Hello, I am new to rendering with Mantra, I have done a few renders with Arnold in Maya.

So now I try to reduce the noise in the rendering of my Houdini shot that I will render with Mantra.

The Useer guide from SideFX about removing Noise says I have to increase the light samples, as I would also do in Arnold. However I don't find this parameter in the light options. For the environment light I have the sampling quality, which is kind of the same (I guess). But for the simple light (I have two point spotlights in my scene) the sampling quality parameter is deactivated. Nevertheless there's a lot of noise in the direct reflection. Do I need another way to remove it?

I really hope you can give me a hint here, thanks in advance!

It's on the light too. It's called "Sampling Quality". It will be disabled on a spotlight if it is a point light, as point lights don't generate noise.

Personally, I almost never change light sampling quality. I use the sample settings on the render node, but mainly ray min, max and pixel samples. Since spot lights don't generate random noise in direct lighting, only pixel samples will reduce aliasing noise.

jsmack
It's on the light too. It's called "Sampling Quality". It will be disabled on a spotlight if it is a point light, as point lights don't generate noise.

Thank you very much, I have just edited my opening post about the point light...

So good to know a point light should not generate noise. Do you have any idea why there is a huge bunch of noise in the direct reflection while direct diffuse is quite clean. I thought this was an effect of less light samples as the user guide describes. Is there another possible source of reflection noise?
If I actually increase the pixel samples now to a very huge value now to improve revlections, is there a way to not affect the render time of the other components as well?

freewind

jsmack
It's on the light too. It's called "Sampling Quality". It will be disabled on a spotlight if it is a point light, as point lights don't generate noise.

Thank you very much, I have just edited my opening post about the point light...

So good to know a point light should not generate noise. Do you have any idea why there is a huge bunch of noise in the direct reflection while direct diffuse is quite clean. I thought this was an effect of less light samples as the user guide describes. Is there another possible source of reflection noise?
If I actually increase the pixel samples now to a very huge value now to improve revlections, is there a way to not affect the render time of the other components as well?

I'm not sure how a point light can show up as noise in direct reflection. That's the specular highlights which don't have any 'noise' since they shouldn't be randomly sampled. A very bumpy surface will have many specular highlights though, which will look noisy. Is the surface bumpy?

A screenshot or a scene file to illustrate the problem would help.

okay this is a close perspective of my scene in the scene view, I created a pedestal of laminated wood with some shivers flying around:
[abload.de]

for the wood shader I used some PBR textures that create some very fine structures.
Unfortunately the rendering seems to be quite heavy - these are some full resolution renderings of the components.
direct_diffuse
[abload.de]

direct_reflect
[abload.de]

direct_coat
[abload.de]

direct_c
[abload.de]

So apparently the noise in reflection results from the hires textures, the raytracing needs a lot more rays. But it looks quite well in the scene view - is there any way to render it in the same quality without such huge amounts of render time?

EDIT: Maybe it looks "better" in the HD renderings than in scene view. I don't know if this look is what Mantra interprets the shader to look in the end, but it doesn't show up as in the scene view. And in half resolution renderings it looked really crappy, that's why I'm not sure.

Have you also tried rendering out per-light AOVs so you can be sure what light(s) is/are causing the noise?

I tried to do that, but I don't know yet how to set this up in the render node, as I only find Combined lighting per light in the extra images presets. (You know a good manual for that?)

So I switched on the lights manually. I have an environment light and two spotlights with different cone angles. One of the spotlights causes the extreme noise. That's why my first approach here was to adjust light samples individually. So if that is not the way to go, how can I solve this otherwise?

This isn't noise. The detail in the texture when used as a bump/normal map is exceeding the frequency limit of the rendered image. It probably looks better in the gl view because the textures are down sampled. Are the textures mip-mapped by chance? If not, then mantra won't be able to anti-alias them and you will get a lot of noise from high frequency details. Try converting to rat format or use imaketx to mipmap exr textures. Once the textures are mipmapped try changing the texture filtering settings to see remove the high frequency details.

The only other option as you've found is to render at a higher resolution or use more pixel samples to improve anti aliasing by brute force.

jsmack
Are the textures mip-mapped by chance? If not, then mantra won't be able to anti-alias them and you will get a lot of noise from high frequency details. Try converting to rat format or use imaketx to mipmap exr textures.

That's jpg files from cgaxis, so I don't think they're mip-mapped.

But I haven't heard about that before. On my campus I have up-to-date Photoshop, can I use that to convert the files?

freewind
But I haven't heard about that before. On my campus I have up-to-date Photoshop, can I use that to convert the files?

No, not with photoshop. Most renderers ship with their own tool to convert to their proprietary texture format and Houdini is no different. icp or iconvert are command line tools to convert jpgs and other non-texture formats to the proprietary .rat format. Since adding OIIO support, houdini also ships with the command line tool, imaketx, to convert images to the open standard mipmapped exr format.

If you have a lot of textures to convert and don't want to write shell scripts, PDG can be helpful although it's a bit complicated for something a google search can usually teach the bash script for in 2 seconds.

Thanks a lot!

I'm still figuring out how to work with command line tools, so I might have to ask some really basic specific questions.

I guess this is about to work:
iconvert -m makemips e:\texture\picture.jpg e:\texture\picture.rat

This creates a new file, but I receive this warning:
HOUDINI_OIIO_EXR=1 is needed for exr MIP levels.

Does this mean I have to add another tag to the line?
And will other properties as bit depth e.g. stay untouched?

I think you can leave out -m makemips as rats already generate mipmaps by default. rat files support 8bit channels so no conversion is needed.

Thank you very much, now the render looks fine even in quarter resolution!

freewind
I tried to do that, but I don't know yet how to set this up in the render node, as I only find Combined lighting per light in the extra images presets. (You know a good manual for that?)

Tank you mrCatfish, this works well!

I also noticed the "Combined lighting per light" preset does not work out as I expected to see the overall impact of a single light. I then can choose AOVs in the render view for every light, but they are all completely black. The same happens, if I just deactivate "Export variable for each component" in the settings from your attached picture (which I thaught should get the same result in my case).

Do you have a guess what I am missing here?

freewind
I also noticed the "Combined lighting per light" preset does not work out as I expected to see the overall impact of a single light. I then can choose AOVs in the render view for every light, but they are all completely black.

It works for me. Are your shaders custom? I've seen these lighting aovs fail when using custom shaders that don't include the proper epilogue.

freewind
The same happens, if I just deactivate "Export variable for each component" in the settings from your attached picture (which I thaught should get the same result in my case).

"Export variable for each component" is required for a component export such as 'direct_comp' since it's an array. It can't be exported without splitting into components.

I don't know yet what's meant by "custom shaders" in Houdini.

However now it's working... it feels like sometimes Houdini decides very spontaneous what to do Well maybe I just picked the wrong render node before. But I also wondered why at first I could not export combined lighting per light and components per light at the same time (one of them was always black). I clicked very hysterical a lot of times and now it seems to work correctly. But I'm still quite confused by all of this.

freewind
But I also wondered why at first I could not export combined lighting per light and components per light at the same time (one of them was always black). I clicked very hysterical a lot of times and now it seems to work correctly. But I'm still quite confused by all of this.

you can, but you have to export 'all_comp' instead of 'all' and then enable light exports.