4000 lines at 30fps. Should render a "real" 1080 picture even after Mr Kell has had his say...
Provided the high resolution camera image is stored retrieved and displayed using a sufficiently dense sampling grid.
To a first approximation the sampling grid needs to have double the horizontal density, and double the vertical density of the target visible resolution, if the image is to retain a fairly smooth non-digital look, as the camera pans across the scene and small details in the scene alternately align with, straddle, and then align with, elements in the pixel grid. (I can even recall reading a recommendation to use a ratio of 3:1, for a particularly smooth image.)
So if the target video visible resolution is 1920 x 1080, storage and display could utilise 3840 x 2160 pixels, to achieve reasonable smoothness.
I've noticed that FTA broadcasters sometimes "cheat" when broadcasting HD sport using an SD stream of 720x576 pixels. Instead of blurring the image when resampling down to to 720x576 they allow through high enough spatial frequencies from the HD source for moiré patterns to become visible (e.g. in the patterning of the tennis court net) and for visible flickering to appear during pans and zooms (e.g. line markings on a tennis court). Such obvious artifacts would be unacceptable for a transfer to Blu-ray disc of a high resolution Hollywood movie. The aim with a 1920x1080 Blu-ray disc is to present a smooth image free of digital aliasing artifacts, even if that comes at the necessary expense of a softer image.
You may possibly already be familiar with these matters, evil_josh, but I think many readers would not be. (To some extent all I am doing is reiterating points Owen has already made.)
A key point is that to display a vertically scrolling test pattern of 540 thin horizontal white lines* on a display panel smoothly, a display consisting of 1080 rows of pixels is inadequate. 2160 rows of display pixels may be sufficient. 2160 rows of display pixels would allow the very high resolution camera to move up or down slightly without creating too obvious a shimmering effect on the display.
* That is 540 white lines with black gaps separating them, for a total of 1080 "lines". This may be described as 540 "line pairs", or 1080 "television lines".
Edited by MLXXX, 10 November 2011 - 12:02 AM.