21 Grams
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Metadata
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DVD
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"Metadata is the production information we use for making a movie that's not on the negative," says Kerlow. "For years, metadata used to be kept in a notebook or on a piece of paper or was transmitted verbally. For technically simple productions, we can still keep metadata in our brain. But today, we're trying to optimize many aspects of production - such as the integration of visual effects, total control over the motion of the camera or color-timing issues - and the more we want to control those details, the more we need to keep track of the metadata in the same media that we record the content."

What makes it more complex, says Kerlow, is that when people in the entertainment community talk about metadata, they're usually talking about different things depending on where they are in the workflow. "There's the metadata that's critical to production people - positional camera data and lens data for visual-effects integration," he says. "That's been done for a few years, and now we're just trying to optimize how we do it. On the other hand, when postproduction people say metadata, they're talking about EDLs and transitional effects. When the distribution people say metadata, they might be talking about viewing rights for streaming or number of viewings allowed. Archivists are interested in other types of information."

Not only is it a challenge to pick the metadata that will answer everyone's needs, but also there needs to be a reliable means of handling metadata between the different stages of production, distribution and archiving. Only this way can cinematographers feel assured that the information input at the capture or scanning stage will be of value by the time the movie - be it film or digital - is projected onto the screen. "That's the value that the ASC can add to this meta-data dialogue," Kerlow agrees. "Cinematographers are the people who capture the image, and they are usually the last to touch the image during color timing."

The ASC's metadata subcommittee will first review items that others have proposed to store in metadata and then decide which features are important from the cinematographer's point of view. They will then submit their recommendations to standards organizations working on metadata, as well as manufacturers of HD cameras, nonlinear editing systems and color-timing systems.

What are the issues that need to be examined? Kodak's Sullivan breaks metadata down in terms of its content. First, he says, is definitional data, which includes spatial characteristics and color space. Information on spatial characteristics ensures that the imagery's aspect ratio and size are maintained. With regard to color space, he adds, it's important to know what the integer values represent. "Saying 'RGB' isn't enough," he notes. Second, metadata must contain variational data, such as where the film was processed. "You can't take the source of variability out of the system, and you can't capture the data file until you have the variability of the sources," he cautions. "If you don't have them, you'll come up with an assumption about how to interpret them that may not be correct." The third arena is the creative side, the intent of how the image should look with information about the contrast range, filters, background densities and other visual parameters.

Indeed, color space is one of the crucial issues, because film, CGI and digital-grading devices all have different color spaces. "What is the primary color space we need to work with?" asks Clark. "It's not the color film space that we've lived with and worked with for decades. There's a struggle to coordinate the dynamics, contrast, tonal range and the color itself between these two different worlds that are intrinsically not linked. How do you match one with the other? Which is the tail and which is the dog?"

Clark lists color, tone scale, grain and motion blur as four elements that need to be correlated between the film and digital worlds. He also emphasizes that a working metadata definition would have to be applicable to both production workflow and archival purposes. "The issue of metadata is to make sure that all the parameters that have gone into achieving a look can be stored and maintained, and have meaning for future generations," he says.

Currently, in the United States, two organizations - SMPTE and the Advanced Authoring Format (AAF) Association - are looking at ways to standardize metadata. SMPTE's metadata committee, chaired by Michael Cox of Mirador Techniques, is focusing on standardizing the mechanisms by which metadata will be carried through the process. At the same time, file formats are being developed which enable the linking of metadata with pictures, sounds and other "essence." Cox reports that some broadcasters, in particular Swedish Television, are well ahead in developing the use of metadata in a real-world environment.