Simulate polished and rough surfaces.
- [Instructor] Arnold and the AI Standard Surface material are physically based. The Standard Surface material simulates the way specular highlights and reflections are affected by roughness. A real world object that's very smooth or highly polished does not really scatter the light like a rough surface does and a smooth or highly polished surface will have coherent reflections or shiny specular hot spots. The balance between the diffused component and the shiny hot spots is controlled by the roughness attribute.
I've got a material all ready assigned to the picture frame. Select that picture frame and open up the attribute editor, CONTROL + A. Also open the Arnold render view, Arnold render. We could of course do our shader editing in the hyper shade window, but for performance reasons I'm going to opt to do it in the node editor, but you can use hyper shade if you want. In the main menu I'll choose windows node editor and with the picture frame still selected from the node editor toolbar click the button to graph the input and output connections.
One of the nodes displayed is a shading group, its got an SG at the end of it. Select that node and click input and output connections again. Now the material node is visible in the node editor and it's labeled AI stand surf. Select that node and click the input and output connections one more time and now we see the entire shading network for that material. Click in an empty area of the node editor to deselect all nodes and display the connections with the two key on the keyboard.
Press two and now we're in displayed connected mode. Let's zoom in a bit with the mouse wheel and pan around with ALT + middle mouse button. Here is the AI Standard Surface material once again and I've got a bump map attached to that. Let's select that bump node and temporally reduce the bump depth down to zero so that we can better visualize how roughness affects the material.
Reselect the material shader node and let's temporarily change the base color to make the behavior of the specular highlights really clear. Click on base color and set that to bright red. In the specular section the weight is at its maximum of one. The color is white, but the roughness is at one and if it's completely rough then that means it's scattering the light and there will be no shiny highlights.
Bring the roughness down to make it a smoother surface. When you get into the range of about .1 or .2 you should see some shiny highlights and they are white because the specular color is white. If we bring the roughness all the way down to zero we still won't get coherent reflections as in a mirror. We'll get very sharp and very shiny specular highlights, but we don't really see mirror reflections.
To achieve that we can increase the metalness attribute. Bring that up to its maximum of one and now we've got a tinted mirror. You can set the base color back to white and you got a perfect mirror reflection now. Let's talk a little bit about what metalness does. It uses a different shading model. The color of highlights is mainly determined by the base color here. If we set this back to red, notice that the highlights are kind of red or pink.
Okay, I'll set it back to white once again. The specular color and specular weight have less influence when you have a non zero metalness. The influence of specular color and weight decreases as a surface points towards the camera. If metalness is one then the influence of specular color and specular weight may be completely eliminated, especially if the base color is white. A fractional value for metalness blends between the two shading modes allowing a range of materials, such as shiny plastic.
In this case we're simulating semigloss metallic paint. Bring the metalness back up to a value of one and let's re-enable our bump map, select that, and set the bump depth back up to .1 and now we've got a very shiny mirror reflection on a rough pitted surface. Reselect the material shading node and we'll finish developing the look of our painted wood frame.
We've got the base weight here. We can bring that down and that will diminish the intensity of a diffused component, but will still have shiny highlights. Let's set the base weight to .2 and finally we still have a roughness of zero, which is a highly polished surface. Let's increase that roughness to a value of 0.2 and let's let that finish rendering so we can evaluate.
It's looking a little bit grainy due to the low values of sampling attributes in the render settings, but it looks pretty much the way we want it to. There's one little detail missing from this, which is specular reflections. We're not getting any specular caustics or light bouncing off of the shiny metal surface. Go into the advanced section. Scroll down a little bit if you need to and enable caustics and you'll see a few little specs of light on the wall.
If we get in closer we'll be able to see this more clearly. So I'll close the node editor and then zoom in the view port using ALT + right mouse button and translate with ALT + middle mouse. Get in very close there and we can see that there's a little bit of light spilling from the frame onto the wall. Once that render completes let's make a snapshot. Click on the camera icon in the lower right and then switch the caustics off to see the difference.
Once that second rendering has completed create another snapshot and then we can compare. Snapshot two has no caustics, snapshot one has caustics and there's a little bit of light there. All right, very good, we can go back to rendering in real time by clicking the I button and close out the snapshot panel. Reposition the frame and of course re-enable caustics and that's how to adjust roughness and metalness to achieve shiny specular highlights.
- Arnold rendering concepts
- Lighting with Maya and Arnold lights
- Controlling exposure
- Filtering light with Gobo
- Light attenuation with Decay
- Image-based lighting with Skydome
- Exterior daylight with Physical Sky
- Arnold Standard Surface material attributes
- Mapping material attributes
- Rendering refractions
- Mesh subdivision and displacement at render time
- Shading effects such as ambient occlusion and vertex color
- Camera effects such as fisheye and depth of field
- Animation image sequence rendering