Most Graphics Configurations in the JDK use a 25-bit image format when
a transparent image is requested. This is an image format that is the
same as the TYPE_INT_RGB format but with one bit assigned to alpha to
allow it to have transparent pixels.

1.4 is missing code to render into or from these image types which means
that generic rendering loops must be invoked whenever these image formats
are used.

A common use of this format is for the icons used by the Metal Look and
Feel for the Swing JTree. Experiments show that implementing this format produces a 10-20% improvement in the performance of the JTree section
of SwingMarks. This is only a factor if there is not enough VRAM on the
display card to accelerate the transparent icons or if the VM is run with
the -Dsun.java2d.ddoffscreen=false flag.