Graphics Reference
In-Depth Information
3
Volume Rendering and
Participating Media
3.1 Volume Visualization Techniques
3.1.1 Volumes: The General Idea
Photorealistic rendering is concernedwith generating synthetic images that mimic
how a scene would look if it were actually constructed and photographed. Com-
puter graphics originated in the more humble problem of simply drawing pictures
with a computer. As 3D rendering developed, primarily in the 1970s, it became
apparent that computer-generated images lacked a certain realism. Indirect light-
ing was identified as a missing element, and beginning in the 1980s this drove
research into global illumination methods.
Photorealism is not always the goal of computer-generated images. The way
we view things depends on the purpose of viewing them. In medical imaging, for
example, a photorealistic rendering of the human body is not particularly useful to
doctors—they can get that by just looking at the patient! What is needed instead
is a way to view the internal organs, layers of tissue, and dynamic elements such
as blood flow. Modeling the surfaces and light reflection is not enough to display
internal structures of normally opaque objects.
Surface reflection alone does not capture all light interaction within an en-
vironment. The basic rendering methods described in the previous chapter all
assume that light rays travel through space without interference. This assumption
is not always valid. Airborne particles such as smoke, pollution, and even water
molecules interfere with the propagation of light. The sky gets bright well before
sunrise due to scattering, and another form of scattering causes the daytime sky to
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