Crate png

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PNG encoder and decoder

This crate contains a PNG encoder and decoder. It supports reading of single lines or whole frames.

The decoder

The most important types for decoding purposes are Decoder and Reader. They both wrap a std::io::Read. Decoder serves as a builder for Reader. Calling Decoder::read_info reads from the Read until the image data is reached.

Using the decoder

use std::fs::File;
// The decoder is a build for reader and can be used to set various decoding options
// via `Transformations`. The default output transformation is `Transformations::IDENTITY`.
let decoder = png::Decoder::new(File::open("tests/pngsuite/basi0g01.png").unwrap());
let mut reader = decoder.read_info().unwrap();
// Allocate the output buffer.
let mut buf = vec![0; reader.output_buffer_size()];
// Read the next frame. An APNG might contain multiple frames.
let info = reader.next_frame(&mut buf).unwrap();
// Grab the bytes of the image.
let bytes = &buf[];
// Inspect more details of the last read frame.
let in_animation =;


Using the encoder

// For reading and opening files
use std::path::Path;
use std::fs::File;
use std::io::BufWriter;

let path = Path::new(r"/path/to/image.png");
let file = File::create(path).unwrap();
let ref mut w = BufWriter::new(file);

let mut encoder = png::Encoder::new(w, 2, 1); // Width is 2 pixels and height is 1.
encoder.set_source_gamma(png::ScaledFloat::from_scaled(45455)); // 1.0 / 2.2, scaled by 100000
encoder.set_source_gamma(png::ScaledFloat::new(1.0 / 2.2));     // 1.0 / 2.2, unscaled, but rounded
let source_chromaticities = png::SourceChromaticities::new(     // Using unscaled instantiation here
    (0.31270, 0.32900),
    (0.64000, 0.33000),
    (0.30000, 0.60000),
    (0.15000, 0.06000)
let mut writer = encoder.write_header().unwrap();

let data = [255, 0, 0, 255, 0, 0, 0, 255]; // An array containing a RGBA sequence. First pixel is red and second pixel is black.
writer.write_image_data(&data).unwrap(); // Save


  • Chunk types and functions
  • Text chunks (tEXt/zTXt/iTXt) structs and functions



  • The filtering method for preprocessing scanline data before compression.
  • Bit depth of the PNG file. Specifies the number of bits per sample.
  • How pixels are written into the buffer.
  • Describes how a pixel is encoded.
  • The type and strength of applied compression.
  • Result of the decoding process
  • Any kind of error during PNG decoding.
  • How to reset buffer of an animated png (APNG) at the end of a frame.
  • The byte level filter applied to scanlines to prepare them for compression.
  • The rendering intent for an sRGB image.
  • Physical unit of the pixel dimensions