swapping the red and green pixels in an image

function swapRedGreen(pixel){
    var tempRedValue = pixel.getRed();
    pixel.setRed(pixel.getGreen());
    pixel.setGreen(tempRedValue);
}
var image = new SimpleImage("drewRobert.png");
print(image);
for(var pix of image.values()){
    swapRedGreen(pix);
}
print(image);