Why Not 853 x 480?
Dear Gary: Stupid me, I just realized that the visible resolution of DVD-Video—720 x 480 pixels —is in a 1.50:1 ratio; not 16:9. Because the NTSC standard includes 480 lines of vertical resolution, I easily figured out that if 480 is the “9” in “16:9,” then the “16” should be about 853. So why was 720 lines of horizontal resolution picked over 853 lines? Why have rectangular pixels with 720 x 480 instead of square pixels with 853 x 480? By the way, your magazine is in my opinion the pinnacle of its genre.
Jason Steg, Chapel Hill, North Carolina
Video Technical Editor Greg Rogers Comments:
There are several reasons that favor the 720 x 480 format. The well established ITU-R 601 video standard used for standard-definition professional video products and digital video interfaces also specifies 720 pixels per active line for both 4:3 and 16:9 pictures. This makes many pieces of pre-existing professional video equipment compatible with DVD development and production. (There is also a rarely implemented provision of ITU-R 601 that provides for 960 pixels per active line for 16:9 pictures.) The 720 x 480 pixel format is also convenient for the 8 x 8 and 16 x 16 block sizes of the MPEG-2 compression technology that is used for DVD. You might note that the two HDTV formats, 720p and 1080i, do use square pixels—1280 x 720 and 1920 x 1080
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