Illumination spectrum recovery

The disclosure concerns processing of electronic images, such as hyperspectral, multispectral or trichromatic images. In particular, but is not limited to, a method, software and computer for estimating parameters of a reflectance model applied to an image is disclosed. Examples of processing of the images using the estimated parameters includes material recognition, re-coloring and re-shading of objects represented in the image. That is, a computer implemented method is provided of estimating one or more of photogrammetric parameters, Ω(u) surface shape N and index of refraction n(u,λ) represented in a reflectance image having one or more known illumination directions L and a known viewing direction V, the method comprising optimizing (802) the difference between the reflectance image and a reflectance model, the reflectance model being based on surface shape N; the material index of refraction n(u,λ) and a set of photogrammetric parameters Ω(u).