The whole process happens in under two seconds. Here is what is actually happening inside it.
The Three Finder Patterns
The three square targets in the corners of every QR code are called finder patterns. They tell the scanner three things simultaneously: where the code begins, what angle it is rotated at, and what scale factor to use when reading the remaining squares. This is why a QR code scans correctly whether it is right-side up, sideways, or upside down. The finder patterns calibrate the read before a single data square is interpreted.
The Data Region
The squares between the finder patterns contain the actual encoded data. Each square — called a module — is either dark or light, representing a binary 1 or 0. The sequence of 1s and 0s encodes the data using one of four encoding modes: numeric (digits only), alphanumeric (letters and digits), binary (any byte data), or kanji (Japanese characters).
For a typical URL of 30 characters, a QR code contains roughly 1,000 to 1,500 modules — each representing one bit of the encoded data.
Error Correction
QR codes include redundant data — copies of the encoded information embedded multiple times in different parts of the code. This is error correction. It is why a QR code with a logo placed in the center still scans correctly — the logo covers some modules, but the redundant data elsewhere in the code supplies the missing information.
There are four error correction levels: L (7% of modules can be damaged), M (15%), Q (25%), and H (30%). Higher error correction means more redundancy, which means a larger code for the same data.
What Your Phone Actually Does
When you point your phone camera at a QR code, the camera's image processor identifies the three finder patterns, corrects for the viewing angle, reads each module as dark or light, assembles the binary sequence, applies error correction to fill any gaps, decodes the binary to the original data format, and hands the result to the operating system — which opens the URL, dials the number, or adds the contact. The entire process takes less than two seconds on any modern phone without any app.
What Standard QR Code Mechanics Cannot Do
Every QR code described above — regardless of how it encodes its data — is permanently silent. The phone reads the pattern, retrieves the data, and opens a URL. The interaction ends there.