# JXL Optim

An ImageOptim-style drag-and-drop optimizer that re-encodes JPG / PNG / GIF into
**JPEG XL** (`.jxl`). Native SwiftUI, macOS 12+. Wraps the `cjxl` encoder from
[libjxl](https://github.com/libjxl/libjxl).

## Prerequisites

```sh
brew install jpeg-xl   # provides cjxl / djxl
```

The app looks for `cjxl` in `/usr/local/bin`, `/opt/homebrew/bin`, `/usr/bin`.
If it isn't found you'll see a red banner with the install hint.

## Build & run

```sh
swift run            # dev: launches the window
./bundle.sh          # builds "JXL Optim.app" (release, double-clickable)
open "JXL Optim.app"
```

## Use

Drop images onto the window. Each is converted to a sibling `.jxl`; the row shows
`before → after` and the percentage saved. A running total sits at the bottom.

Controls:
- **Lossless** — pixel-exact (`cjxl -d 0`). PNG/GIF stay perfect; JPEG is
  transcoded losslessly (decode-back gives the original).
- **Quality** — visual distance `d0.5`–`d3.0` (lower = better). `d1` ≈ visually lossless.
- **Effort** — encoder effort 1–9; higher is slower but smaller.
- **Keep original** — off deletes the source after a successful encode.

## How it maps to cjxl

`cjxl in.png out.jxl -e <effort> --num_threads 0 [-d 0 | -d <distance>]`

讲解文章在 Niamos vault: `wiki/projects/自己写一个 JPEG XL 压缩器.md`。