Package png

import "image/png"

Overview

Index

Examples

Overview ▸

Overview ▾

Package png implements a PNG image decoder and encoder.

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

Index ▸

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 (Expand All)

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

▾ Example

package main

import (
	"encoding/base64"
	"fmt"
	"image/color"
	"image/png"
	"io"
	"log"
	"strings"
)

const gopher = `iVBORw0KGgoAAAANSUhEUgAAAEsAAAA8CAAAAAALAhhPAAAFfUlEQVRYw62XeWwUVRzHf2+OPbo9d7tsWyiyaZti6eWGAhISoIGKECEKCAiJJkYTiUgTMYSIosYYBBIUIxoSPIINEBDi2VhwkQrVsj1ESgu9doHWdrul7ba73WNm3vOPtsseM9MdwvvrzTs+8/t95ze/33sI5BqiabU6m9En8oNjduLnAEDLUsQXFF8tQ5oxK3vmnNmDSMtrncks9Hhtt/qeWZapHb1ha3UqYSWVl2ZmpWgaXMXGohQAvmeop3bjTRtv6SgaK/Pb9/bFzUrYslbFAmHPp+3WhAYdr+7GN/YnpN46Opv55VDsJkoEpMrY/vO2BIYQ6LLvm0ThY3MzDzzeSJeeWNyTkgnIE5ePKsvKlcg/0T9QMzXalwXMlj54z4c0rh/mzEfr+FgWEz2w6uk8dkzFAgcARAgNp1ZYef8bH2AgvuStbc2/i6CiWGj98y2tw2l4FAXKkQBIf+exyRnteY83LfEwDQAYCoK+P6bxkZm/0966LxcAAILHB56kgD95PPxltuYcMtFTWw/FKkY/6Opf3GGd9ZF+Qp6mzJxzuRSractOmJrH1u8XTvWFHINNkLQLMR+XHXvfPPHw967raE1xxwtA36IMRfkAAG29/7mLuQcb2WOnsJReZGfpiHsSBX81cvMKywYZHhX5hFPtOqPGWZCXnhWGAu6lX91ElKXSalcLXu3UaOXVay57ZSe5f6Gpx7J2MXAsi7EqSp09b/MirKSyJfnfEEgeDjl8FgDAfvewP03zZ+AJ0m9aFRM8eEHBDRKjfcreDXnZdQuAxXpT2NRJ7xl3UkLBhuVGU16gZiGOgZmrSbRdqkILuL/yYoSXHHkl9KXgqNu3PB8oRg0geC5vFmLjad6mUyTKLmF3OtraWDIfACyXqmephaDABawfpi6tqqBZytfQMqOz6S09iWXhktrRaB8Xz4Yi/8gyABDm5NVe6qq/3VzPrcjELWrebVuyY2T7ar4zQyybUCtsQ5Es1FGaZVrRVQwAgHGW2ZCRZshI5bGQi7HesyE972pOSeMM0dSktlzxRdrlqb3Osa6CCS8IJoQQQgBAbTAa5l5epO34rJszibJI8rxLfGzcp1dRosutGeb2VDNgqYrwTiPNsLxXiPi3dz7LiS1WBRBDBOnqEjyy3aQb+/bLiJzz9dIkscVBBLxMfSEac7kO4Fpkngi0ruNBeSOal+u8jgOuqPz12nryMLCniEjtOOOmpt+KEIqsEdocJjYXwrh9OZqWJQyPCTo67LNS/TdxLAv6R5ZNK9npEjbYdT33gRo4o5oTqR34R+OmaSzDBWsAIPhuRcgyoteNi9gF0KzNYWVItPf2TLoXEg+7isNC7uJkgo1iQWOfRSP9NR11RtbZZ3OMG/VhL6jvx+J1m87+RCfJChAtEBQkSBX2PnSiihc/Twh3j0h7qdYQAoRVsRGmq7HU2QRbaxVGa1D6nIOqaIWRjyRZpHMQKWKpZM5feA+lzC4ZFultV8S6T0mzQGhQohi5I8iw+CsqBSxhFMuwyLgSwbghGb0AiIKkSDmGZVmJSiKihsiyOAUs70UkywooYP0bii9GdH4sfr1UNysd3fUyLLMQN+rsmo3grHl9VNJHbbwxoa47Vw5gupIqrZcjPh9R4Nye3nRDk199V+aetmvVtDRE8/+cbgAAgMIWGb3UA0MGLE9SCbWX670TDy1y98c3D27eppUjsZ6fql3jcd5rUe7+ZIlLNQny3Rd+E5Tct3WVhTM5RBCEdiEK0b6B+/ca2gYU393nFj/n1AygRQxPIUA043M42u85+z2SnssKrPl8Mx76NL3E6eXc3be7OD+H4WHbJkKI8AU8irbITQjZ+0hQcPEgId/Fn/pl9crKH02+5o2b9T/eMx7pKoskYgAAAABJRU5ErkJggg==`

// gopherPNG creates an io.Reader by decoding the base64 encoded image data string in the gopher constant.
func gopherPNG() io.Reader { return base64.NewDecoder(base64.StdEncoding, strings.NewReader(gopher)) }

func main() {
	// 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

▾ Example

package main

import (
	"image"
	"image/color"
	"image/png"
	"log"
	"os"
)

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 {
		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 ¶ 1.4

CompressionLevel indicates the compression level.

type CompressionLevel int

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

type Encoder ¶ 1.4

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 // Go 1.9
}

func (*Encoder) Encode ¶ 1.4

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

Encode writes the Image m to w in PNG format.

type EncoderBuffer ¶ 1.9

EncoderBuffer holds the buffers used for encoding PNG images.

type EncoderBuffer encoder

type EncoderBufferPool ¶ 1.9

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
    Put(*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