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In which of the following shading models of polygons, the interpolation of intensity values is done along the scan line?

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1. Shading “ Shading is referred as the implementation of illumination model at the pixel points or polygon surfaces of the graphics objects .”
2. Gouraud shading removes the intensity discontinuities associated with the constant-shading model, but it has some other deficiencies. Highlights on the surface are sometimes displayed with anomalous shapes, and the linear intensity interpolation can cause bright or dark intensity streaks, called Mach bands, to appear </li></ul><ul><li>on the surface.
by Active (4.9k points)
The gouraud shading computes the intensity calculations down and then across each scan lines thus eliminating the sharp edges.

Phong shading is one of the most useful shading algorithms in computer generated images as it provides high degree of practicality. It is slowest but provides best quality of images. The first stage in the process is the same as for the Gouraud Shading - for any polygon we evaluate the vertex normals [9]. For each scan line in the polygon we evaluate by linear interpolation the normal vectors at the end of each line. These two vectors Na and Nb are then used to interpolate Ns . We thus derive a normal vector for each point or pixel on the polygon that is an approximation to the real normal on the curved surface approximated by the polygon. Ns, the interpolated normal vector, is then used in the intensity calculation. The vector interpolation tends to restore the curvature of the original surface that has been approximated by a polygon mesh. Phong shading species how to calculate color on every point of surface. But calculating of color at every point may be slow therefore phong shading employs calculating intensities at vertices only and then apply interpolation to calculate in between points(between pixels) [7]. The algorithm is as follows: 1) Compute a normal N for each vertex of the polygon. 2) From bi-linear interpolation compute a normal, Ni for each pixel. 3) From Ni compute intensity Ii for each pixel of the polygon. 4) Paint pixel to shade corresponding to Ii.

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Gouraud shading extends the concept of interpolated shading applied to individual polygons by interpolating polygon vertex illumination values that take into account the surface being approximated. The Gouraud shading process requires that the normal {perpendicular vector} be known for each vertex of the polygonal mesh. Gouraud was able to compute these 'vertex normals' directly from an analytical description of the surface. Alternatively, if the vertex normals are not stored with the mesh and cannot be determined directly from the actual surface, then, Gouraud suggested, we can approximate them by averaging the surface normals of all polygonal facets sharing each vertex . If an edge is meant to be visible (as at the joint between a plane's wing and body), then we find two vertex normals, one for each side of the edge, by averaging the normals of polygons on each side of the edge separately. Normals were not averaged across the teapot's patch cracks in Color Plate

The next step in Gouraud shading is to find 'vertex intensities' by using the vertex normals with any desired illumination model. Finally, each polygon is shaded by linear interpolation of vertex intensities along each edge and then between edges along each scan line in the same way that we describe interpolating z values . The term 'Gouraud shading' is often generalized to refer to intensity interpolation shading of even a single polygon in isolation, or to the interpolation of arbitrary colors associated with polygon vertices {as is the case in computer games}.

The interpolation along edges can easily be integrated with the scan-line visible-surface algorithm . With each edge, we store for each color component {red, green and blue} the starting intensity and the change of intensity for each unit change in y. A visible span on a scan line is filled in by interpolating the intensity values of the two edges bounding the span. As in all linear-interpolation algorithms, a difference equation may be used for increased efficiency.

by Active (3.9k points)
option A )

u can refer to this link

by (281 points)