Hey guys,
I'm used to rendering in Vray (using their unified DMC sampling setup) and just wondering what the balance is when using reflection/refraction heavy scenes.
Im using a few area lights and an environment light with a hdr environment map and a decent amount of geo with mantra surface shaders with a bit of blury reflections and refractions (think frosted glass chunks in an outside scene).
Im having trouble getting rid of flickering in what looks like the refraction. Im not sure where to put all my extra samples, in the Max Rays, the refraction quality or the environment.
It seems I need the pixel sampling to be about 3x3 for decent AAed edges, then I should play with the MaxRays and the noise level (just like Vray!) to clean up the blurry refractions. IS this right?
Modifying the reflection/refraction quality in the mantra shader doesn't seem to do a thing.
And should I be using PBR, or Micropoly/PBR or raytrace for this stuff?
Any tips (as im quite new to mantra) would be great!
Thanks

Hi,
first of all congratulations on your decision to give mantra a try. It's a great renderer.

I'm no expert in VRAY but as I understood it the adaptive DMC sampling decides how many PRIMARY rays are shot into the scene while Houdini has a fixed amount of antialiasing (primary) samples and uses the noise threshold to determine the amount of SECONDARY samples to be shot into the scene.
As a consequence you are totally right in using the pixel samples to determine your antialiasing quality and use maxrays and noise threshold to clean up the noise levels. I found however that this sometimes results in weird artifacts when the scene has a lot of contrast so I tend to use quite high pixel sample values (between 4x4 to 12x12) and use the noise level to clean up the remaining noise.
I would suggest you use PBR as this gives me the best results and does a wonderful job at importance sampling, especially if you have a lot of reflective surfaces. With refractive surfaces PBR sometimes behaves unexpected and produces a lot of noise if you choose to use ALL PATHS for the allowable paths parameter. Also geometry with constant shaders tend to give me cleaner reflections/refractions than using area lights.
Remember at all times to linearize your textures and display your renders with a gamma of 2.2 or a LUT if you have one.

-dennis

Thanks Dennis, good info
So would you use geo+constant material to emit light into the scene as well or just for reflect/refract and use an area/environment light for lighting (turning off reflect/refract lights on the object materials)

I would just try it for reflection/refraction. For diffuse lighting area/environment lights are much faster and cleaner.

Another important trick for working with transparent objects is to always play with faux caustics and the shadow intensity values. I never turn on all paths in the allowable paths parameter as faux caustics can imitate these lighting effects good enough in almost all cases.