Graphics Reference
In-Depth Information
Curvature
Direct
Relected
Figure 34.2: Three kinds of shadows (left to right): direct shadow, reflected shadow, and
curvature shadow.
lesser degree). But aside from this, a
choice
is made in everything a human does in
creating a picture. The choices all influence what the picture communicates to the
viewer. Sometimes the choices are about
style
—the characteristics of the work
that make it personal, or the work of
that particular person,
or something that
conveys a certain tone or mood in a work—but mostly they're about
abstraction,
a mechanism for representing the essence of an object with no unnecessary detail.
When pictures fall into this second category, they indirectly tell us something
about what matters to our visual systems: Just as when we are telling a story
we try to give pertinent details and leave out the irrelevant, in making a picture
there's good reason to omit the things that have less impact, or might have large
impact but are not what's important. Thus, various simplified picture-making tech-
niques reveal to us something about perception: People often communicate shape
by drawing outlines or contours, suggesting that these are important cues about
shape. They sometimes draw stick figures, suggesting that poses may be well
communicated by relatively simple information about bone positions. To indi-
cate relative positions (is he standing on the ground, or in mid-jump above it?),
they sometimes use shadows, although the precise shape of the shadow seems less
important than its presence, as we saw in Chapter 5.
Perceptual relevance is only one influence in expressive rendering. The most
important is abstraction, the removal of irrelevant information and the consequent
emphasis of what is important (to the creator of the image). There are three kinds
of abstraction to consider in expressive rendering [BTT07].
• Simplification: The removal of redundant detail, such as drawing only a
few bricks in a brick wall, or the largest wrinkles in a wrinkled shirt that's
far from the viewer.
• Factorization: Separating the generic from the specific. In drawing a picture
of a short-tailed Manx cat, you can either draw a
particular
cat or you
can draw a generic cat—one that's recognizable as a Manx, but not as a
particular one. In this case, you have factored out the identity of the cat
from its type.
• Schematization: Representing something with a carefully chosen substitute
that may bear little relation to the original, as in the schematic representa-
tion of a transistor in an electrical circuit (Figure 34.3) or a stick-figure
drawing of a human.
Figure 34.3: The schematic
representation of a transistor
encodes function and the fact
that there are three conductors,
but little else.
As Scott McCloud [McC94] observes, “By stripping down an image to its
essential 'meaning,' an artist can
amplify
that meaning in a way that realistic art
can't
.... Themore cartoony a face is, for instance, the more people it could be
said to
describe
.”
Research in expressive rendering is relatively new. Many early papers con-
centrated on emulating traditional media—pen-and-ink, watercolor, stained glass,
mosaic tiles, etc. Some of the pictures produced were rather surprising, when
