HD is defined as either 1920 x 1080 (at various scanning schemes), or 1280 x 720p/60. Because the naming convention is a bit confusing (and different from the past), many people do not realize that the most commonly employed HD format today, 1920 x 1080i/60, means only 540 vertical lines are displayed in each 1/60th of a second --- we used to call that 30-frames per second (60 half pictures, or fields, equal 30 full pictures, or frames, per second). One of the reasons that 720p looks good is that 720 V lines, a full frame, are displayed 60 times a second.

Humans are more sensitive to vertical resolution than we are to horizontal resolution. The 720p format definitely has lower H res than 1080, but we don't seem to notice it much. (And, readily available monitors cannot display the difference.) Sony has made good use of the fact that humans will give up H res in their HDCAM format. HDCAM can only record about 75% of the 1920 pixels, but like the 1280 H pixels in 720p, the picture still looks good. Panasonic's just-introduced DVCPRO HD uses pre-filtering techniques similar to HDCAM's to make portable recording possible.

Bottom line is that both HD formats look very good. 1920 x 1080, recorded on a VTR that can capture that resolution, has the largest pixel map, but the 60-full frames per second of the progressively scanned 720p format handles motion better. Users should make their choice accordingly. NBC and CBS prefer 1080, ABC and FOX (when Fox does HD) prefer 720p