Bouguer and Lambert’s pioneering contributions to goniophotometric reflectance measurements and models: retrospective

Written independently and published in the same year, 1760, Bouguer's <i>Traité d'optique</i> and Lambert's <i>Photométria</i> are the foundations of photometry. We discuss their thoughts and pioneering contributions to the measurement and modeling of light reflected by matte materials, as well as the scattering of sunlight by the Moon and other planets toward Earth. With the law that now bears his name, Lambert introduced an approximation that is still widely used today, thanks to its simplicity. Bouguer presented the first goniophotometric measurements of diffuse reflectance. He developed models representing a rough surface by a set of either small hemispheres for astronomical observations or small randomly oriented facets to describe matte materials. In the latter case, he proposed a graphical representation of the distribution of surface asperities. We look at how Bouguer's work has been perceived over time, and in particular how it gave rise to the microfacet models developed from the end of the 20th century and widely used in computer graphics. This historical overview highlights the relevance of these two 18th-century scientists' reflections, which are a source of inspiration for new perspectives in the photometric characterization of matte materials.