Tips on keeping a scene lightweight

Mr_Fluffkin

Hello,

i´m basically looking for general tips to keep a scene lightweight, rendertime wise. I know every scene is different, but what are the main factors to keep the rendertime low(besides the number of polygons/quality of textures)? For example, i did this render lately and tried to keep it lightweight, basically by controlling the colors via tonemapping/render settings instead of extra lights and using the matte fog instead of fog.props:

With DS´s sun-sky and matte fog(as shown here), the render time was <20 min., which is blazing fast for my old mill.

Then i changed the lightning to a multicolored HDRI in the first try and replaced the matte fog with a multi-plane fog-cube in a 2nd try. Both resulted in a rendertime of multiple hours, so i.e. HDRI-lightning seems obviously to be a possible heavy hitter for the rendertime(depending on the HDRI). But it´s laborious to learn this all by experimenting, so i´m looking for some kind of expert guidelines to keep a scene lightweight. I´m not even sure if it´s true that the sun-sky always renders faster than a HDRI, it´s just what i believe i have regonized over the last year.

Maybe someone knows some good tutorials or websites regarding heavy hitters in render times, that would be great. I already searched by myself of course, but i can´t find much useful stuff.

margrave

There's a misconception that needs to be cleared up first.

Iray doesn't have a "render time". A render will continue indefinitely, incrementally clearing up noise and getting progressively closer to photorealism (known as "converging") with every iteration. You can optionally set it to stop when the difference between iterations turns to diminishing returns, but it's not necessary.

What you want to do is to remove noise to approach convergence more quickly.

• Avoid highly specular surfaces, which will create intense highlights called fireflies.
• Cut down on the number of transparency effects, such as fog cubes--you can always just render out a depth canvas and apply fog in a photo editor.
• Add point and spot lights to cover more of your scene, so Iray can calculate more quickly. You said you're hesitant to add more lights, but the impact of a light is minimal compared to the benefit of having more light rays providing coverage.

Of course, the biggest time saver will always be smaller texture sizes. Smaller textures render quicker. Even reducing your maps to 2048x2048 means you've reduced the texture load by 3/4ths, and unless you're doing a close-up, you really can't tell anyway. So if time is a factor, I recommend you invest in Scene Optimizer as soon as possible.

Mr_Fluffkin

Thanks for your input so far, margrave.

Got the render time part, i just meant the time your computer needs to reach a specific number of iterations(i.e. 2000). But that are already some good tips, i didn´t knew that specular surfaces are a main reason for fireflys or that texture size massivly matters. For me, it always felt like bigger textures just need more ram but doesn´t slow down the iterations a lot. Just from my feel, i always thought the number of polygons is THE main factor. That´s why i already invested into the Decimator when it was in a crazy sale, but i gonna check that Scene Optimizer out.

Maybe i should be more concrete why this is a thing for me at all. I´m writing a visual novel with unity as a personal project, which basically shows backgrounds with figures in front, depending on your choices. Therefore i´ve build lots of places/scenes in Daz, for example a skatepark in a city. For some kind of events/subscenes, i want to take lot´s of renders of the same place now. Different perspectives, but the same place/scene, let´s say 30 from the skatepark for example. That´s why i´m looking for tips to make scenes render fast. For the skatepark i.e., i first used a HDRI dome as a single light solution and each render took almost 2 hours(for let´s say 2000 Iterations again). Then i changed it to sun-sky without the environment map(+ some render/tonemapping settings to get the same look), which reduced the time to 30 minutes.

So i wonder if the sun-sky is always faster than using an environment map, or is it just scene/HDRI depending? That´s pretty much my main question, but as i said, any tips to keep things fast are welcome. :)

margrave

I can't say I'm an expert on HDRI vs. Sun-Sky, but I haven't really noticed a difference. Of course, an HDRI is basically a very large texture, so it's possible it slows your render down like every other massive texture. A 16K HDRI is 16,384 x 8,192 pixels, so that's over 3 gigabytes of memory.

You really don't need to worry about polygons at all. Computers can render millions of triangles without breaking a sweat these days. Texture size is much more of an issue, so slimming that down will be orders of magnitude faster.

chris-2599934

margrave said:

• Cut down on the number of transparency effects, such as fog cubes--you can always just render out a depth canvas and apply fog in a photo editor.

If anybody is wondering how to do this, I have a tutorial: https://www.daz3d.com/forums/discussion/334586/tutorial-adding-atmosphere-with-a-depth-canvas

Mr_Fluffkin

margrave said:

I can't say I'm an expert on HDRI vs. Sun-Sky, but I haven't really noticed a difference. Of course, an HDRI is basically a very large texture, so it's possible it slows your render down like every other massive texture. A 16K HDRI is 16,384 x 8,192 pixels, so that's over 3 gigabytes of memory.

You really don't need to worry about polygons at all. Computers can render millions of triangles without breaking a sweat these days. Texture size is much more of an issue, so slimming that down will be orders of magnitude faster.

I´m no HDRI expert either, but beside the texture size, the HDRI have to own the lightning informations as well, or is it just emissive or smth? I like to use the "iRadiance - Light Probe" series by DimensionTheory for example. An awesome HDRI set, as they light your scenes by all sides with multiple light sources, but i wonder on what "costs"? Depending on the scenario, maybe it´s more handy to go with the sun + some tone mapping to achieve a very similar result sometimes, with a possibly much faster render process? I´m too unexperienced with this, maybe my thoughts are just utter nonsense. That´s why i´m looking for infos. :)

 

chris-2599934 said:

margrave said:

• Cut down on the number of transparency effects, such as fog cubes--you can always just render out a depth canvas and apply fog in a photo editor.

If anybody is wondering how to do this, I have a tutorial: https://www.daz3d.com/forums/discussion/334586/tutorial-adding-atmosphere-with-a-depth-canvas

I bookmarked this from your gallery some time ago, but just read it and never tried it out myself. Thanks for the link again, gonna check it out now!

margrave

Mr_Fluffkin said:

I´m no HDRI expert either, but beside the texture size, the HDRI have to own the lightning informations as well, or is it just emissive or smth? I like to use the "iRadiance - Light Probe" series by DimensionTheory for example. An awesome HDRI set, as they light your scenes by all sides with multiple light sources, but i wonder on what "costs"? Depending on the scenario, maybe it´s more handy to go with the sun + some tone mapping to achieve a very similar result sometimes, with a possibly much faster render process? I´m too unexperienced with this, maybe my thoughts are just utter nonsense. That´s why i´m looking for infos. :)

HDRIs are in the OpenEXR file format. It's a texture, but it has support for storing the lighting information too.

As I mentioned, if you want faster render times, then shrinking your textures with Scene Optimizer is the way to go. At a distance, you can't tell the difference.