How to write a base64 decoded png image to file?

Question

I try to write a base64 png image to file with following code:

imageReader := base64.NewDecoder(base64.StdEncoding, strings.NewReader(Images[i]))
pngImage, _, err := image.Decode(imageReader)
if err != nil {
  beego.Error(err)
}
bounds := pngImage.Bounds()
if imgFile, err = os.Create(fileName + ".png"); err != nil {
   return Data{}
}
defer imgFile.Close()
_, err = imgFile.Write([]byte(pngImage))

The bounds are ok. The error message for the last line is

cannot convert pngImage (type image.Image) to type []byte

Obviously, because an image.Image is not a byte[]. But how can I convert it? Or is there even a simpler version to do this.

Do you you need to have the decoded image? It's much faster to write the data directly to the file. If you only want the bounds, you can use DecodeConfig. — JimB, Oct 15 '15 at 14:07

score 4 · Accepted Answer · edited May 23 '17 at 10:32

Use png.Encode() to encode an image.Image to a file (io.Writer).

The last line should be replaced with:

err = png.Encode(imgFile, pngImage)

png.Encode() will produce and send the byte sequence to the specified io.Writer (which can be an os.File of course), describing the specified image in PNG format.

Also check out this answer which contains a complete example writing an image to a file (in PNG format):

Draw a rectangle in Golang?

How to write a base64 decoded png image to file?

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