Page 191 - DCAP504_Computer Graphics

Computer Graphics

each row of pixels can be displayed by horizontally interpolating the RGB values between left and right
edges of that row. This often results in a remarkably smooth-shaded polygon.
Gouraud shading calculates the illumination formula at the vertices of the polygon mesh. We then
estimate the obtained color components to get complete shading of the polygon.
The figure 12.8 depicts the calculation of the illumination formula at each vertices of the polygon and
then the interpolation of the obtained color components to get complete shading of the polygon.

Figure 12.8: Calculation of Illumination Formula using
Gouraud Shading

When the illumination formula is calculated at the vertices A, B, and C, interpolation can be done as
follows:
aA=PBC/ABC
aB=APC/ABC
aC=ABP/ABC
aA+aB+aC=1

P=aAA+aBB+aCC

Bilinear interpolation can be used to find the color of point E inside a triangle
whose vertices are E1, E2, and E3 as shown in figure 12.9. The scan line
containing E intersects the two edges at points E' and E". We estimate the color
of E1, and the color of E2 to get the color of P'. We then estimate the color of E2
and the color of E3, to get the color of P". Finally, we estimate the color of E' and
the color of E" to get the color of E.

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