Just a followup on my last post. So I had a render that was kicking my system's ass, involving four characters. I had to drastically simplify the scene to get it to fit in the graphics cards VRAM, and was already usng a HDRI as a 'primary' light source. As I remember, this scene took me about 10 minutes to render in Iray, as there aren't any walls or floors to worry about.
So I set up a three point lighting config, and rendered the scene in three passes, one light per pass (scene only), then combined the images via layers in photoshop, and started fiddling with the opacity of each layer. I had a 'no ground shadow' issue, so I did another HDRI only render (show dome off) to add a quick ground shadow. The HDRI pass took me about 8 minutes.
I'd recommend adding a ground plane primitive at the very least so that the shadows from your other three lights will cast on some sort of floor. But I digress, this was just a test.
So I began fiddling with the opacity of each layer, with the HDRI layer at the bottom, my 'back light' next, a 'front highlight' light layer next and the primary light (roughly 180 degrees offset from backlight) at the front.
My impressions in this particular situation is that the light/shadow colors aren't as vivid, as the darker colors from the backlight tend to mute the foreground colors, but that you can definitely do some experimentation with the lighting levels and come up with wildly different looks with a minimum of effort via layer opacities.
Here's my original WIP HDRI with highlight spotlight render. Don't mind the embedded fingers and such, this isn't a final render, I'll be adjusting the hands and such shortly...
And here's the 'multi pass photoshop layers at varying opacities' in use:
The backgound is a photoshop gradient layer btw, for those that might be wondering.
I can see this maybe being more useful for low light situations, where you are trying to hit a balance between 'characters look too bright' and 'I can't see the characters'
Each situation will be different of course, but in my experience this would be better used as a 'setting up that perfect promo render' sorta tool, and also where you might be dancing at the edge of your VRAM, perhaps rendering each light on a separate pass might help with squeezing under the VRAM bar. Otherwise, I'm not seeing a huge time saver here, as my original HDRI + extra spotlight render only took about twice as long as each individual light pass.
Another place where this might be useful is when setting up lighting for a room. You could do individual passes for each light source, and then fiddle with the 'light levels' of each light in Photoshop using layer opacity, and when you hit on what looks like a winning combination use your opacity percentages as a guide of sourts to set the luminosity of each light source. I can see this being a bit of a timesaver as waiting for the Iray viewport to resolve every time you make a minor adjustment is a significant time sink.
In more complex lighting situations, with lots of reflective surfaces, the 'multi pass method' might also be helpful, but overall this seems more like a 'setting up that perfect render' kind of thing, not something that I'd want to do for each 'ingame' render when you are doing a bunch of back to back renders.
Just wanted to share these thoughts. I'd certainly recommend experimenting with this at least as there are situations where it might be quite useful, but it's not something I'm going to use a lot. YMMV.
But yeah, love those free tutorials! It's good to learn new things!
