Example of the sunspot classification. Left: normalized six-hour average continuum map of AR 11158. The axis labels are relative to the center of the leading polarity, as defined in Sect. 3.2. Right: same as left, with a colored overlay of pixels for which |B_z| is higher than 10 Gauss. Colors indicate no intensity darkening (green), penumbra (yellow), and umbra (red; see text for definition). The blue cross indicates the center of the largest umbral region. The time step shown here has the sunspot classification SSQ = 0.