README
¶
format/png
This version of image/png has been modified to support reading and writing
custom chunks (e.g. tEXt data). It also supports optional Zstd compression
for image data.
License and Copyright Notice
Copyright © 2009 The Go Authors
Copyright © 2022 Ronsor Labs
Documentation
¶
Overview ¶
Package png implements a PNG image decoder and encoder.
The PNG specification is at https://www.w3.org/TR/PNG/.
Index ¶
- func Decode(r io.Reader) (image.Image, error)
- func DecodeConfig(r io.Reader) (image.Config, error)
- func DecodeWithOptions(r io.Reader, o *DecodeOptions) (image.Image, error)
- func Encode(w io.Writer, m image.Image) error
- type Chunk
- type CompressionLevel
- type DecodeOptions
- type EncodeOptions
- type Encoder
- type EncoderBuffer
- type EncoderBufferPool
- type FormatError
- type UnsupportedError
Examples ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Decode ¶
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 ¶
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")
}
}
Output:
func DecodeConfig ¶
DecodeConfig returns the color model and dimensions of a PNG image without decoding the entire image.
func DecodeWithOptions ¶
DecodeWithOptions reads a PNG image from r and returns it as an image.Image. The type of Image returned depends on the PNG contents. Additional options can be passed to the decoder as DecodeOptions.
func Encode ¶
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)
}
}
Output:
Types ¶
type Chunk ¶
type Chunk struct {
// Name is the 4-byte chunk ID.
Name string
// Data is the chunk payload.
Data []byte
// AfterIDAT specifies whether the chunk should be placed
// before or after the image data.
AfterIDAT bool
}
Chunk is a PNG chunk.
type CompressionLevel ¶
type CompressionLevel int
CompressionLevel indicates the compression level.
const ( DefaultCompression CompressionLevel = 0 NoCompression CompressionLevel = -1 BestSpeed CompressionLevel = -2 BestCompression CompressionLevel = -3 )
type DecodeOptions ¶
type DecodeOptions struct {
// ParseUnknownChunk specifies a function to call when an
// unrecognized PNG chunk is encountered.
ParseUnknownChunk func(Chunk) error
}
DecodeOptions are additional options that can be passed to the PNG decoder.
type EncodeOptions ¶
type EncodeOptions struct {
// CustomChunks specifies custom chunks to include in the PNG file.
CustomChunks []Chunk
// FallbackImage specifies a fallback image when Zstd compression is
// used.
FallbackImage image.Image
}
Options are the encoding parameters.
type Encoder ¶
type Encoder struct {
CompressionLevel CompressionLevel
// BufferPool optionally specifies a buffer pool to get temporary
// EncoderBuffers when encoding an image.
BufferPool EncoderBufferPool
// UseZstd optionally specifies whether or not to use Zstd compression
// instead of zlib compression.
UseZstd bool
}
Encoder configures encoding PNG images.
func (*Encoder) EncodeWithOptions ¶
EncodeWithOptions writes the Image m to w in PNG format, taking into account the extra options specified.
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
Source Files