# Per-corner eye styling: three eyes, three looks

> The three QR eyes can each carry a different shape or colour, because detection checks every finder pattern's 1:1:3:1:1 ratio individually rather than requiring the corners to match. Each corner must independently keep a solid ring, clear light gap and full contrast: replacing an eye's centre with a brand glyph is where per-corner styling breaks.

Source: https://useqr.app/docs/design/per-corner-eye-styling · Last reviewed 2026-08-21 · UseQR is free forever, no signup.

---

## Detection does not compare corners

A scanner finds a QR code by locating three candidate [finder patterns](/glossary/finder-pattern)
and checking each one for the **1:1:3:1:1** dark-light ratio through its centre. It
never checks whether the three look alike. Orientation comes from their *positions*
(three found, one corner empty), not from their shapes matching. So a code with a
rounded top-left eye, a circular top-right and a square bottom-left is, to a decoder,
simply three valid finder patterns. Per-corner styling is legitimate, not a hack.

UseQR's core renderer supports this directly: the `@useqr/core` render options accept
per-corner eye overrides (frame style, ball style, frame colour, ball colour for each
of the three corners), while the web generator's `eye=` and `ball=` parameters apply
one style to all three: see [custom eye shapes](/docs/design/custom-eye-shapes) for
the five available shapes and their individual risk order.

## The rules apply per corner, three times

Nothing about varying the corners relaxes the constraints. It multiplies them. Each
eye must independently satisfy:

- **A closed, solid dark ring** one module thick around a clear light ring around a
  solid ball, the concentric structure that produces the ratio.
- **Full contrast**: every frame and ball colour passing the
  [40-point luminance rule](/docs/design/qr-code-contrast-ratio-minimum). One
  fashionably pale eye out of three still sinks detection reliability, because many
  decoders want all three before committing.
- **Sane scale**: at [small print sizes](/docs/print/qr-code-size-for-print), the
  riskier shapes (leaf, diamond) erode first: mixing means your weakest corner sets
  the code's reliability.

A useful discipline: make the *bottom-left* eye the most conservative shape when
mixing, keep colours within the same dark range, and let one corner carry the flair.

## Where per-corner styling actually breaks

The failure is almost never the mixing. It is what people mix *in*:

- **A brand glyph replacing a ball.** A logo mark is not a solid 3 × 3 block; its
  outline breaks the ratio and that corner stops being a finder pattern. If the mark
  must appear, put it in the centre of the code within the
  [logo budget](/docs/design/logo-size-limits-by-error-correction-level), following
  the [logo best practices](/docs/design/qr-code-with-logo-best-practices), never in
  an eye.
- **Ornamental frames that open the ring**: gaps, notches, sparkle cut-outs.
- **Decorating the fourth corner.** The bottom-right corner deliberately has no eye;
  larger codes place [alignment patterns](/glossary/alignment-pattern) in that region.
  Adding a fake fourth eye or ornament there can both damage alignment data and feed
  detectors a false candidate.

Because eye validity is binary, verification is trivially reliable: decode the export
with the [validator](/validate). A per-corner design that decodes has three working
finder patterns; one that does not will fail every time, not intermittently.

## FAQ

### Can each QR code eye be a different shape?

Yes. Scanners validate each finder pattern's dark-light ratio independently and use
their positions, not their similarity, to orient the code. Any mix of valid solid
shapes (square, rounded, circle, leaf, diamond) decodes normally.

### Can the three eyes be different colours?

Yes, provided every frame and ball independently keeps at least a 40-point luminance
difference against the background. The risk of mixed colours is that the lightest eye
becomes the weakest link, so keep all three clearly dark.

### Can I put my logo inside a QR code eye?

No. The eye's centre must be a solid dark block for the detection ratio to exist;
replacing it with a glyph disables that finder pattern. Place logos in the centre of
the code within the error-correction budget instead.

### Why is there no eye in the fourth corner?

Three eyes are how the scanner establishes position and orientation: the empty corner
is information. Larger codes also carry alignment patterns near that region, so adding
decoration there risks both confusing detection and damaging real structure.

## Try it

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