Package png

import "image/png"
Overview
Index
Examples
Documentation

Overview

Package png implements a PNG image decoder and encoder.

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

Index

func Decode(r io.Reader) (image.Image, error)
func DecodeConfig(r io.Reader) (image.Config, error)
func Encode(w io.Writer, m image.Image) error
type CompressionLevel
type Encoder
func (enc *Encoder) Encode(w io.Writer, m image.Image) error
type EncoderBuffer
type EncoderBufferPool
type FormatError
func (e FormatError) Error() string
type UnsupportedError
func (e UnsupportedError) Error() string

Examples

Decode
Encode

Documentation

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.

Code:

// 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 {
    log.Fatal(err)
}

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 {
            level--
        }
        fmt.Print(levels[level])
    }
    fmt.Print("\n")
}

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.

Code:

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 {
    log.Fatal(err)
}

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

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

type CompressionLevel

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

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 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

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