r was not constructed
 with an explicit pixel buffer to hold the pixels then this method
 will return null until the size and format of the image data is
 known.
 Since the PixelGrabber may fall back on accumulating the data
 in the default RGB ColorModel at any time if the source image
 uses more than one ColorModel to deliver the data, the array
 object returned by this method may change over time until the
 image grab is complete.<DD><DL>
<DT><B>Returns:</B><DD>either a byte array or an int array<DT><B>