生命不止，繼續 go go go !!!

golang同樣為我們提供了很多關于圖片處理的標準庫，這里與大家一起學習分享。

image package

作用：
Package image implements a basic 2-D image library.
image包實現了一個基本的2D圖像庫.

方法：
func NewNRGBA

func NewNRGBA(r Rectangle) *NRGBA

NewNRGBA returns a new NRGBA image with the given bounds.

什么是NRGBA？
NRGBA is an in-memory image whose At method returns color.NRGBA values.

type NRGBA struct {
        Pix []uint8
        Stride int
        Rect Rectangle
}

func (*NRGBA) Set

func (p *NRGBA) Set(x, y int, c color.Color)

設定指定位置的color，image/color稍后會介紹。

func Rect

func Rect(x0, y0, x1, y1 int) Rectangle

Rect is shorthand for Rectangle{Pt(x0, y0), Pt(x1, y1)}.

image/color package

作用：
Package color implements a basic color library.

func (NRGBA) RGBA

func (c NRGBA) RGBA() (r, g, b, a uint32)

func DecodeConfig

func DecodeConfig(r io.Reader) (Config, string, error)

DecodeConfig decodes the color model and dimensions of an image that has been encoded in a registered format.
更通俗說就是獲得image的信息。

image/png package

作用：
Package png implements a PNG image decoder and encoder。

func (*Encoder) Encode

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

編碼png文件。

image/jpeg package

作用：
Package jpeg implements a JPEG image decoder and encoder.

func Encode

func Encode(w io.Writer, m image.Image, o *Options) error

編碼JPG文件。

應用

生成圖片

package main

import "image"
import "image/color"
import "image/png"
import "os"

func main() {
    // Create an 100 x 50 image
    img := image.NewRGBA(image.Rect(0, 0, 100, 50))

    // Draw a red dot at (2, 3)
    img.Set(2, 3, color.RGBA{255, 0, 0, 255})

    // Save to out.png
    f, _ := os.OpenFile("out.png", os.O_WRONLY|os.O_CREATE, 0600)
    defer f.Close()
    png.Encode(f, img)
}

運行結果，就是生成了一張png文件。

生成復雜色彩的圖片

package main

import (
    "fmt"
    "image"
    "image/color"
    "image/png"
    "math"
    "os"
)

type Circle struct {
    X, Y, R float64
}

func (c *Circle) Brightness(x, y float64) uint8 {
    var dx, dy float64 = c.X - x, c.Y - y
    d := math.Sqrt(dx*dx+dy*dy) / c.R
    if d > 1 {
        return 0
    } else {
        return 255
    }
}

func main() {
    var w, h int = 280, 240
    var hw, hh float64 = float64(w / 2), float64(h / 2)
    r := 40.0
    θ := 2 * math.Pi / 3
    cr := &Circle{hw - r*math.Sin(0), hh - r*math.Cos(0), 60}
    cg := &Circle{hw - r*math.Sin(θ), hh - r*math.Cos(θ), 60}
    cb := &Circle{hw - r*math.Sin(-θ), hh - r*math.Cos(-θ), 60}

    m := image.NewRGBA(image.Rect(0, 0, w, h))
    for x := 0; x < w; x++ {
        for y := 0; y < h; y++ {
            c := color.RGBA{
                cr.Brightness(float64(x), float64(y)),
                cg.Brightness(float64(x), float64(y)),
                cb.Brightness(float64(x), float64(y)),
                255,
            }
            m.Set(x, y, c)
        }
    }

    f, err := os.OpenFile("rgb.png", os.O_WRONLY|os.O_CREATE, 0600)
    if err != nil {
        fmt.Println(err)
        return
    }
    defer f.Close()
    png.Encode(f, m)
}

運行結果：

獲取一張圖片的尺寸

package main

import (
    "fmt"
    "image"
    _ "image/jpeg"
    _ "image/png"
    "os"
)

func main() {
    width, height := getImageDimension("rgb.png")
    fmt.Println("Width:", width, "Height:", height)
}

func getImageDimension(imagePath string) (int, int) {
    file, err := os.Open(imagePath)
    defer file.Close()
    if err != nil {
        fmt.Fprintf(os.Stderr, "%v\n", err)
    }

    image, _, err := image.DecodeConfig(file)
    if err != nil {
        fmt.Fprintf(os.Stderr, "%s: %v\n", imagePath, err)
    }
    return image.Width, image.Height
}

生成縮略圖
借助github開源項目：
https://github.com/disintegration/imaging
文檔地址：
http://godoc.org/github.com/disintegration/imaging