version: 1.10

package png

import "image/png"

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

Package files

paeth.go reader.go writer.go

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.

Example:

// 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.

Example:

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