Depth perception is the ability to perceive objects three-dimensionally. It relies on two types of cues: binocular and monocular. Binocular cues depend on the combination of images from both eyes and how the eyes work together. Since the eyes are in slightly different positions, each eye captures a slightly different image. This disparity between images, known as binocular disparity, helps the brain interpret depth. When the brain compares these images, it determines the distance to an object. If the images are very different, the object is close; if they are similar, the object is far away. Another binocular cue is convergence, which refers to the inward rotation of the eyes to focus on an object. The closer the object, the greater the convergence, much like crossing the eyes.
Monocular cues, also known as pictorial depth cues, provide depth information using just one eye. Artists use these cues to create the illusion of depth in two-dimensional artworks. Linear perspective is a monocular cue where parallel lines appear to converge in the distance, as seen when looking down a long highway. This convergence suggests that the lines extend far away from the viewer. Relative size is another cue, where objects expected to be of a certain size appear smaller when they are farther away. This principle is often used in filmmaking to create the illusion of distant large objects using small models. Overlap, or interposition, occurs when one object blocks part of another, indicating that the blocked object is behind. This means that the blocked object is farther away.
Aerial perspective, also known as atmospheric perspective, describes how distant objects appear hazier due to particles in the air. This effect makes distant mountains look fuzzy and distant buildings appear blurrier than closer ones. Texture gradient is a cue where the texture of objects becomes finer and less distinct as they recede into the distance. For example, pebbles or cobblestones look detailed up close but appear less textured as they move farther away. Motion parallax is observed when objects near a moving viewer, such as those seen from a car window, seem to move quickly, while distant objects appear to move slowly. This discrepancy in the motion of near and far objects provides depth information.
Accommodation is a monocular cue that involves changes within the eye itself. The eye's lens adjusts its shape to focus on objects at different distances. This process, known as visual accommodation, provides the brain with information about the distance of objects based on the degree of adjustment required. This cue, also referred to as a "muscular cue," relies on the eye's internal adjustments to aid in-depth perception. By integrating both binocular and monocular cues, the brain constructs a three-dimensional understanding of the environment, allowing for accurate depth perception.
