Scan Reliability
How contrast, quiet zone, logo size and error-correction level (L, M, Q, H) affect whether a printed QR code scans cleanly.
A QR code can fail to scan for reasons that have nothing to do with the data inside it - low contrast, a missing quiet zone, a logo that covers too much of the pattern, or printing it too small. UNI-QR's error-correction setting and built-in scan test both help, but good contrast and sizing still matter most.
Error correction levels
QR codes can rebuild a portion of their data even when part of the printed code is damaged, dirty or covered by a logo. UNI-QR offers the four standard levels, labeled with their approximate recovery capacity directly in the app:
| Level | Approx. damage it tolerates | When to use it |
|---|---|---|
| L | about 7% | Clean digital use, no logo, maximum space for data |
| M | about 15% | General printed use with no logo (UNI-QR's default) |
| Q | about 25% | A small logo, or printing somewhere it might get a little worn |
| H | about 30% | A larger logo, or codes on stickers, packaging or outdoor signage |
Higher levels survive more damage and a bigger logo, but they also add more data modules, making the pattern denser - so only raise the level as far as you actually need.
Contrast and color
Scanners rely on a strong difference between the dot color and the background. Dark dots on a light background (UNI-QR's own default) is the safest combination; if you use a theme or custom colors with lower contrast, always run the scan test and try a real phone before printing in bulk, and be extra cautious with a transparent background placed over a busy photo.
Quiet zone and logo size
Keep a visible blank margin around the code (see Download Formats and Printing) and keep an added logo modest in size relative to the whole code. A bigger logo needs a higher error-correction level to compensate, and at some point even H-level correction cannot make up for a logo that covers too much of the pattern.
UNI-QR's built-in scan test, and testing for real
After every design change, UNI-QR shows a "Scan test passed" badge - it automatically decodes the code it just generated and confirms the result still matches what you entered. That catches encoding problems instantly, but it cannot tell you how the code will look printed on paper, laminated, under shop lighting or on a small phone screen. Several of UNI-QR's own payment and WiFi pages recommend scanning the final printed or displayed code with two or three different phones before relying on it - that step is worth doing for any code you plan to print in quantity.
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