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Shading Models

Shading Models. Every pixel interior to the polygon is assigned the same intensity. The normal at a point on the polygon is the normal of the plane determined by the polygon. (Use cross product of edge vectors to compute normal.)

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Shading Models

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  1. Shading Models

  2. Every pixel interior to the polygon is assigned the same intensity. The normal at a point on the polygon is the normal of the plane determined by the polygon. (Use cross product of edge vectors to compute normal.) •Fast and simple, uses standard polygon fill provided by most frame buffers •Shading of a polygon independent of shade of adjacent polygons •Gives object a faceted appearance Flat Shading

  3. 3. Use linear interpolation along a polygon edge to compute the intensity at each edge pixel. 4. Use linear interpolation along a scan line to compute the intensity at each interior pixel of a polygon. Gouraud Shading 1. Approximate the normal to the surface at a vertex by averaging all normals of abutting polygons. 2. Calculate the intensity at each vertex using illumination equations. DA = (bD1 + aD4)/(a+b)

  4. Phong Shading 1. Approximate the normal to the surface at a vertex by averaging all normals of abutting polygons. 2. Interpolate normals along the edge between two vertex points.

  5. Flat Shading Pro: Simple and fast Con: Flat appears and polygon sections looks discontinuous. Gourand Shading Pro: Polygon section looks continuous. Con: May miss specular reflections. Phong Shanding Pro: Keeps specular reflections Con: High complexity because illumination is compute at every pixel. Pros and Cons

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