convert image to grayscale

I needed a function that would convert an image to grayscale, after  
trying 6 different functions this one seems to be the fastest:

function convertToGrayscale(img){
        var img = img.getBufferedImage();
        var w=img.getWidth();
        var h=img.getHeight();
        var type = java.awt.image.BufferedImage.TYPE_BYTE_GRAY;
        var grayImage = new java.awt.image.BufferedImage(w, h, type);
        var g = grayImage.createGraphics();
        g.drawRenderedImage(img, null);
        g.dispose();
        return new Image(grayImage);
}

So I thought I would share..

grts-
Jonathan