Computer Graphics Part 7 (Texture mapping)

• adding details to an object using high resolution polygon meshes is costly and not suitable for real time applications
• texture mapping improves surfaec appearance by mapping images onto the surface

• for each triangle in the model/mesh esatblisha  corresponding regino in the texture image
• image has much higher resolution than mesh
• during rasterization, color the surface by that of texture
• UV coordinates: 2D coordinates of texture map

• orthogonal
• cylindrical
• spherical

• Uniform steps on the image plane does not correspond to uniform steps in the original 3D scene
• affine texture mapping does not take into account the depth information about a polygon's vertices

OR: two triangles per sqaure

Sampling frequency is too low w.r.t the signal frequency (e.g. pixel size is too large ccompared to original scene)

• Irregular/stochastic sampling makes high frequencies in the image appear as noise rather than aliases
• humans are more sensitive to aliases than noise
• Jittering (random sampling with n subregions)

pixel of the texture

one texel covers more than one pixel in the polygon/surface/object

or texture minifaction, too many texels for one pixel

solution1 - bilinear interpolation, mapping pixel center to uv coordinates and computing pixel color by interpolating the surrounding texel values

solution2 - mipmapping

• 1. get pixel centre and map into texture space
• 2. get the texture color at that point and the surrounding texels in barycentric coordinates
• 3. interpolate colors and map onto scene