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Compare Gouraud and Phong shading

Short answer

Gouraud shading interpolates vertex intensities, while Phong shading interpolates normals and computes illumination per pixel. Phong correctly captures specular highlights inside polygons, reduces Mach bands, and gives more realistic results for shiny surfaces, but is slower. Gouraud is faster but may miss highlights and show Mach bands.

Compare and contrast Gouraud shading and Phong shading (mention the advantages of Phong shading over Gouraud shading).

Both are polygon-rendering (smooth shading) methods that remove the faceted look of a polygon mesh.

  • Gouraud shading computes the illumination at the polygon vertices and interpolates the intensity linearly across the polygon.
  • Phong shading interpolates the normal vectors across the polygon and computes the illumination at every pixel.
PointGouraud shadingPhong shading
Quantity interpolatedIntensity (colour)Surface normal
Illumination model appliedAt vertices onlyAt every pixel
ComputationLess, fastMore, slow
Specular highlightsMissed or distorted, especially inside a polygonRendered correctly
Mach-band effectPresent (intensity changes slope at edges)Greatly reduced
Image qualityGoodBetter, more realistic
Memory/timeLowHigh
HardwareCommon, easyNeeds more powerful hardware
Also calledIntensity-interpolationNormal-vector interpolation

Advantages of Phong over Gouraud

  1. Highlights are correct, even if they fall inside a polygon (Gouraud may miss them).
  2. Smoother shading and far fewer Mach bands.
  3. More accurate for shiny (high specular) surfaces.
  4. Better results with fewer polygons.

The extra cost is its disadvantage; Gouraud is preferred when speed matters.

✓ Answer checked by Claude Opus 5.5 (high effort)

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