Go: image/png Index | Examples | Files

package png

import "image/png"

Package png implements a PNG image decoder and encoder.

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

Index

Examples

Package Files

paeth.go reader.go writer.go

func Decode Uses

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 Uses

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 Uses

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:play 

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 Uses

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

type Encoder Uses

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 Uses

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

Encode writes the Image m to w in PNG format.

type EncoderBuffer Uses

type EncoderBuffer encoder

EncoderBuffer holds the buffers used for encoding PNG images.

type EncoderBufferPool Uses

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 Uses

type FormatError string

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

func (FormatError) Error Uses

func (e FormatError) Error() string

type UnsupportedError Uses

type UnsupportedError string

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

func (UnsupportedError) Error Uses

func (e UnsupportedError) Error() string

Package png imports 10 packages (graph) and is imported by 1993 packages. Updated 2017-08-25. Refresh now. Tools for package owners.