We analyse the signal formation process for scanning electronmicroscopic imaging applications on crystalline specimens. Inaccordance with previous investigations, we find nontrivialeffects of incident beam diffraction on the backscattered elec-tron distribution in energy and momentum. Specifically, inci-dent beam diffraction causes angular changes of the backscat-tered electron distribution which we identify as the dominantmechanism underlying pseudocolour orientation imaging us-ing multiple, angle-resolving detectors. Consequently, diffrac-tion effects of the incident beam and their impact on the sub-sequent coherent and incoherent electron transport need tobe taken into account for an in-depth theoretical modelling ofthe energy- and momentum distribution of electrons backscat-tered from crystalline sample regions. Our findings have impli-cations for the level of theoretical detail that can be necessaryfor the interpretation of complex imaging modalities such aselectron channelling contrast imaging (ECCI) of defects in crys-tals. If the solid angle of detection is limited to specific regionsof the backscattered electron momentum distribution, the im-age contrast that is observed in ECCI and similar applicationscan be strongly affected by incident beam diffraction and topo-graphic effects from the sample surface. As an application, wedemonstrate characteristic changes in the resulting images ifdifferent properties of the backscattered electron distributionare used for the analysis of a GaN thin film sample containingdislocations.