High-definition video is video of higher resolution than is standard. While there is no specific meaning for high-definition, generally any video image with more than 480 horizontal lines (North America) or 570 lines (Europe) is considered high-definition. 720 scan lines is generally the minimum even though many systems greatly exceed that. Images of standard resolution captured at rates faster than normal (60 frames/second North America, 50 fps Europe), by a high-speed camera may be considered high-definition in some contexts.
From a historical perspective, the first electronic scanning format 405 lines was the first "high definition" television system as the previous mechanical systems had far fewer scanning lines.
From 1939, the US and other European countries experimented with 441 lines and 605 lines until, in 1941, the Federal Communications Commission (FCC) mandated 525 lines for the US. In wartime France, Rene Barthelemy experimented with higher definitions, reaching 1015 and even 1042 lines. Official French transmissions finally began with 819 lines in late 1949; however, this standard was abandoned in 1984 upon the adoption of 625-line color on the TF1 network.
HD in filmmaking
Film as a medium has inherent limitations, such as difficulty of viewing footage while recording, and suffers other problems, caused by poor film development/processing, or poor monitoring systems. Given that there is increasing use of computer-generated or computer-altered imagery in movies, and that editing picture sequences is often done digitally, some directors have shot their movies using the HD format via high-end digital video cameras. While the quality of HD video is very high compared to SD video, and offers improved signal/noise ratios against comparable sensitivity film, film remains able to resolve more image detail than current HD video formats. In addition some films have a wider dynamic range (ability to resolve extremes of dark and light areas in a scene) than even the best HD cameras. Thus the most persuasive arguments for the use of HD are currently cost savings on film stock and the ease of transfer to editing systems for special effects.
Depending on the year and format in which a movie was filmed, the exposed image can vary greatly in size. Sizes range from as big as 24 mm Ã— 36 mm for VistaVision/Technirama 8 perforation cameras (same as 35 mm still photo film) going down through 18 mm Ã— 24 mm for Silent Films or Full Frame 4 perforations cameras to as small as 9 mm Ã— 21 mm in Academy Sound Aperture cameras modified for the Techniscope 2 perforation format. Movies are also produced using other film gauges, including 70 mm films (22 mm Ã— 48 mm) or the rarely used 55 mm and CINERAMA.