Mental Ray, DSG Shiny Value, and Artifacts, oh my!

[Theta-Dot]

I spelled it "DSG" instead of "DGS" in the title :D
oopsie!

[3DMadness]

The problem is with your Glossy Highlights, this is what is causing the white dots. I've replicated your scene here and if I put black in the glossy highlights these white dots disappear. So you should use the glossy highlights only when the you have a high shiny value, in this case you can add some specular to give it some reflection.

But I think DGS should be used in specific situation because it's a physic phenomen and can slow your render, so in animations I usually don't use DGS.

[Theta-Dot]

I see. I've been out of town for a few days, but before I left I just started using DGS materials directly (Instead of assigning DSG to slots of a Mental Ray first-tier shader). It fixed things but I guess I don't fundamentally understand the difference between the two.

I guess I also don't get why using a physics related material would ever NOT be desired (at least in single frame renders). Aren't they supposed to be the most physically accurate?

There seems to be a redundancy, or overlapping of sorts in a lot of these shaders. You can achieve a similar look in several different ones. It almost makes choosing one over another completely arbitrary.

[3DMadness]

I guess someone like jeff patton could answer better than me, but what I know is that the DGS Material have all the shaders inside like surface, shadow, photons, etc... when you use the DGS as a surface shader in a MentalRay material, you have more control over the other shaders.

And we always want to use physical accurated materials in our render, but sometimes we can fake it with a differente material, like a raytrace material, getting much faster render times. Of course that if you have a fast computer or render farm you don't bother with render time, but in small companies and with short deadlines we have to avoid long render times.

And I agree with you, we have many differents ways to get to the same result. ;)

[rodrigogua]

dgs materials work in a very particular way. they replicate in a physically accurate way real-world materials. it is called DGS responding to a Diffuse color or map, a Glossy color or map, and a Specular color or map.

Diffuse. This is the main "color" of the material. A wooden table, for example, would have a wooden texture map applied here.

Glossy. This parameter determines how blurred the reflections on your object will be. When you click the color, the Value parameter can range from 0-1. 0 means the object will b 0 percent glossy. that is, it won't have glossy reflections, (it won't have 'blurry' reflections). a value of 1 will mean 100% glossy reflections, that is, very blurred. Glossy reflections take much longer to render than straightforward reflections and will need much more samples for them to look any good. those white points in your render are caused by the fact that you have glossy reflections in your material and not enough samples to make them look smooth, at least not as smooth as you'd like them to.

Specular. this parameter determines the specularity of the material, that is, the straightforward, raytraced reflections in your object. as in the glossy parameter, 0 means no reflections at all, and 1 means 100% reflective. speculars don't take as long to render as glossiness, but it will still take longer to render than a 0% specular, 0% glossy material. It will take as long to render as an ordinary raytraced material.

For instance, let's say you want a chrome material. then, you would set D to black, G to black (V:0) and S to 1, so it would be 100% reflective.

An important thing is that the values of G and S, added, SHOULD NOT exceed 1, or you might get unexpected and unrealistic results.

good luck

[Theta-Dot]

Oops. I thought glossy, specular, AND diffuse had to add up to 1...
Knowing that it's only glossy and specular is helpful. Thanks.

[3DMadness]

Oops. I thought glossy, specular, AND diffuse had to add up to 1...
Knowing that it's only glossy and specular is helpful. Thanks.
I thought that too.

Thanks Rodrigo for the explanation. ;)

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