Gouraud Shading Topics

• adaptive tessellation
• flat shading
• vertex of a polygon
• interpolation method
• lighting model
• polygon models
• lighting effects
• computational requirements
• localized lighting
• glint
• vertices
• polygons
• highlight
• intensity
• pixel
• density
• surfaces
• apple

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Gouraud Shading, Gouraud Shading

In practice, Gouraud shading is used to achieve smooth lighting on low-polygon surfaces without the heavy computational requirements of calculating lighting for each pixel.

However, highly localized lighting effects (such as specular highlights, e.g. the glint of reflected light on the surface of an apple) will not be rendered correctly, and if a highlight lies in the middle of a polygon, but does not spread to the polygon's vertex, it will not be apparent in a Gouraud rendering; conversely, if a highlight occurs at the vertex of a polygon, it will be rendered correctly at this vertex (as this is where the lighting model is applied), but will be spread unnaturally across all neighboring polygons via the interpolation method. The problem is easily spotted in a rendering which ought to have a specular highlight moving smoothly across the surface of a model as it rotates. Gouraud shading will instead produce a highlight continuously fading in and out across neighboring portions of the model, peaking in intensity when the intended specular highlight passes over a vertex of the model. (This can be improved by increasing the density of vertices in the object, or alternatively an adaptive tessellation scheme might be used to increase the density only near the highlight.) Despite the drawbacks, Gouraud shading is considered superior to flat shading, which requires significantly less processing than Gouraud, but gives low-polygon models a sharp, faceted look.

Source: Wikipedia > Gouraud Shading