Towards more realistic images

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Towards more realistic images

• Chris Handley

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Towards more realistic images

• So now we have an image.

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Towards more realistic images

• So now we have an image. It still doesnt look
  real.

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Towards more realistic images

• So now we have an image. It still doesnt look
  real.
• A major problem is surface detail.

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Towards more realistic images

• So now we have an image. It still doesnt look
  real.
• A major problem is surface detail. Now what?

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Towards more realistic images

• So now we have an image. It still doesnt look
  real.
• A major problem is surface detail. Now what?
• Add more polygons or primitives.

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Towards more realistic images

• So now we have an image. It still doesnt look
  real.
• A major problem is surface detail. Now what?
• Add more polygons or primitives. (slow!)

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Towards more realistic images

• So now we have an image. It still doesnt look
  real.
• A major problem is surface detail. Now what?
• Add more polygons or primitives. (slow!)
• Add detail with a texture!

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Towards more realistic images
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Towards more realistic images
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The Algorithm

• Mapping 2D (texture) image to a 3D object.
• Set up texture coordinates (u,v).
• Usually scaled to be 0.0 .. 1.0.
• Specify a texture location (texel).
• Each point on surface of the object (x,y,z) is
  mapped to a point in texture space (u,v).

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Texture Mapping
(x, y, z)
(u, v)
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The Simple Case
Pixels
Texels
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The Simple Case
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Problems

• Tiling the area of the texture is smaller than
  the area to be textured.
• Scaling an object pixel is bigger (smaller)
  than a texel.
• When do we do the interpolation?
• How do we map a flat image (texture) onto a 3D
  surface (sphere, cylinder)?
• Animation.

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Tiling
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Tiling
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Sampling

• Problems arise when there is a mis-match between
  the size of a pixel and the size of a texel.
• Much confusion in terminology authors are often
  inconsistent and sometimes just plain wrong.

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Over/Under Sampling

• Two situations can arise
• One pixel maps to several (many) texels
  (under-sampling).
• Several (many) pixels map to one texel
  (over-sampling).

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Under-sampling
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The Texture
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Under-sampling
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Under-sampling
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Over-sampling
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Over-sampling
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Interpolation

• Perspective projection is a non-linear
  transformation.
• Makes a big difference whether we interpolate
  before or after.
• For correct results, interpolate before
  perspective projection.

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Interpolation
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Interpolation
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Mapping onto a Sphere
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Next Lecture
Anti-Aliasing