Inconsistent rendering time (Iray)

Jayn25

I want to ask what is potential reason of very inconsistent rendering time.

Let me explain what I mean. I have a scene with empty room, windows with curtains, one light source, sofa, skydome, and a character. It takes around 30 minutes to render. FHD resolution.

Scene with exact same settings but made out of premade room with a lot of details (objects and light sources) and even a mirror takes no more than 10 minutes to render.

Doesn't make sense to me, the first one should be easier to render.

Richard Haseltine

Iray isn't a simple process of rendering and then being done - it keeps refining the render until a set level of convergence (pixels that seem to have achieved their final value) is reached. In your first scene the light was probably having to bounce several times before it reached some areas, which meant that it took longer for those areas to settle. In the second scene, with more light sources, most areas were lit directly and so reached a settled value sooner.

Kainjy

If you render a room, light bounces many times on walls, floor and ceiling. It stop bouncing only when find an opening (window) or a light source (lamp). In an open area light bounces on the ground and come back to sky.. so it's more quick the render. If you want to test, render a room without ceiling

Jayn25

I partially understand, but there are scenes as simple as the first one that take around 5 minutes to render. But I will have to test how it behaves with different light sources to be sure.

nakamuram002

Someting to try:

When I render a scene and find it taking "a long time", I save the scene, close DS, then start DS, load the scene, and render.  This can result in significantly reduced rendering times.  So far, when I use Task Manager to monitor performance, I have found little difference in the "measured" results.  It is likely that Task Manger is not showing the measurements that are significant to my observation.  I need to do more monitoring to try to figure out what is really happening.

Jayn25

I think I understand. The less "holes" room has, the longer it takes to render. So room with normal windows will take a lot of time to render. Flat surface takes a few minutes, and detailed room with big windows for example 15 minutes.

I do realize very advanced scenes in high resolution probably take long hours to render, but I'm not there yet.

Padone

All rays bounce around until they meet a light or a black body, as a 100% black diffuse for example. So the more lights and the less diffuse/reflective surfaces the faster is the rendering. Having a HDRI environment around the scene ensures that most rays meet a light.

The worst you can do is place a light inside a closed box with high diffuse surfaces, as a 100% white diffuse for example. The rays will bounce around forever and never converge. You can try with a point light inside a cube primitive.

Anarkia333

4.20 version has a problem has think with denoiser...

I make render in 7000*4000 with denoiser in 4.16 version, no problem, now time is about *100 when Denoiser activeted in hight resolution.....

I have a solution for the moment, put Denoiser at 500 or 1000, just activate it before end.

Padone

The denoiser takes extra vram may be 4.20 takes more vram with the new iray. Check in the log if it is reversing to cpu. Anyway as I understand it there's no difference trigging the denoiser before the last iteration, I mean it only considers albedo it's not "interpolating" among iterations. So if you go for 500 iterations you can trigger the denoiser at 500.

Anarkia333

Padone said:

The denoiser takes extra vram may be 4.20 takes more vram with the new iray. Check in the log if it is reversing to cpu. Anyway as I understand it there's no difference trigging the denoiser before the last iteration, I mean it only considers albedo it's not "interpolating" among iterations. So if you go for 500 iterations you can trigger the denoiser at 500.

 

yea I find too this solution :)

Make denoiser at end at 500-800.... xD

Before when render at 7000*4000 my VRAM up to 11.7/12Go, same with 4.20, and id denoiser has no RAM, just he not doo, but never conitnue before as this very very very slow....