Weak magnetic fields and coronal voids. To highlight the regions of weaker magnetic field, we smoothed the LOS magnetic field strength |B_LOS| using a Gaussian kernel of 20 Mm FWHM. To emphasise the structuring, we use a discrete colour table. The weak-field regions are found in areas displayed mainly in blue. The contours of coronal voids are overplotted (the six major voids listed in Table 1 in thick white, smaller voids in black; same contours as in Fig. 1). See Sect. 3.3.3.