Contributed editorial appearing in
Scientific Computing & Instrumentation 19:6, May 2002, pg. 16.
In a recent interview with Digital Cinema Magazine, Star Wars Creator George Lucas commented on film-based cinematography by saying “We don‘t live in the 19th century. We don‘t live in the sprockets and gears and celluloid and photochemical processes like we did then. We’ve advanced beyond that. We are in the digital age...” Lucas was commenting on his decision to shoot Star Wars: Episode II exclusively using digital cameras. Scientific flow visualization techniques, including Particle Image Velocimetry, Planar Doppler Velocimetry, and Pressure-Sensitive Paint have enjoyed vast improvements in measurement accuracy and image processing through the use of digital charge-coupled device (CCD) cameras. CCD-based digital home-video camcorders have been available for sometime, however, even given the renaissance experienced in the music industry by the deployment of digital recording studios and Compact Disc (CD) audio, there is palpable resistance to digitize the motion picture industry.The primary issue preventing widespread adoption of digital cinematography is the difference in image acquisition rate or “frame” rate between digital-video and celluloid-film cameras. The standard frame exposure and projection rate for film-based cameras is 24-frames per second while digital video has been standardized at 60- or 50-frames per second, depending on geographic region. Motion picture cinematographers deride the high frame rates of digital video cameras for producing amateurish, television-like pictures having an overbearing high-frequency “treble” quality that cannot be used to capture the low-frequency -rich “optical bass” present in 24-frame celluloid cinema. The Sony Corporation, an acknowledged leader in digital cameras, is the first to remove this argument through the development of a 24-frame-per-second digital camera. Dubbed the “CineAlta” system, Sony has produced the HDW-F900 digital camcorder capable of capturing 1920 x 1080 digital video images at 24 frames-per-second.
Incorporating Sony’s latest CCD research, the HDW-F900 utilizes a “progressive scan” CCD in which all pixel intensities of every frame are read out independently and in order without interlacing. Traditional digital camcorders cannot read out the entire CCD imager at 60 or 50 Hz and must read every-other row of pixels in successive frames, earning the label 60i or 50i. Since 24 Hz is below the 30- and 25-Hz scan rate of the 60i and 50i camcorders, the progressive scan “24P”, as it is known, can record every pixel of every frame. In order to record color information, each element of the CCD is masked by a primary Red (R), Green (G), or Blue (B) color filter that are arranged in a mosaic pattern of alternating rows of G-B-G-B and R-G-R-G filters. A 12-bit analog-to-digital converter acquires the intensity of each pixel and a 2-million gate VLSI chip interpolates over 30-bit RGB values for every pixel based on the values of neighboring pixels and leverages the greater abundance of Green pixels to adjust overall image intensity.
The HDWF900 also uses Sony’s Hole Accumulation Diode (Super-HAD) technology used to improve the camcorder’s sensitivity to light. As CCD pixel density increases, the smaller size of each pixel results in a decrease in the effective light-gathering aperture of each pixel. Super-HAD technology places an on-chip micro-lens above each of the chip’s 2.2 million pixels thereby increasing the virtual aperture size of each pixel. The HDW-F900 streams the acquired images to 50-mm digital video tape cartridges, more than quadrupling the 11-minute recording time of a reel of standard 35mm VistaVision celluloid film. At the moment, nearly all movie theaters are equipped with celluloid film projectors. This requires the transfer of the final 24P digital movie master to celluloid film in a 1 frame to 1 frame process. This step is also required for the distribution of movies shot on 35-mm film, however, each 24P copy is produced directly from the digital master, resulting in higher quality.
As the number of motion pictures shot digitally increases, more theaters will install large-screen digital projectors, such as those based on the Texas Instruments Digital Light Processing (DLP) system. Gone will be the days of jittery projectors that scratch and pit the film during each showing. That is, of course, if the current industry moguls don’t claim that the shouting of “Focus!” by movie patrons is an integral part of the movie-going experience.
