Golang : Convert []byte to image


Tags : golang image convert byte

There are times when you need to convert []byte to image for saving into file purpose. I encountered one of this situation today as I need to save a generated QR code into PNG file.

In this short tutorial, we will learn how to convert []byte into image and save to a PNG file. Basically to convert to image, you just need to process the []byte variable with bytes.NewReader() function and wrap it with image.Decode() function.

See example :

 imgByte := code.PNG()

 // convert []byte to image for saving to file
 img, _, _ := image.Decode(bytes.NewReader(imgByte))

 //save the imgByte to file
 out, err := os.Create("./QRImg.png")

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 err = png.Encode(out, img)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

and the entire program :


 package main

 import (
 "bytes"
 "code.google.com/p/rsc/qr"
 "crypto/rand"
 "fmt"
 "image"
 "image/png"
 "os"
 "runtime"
 )

 func randStr(strSize int, randType string) string {

 var dictionary string

 if randType == "alphanum" {
 dictionary = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 }

 if randType == "alpha" {
 dictionary = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
 }

 if randType == "number" {
 dictionary = "0123456789"
 }

 var bytes = make([]byte, strSize)
 rand.Read(bytes)
 for k, v := range bytes {
 bytes[k] = dictionary[v%byte(len(dictionary))]
 }
 return string(bytes)
 }

 func main() {

 // maximize CPU usage for maximum performance
 runtime.GOMAXPROCS(runtime.NumCPU())

 // generate a random string - preferbly 6 or 8 characters
 randomStr := randStr(6, "alphanum")
 fmt.Println(randomStr)

 // generate the link or any data you want to
 // encode into QR codes
 // in this example, we use an example of two factor
 // authentication link. Replace the authTFAlink
 // with yours.

 authTFAlink := "otpauth://socketloop.com?key=" + randomStr + "&issuer=SocketLoop"

 // Encode authTFAlink to QR codes
 // qr.L = 20% redundant level
 // see https://godoc.org/code.google.com/p/rsc/qr#Level

 code, err := qr.Encode(authTFAlink, qr.L)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 imgByte := code.PNG()

 // convert []byte to image for saving to file
 img, _, _ := image.Decode(bytes.NewReader(imgByte))

 //save the imgByte to file
 out, err := os.Create("./QRImg.png")

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 err = png.Encode(out, img)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 // everything ok
 fmt.Println("QR code generated and saved to QRimg.png")

 }

References :

https://www.socketloop.com/tutorials/golang-save-image-to-png-jpeg-or-gif-format

https://www.socketloop.com/tutorials/golang-convert-an-image-file-to-byte

  See also : Golang : Convert an image file to []byte



Tags : golang image convert byte

By Adam Ng

IF you gain some knowledge or the information here solved your programming problem. Please consider donating to the less fortunate or some charities that you like. Apart from donation, planting trees, volunteering or reducing your carbon footprint will be great too.


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