Ive always wondered this about bluray, but have never found the answer. On a standard dvd using Mpeg2, the horizontal resolution is 480. When watching a movie with an aspect ratio wider than 1.78:1, some of that resolution is used on black bars. So your resulting image is less resolution than 480, depending on exact aspect ratio. (2.20, 2.35, 2.40, 2.55, etc) Is the same true of bluray? Is a movie with an aspect ratio wider than 1.78:1 using some of its 1080 lines towards black bars?