1920*1080i or 1920*540p

1080i and 540p in analog form are approximately the same and usually interchangeable.


1080i source has picture detail captured from 1080 (x up to 1920) possibly positions in the scene. 540 source has picture detail captured from 540 (x up to 1920) possible positions in the scene.


1080i analog format has 1125 total scan lines per full frame and encoding somewhere in lines 1081 throuth 1125 indicating which field is odd and which field is even. I think 540p analog format has 1124 or 1126 scan lines for every two frames and no way of identifying some frames as odd fields.


1080i on the screen has picture information on 1080 unique scan line positions (i.e. pixel rows) on the screen. 540p has picture information on 540 unique scan line positions on the screen. A TV with those settings can be set to either 540p or 1080i for material originally at or converted to either 540p or 1080i. Depending on the electron beam fatness you may see more pronounced gaps between scan lines when you switch a CRT HDTV to 540p.

Way back, when the 1080i and other ATSC formats were tested for approval, a committee of video experts measured 800 lines of effective vertical resolution with the 1920X1080i format. A setup that only uses 540p, such as bob-only deinterlacing, obviously can't deliver 800 lines. (The sublink for the original data source, table 2.3, no longer works, but is now a pdf ATSC link .) Also, the intro "resolution" paragraph (2.1) in that ATSC link mentions that 540p tends to look like 1920X1080i when motion takes place. Motion, as the first linked test table above shows (dynamic data), sharply reduces interlaced vertical resolution. But progressive images aren't necessarily a cure for vertical resolution loss with motion, as the test data for 720p shows, as well as some authoritative sublinked articles outlining resolution for both HD formats. -- John