Originally posted by lland:
It happens in iPhoto and Preview
display the images at full size, and they will not be antialiased at all. antialiasing (smoothing) only happens when an image is scaled.
Also, if you like, you can turn this feature off completely in Preview (under Preferences) -- iPhoto doesn't seem to have such a preference (since the majority of the time, you'd want things to be antialiased).
Just view the images at full size.