Progressive segmented Frame (PsF, 24PsF, 48sF, 1080sf24, 1920x1080/24/1:1SF) 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 for 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 separated into "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 common electronic circuitry that is used to store, process and route interlaced video. Technically, progressive segments are equivalent to interlaced fields, but unlike native interlace video, there is no motion between the two segments that make up the video frame. Both fields represent the same instant in time.
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."[2]
PsF vs. PAL/SECAM 2:2 pulldown
Progressive segmented frame technique is equivalent to 2:2 pulldown pattern, which is used in PAL/SECAM television for at least half a century. 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" seems to be used for telecine process, and in broadcast. Poynton does not question the usefulness of 2:2 pulldown scheme for broadcast purposes.
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 as well as Web delivery format.
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.
Examples of using PsF for acquisition
PsF technology is used in HDCAM and XDCAM video cameras, including famous CineAlta camera. This camera was used by George Lucas to shoot the Star Wars, Episode 2 movie.
In regards to consumer camcorders, PsF is used in the PAL version of the Canon HV20 camcorder, providing 25PsF shooting mode. PsF is also used in the NTSC version of the Canon HV30 camcorder, which adds 30PsF mode to 24p mode that was already available on its predecessor, the HV20.
Examples of using PsF for mastering
Terminator 2: Extreme Edition
One of the examples of practical usage of PsF is the "Terminator 2: Extreme Edition" DVD release. Earlier releases for videotape, LaserDisk and DVD were done by transferring the original theatrical release to 60i video using 2:3 pulldown scheme, then by editing the resulting video. The final result was interlaced video with 2:3 cadence being constantly interrupted. The broken cadence made no difference for analog television, but became a problem when progressive scan TV sets with 2:3 cadence detection became commonplace.
Considering tremendous popularity of the "Terminator 2", Artisan and THX performed a completely fresh transfer of the movie to digital form in 2003. They 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.[3] It is also worth nothing that this digital master appears to be used for 2006 Blu-Ray transfer of the movie.[4]