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Graphics

Texture Mapping 고려대학교 컴퓨터 그래픽스 연구실

cgvr.korea.ac.kr

1

Graphics Lab @ Korea University


3D Rendering Pipeline 3D Primitives

CGVR

3D Modeling Coordinates

Model Model Transformation Transformation 3D World Coordinates Lighting Lighting 3D World Coordinates Viewing Viewing Transformation Transformation 3D Viewing Coordinates Projection Projection Transformation Transformation 2D Projection Coordinates Clipping Clipping 2D Projection Coordinates Viewport Viewport Transformation Transformation

Texture Mapping

2D Device Coordinates Scan Scan Conversion Conversion Image

2D Device Coordinates Graphics Lab @ Korea University


Textures 

CGVR

Color variation in interior of 3D polygon 

When scan converting a polygon 

Vary pixel colors according to values fetched from a texture y

s

ys

x

t

Texture z

Surface

Image

xs

Graphics Lab @ Korea University


Texture Surface ď Ž

CGVR

Add Visual Detail to Surfaces of 3D Objects

With Surface Texture Polygonal Model Graphics Lab @ Korea University


Overview 

Texture mapping methods  

CGVR

Mapping Filtering

Texture mapping applications      

Modulation textures Illumination mapping Bump mapping Environment mapping Image-based rendering Non-photorealistic rendering Graphics Lab @ Korea University


Texture Mapping

CGVR

Steps:

  

Define texture Specify mapping from texture to surface Lookup texture values during scan conversion (0,1)

s

(1,0)

v t

Texture Coordinate System

(0,0)

u

Modeling Coordinate System

y x

Device Coordinate System Graphics Lab @ Korea University


Texture Mapping

CGVR

When scan converting

  

Device coordinate system (x,y) Modeling coordinate system (u,v) Texture image (t,s) (0,1)

s

(1,0)

v t

Texture Coordinate System

(0,0)

u

Modeling Coordinate System

y x

Device Coordinate System Graphics Lab @ Korea University


Texture Mapping 

CGVR

2D projective transformation  

Texture coordinate system (t,s) to Device coordinate system (x,y)

Graphics Lab @ Korea University


Texture Mapping 

CGVR

Scan conversion  

Interpolate texture coordinates Distortion due to bilinear interpolation approximation  

Cut polygons into smaller ones, or Perspectively divide at each pixel

(u1, v1) α γ β

(u2, v2)

(u3, v3) Graphics Lab @ Korea University


Texture Mapping

Linear Interpolation of Texture Coordinate

CGVR

Corrected Interpolation with Perspective Divide Graphics Lab @ Korea University


Texture Mapping 

Texture mapping methods  

CGVR

Mapping Filtering

Texture mapping applications      

Modulation textures Illumination mapping Bump mapping Environment mapping Image-based rendering Non-photorealistic rendering Graphics Lab @ Korea University


Texture Filtering ď Ž

CGVR

Must sample texture to determine color at each pixel in image y

s

ys

x

t

xs z

Graphics Lab @ Korea University


Texture Filtering ď Ž

CGVR

Aliasing is a problem

Point Sampling

Area Filtering

Graphics Lab @ Korea University


Texture Filtering 

CGVR

Ideally, use elliptically shaped convolution filters 

In practice, use rectangles

Texture

Screen Graphics Lab @ Korea University


Texture Filtering 

CGVR

Size of filter depends on projective warp 

Prefiltering images  

Mip maps Summed area tables

s

ys

s

Texel

ys Texel

Pixel t Magnification

Pixel xs

t

xs

Minification Graphics Lab @ Korea University


Mip Maps 

CGVR

Keep textures prefiltered at multiple resolutions  

For each pixel, linearly interpolate between two closest levels (e.g., trilinear filtering) Fast and easy for hardware

Graphics Lab @ Korea University


Overview 

Texture mapping methods  

CGVR

Mapping Filtering

Texture mapping applications      

Modulation textures Illumination mapping Bump mapping Environment mapping Image-based rendering Non-photorealistic rendering Graphics Lab @ Korea University


Modulation Texture Map Texture Values to Scale Factor

Texture Value

er ut xe T doo W

CGVR

I = T ( t , s ) ( I E + K A I A + ∑L ( K D ( N ⋅ L ) + K S ( V ⋅ R ) ) S L I L + K S I R + KT IT ) n

Graphics Lab @ Korea University


Illumination Mapping 

CGVR

Map Texture Values to Surface Material Parameter 

KA

KD

KS

KT

n

KT = T ( t , s )

I = I E + K A I A + ∑L ( K D ( N ⋅ L ) + K S ( V ⋅ R ) )S L I L + K S I R + KT IT n

Graphics Lab @ Korea University


Bump Mapping ď Ž

CGVR

Map Texture Values to Perturbations of Surface Normals

Graphics Lab @ Korea University


Bump Mapping

CGVR

Graphics Lab @ Korea University


Environmental Mapping ď Ž

CGVR

Map Texture Values to the Environment Map Surface

Pixel Projection onto Environment Map

Pixel Area Projection Reference Point Graphics Lab @ Korea University


Image-Based Rendering ď Ž

CGVR

Map Photographic Textures to Provide Details for Coarsely Detailed Polygonal Model

Graphics Lab @ Korea University


Nonphotorealistic Rendering

CGVR

Graphics Lab @ Korea University


Summary 

Texture mapping methods  

CGVR

Mapping Filtering

Texture mapping applications      

Modulation textures Illumination mapping Bump mapping Environment mapping Image-based rendering Non-photorealistic rendering Graphics Lab @ Korea University

12texture  

??????????????? cgvr.korea.ac.kr Graphics Lab @ Korea University Graphics Lab @ Korea University 1

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