Blurring Techniques

Zhenyu Shu

2006.4.17

Scene Rendering

Object Space -> Image Space

Method: Scan line rendering, Ray tracing, etc

Traditional method focused at all depth without depth of field

Advantage of Blurring

Add realism to a scene

Draw viewer’s attention to a particular place

Example

without blurring with blurring

How to add blurring? Object Space

Synthetic Image Generation with and Aperture Camera Model, M. Potmesil, I. Chakravarty, 1981, Siggraph

Distributed Ray Tracing, R.L. Cook, 1984, Siggraph

Camera Models and Optical Systems Used in Computer Graphics: Part I, Object-Based Techniques, Brian A. Barsky, Daniel R. Horn, Stanley A. Klein;Jerrey A. Pang,and Meng Yu, 2003, ICCSA

How to add blurring? Image space

Camera Models and Optical Systems Used in Computer Graphics: Part II, Image-Based Techniques, Brian A. Barsky, Daniel R. Horn, Stanley A. Klein;Jerrey A. Pang,and Meng Yu, 2003, ICCSA

Elimination of artifacts due to occlusion and discretization problems in image space blurring techniques, Brian A. Barsky, Michael J. Tobias, Derrick P. Chu, Daniel R. Horn, 2005, Graphical Models

The Finite Aperture Camera Model

Depth of field

Circle of confusion

Synthetic Image Generation

1. Hidden-Surface Processor

Synthetic Image Generation

2. Focus Processor

Example

Distributed ray tracing

Thin Lens Approximation

Thin Lens Approximation

Thick Lens Approximation

Thick Lens Approximation

Full Lens Systems

Full Lens Systems

Example

Object space blurring’s defects Computationally expensive

The increase in computation cost is proportional to the number of rays per pixel

Image space blurring

Image Depth Information

Image separated by depth

Final blurred image

Problems with image space blurring techniques

1. Occlusion problem

Problems with image space blurring techniques

2. Discretization Problem

Problems with image space blurring techniques

2. Discretization Problem

How to eliminate artifacts

1. Object Identification: detect large objects straddling several sub-images 1.1 Edge detection technique 1.2 Adjacent pixel difference technique

2. Extend each sub-images and blur respectively

Edge detection technique

Get edges of subimages Use Canny edge detection algorithm

Edge detection technique

Extend the region

Example

Original image and depth information

Example

Blurred image without object identification

Example

Blurred image with object identification

Adjacent pixel difference technique

Use depth’s difference

Set the bound, adjacent pixels within the bound belong to the same object

Example

Example: Original Image

Example: blur without object identification

Example: blur with object identification

Example: blur with object identification