In article , jmk@cbvox1.cb.att.com (Joe Knapp) wrote: > It seems to me that since the scene is sampled line-by-line, > the "exposure" for any given small region of the frame will be exceedingly > short, so no smearing or blur. A conventional film camera has its shutter open for about half the frame time; the other half is needed to mechanically advance the film. A film projector projector flashes each frame twice in order to alleviate the excessive flicker that would result from flashing at 24 Hz. So a cinematographer arranges that things in film move relatively slowly across the frame. A conventional video camera integrates for a frame time, hence video is usually a little blurrier than film. However the viewing angle of television viewing is usually very small, 10 degrees per picture width or so, much narroweer than film. So the extent of the blur is not objectionable. Some video cameras have provisions to mechanically or electronically shutter. This reduces blur due to motion in the scene, but potentially causes strobing if the viewer tracks motion across the screen. The choice of exposure time in a video camera is inevitably a compromise between blur (for long exposures) and strobing (for short exposures). Anecdotal evidence suggests that an exposure time of 1/3 the frame time is a good compromise. Charles Charles Poynton vox: +1 416 486 3271 fax: +1 416 486 3657 poynton@poynton.com [Mac Eudora, MIME, BinHqx]