Computer Graphics& 3D Painting

Xia Jiazhi

Central South University

Xia Jiazhi

• Lecturer at Central South University

• Received Ph.D. at Nanyang Technological University, Singapore, in 2011

• Research: Computer Graphics and Human-Computer Interaction

What is Computer Graphics?

What is Computer Graphics

• A technique to generate digital images from 3D models using computer.

Which one is the real BMW?

Is it Fake or Photo?

The image may cheat us

Why Computer Graphics?

Why computer graphics

• About 50% of the brain neurons are associated with vision.• Dominant form of computer output.• Enable scientists (also engineers, doctors, and general users) to

observe their simulation and computation.• Computer graphics is application driven!

– Movie

– Game

– Computer-aided design (CAD)

– Medical imaging

– Computer art

– Graphical user interface (GUI)

– Scientific visualization

Movies

• If you can imagine it, it can be done with computer graphics.

• More than one billion dollars on special effects. More and more of these images exist only within the memory of a computer. No end in sight for this trend!

• Computer graphics is now as much a part of the video and movie production industry as stuntmen and makeup.

Video Games

• Games are the driving force in computer graphics.

• Games market is the stimulus for the powerful graphics processors (GPU)

Spacewar 1961 Counter Strike 2005

Crysis 3 2013

Computer-Aided Design(CAD)• Today, most mechanical and electronic designs are executed entirely on computer.

Increasingly, architectural and product designs are also migrating to the computer. Automated tools are also available that verify tolerances and design constraintsdirectly from CAD designs.

• CAD can significantly reduce the design cycles for industrial products, e.g., the mobile phones

Graphical User Interface(GUI)

Visualization

How Computer Graphics Works?

Simulating the Everyday World

• Three broad areas:– Modeling(Geometric) = Shape– Animation = Motion/Behavior– Rendering = Appearance

Representing the Shape

Geometric Modeling

Geometric Modeling

Geometric Modeling

Animating the world

Animation

Natural phenomena simulation

Rendering

Rendering• Rendering is the process of generate an image from a scene, which contains

geometry, viewpoint, texture and lighting information. It is similar to photography or cinematography.

• Simulation of realistic lighting, shadows, atmosphere, color, texture and optical effects such as refraction of light or motion-blur seen on moving objects.

Representing the Surface Details

Texture Maps

• How is texture mapped to the surface?– Dimensionality: 1D, 2D, 3D

– Texture coordinates (s, t)• Surface parameters (u, v)

• How to assign the Surface parameters?– Parameterization!

3D Painting

• Assign colors to vertices directly in a painting interface– WYSIWYG(What You See Is What You Get) system

• Painting on self-occluded model

– A lot of manual work, even impossible

Start from Reality

From Jeremy Birn

Model

Start from Reality

Model + illumination

model

From Jeremy Birn

Start from Reality

Model + illumination + Texture

Model + illumination

Model

From Jeremy Birn

3D Painting

• An interactive technique for 3D model surface properties editing

• 3D model surface properties are required by reconstructing the surface details of the real object– Color– Illumination– Transparency– Normal （ bump mapping）– Displacement mapping– ……

The 3D Painting System

The Challenge of 3D Painting

• The dimension– 3D interaction + 3D display– 2D interaction interface is still the major method

of industry [P. Hanrahan et al. 1990]

• Operation– The occlusion is a challenge to interaction even

in real world

• The Creation skill– General users lack the professional creation skill

1. Occlusion

Our Method

Depth Layer

Layer 1 Layer 2

Depth peeling

Layer 1 Layer 2

Region Segmentation

The pixel adjacent

information

Region adjacent

information

Region Segmentation

Depth Information

Layer-aware Interaction

Layer-aware Interaction

A complete painting demo

2. The difficulty of creation

• 3D painting requires professional creation skill

Decal System

• Copy+Paste

Schmidt et al. 2006

Exponential Map

Can only control the center point and the direction

Sketch-based texture mapping

• Free control of the texture deformation

• More close to painting experience of general users

Sketch-based texture mapping

Extended exponential map

Texture map

Extended exponential map

Comparison

Extended exponential map[Sun et al. 2013]

Exponential map[Schmidt et al. 2006]

A painting demo

Thanks! & Question?