<p>You need to know how letterbox and pillarbox work, it's the same for any time the aspect ratio is different from the media. It's the same for an HDTV image on a standard TV and the same for a standard TV image on an HDTV. It's common when you want to put a picture on a slide that doesn't fit the screen size. When the image is wider then the screen, such as a movie on a standard definition TV (SDTV), the technique that has the least distortion, is the letterbox. When your using a TV, you get the infamous black bars top and bottom, that allow the full width image to be used. These are usually the same size, but not always. Say you have a movie in Swedish, you don't want to cover the original dialog, so you decide to use subtitles. In a letterbox version you can put the subtitles in the black bars, allowing the viewer full view of the picture.</p><p>When the image is taller then the screen, such as an SD movie on an HDTV you can put the bars on the sides, this is called pillarboxing, it's common on older programs on an HDTV. On a projection screen neither letterbox or pillarbox are visible to the user, because the image appears to be simply smaller. I've seen movies where they reformatted it using letterbox to fit a 4:3 screen, and then watched on an HDTV where it's also pillarboxed. </p><p> </p>