QR code troubleshooting

Something isn't scanning. Find the cause, in order of likelihood.

• QR code colours not scanningDecoders convert the image to greyscale before deciding dark from light, so what matters is luminance difference, not how different the colours look. Two…
• QR code not scanning: the checklistWork through these in order, because they are ranked by how often they are the actual cause: quiet zone, contrast, size for distance, glare, blur from…
• QR code scans on screen but not in printThree causes account for nearly all of these: the raster image was scaled up in the layout, ink spread on the substrate closed the gaps between modules,…
• QR code too dense to scanA dense code means too many modules for the printed size. The fix is almost always to shorten the payload rather than to enlarge the code or raise error…
• QR code with a logo not scanningA logo works up to roughly 20–25% of the code area at error-correction level H, and only in the centre. Covering a finder pattern, the timing patterns, or…
• WiFi QR code not connectingThe usual causes, in order: an unescaped special character in the password or SSID, a hidden network without the hidden flag, choosing WEP or nopass when…
• QR code opens the wrong link or a 404Decode the code first to see the string it actually contains. If the string is right, the problem is the destination: a deleted page, a retired shortener,…
• vCard QR code imports with missing or wrong fieldsTwo causes cover almost all of these: unescaped commas and semicolons inside a value, which split the field, and a missing FN line, which leaves the…