I’ve created a UsdPreviewSurface shader and want to plug a texture image into the specularColor property. However, this particular texture image doesn’t actually represent a specular color – but the alpha channel contains the specular intensity which is still useful. (And the r, g, b channels contain other data not relevant to specular)
How can I take the alpha channel of the image (a Float) and connect it to the specularColor property (a Color3f)? Do I need to create some intermediary node that converts the float into a Color3f with the same value repeated? I haven’t been able to find any examples or documentation of this online.
Hi @hzwus , the UsdPreviewSurface family of nodes are deliberately quite restricted, and we don’t provide any mechanism for expanding or merging texture channels beyond the simple transformations internal to UsdUVTexture for reduced-channel textures described in that doc.
If you need to do more sophisticated operations with channels, like the one you are describing, and want it to be portable, we’d recommend switching over to using a MaterialX shading network. It’s not quite as portable as PreviewSurface, but it is rapidly getting there, it already contains a NodeGraph implementation of PreviewSurface, and it is our guidance for forward-looking portable shading.