Waterfall Tails Hair slow Iray render time

Black Snow Princess

I am experiencing slow render times when using the Waterfall Tails Hair. I would like to know if anyone else has experienced the same problems that I have or if anyone has suggestions to improve my render times.

I have conducted the following experiment to show the impact that the waterfall tails hair is having on my render times.

1. Create a new empty scene
2. Switch to perspective view and set to default location
3. Set Iray render settings to default
4. Change dimensions of render to 1080x1080
5. Check OptiX Prime Acceleration

Here are the results of experiment with different hair styles:

• Aiko 7 No Hair - Iray iterations: ~400, Time: 51 sec
• Aiko 7 Waterfall Tails Hair Default Settings - Iray Iterations: ~740, Time: 2 min 50 sec
• Aiko 7 Waterfall Tails Hair Low Specularity - Iray Iterations: ~670, Time: 2 min 25 sec
• Aiko 7 Rochelle Ponytail Hair - Iray Iterations: ~450, Time: 1 min 15 sec
• Aiko 7 Leyton Hair- Iray Iterations: ~450, Time: 1 min 12 sec
• Aiko 7 Toulouse Hair - Iray Iterations: ~425, Time: 1 min 5 sec

This experiment shows that the Waterfall Tails Hair adds about 90-120 seconds to the render time; while, most other hairs only add about 15-25 seconds. This means that the Waterfall Tails Hair causes 4-5 times longer render times. I first notice this problem when a scene rendered in 20 minutes with the Rochelle Ponytail Hair and 1 hour and 40 minutes with the Waterfall Tails Hair. Is there a reason for such a increase in render times? Is there anything I can do to prevent the Waterfall Tails Hair from increasing my render time by such a large factor?

 

Machine Specifications:

• MSI GT72 Dominator Pro Laptop
• OS: Windows 10 Pro (64-bit)
• CPU: Intel Core i7-4720HQ CPU @ 2.60GHz
• RAM: 16 GB
• Graphics Card: Nvidia Geforce GTX 980M
• Daz Studio Pro 4.9.2.70 (64-bit)

Richard Haseltine

That's the glossiness of the hair allowing the light paths to bounce around before they reach a point where no further bounces will affect them greatly I think - that's why the lower glossiness renders more quickly. One thing you can try is adjusting the Maximum Path Length in Render Settings, under Optimisation, but not that anything under 6 will not render the eyes correctly (any positive number under 6 - the default -1 keeps bouncing until, I think, some brightness threashold is crossed). I've found that to give a slight speed increase with hair.

Black Snow Princess

Thank you the tip about the glossiness. I have tried a few quick test by changing the Maximum Path Length and adjusting the glossiness of the hair surfaces and I was able to get the render time down to 1 min and 40 seconds with decent looking hair. I am sure with more fine tuning and testing I will be able to get the look that I am going for without larger render times.

Richard Haseltine

Not that it's something you are likely to want to change, but the hair colour also makes a difference. I've been going through trying out the (large) backlog of hair models I'd bought and it's noticeable that blondes almost always take longer than brunettes - presumably because there's less attenuation (which is the word I wanted earlier) on the bounces with the lighter surface.