Version, module count and error correction — the line under the preview

Below the code preview the editor shows a caption such as
V3 · Mask 2 · 29×29 modules · ECC QUARTILE. It surfaces four
related properties of the generated QR code.

Version (V1–V40)

The QR standard defines 40 versions with fixed module counts —
V1 is 21×21, V2 25×25, V3 29×29, … V40 is 177×177. The version
that actually gets used falls out of payload length plus ECC.
By default the encoder picks the smallest fitting version — the
densest module layout, optimal for most applications.

Forcing a minimum version

Sometimes you want a deliberately larger version than the smallest
fit. Two classic pro use-cases:

• Consistent sizing across multiple codes — a print campaign with
  ten QR codes side by side looks unprofessional if every code has a
  different module count (payload lengths usually differ by a few
  characters). Pick the same minimum version for all of them and they
  draw identically.
• Longer scan distance — rule of thumb: scan distance ≈ 10× the
  code's edge length. To scan from 2 m you need ≥ 20 cm of edge.
  At a fixed print size, module count is inversely proportional to
  module size — more modules = smaller modules = harder to scan from
  far away. Pick the minimum version conservatively; the encoder will
  bump higher automatically if the payload doesn't fit.

The editor exposes a Minimum version field under the ECC selector.
Default is auto (smallest that fits). Values 1–40 are honoured as
long as payload + ECC fit; otherwise the encoder rolls forward to a
higher version on its own.

Mask (0–7)

Every QR code is XOR-ed with one of eight mask patterns so the
module distribution looks random enough for scanner algorithms to lock
onto it reliably. The encoder picks the mask automatically by a
penalty score (which pattern yields the best readability). The
caption surfaces the chosen mask as a number 0–7.

Module count

Modules are the square cells inside the QR code. We show the data
matrix only; the four-module quiet zone (scanner-relevant safe area)
is added around it on export.

Error correction (ECC)

Error correction reserves a fraction of the module bits for recovery
data. Higher levels tolerate more physical damage at the cost of
data capacity.

When the payload exceeds the capacity of an ECC level, the editor
disables that option in the dropdown — either shorten the payload or
pick a lower ECC.

When is higher ECC worth it?

• Logos inside the code (pro feature, on the roadmap): higher
  ECC tolerates over-painting a logo area without breaking the scan.
• Printing on rough surfaces (wood, fabric, cardboard): more
  margin against ink bleed and fibre defects.
• Outdoor stickers: sun and rain destroy a LOW code faster than
  a HIGH code.

When is LOW enough?

• Pure screen display.
• Print on glossy paper under good lighting.
• Very long payloads where MEDIUM/QUARTILE/HIGH would exceed the
  encoder's capacity.