Golang : Save image to PNG, JPEG or GIF format.

This tutorial will demonstrate how to save images into files. We will learn how to generate some random images and save the content from memory into PNG, JPG and GIF file. Basically, the codes are almost the same except for the slight variants to demonstrate how to use the Encode functions.

JPG :

 package main

 import (
 "flag"
 "fmt"
 "image"
 "image/color"
 "image/draw"
 "image/jpeg"
 "math/rand"
 "os"
 "time"
 )

 func main() {
 flag.Parse()
 rand.Seed(time.Now().UTC().UnixNano())

 out, err := os.Create("./output.jpg")
 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // generate some QR code look a like image

 imgRect := image.Rect(0, 0, 100, 100)
 img := image.NewGray(imgRect)
 draw.Draw(img, img.Bounds(), &image.Uniform{color.White}, image.ZP, draw.Src)
 for y := 0; y < 100; y += 10 {
 for x := 0; x < 100; x += 10 {
 fill := &image.Uniform{color.Black}
 if rand.Intn(10)%2 == 0 {
 fill = &image.Uniform{color.White}
 }
 draw.Draw(img, image.Rect(x, y, x+10, y+10), fill, image.ZP, draw.Src)
 }
 }

 var opt jpeg.Options

 opt.Quality = 80
 // ok, write out the data into the new JPEG file

 err = jpeg.Encode(out, img, &opt) // put quality to 80%
 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 fmt.Println("Generated image to output.jpg \n")
 }

PNG :

 package main

 import (
 "flag"
 "fmt"
 "image"
 "image/color"
 "image/draw"
 "image/png"
 "math/rand"
 "os"
 "time"
 )

 func main() {
 flag.Parse()
 rand.Seed(time.Now().UTC().UnixNano())

 out, err := os.Create("./output.png")
 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // generate some QR code look a like image

 imgRect := image.Rect(0, 0, 100, 100)
 img := image.NewGray(imgRect)
 draw.Draw(img, img.Bounds(), &image.Uniform{color.White}, image.ZP, draw.Src)
 for y := 0; y < 100; y += 10 {
 for x := 0; x < 100; x += 10 {
 fill := &image.Uniform{color.Black}
 if rand.Intn(10)%2 == 0 {
 fill = &image.Uniform{color.White}
 }
 draw.Draw(img, image.Rect(x, y, x+10, y+10), fill, image.ZP, draw.Src)
 }
 }

 // ok, write out the data into the new PNG file

 err = png.Encode(out, img)
 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 fmt.Println("Generated image to output.png \n")
 }

GIF :

 package main

 import (
 "flag"
 "fmt"
 "image"
 "image/color"
 "image/draw"
 "image/gif"
 "math/rand"
 "os"
 "time"
 )

 func main() {
 flag.Parse()
 rand.Seed(time.Now().UTC().UnixNano())

 out, err := os.Create("./output.gif")
 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // generate some QR code look a like image

 imgRect := image.Rect(0, 0, 100, 100)
 img := image.NewGray(imgRect)
 draw.Draw(img, img.Bounds(), &image.Uniform{color.White}, image.ZP, draw.Src)
 for y := 0; y < 100; y += 10 {
 for x := 0; x < 100; x += 10 {
 fill := &image.Uniform{color.Black}
 if rand.Intn(10)%2 == 0 {
 fill = &image.Uniform{color.White}
 }
 draw.Draw(img, image.Rect(x, y, x+10, y+10), fill, image.ZP, draw.Src)
 }
 }

 var opt gif.Options

 opt.NumColors = 256 // you can add more parameters if you want

 // ok, write out the data into the new GIF file

 err = gif.Encode(out, img, &opt) // put num of colors to 256
 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 fmt.Println("Generated image to output.gif \n")
 }

Hope this simple tutorial will be able to assist you in dealing with popular image file formats.