That's a tricky one. Assuming that your CG scene setup is using linear workflow, physically-based lights and physically-based or plausible materials, global illumination of some sort, an unbiased renderer, and you're doing minimal color-correction and compositing to make it look "right," you can in principle translate the light intensities to real-world units.
In practice, that's probably not worth doing. The differences between the CG lights' characteristics and the bewildering array of real-world lighting instruments, as well as availability and the DP's preferences make this pretty moot. The fact that your CG scene probably doesn't account for things like ISO and physical lens aperture makes absolute light values nearly worthless. If that's the case, what you do need to convey is a sense of the *relative* intensities of different lights. Google "key-to-fill ratio" if you're not familiar with the concept. I think I would do this: Render in hidden-line or super-simple shading (maybe AO if you want pretty pictures) very clear plan, elevation, and perspective views of the entire setup, including a visible camera. Indicate scale and accurate dimensions, measured with respect to things that make sense on-set (like height from the floor, or distance from either camera or subject, not some point hanging in space). If your scene is getting illumination from an HDRI, you will need to try and roughly figure out the size and location of the sources in the image, scaled to fit the live-action set-up. You could also render chrome, gray and white diffuse spheres in the lighting setup, and make them look "right." Provide the renders and a set of real chrome, gray and white balls to the DP, who will likely be able to match the renders very well. If you are shooting live actors on green (or whatever) to put into a CG environment, provide renders of the environment, and ask the production to provide for the video-assist crew to be able do at least some good still-frame comps on-set (you may want to offer to do this yourself if you feel up to it and will be on-set with a suitable computer). The most valuable thing you can do, however, would be to start having conversations, ASAP, with the DP, producer and director. Get everybody familiar with the Scenes and the elements. A good pre-vis for the shoot might be helpful to prepare, but only if it's something that the live-action production team will actually use. Good luck! On Wed, Feb 26, 2014 at 6:49 AM, Neil Kidney <[email protected]>wrote: > Hi list, > > Anyone ever had to give a CG light set up to on-set lighters? > > I need to deliver the light set up from a scene lit with spots and HDR so > it can be matched on set. > > Cheers. >
