The reason I assumed the MXI files were actually light layers is because he has five of them, and five lights in the scene, but I think I understand now…
OK so the MXI is a precomputed part of an image, right? So you do have to render something before you can use this relighting tool, the same as if you used LPICS or IPR caching or just used a compositor to relight a shot. In this Maxwell scenario you have to render at least a rough version of the image, then keep adding MXIs to it to refine it. Looking at the video, he’s not relighting a render in progress which is what some people here seem to be suggesting. He has an image and adds the precomputed MXI files. Adding the precomputed MXIs improves the granularity of the resulting image, however, it still a long long way from being a final frame, and I’m sure they took considerable cycles to generate the MXI files. I don’t really see how this can be considered an improvement over LPICs or IPR Caching or even rendering multiple layers and relighting in a compositor. In all those scenarios you can move, add and remove lights, in addition to manipulating their parameters and the parameters of the surface shaders. It’s interesting in that you can apparently keep the image caches you generate and add to them for progressive refinement and the final output, but you can already do that in to some extent with the other methods people are using.
If you can actually move the lights in the shot and change shaders while using the existing image and MXI files I’ll be impressed, but I’m inclined to believe that’s not possible because of the nature of Maxwell as a renderer, and the fact that he’s relighting a full image, not a cache; unless someone can demonstrate otherwise. A relighting tool isn’t worth a whole lot to a lighter if they are limited to just manipulating existing light parameters in their current positions. That’s kind of the whole point of these other relighting systems, the ability to make sweeping changes to the light setup and parameters of the lights and shaders. If you can’t move the lights in Maxwell’s “relighting” system, you are going to be stuck in the usual cycle of setting up lights, test render, revise setup, test render, on and on until you have a setup that works. Then you can move on to the relighting tool and generate additional MXI files. If that’s the case, it probably won’t save you much time if any.