Help with multpile post processes

I am trying to create an effect where there are outlines on the objects in the scene. I have one post process material that applies the lines, then another that distorts them. These output as just the outlines, with no material information. I want to subtract the outlines from the image before postprocesses to get the final image, but I can’t figure out a way to get the original image. SceneTexture: PostProcessInput0 gives the image after it has been modified by postprocesses, and SceneTexture: SceneColor gives an error when uses in a post process material. Please help!