chuda

A CPU and CUDA high-quality truecolour ANSI renderer for image-training pipelines. It implements the expensive part of Chafa's effort-9 symbol mode: exhaustive foreground/background fitting and error scoring over the narrow symbol atlas. PNG decode, high-quality resize and stateful ANSI emission stay in Rust; independent cell/symbol evaluation runs on CUDA.

RGBA images are optimized jointly for either a detailed opaque foreground and background cell or a composable foreground-only cell. Alpha-mask agreement is part of symbol scoring, so antialiased sprite edges do not require two renders and a cell-level merge pass. --transparent-threshold controls the bias toward opaque interior detail and defaults to 0.10.

The atlas is generated from the vendored Chafa reference source and checked into the Rust binary. Chafa is not a build-time or runtime dependency.

Requirements

• Rust 1.85 or newer
• CUDA Toolkit and an NVIDIA driver only when building or selecting the optional CUDA backend

Build and run

cargo build --release
cargo run --release -- --size 80 image.png > image.ansi
cargo run --release --features cuda -- --backend cuda --size 80 image.png > image.ansi

Directory mode recursively mirrors PNG paths and changes their suffix to .ansi:

cargo run --release -- --size 80 corpus --output rendered

Only ANSI is written. Directory mode does not leave resized images or other intermediates behind.

Architecture note

The public Rust and Python APIs share decoding, resizing, structured frames, and ANSI emission. Rayon and CUDA implement interchangeable cell scorers.

Python

The PyPI distribution is chuda-ansi and its import name is chuda:

import chuda

renderer = chuda.Renderer("auto")
image = chuda.Image.open("image.png")
frame = renderer.render(image, 80)
ansi = frame.to_ansi()

Updating the symbol atlas

After updating the Chafa sources in vendor/chafa, run:

python3 tools/generate_symbols.py
cargo fmt

The generated atlas is LGPL-derived and this project is correspondingly licensed LGPL-3.0-or-later. See LICENSE and NOTICE.

Benchmark against Chafa

The benchmark excludes compilation, warms both programs once, and reports the median end-to-end batch time. It also writes one output from each renderer for visual inspection:

python3 tools/benchmark.py ../ansi-scaler/data/artifacts/rasters \
  --width 80 --images 100 --repeats 3
less -R benchmark-results/sample-chuda.ansi
less -R benchmark-results/sample-chafa.ansi

Machine-readable measurements are saved in benchmark-results/report.json.