ADVANCED TOPICS IN SCIENCE AND TECHNOLOGY IN CHINA ADVANCED TOPICS IN SCIENCE AND TECHNOLOGY IN CHINA Zhejiang University is one of the leading universities in China. In Advanced Topics in Science and Technology in China, Zhejiang University Press and Springer jointly publish monographs by Chinese scholars and professors, as well as invited authors and editors from abroad who are outstanding experts and scholars in their fields. This series will be of interest to researchers, lec- turers, and graduate students alike. Advanced Topics in Science and Technology in China aims to present the latest and most cutting-edge theories, techniques, and methodologies in var- ious research areas in China. It covers all disciplines in the fields of natural scienceandtechnology,includingbutnotlimitedto,computerscience,mate- rials science, life sciences, engineering, environmental sciences, mathematics, and physics. Weidong Geng The Algorithms and Principles of Non-photorealistic Graphics Artistic Rendering and Cartoon Animation With 314 figures, mostly in color Author Prof. Weidong Geng State Key Lab of CAD&CG Digital Media Technology Department College of Computer Science Zhejiang University, Hangzhou 310027, China E-mail: [email protected] ISSN 1995-6819 e-ISSN 1995-6827 Advanced Topics in Science and Technology in China ISBN 978-7-308-06600-6 Zhejiang University Press, Hangzhou ISBN 978-3-642-04890-6 e-ISBN 978-3-642-04891-3 Springer Heidelberg Dordrecht London New York Library of Congress Control Number: 2009935705 (cid:2)c ZhejiangUniversityPress,HangzhouandSpringer-VerlagBerlinHeidelberg2010 Thisworkissubjecttocopyright.Allrightsarereserved,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse ofillustrations,recitation,broadcasting,reproductiononmicrofilmorinanyother way, and storage in data banks. Duplication of this publication or parts thereof is permittedonlyundertheprovisionsoftheGermanCopyrightLawofSeptember9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Cover design: Frido Steinen-Broo, EStudio Calamar, Spain Printed on acid-free paper Springer is a part of Springer Science+Business Media (www.springer.com) Preface Non-photorealistic computer graphics is a multidisciplinary field in the re- search community, involving computer arts, computer graphics, computer vision, digital image/video processing and visual cognitive psychology. It aims at the computer generation of images and animations that are made in part “by hand” in appearance, and are characterized by their use of ran- domness, abstraction, ambiguity, or arbitrariness rather than completeness and adherence to the portrayed objects’ properties. In essence, it mimics the eyesandmindsofartistsanddesignerstocreate,viewanddepictthegraphics world, effectively carrying-out the visual communication between computers and human beings. Coverage and Audience Thisbookmainlyfocusesonthefollowingfivecoreissuesinnon-photorealistic computer graphics. (1) Howtocreatethepaintings,artworksorsculpturesfromadigitizedblank canvas or a standard shape with the tools simulated by the computer. (2) How to convert a series of reference images into the resultant depiction with the desired visual effect. (3) Howtoautomaticallygeneratetheartisticrenditionortechnicalillustra- tions from the 3D models in terms of the stylized parameters. (4) How to produce the comprehensive and expressive visualizations from a set of graphical and textual information on the basis of the semantic meanings to be conveyed. (5) How to speed up the production of cartoon animation by computer- assisted refinement of traditional pipeline and the exploration of novel approaches. The author not only take a survey of the state-of-the-art research as well as trends and open-ended questions regarding the aforementioned five VI Preface core issues, but also discuss the theoretical underpinnings of the field. This includesdetailingahostofusefulalgorithmsandaddressingtwoapplications of particular interest: artistic rendering and cartoon animation. The book will be useful to practitioners in the field. It contains a wealth of examples, particularly in the form of images, which the authors hope will motivate the reader in the use of non-photorealistic computer graphics. The methods introduced are explained in enough detail so that programs can be written directly without a major conceptual effort. Anothers use of the book is for reference by researchers in the field. The bibliographic references at the end of the chapters give the necessary pointers to the important publications. In the case of researchers in the field of non-photorealistic computer graphics, the methods that are built up are referenced appropriately, and a comprehensive index aids in selective readings. Objective Non-photorealistic computer graphics is a relatively young field, and new works are constantly being published. The intent of this book is to bring together a coherent conceptual framework for all of the research to date in the context of computer graphics, art history and theory, and cognitive psychology. Although the field of non-photorealistic rendering has existed for more thantwodecades,ithasforalongtimenotbeentakenseriouslybylargeparts of theresearchcommunity.Theareahasthusfarbeen unstructured,making it increasingly difficult to identify and assess new open problems. Indeed, sometimes papers have even “reinvented the wheel,” albeit in a different context and application concern. Recent years have seen many algorithms, papers, and software tools devoted to artistic rendering and computer- assisted cartoon animation. The time has become ripe for a systematic assessment of the literature. The following are our goals: (1) To become the seminal reference for core issues surrounding artistic ren- dering and cartoon animation. (2) To describe and review state-of-the-art advances in the field of non- photorealistic computer graphics, and to distill the breadth of cutting- edge non-photorealistic modeling, rendering and animation technologies into a coherent, accessible treatise. (3) Toprovidetheguidelinesforresearchersandsoftwaredeveloperstoassess and implement the best solution for their interactive arts application. Acknowledgement I would like to thank my family for their love, support, and patience, and a few of the great many people for their instrumental contributions in taking Preface VII thisbookfromaninitialsuggestiontoafinalproduct.Iexpressmygratitude to Prof. Yunhe Pan, fellow of Chinese Academy of Engineering, for his time reviewing this book and contributing his many deep insights into the topic in the final chapter of the book. A number of colleagues in the State Key Lab of CAD & CG at Zhejiang University gave the author support, offered constructive criticisms, or provided illustrations to include in the book. These include Profs. Hujun Bao, Yueting Zhuang, Dongming Lu, and Duanqing Xu. I am also indebted to the graduate students, faculty, and researchers in the research group of Computer Animation and Perception at Zhejiang University. I wishes to thank those persons who provided the support to make this book appear, including the administrative, technical, and secretarial staff in our college who kept things up and running, even under adverse workloads (Ms Qi Shen, Ms Xuefang Zhang, etc.). I also thanks the graduate students at Zhejiang University who studied the topic with previous versions of the manuscript, and all of the colleagues and peers around the world who did great research and gave me the copyrights of their images. Thecontinuousresearchanddevelopmentonnon-photorealisticcomputer graphics in the past years were supported by the following grants: National Natural Science Foundation of China (Grant Nos.: 6960302, 69973044, 60373032, 60773183 and 60633070), National High Technology Research and Development Program of China (Grant Nos.: 2006AA01Z313 and 2006AA01Z335), New Century Excellent Talents in University (NCET-07- 0743), and Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT0652). Finally,IalsoacknowledgestheprodigiousworkofthepeopleatZhejiang University Press and Springer. Weidong Geng Hangzhou, China August 16, 2009 Contents 1 Introduction.............................................. 1 1.1 The Brief History: from Photorealism to Non-photorealism .. 1 1.2 What is Non-photorealistic Computer Graphics ............ 2 1.2.1 Image, Picture, and Visualization................... 3 1.2.2 Photorealistic versus Non-photorealistic Rendering ... 4 1.3 The Framework for Non-photorealistic Computer Graphics .. 6 References ................................................. 9 2 Simulating Artistic Media for Digitized Creation of Artworks ................................................. 11 2.1 Stroke-based Artistic Drawing............................ 11 2.1.1 Interactive Drawing Based on Brushstrokes .......... 11 2.1.2 Pen-and-ink Illustration by Stroke Textures.......... 15 2.1.3 Interactive Pencil Drawing......................... 18 2.1.4 Simulating Wax Crayons .......................... 26 2.2 Oriental Calligraphy and Black Ink Painting ............... 30 2.2.1 Modeling of Soft Brushes.......................... 31 2.2.2 Calligraphy with Soft Brushes...................... 39 2.2.3 Oriental Black Ink Painting........................ 43 2.3 Simulation of a Colored Painting ......................... 54 2.3.1 The Computational Model of Rendering Colored Pigments........................................ 55 2.3.2 Simulation of Watercolor Painting .................. 58 2.3.3 Simulation of Oil Painting......................... 68 2.4 Digitized Sculpting ..................................... 77 2.4.1 Digitized Wood Sculpting ......................... 78 2.4.2 Digitized Metal Embossing ........................ 81 2.5 Creation of Artwork in a Virtual Environment ............. 83 2.6 Summary.............................................. 86 References ................................................. 87