@dusrel/image-resize

High-quality image resampling for the @dusrel/image family, powered by the Rust resize crate compiled to WebAssembly — the same engine family Squoosh and jSquash use. The Canvas fast path in @dusrel/image-core stays the default; this package is the quality path you opt into when pixels matter (thumbnails, avatars, print exports).

npm install @dusrel/image-resize

import { resize } from '@dusrel/image-resize';

const thumb = await resize(imageData, { width: 320, height: 240, filter: 'lanczos3' });

API

| Export | What it does | | --- | --- | | resize(ImageData, options) | Resample to width×height, returns a new ImageData | | init() | Preload the WASM module | | setCodecAssets({...}) | Override asset URLs (CDN hosting, tests) | | resolveOptions(options) | The validated options with defaults applied |

Options

| Option | Values | Default | | --- | --- | --- | | width / height | positive integers | (required) | | filter | 'nearest' \| 'triangle' \| 'catmull-rom' \| 'mitchell' \| 'bspline' \| 'gaussian' \| 'lanczos3' | 'lanczos3' | | alpha | 'premultiplied' \| 'straight' | 'premultiplied' |

Alpha, handled correctly

ImageData stores straight (unpremultiplied) alpha. Resampling straight-alpha pixels directly lets the RGB of fully transparent pixels bleed into visible edges (a red photo edge next to transparent-green padding turns muddy). With the default alpha: 'premultiplied' the module premultiplies, resamples via the crate's premultiplied format, then unpremultiplies — verified in tests: the boundary stays pure red as it fades. Use alpha: 'straight' only for non-colour data (masks, depth maps).

Honest scope

• hqx is not included. The resize crate has no hqx implementation; it is tracked as future work in docs/CODEC_GUIDE.md rather than promised here. For pixel art, 'nearest' is the correct v1 choice.
• Module size as committed: codec/resize.wasm 161,317 B.

Provenance

Built reproducibly from native/rust (pinned rust:1.99.1 + wasm-bindgen 0.2.130, resize = 0.8.9) by the repo's wasm-build workflow; the Docker build ends with a functional smoke gate (exact nearest blocks, stable lanczos solid). Verified again in Chromium, Firefox and WebKit by tests/browser/resize.spec.ts.

Licences: this package MIT; resize and rgb crates MIT (see the repo's THIRD_PARTY_LICENSES.md).