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청색잡음 마스크 임계값변조를 이용한 경계강조 오차확산법
이을환,박장식,박창대,김재호,Lee, Eul-Hwan,Park, Jang-Sik,Park, Chang-Dae,Kim, Jae-Ho 대한전자공학회 1999 電子工學會論文誌, S Vol.s36 No.10
오차확산법은 연속계조 화상을 이진화상으로 표현하는데 있어서 연속계조 화상의 재현 능력뿐만 아니라, 우수한 경계 재현 능력을 가지고 있다. 그러나 이진화상에 눈에 거슬리는 패턴이 발생하는 단점을 가지고 있다. 한편 연속계조 화상의 화소와 청색잡음 마스크(blue noise mask)의 각 임계값을 화소별로 비교하여 이진화상으로 나타내는 방법도 있다. 이것은 규칙적인 패턴은 없지만 양자화 오차로 인해 이진화상이 흐려보이는 현상이 있다. 본 논문에서는 청색잡음 마스크 임계값변조를 이용한 경계강조 오차확산법을 제안한다. 제안하는 이진화 기법을 적용한 이진화상은 규칙적인 패턴이 없고 경계가 강조되어 시각적으로 선명하다. 제안하는 이진화 기법을 등가화상 개념으로 분석하며, 환상 평균 전력 스펙트럼과 경계상관도를 이용하여 기존의 알고리듬과 비교한다. The error diffusion algorithm is excellent for reproducing continuous gray-scale images to bianry images and also has good edge characteristics. However, it is well known that artifacts with objectionable patterns can occur in the halftoned images. On the other hand, a halftone algorithm using blue noise mask has been proposed. where the halftoning is achieved by a pixelwise comparison of gray-scale image with an array, the blue noise mask. It doesn't have pattern artifacts, but the halftoned image looks unclear because the quantization errors are not feedbacked compared to the error diffusion. In this paper, edge enhanced error diffusion which dithers the threshold with the blue noise mask is proposed. We show that the proposed algorithm can produce unstructured and edge enhanced halftone images. This algorithm is analyzed by the concept of an equivalent input image. The performace of the proposed algorithm is compared with that of the conventional halftoning by measuring the radially averaged power spectrum and edge correlation.
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.
컬러 벡터 오차확산법을 이용한 6색 프린터에서의 측색적 색 재현
이을환(Lee Eul Hwan),김재호(Kim Jae Ho),이남훈(Lee Nam Hoon),송은아(Song Eun Ah) 한국화상학회 1999 한국화상학회지 Vol.5 No.1
This paper describes colorimetric color reproduction using color vector error diffusion in six-color printer. Color vector error diffusion using Pappas`s printer model, which considers the dot overlap effect between neighboring dots, is applied to six-color printer. The dot size is estimated using color samples, and the smear artifact is also reduced by thresholding the modified value in error diffusion technique. Compared with three-color printer, six-color printer extends the printer gamut and reproduces the bright regions very well by adding light cyan and light magenta inks.