In order to use an image in an input parameter for a Substance, you need to modify the Read/Write parameter for the texture. You will also need to set the compression type to None.
This is works different from the native integration in 2017 because we can't decompress the images in a plugin form. When we had a native integration, the c++ code exposed it. We can't duplicate this in our plugin because dxt decompression is patented.
- Select the texture you want to use in the input of the Substance in the Project Window
- In the Inspector under Advanced, enable the Read/Write Enabled value
- Set the compression to None
Once the texture has had Read/Write Enabled, you can then apply it to the Substance Texture Input