Grayscale

Grayscale represents images using brightness levels only (256 levels in 8-bit). QR code scanners internally convert camera color images to grayscale, then binarize (convert to black/white) to identify modules. This is why QR codes work in any color - what matters is grayscale contrast, not color itself.

This principle reveals problematic design color combinations. Red and green appear distinct to humans but may have similar grayscale brightness, confusing scanners. Use low-brightness colors for dark modules and high-brightness for light modules, ensuring sufficient post-grayscale contrast.