Iray lighting 'in a cube'

SnowSultan

I watched a video yesterday where Dreamlight added a large cube that completely surrounded his scene in order to bounce light around. Today I tried it, and although I'm getting nice results, there are two unusual problems.

- If the cube is colored pure white, the scene renders for a bit and then floods with light (which I assume is from the bouncing). It unfortunately adds just more than is necessary, wiping out all shaded areas. If the cube is changed to any other color (including light gray), the light flood does not occur but the bounced light effect is heavily reduced. Why is this?

- It takes an amazingly long time to render with the 'environmental cube', which I don't quite understand because Iray supposedly performs better with a lot of light. I let a render with a single figure run for 20 minutes and it hadn't even shown 1% on the progress bar when I stopped.

I like the way Iray bounces light and helps remove the telltale hard shaded areas, it's just doing it too much in this case. Does anyone have any suggestions for rendering within a cube or any alternatives that would bounce light well but not take so long to render? Thanks in advance for any thoughts.

SnowS

BeeMKay

The problem with a light cube is that it need a lot of extra calculation time, and it blocks off all other external light, like the sun&dome; light.
You could get the same effect by simply plugging an all-white HDRI image into the Dome setting of the render engine, with the advantage that you can turn off the dome and still get the light emission.
Below, I have plugged plain colored png images into the Environment; as you can see the white gives a nice, even light. A real HDRI would be better, of course.
There's also a comparision between the cube and the PNG version. Sorry that it is a bit grainy.

EDIT: Ah, sorry, I misread. I thought I read that the cube was a light emitter; on re-reading, I see that it's not a light emitter, but just a "bouncing box".
Yes, a bouncing box will reflect the light, but as the bouncing paths have to be calculated, render times go up - because each lighht ray is bouncing around a lot, influencing shadows, reflections, etc. As the box encloses everything, the light will not "escape" eventually, like in your regular "open" scene.
Besides, in "real life", you also don't have a regular white box around your rooms&people;. In a photo studio, perhaps, to achieve perfect results, but not normally. :)

SnowSultan

Ahh, I'd done that before in 3Delight to fake ambient lighting before we had Age of Armour's lights, but I'd forgotten about it since. Thanks very much, I will give it a try and compare it to the tests I did earlier.

EDIT: Oh, now I saw you edited your post too...this should still help though because all I'm really using the cube for is to bounce a little global light around the scene. Adding an all white HDRI (you said it's better than a png though, why if it's all white?) at a low value should provide something similar.

BeeMKay

Sorry for the confusion. :red:
The difference is that the Dome version gives even, all-arround illumination, while the bounce-box version is lighting up the shadows with the bounced lights just like it would do in a photo studio - there, you have dark corners lightened by white bounce screens that are set up out of the screen.