Creating Masks for VRayBlendMtl Sub-shaders

To create matte masks of materials that are part of the VRayBlend material, you can use the three different render elements: Material ID, Multi Matte and Multi Matte ID. Here is explained how to create a mask for compositing with each of them.

For each sub-shader that you want to create mask for, go to Attributes > V-Ray and select Material ID. For more information on V-Ray Attributes for materials, see the Material Attributes page.

Depending on the render element creating the mask, either put a value to the Multimatte ID parameter, or select a color for the Material ID parameter.

The Material ID render element shows a color mask based on the selected Material ID color in the V-Ray Extra Attributes of the material. In this example, the selected color is magenta.

Then, go ahead and add the Material ID render element from Render Settings > Render Elements.

The sub-shader has a magenta colored mask in the Material ID channel.

The Multi Matte ID render element uses the MultiMatte ID we set (a value of 2) to create a mask.

Add it to the list of Render Elements.

Once you render, the selected sub-shader now has a separate mask in the Multi Matte ID channel.

Another method to obtain a mask based on a sub-shader in VRayBlendMtl is to use the Multi Matte render element.

From the Render Elements tab, as shown above, select the Multi Matte render element.

In its extra attributes, enable the Use material IDs option. Also, the material ID assigned to the shader is set to one of the object ID color channels. In this example, the Red object ID channel is selected and a value of 2 is set. This way, all shaders with Multimatte ID of 2 get a red mask in this channel.

Now the selected sub-shader has a red mask in the Multi Matte channel.