposed method is useful and valid for the ink jet printer.