How QR codes actually work

1. 1

   Find the finder patterns

   Three big squares in the corners orient the scanner.

2. 2

   Spot the timing patterns

   Alternating black/white strips between finders calibrate the grid.

3. 3

   Read the format info

   A small strip around a finder tells the scanner the error-correction level and mask.

4. 4

   Decode the data

   The rest of the grid encodes your payload with Reed–Solomon redundancy.

A QR code is a 2-D matrix of black and white modules. The three big squares at the corners — called finder patterns — let a camera recognize the code from any angle. A fourth smaller square (the alignment pattern) appears in larger versions.

Data is encoded in segments: numeric, alphanumeric, byte, and kanji. A mask pattern is XOR'd over the data so the module distribution looks noisy — this keeps the code scannable under uneven lighting.

Reed–Solomon error correction adds redundancy so the code still decodes if up to 30% is damaged or obscured (level H). That's how logos inside QR codes work.