American Cinematographer - October 2008 - 76

ASC CDL: Key Terms ALE (Avid Log Exchange): Avid’s standard file format for logging information. The CDL can be added in the form of two new fields, SAT and SOP. Baked-in Correction: A color correction that is applied to the signal and therefore visible. CMX: The longtime standard list of time code in- and outpoints used to conform the final edit to a master. The CDL can be added in the form of comments. EDL (edit decision list): List of time code in- and outpoints that comprise a video edit. Film-Emulation LUT (or Viewing Transform): A transform function or LUT often used to previsualize on a video monitor what the final film print will look like. FLEX (Film Log EDL Exchange): Da Vinci’s standard list of telecine shot starts and stops, and associated film key numbers. The CDL can be added as two extra fields, SAT and SOP. LUT or 3-D LUT: Look-up table. A form of color dictionary that replaces every input color with another output color in order to change a look, or emulate the look of film on a video monitor. A 3-D LUT can yield more accurate emulations. Offset: Akin to brightness. Offset changes the brightness of the R, G or B input. The normal value of 0 yields a line that goes through the graph’s origin. Power: The only nonlinear CDL function. It changes in the middle of the transfer curve, bending the R, G or B mid-tones while leaving the black and white extremes the same. The normal value is 1. Saturation or SAT: The amount of color in the signal. The normal value is 1. Zero yields a black-and-white image. Slope: Akin to contrast. Slope changes the R, G or B highlights without changing the black reference. The normal level for slope is 1, which yields a transfer line at 45 degrees. SMPTE Rec 709: The modern standard for a video signal or its associated color space, typically used for projects destined to be viewed on television. SOP (slope, offset, power): CDL parameters with RGB values. XML: A simple, flexible format for making lists of data. see more exotic previz coming out of applications such as Maya, which could potentially export CDL information.” The CDL is an example of metadata — data about data — and this means that while the color-correction data is associated with the image data, the image itself is not necessarily corrected. “The CDL was designed as an inherently non-destructive process,” notes Levinson. “You can choose to bake [the corrections] in for a particular delivery, but it doesn’t happen automatically.” Clark adds, “You can bake the corrections into Avid or Final Cut Pro files, but you still want to have a separate capability to associate that color-correction data with its corresponding image and alter it later — for example, for previews or the DI.” (According to Levinson, discussions are ongoing with Avid regarding the potential for assembling the CDL color corrections for display within editorial — in other words, having a CDLconform button in the Avid that could turn the corrections on and off.) Detailing the possible application of the CDL workflow for HD preview screenings, Clark hypothesizes, “If you want to take the CDL color corrections done for the dailies and make adjustments for shot-to-shot variances in the cut, you can use the same CDL functionality in compliant applications. Then, in principle, the information associated with those images and that preview cut will make its way to the final color-correction session.” The CDL should save valuable time in the DI suite, but Levinson says he sees it “more as a control for your own look management. But if you give me raw shots and a CDL, when I punch conform on a Baselight or Lustre, for example, all the images for a particular film reel will, in theory, come up in the right place with their color corrections. So you’re not working backwards; you’re picking up where you left off.” To date, the CDL has proven to be “a robust foundation for colormanagement workflow,” says Pines. Looking forward, Levinson says, “We hope it will become a functional piece of a larger, unified metadata scheme. It will include a way of exchanging LUTs without giving away intellectual property. “The CDL is a fairly simple thing, and it’s doing what we intended it to do,” continues Levinson. “We put it out there as a good idea, and a number of vendors have already adopted it, which is wonderful. The game now is to get it out there so people can use it easily.” The ASC is working closely with the Academy of Motion Picture Arts and Sciences and the Society of Motion Picture and Television Engineers to continue to address post problems, and Clark says they are turning their attention to defining standards for LUTs and a post file format. “I see the ASC CDL as the first wave,” Clark opines. “The LUT and the file format, both equally important, are the second and third phases of regaining some kind of coherence in this increasingly complex and frustrating workflow.” To view illustrations of the ASC CDL, visit www.theasc.com/magazine in October. I 76 October 2008

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American Cinematographer - October 2008

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