Set color-depth via any fop-package

Hi,

I am using the org.apache.fop.apps.Driver class and a renderer
to render TIFF-images. My problem is that the images are to big (in
bytesize).
I am using maximum compression when rendering the images.

I wonder, is there any classes in org.apache.fop where I can define
color-depth,
number of colours etc. etc. for the rendered image, so the size will be
smaller ?

I am not so familiar with graphics, there are maybe other settings I can do
to
reduce the image-size ?

Thanks in advance
/Gergely