Progressive segmented frame

Progressive segmented Frame (PsF, sF, SF) is a scheme designed to acquire, store, modify, and distribute progressive scan video using interlaced equipment and media.

With PsF, a progressive frame is divided into two segments, with the odd lines in one segment and the even lines in the other segment. Technically, the segments are equivalent to interlaced fields, but unlike native interlaced video, there is no motion between the two fields that make up the video frame: both fields represent the same instant in time. This technique allows for a progressive picture to be processed through the same electronic circuitry that is used to store, process and route interlaced video.

The PsF technique is similar to 2:2 pulldown, which is widely used in 50 Hz television systems to broadcast progressive material recorded at 25 frame/s, but is rarely used in 60 Hz systems. The 2:2 pulldown scheme had originally been designed for interlaced displays, so fine vertical details are usually filtered out to minimize interline twitter. PsF has been designed for transporting progressive content and therefore does not employ such filtering.

The term progressive segmented frame is used predominantly in relation to high definition video. In the world of standard definition video, which traditionally has been using interlaced scanning, it is also known as quasi-interlace^[1] or progressive recording.^[2]

History

PsF was designed to simplify the conversion of cinematic content to different video standards, and as a means of video exchange between networks and broadcasters worldwide.^[3] Brought to life by the movie industry in the end of the 1990s, the original PsF specification was focused on 24 frame/s content, resulting in existing interlaced equipment having to be modified for 48 Hz scanning rate in order to work properly with 24 frame/s content.

Not everyone welcomed the PsF standard, however. Some industry observers maintained that native 24p processing would have been a better and cleaner choice. Charles Poynton, an authority in digital television, made the following remark in his book: "Proponents of [PsF] scheme claim compatibility with interlaced processing and recording equipment, a dubious objective in my view."^[1] William F. Schreiber, former Director of the Advanced Television Research Program at MIT, suspected that the continued advocacy of interlaced equipment originated from consumer electronics companies that were trying to get back the substantial investments they had made in obsolete technology.^[4]

Usage

Despite the criticism, PsF quickly became a de facto standard for high quality film-to-video transfer. One of the documented examples of PsF usage is the 2003 transfer of the film "Terminator 2: Judgment Day" to DVD, performed by Artisan Entertainment and THX. The original 24 frame/s movie was converted to PsF format and recorded to HD-D5 videotapes. This allowed for the creation of a digital master that was nearly identical to the original film, and made it possible to edit digitally at the native frame rate.^[5] The same digital master appears to be used for the 2006 Blu-ray Disc transfer of the movie.^[6]

PsF has been recognized by Recommendation ITU-R BT.709 as a legitimate way to transport progressive frames within an interlaced system. 25PsF and 30PsF rates have been added to the specification in addition to the more established 24PsF. "Fractional" frame rates, having the above values divided by 1.001, are also permitted; the resulting 23.976PsF and 29.97PsF rates are used in 60 Hz systems.

PsF became a means of initial image acquisition in professional Sony video cameras. It is employed in HDCAM and XDCAM video cameras, including the HDW-F900 CineAlta camera which was used by George Lucas for creating Star Wars, Episode 2, and by Alexander Sokurov for creating Russian Ark fully in the digital domain.

PsF is utilized in some DV, HDV and AVCHD camcorders for 25-frame/s and 30-frame/s progressive-scan recording, and can be called Progressive recording (Sony), Progressive scan mode (Sony), Frame mode (Panasonic and Canon), Digital Cinema mode (Panasonic) or Cinema mode (Canon). Consumer and many professional camcorders do not use PsF to record 24-frame/s video; instead they either record it natively in progressive form or apply 2:3 pulldown.

Sony's "Frame shutter mode"

"Frame shutter mode" or "progressive shutter mode" is Sony's trademarked progressive scan charge-coupled device (CCD) mode for video cameras. This mode allows full-frame acquisition with conventional interlaced field output. It is conceptually identical to PsF, except PsF is used in high definition video, while "frame shutter mode" is used by Sony for its standard definition products.

In frame shutter mode, a camera acquires 30 (NTSC) or 25 (PAL) independent images per second. These images are output as 60 (NTSC) or 50 (PAL) interlaced fields. The result is a progressive-scan signal, which is also compatible with traditional interlaced scanning systems.

Sony used frame shutter mode, later renamed to progressive recording, in several consumer products. For example, the DCR-HC96 camcorder is capable of shooting in 30p progressive mode; its European cousin, the DCR-HC96E, has matching 25p progressive mode.

The operating guide for a 60 Hz ("NTSC") Sony DCR-HC96 camcorder describes the progressive recording mode as follows:

Note on the progressive recording mode

In a normal TV broadcast, the screen is divided into 2 finer fields and these are displayed in turn, every 1/60 of a second. Thus, the actual picture displayed in an instant covers only half of the apparent picture area. In progressive recording, the picture is fully displayed with all the pixels.

— ^[2]

The booklet for the 50 Hz ("PAL") Sony DSR-PD175P camcorder describes its progressive recording mode as follows:

Progressive Scan Mode

The 25p image captured by the sensor system is recorded as an interlaced signal by dividing each frame into two fields. This enables compatibility with current editing and monitoring equipment that only accept interlaced signals, while maintaining the quality of the 25p image.

— ^[7]

Encoding of color information

Most video formats including professional ones utilize chroma subsampling to reduce amount of chroma information in a video, taking advantage of the human visual system's lower acuity for color differences than for luminance.^[8] Such a reduction improves compression of the video signal, which is always desirable because of storage and transmission limitations.

To ensure compatibility with interlaced-based systems, chroma information in PsF video is often recorded in interlaced format, despite that the content is progressive. This may result in interlaced artifacts being noticeable on colored objects.^[9]

Variants

• 24PsF (48sF, 1080sf24, 1920×1080/24/1:1SF) is the original PsF format, which is used in professional equipment for film-to-video transfer, for high definition mastering and for video exchange between networks. This may be the first universal video standard which transcends continental boundaries, an area previously reserved for film.^[10]

• 25PsF (1080sf25, 1920×1080/25/1:1SF) is used in 50 Hz systems for production that originates on video and is targeted for television distribution.

• 29.97PsF (1080sf29, 1920×1080/29.97/1:1SF) formats are sometimes used in 60 Hz systems for sitcoms and music shows.^[11][12] 29.97PsF as well as 30PsF (30p, 1080sf30, 1920×1080/30/1:1SF) formats are gaining popularity as an acquisition format for Web video delivery, because most video hosting web sites cannot stream video with rates higher than 30 frame/s.

References