png

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 FormatError
  • func (e FormatError) Error() string
• type UnsupportedError
  • func (e UnsupportedError) Error() string

Examples

• Decode
• Encode

Functions

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

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)
	}
}

Types

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
}

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 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