QR Code Performance: Generation and Scanning Speed

QR Code Performance: Generation and Scanning Speed

Optimising QR code generation and scanning speed matters for high-traffic APIs, real-time applications, and mobile scanning experiences.

Generation Benchmarks

Approximate generation times (single QR code, module count." data-category="QR Code Structure">Version 5, EC-M):

Optimising Generation Speed

Caching: The most impactful optimisation. Cache generated QR code images keyed on a hash of the input data:

import hashlib
from functools import lru_cache

@lru_cache(maxsize=10000)
def get_qr_image(data: str, ec: str = "m") -> bytes:
    qr = segno.make(data, error=ec)
    buffer = io.BytesIO()
    qr.save(buffer, kind="png", scale=8)
    return buffer.getvalue()

Pre-generation: Generate QR codes at data creation time (not at request time).

SVG over PNG: SVG generation skips pixel rendering, reducing time by 50-80%.

Reduced scale: Generate at the minimum viable resolution.

Scanning Speed Optimisation

For mobile and web-based scanning:

• Reduce video resolution: 720p is sufficient for QR detection (1080p/4K is wasted)
• Throttle frame processing: Process every 3rd-5th frame (10-15 fps effective scan rate)
• Region of interest: Only process the centre portion of the camera feed where the QR code is likely positioned
• Hardware acceleration: Use platform-native APIs (Vision on iOS, ML Kit on Android) rather than pure-JavaScript decoders

Image Preprocessing

For batch decoding of QR code images:

1. Convert to greyscale first (skip RGB processing)
2. Apply bilateral filter for noise reduction without edge blurring
3. Adaptive thresholding for binarisation
4. Crop to the QR code region if position is known

Key Takeaways

• Caching is the single most impactful generation optimisation
• Go and Rust libraries are 10-50x faster than Python for raw generation
• SVG output is 50-80% faster than PNG (no pixel rendering)
• Reduce camera resolution and frame rate for scanning efficiency
• Platform-native scanning APIs outperform JavaScript decoders