Value
Lightness differs.
PRINCIPLE 02 · DIFFERENCE
Contrast.
The perceptible degree of difference between visual elements.
Contrast can occur through value, color, scale, shape, texture, direction, type, density, or space. Black against white is only one strong example.
More is not automatically better. The useful amount depends on what must be distinguished, compared, read, or emphasized.
CONTROLLED DEMONSTRATION 01
Difference exists by degree.
Geometry and placement remain fixed. Only the value interval between the two squares changes.
CONTROLLED DEMONSTRATION 02
Difference has more than one dimension.
Each field contains five related units. One unit differs through the named variable only.
Scale
Size differs.
Shape
Contour differs.
Texture
Surface information differs.
Direction
Orientation differs.
CONTROLLED DEMONSTRATION 03
Global range and local edges are different questions.
Both sequences use the same darkest and lightest values. Only the two middle values change.
MANIPULATE · ONE VARIABLE
Change the kind and degree of difference.
The left form stays fixed. Choose one visual variable, then adjust only that variable on the right form.
Current comparison: value differs; the right square is lighter. Control setting 60 of 100.
DISTINCTION · DESIGN / ACCESSIBILITY
A broad design principle is not a compliance score.
Design contrast can involve many variables. WCAG contrast ratio is a specific luminance-based measure applied to particular text and non-text requirements.
DESIGN CONTRAST
Any perceptible visual difference
Value, hue, scale, contour, texture, direction, density, type, or space may establish contrast. Hue difference alone does not guarantee enough luminance contrast for text.
WCAG 2.2 · TEXT
Measured luminance relationship
Level AA requires at least 4.5:1 for normal text and 3:1 for large-scale text, with defined exceptions.
Read W3C Understanding SC 1.4.3WCAG 2.2 · NON-TEXT
Meaningful graphics and controls
A minimum 3:1 contrast is required for specified user-interface components and graphical objects needed to understand content.
Read W3C Understanding SC 1.4.11VOCABULARY
Name the relationship and its scope.
Identify both the variable that differs and where the difference occurs.
- Contrast
- The perceptible degree of difference between visual elements.
- Local contrast
- Difference between neighboring or nearby areas.
- Global contrast
- The range of difference across a whole composition.
- Simultaneous contrast
- A change in how a stimulus appears because of its surrounding context.
- Legibility
- How readily characters or visual signs can be distinguished.
- Contrast ratio
- A calculated comparison of relative luminance used in accessibility criteria.
ANALYZE · LOCAL VALUE CONTRAST
The Denial of Saint Peter
Begin with observable differences. Bright faces, hands, and cloth meet a field that is largely very dark. The strongest local value changes make selected gestures and expressions easier to distinguish without requiring every part of the canvas to be equally different.
- Locate the darkest and lightest visible areas.
- Where are adjacent values most different?
- Which passages remain low-contrast, and how does that affect what is immediately legible?
Rights: the Met identifies the work and image as Public Domain and provides it through Open Access.
View the official Met object recordCHECK UNDERSTANDING
What differs, by how much, and where?
Is black against white the definition of contrast?
No. It is one example of high value contrast. Contrast can occur through many visual variables and at low, moderate, or high degrees.
Do the two local-contrast sequences above have different global value ranges?
No. Their darkest and lightest endpoints match. The central neighboring values create the difference.
Does strong hue contrast guarantee accessible text?
No. Accessibility criteria for text use a calculated relative-luminance contrast ratio; different hues can still be too similar in luminance.
CONNECT