Hello.

I'm looking for help (newbie) to decrease too long render times. Is there a documentation page about that? Or some videos?
The enclosed picture was rendered in 1 hour and 34 minutes!! Although my Mantra_Ipr settings are almost untouched.
And the result is still kind of grainy.

Image size : 1280x720
Intel Core i7-6700 2.60Ghz
Ram : 16Gb
output picture : exr
Rendering engine : Mantra, , physically based rendering
Depth of field and motion blur : off
Min max ray samples = 1 & 9
Reflect and refract limits = 3
Opacity limit = 0.995

Notes :
The render is quicker when these carafes are not visible in the camera's POV, or if the camera is farther from these objects.
So perhaps the problem is related to transparency. But even when these transparent objects are not in the camera's pov, the render is too slow.

Hi, looking at your render, do you have Preview enabled? If so, try disabling preview and use buckets instead.

I'm using the preview tab, it used /out/mantra_ipr. I've been looking for the Preview / bucket toggle, but couldn't find it. Where is it hidden? Thanks

Hi, on the Render View tab, I've attached a screenshot with the button circled in red.

Wow Thanks!
Here's a new picture. The render time went from 1h34mn to 33mn!
The result looks even better than with preview. It is still a bit grainy but acceptable IMO.

Just to be sure I get the same time saving in my final render, how can I be sure mantra_IPR does not use “Preview”? I couldn't find this option in the mantra_ipr's parameters pane, and I didn't find “box filtering” neither.

33mn is much better but it is still too long for an image sequence rendering. More tips or learning material would be welcome.

Thanks
GZ

Please download the Redshift [www.redshift3d.com] demo, and give it a try. It is a GPU renderer.

You can render this frame in seconds instead of minutes.

Yeah Daryl thanks I thought about that. But before I try other renderers I was thinking that maybe Mantra is worth giving a chance? Some people must be using it happily…

As far as I'm aware, you can only preview with progressive rendering when you are using the Render View tab. (where it's enabled as default from start-up). All final outputs will use buckets instead.

The Pixel Filter options are located in the mantra rop, Images > Output. (you can also click the search button on the top of the parameters to find things)

As for reducing noise and render time together, you may be able to optimise but nothing compared to GPU rendering speeds. In general, to reduce noise in Mantra, you increase render times. The best tip I can give is to refer to the documentation… http://www.sidefx.com/docs/houdini/render/noise.html [www.sidefx.com]
Once you have a good understanding of where the noise is coming from using Extra Image Planes, it becomes easier to know which settings to alter.

Turn On Multiprocessing
Clean up your Compositions
Trim Layers Off-Screen

Regards,
Adrian Gates
System Admin

Thanks guys.

Well I think I cannot reduce noise more as it would mean having a render time that's more than 30mn on this picture.
Thanks Rob for the link. Judging from this page, If I keep working with Mantra, I will have a lot of things to learn!!

“Multiprocessing” : are you speaking about this : http://www.sidefx.com/docs/houdini/ref/windows/mainprefs.html [www.sidefx.com] > compositing > cooking > threads
“Clean up your Compositions” you mean hide objects that are not in the camera's field of view?
“Trim Layers Off-Screen” : this ? http://www.sidefx.com/docs/houdini/nodes/chop/layer.html [www.sidefx.com]

If part of a sequence you can get away with a little noise.
Also consider removing some of the render noise in post with a plugin like Neat Video.

Hello
New pictures enclosed, this time only 11mn!

Render time : 11mn
Image size : 1280x720
Intel Core i7-6700 2.60Ghz
Ram : 16Gb
output picture : jpg
Rendering engine : Mantra, , physically based rendering
Depth of field and motion blur : off
Pixel samples : 3 3
Min max ray samples = 1 & 6
Reflect and refract limits = 3
Opacity limit = 0.995

What I changed : I used less hoggish materials. Previously I was using “Glass” presets. Now I changed them to principle shader with some transparency , etc.

I still have some big render times and noise on scenes with reflections in shadows, but I'm studying that now.

Thanks Rob for the extra image planes tip, it has helped me to locate where the noise was coming from in these other scens.

I also tested Redshift demo. It's true that it's quick. But so far I didn't test it extensively, I get some black and white renders. I think to get it right I have to replace all my materials and lights by Redshift ones, right?

Hi, yes that's correct, you need to build the scene using Redshift mats/lights.

Regarding the Mantra render. It's been a while since I've used it (as I now use Redshift for the majority of my work) but here are some tips I can remember…

1) “Constrain by maximum roughness” works pretty well and might be suitable for your scene. It's located on the Mantra rop in Rendering > Shading. In most cases the accuracy loss isn't noticeable and it can speed up the render a bit.

2) Reduce the “Noise level” by adding a zero or two (ie. 0.001 or 0.0001) and compare the extra render time difference. This is located on Mantra rop, Render > Sampling.

3) For the direct reflection noise, try increasing the “Sampling Quality” on your light(s). You can often set this quite high with minimal effect on render time compared to other methods. This is located on the light itself. (not the mantra rop) Also, if using an environment light, try increasing the “Glossy Filter Amount”.

4) If you have some “fireflies” remaining, try reducing the “Colour Limit” located on the Mantra rop, Rendering > Limits.

Rob

Decreasing noise lvl to .001 usually produces very high render times as it's 10x smaller than the default .01 IIRC. .0001 is probably not practical for most scenes, but it does hurt to try it in yours.

Also, the max ray samples of 6 seems pretty low. I would go with at least 16, but wouldn't rule out 32, 64 or even more. Also pixel samples should be 5 at minimum for final shots in my experience.

If you don't have a renderfarm and special need for effects in your sequences, Redshift should make your life easier.