Change color of a single pixel - Golang image

Question

I want to open jpeg image file, encode it, change some pixel colors, and then save it back as it was.

I\'d like to do something like this

imgfile, er         


        

Answer 1

The image decode returns an image interface which has a Bounds method to obtain the image pixel width and height.

img, _, err := image.Decode(imgfile)
if err != nil {
    fmt.Println(err.Error())
}
size := img.Bounds().Size()

Once you have the width and height you can iterate over the pixels with two nested for loops (one for the x and one for y coordinate).

for x := 0; x < size.X; x++ {
    for y := 0; y < size.Y; y++ {
        color := color.RGBA{
            uint8(255 * x / size.X),
            uint8(255 * y / size.Y),
            55,
            255}
        m.Set(x, y, color)
    }
}

Once your are done with the image manipulation you can encode the file. But because image.Image does not have Set method, you can create a new RGBA image, which returns an RGBA struct, on which you can use the Set method.

m := image.NewRGBA(image.Rect(0, 0, width, height))
outFile, err := os.Create("changed.jpg")
if err != nil {
    log.Fatal(err)
}
defer outFile.Close()
png.Encode(outFile, m)