3D列印設備逐漸普及，讓這項原本只有專業人士才會使用的新科技，慢慢進入到人們日常的工作和生活中：設計師為了能快速製作模型給客戶、藝術家為了表現複雜的3D形體、消費性為了取得個人化的公仔模型、工程師為了製作不容易取得的零件….。為了滿足這些彩色3D列印的需求，近年有不少廠商投入商業化彩色3D列印產設備的研發工作。目前3D列印在彩色化上較大的難題有缺乏合適的全彩列印技術、色域不足和物件表面色彩不均勻等問題。
本研究以優化3D列印物件的表面色彩均勻度為目標。為了量測色彩在不同方向的平面色差，本研究設計一3D列印專用的色彩導表，以得到彩色3D列印的物件中，色彩和表面法向量的關係，導表上的色塊亦可用來進行色彩管理工作。色彩均勻化校正則是計算不同表面的色調變化的比例，並以對照表記錄，再運用對照表內插技術，校正下次要列印的3D模型色調。這套色彩校正流程能讓彩色3D列印物件表面色彩不均勻的現象，使用本研究的方法得到補償。
在進行3D列印的過程中，為了將模型的色彩轉換成3D列印機的噴印訊號，需要對色彩階調做半色調轉換，才能得到噴印時需要的位元資訊。然而，將傳統的半色調技術套用在3D物件時，會因為重複堆疊同樣的半色調墨點，而在3D列印的物件側面產生條紋或斑點。由於3D列印的解析度有限，物件表面的半色調墨點相當明顯可見，會對均勻度造成影響。故本研究提出使用新的3D門檻矩陣與五原色色彩轉換法，對彩色3D物件做半色調轉換，讓半色調墨點在每一面均得以均勻分布。為了得到更好的3D門檻矩陣，本研究根據自定的原則，調變門檻矩陣，以均勻度極大化的搜尋方式，獲得優化的門檻矩陣。此外，為了提高影像的解析度，本研究結合誤差擴散技術，提出混合式半色調技術，獲得較佳的彩色3D列印品質。

3D printing which was used by professionals is now more and more popular and affordable: designers use it to generate prototypes rapidly to their customers, artists use it to create complex sculptures, consumers use it to get personalized doll models, engineers use it to produce precision components which are not easy to obtain, etc. To fulfil the demands of full color 3D printing, many manufacturers is now developing commercial color 3D printing systems. However, the full color 3D printing has not yet widespread as lack of suitable full-color printing technologies, insufficient color gamut, the color on the surface is not evenly distributed, etc.
The aim of this study is to optimize color uniformity of 3D printing surfaces across different orientations. In order to estimate the color variations of different surface directions, a puzzle-like 3D color target is proposed. The relationship between the surface normal vectors of their color appearance can be quantified by printing and measuring the target. The color variations of a printed object can be reduced by correcting the colors in its 3D model using the quantified data.
In order to convert the color of a 3D model to its binary color inkjet signals, a color halftoning process is needed. However, while we apply the traditional halftone technique on the 3D models, some unwanted stripe- and dot-patterns appear on the side of the 3D prints. It is likely caused by the repeated stacks of the same halftone dots. Due to the limited resolution in 3D printing, the halftone dots are quite obvious and affect the uniformity of 3D printing surfaces. Therefore, a new 3D threshold matrix with five-primary color conversion method is proposed to do the halftoning process for printing color 3D models. With this method, the halftone dots on each side can be distributed evenly. To get better 3D threshold matrix, this study also proposed an optimization method to search and maximize the effect of uniformity for the threshold matrix. In addition, a hybrid halftoning method is proposed which used different sizes of threshold matrix in conjunction with error diffusion technology to improve the resolution of the printed color images.

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