How Do I Slow Iray Down?
Nathanomir
Posts: 133
Yes, that is the opposite of the question most people ask.
I'm working on a scene with four V7HDs, each with Goldtassel hair. That should tell you this will be a slow scene. It is. It finished in 50 minutes. But the shadows were grainy. It needed to cook a lot longer. I don't mind slow -- I'm used to letting Luxrender run all night. I thought increasing samples to 12,000 and seconds to 10,000 would give it the time it needs, but I swear I sped it up! The rate it's clipping along, it will finish in 40 minutes, and I know darn well those shadows will be grainy.
So, how do I slow Iray down to give it the time it needs to clear?
The light setup is a room HDRI, and two mesh lights. I can provide the specifics if that will help.
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Comments
increase quality, samples, time, rendering converged ratio.
spot render the parts that need more, and composite them in post.
then there's the fact that renders shouldn't be too clear or sharp; one of the things that looks odd to the human eye. :)
Grainy shadows look odd too.
Set your Render Quality to somewhere between 1.2 and 1.6, and be prepared for that overnight wait.
Thanks. I didn't think about Render Quality and Converged Ratio. I'll give them a latch.
This isn't just grainy. It's GRAINY! As in somewhere beyond rare but not medium yet.
One thing you can do, and it sounds wrong but works, is to look down your camera, change the camerangle, then move back. Honest, it works!
Go into the Render Settings->Progressive Rendering and:
Now the only parameter controlling how long Iray will render before stopping automatically is Max Samples. How long you need will vary from image to image. The default of 5000 is usually more than enough.
Go into the Render Settings->Optimization
I don't have anything to back this up other than personal observation, but I've noticed without the sampler images appear "finished" in the light areas while the dark areas are still grainy/noisy. With Architectural Sampler on, the image is rendered uniformly. When the light areas are "finished," so are the dark areas.
While there are other things you can and should try, like Valandar's suggestion, I suspect you'll find the changes I recommended to the render settings become your default. I know they are mine. I have a "default" file that is loaded at startup and whenever I click on "New" so I no longer have to remember to set those parameters with each new project.
How Do I Slow Iray Down?
Easy! Run it on my computer!
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Thanks, I was actually experimenting with setting Max Time to 0 yesterday but it didn't seem to have any effect. Turning Quality off seems to be necessary for it to work, I can see.
Another thing to consider with scenes with many instances is Instancing Optimization. I tried to render Harpwood Trail but after 50 minutes with high CPU activity nothing had happened at all. I then discovered a note on the product page about setting Instancing Optimization to "Memory" instead of "Speed", after doing that is started rendering after a minute. Even on a PC with only 8 GB RAM that huge scene renders fine that way (uses a little over 6 GB RAM and 3 GB VRAM).
You're welcome. If you leave Quality on and set Max Time to zero, you may need to increase the Quality setting to something higher than 1 to see a difference. I have no idea what goes on behind the curtain, but with Quality on, the algorithm determines how many samples it takes to reach convergence. A higher Quality setting means more samples are needed to reach convergence. Before I finally tried turning Quality off altogether, I had tried Quality settings as high as 50 trying to force Iray to keep going. By setting Quality to off, the render engine is no longer concerned with convergence, (which may mean a slight increase in speed, too, something one might notice if one is stuck rendering in CPU Only mode as I was.)
You may already know this, but when the first 4.8 beta with Iray came out, "Memory" was default. It caused numerous headaches for a lot of people, and the solution turned out to be changing that setting to "Speed," so DAZ made "Speed" the default by the time 4.8 was released. Of course, Iray has changed a lot in the past couple of years! Now I'm thinking I should pull up one of those old scenes and try rendering it with "Memory" selected, see if it still has the same issues...
Sorry to start this thread and not get back to all y'all's great suggestions. I was called away by the need to clean a carpet.
Last night, I ran the render again. First, I removed one V7HD (her skin textures and costume just weren't right). That freed up some resources! I also switched out hair (it's going to take some time before I understand Goldtassel's complex movement and style system). I applied L'Adair's recommendations, but increased iterations to 6500.
The scene rendered for four hours. But to a Luxrender user, that's still a significant savings of time (6,500 iterations is 6 1/2 hours on my machine). The result was WOOZAH!
Look for yourself:
A few textural issues (namely the red hair) and I may switch back to Goldtassel's hair, but I'm really happy with the shadows.
Thank you everyone for your help.
...
...had a similar issue and upped the Max Time set Convergence to 100% turned Render Quality off and turned the Architectural Sampler on. Took all night but got a nice clean result.
Update: Last night I reworked one of the images that, two years ago, wouldn't play nice with Iray optimized for Memory. It turned out pretty good. An interesting thing happened though. When rendering the image while optimized for Speed, there were some strange, unexplanable shadows. The lighting is different, using an hdri instead of the Distant Light, spotlight setup I had for 3Delight. That might have something to do with it... I had already started and paused one optimized for Memory at 120 samples, so I let the "speed" render go to 120 samples as well. It took less than half the time to get there. I saved it, in it's grainy glory, for comparison, then restarted the "memory" render and let it run all night while I slept. It worked like a champ. Whatever was causing problems in the earlier version of Iray appears to have been fixed.