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«3D DIGITAL RELIEF GENERATION MEILI WANG July 2011 National Centre for Computer Animation Bournemouth University This copy of the thesis has been ...»

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3D DIGITAL RELIEF GENERATION

MEILI WANG

July 2011

National Centre for Computer Animation

Bournemouth University

This copy of the thesis has been supplied on condition that anyone who

consults it is understood to recognise that its copyright rests with its author

and due acknowledgement must always be made of the use of any material

contained in, or derived from, this thesis.

i

3D DIGITAL RELIEF GENERATION

MEILI WANG A thesis submitted in partial fulfilment of the requirements of the Media School of Bournemouth University for the degree of Doctor of Philosophy July 2011 National Centre for Computer Animation Bournemouth University ii Copyright © 2011 MEILI WANG All rights reserved iii ABSTRACT This thesis investigates a framework for generating reliefs. Relief is a special kind of sculptured artwork consisting of shapes carved on a surface so as to stand out from the surrounding background. Traditional relief creation is done by hand and is therefore a laborious process. In addition, hand-made reliefs are hard to modify. Contrasted with this, digital relief can offer more flexibility as well as a less laborious alternative and can be easily adjusted.

This thesis reviews existing work and offers a framework to tackle the problem of generating three types of reliefs: bas reliefs, high reliefs and sunken reliefs.

Considerably enhanced by incorporating gradient operations, an efficient bas relief generation method has been proposed, based on 2D images. An improvement of bas relief and high relief generation method based on 3D models has been provided as well, that employs mesh representation to process the model. This thesis is innovative in describing and evaluating sunken relief generation techniques. Two types of sunken reliefs have been generated: one is created with pure engraved lines, and the other is generated with smooth height transition between lines. The latter one is more complex to implement, and includes three elements: a line drawing image provides a input for contour lines; a rendered Lambertian image shares the same light direction of the relief and sets the visual cues and a depth image conveys the height information.

These three elements have been combined to generate final sunken reliefs. It is the first time in computer graphics that a method for digital sunken relief generation has been proposed.

The main contribution of this thesis is to have proposed a systematic framework to generate all three types of reliefs. Results of this work can potentially provide references for craftsman, and this work could be beneficial for relief creation in the fields of both entertainment and manufacturing.

–  –  –

First and foremost, I would like to express my deepest gratitude to my supervisors, Professor Jian J. Zhang and Dr. Jian Chang, whose encouragement, patience, devotion, guidance and support have enabled me to develop a good understanding of the subject throughout various stages of my research. They have great personalities and extensive knowledge. I would not have finished writing the thesis so quickly without their invaluable advice. I shall never forget them.

I would also like to thank Dr Xiaosong Yang, Dr Richard Southern, Fangde Liu, Shihui Guo in our group for kindly providing me with valuable suggestions and helps. I am also grateful to Mrs. Jan Lewis and Mr. Dan Cox for their daily support and kind assistance with non-academic matters.

Special thanks to my friends Robert Hardy and Alan Sanca for proofreading my paper carefully, also I would like to thank Yuanlong Liu, Longjiang Niu, Sola Aina and Safa Tharib, my collaborator Jens Kerber in Germany who provided me with excellent ideas and helped me to improve my thesis.

I gratefully acknowledge Chinese Scholarship Council (CSC) for their financial support. I would also extend my regards and blessings to all of those who supported me in any respects during the completion of my PhD.

Speacial thanks to Aim@Shape project (www.aimatshape.net) for providing 3D mesh models online to share.

My great tribute is due to my parents, and my boyfriend in Germany and for their loving consideration and invaluable support through my long student life.

Finally, I dedicate this thesis to my family, for their love and encouragement on my journey of growth.

–  –  –

1. INTRODUCTION

1.1 BACKGROUND

1.1.1 Sculpture

1.1.2 Relief sculpture

1.2 MOTIVATIONS

1.3 AIMS AND OBJECTIVES

1.4 CONTRIBUTIONS

1.5 PUBLICATIONS

1.6 THESIS OUTLINE

2. RELATED WORK

2.1 OVERVIEW

2.2 IMAGE-BASED RELIEF GENERATION

2.2.1 Bas relief generation by image processing

2.2.2 Techniques relating to texture mapping

2.2.3 Shape from Shading

2.3 RELIEF GENERATION BY 3D DESIGN SOFTWARE OR DIGITAL SCULPTURE PACKAGES....... 18

2.4 RELIEF GENERATED FROM 3D SHAPES

2.5 SUMMARY

3. BAS RELIEF GENERATION BASED ON 2D IMAGES

vi

3.1 OVERVIEW

3.2 BACKGROUND

3.3 METHOD DESCRIPTION





3.3.1 Gradient computation

3.3.2 Attenuation

3.3.3 Boosting by Unsharp Masking

3.3.4 Image reconstruction from gradient field

3.3.5 Gamma correction

3.3.6 Mesh triangulation and simplification

3.4 RESULTS AND DISCUSSIONS

3.5 SUMMARY

4. RELIEF GENERATION BASED ON 3D MODELS

4.1 OVERVIEW

4.2 BACKGROUND

4.3 OVERVIEW OF METHOD

4.3.1 Mesh enhancement by 3D USM

4.3.2 Laplacian smoothing

4.3.3 Non-linear scaling scheme

4.4 RELIEF GENERATION

4.4.1 High relief generation

4.4.2 Bas relief generation

4.4.3 Different view angles

4.4.4 Parameter testing

4.5 SUMMARY

5. DIGITAL SUNKEN RELIEF GENERATION BASED ON 3DMODELS

5.1 INTRODUCTION

5.2 BACKGROUND

5.3 3D LINE DRAWINGS

5.3.1 Lines in sunken relief and 3D Line drawings

5.3.2 Line drawings algorithm

5.3.3 Pre-processing: Image processing

5.4 SUNKEN RELIEF GENERATION USING FEATURED LINES

5.5 ADVANCED SUNKEN RELIEF GENERATION USING MULTIPLE INPUTS

5.5.1 Three inputs

vii 5.5.2 Relief Height Generation

5.5.3 Results

5.6 SUMMARY

6. CONCLUSIONS AND FUTURE WORK

6.1 CONCLUSIONS

6.2 FUTURE WORK

REFERENCES

–  –  –

Figure 1.1 Two views of a wooden statue of the Buddha from Chinese Song Dynasty, Museum of Shanghai

Figure 1.2 Three types of relief

Figure 2.1 Bas reliefs produced by Photoshop with different parameters.

......... 12 Figure 2.2 ArtCAM failed to generate the relief from the image with complex colour distribution.

Figure 2.3 Bump mapping result

Figure 2.4 Normal map and the reconstructed surface.

Figure 2.5 A lion head modelled by Exchange3D

Figure 2.6 The templates ArtCAM provided and an example.

Figure 2.7 Bas reliefs produced by existing methods.

Figure 2.8 Bas relief of a building model

Figure 3.1 Procedures of the proposed method

Figure 3.2 Gradient components of the Sphinx model; x-component of gradient:

Gx(left) and y-component of gradient: Gy(right)..

Figure 3.3 Updated x-component of gradient Gx(left) and y-component of gradient Gy(right) after attenuation compared to Figure 3.

2........... 34 Figure 3.4 Updated x-component of gradient Gx(left) and y-component of gradient Gy(right) after USM compared to Figure 3.3.................... 35 Figure 3.5 Influence of different δ values

Figure 3.6 Gamma correction.

Figure 3.7 The reconstructed Sphinx model and the claw of the Sphinx model.

38 Figure 3.8 Input image of the Sphinx and results.

Figure 3.9 Lateral Sphinx models generated by the proposed methods, ArtCAM and Photoshop.

Figure 3.10 Examples rendered with different textures.

Figure 3.11 Other examples

Figure 4.1 Flowchart of the algorithm

Figure 4.2 Vertex i and its one-ring neighbours

ix Figure 4.3 High reliefs with Bunny model

Figure 4.4 High reliefs with Skull model

Figure 4.5 Bas reliefs generated by the proposed algorithm: Bunny and Skull.

51 Figure 4.6 The bas relief generated by the proposed algorithm: Vase lion and rendered Vase lion with frame.

Figure 4.7 Reliefs of Different view angles of Chinese lion.

Figure 4.8 Different δ from 0.

2 to 1.0

Figure 5.1 A sunken relief of ancient Egypt.

Figure 5.2 Image processing example of generated lines of the horse model.

.. 62 Figure 5.3 Bunny model

Figure 5.4 Line drawings of bunny model with different levels of smoothing.

. 64 Figure 5.5 Comparison of reliefs with different line density

Figure 5.6 Reliefs generated with the proposed method

Figure 5.7 Procedures of the proposed method

Figure 5.8 The surface discretization of the relief in relation to pixels of an input image

Figure 5.9 Comparison of reliefs with different inputs.

Figure 5.10 Comparison of reliefs with different line density

Figure 5.11 Bas reliefs produced by existing methods.

Figure 5.12 The results of sunken reliefs.

–  –  –

INTRODUCTION

1.1 Background 1.1.1 Sculpture Sculpture is one of the most important art forms producing three dimensional (3D) representations of natural or imagined objects. It is also of significance in depicting a certain kind of symbolic view of objects and monuments.

Sculpture has a long history, which can be divided into the following: ancient sculpture, western sculpture from the Middle Ages to the seventeenth century, and modern sculpture (Causey 1998).

Sculpture has been developed since prehistoric times. Sculptures produced by ancient Egypt, for example, the Sphinx, the Palette of King Narmer etc. were more influenced by ritual significance than aesthetic considerations. In Europe, there emerged a great number of religious architectural sculptures, for example, church buildings, especially cathedrals. Many renowned sculpture masters, such as Ghiberti, Donatello, the Della Robbia family etc. emerged during the highly formative Renaissance period. Recent development of sculpture has introduced different and complicated materials, textures, and techniques.

Sculptors have also explored various and highly original applications of this special art form. Modern sculpture has incorporated light, sound, etc., which has made this art form even more interesting and attractive.

Sculpture is traditionally created by carving, welding, firing, moulding, casting or painting. There are varieties of materials for making sculpture, for example, marble, metal, glass, and wood, these materials are renowned for their enduring properties. Other materials, which are slightly less enduring, such as clay, textiles and softer metals, can also be used.

–  –  –

In general, sculpture can be classified into round sculpture and relief depending on the space occupied by this art form. Round sculpture is surrounded on all sides except the base. It is also known as sculpture "in the round", which means it can be appreciated from any direction (as shown in Figure 1.1). In this way, different perception angle may deliver different information.

A relief sculpture spans two dimensional and three dimensional art forms. This form of sculpture differs from painting and drawing, which can only depict a virtual 3D image in 2D space. Contrasted with this, a 3D object can be represented immediately and vividly by relief sculpture. There are other differences between relief and other art forms: such as the method of production process, material used etc. The advantage of relief sculpture is that it takes up less than half of the space, while it still presents almost the same amount of detail that round sculpture does. Compared with drawings and paintings, relief sculpture portrays a vivid 3D object. It is a special and very distinct art form. More details are introduced in the following section.

1.1.2 Relief sculpture

Relief is a type of sculptured artwork which is carved on a plane or a surface unlike general free-standing sculptures (Flaxman 1829; Rogers 1974). The most distinguishing feature of reliefs compared with round sculptures is that

they physically lie on some kind of background. There are three types of relief:

high relief, (attached to a surface (Figure 1.2(a)), or free standing (Figure 1.2(b))), bas relief and sunken relief (as shown in Figure 1.2(c) and Figure 1.2(d)).

In high relief (alto relievo), the forms have over half of their natural depth attaching to a surface or separating from it; and in bas relief (basso relievo, low relief), the forms have under half of their natural depth always attaching to a surface. A piece of bas relief is suitable for scenes with several objects, landscape elements or architectures. In sunken relief, also known as intaglio or hollow relief, the objects are carved into a flat surface (Rogers 1974).

–  –  –

Nowadays, reliefs have an enormous number of applications ranging from aesthetic perspective to practical use. Pseudo-reliefs, also known as relief-style images generated by computer can be used to design webpage logos, cartoon figures and packaging etc. Real carving relief or Computer Aided Machinery (CAM) generated relief can be represented as single pieces of artwork or be used as decorations to adorn the surfaces of furniture, walls, and a vast range of other items.

1.2 Motivations



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