@onadiet/image

The image format adapter for onadiet — put your images on a diet, locally. Part of the @onadiet/* engine; you normally use the onadiet CLI (diet photo.jpg --to 500kb), not this package directly.

It implements the @onadiet/core seams for standalone raster images (JPEG / PNG / WebP / AVIF):

• detect — is this a raster image? (magic-byte sniff, not the extension)
• weigh — dimensions, format, and a photo-vs-flat content estimate
• slim — hit a size target (or a plan) by re-encoding + downscaling, held to a measured SSIM quality floor, with an optional format switch (--format auto re-encodes to the smallest floor-holding format — WebP/AVIF)

The pixels are done by sharp/libvips (permissive). Every result is measured, never estimated — the engine keeps the original if it can't beat it, never writes a larger file, and holds the plan's perceptual floor. No uploads, no copyleft engines bundled.

Hot-path notes

slim is a pure (bytes, request) → SlimResult call with no cross-call state, so it's safe to call from many concurrent requests. Multi-format searches (--format auto / keto / crash) run their candidate formats concurrently; fast: true skips the ladder search for a ~9× lower per-call latency. To keep a server's event loop free, offload a slim to a worker thread — examples/worker-offload.

Exports

| Export | What it is | | ------------------ | -------------------------------------------------------------- | | imageAdapter | FormatAdapter — detect + weigh + slim (kind 'image') | | sniffImageFormat | magic-byte format detection (jpeg / png / webp / avif) |

License

Apache-2.0.