Graphics Reference
In-Depth Information
Figure 34.23: Photo editing with gradient-domain painting. The roof tiles and drain pipe
have been altered, and the left wall eliminated, all in just a few strokes. (Photo courtesy of
Christopher Tobias, ©2009; Courtesy of Nancy Pollard and James McCann, ©2008 ACM,
Inc. Reprinted by permission.)
In both of these media, animation is quite natural. As strokes interpolate
between specified positions at key frames, the global solutions for which they pre-
scribe boundary conditions also change smoothly. Temporal coherence is almost
automatic. The exception is in handling the appearance and disappearance of
strokes, which still must be addressed. Nonetheless, the global effect of each
stroke means that animation in one portion of an image can generate changes else-
where, which may distract the viewer. By the way, temporal coherence in stylized
strokes—things like wiggly lines in pen-and-ink renderings—remains a serious
challenge as of 2013.
Video games are now often using deliberately nonphotorealistic techniques
to establish mood or style, but maintaining a consistent feel throughout a game
requires high-level art direction as well as an expressive rendering tool. There's a
need for tools to assist in such art direction, and for authoring tools for scenes to
be nonphotorealistically rendered so that modelers can indicate objects' relative
importance (and how these change over time) as cues to simplification algorithms.
Tools like gradient-domain painting and diffusion curves let artists work
with what might be called “perceptual primitives,” but at the cost of global
modifications of images, which may be inconvenient. It would be nice to find
semilocal versions of these tools, ones whose range of influence can be conve-
niently bounded.
Figure 34.24: A figure drawn
with just a few diffusion curves.
(©L. Boissieux, INRIA) (Cour-
tesy of Joelle Thollot.)
 
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