Pseudo-3D shape descriptors are proposed for characterizing the complexity of the surface of facetted particles observed by reflection. They are based on the complete coverage by a set of squares of decreasing size of the image of the particle facets. Quasi position invariance was obtained by normalization with respect to the particle silhouette. The descriptors were tested on synthetic particles (3D polyhedra), complex molecules (fullerenes, zeolites) and bulk hydrargillite particles.