How can I smoothen the (GIF)-output of the mapserver

[Wolfgang Qual]

Hello list,
When I create a mapserver-map, I sometimes have the impression that the
maps look quite square-edged. Especially, if the color contrast of
certain themes is high (b/w.). That's the reason why I am looking for a
way to smoothen the output-GIFs of the mapserver - just something like
the blur-filtering in Photoshop or GIMP...

Thanks,

Wolfgang