1. An inspection system for inspecting cells of a cellular ceramic substrate having an endface, comprising: an illuminator configured to provide normal-incidence line illumination on the endface over a plurality of cells; a movable stage that movably supports the ceramic structure so that the line illumination scans over the endface over a scan path; an optical imaging system having an axis and configured to form a line image of the illuminated plurality of cells; a line-scan image sensor arranged to receive and detect the line image and generate therefrom corresponding line-image signals; and a controller configured to process the line-image signals to form a composite image of the endface and determine therefrom at least one parameter of at least one cell.