Image Processing Reference
In-Depth Information
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Fig. 7.8. Reflectance model for shading: ( a ) Diffuse reflection; ( b ) specular reflection
(smooth surface); ( c ) specular reflection (uneven surface).
To do this we first assume a virtual light source in the above virtual 3D
space and consider light and darkness of a surface by this virtual light source.
Brightness at each point P on the surface determined by this light source
is calculated using a suitable model of reflection by surface. This value of
brightness depends on both the position of the point P on the surface and
the position of the viewpoint set in 3D virtual space. The brightness value of
the point P on an image plane, which is a projection of a point P onto an
image plane H P , is determined by giving the above brightness value of P to P .
That is, the density value at a point P on an image plane H P (= a 2D image
rendered on H P ) is equal to the brightness value of P in 3D space when it was
observed from the direction connecting P and the viewpoint. Using physical
analogy, the amount of the brightness at a point P on an image plane H P
is considered to be the amount of energy radiated from a point P toward the
viewpoint passing through a point P .
7.6.1 Calculation of the brightness of a surface
Properties concerning the reflectance of a surface are suitably assumed. The
following examples are adopted frequently (Fig. 7.8).
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