Visually Conveying Volume
From “How We Perceive Surfaces¨ from Light for Visual Artists
A basic volume can be described very simply. […] we can read […] a volume in space with a distinct surface. The planes of the cube help to give a sense of depth and of space.
This is to say, the existence of distinct surfaces can allow us to infer or intuit the rotational position of a solid in space (Yot 2020, 65). This is because any given geometric plane has deformed versions that suggest optical perspective shifts, although these optical perspective shifts are only more decisively inferred for surfaces, sole or joint, that in three-dimensional space have some kind of geometric transformational asymmetry when projected onto, or sliced by, a two-dimensional space. That is, for a solid made of distinct surfaces, the planar counterpart of a solid tends to vary along with its own rotational transformation.
For example, provided a fixed light upon it, a sphere as opposed to a cube may not have any perceptible rotational change due to the symmetry its two-dimensional slice or projection has as it is rotated. The circular shape is invariant on the two-dimensional projection or slice, i.e. the planar counterpart of this particular solid does not vary along with its own rotational transformation. Hence (Ibid):
From “How We Perceive Surfaces¨ from Light for Visual Artists
[…] replaced by a sphere […] it is now much harder to interpret the sense of three-dimensional space because the form no longer has definite planes with which we can anchor it visually in the scene. It still looks solid, but it is a little more difficult to gauge in terms of its position in space.
However, there is one benefit to a sphere over a cube, and that is that when light hits it, the gradual progression of the increase in shade, or decrease in light, upon its surface and the blocked surface of an adjacent solid makes the origin of the light source easy to infer (Ibid):
From “How We Perceive Surfaces¨ from Light for Visual Artists
[…] the rounded form has given us a much clearer indication of where exactly the light is coming from, since we can see the transition into shadow on the surface of the sphere, […]
For something with distinct surfaces, like a cube, this can be harder to infer as shade differences are starker while sides and corners are the most reflective, ceterus paribus.
Summary
Sharply distinguished higher number of planes are important for making degree of rotation in space for a form explicit in a drawing, while curvaceous, indistinct lower number of planes allow for greater expressed gradation and more independent shape for shades and shadow depicted in a drawing. The latter case makes it easier to infer the light source for the form being conveyed. Nonetheless, in both cases it is shading or shadow that convey volume insofar as it is all that is necessary to express edges and planes.
cognitive_science cognitive_psychology perception visual_perception gestalt_psychology psychology psychology_of_art psychology_of_space deformation geometric_deformation transformation geometric_transformation geometry optics invariance surface two-dimensionality three-dimensionality dimensionality dimension dimensions stereometry rotation light_source volumes shade shadows edge plane social_science
bibliography
- “How We Perceive Surfaces.” In Light for Visual Artists: Understanding and Using Light in Art & Design, 2nd ed., by Richard Yot. Laurence King Publishing, 2020.