Chess,
Nice find. There are three basic display sizes for ATSC. Basic and enhanced NTSC and PAL image sizes are at the bottom level at 480 or 576 lines. Medium-sized HDTV images have 720 scanlines and are 1280 pixels wide. The top tier has 1080 lines 1920 pixels wide. 1080-line video is actually encoded with 1920×1088 pixel frames, but the last eight lines are discarded prior to display. This is due to a restriction of the MPEG-2 video format, which requires the number of coded luma samples (i.e. pixels) to be divisible by 16.