480p production systems
My work as director of photography has afforded me the capacity to work with numerous film and digital videotape formats during my career. In early 1999, after shooting countless projects using NTSC, PAL and HDTV interlace formats, I was given the opportunity to work in progressive scan using Panasonic's DVCPRO Progressive format, also known as 480p. After conducting camera tests and research with various digital formats including digital betacam and 1080i HDCAM (at the time of this production 24psf or 720p were not available), I selected 480p to shoot my first project - a short digital film entitled "Crystal Clear." After comparing image quality, it was apparent acquisition in a progressive scan format offered significant improvements over interlace.
The most astounding aspect of the entire project was screening the D5 HD master on a 50-foot movie screen, which clearly proved 480p origination was ideal for large-screen video projection. The primary benefits of starting with 480p are: progressive scan recording allows increased vertical resolution and it significantly reduces interlace motion and detail artifacts; 60 progressive frames are recorded per second resulting in a sharper image with less motion blur than interlace; and 480p allows the use of existing NTSC support equipment and infrastructure during both field and post-production.
The 480 progressive recording format captures each image as a full frame, 60 times per second compared with interlace - where the frame is scanned as two fields creating an odd and an even sequence. Even when a recording that originated in progressive mode is downconverted to NTSC, the images maintain a substantial improvement in the reduction of interlace artifacts such as interline twitter and jaggies. Slow motion playback in 480p is very smooth and fluid and it must be seen firsthand to truly appreciate the advantages of shooting 60 progressive frames per second.
The budgetary aspects of using 480p as an origination format are quickly realized with location production. The cost of renting a camera package is comparable to that of a standard definition, but the progressive image quality exceeds any current interlace 601 format.
The Panasonic AJ-PD900WP Camcorder has the unique ability to select different record modes in DVCPRO (4:1:1), DVCPRO50 (4:2:2) or 480 progressive (4:2:0) in addition to being switchable between 4:3 or 16:9 aspect ratios. The PD900's diversity is unheard of in the world of digital production equipment and makes this camera an extremely flexible unit. The camcorder includes two internal 480p to NTSC downconverted outputs allowing for compatibility with existing NTSC monitors, playback and video assist stations. In contrast, shooting in HDTV and monitoring in NTSC requires external downconversion equipment on set. Using 480p allows a director the assurance that, while the camcorder records in 480 progressive mode, an NTSC output is available and suitable for evaluation of content, framing, depth of field and lighting design.
The field production process for my digital feature started with an AJ-PD900WP camcorder outfitted with Canon high-definition zoom lenses. My primary objective in choosing HD lenses instead of standard definition lenses was to maximize image quality for transfer to 35mm film. I firmly believe in applying a film production philosophy to electronic cinematography by starting with the superior glass in the front of the camera to maximize optical image quality. The results were quite apparent when, during the screening of a 480p to 35mm transfer at a major high definition facility in Los Angeles, the images were mistaken to have originated on 1080/60i high definition.
As a director of photography my intent is to create images that maximize electronic cinematography. I personally place a strong emphasis on using "film style" lighting while working within the limited dynamic range that all digital camcorders have to contend with. I have termed this lighting technique "film-for-tape style lighting." Regardless of what manufacturers have said about the ability their digital camcorders have to faithfully reproduce a scene compared to a motion picture film, it is apparent in my experience that film maintains greater exposure latitude - especially in the highlight areas. Careful attention to avoid excessive white clipping and crushing of blacks will offer an ideal digital emulsion for transfer to film.
Post production with 480p can be accomplished using the Panasonic AJ-PD950A studio VTR, which outputs a downconverted video signal via 601 serial digital, analog component, composite or 480 progressive analog or serial digital. During the downconversion, the original 59.94 progressive frames are downconverted to 59.94 fields. Progressive frame one becomes interlace field one, progressive frame two becomes interlace field two. 480p utilizes 29.97 non-drop or dropframe timecode, which makes downconversion to NTSC extremely simple. The use of 29.97 timecode within a 59.94 frame rate can be confusing. However, it can be easily understood by carefully examining how 480p scans and records the progressive image.
In interlace, a second of time is made up of 59.94 odd and even fields that make up a total of 29.97 frames. It is a commonly accepted practice to round off the fields to 60 and the frames to 30. Since each field (half a frame) is captured at 1/60 sec, a progressive frame can be scanned in the same amount of time by doubling the horizontal scan rate to 31.468Hz. This method allows for squeezing in a full progressive frame in the same temporal period 1/60 sec, which previously represented a field. The timecode in 480p can therefore use 29.97, which makes it compatible with a multitude of existing production and post production NTSC equipment. The same timecode method is also used for 720 progressive. 480p can later be converted to a segmented frame via Panasonic's AJ-UFC1800 Universal Format Converter by dividing the progressive frame into odd and even fields that each contain the same temporal information. This method will allow for post-production editing using interlace equipment while maintaining the progressive temporal advantages.
I have used 480p as an interim acquisition format for delivery of high definition programs by acquiring in 480p and upconverting to high definition 720p or 1080i during online editing. The results have proven that originating in progressive is beneficial when upconverting to high definition or when transferring to 35mm film. 480p is an effective and high-quality alternative for productions that are seeking progressive frame imagery suitable for airing on SDTV, upconverting to HDTV and/or transferring to 35mm film. 480p represents an economical entry point for eventual conversion to high definition, but maintains compatibility within an established NTSC infrastructure.
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