contrast

Contrast is a difference between elements that makes them distinguishable. In perception, contrast arises when two or more properties—such as brightness, color, size, shape, or texture—differ, allowing the observer to separate objects from their surroundings and from one another. The concept is central across disciplines, from visual arts to data analysis, and can be intentional or emerge from lighting and context.

Visual contrast is described in terms of luminance and color. Luminance contrast compares the brightness of two areas and is often expressed as a contrast ratio. The ratio is defined as (L1 + 0.05) / (L2 + 0.05), with L1 the higher luminance and L2 the lower. Standards such as WCAG use thresholds like 4.5:1 for normal text to support readability; higher ratios improve legibility for many viewers. Color contrast also depends on hue, saturation, and context, and low contrast can hinder perception even when brightness differences exist.

In art and design, contrast creates emphasis, organizes information, and conveys mood. Pairing light with dark, opposing hues, or varying texture and scale helps guide attention and improve legibility. In linguistics, contrast denotes a systematic difference in meaning between linguistic units, such as phoneme contrasts (p vs. b) or semantic opposites (hot vs. cold), enabling speakers to distinguish words and expressions.

Other uses include medicine and imaging, where contrast agents enhance visibility in radiography and MRI, and statistics, where a contrast is a linear combination of group means used to test hypotheses in analysis of variance.