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Wednesday, March 7, 2012

V-ray Maya Adaptive sampling/antialiasing tid bits

This was gleaned off a forum and posted by a user called PerfectLine. There is some very useful information in here if you are trying to figure out the DMC and Adaptive DMC sampling in v-ray for Maya.

------ First off the ADMC settings ------ The anti aliasing engine.

ADMC MIN Subdivs (anti-aliasing sampler) --- Determines the initial (minimum) number of samples taken for each pixel. You will rarely need to set this to more then 1, except if you have very thin lines that are not captured correctly, or fast moving objects if you use motion blur. The actual number of pixels is the square of this number (e.g. 4 subdiivs produce 16 samples per pixel).

ADMC MAX Subdivs (anti-aliasing sampler) -- Determines the maximum number of samples taken for each pixel. The actual maximum number of pixels is the square of this number (e.g. 4 subdiivs produce 16 samples per pixel). NOTE... that vray may take less then the number of samples asked here IF the difference in intensity of the neighboring pixels is small enough.

ADMC Threshold --- The threshold that will be used to determine if a pixel needs more samples. Lower numbers produce more scrutiny. Meaning that the lower the number the more samples it will take until the threshold is met. Hence a lower number is a higher setting. 

So 0.01 is a lower quality setting and something like 0.003 is a high quality setting.

------------------ DMC SAMPLER ----------- 

Adaptive Amount -- Controls the extent to which the number of samples depends on a blurry value. It also controls the minimum number of samples that will be taken. A value of 1.0 is a full adaptation. A Value of 0 is no adaptation being performed. 

Default. 0.850. The higher this number is the lower the quality. Lower the number the higher the quality but at cost of time. Often 0.9 works in most cases too. I've taken it down to .7 in extreme cases but could probably have just tuned the shaders and lights slightly better.

Adaptive Threshold -- Controls Vray's judgment of when a blurry value is "good enough" to be used. This directly translates to noise in the result. Smaller values mean less noise, more samples and higher quality. Value of 0.0. means no adaptation will be performed. 0.01 Is a good value here for many instances.

Adaptive Min Samples -- Determines the minimum number of samples that must be made before the early termination algorithm is used. Higher values will slow things down but make the early termination algorithm more reliable. I like a value of 12 here though the default of 8 is a good start for lookdev, moving it up to 12 for finals or higher if your blurry values need more scrutiny. 

SubDivs Multi (multiplier) --- This will multiply all subdiv values everywhere during rendering. default 1.0. You can use this to increase or decrease sampling quality everywhere. Kind of a nice quick knob for proxy tests in some cases with larger scenes. 0.5 cuts your subdiv settings in half, etc etc. 

This effects everything except for the lightmap, photon map, caustics and the AA subdivs in the ADMC. 

Which is.... DoF, motion blur, irradiance map, brute force GI, area lights, area shadows, glossy reflections/refractions are affected by this parameter.

-----------------------------TRY TO REMEMBER THOUGH--------------

1. That you will still want to get your shaders blurry values (reflection/refraction glossiness) set correctly. The farther down from 1.0 glossiness the more samples you'll need. 

Glossiness - 
1.0 - 8 samples. 
.99 to .9 - 16 samples.
.89 to .7 - 24-32 samples.
.650 to 500 - 48 - 64 samples.
lower... etc etc. 

2. your light shadows area lights should probably default at 16 samples. depending on size vs scene rendered I've seen as high as 64. But often 16 - 32 is fairly enough in most cases. Just render the light with something to shadow and test render. 24 is a good average final light for most of my lights that are flat area lights. Sphere lights and dome lights need more depending on the situation. 

3. DoF and Motion Blur have their own SubDiv settings too. Keep it default for all render lookdev and tests. Then raise them up as needed incrementally until you feel the noise ( or lack thereof) fits the quality you need. 

4. GI flickers are their own group of settings (IR, LCache, Brute force). Thankfully GI is rarely seen as noise but rather splotchies when its not set correctly. Make sure you are adjusting the correct parameter when using Vray, though brute force can make addressing noise challenging. Which is why its good to tune the scene before adding GI this way you can trouble shoot each thing, one at a time. I've seen people try to correct GI problems by making the ADMC higher. Which is useless. More AA is not going to smooth the GI solution.

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