Iray render mode comparison

Tobor

Forgive me if this has been posted elsewhere, but I thought I'd share a short test I recently did.

Iray has several rendering modes. Most of us use "Photoreal," which is the default. But there's also Interactive. (Photoreal and Interactive are nVidia terms, by the way.) The render mode is changed by choosing Render Mode in the Render tab, then selecting either Photoreal or Interactive.

Iray's interactive mode uses the same lights, shaders, and other objects, but processes the image using a simplified set of algorithms, and is a quasi-biased renderer. Renders take maybe half the time, or less, and depending on the lighting and other conditions, can look quite good. In Interactive mode, you have different settings available. For example, you can disable shadows, use ambient falloff and occlusion, and set the number of ray traces. Certainly not the rich variety of options in 3DL Advanced, but it's nice to have these if you're going for a biased render.

Here are two renders of a decidedly non-real subject, so that only the qualitative differences between the modes can be examined. One is in Photoreal, the other Interactive. Both use the same lighting (just the "Ruins" HDR, with dome turned 70 degrees, and no scene lights or camera headlamp), Iray Uber shading for all materials, and pretty much default settings everywhere else. I let the Photoreal version go to about 93%. On my dual-Xeon machine, CPU only (eight cores), the Photoreal render took about 12 minutes -- output was a 2048x2048 image. In Interactive mode, the iterations feedback is different, and I merely stopped it after 4 minutes. It could have gone for another minute or two, but with diminishing improvements.

The biggest difference is the shadows. Her ears should be in shadow, but they're fully lit in the Interactive example. Probably some fiddling with ambient and IBL settings might address this.

One final note: Some previous tests with Interactive using other scenes turned out AWFUL. Lighting that looked great (fairly dramatic, using multiple spots) in Photoreal looked terrible in Interactive. Bad shadows, light up the nostrils, that sort of thing. So like everything, some tweaking may still be required if you're switching back and forth.

RAMWolff

Aside from the backlighting on her thigh I really can't tell much difference in either render.  So I don't think that the Interactive render option is so horribly limited.... I guess I'll find out!  lol Thanks for the info!

Tobor

Be sure to play with the shadow and occlusion parameters, which become visible once you choose Interactive. The example here uses only the defaults.

 

Padone

The main big difference I found out is that interactive has an horrible management of textures transparency. It just "clips" them. So it's not usable for any real character. In your example the hair doesn't use transparency so this issue is not visible. I include an example picture where the issue comes out.

Please let me know if there's any way to correctly handle transparency with interactive mode since I'd be very interested to use it instead of photoreal.

 

Mattymanx

Interactive does not do glass very well either.  Also noticed it does not use mesh lights.  Interactive is just there for setting up the scene with the basics.  For the final render you want to use the Photoreal setting.

grinch2901

I did an experiment with cutout opacity and found that for any cutout opacity setting over 50% it ignored it and the object was opaque. For settings under 50%, the object was totally invisible. It's binary. So if you have a transmap with shades of gray, it could be pretty weird looking.