Help needed with Mental Ray artifacts.

[louismartin]

Hi there,

 

I am working on a render at the office for an amenity room.

While initial renders were looking good, when I rendered with higher FG settings and Resolution, the image came out with lots of grainy artifacts and these glows in the ceiling edges that keep happening from place to place.

please see the photo below.

 

any input you have would be appreciated!

[Matt McDonald]

the graininess could be caused by low glossy reflection settings on the materials, low AA settings or a combination of both. The light blobs look like they are either caused by FG interpolation settings which are too high or photons which are too large (if you are using GI)/

[louismartin]

Thank you, I was able to eliminate the glow by a total reset and keeping the settings lower as suggested.

I think i was going through so many forum threads and trying so many things that the render setting was getting insane...

 

1 problem fixed,thank you! but as for the grainy image. i still get the white speckle though out the image.

I will look as the glossy reflections, but is there a general value (Glossiness and Samples) that I should be using for the wall and ceiling?

 

I appreciate your help!

[Matt McDonald]

Others might disagree but generally if I have a glossiness value below 5 I tend to turn on the highlights + FG only setting. With this engaged you won't have true reflections but your render times will come down. You also don't have to worry about glossiness samples with highlights + FG only because it's not a true reflection.

 

If you want to have true reflections, the lower your glossiness setting the more samples you'll need. If you aren't using Unified Sampling you might need to try something like 32 samples on materials with glossiness below 5.

 

Another trick is to reduce the brightness of the object that is being reflected. To do this, you turn off the "light shape visible in rendering" option. Model a light bulb and apply a self-illuminated material that is not nearly as bright as the actual bulb. Be sure that "visible in reflections" is turned on and "illuminates scene using final gather" is turned off.

[CJI]

I agree with everything that Matt has suggested. When switching to Highlights + FG reflections be careful of the reflection amount. I have found that if you dont reduce this it can really over brighten your material. Something to keep an eye on.

[louismartin]

Thanks again. so i rendered out with the highlights +FG only setting on all of the walls and ceiling material since those were the problematic areas.

below is the render (800x600) which took all night.

 

I've read in many tutorials that most of those small artifacts will go away as you increase resolution, but is that true?

 

[Matt McDonald]

No. It's not true. Rather than using high AA settings, some folks render at 2x the resolution and then resize down in photoshop using a softening filter this can fix some issues around edges or super bright pixels on super reflective objects but it won't eliminate all the issues.

 

The remaining noise and grain you are seeing can probably be resolved by increasing shadow samples on your lights and sky portals...if you are using them...and you should be (this will address overall grain) and increasing your AA settings (this will address some fireflies on chrome objects). Both of these settings will increase your render time. Consider that self-illuminated material I mentioned above to help with the chrome objects.

 

All night sounds like quite a bit of render time fro 800x600. What are the specs of the computer you rendered on?

[CJI]

 

All night sounds like quite a bit of render time fro 800x600. What are the specs of the computer you rendered on?

 

Very curious what your specs are and rendering settings. all night for an 800 x 600 seems pretty excessive.

[marius e]

Think some grain speckles is from your light shade material, transparency gloss is set to low, just disable gloss and see what happens...

[blank...]

below is the render (800x600) which took all night.

 

Unless you're using P1@120Mhz there is something very wrong with your materials, lights and MR setup.

The best way to solve this scene is to post it for people to take a look at it. If you can't post the scene, make a dummy one, bunch of cubes with assigned materials, keep the lighting setup and MR settings the same as in your scene.

[louismartin]

Thank you everyone for your input. I apologize for the late reply, got caught up with other stuff at the office...

 

back to the rendering now.

 

Im running a i7-2600K CPU @ 3.40Ghz. 32Gig RAM. The computers are custom built by one of the architects here to have optimum performance for Revit.

I dont think I can load the file but I'll see if I can create a dummy when I get a chance.

 

here is my render settings...

 

and also a few materials...

 

and I've realized that the material for the shade is way messed up. I totally missed this one. Once I have some feed back on the settings and materials, I will do another render and post it on here.

 

i almost forgot, the Skyportals settings ...

shadow sample at 64 w GI photons of 200000

 

Thanks again for your help and support!

[CJI]

Well it's definitely not the computer then

 

There is a few things that stick out to me. I will try and keep it structured.

 

Final gather - density is very high and will cripple render speed. In combination with GI I have rarely if ever gone over 0.4

- noise filter. None or standard. Probably standard as I see you are using ibl. Helps with hdri artifacts.

 

GI - when using GI I have seen quite a few methods here but I personally have had good success with Justin Hunts method of smaller sample radius with lots of samples.

-radius is too small. I work in mm but as far as I can tell that's a radius of 1inch so 25mm which is pretty small. Try increasing this to around 150mm-200mm(6"-8")

- you can reduce max photon per sample to 100 - 200

-optimise for final gather on

-increase photons per light to 500000+ Start here and work up if necessary. Don't be afraid of 1 or 2 million of needed.

-trace depth 300 with reflect and refract at 150 each. This is how much the photons bounce about. The idea is to get the small amounts of photons to bounce loads across the scene.

 

Sampling - I can't comment on unified sampling as haven't really used it (mr here is slightly outdated :s)

-spatial contrast seems quite low for that scene. 0.03 should be more than enough.

 

Materials - the lamp material likely takes quite a bit to render. 0.1 glossy refractions is massively overkill in my opinion especially as at the moment you won't see it. Maybe replace the geometry with single sided faces and use the transparency function instead.

- 0.2 reflection glossiness on the lamp is a super diffuse material and even with 32 samples you will see loads of grain. I rarely go below 0.6 - 0.5 at 32 samples. Below this switch to FG + highlights.

 

Skylight - 64 samples may or may not be too much. Depending how other issue are resolved. I have certainly gone that high before.

- I would ask why you chose to set the GI manually. I usually allow auto calculation and use the global multipliers for more finite control. Unless you REALLY know what you were doing I would steer clear of setting these yourself. Not saying don't but I think most find it more efficient to use the global multipliers setting instead.

 

Ok I think that's everything. Bear in mind other might/will have differing and opinions. Hope mine help, keep us posted

[Francisco Penaloza]

Like Curtis said I would first reduce all the factor involved in this problem. Set all light to default, all GI to default. Then overwrite your whole scene with a medium gray color, and render, then you'll see all the problems related only with Illumination and GI, the noise that I see in your latest rendering, I am pretty sure it is shadows samples related, increasing your IBL shadow accuracy will help you to fix that or adding more light samples. but again don't be afraid of scratch everything and re evaluate your scene, sometimes this is faster than keep clicking here and little there, and other places.

If your exterior windows are not in the shot, turn them off. When your Lighting and GI is clean, then add reflections and refraction to your scene, any noise that you'll see, you know is is material related and not lighting!.

 

If you are using self illuminated materials or lights inside of a lamp shade with glossy reflections, that's a big killer for Mental Ray, you need to increase the samples a lot in that shader to make the light go through without producing noise. I would recommend to exclude that lam shade from that light or reduce the reflection amount on it.

Also your wall have a 0.1 percent of reflection?? I don't think that's is visible at all, and you are making each light and final gather point to bounce at least 5 time every time that hit that wall, that's a overkill for your scene.

 

The best method for Gi is using the right size of photon, as a rule of thumb I take the thickness of the thinness wall in my scene, 4" or 6" and use that as start point, then increase the photon number, hundred thousand, a million is OK they are cheap. then a mudium value of FG will help to clean that up.

[Justin Hunt]

the high noise filtering is also very slow, often un-necessary too.

 

agree with the other comments

 

Jhv

[louismartin]

Thank you guys so much,

 

very helpful information here.

I will try and get a render to show you guys in the morning.

 

Curtis, I set the GI to manual when I was following a couple different tutorials for example. I cant remember what the exact reasoning it was but I'm gonna get back to you on that.

 

A question about material over ride... how can I get the windows to stay as glass material? I've tried hiding the windows all together, but then i lose detail in the window frames?

after meeting with my boss and the client yesterday, they have asked for a new view. Now getting more windows in the shot.

I will have an update for you early tomorrow.

 

[Matt McDonald]

Ok, a couple of thoughts here: I agree with the others that your FG setting are too high and you probably don't need your photons to be so small. I typically set them to be half the width of a wall.

 

But here are my other thoughts. You have user IBL enabled. Are you using a HDRI for environment lighting? If so, get rid of the sky portals. The purpose of sky portals is to focus the FG solution on the MR sun & sky as seen from the windows. If you are not using an HDRI for environment lighting you should disable user IBL and use FG for environment sampling. On exteriors I have seen scenes lit with a sun & sky but rendered using user IBL taking twice as long as the FG solution with no improvement in quality.

 

Another thought, because you are using unified sampling you really don't need to mess around with all the different sample settings. As Nvidia recommends use of unified, you set all of your samples at a base level and then adjust the quality setting until you reach an acceptable level of grain. Nvidia says to set local samples (glossy reflections, shadows, etc.) as low as they can go and then drive them with the quality setting in the unified controls. The theroy is that use save time on scene setup. I'm not sure I agree in an arch-vis workflow as I have tried this multiple times and experienced very high render times.

 

I hope some of this makes sense. I've been thinking about it all afternoon and wanted to post but I'm in a hurry and have to run. I'll reiterate that I don't think anyone has given you advice that is incorrect.

[blank...]

What you have here is a scene that is not properly set up for unified sampling. Set all samples to one, and for unified set max to 100, or 200, or 300!

 

Read this:

It's a shame there is no "how to unified" with max 2014. If you don't go out and look for yourself, you're probably not using it right. I've been using it for some time now, before it was exposed in max UI (with Thorsten script), and there is enough info on it out there if one wants it.

But, long story short: where ever you see a sample setting, set it's value to one. Glossy samples in materials, shadow samples in ligth, samples in ambient occlusion, etc... All to one. Unified takes care of the rest (lights, i.e. shadows and glossy materials could still need 2 or 4 in some cases).

That's why you can get away with crazy settings like 200 or 300 for max value.

 

http://elementalray.wordpress.com/2011/11/30/unified-sampling-visually-for-the-artist/ (it's got even better since this post, it samples more in light areas, less in dark)

http://www.infinity-vision.de/blog/render_optimizer

[louismartin]

Thanks you all of the helpful tips! A lot of feedback here and I am working on it right now.

 

I thought I posted a reply last night but for some reason its not on here.

Curtis, the Gi was set manually as i was following a tutorial online which recommended it. I cant remember the reasoning they had, but i'll try to see if i can find that here. I printed out bunch of stuff... and thank you for all of the info on the values and setting. helps to know what range of numbers i should be in rather than shooting in the dark. thank you.

 

Francisco, should i just do a reset by switching assigned renderer to Scanline and back to Mental Ray, then adjust setting accordingly? probably would be the easiest haha. And as far as material override, is there a way i can keep the windows as glass material? I cant seem to hide the glass plane individually for some reason. Maybe the way it was modeled in revit? i suppose i could just hide them as a whole.

for the lamp shades... it is self illuminating material inside... oops. but i think it is excluded from the lights.

what would be a reasonable reflection value for the walls and columns? and bounce#?

 

Justin, I am now realizing that "very high" setting was unnecessary. thank you. I dont see much difference from standard to high in the noise i see within the renders.

 

Matt, I am not using a HDRI. in that case, I should switch to the FG method. For any renders, interior or exterior, would you recommend using HDRI method? regarding the quality setting value, I read in a tutorial that the person goes as high as 20 if neccessary, but i bumped it up a lil and saw significant render time increase. how high would you typically go for this?

 

Dario, Thank you for the tip there. very helpful. I will give it a shot.

 

Thanks again everyone. I will get a render out today or possibly tomorrow. getting caught up with other stuff around the office... wish i could just work on the renders constantly than jumping form task to task getting lost where i was with the renders.

 

Louis

[Matt McDonald]

Matt, I am not using a HDRI. in that case, I should switch to the FG method. For any renders, interior or exterior, would you recommend using HDRI method? regarding the quality setting value, I read in a tutorial that the person goes as high as 20 if neccessary, but i bumped it up a lil and saw significant render time increase. how high would you typically go for this?

 

Yes, switch skylight mode to "Skylight Illumination from Final Gather (FG)" if you are not using an HDRI for illumination. A high quality HDRI can provide beautiful lighting on an exterior scene so it's worth trying. On an interior...maybe. I think it depends on how much influence the outside lighting should have on your scene. In what you have been showing us so far I would say that it is not worth messing with.

 

Regarding "quality" in the Unified Sampling controls...here's the thing, it's a technology only recently exposed by Autodesk though it has been in MR for a version or two. So workflows, specifically arch-vis workflows are not yet clear. Dario describes exactly how Nvidia intends for it to be used. I've read quite a few posts from arch-vis people complaining about render time with it. In my own experience using it as Nvidia intends I have had issues with render time. I've never seen a tutorial where the max AA setting is as low as yours nor have a seen anyone recommend a quality setting of 20 or anything near that.

 

I'm tempted to tell you to ditch unified sampling and switch over to "Classic/Raytraced" because most of the advice you have been receiving, e.g.: add samples is in keeping with that workflow and it might be faster in terms of render time.

[blank...]

Yes, switch skylight mode to "Skylight Illumination from Final Gather (FG)" if you are not using an HDRI for illumination.

 

Definitely, mr sun/sky with sky portals should be the way to go and ditch HDR lighting for interiors altogether. MR native IBL, if i'm not mistaken, is actually not meant to be used in that way at all.

If you have one object of interest (car render for example) then IBL is great. But with anything that is not directly exposed to HDRI (bridge underside render for example) IBL will not work, i.e. FG will need to come to the rescue.

 

I'm tempted to tell you to ditch unified sampling and switch over to "Classic/Raytraced" because most of the advice you have been receiving, e.g.: add samples is in keeping with that workflow and it might be faster in terms of render time.

Please, please don't do it without testing it first. Offcourse every scene is different, everything is possible, but i'm confident that unified will be faster.

First scene i used it on - rendered it in half the time it took vray to render (i had experienced vray users examine the scene, there is nothing wrong with it). And MRs velvet looked much nicer.

So, i'm 99% sure unified will be faster then classic (if everything else in the scene is set up properly)

 

Just one more note, filtering can make huge difference with unified. Don't just stick with default gauss, try Mitchell and Lanczos.

[louismartin]

Happy new year to everyone and thank you for all of the input.

 

After the odd holiday hours, I was able to eliminate the noise and artifacts in the render.

Its looking a lot better now, but having trouble with the rendertime... this 1600x 1200 image is taking so far 8hours and its only at 31.1%.

This seems a bit too much. This is also with precalculated FG and GI.

 

I've also looked into "submit to network render" where the image gets split in strips then sent to the other 3 computers available in the office to render, but there seems to be problems with the lights. I keep getting error messages in the dialogue noting problems with the 100w bulb lighting and 60w bulbs. the image will render out just fine until it comes across one of the bulbs and resets to start over...

 

has anyone tried network render and experienced similar problems?

[louismartin]

Thank you for the help everyone.

 

I think the images are turning out fairly well.

 

This is photoshopped, but let me know what you guys think.

 

 

also attached is a fitness room rendering.

 

Thanks again,

 

Louis