png

README

PNG image library

Documentation

Overview

Package png implements a PNG image decoder and encoder. It is a fork of the standard library's png package, but with a focus on memory usage and speed on image.NRGBA images.

Index

• type CompressionLevel
• type Decoder
  • func NewDecoder(r io.Reader) (*Decoder, error)
  • func (d *Decoder) Bounds() image.Rectangle
  • func (d *Decoder) Close() error
  • func (d *Decoder) DecodeRow() ([]byte, error)
• type Encoder
  • func NewEncoder(level CompressionLevel) *Encoder
  • func (enc *Encoder) Encode(w io.Writer, m *image.NRGBA) error
• type EncoderBuffer
• type EncoderBufferPool
• type FormatError
  • func (e FormatError) Error() string
• type UnsupportedError
  • func (e UnsupportedError) Error() string

Types

type CompressionLevel

type CompressionLevel int

CompressionLevel indicates the compression level.

const (
	DefaultCompression CompressionLevel = 0
	NoCompression      CompressionLevel = -1
	BestSpeed          CompressionLevel = -2
	BestCompression    CompressionLevel = -3
)

type Decoder

type Decoder struct {
	// contains filtered or unexported fields
}

A Decoder is a row-by-row decoder for png image.NRGBA images. Compared to the standard library, it reduces memory usage by loading only the current row.

func NewDecoder

func NewDecoder(r io.Reader) (*Decoder, error)

NewDecoder decodes the metadata of an image data stream.

func (*Decoder) Bounds

func (d *Decoder) Bounds() image.Rectangle

Bounds returns the bounds of the decoded image.

func (*Decoder) Close

func (d *Decoder) Close() error

Close checks the validity of the decoded image stream at the end.

func (*Decoder) DecodeRow

func (d *Decoder) DecodeRow() ([]byte, error)

DecodeRow decodes the current row. Users must take care of not modifying the returned buffer, as it is used in the decoding of subsequent rows.

type Encoder

type Encoder struct {
	CompressionLevel CompressionLevel

	// BufferPool optionally specifies a buffer pool to get temporary
	// EncoderBuffers when encoding an image.
	BufferPool EncoderBufferPool
}

Encoder configures encoding PNG images.

func NewEncoder

func NewEncoder(level CompressionLevel) *Encoder

NewEncoder returns a png image encoder. It supports only image.NRGBA images. It is roughly 5x (10x for identical RGBA images) faster than the standard library, according to the profiling results in https://github.com/golang/go/issues/51982#issuecomment-1085538951

func (*Encoder) Encode

func (enc *Encoder) Encode(w io.Writer, m *image.NRGBA) error

Encode writes the Image m to w in PNG format.

type EncoderBuffer

type EncoderBuffer encoder

EncoderBuffer holds the buffers used for encoding PNG images.

type EncoderBufferPool

type EncoderBufferPool interface {
	Get() *EncoderBuffer
	Put(*EncoderBuffer)
}

EncoderBufferPool is an interface for getting and returning temporary instances of the EncoderBuffer struct. This can be used to reuse buffers when encoding multiple images.

type FormatError

type FormatError string

A FormatError reports that the input is not a valid PNG.

func (FormatError) Error

func (e FormatError) Error() string

type UnsupportedError

type UnsupportedError string

An UnsupportedError reports that the input uses a valid but unimplemented PNG feature.

func (UnsupportedError) Error

func (e UnsupportedError) Error() string