Low lit room issues

[steven07]

Hey all,

I'm trying to get a low lit room rendered and I can't seem to get the room lit without blowing out the lights. I'm using 3 area lights.
Here's what the scene looks like / settings.

[Fer]

Try to use linear workflow, it will help you get a more realistic and even light distribution.

And add more diffuse FG bounce if you want to use less light in an interior scene.

No need to use Unified Sampling in such simple scene, Adaptive Subdivision is faster in this scenario.

[steven07]

Thanks so much!! What do you mean by diffuse FG bounce? is that the trace depth diffuse parameter in my picture?

[Letterbox]

Thanks so much!! What do you mean by diffuse FG bounce? is that the trace depth diffuse parameter in my picture?

Yes, create a split render region, make one as you have, the other with a higher value to see the difference it makes.

[steven07]

What kind of scenes take the most advantage out of unified sampling?

[steven07]

how do I get rid of splotchies with Unified sampling? Here the image with more diffuse and gamma correction!

[steven07]

would good production settings for AA be a quality of 5ish?

[Falam]

would good production settings for AA be a quality of 5ish?

Depends on your system, I do 1/3 (min/max) for a 1080p resolution. I spend a fair amount of time adjusting FG and GI, takes work, it's a learning experience.

[steven07]

Is that with the unified sampling or the regular system? I guess it will depend too on resolution right? Do you up differend numbers for bigger resolutions? I'm doing 1280x720

[Kzin]

What kind of scenes take the most advantage out of unified sampling?

scenes with alot of sampling, like area lights, glossi reflection, stuff like that. unified also covers details way much better then adaptive, so thin objects, like fooliage, grass for example.
the decision if unified or adaptice is resolution independent and it hast also nothing todo with interpolated fg. it can help to reduce noise when using brute force fg or path tracing.

good production settings depends on the shaders and the scene, lots of glossis, then unified with min1/max100 and 3 for quality as starting point for 720p.
adaptive settings for this resolution: min0/max3; treshold 0.025 and gaussain with 2 for all aa modes as filter.#

unified will not help with fg splotches because it has nothing to do with fg.
you can increase the density, use 2 for example, interpolation points of 35 and 200 rays.

[steven07]

Awesome!! Thanks so much for your help! I'm gonna get home and do a few texts after I texture some things. Is there somewhere I can read more on unified sampling or just mental ray for XSI in general?

[Fer]

Those are FG splotches, you get rid of them by increasing the number of rays, point interpolation or filter size.

FG in an interior low lit or indirect lighting scene is really hard to tweak, but you have a fair amount of light in you scene so it should do it.

-Decrease the presample density to a minimum level, and concentrate on rays and point interpolation, something like 0.25 to 0.4 for presample density (depends on the complexity of your geometry in the scene)

-250 to 450 FG Rays, sometime it can go in the thousands. Point interpolation is a areal player, it can get rid of splotches real quick at the expense of realism, start from 15 to 50 or more. interpolation work in conjunction with FG rays, more FG rays less point interpolation need it, more realistic result, yes you get it. The real spoiled Princess is FG rays.

-If you are looking for good indirect lighting with FG forget filter it discard fg rays that can cause splotches, unfortunately it eat indirect illumination a lot. so put it at Zero if you want, and use FG rays and point interpolation.

-Ambient occlusion is important if you want to bring back the detail that you scarified in lowering the presample density, activate it in every materials you see that need it. increase the shadow color the get softer look.

-Unified Sampling (US) it's a long story and I'm still at half the book, I'll give you the quick resume: US is clearly superior to Adaptive subdivision (AS) in mental ray. If you had sampling problem with glossy reflection, direct specular reflection in the past with AS, US get rid of it beautifully, it just cut trough everything, and sometimes it faster than AS, as a say "sometimes" because AS is still faster in some scenario like your scene with simple diffuse lighting low glossy reflection, and simple geometry, but when you start lowering your glossy reflection, refraction, adding fine detail geometry and high direct and direct light specular, DOF. just switch to Unified is just easy.

You start at min of 1 and max to big numbers like hundreds of samples, depends on your scene, and you control your result with quality slider, when it stop having effect and you still not happy with the sampling, you know you should increase the max sample.

-Some sampling numbers for your materials and lights if you are using US.

Glossy refection: 1 to 12, why ? Sometimes you get rid of noise with just 1 sample, but Unified is still not smart enough to know where to concentrate it sampling and energy. 1 sample will get rid of your noise sometimes, but also of your light energy so you need to help the sampling a bit by increasing the glossy reflection

Area Lights: 1 to 8, same music, like glossy reflection.

AO: 1 to 6 or 12, this one I'm not clearly sure, I just put it to 4 a leave it be.

Well that's it I think. Good luck. Don't hesitate to ask more questions.

[steven07]

Whoa!! Thanks so much fer!! That's awesome! What book are you reading? I'd love to learn all the technicalities of mental ray or US / AS. Ill have slightly reflective surfaces since there will be porcelein. But ill post some tests later on.

[Kzin]

for ao, try to use ao color bleed option with 16 sample and let the shadow color to black. i am not a fan of normal ao in interiors because you have this typical ao look which destroys the look very easy. the ao colorbleed is a brute force color bleeding tech, means it creates great indirect lighting and shadowing details without interpolation, its more like path tracing. the downside is the much higher rendertime, so best is to use it with smaller distance.

its right what fer wrote about more rays for fg. but there is a big downside of this. if you increase the rays and also increase the interpolation, you will end up in much higher rendertimes without much bigger quality. interpolation should always be as low as possible. from my experience, you need density of, at least, 1 minimum. i did alot of test last week with density of 400 for example, low rays and interpolation of 1, but also with low density like 0.2 and really high raycount like 100.000. the conclusion is that you need a minimum density to make the solution to work. and the minimum was 1 for more realistic raycounts like 2000 (interpolation can be low like 5 in this case).

so do some tests with fer's comment in mind and play a bit with your scene to understand what happens when you change the settings.

[steven07]

I'm trying to get two black and white images on this wall.. One on the top and one on the bottom. I've made a cubic projection so that I can control the size better. It seems like when I try to mix them that only one of them shows. I can't figure out how to make the black and white image work as a transparency map.
So basically it's a tiled wall.. and then the image "grunge" image on the top.. then rotated 180 degrees and added on the bottom.. except you can't see it that well on the top and the bottom doesn't even show.

[steven07]

I hope my question made sense