Graphics Reference
In-Depth Information
III
Coalescence of
Geometry-Based and
Image-Based Approaches
The development of high dynamic range image-based methods has allowed pho-
tographs to be integrated into the traditional rendering pipeline as physically ac-
curate sources of lighting. This has accelerated the coalescence of traditional
rendering techniques (geometry-based approaches) and rendering techniques us-
ing photographs (image-based approaches).
One of the most significant aspects of this coalescence lies in the combination
of geometry-based and image-based approaches to problems that are difficult or
impossible to solve using either approach separately. Accurate rendering of real-
world materials is a representative example. Geometry-based approaches render
materials using mathematical approximations to the interaction of light with the
environment. Highly accurate rendering, however, requires high computational
cost. In contrast, rendering with photographic data captured from real objects can
represent appearance characteristics that are extremely difficult to reproduce us-
ing only geometric models and mathematical simulation. A drawback, though, is
that image-based approaches are often limited in terms of reproducing appearance
under arbitrary lighting conditions and viewing directions. In many applications,
such as movie production, limitations of this nature are not acceptable. An opti-
mal combination of the two approaches is, of course, the ideal.
While geometry-based approaches are gradually moving from software to
graphics hardware, which often allows for rendering at interactive rates, modern
hardware is not advanced enough for all rendering tasks. Employing image-based
methods is one way of speeding up software rendering; when these approaches
can be modified to work in hardware, the speed improvement can be quite signif-
icant.
Geometry-based and image-based approaches have also coalesced for the
task of interactive synthesis of realistic rendering of human beings, particularly
of facial expressions.
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