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| On Feb 2, 2012, at 6:48 PM, Chris Zwar wrote: > Not sure if other software such as Nuke can do this, you might have to render out 32bit dpx or exr and have them converted back to Arri LogC in a different package. I don't know of any software that can invert a 3D LUT. This is a problem you're going to have with any film look. You just have to try your best to integrate your elements with standard color correction tools. Here's another way to look at the impossibility of inverting a 3D LUT: we were working on the movie Hellboy, which has a big blue glowing cloud (the "hell hole") at one point. The director kept on saying he wanted the thing to be more saturated, but no matter what we did we couldn't get the blue as saturated as he wanted. If you applied one of these film previews, no matter what color you put in your log file, you just couldn't get the saturated blue that you could pick through the regular color picker. Why? Because that color blue was out of gamut for the film being previewed. A film print was simply not capable of producing a blue as saturated as the director wanted. Our inability to produce a saturated blue through the film look was telling us that. So if the director were to pick a saturated blue in Photoshop and tell us to put it on screen, it just wasn't possible. If 3D LUTs could be inverted, it would be possible to pick any output color and get back the required source color. But it's not possible. Now, you could make a 3D LUT using a simple gamma operation. And then another 3D LUT made with the inverse gamma would in fact be its inverse. But I know of no software that can figure out if a 3D LUT is invertible and then actually do it. Sounds like a good Ph.D thesis to me. This might be worth a try though: convert a 3D LUT into a 1D RGB LUT, and then try to invert that (this can be done with LUT Buddy, I think). Might get you part way there. Brendan |
