long rendering time

[OndraZ]

Hi,

I have rendered image with 7 light channels (sun, HDRi sky, interior lights, material glow...). Image has 245 passes (pathtracer engine) and it took 38 hours to render on quad core CPU. When are all channels on, everythnig is fine as expected (first image - photo merge). But when sky and sun channels are turned off and only interior lights and sign (material glow channel) are on, quality of rendering drops radically - second image. I know that long rendering time is something we can expect in this case, but the quality after 38 hours isn't very usable...is it normal to resolve this long? Is there a way to improve the "night" result (f.e. new engine)? Also it seems strange that when only material glow channel is on (the sign on the third image) nothing around is illuminated - I would expect at least some light on the wall beneath...so is this result correct or no?

[Roy Hirshkowitz]

It's all "correct."  Material glow does not light anything-- you need to make the sign a light source for it to work that way.

This is going to be a very difficult night scene to do given the nature of the lighting and the amount of obscuration.  You may not live long enough to see it converge.  I would approach a night shot by adding some ambient light to wash out some of the noise.  For example, use our standard sky or an hdr and give it night-time intensities.  Start by setting the intensity to 0.001, but keep it on a separate channel since you may have to go much lower.  I'm not sure this approach will work, but it might.  You also might try the standard engine since it will automatically add some constant ambient.

Whether the new engine will improve things is hard to say-- I doubt it-- but you never know.  If you want me to try it out, upload the model and I'll take a look.

[OndraZ]

Ok, thanks for quick response. I've attached image where sky (night HDRi) channel is set to 0.001. You are right that result is better and more usable (but still "unfinished")...I turned the sky channel off in previous image to make my point obvious.

[Roy Hirshkowitz]

I'm not sure it gets a whole lot better than this.  You can try more HDRI light-- the noise will be a little less apparent.  Some actual street lights might help, although clearly these options may take away from what you're trying to show. Some PhotoShop denoising type filters could also help.  We can try the new engine if you like.

Nifty design-- the screens remind me of Islamic Tracery.