grayscale_three.go

func main() {
  
  ...
  
  for _, f := range r.File {
		if f.FileInfo().IsDir() {
			os.MkdirAll(*dest+"/"+f.Name, os.ModePerm)
			continue
		}

		fmt.Printf("converting image: %s\n", f.Name)
		zipped, err := f.Open()
		if err != nil {
			fmt.Printf("error reading '%s': %s\n", f.Name, err.Error())
			continue
		}

		// grayscale images
		img, _, err := image.Decode(zipped)
		if err != nil {
			fmt.Printf("error decoding image '%s': %s\n", f.Name, err.Error())
			continue
		}

		gray := image.NewGray(img.Bounds())
		for x := 0; x < img.Bounds().Max.X; x++ {
			for y := 0; y < img.Bounds().Max.Y; y++ {
				color := img.At(x, y)
				gray.Set(x, y, color)
			}
		}
    
    ...
    
}