1. A method of determining a colour component of a relightable texture and a set of surface normals for use in rendering an image from a rendering viewpoint under arbitrary lighting conditions, wherein at least one view of a scene from a respective at least one camera viewpoint represents the image, the method comprising: analysing the at least one view of the scene to estimate scene geometry and to segment an initial texture into a plurality of materials, the initial texture being separable into a colour estimate and a corresponding shading estimate; determining an initial coarse colour estimate for each of the materials; determining one or more scale factors, for scaling a respective one or more of the initial coarse colour estimates, the scale factors being determined based on differences between irradiance estimates determined for the materials based on shading estimates which correspond with scaled versions of the initial coarse colour estimates of the materials; determining a global irradiance function for the scene using the determined scale factors; using the global irradiance function and the initial texture to determine a further colour estimate and a corresponding further shading estimate, wherein the further colour estimate represents the colour component of the relightable texture; and determining the set of surface normals using the global irradiance function and the further shading estimate.