# QR code colour inversion and polarity

> The QR specification assumes dark modules on a light background, and nothing in the symbol declares its polarity. Reading an inverted, light-on-dark code is a decoder heuristic — ZXing exposes an explicit try-invert option and modern phone cameras usually cope, but plenty of scanners still fail. Print dark-on-light unless you can test every scanner.

Source: https://useqr.app/docs/spec/qr-code-color-inversion-and-polarity · Last reviewed 2026-08-21 · UseQR is free forever, MIT licensed, no signup.

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## What the specification actually says

ISO/IEC 18004 defines a QR symbol in terms of **dark modules on a light background** — the
nominal form every conformant encoder produces and every conformant decoder must read.
"Dark" and "light" are reflectance roles, not specific colours: navy on cream is fine, as
long as the modules reflect less light than the background by a healthy margin (the working
rule is a **luminance difference of at least 40%**, covered on
[QR colours that scan](/docs/design/qr-code-colors-that-scan)).

The crucial detail: **nothing inside the symbol records its polarity**. There is no flag in
the [format information](/docs/spec/format-information) saying "this one is inverted". A
light-on-dark code is, from the standard's viewpoint, simply a photographic negative of a
QR code — not an alternate valid form of one.

## Inverted reading is a decoder heuristic

Because polarity is not signalled, a decoder that reads inverted codes does so by
guessing: it fails to find finder patterns in the normal polarity, inverts the image, and
tries again. Support is therefore a property of the *scanner*, not the code:

- **ZXing**, the most widely embedded open-source decoder, treats inversion as an explicit
  option (`tryInvert` in current zxing-wasm builds) — hosts that leave it off simply do
  not read inverted codes.
- **Recent iOS and Android cameras** generally handle inversion in practice.
- **Embedded scanners** — payment terminals, access-control readers, warehouse guns,
  kiosk webcam software — are the long tail where inverted reads most often fail, because
  they run one decode pass, tuned for the nominal form, on limited hardware.

That asymmetry is the trap: an inverted code passes the designer's own phone test and then
fails quietly in the field on scanners nobody thought to try. You will not get a crisp
failure rate for "the field" — it depends entirely on which devices your audience carries —
which is itself the argument: you cannot bound the loss, only avoid it.

## The rule, and the escape hatches

**Print dark modules on the lighter colour.** On a dark background, the standard-compliant
move is not to invert the modules but to give the code its own light panel: a white or
pale rounded rectangle behind the full symbol, including the four-module
[quiet zone](/glossary/quiet-zone), with the dark modules on top. The design patterns for
dark layouts — including [dark-mode websites](/docs/design/qr-code-in-a-dark-mode-website) —
are on [inverted QR codes](/docs/design/inverted-qr-codes) and
[why light-on-dark QR codes fail](/docs/design/why-light-on-dark-qr-codes-fail).

Note that the quiet zone's polarity must match the background role: a dark-on-light code
needs a *light* quiet zone. Inverting the modules but leaving a white margin — a common
half-inversion from design tools — fails both polarities at once.

If you have inherited an inverted code that will not read, the recovery steps are on
[QR code inverted and unreadable](/docs/troubleshooting/qr-code-inverted-and-unreadable).
And whichever way you go, [/validate](/validate) reads your rendered artwork back with a
real decoder — the only polarity opinion that counts.

## FAQ

### Can a QR code be white on black?
Sometimes — many modern phone cameras invert the image and retry — but support is a per-scanner heuristic, not part of the standard, and embedded scanners frequently fail. If you cannot test every scanner your audience uses, keep dark modules on a light background.

### Why does my inverted QR code scan on iPhone but not on other devices?
Recent phone cameras retry the decode on an inverted copy of the image; many other decoders run a single pass expecting dark-on-light and give up. The code did not change between devices — the guessing strategy did.

### Does a QR code store whether it is inverted?
No. The format information records error correction level and mask pattern only; there is no polarity flag anywhere in the symbol. An inverted code is just a negative image, which a decoder may or may not think to try.

### How do I put a QR code on a dark design without inverting it?
Give the code a light panel — white or a pale brand tint — covering the full symbol plus its four-module quiet zone, and print normal dark modules on that. It reads on effectively every scanner and still sits comfortably in a dark layout.

## Try it

- https://useqr.app/url
- https://useqr.app/validate
- https://useqr.app/scan