tiny-webp 0.1.1

Lossy WebP encoder in Rust with a cwebp-shaped command line
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# tiny-webp

Lossy WebP encoder in Rust, with a cwebp-shaped command line.

The encoder writes a single VP8 key frame inside a RIFF WebP container, from
the RGB or RGBA bytes a caller already holds. The library is `no_std` and
allocates through `alloc`. It works on byte slices in memory, so paths and
file handles stay with the caller.

## Status

Version 0.1.0 writes one lossy VP8 key frame in a RIFF WebP container. Opaque
images use a bare `VP8 ` chunk. Images with transparency use `VP8X`, an
uncompressed `ALPH` chunk, and `VP8 `. The alpha bytes stay exact.

The encoder uses DC prediction for luma and chroma, the Y2 transform path, one
token partition, and a fixed quantizer selected by `q`.

Size and RGB PSNR relative to cwebp vary by image and `q`.
[CALIBRATION.md](CALIBRATION.md) records results at `q` 50, 75, and 90.
At all three settings, `flat` and `one-pixel` produce smaller files than
cwebp. Every other fixture produces larger files.

At `q` 75, `photo-large` uses 1.59 times cwebp's bytes. Its RGB PSNR is
30.5 dB against cwebp's 29.5 dB.

The command reads PNG, JPEG, and WebP from a path or stdin. It writes WebP to a
path or stdout.

## Install

Install the command:

```sh
cargo install tiny-webp
```

Add the library to `[dependencies]`:

```toml
tiny-webp = "0.1"
```

## Library

`Options` is `#[non_exhaustive]`, so build one from its default and assign the
fields that change.

```rust
let mut opts = tiny_webp::Options::default();
opts.quality = 90;
opts.alpha = tiny_webp::Alpha::Discard;

let webp = tiny_webp::encode_rgba(&rgba, width, height, &opts)?;
```

`encode_rgb` takes the same arguments over three bytes per pixel and writes an
opaque image.

## Command line

```
usage: tiny-webp [options] <input> -o <output.webp>

  -q <0..100>, --quality <0..100>   quality, default 75
  -o <file>,   --output <file>      output path, or - for stdout
  -noalpha                          drop the alpha plane
  -quiet                            no output on success
  -v                                print dimensions, bytes, and encode time
  -version, --version
  -h, --help
```

cwebp spells `-noalpha`, `-quiet`, and `-version` with one dash, and both
spellings reach the same flag here. A bare `-` means stdin on the input and
stdout on the output.

A usage error exits 2 and puts the problem and this text on stderr. Any other
failure exits 1 with one line on stderr.

## License

Licensed under either of

- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE))
- MIT license ([LICENSE-MIT](LICENSE-MIT))

at your option.