Example of PK-027 (top panels) observations analysed in this study and of the corresponding mask images (bottom panels). The observations were taken on 2007 June 7 (left side) and June 21 (right side). The disk features on mask images are identified by color: blue, light blue, green, and yellow show quiet Sun, network, enhanced network and plage regions, respectively; white and red show penumbral and umbral regions (visible only when enlarging the figure).