Package png


Package png implements a PNG image decoder and encoder.

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




Package files

paeth.go reader.go writer.go

func DecodeSource

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 DecodeConfigSource

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 EncodeSource

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.


package main

import (

func main() {
	const width, height = 256, 256

	// Create a colored image of the given width and height.
	img := image.NewNRGBA(image.Rect(0, 0, width, height))

	for y := 0; y < height; y++ {
		for x := 0; x < width; x++ {
			img.Set(x, y, color.NRGBA{
				R: uint8((x + y) & 255),
				G: uint8((x + y) << 1 & 255),
				B: uint8((x + y) << 2 & 255),
				A: 255,

	f, err := os.Create("image.png")
	if err != nil {

	if err := png.Encode(f, img); err != nil {

	if err := f.Close(); err != nil {

type CompressionLevelSource

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

type EncoderSource

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) EncodeSource

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

Encode writes the Image m to w in PNG format.

type EncoderBufferSource

EncoderBuffer holds the buffers used for encoding PNG images.

type EncoderBuffer encoder

type EncoderBufferPoolSource

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 FormatErrorSource

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

type FormatError string

func (FormatError) ErrorSource

func (e FormatError) Error() string

type UnsupportedErrorSource

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

type UnsupportedError string

func (UnsupportedError) ErrorSource

func (e UnsupportedError) Error() string

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Licensed under the Creative Commons Attribution License 3.0.