Glossary
DPI (dots per inch)
DPI is printing resolution. For QR codes it matters because each module must be rendered from a whole number of printer dots: 300 dpi is the practical minimum, and generating from vector rather than raster avoids the problem entirely.
The arithmetic
At 300 dpi, one dot is 0.085 mm. A 0.5 mm module is about 6 dots, comfortably resolvable. At 150 dpi it is 3 dots, and rounding errors start shifting module boundaries.
Why vector is better
An SVG has no resolution: the RIP renders each module at the output device's native resolution with exact edges. A raster PNG scaled up to fit a poster interpolates, softening every boundary, and soft boundaries are precisely what a decoder's thresholding step struggles with.
Always send SVG or PDF to a printer. Use PNG only when the destination cannot take vector.
If you must use raster
Generate at final size × target dpi, and never scale up. For a 5 cm code at 300 dpi that is 591 px. Turn off any smoothing or resampling in the layout tool.
Related
- Contrast ratio, Contrast ratio is the luminance difference between a QR code's dark and light modules. Decoders need a clear threshold; the practical floor is about 40%…
- Vector graphic, A vector graphic describes shapes mathematically rather than as a grid of pixels, so it can be scaled to any size without loss. For QR codes it is the…
- SVG, SVG is a vector image format, and the right one for QR codes. Because the pattern is described as shapes rather than pixels, it prints crisply at any size…