Golang : How to read JPG(JPEG), GIF and PNG files ?



Tags : golang image jpg jpeg gif png

Was having a hard time trying to figure out why all my attempts to open and read JPG or JPEG format image files will cause memory pointer error(when trying to get At() and Bounds() functions to work).

Apparently, in Golang, one must register the format in the init() section first before attempting to open/read image files and perform operation on the files.

The code below is a simple guide on how to open and read JPEG/JPG format image files :

 package main

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

 func init() {
 // damn important or else At(), Bounds() functions will
 // caused memory pointer error!!
 image.RegisterFormat("jpeg", "jpeg", jpeg.Decode, jpeg.DecodeConfig)
 }

 func main() {
 imgfile, err := os.Open("./img.jpg")

 if err != nil {
 fmt.Println("img.jpg file not found!")
 os.Exit(1)
 }

 defer imgfile.Close()

 img, _, err := image.Decode(imgfile)

 fmt.Println(img.At(10, 10))

 bounds := img.Bounds()

 fmt.Println(bounds)

 canvas := image.NewAlpha(bounds)

 // is this image opaque
 op := canvas.Opaque()

 fmt.Println(op)
 }

Sample output :

{255 128 128}

(0,0)-(760,479)

false

This should apply to the PNG and GIF encoded images as well. ( see https://www.socketloop.com/references/golang-image-registerformat-function-example )

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



Tags : golang image jpg jpeg gif png

By Adam Ng

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