Contrast Ratio

Contrast ratio quantifies the luminance difference between dark QR code modules and the light background. Scanners rely on this brightness difference to determine module presence, so low contrast ratios cause scanning errors.

Black and white provides the highest contrast ratio (21:1) and most reliable scanning. When using brand colors, keep the luminance difference between modules and background at the practical working floor of 4:1 or higher. WCAG's 4.5:1 belongs to a separate domain — humans reading text — and does not guarantee a scan. Avoid low-contrast combinations like pastel-on-pastel or light gray on white.