acrobat

sub-pixel rendering has nothing to do with your figures,
it applies only to text, and only on LCD displays, where
RGB pixels are composed of subpixels whose only variable
is intensity. Normally one only writes only to the virtual
pixels, but with sub-pixel rendering the sub-pixels are
exposed to the programmer. They're fairly useless for
everything but anti-aliasing small, black curves as found
in text, and AFAIK only things going through the font
renderer use it (not images).

Are you using Acrobat 6? In theory you one could recover
every bit of the files you sent me from the pdf. So
there's something in your display methodology if the pdf
doesn't look as good as the bmps.

-Carl