http://www.javagaming.org/discus/messages/2/113.html

Yieeeha!

If anyone else out there has similar problems, try this, after creating the MemoryImageSource:

cm=new DirectColorModel(32,0x00ff0000,0x0000ff00,0x000000ff);
memimgsrc.newPixels(aPixels,cm,0,iW);

Subsequent calls to newPixels does not need the color model (Once set, it appears as if the MemoryImageSource keeps on using it)...

とか書いてあります。よくわからないけど、
32bitのほうが速いのかなぁ？？？謎。