Progressive segmented Frame (PsF, sF, SF) is a High Definition mastering video format designed to acquire, store, modify and distribute progressive content using interlaced equipment and media.
History
Originally, PsF was not meant neither for broadcast nor for usage in home video devices. PsF was designed as a standard to simplify the conversion of cinematic content to different video standards, and as means of video exchange between networks and broadcasters worldwide.[1] Brought to life by the movie industry in the end of 1990-ies, the original PsF specification was focused on 24 fps content. Existing interlaced equipment had to be modified for 48i scanning rate in order to work properly with PsF video.
With PsF, a progressive frame is sliced into two "segments", with the odd lines in one segment and the even lines in the other segment. This allows for a progressive picture to be processed through the same electronic circuitry that is used to store, process and route interlaced video. Technically, progressive segments are equivalent to interlaced fields, but unlike native interlaced video, there is no motion between the two segments that make up the video frame. Both fields represent the same instant in time.
PsF allows the progressive format to be maintained, while minimizing bandwidth requirements using interlaced equipment. When translated to TV rates (either at 2:3 or 2:2 pulldown), the progressive image has a closer temporal match to the original film than is possible with a true interlace system, particularly now that modern displays (LCD & plasma) are natively progressive scan devices.[2]
Not everyone welcomed the PsF standard. Some industry observers maintained that native 24p processing would have been a better and cleaner choice. Others accused Sony Pictures in lobbying products of its parent company, Sony Corporation, which at that time was producing interlaced equipment. Charles Poynton, an authority in digital television, makes the following remark in his book: "Proponents of [PsF] scheme claim compatibility with interlaced processing and recording equipment, a dubious objective in my view."[3]
PsF technology is implemented in HDCAM and XDCAM video cameras, including famous CineAlta camera that was used by George Lucas for the Star Wars, Episode 2 movie.
PsF vs. 2:2 pulldown
Progressive segmented frame technique is equivalent to 2:2 pulldown pattern, which is widely used in PAL/SECAM television. As Charles Poynton explains, "film is transferred to 576i video using 2:2 pulldown: Each film frame is scanned into two video fields (or frames); the film is run 4% fast."
It seems that "PsF" is used for material originated on video, while "2:2 pulldown" is used for telecine process, and in broadcast. Poynton does not question the usefulness of 2:2 pulldown scheme for broadcast purposes.
24PsF
24PsF (48sF, 1080sf24, 1920x1080/24/1:1SF) is the original PsF specification, which is used exclusively in professional equipment for film-to-video transfer, mastering and exchange between networks. This may be the first universal video standard which transcends continental boundaries, an area previously reserved for film.[4]
One of the documented examples of 24PsF usage is 2003 transfer of the "Terminator 2" movie to DVD. Artisan and THX started with creating a new high definition digital master by converting original 24fps film to 1080PsF24 format and recording it to HD-D5 videotapes. Usage of progressive segmented frame allowed creating a digital master that was identical to original film, and made possible to perform all digital editing in 24p mode.[5] The same digital master appears to be used for 2006 Blu-Ray transfer of the movie.[6]
25PsF
25PsF (1080sf25, 1920x1080/25/1:1SF) is used in 50i systems for production that originates on video and is targeted for television distribution.
Along with many professional video cameras, this standard is supported by some consumer camcorders like European version of the Canon HV20, which has both interlaced 1080i50 (HDV) mode as well as progressive 1080PsF25 (HDV25) mode.
30PsF
30PsF (1080sf30, 1920x1080/30/1:1SF) gains increased popularity in 60i systems as progressive mastering standard targeted for Web delivery.
Along with many professional video cameras, this standard is supported by some consumer equipment like North American/Japanese version of the Canon HV30 camcorder, which has native interlaced mode (1080i60, HDV), progressive 24p mode with 2:3 cadence (1080p24, HDV24) as well as PsF mode (1080PsF30, HDV30) mode.
At present time 30PsF is not well suited for television distribution, because very few television sets are able to detect 2:2 cadence of 30PsF video. As such, these TV sets may try to deinterlace video by dropping one field of each frame, halving vertical resolution.
References
- ^ "Jim Mendrala, A discussion of 24p frame and the new 48sF frame format".
- ^ "pro-bel, Vistek HD Poster" (PDF).
- ^ "Charles Poynton, Digital Video and HDTV: Algorithms and Interfaces".
- ^ "Steve Wiedemann, 24/P HDTV: The Fall of Film Production".
- ^ "Terminator 2: Extreme Edition".
- ^ "Terminator 2: Judgment Day (Blu-ray)".