Run Format

Package png

import "image/png"

Overview ▾

Package png implements a PNG image decoder and encoder.

The PNG specification is at https://www.w3.org/TR/PNG/.

func Decode

func Decode(r io.Reader) (image.Image, error)

Decode reads a PNG image from r and returns it as an image.Image. The type of Image returned depends on the PNG contents.



// This example uses png.Decode which can only decode PNG images.
// Consider using the general image.Decode as it can sniff and decode any registered image format.
img, err := png.Decode(gopherPNG())
if err != nil {

levels := []string{" ", "░", "▒", "▓", "█"}

for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
        for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
                c := color.GrayModel.Convert(img.At(x, y)).(color.Gray)
                level := c.Y / 51 // 51 * 5 = 255
                if level == 5 {

func DecodeConfig

func DecodeConfig(r io.Reader) (image.Config, error)

DecodeConfig returns the color model and dimensions of a PNG image without decoding the entire image.

func Encode

func Encode(w io.Writer, m image.Image) error

Encode writes the Image m to w in PNG format. Any Image may be encoded, but images that are not image.NRGBA might be encoded lossily.


type CompressionLevel

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

type Encoder

Encoder configures encoding PNG images.

type Encoder struct {
        CompressionLevel CompressionLevel

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

func (*Encoder) Encode

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

Encode writes the Image m to w in PNG format.

type EncoderBuffer

EncoderBuffer holds the buffers used for encoding PNG images.

type EncoderBuffer encoder

type EncoderBufferPool

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 EncoderBufferPool interface {
        Get() *EncoderBuffer

type FormatError

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

type FormatError string

func (FormatError) Error

func (e FormatError) Error() string

type UnsupportedError

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

type UnsupportedError string

func (UnsupportedError) Error

func (e UnsupportedError) Error() string