Iray caustics

JPayne

This is a cropped image that featured caustics... The image took nearly 5 hours and I stopped it at 46% complete at 10k iterations at 5 quality. I think this image would have needed at least 16k iterations just to be good enough The second small image is an area render of the same scene, note there are no caustic effects in the area render. Why is this?

Tobor

The images are very small to make anything out. What are you trying to point out in these?

It is not clear why you're using the caustics feature. Is it for the necklace? Something else?

For the close-up, if you mean you lost any caustics when you cropped it in camera during the render, this is a known effect.

To get useful (interesting) caustics, you need to set the scene up for it. This means placing camera, lights, and transmissive or reflective object(s) at just the right places in order to take advantage of the sampler. It would not be unusual for a render with the caustics sampler on to take a long time, as there are a lot more calculations to perform. Obviously, you only want to make the effort when you get interesting stuff in the render.

http://docs.daz3d.com/lib/exe/fetch.php/public/software/dazstudio/4/new_features/4_8/caustics1.jpg

Tobor

Sorry... hit the button before I was finished. Anyway, from what I see in the larger image, there appears to be caustics from some object nearby, though its unclear what that is from the post. It looks like scars on her face or neck, or something else unintentional.  This is what I meant about interesting stuff. Without a high-HP rendering setup, caustics like the kind I *think* you're going after can be very "expensive," resource wise, so save it for when it really makes a difference. What's your system like?

JPayne

I put in a ticket and already got a response. Caustics will not render in the raytracer if the object creating caustics is not in the image. I would consider that a bug myself. An area render should calculate the entire image even if it's a small area render.

 

What I was trying to point out was on the larger cropped image is it shows caustic effects. and the area render does not. Most renderers that can handle caustics or radiosity effects calculate the entire image no matter how small the area render.

Tobor

It always helps to post larger images. There's a forum limit to the dimensions, but it's considerably bigger than <200px on a side.

From what I understand, Iray's caustic sampler uses some biased tricks in order to render in a reasonable amount of time. This means light sources outside of the 'eye' path will be ignored; otherwise, with possibly multiple direct and indirect lighting sources, you could be looking at an ungodly amount of time to finish the thing.

As a "pushbutton" renderer, Iray leaves a bunch of stuff out that's found in many other renderers. I'd be surprised if nVidia's other offerings, like mental ray, didn't behave the way you mention. These tend to be fairly expensive -- mental ray standalone is s $700 per seat, or put another way, $700 more than what D|S costs. I wouldn't characterize Iray as the "junior" version of anything, as it's designed for a different business case, but by design there are many features it simply doesn't have.

Jim_1831252

I haven't tried to render caustics from off-screen locations, so I hadn't encountered this. The Iray "caustics sampler" uses the metropolis algorithm, so I’m now wondering if Lux behaves in a similar way. If not, there should be some way to get Iray to behave, possibly a feature request to expose some additional settings.