Making Sure Your Whites Are Really White
If you have an image that appears to have solid white areas (maybe the background surrounding a logo), but when you put the Eyedropper on that area, it gives you a 1% or 2% reading in one of the CMYK values in your Info palette, you can use Levels to gets those areas back down to 0% so they don't print with a dot. Here's how: Go under the Image menu, under Adjustments, and choose Levels. The third field from the left (at the top of the dialog) shows your current highlight value (your white point setting). The default value will be 255. Enter 252 or 250, then move your cursor over the white area in question and look in the Info palette to see if the readings are now all 0% (that change should be enough to remove the stray colors). When it's right, click OK, and you'll have solid white in your white areas.