A guest cannot scan the code

The margin, first every time

A camera finds a code by its edges, and it needs empty space to see them. A code trimmed flush to a border, or set right against a photograph, gives it nothing to lock onto. The band should be about 4 of the code s own small squares wide on all 4 sides.

Our sign templates include this band already. A design laid out by hand is where it goes missing.

1. Look at the margin. The code needs an empty band around it, roughly 4 of its own squares wide.
2. Measure the width. About 5 cm for arm s length. Roughly a tenth of the scanning distance beyond that.
3. Offer the link instead. Read out the address or send it in the group chat. It leads to the same page.

Too small for the distance

A code that scans on your desk can fail on a wall. The width has to grow with the distance — roughly a tenth of it — so a sign people read from 2 metres away wants about 20 cm, not the 5 cm that works on a table card.

A guest holding a phone in a dim room also holds it less steadily, which costs a little more size again.

Rounding up costs paper. Rounding down costs the contribution, because nobody tries a second time.

Contrast, not colour

A camera reads light against dark. A mid-tone code on a mid-tone background can look elegant on a screen and be unreadable on card, and a code laid over a busy photograph is the same problem with extra noise. Keep whatever sits behind the code plain and far from it in tone.

A light code on a dark field works, but only when it was exported that way rather than inverted afterwards.

The light in the room

Gloss card under a spotlight throws the light straight back, and the phone sees a white patch where the pattern should be. Candlelight is the opposite problem: too little, and from the wrong angle. Matt card and ordinary room lighting solve both.

If a sign fails only in the evening, this is why. Nothing about the file has changed.

When it is the phone

Some older cameras need the code centred and held still for a moment, and some third-party camera apps do not read codes at all. Ask the guest to use the built-in camera app and to hold the phone 20 to 30 cm away rather than pressing it against the card.

A cracked or greasy lens is worth a mention too. It sounds trivial and it is a real cause.

The fallback that always works

Give them the address. Every sign should carry the web address in plain text underneath the code, and you can send the same link to the group chat in 5 seconds. It reaches the identical page, and it works on a phone whose camera is refusing.

This is also the answer for anyone reading a digital invitation, since a phone cannot scan a code on its own screen.

Preventing all of it

Print 1 sign, stand it where it will stand, and scan it from a borrowed phone at a normal sitting distance, in the light the room will have. That single check catches margin, size, contrast and gloss in 1 go, before you have printed 40 of them.

Do it again the day before if anything about the artwork changed in between.