Texture Mapping

Presented byPOTLURI,KIRAN

Introduction Texture :

A detailed pattern that is repeated many times to tile the plane.

Texture mapping is a powerful technique for adding realism to a computer-generated scene.

Texture Mapped on to Tea Pot

Texture Mapped on to Tea Pot

Introduction (contd ..) The First use of texture was

developed by Catmull in the year 1974.

Algorithm is applied to bicubic parametric patch model, since the parametric patch models already possesses the U,V values everywhere on its surface.

How is texture mapping done

Two Dimensional Texture Mapping ::

TextureSpaceT(u,v)

ObjectSpace(x,y,z)

ScreenSpace

(Xs,Ys)

surface

parameterization

Projection

Algorithm The Algorithm divides the surface patch

in object space. At the same time , executes subdivision

in texture space. Patch subdivision proceeds until it ends

in single pixel. After it reached this point, Subdivision

process terminates . The required texture value for each

pixel is obtained from texture domain.

Difficulties Two difficulties

1. Inventing suitable surface parameterization

2. Anti-aliasing.

Types of Texture Mapping Two Types

1. Forward texture mappingcomputing 3D positions of

the texture points and then projecting them onto the image plane.

2. Inverse texture mappingselecting every pixel in the

image plane and finding what point of the texture plane is projected there.

Drawbacks Forward Texture mapping :

Adjacent texture points may project onto non adjacent image points, thus creating a non colored area .

Drawbacks Inverse Texture Mapping :

Aliasing would appear, if sampling the texture map is done at a frequency higher than its Nyquist rate.

Nyquist rate :the minimum theoretical sampling rate .

Polygon Mesh Texture Mapping It is also called Two-part texture

mapping Introduced by Bier and Sloan Year 1986. The texture is mapped onto an

intermediate surface before being mapped onto the object

How this Method Works Step 1 : mapping from two-

dimensional texture space – simple three dimensional intermediate surface .

e.g. : cylinder , sphere .T(u,v) T’(xi,yi,zi)

This is know is S-mapping .

Mapping to sphere or cylinder Scylinder :: (,h) (u,v)

= (r/c(-o),1/d(h-ho))

Ssphere :: (,) (u,v)

= (2q/1+(1+p2+q2)1/2, (2q/1+(1+p2+q2)1/2 )P=tan()cos() q= tan()sin()

O-mapping Step 2 : Mapping from 3-

dimensional texture pattern onto object surface.

T’(xi,yi,zi) O(xw,yw,zw)

This is know as O-mapping.

Map to object surface There are four possible ways

1. The intersection of the reflected view ray with intermediate surface

View point Intermediate surface

(xi,yi,zi)

(xw,yw,zw)

Map to object surface(Contd..)

2 . The intersection of the surface normal at (x,y,z) with the intermediate surface.

Intermediate surface

(xi,yi,zi)

(xw,yw,zw)

Map to object surface(Contd..)

3 .The intersection of a line through (x,y,z) and object centroid with intermediate surface.

Intermediate surface

(xi,yi,zi)(xw,yw,zw)

Map to object surface(Contd..)

4 . The intersection of line from (x,y,z) to T’ whose orientation is given by surface normal at (xi,yi,zi)

Intermediate surface

(xi,yi,zi)

(xw,yw,zw)

Applications

Molecular Graphics Isocontouring of

the hydrophobic potential on the solvent-accessible surface of Gramicidin A

Molecular Graphics Solvent-accessible

surface of ethanol, color coded against the electrostatic potential, using the traditional color coding (left) and using texture mapping (right).

Molecular Graphics The 13,767

spheres of a hydrated phospholipid bilayer (DLPE), part of a cell membrane can be rotated in real time.

Crash Simulations

Wire Frame Mapping

Force tube

Drawback Major draw back is the image

quality . Usually for high quality images Ray Tracing is used .

References Alan Watt, 3D Computer graphics . Addison –

Wesley 1993. Fredrick M Weinhaus, Venkat

Devarajan,Texture mapping 3D models of real-world scenes .ACM computing survey , Volume 29 1997.

James F. Blinn and Martin E. Newel,Texture and Reflection in computer generated images. ACM computing survey.

References (Contd ..)  http://www.cs.csustan.edu/~rsc/

CS3600F00/TextureMapping.pdf http://www.sgi.com/grafica/texmap/

index.html http://www-2.cs.cmu.edu/~ph/

texsurv.pdf