Graphics Reference
In-Depth Information
Figure 14.2: A map contains less information and detail than a satellite photograph, but
presents its information in a way that better communicates the salient elements to a human
viewer. This is evidence that capturing many aspects of reality is not always the most effec-
tive way to model a scene. (Credit: © 2012 Google - Map data © 2012 Cnes/Spot Image,
DigitalGlobe, GeoEye, MassGIS, Commonwealth of Massachusetts EOEA, New York GIS,
USDA Farm Service Agency)
communicate their ideas. This kind of image quality is beyond objective measure-
ment, which is one of the reasons that designing a graphics system is a subjective
art as well as an engineering exercise.
Space and time efficiency and implementation complexity go beyond math-
ematical modeling and into implementation. We seek to actually implement the
algorithms that we design and apply them to real problems. For real-time interac-
tive rendering, efficiency is paramount. A low-quality animation that is interactive
almost always leads to a better experience in a virtual world than a high-quality
one with limited or high-latency interaction. The accessibility and viability of a
system in the market is driven by price. The computational and memory require-
ments, and developer-time costs to build a system, must be balanced against the
quality of the images produced.
We can draw some lessons by considering measurements of image quality.
Advances in graphics have largely focused on space and time efficiency and
physical image quality, even though we claim that perceptual quality, fidelity
to the designer's vision, and implementation complexity are also important fac-
tors. This is likely because efficiency and physical quality are more amenable
to objective measurement. They aren't necessarily easier to optimize for, but
the objective measurements allow quantitative optimization. So the first lesson
is that if you want something to improve, find an objective way to quantify it.
Today's physical image quality is very high, and within some limits we can also
achieve very good perceptual image quality. Feature films regularly contain com-
pletely computer-generated images that are indistinguishable from photographs,
and even low-power mobile devices feature interactive 3D graphics. The second
lesson is to make sure that you optimized for what you really wanted. (This is
an instance of the Know Your Problem principle from Chapter 1!) Despite the
many advances in image quality, the process of modeling, animating, and ren-
dering scenes using either tools or code has not advanced as far as one might
