Axis lengths of shape descriptors capture the complexity of shapes in synthetic images. a) We use several synthetic shapes to illustrate the utility of Fourier shape descriptors in capturing shape complexity. The green and light green shapes are the simplest elliptical shapes. b-d) Major and minor axis lengths (in pixels) of the Fourier descriptor ellipses in (a), for harmonics n = 1, 2 and 3. Marker colors in (b-d) correspond to shape colors in (a). For first harmonic (n = 1), axis lengths represent size and eccentricity of the shape. For n > 1, axis lengths represent the detail or complexity of the shape. Therefore, simple green shapes (closer to an ellipse) have small axis lengths, while other complex shapes have larger axis lengths.