[pdftex] Image downsampling

[Robin Fairbairns]

> For what reason should anyone transform bitmap images to PDF first to 
> include them into PDFTeX? PDFTeX can include PNG files directly.

you downsample to make the image a sensible size for inclusion; that
way you don't rely on your viewer's/printer's capabilities for
downsampling.  this is sensible if you have serious bitmap
manipulation capability.  also, if it's a "public" file for
distribution, downsampling is highly sensible since it drastically
reduces the resulting file size.

the reason publishers tend not to want you to do this is that they
have graphics manipulation packages of their own that they know and
trust, and would rather not piggy-back on some effort of yours.