Graysacling an image?

[Pojahn_M]

I have imported an image(into a BufferedImage), I want to grayscale this image. How can I do it?
One guy said something like this:

The way to convert an RGB value to grayscale is to use the following formula: brightness = 0.212671 * R + 0.715160 * G + 0.072169 * B. Assign brightness to the Red, Green, and Blue components of the a new RGB value.

But I have no clue how to do this. BufferedImage store its RBG in a int. If I could use WriteableRaster and use the formula above, but I dont know how to convert a WriteableRaster to BufferedImage.
Some help?

[Pojahn_M]

This work:

    public static void main(String[] args) throws Exception
    {
		BufferedImage img = ImageIO.read(new File ("C:\\ngchem.png"));
		BufferedImage grayimg = new BufferedImage (img.getWidth (), img.getHeight (), BufferedImage.TYPE_BYTE_GRAY);

		for (int i = 0; i < img.getHeight (); i++)
			for (int j = 0; j < img.getWidth (); j++)
			{
				int pixel = img.getRGB (j, i);
				grayimg.setRGB (j, i, pixel);
			}

		ImageIO.write(grayimg, "PNG", new File ("C:\\test.png"));
	}

But the quality is poor

[doWhile]

See the following class: ColorConvertOp (Java Platform SE 6)
It makes convertion of Images to different color spaces much easier, you just need to specify which ColorSpace's for the conversion, and supply the appropriate BufferedImages of a given type...the example below demonstrates an example of how to accomplish this.

BufferedImage image = //get color image
BufferedImage bw = new BufferedImage(image.getWidth(), image.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
BufferedImageOp op = new ColorConvertOp(image.getColorModel().getColorSpace(), ColorSpace.getInstance(ColorSpace.CS_GRAY), null);
bw = op.filter(image, bw);

I'd recommend immersing yourself in the API of these classes and methods, as there are many different options you can set for the conversion.