636:, 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.
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In comparison to Phong shading, Gouraud shading's strength and weakness lies in its interpolation. If a mesh covers more pixels in screen space than it has vertices, interpolating colour values from samples of expensive lighting calculations at vertices is less processor intensive than performing the
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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
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in a polygonal 3D model is either specified for each vertex or found by averaging the surface normals of the polygons that meet at each vertex. Using these estimates, lighting computations based on a reflection model, e.g. the
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covered by the triangle. Gouraud first published the technique in 1971. However, enhanced hardware support for superior shading models has yielded
Gouraud shading largely obsolete in modern rendering.
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as a perspective correct alternative to linear interpolation. Both the linear and hyperbolic variants of interpolation of colors from vertices to pixels are commonly called "Gouraud shading".
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Gouraud's original paper described linear color interpolation. In 1992, Blinn published an efficient algorithm for hyperbolic interpolation that is used in
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lighting calculation for each pixel as in Phong shading. However, highly localized lighting effects (such as
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intended specular highlight aligns with a vertex of the model. While this problem can be fixed by
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Gouraud, Henri (1998). "Continuous shading of curved surfaces". In
Rosalee Wolfe (ed.).
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Any linear interpolation of intensity causes derivative discontinuities which triggers
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A Gouraud-shaded sphere-like mesh - note the poor behaviour of the specular highlight.
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of this approach will favour switching to a more detailed shading model.
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that is covered by the polygonal mesh, colour intensities can then be
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Another sphere-like mesh rendered with a very high polygon count
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by computing the lighting at the corners of each triangle and
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Seminal
Graphics: Pioneering efforts that shaped the field
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Gouraud shading works as follows: An estimate to the
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Computer
Display of Curved Surfaces, Doctoral Thesis
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192:. Unsourced material may be challenged and removed.
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624:and requires significantly less processing than
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53:Learn how and when to remove these messages
620:Gouraud shading is considered superior to
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270:Learn how and when to remove this message
252:Learn how and when to remove this message
150:Learn how and when to remove this message
16:Interpolation method in computer graphics
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604:Comparison with other shading techniques
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833:IEEE Computer Graphics and Applications
758:"Continuous shading of curved surfaces"
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495:Gouraud-shaded triangle mesh using the
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86:Please improve this article by adding
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190:adding citations to reliable sources
678:Linear vs. hyperbolic interpolation
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708:List of common shading algorithms
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827:Blinn, James F. (July 1992).
745:(Thesis). University of Utah.
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829:"Hyperbolic Interpolation"
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382:Virtual cinematography
286:Three-dimensional (3D)
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347:Computer-aided design
186:improve this article
646:diminishing returns
634:specular highlights
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372:Virtual engineering
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334:Primary uses
303:Fundamentals
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184:Please help
179:verification
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36:Please help
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575:Description
357:Video games
866:Categories
724:References
696:Mach bands
690:Mach bands
423:3D display
242:March 2012
212:newspapers
110:newspapers
77:references
39:improve it
853:207973430
785:123827991
406:Animation
342:3D models
321:Rendering
45:talk page
702:See also
583:of each
543:, is an
416:skeletal
411:computer
326:Printing
316:Scanning
311:Modeling
872:Shading
553:shading
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233:JSTOR
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117:books
808:ISBN
769:C-20
684:GPUs
533:goo-
205:news
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841:doi
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188:by
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