잉크량과 도트 가시성에 기반한 6색 분리 방법 = Six-color separation based on ink-amount and dot visibility

다국어 초록 (Multilingual Abstract)

With a rapid development of Hi-Fi printer, the method of six-color separation to reproduce photo quality image is need. Six-color separation is to decompose the digital values of four colorant CMYK (cyan, magenta, yellow, and black) into the digital values of six colorant CMYKlclm (cyan, magenta, yellow, black, light cyan, and light magenta). In the conventional method, excessive amounts of ink are used to reproduce smoother gradation. However, excessive colorants brings about the wetness and rumple of photo ink jet paper and the waste of unnecessary ink when an image is printed. Accordingly, the reduction of excessive colorants are required to obtain more pleasing printing. Therefore, this paper proposes a method of six-color separation using limit of total ink-amount and having lesser dot-visibility. First, the proposed method generates CMY input digital values with 6 steps each channel and CMYlclm candidates digital values with 19 steps each channel. The generated CMY input digital values are printed and then measured for obtaining values of CIELAB space. And then, using the generated CMYlclm candidates, spectral reflectances of CMYlclm candidates are estimated. This is carried out through the printer characterization based on Neugebauer model. Next, to acquire the values of CIELAB space of estimated spectral reflectances for CMYlclm candidates, preferentially, spectral reflectances of candidates are transformed into values of CIEXYZ. And values of CIEXYZ are transformed into values of CIELAB. In order to obtain visually similar values in the CIELAB space between input and output, it is required to extract values of CIELAB candidates corresponding to values of CIELAB space for CMY input digital values for CMYlclm digital values. This needs the calculation of the color difference. And it is needed to reduce global excessive colorants. Using the sum of C, M, Y, lc, and lm as threshold, it is conducted to extract candidates which reduced total ink-amount for extracted candidates using the color difference metric. This is the process to minimize excessive colorants in all the regions including the bright and dark regions. And, to reduce excessive colorants of limited parts, maximum digital values of lc and lm are used as threshold. CMYlclm digital values reducing all excessive colorants are extracted through selective method of candidates applying different dot-visibility ordering according to maximum digital values of lc and lm. Last, the look-up table of digital values which is separated into six-color is made out. Consequently, the proposed method has advantage which saves the wasted ink-amounts according to the reduction of excessive colorants.

목차 (Table of Contents)

• Ⅰ. 서론 = 1
• Ⅱ. 기존의 색 분리 방법 = 5
• 2.1. 프린터 모델링 기반의 CMYKlclm 프린터의 6색 분리 방법 = 5
• 2.2. 기존의 6색 분리 방법의 문제점 = 7
• Ⅲ. 제안한 CMYKlclm 프린터의 6색 분리 방법 = 12
• 3.1. CMY 입력 디지털 값과 CMYlclm 후보군 생성 = 14
• 3.2. 프린터 특성화 모델을 이용한 후보군의 분광 반사율 추정 = 16
• 3.3. 색차를 이용한 CMYKlclm 후보군 추출 = 26
• 3.4. 잉크 사용량과 도트 가시성에 기반한 과다 잉크 제거 = 28
• 3.5. 6색 분리를 위한 참조표 작성 = 34
• Ⅳ. 실험 및 고찰 = 35
• 4.1. 제안된 방법의 객관적 성능 평가 = 35
• 4.2. 실영상을 이용한 주관적인 화질 평가 = 38
• Ⅴ. 결론 = 41
• 참고문헌 = 43
• 영문초록 = 47