Golang : Set image canvas or background to transparent



Tags : golang png image-transparentdraw alpha

Putting this down here for my own future reference. Maybe useful to you too. Anyway, basically what I need is to make an image canvas or background to transparent before drawing over it.

For example, I need to set the foreground color to black and set the background to transparent :

 foreGroundColor  := image.NewUniform(black)
 backGroundColor := image.Transparent
 backgroundWidth := 700
 backgroundHeight := 50
 background = image.NewRGBA(image.Rect(0, 0, backgroundWidth, backgroundHeight))

 draw.Draw(background, background.Bounds(), backGroundColor, image.ZP, draw.Src)
 // draw something with foreGroundColor.....

alternatively, this method will work as well.

 // make every pixel transparent
 for y := 0; y < backgroundHeight; y++ {
 for x := 0; x < backgroundWidth; x++ {
 background.Set(x, y, image.Transparent)
 }
 }

To test, save the background to a PNG file.

 // Save that background image to PNG.
 imgFile, err := os.Create("background.png")
 if err != nil {
 fmt.Println(err)
 os.Exit(-1)
 }
defer imgFile.Close()
buff := bufio.NewWriter(imgFile)
err = png.Encode(buff, background)
if err != nil {
 fmt.Println(err)
 os.Exit(-1)
 }
 err = buff.Flush()
 if err != nil {
 fmt.Println(err)
 os.Exit(-1)
 }
 fmt.Println("Save to background.png")

Remember...... that JPEG does not support transparency.

Happy coding!

References:

https://www.socketloop.com/references/golang-image-alpha-set-and-setalpha-functions-examples



Tags : golang png image-transparentdraw alpha

By Adam Ng

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