Crate png

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[..info.buffer_size()];
// Inspect more details of the last read frame.
let in_animation = reader.info().frame_control.is_some();

Encoder

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_color(png::ColorType::Rgba);
encoder.set_depth(png::BitDepth::Eight);
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)
);
encoder.set_source_chromaticities(source_chromaticities);
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

Modules

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

Structs

• Adam7Info
  Describes which stage of the Adam7 algorithm applies to a decoded row.
• AnimationControl
  Animation control information
• CodingIndependentCodePoints
  Coding-independent code points (cICP) specify the color space (primaries), transfer function, matrix coefficients and scaling factor of the image using the code points specified in ITU-T-H.273.
• ContentLightLevelInfo
  Content light level information of HDR content.
• DecodeOptions
  Decoder configuration options
• Decoder
  PNG Decoder
• Encoder
  PNG Encoder.
• FrameControl
  Frame control information
• Info
  PNG info struct
• InterlacedRow
  A row of data with interlace information attached.
• Limits
  Limits on the resources the Decoder is allowed too use
• MasteringDisplayColorVolume
  Mastering Display Color Volume (mDCV) used at the point of content creation, as specified in SMPTE-ST-2086.
• OutputInfo
  Output info.
• ParameterError
• PixelDimensions
  Pixel dimensions information
• Reader
  PNG reader (mostly high-level interface)
• ScaledFloat
  An unsigned integer scaled version of a floating point value, equivalent to an integer quotient with fixed denominator (100_000)).
• SourceChromaticities
  Chromaticities of the color space primaries
• StreamWriter
  Streaming PNG writer
• StreamingDecoder
  PNG StreamingDecoder (low-level interface)
• Transformations
  Output transformations
• Writer
  PNG writer

Enums

• AdaptiveFilterType
  Adaptive filtering tries every possible filter for each row and uses a heuristic to select the best one. This improves compression ratio, but makes encoding slightly slower.
• BitDepth
  Bit depth of the PNG file. Specifies the number of bits per sample.
• BlendOp
  How pixels are written into the buffer.
• ColorType
  Describes how a pixel is encoded.
• Compression
  The type and strength of applied compression.
• Decoded
  Result of the decoding process
• DecodingError
  Any kind of error during PNG decoding.
• DisposeOp
  How to reset buffer of an animated png (APNG) at the end of a frame.
• EncodingError
• FilterType
  The byte level filter applied to scanlines to prepare them for compression.
• InterlaceInfo
  Describes which interlacing algorithm applies to a decoded row.
• SrgbRenderingIntent
  The rendering intent for an sRGB image.
• Unit
  Physical unit of the pixel dimensions

Functions

• expand_interlaced_row
  Copies pixels from interlaced_row into the right location in img.