QR Code Reader Benchmark: zbar vs zedbar

Standalone benchmark comparing old (zbar, qrdetect) and new (zedbar) QR code readers used in VxSuite ballot scanning.

Prerequisites

• Rust toolchain (stable)
• Node.js 20+
• libzbar-dev (for the zbar-rust crate)

Setup

# Rust benchmark
cargo build --release

# Node benchmark
cd node && npm install && cd ..

Usage

# Rust (rqrr, zbar, zedbar) — uses rayon for parallelism
./target/release/qr-benchmark /path/to/ballot/images/
./target/release/qr-benchmark --limit 100 /path/to/ballot/images/

# Node (quirc, qrdetect, zedbar-wasm)
node node/benchmark.mjs /path/to/ballot/images/
node node/benchmark.mjs --limit 100 /path/to/ballot/images/

Both accept --output <file> to write detailed per-image JSON results (defaults to rust_results.json / node_results.json).

---

Results

Benchmarked 5 QR code readers on 2,472 real ballot PNG images from a TRR CVR export. Each image was cropped to bottom-left and top-right corners (width/4 square) matching production detection logic, then tested with each reader.

Rust Readers (native)

Reader	Success	Fail	Rate	Mean	Median	Min	Max	p95
rqrr	1,968	504	79.6%	3.26ms	2.87ms	2.44ms	21.42ms	4.84ms
zbar (old)	2,429	43	98.3%	1.71ms	1.43ms	1.33ms	16.77ms	2.71ms
zedbar (new)	2,429	43	98.3%	3.08ms	2.57ms	2.01ms	18.77ms	6.37ms

Node Readers (addon/WASM)

Reader	Success	Fail	Rate	Mean	Median	Min	Max	p95
quirc	2,001	471	80.9%	1.37ms	1.32ms	0.78ms	8.43ms	2.28ms
qrdetect (old)	2,429	43	98.3%	2.57ms	2.34ms	1.80ms	8.33ms	3.88ms
zedbar-wasm (new)	2,429	43	98.3%	4.43ms	4.10ms	3.30ms	18.33ms	6.64ms

Discrepancies

Comparison	Old succeeded, new failed	New succeeded, old failed	Data mismatches
zbar vs zedbar (Rust)	0	0	0
qrdetect vs zedbar-wasm (Node)	0	0	0

Summary

• Accuracy is identical. zedbar detects the exact same 2,429/2,472 images as zbar. zedbar-wasm detects the exact same 2,429/2,472 images as qrdetect. Zero discrepancies in either direction, zero data mismatches.
• Performance is ~1.8x slower. zedbar median is 2.57ms vs zbar's 1.43ms (Rust native). zedbar-wasm median is 4.10ms vs qrdetect's 2.34ms (Node). Both are well within acceptable bounds for ballot scanning.
• rqrr and quirc remain weaker. Both miss ~20% of ballots, confirming why the fallback chain (rqrr then zbar/zedbar) is necessary.

Methodology

• Rust binary: rqrr 0.7.1, zbar-rust 0.0.23, zedbar 0.2.1 via image crate, parallelized with rayon
• Node script: node-quirc 2.3.0, @votingworks/qrdetect 1.0.1, zedbar 0.2.1 (WASM) via sharp for image loading
• Cropping logic replicated from detect.rs:get_detection_areas — crop_size = width/4, bottom-left then top-right corners
• Timing covers only the detection call, not image loading or cropping