Originally Posted by ella

first of all, I don't know why you are slicing the files in photoshop and not with Image Ready, however, if you do all that and you are still getting a dithered preview, check out the "preview menu" (should be a round button with an arrow on it, in the upper right corner) and uncheck the "browser dither" option. If its not checked, then I have no idea what else it is that you are doing wrong.