Trace bitmap glyph images to bezier contours and insert them directly into UFO font sources.

Designed for agentic AI type design pipelines — takes scanned or rendered letterforms and produces cubic outlines ready for editing or compilation into fonts.

Built on the Linebender ecosystem: kurbo for bezier curve math and optimal curve fitting via fit_to_bezpath_opt, and norad for UFO reading/writing.

cargo install --git https://github.com/eliheuer/img2bez

The autoresearch loop generates per-glyph bezier structure comparison images. This requires designbot:

cargo install --git https://github.com/eliheuer/designbot designbot-cli

Once installed, autoresearch/run_experiment.sh will automatically render viz_uni<XXXX>.png files for the weakest glyphs after each experiment run. If designbot is not on your PATH the viz step is silently skipped.

Or to use as a library, add to your Cargo.toml:

[dependencies]
img2bez = { git = "https://github.com/eliheuer/img2bez" }

# Basic usage: trace a glyph image and insert it into a UFO source
img2bez --input glyph.png \
  --output MyFont.ufo \    # target UFO (must already exist)
  --name A \               # glyph name in the UFO
  --unicode 0041           # Unicode codepoint in hex

# With font metrics: scale and position the outline to match your UPM
img2bez --input glyph.png \
  --output MyFont.ufo \
  --name A \
  --unicode 0041 \
  --target-height 1024 \    # ascender - descender in font units
  --y-offset -256 \         # shift down by the descender value
  --grid 2                  # snap coordinates to a 2-unit grid

# Compare the traced output against a reference glyph
img2bez --input glyph.png \
  --output MyFont.ufo \
  --name A \
  --unicode 0041 \
  --reference MyFont.ufo/glyphs/A_.glif

use img2bez::{trace, TracingConfig};
use std::path::Path;

let config = TracingConfig {
    target_height: 1088.0,
    y_offset: -256.0,
    grid: 2,
    ..TracingConfig::default()
};

let result = trace(Path::new("glyph.png"), &config)?;
// result.paths: Vec<kurbo::BezPath>
// result.advance_width: f64
// result.contour_types: Vec<ContourType>

 Input image
      |
 1. Threshold (Otsu or fixed) ─── bitmap.rs
      |
 2. Pixel-edge contour extraction (dual grid) ─── vectorize/decompose.rs
      |
 3. Optimal polygon approximation (DP) ─── vectorize/polygon.rs
      |
 4. Sub-pixel vertex refinement ─── vectorize/polygon.rs
      |
 5. Corner detection + curve fitting ─── vectorize/curve.rs
      |
 6. Post-processing ─── cleanup/
      ├── Contour direction (CCW outer, CW counter)
      ├── Grid snapping
      ├── H/V handle correction
      └── Optional chamfer insertion
      |
 7. Reposition + advance width ─── metrics.rs
      |
 8. UFO output ─── ufo.rs

• Potrace-style pipeline: decompose, polygon, curve — adapted for font outlines
• Extrema-aware splitting: curves are split at bounding-box extrema so handles naturally align H/V
• Grid snapping: on-curve points snap to an integer grid while off-curve handles preserve curve accuracy
• Rayon parallelism: contours are fitted in parallel
• Raster IoU evaluation: compare traced output against a reference with pixel-level accuracy

Prefix your command with VAR=1 to enable debug output for a single run:

IMG2BEZ_DEBUG_SPLITS=1 img2bez --input glyph.png --output MyFont.ufo --name A

An overnight research loop that autonomously improves img2bez by tracing hand-drawn reference glyphs and comparing raster + vector quality metrics. Inspired by karpathy/autoresearch.

reference.ufo (hand-drawn glyphs)
      |
render_glyph.py  →  glyph.png   (drawbot-skia renders each .glif to bitmap)
      |
img2bez          →  traced.glif  (trace the bitmap back to bezier outlines)
      |
--reference flag →  metrics     (raster IoU + weighted vector quality score)
      |
agent loop       →  keep/discard  (Claude proposes changes, keeps if mean_iou improves)

# 1. Create a research branch
git checkout -b autoresearch/$(date +%b%d | tr A-Z a-z)

# 2. Activate the Python venv (needs ufoLib2 + drawbot-skia)
source ~/Py/venvs/basic-fonts/bin/activate

# 3. Run the experiment harness
./autoresearch/run_experiment.sh

# 4. Tell Claude to follow the instructions and run overnight
# "Follow autoresearch/program.md and improve img2bez"

Reference font: Virtua Grotesk Regular (autoresearch/reference.ufo → symlink to ~/GH/repos/virtua-grotesk/sources/VirtuaGrotesk-Regular.ufo)

Glyphs tested: A–Z + a–z (52 glyphs, all with real hand-drawn outlines)

Established on commit 82acffa (2026-03-20). Results logged to autoresearch/results.tsv (gitignored).

# Point at a different UFO
ln -sf /path/to/other.ufo autoresearch/reference.ufo

# Or override per-run without changing the symlink
REFERENCE_UFO=/path/to/other.ufo ./autoresearch/run_experiment.sh

# Run a focused subset of glyphs
GLYPHS_FILTER="O S G" ./autoresearch/run_experiment.sh

MIT