Crate png

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Expand description

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_trns(vec!(0xFFu8, 0xFFu8, 0xFFu8, 0xFFu8));
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


Animation control information

PNG Decoder

PNG Encoder.

Frame control information

PNG info struct

Limits on the resources the Decoder is allowed too use

Output info.

Pixel dimensions information

PNG reader (mostly high-level interface)

An unsigned integer scaled version of a floating point value, equivalent to an integer quotient with fixed denominator (100_000)).

Chromaticities of the color space primaries

Streaming PNG writer

PNG StreamingDecoder (low-level interface)

Output transformations

PNG writer


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