Location of PEBs compared to the vertical magnetic field B_z. The top-left panel shows a split image of the sunspot observed on 22 September 2017, with the left part in the Hβ blue wing at −0.2 Å offset and the right part at −0.6 Å. The blue contours indicate the radial distance r/R_spot to the umbral center that is marked with the blue cross. The contour for r/R_spot = 1.00 is the outer penumbra boundary, defined from the associated WB image. The top-right panel shows the B_z map, derived from ME inversions of the Fe I lines, scaled between −400 and +1600 G. Regions with artifacts due to the de-projection method are marked in green. The sets of panels at the bottom show four ROIs in Hβ −0.2 Å, −0.6 Å, and B_z, respectively. Red contours outline PEBs detected through the k-means method.