pdf output on mapserver 4.4 (raster rendering color)

[Webloper Dedouze]

Hi,
I'm outputting a map with this outputformat:

OUTPUTFORMAT
  NAME pdf1
  MIMETYPE "application/x-pdf"
  DRIVER pdf
  IMAGEMODE RGB
END

All vectors are very good outputted, but it seems that raster (orthophoto)
are only outputted with 8 bits colors. It's rather bad.. Isn't it possible
to output raster images at 32 or 24 bits with the  IMAGEMODE RGB or
IMAGEMODE RGBA mode?? Does pdf output support that?
Thanks in advance!
Rèmy