How QR Codes Work Internally (Technical Breakdown)

Introduction

QR codes are everywhere — on product packaging, restaurant menus, business cards, and advertisements. But how do these square black-and-white patterns actually store information?

Understanding the internal structure of QR codes is essential for technical users, programmers, and students studying computer science or digital technology. This article provides a detailed technical breakdown, covering:

QR code history and standards

Data encoding and modes

Error correction mechanisms

QR code structure and patterns

How QR scanners decode information

Practical applications for developers

Generating QR codes using qrcodegen.online

By the end of this guide, you’ll have a solid understanding of the science and engineering behind QR codes.

1. A Brief History of QR Codes

QR codes (Quick Response codes) were invented by Denso Wave, a Japanese company, in 1994. They were designed to overcome limitations of traditional barcodes:

Store more information

Enable faster scanning

Handle complex data like URLs, text, and numbers

Since then, QR codes have evolved into an essential tool in digital marketing, finance, logistics, and education.

2. QR Code Standards and Versions

QR Code Versions

QR codes come in versions 1–40, each defining the size of the QR code:

Version 1: 21×21 modules

Version 2: 25×25 modules

Version 40: 177×177 modules

Modules = black or white squares representing bits of information.

Error Correction Levels

QR codes use Reed-Solomon error correction to recover data if damaged. Four levels exist:

3. Data Encoding in QR Codes

QR codes can encode data in multiple modes:

1. Numeric Mode

Stores digits 0–9

Most efficient: up to 7,089 digits in version 40

2. Alphanumeric Mode

Encodes letters A–Z, digits 0–9, and special characters: space, $, %, *, +, -, ., /, :

Capacity: 4,296 characters

3. Byte Mode

Stores binary data (ISO-8859-1 charset)

Allows URLs, UTF-8 text, and complex characters

Capacity: 2,953 bytes

4. Kanji Mode

Encodes Japanese Kanji characters using Shift JIS

Capacity: 1,817 characters

4. QR Code Structure and Patterns

A QR code is divided into functional areas:

1. Finder Patterns

Large squares in three corners

Help scanners detect the code orientation

2. Alignment Patterns

Smaller squares in larger codes

Correct distortion when scanned from an angle

3. Timing Patterns

Alternating black/white modules between finder patterns

Help determine module size and grid coordinates

4. Format Information

Encodes error correction level and mask pattern

Located near finder patterns

5. Version Information

Present in versions 7+

Stores version number

6. Data & Error Correction Codewords

Encodes the actual information and redundancy for recovery

7. Quiet Zone

Margin around QR code

Ensures proper scanning

5. Error Correction Mechanism

Reed-Solomon Error Correction

QR codes use Reed-Solomon (RS) codes, a mathematical algorithm that allows data recovery even if part of the code is damaged.

Up to 30% of code can be destroyed or obscured (H level)

Used in barcodes, CDs, DVDs, and QR codes

How It Works

Original data converted to codewords (8-bit blocks)

RS algorithm generates redundant codewords

Scanner uses these to detect and correct errors

6. Data Masking in QR Codes

To prevent large blocks of black or white (which can confuse scanners):

QR codes apply mask patterns (8 predefined patterns)

Masks alternate black/white modules in specific ways

Ensures readability under various lighting conditions

7. How QR Code Scanners Decode Information

Step 1: Detect Finder Patterns

Identify orientation and module size

Step 2: Apply Mask

Undo mask pattern to reveal actual data

Step 3: Extract Codewords

Read bits row-by-row following QR standard

Step 4: Error Correction

Apply Reed-Solomon algorithm to fix damaged bits

Step 5: Decode Data

Convert numeric, alphanumeric, or byte mode back to readable content

8. QR Codes in Practice for Developers and Students

1. Generating QR Codes

Use libraries or platforms like qrcodegen.online:

Input data (URL, text, contact)

Select version & error correction level

Generate code in PNG, SVG, or vector formats

2. Scanning QR Codes

Use mobile apps or libraries (ZXing, ZBar)

Decode data for apps, payment systems, or inventory

3. Custom QR Code Applications

Tracking attendance in classrooms

Inventory management

Secure authentication

Marketing campaigns with dynamic QR codes

9. Advanced Topics

1. QR Code Modulation

Each module represents a bit or combination of bits

Scanner interprets patterns as binary data

2. Data Compression

Numeric and alphanumeric modes compress data efficiently

Reduces QR code size while maximizing storage

3. Security Features

Dynamic QR codes can add:

Password protection

Expiration dates

Encrypted content

10. Common Mistakes and Best Practices

Too Dense QR Codes → Limit version size for scanning ease

Low Contrast → Always use black modules on white background

Ignoring Quiet Zone → Essential for reliable scanning

Overcomplicated Data → Use URLs or short codes when possible

Testing Across Devices → Ensure compatibility with Android, iOS, and web scanners

Conclusion

QR codes are mathematically elegant, technically sophisticated, and widely practical. Understanding their internal structure helps students, developers, and technical users:

Generate efficient codes

Implement dynamic or secure QR systems

Integrate QR codes into apps, marketing, or fintech

For easy and professional QR code generation with full customization, visit qrcodegen.online.

QR codes combine error correction, modular design, and encoding efficiency, making them a reliable tool for modern digital solutions.