Computer Graphics Part 7 (Texture mapping)
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Explain the general need and idea of 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
principles of texture mapping (4)
- 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
List three common texture coordinate mappings
why does this problem occur?
- 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
How do can you solve the affine texture mapping problem?
OR: two triangles per sqaure
Why does aliasing happen?
Sampling frequency is too low w.r.t the signal frequency (e.g. pixel size is too large ccompared to original scene)
Why does stochastic sampling show better results than regular sample patterns?
- 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)
Explain the Accumulation Buffer
What is a texel?
pixel of the texture
explain the problem with texture aliasing. How can you fix it?
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
explain the steps of bilinear interpolation with regard to texture antialiasing (3 steps)
- 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
What would you like to do?
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