Learn how to assign textures and control transparency.
- [Narrator] Mapping the base color, or the diffuse channel of an Arnold standard surface material is a straightforward operation, however, as we will see, opacity mapping requires a couple extra steps and considerations. First of all, any object that we wish to opacity map must have its opaque flag disabled in the Arnold properties. In this case, we want the leaves opacity to be driven by a bitmap. Select the leaves, go to the modify panel, and in the modifier list choose Arnold properties.
Open up general properties, enable the general section, and disable the opaque flag. And if you don't do this your opacity mapping will not work. Now let's open the material editor. We've got the petal material here already from the last lesson, let's duplicate that, hold down shift and drag to create another node and double-click the new one, and rename it.
We'll call it leaf Arnold standard. Once again, because this is an xref object I want to ensure that I don't lose this material if I ever unload that xref. I've got the sample slots over here on the left. Drag the output of the new leaf Arnold standard node onto an empty slot and choose instance. And now that material is saved even if we need to unload the xref. We're going to map the base color with an image, but let's change that base color swatch just for clarity.
Let's change the base color to green, just click on the base color and set the hue to 0.33, click okay, with the leaves selected and the leaf Arnold node selected in the material editor. Click on assign material to selection, and now we've got green leaves. Let's switch over to the active shade window. Click on active shade, and the close-up camera that I've set up renders in the active shade window. Depending upon your version of the software, the material editor previews over here may not update while active shade is open.
That's probably why one of mine is showing up as black here. As long as this window is open, none of these previews are going to update in the current version of Arnold. But this is an issue that will probably be addressed someday. Okay, let's play around with the parameters of the Arnold standard. We've still got our sub-surface scattering color set to pink, so let's change that, click on sub-surface scattering color, and set the hue to 0.33.
The saturation to 0.8 and the value to 0.5. Click okay, and now our sub-surface scattering is a bit more believable there. Before assigning any bitmaps let's also sort out our specular roughness. Back up here we previously set the petal roughness to a value of one. In this case, let's bring it down a little bit to 0.7 which will give us a little bit of a shiny highlight on the leaves.
We can also knock that down a bit in intensity, set the general weight of the specular reflections to 0.7 also. To assign the base color map we can click on the button immediately to the right of the bass color. Or we can do it from the bottom of the dialog, we have a bass color no map button here too. And we'll just assign a bitmap. Open up maps, general and double click on bitmap.
In our current projects, scene assets, images scroll through until you see leafSerrate.tif, select it, and note by the way, in it's icon it's got transparency, and it actually has an alpha channel in it. Click open, and that new bitmap node is connected to the base color. Let's make our window a little bit larger here. Navigate with the middle mouse button. Double click with that bitmap node and rename it, call it leaf diffuse.
In our active shade window we can see that there's a pattern there on the leaves and if we need to we can get in closer, and that's in this physical camera view. We can use the dolly camera tool and get closer in that view if we want. And move the view with the middle mouse button. Now we've got an extreme close-up on those leaves in the active shade window. Back to our material editor, there is actually an alpha channel in this bitmap.
And normally we'd be able to set these parameters to make sure that the output that is sent from this bitmap output is actually the alpha channel we want. However, there's a major limitation with the current version of Arnold, which is that it does not support the grayscale color space, you can't use a grayscale image anywhere in an Arnold shader network. And this tif has a grayscale alpha channel, so I actually had to take to take that alpha and extract it and save it as a separate file with an RGB color space.
So let's bring that in, I'll select that bitmap node and hold down shift to duplicate it. Double-click it, and change its name to leaf alpha. In the bitmap parameters, click on the bitmap slot button. And you want to choose leafSerrateAlphaRGB.png. Click open and then connect to the bottom of your standard surface material.
You've got the opacity input. Once again, that's an RGB image and that's what the opacity input needs to see. In the active shade window we can double-click on its title bar to make it go full screen while we wait for it to complete the rendering, but we can already see that the opacity mapping is working correctly. That's how to map a base color and opacity of an Arnold standard surface.
- Arnold rendering concepts
- Arnold lights such as quad, spot, and distant
- Modifying Arnold object properties
- Filtering light with the gobo filter modifier
- Image-based lighting with Skydome
- Daylight simulation with Physical Sky
- Arnold Standard Surface material parameters
- Diffuse, opacity, and bump mapping
- Rendering refractions with Transmission
- Building an Arnold shading network
- Test rendering with utility map
- Mesh subdivision and displacement at render time
- Atmospheric perspective with scene environment fog
- Rendering a spherical environment with VR Camera