Hack 22. Depth Matters
Our perception of a 3D world draws on multiple depth cues as diverse as atmospheric haze and preconceptions of object size. We use all together in vision and individually in visual design and real life.
Our ability to see depth is an amazing feature of our vision. Not only does depth make what we see more interesting, it also plays a crucial, functional role. We use it to navigate our 3D world and can employ it in the practice of visual communication design to help organize what we see through depth’s ability to clarify through separation1.
Psychologists call a visual trigger that gives us a sense of depth a depth cue. Vision science suggests that our sense of depth originates from at least 19 identifiable cues in our environment. We rarely see depth cues individually, since they mostly appear and operate in concert to provide depth information, but we can loosely organize them together into several related groups:
Binocular cues (stereoscopic depth, eye convergence)
With binocular (two-eye) vision, the brain sees depth by comparing angle differences in the images from each eye. This type of vision is very important to daily life (just try catching a ball with one eye closed), but there are also many monocular (single-eye) depth cues. Monocular cues have the advantage that they are easier to employ for depth in images on flat surfaces (e.g., in print and on computer screens).
Perspective-based cues (size gradient, texture gradient, linear perspective)
The shape of a visual scene gives cues to the depth of objects within it. Perspective lines converging/diverging or a change in the image size of patterns that we know to be at a constant scale (such as floor tile squares) can be used to inform our sense of depth.
Occlusion-based cues (object overlap, cast shadow, surface shadow)
The presence of one object partially blocking the form of another and the cast shadows they create are strong cues to depth. See [Hack #20] for examples.
Focus-based cues (atmospheric perspective, object intensity, focu
Greater distance usually brings with it a number of depth cues associated with conditions of the natural world, such as increased atmospheric haze and physical limits to the eye’s focus range. We discuss one of these cues, object intensity, next.
Motion-based cues (kinetic depth, a.k.a. motion parallax)
As you move your head, objects at different distances move at different relative speeds. This is a very strong cue and is also the reason a spitting cobra sways its head from side to side to work out how far away its prey is from its position.
There isn’t room to discuss all of these cues here, so we’ll look in detail at just two depth cues: object intensity and known size (a cue that is loosely connected to the prespective-based cue family). More information on depth cues and their use in information design can be found in the references at the end of this hack.
2.11.1. Object Intensity
Why do objects further away from us appear to be faded or faint? Ever notice that bright objects seem to attract our attention? It’s all about intensity.
If we peer into the distance, we notice that objects such as buildings or mountains far away appear less distinct and often faded compared to objects close up. Even the colors of these distant objects appear lighter or even washed out. The reason for this is something psychologists call atmospheric perspective or object intensity. It is a visual cue our minds use to sense depth; we employ it automatically as a way to sort and prioritize information about our surroundings (foreground as distinct from background).
Designers take advantage of this phenomenon to direct our attention by using bold colors and contrast in design work. Road safety specialists make traffic safety signs brighter and bolder in contrast than other highway signs so they stand out, as shown in Figure 2-14. You too, in fact, employ the same principle when you use a highlighter to mark passages in a book. You’re using a depth cue to literally bring certain text into the foreground, to prioritize information in your environment.
Figure 2-14. Important street signs often use more intense colors and bolder contrast elements so they stand out from other signage2
Taken From : Mind Hacks
