Table Cell Background Opacity

I'm trying to change the opacity of a background image for a table cell
using

<td style="background: url('foo.png') ; filter: alpha(opacity=0.8);
-moz-opacity: 0.8; opacity: 0.8;">

Unfortunately, this filter applies to not only the background image but
the text in the cell as well. Any ideas how to have a translucent
background image but maintain fully opaque text?

Thanks in advance,

Troy Henderson