Manipulations were performed on specular and diffuse images separately before being recombined: as with the original feature measurements, the specular component was obtained by subtraction of the diffuse component from the full rendering (Supplementary Fig. 9 ). The sharpness of reflections was first modified by blurring pixels of the specular component that have sufficiently similar normals ( Methods ). The subsequent filters adjusted the colour and intensity of each component. For example, for materials like gold (top manipulated image), the specular component is first multiplied by a colour (the diffuse component is multiplied by 0), then its intensity and saturation are adjusted. For materials like pearl (bottom manipulated image), the intensity of the diffuse component is also adjusted. See the Methods for a detailed description of each filter, along with the special filter used for velvet, based on a non-monotonic remapping of the specular component.
