1. Computer Graphics Imaging
Lecture 11 and 12
Texture Mapping

2. Texture mapping
The question: how to modify the color of an object to make it look real or interesting?
Lighting and surface materials settings produce smooth and uniform visual appearance
Often not realistic enough
The solution: use texture image to further modify the color of the object

3. Texture mapping
The final color of an object is often a combination of several layers of effects
Lighting + Base material + textures
There are different ways to mix the textures and materials

4. Texture channels
In the “Texture” tab under the “Material Buttons panel”
You can apply multiple textures to an object
Applied from bottom to top – layered upon each other
Can create a new texture for each channel
Can copy and paste texture settings between channels and between objects
Can turn on and off individual texture channels

5. Types of textures
Press the “Add New” button in the “Texture” tab under the “Material Buttons” panel
Then click the “Texture Buttons” icon
Procedural texture
Usually semi-random patterns
Generated through mathematical models
Image or video
Can use video as texture
Environment map

6. Repeat or extend a texture image
You may want to make a small texture image cover a large area
Click on the “Texture Buttons” icon
Under the “Map Image” panel
Extend: extend the color of edge pixels along the two axes
Clip: one image only (no repeating or extending)
ClipCube
Repeat: repeat the image along the two axes
Checker: repeat image in checker pattern

7. Crop a texture image In “Texture buttons” panel, “Map Image” panel
Set MinX, MinY, MaxX, MaxY

8. Texture color In “Texture buttons” panel, “Colors” tab
May tint the color of a texture by brightening each red, green and blue channel
All textures may be modified by the Bright(ness) and Contr(ast) buttons in the Colors panel.

9. Texture decal Apply decals to a 3D object Steps
E.g. attach a logo to a T-shirt
Steps
Insert an Empty object into the scene
You may want to give it a meaningful name
Move it close to the object that you want to apply the decal to
The Empty object’s Z axis should point away from the mesh
Add an image texture to the mesh. Set UseAlpha and ClipCube in the Map Image panel
In the Map Input field, press Object and type in the name of the Empty object

10. Texture decal
Can move, rotate, and scale the Empty object to move, rotate, and scale the texture image
You may want to make the Empty object the child of the object you are texturing
So that the decal moves with the object
Or animate the Empty object to animate the decal

11. Understanding “Map Input”
Where do you want to place the texture image?
Glob: texture image is placed at global (0, 0, 0)
Texture mapping happens when the target object covers the origin
Object: texture image is attached to an object other than the target object
Usually an Empty object
Texture mapping happens if the two objects are close enough
UV: texture mapping is determined by a UV map
Most accurate but also quite time consuming to do

12. Understanding “Map Input”
Where do you want to place the texture image?
Orco: texture image is attached to the target object
Win: texture image is placed over the window
Only part of the image is mapped to the object
Imagine that a texture image is placed at certain location and is projected through a certain axis (the default is Z)
When the target object intersects with that projection, texture mapping happens.

13. Understanding “Map Input”
Do you want to change the shape of the texture (image)?
Flat (image)
Cube
Tube
Sphere

14. Understanding “Map Input”
By default, the center of the image is mapped to the (x=0, y=0) of the coordinate system that it’s attached to
See “where do you want to place the texture image?”
Do you want to move the texture away from (0, 0)?
Change “ofsX”, “ofxY”, “ofsZ”
Do you want to scale the texture image?
Modify “sizeX”, “sizeY”, “sizeZ”

15. Understanding “Map Input”
By default, the texture image is placed on the X-Y plane, and is projected through Z axis
What if you want to project it through another axis?
Project through Y: click the X button on the first row, and click the Z button on the second row
Project through X: click the Y button on the first row, and click the Z button on the second row
What if you want to rotate the image for 90 degrees?
Switch the axes on the first and second row
What if you want to rotate the image for 180 degrees?
Set “sizeX” and “sizeY” to the negative values

16. 3D view texture space transform
Select the object
Press T
Select “grab/move” or “size” to shift or scale the texture image
Equivalent to changing ofsX/Y/Z or sizeX/Y/Z in the “Map Input” field

17. Understanding “Map To”
You can control how images are used in the texture mapping process
Col: image mapped to color. This is the standard usage.
Nor: image mapped to normals. This is for bump mapping.
Disp: image used to displace vertices. This is for displacement mapping.
And a number of other options

18. Understanding “Map To”
Blending mode: how this texture channel is combined with other texture channels
Mix, add, substract, multiply, divide, etc.
See for details

19. Understanding “Map To”
Impact sliders: how much impact will the texture have?
Col: how much impact will the texture has on color? (standard texture mapping)
Nor: how much will the normal map change the normal vectors? (bump mapping)
Disp: how will the texture intensity displace the vertices? (displacement mapping)

20. Understanding “Map To”
Stencil: use one texture channel as a mask
Create and load a black and white image for this channel
By default the areas that is black will prevent the subsequent texture channels from being applied
Can reverse this by pressing “Neg” button
Add the texture image to the next channel
Press “Stencil” button and “No RGB” button

21. Understanding “Map To”
Warp: use the current texture channel to distort the texture coordinates of the texture channel
Press “Warp” button
Adjust the “Fac” value

22. Bump mapping
Bump mapping is a technique to create the visual appearance of uneven and bumpy surface out of smooth objects
Avoid using too many vertices
The process
Create a normal map
Use the normal map to change the directions of normal vectors of the vertices
The end result: the surface will look uneven

23. Bump mapping A common practice in video games
Create two versions of a 3D model: a high resolution model and low resolution model
Generate a normal map out of the high resolution model
Use the normal map to do bump mapping on the low resolution model
After bump mapping, the low resolution model will look like a high resolution model, but with far fewer vertices
See

24. Bump mapping Basic ideas behind bump mapping
Each vertex has a normal vector, which is used for calculating the vertex color.
On a smooth surface, the normal vectors are either uniformly oriented, or the change of the normal orientation is gradual
During bump mapping, a normal map is used to change the directions of the normal vectors
Vertex colors are then calculated based on the modified normal vectors
This may create the illusion of a bumpy surface

25. How to create normal map in Blender?
Create the 3D model
Preferably a high resolution model
Create a new material for the 3D model, if it doesn’t have one
Set the diffuse color of material to black (0.0, 0.0, 0.0)
Under “Material buttons”, press “Shadeless”

26. How to create normal map in Blender?
Create three texture channels for the object
Set the texture type to “Blend” for three channels
For the first channel,
Under “Map Input”, press “Nor”, and only select X axis
Under “Map To”, set the color to Red (1, 0, 0)
For the second channel
Under “Map Input”, press “Nor”, and only select Y axis
Under “Map To”, set the color to Green (0, 1, 0)
For the third channel
Under “Map Input”, press “Nor”, and only select Z axis
Under “Map To”, set the color to Blue (0, 0, 1)

27. How to create a normal map in Blender?
Under “World Buttons”, set the background color to be black (0, 0, 0)
Place the camera so that it’s directly above the object
Under “Editing”, press “Orthographic” (projection)
Press F12 to render the scene
Press F3 to save the image (e.g. as jpg)

28. How to create a normal map in Blender?
See and for more details

29. How to do bump mapping? Select the target 3D object
Create texture channel and load a normal map
Press the "Normal map" button in the Image Panel under “Texture buttons”
Select “object” instead of the default “tangent”
Under “Material buttons”, in "Map To" panel, press "Nor“ and un-press “Col”
Adjust “Nor” impact slider

30. Displacement mapping Use an image to displace vertices
Create true bumpy surfaces, but need to use a lot more vertices
Quite expensive
Works better on very dense mesh models

31. Displacement mapping
You may need to subdivide the 3D model multiple times to increase the number of vertices
Load a displacement map into a texture channel
Under “Material buttons”, in "Map To" panel, press “Disp“ and unpress “Col”
Adjust “Disp” impact slider