Go Linear...Or Not
Ron Heidt
Senior Editor
Crawford Post/Atlanta
Recent HD Projects: The Concert for World Children’s Day, Great Museums
The questions you should answer to make a decision on whether to finish linear or nonlinear are:
What is the length of the final project? Will there be a lot of changes to the offline? Where will final color correction be done? How many multilayered or slo-motion effects are there? How important is it for the slo-mos to to ramp?
A tightly offlined long-format program is best suited for a linear room with enough disk storage to store all the source material. First you’d load the offline EDL, have the system load source material to disk and then play out the program to HD while adding effects, dissolves and color corrections in real time. Typically, all effects and color corrections are done on the video switcher with the information to recall these effects stored in the editor. Special effects portions can be loaded into an NLE and then inserted into the master.
Often short-form programming is best suited for a non-linear system. Project information comes via either an OMF, AAF or project file. In this scenario all effects, color correction and layering information can be transferred directly from the offline system to the online system. The source material is then reloaded into the system and all the effects are rendered and the program is output to tape.
Calibrate Your Monitor Carefully And Often
John Perischetti
Colorist
Post Logic Studios/Hollywood
Recent HD Projects: Spy Kids 3D: Game Over, Once Upon a Time in Mexico
Most of the issues I see in HD mastering are the result of poor lighting and improper exposures. Think of it this way: if something— highlights or blacks— is not recorded by the camera, there’s nothing even today’s powerful color correction tools can do to bring it out. Ultimately, HD shooters have to light with contrast ratios in mind, just as they would with film. You can’t light flat and expect the work to come out looking like a high-contrast film noir! Occasionally you may find yourself in some difficult lighting situations. For example, if you are shooting in extremely bright exteriors with skies that may "blow out," consider using gradation filters to knock down some of the overexposed sky. On dark interiors you may throw some fill light in the shadow areas so you can see more detail. It’s always easier to darken the shadow areas in post than try to lighten video information that is not there.
Having the right monitor set-up on set is critical as well. Be aware that instability of color temperature and luminance results from the constant moving of production monitors, so calibrate using a probe that accurately measures both color balance and luminance (I use a Philips PM 5639 Color Analyzer).
Know Your Downconverter Before Shooting
Jeff Cree
Bandpro Film & Digital/Burbank
HDVS Market Development Manager
Recent HD Projects: Instructing camera crews for James Cameron’s HD 3D Titanic/Bismark projects, Spy Kids 3D: Game Over and Once Upon a Time in Mexico
Whether your production is downconverted prior to, or after post, can alter the look of the project greatly. Not only does downconversion add 3:2 pulldown going from 24 (23.98) to 30 (29.97) frames, the process affects many factors that should be considered by the DP, like detail level, detail frequency and detail limiters as well as levels— white, gamma and black. Certain boxes even apply their own color matrix to the downconverted signal.
Some DPs assume that detail is based on the original HD image and scaled to the proper levels for SD during the conversion, but that is not the case. The detail frequency of the HD signal is far above the bandwidth of the SD signal and rolled off by the downconversion process; new detail is added just as it would be done by an SD camera system. The specific downconverter determines the level, the edge frequency, and sets any detail limiters for the SDI or NTSC signal.
Black and gamma levels are also affected during this process, especially with a conversion to NTSC. Establish with the facility what downconverter is being used and run tests through their system and then set the parameters for the conversion. Annotate these settings with each cassette. This returns control back to the DP who should have ultimate control of the look of the production.
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