Computer Graphics Part 7 (Texture mapping)

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Computer Graphics Part 7 (Texture mapping)
2013-05-01 21:47:30
computer graphics informatics science

University of Edinburgh School of Informartics Copmuter Graphics (Level 10) Revision Cards created by Simon M.
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  1. 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
  2. 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
  3. List three common texture coordinate mappings
    • orthogonal
    • cylindrical
    • spherical
  4. 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
  5. How do can you solve the affine texture mapping problem?

    OR: two triangles per sqaure
  6. 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)
  7. state the Nyquist limit
  8. 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)
  9. Explain the Accumulation Buffer
  10. What is a texel?
    pixel of the texture
  11. 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
  12. 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