Lib.rs

minipng

crates.io page · repository

Tiny Rust PNG decoder with no dependencies (not even std or alloc) and tiny code size (e.g. >8 times smaller .wasm.gz size compared to the png crate — see check-size.sh).

Goals

• Correctly decode all valid non-interlaced PNG files (on ≤32-bit platforms, some very large images might fail because of usize::MAX).
• Small code size & complexity
• No dependencies other than core
• No panics
• Minimal unsafe code

Non-goals

• Adam7 interlacing (increases code complexity and interlaced PNGs are rare anyways)
• significantly sacrificing code size/complexity for speed
• checking block CRCs (increases code complexity and there’s already Adler32 checksums for IDAT chunks)
• ancillary chunks (tEXt, iCCP, etc.)
• correctly handling non-indexed image with tRNS chunk (who uses this?)
• animated PNGs

Example usage

Basic usage:

let mut buffer = vec![0; 1 << 20]; // hope this is big enough!
let png = &include_bytes!("../examples/image.png")[..];
let image = minipng::decode_png(png, &mut buffer).expect("bad PNG");
println!("{}×{} image", image.width(), image.height());
let pixels = image.pixels();
println!("top-left pixel is #{:02x}{:02x}{:02x}", pixels[0], pixels[1], pixels[2]);
// (^ this only works for RGB(A) 8bpc images)

More complex example that allocates the right number of bytes and handles all color formats:

let png = &include_bytes!("../examples/image.png")[..];
let header = minipng::decode_png_header(png).expect("bad PNG");
let mut buffer = vec![0; header.required_bytes_rgba8bpc()];
let mut image = minipng::decode_png(png, &mut buffer).expect("bad PNG");
image.convert_to_rgba8bpc();
println!("{}×{} image", image.width(), image.height());
let pixels = image.pixels();
println!("top-left pixel is #{:02x}{:02x}{:02x}{:02x}", pixels[0], pixels[1], pixels[2], pixels[3]);

Features

• adler (default: disabled) — check Adler-32 checksums. slightly increases code size and slightly decreases performance but verifies integrity of PNG files.

Development

A pre-commit git hook is provided to run cargo fmt and cargo clippy. You can install it with:

ln -s ../../pre-commit .git/hooks/

Testing

All PNG files in the test directory are tested by cargo t (NOTE: cargo test doesn‘t log as much progress because there’s no way of dynamically generating tests and no way of enabling --nocapture by default grumble grumble).

Performance

Benchmarks (see cargo bench) show that minipng is about 50% slower than the png crate for large images, but faster than png for small images.

License

Zero-Clause BSD

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted.

THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.