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24P

A video term that is an abbreviation of 24 frames per second, progressive scan. 24P is a more recent development in digital video technology that’s quite popular due in part to its similarity with the way in which motion picture film works. Not only does it take on some of the visual characteristics of film, but it also makes the transition of film to video (necessary for television broadcast, VCR tapes, etc.) much easier. It makes the introduction of digital video (particularly high-definition video and special effects) in motion pictures smoother and more natural looking.

Here’s the history: Most motion pictures (since the advent of sound film) are shot (or at least shown) at a constant rate of 24 frames per second; each second, 24 separate and distinct pictures, or “frames”, pass by the lens of the camera and the projector. Each frame is its own unique and complete image; that’s called “progressive”.

Video tape standards are different: original black and white video ran at a straight 30 frames per second, while color video runs at approximately 29.97 frames per second only they aren’t true “frames” in the film sense. Due to video’s nonstop scanning of magnetic tape, a frame is spread across the tape as precisely oriented magnetic particles. Furthermore, video tape “draws” an image on the cathode ray tube in two alternating sets of scan lines: one composed of the even-numbered lines and the other making up the odd-numbered lines. This is why video signals are called “interlaced“. When motion pictures (or any material shot on film) are processed for video playback they undergo a re-scanning process (often through a telecine machine) that converts the frame rate, in part by doubling some film frames in the video. The change from progressive to interlaced scanning, in many viewers’ opinions, visibly changes the quality of the original image. Likewise, visual effects created using existing video frame rates sometimes do not translate well to film.

Digital video created at 24P, however, requires no frame-rate conversion and can freely translate film into video. Progressive scan combines all the horizontal lines in the screen into a single field that lights up at the selected frame rate. It is proving to be particularly effective in high-definition video projects and has blurred the line between film and video shoots. “Star Wars Episode II: The Attack of the Clones” was the first feature-length motion picture shot using 24P high definition digital video cameras; cameras used for Episode III are second-generation versions of the equipment. This means that the live action shots and computer-generated special effects have the same resolution, same brightness, and same overall quality without the need for additional conversion.

Finally, in one of those technological puzzles that are so common, there are actually two versions of 24P: one is more of a “true 24P as it applies to film and other specialty equipment, while the other is a slightly slowed down rate (.1% slower) used by NTSC video equipment. That rate is about 23.976 frames per second and is sometimes referred to simply as 23.8. The 23.976 rate applies to progressive scan DVD and other NTSC video applications.

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