Surfaces of 12 + log O/H versus x ≡ log([N II]/[S II]) and y ≡ log[O III]/[S II], as described by the SF calibrator or Eq. (2) (top panels), COMP calibrator or Eq. (4) (center panels) and AGN calibrator or Eq. (3) (bottom panels), rotated of an angle of 0° (right), 90° (center) and 45° (left). The surfaces are obtained by fitting with a least-squared method the observed [O III]/[S II] and [N II]/[S II] line ratios and the 12 + log O/H computed with NEBULABAYES inside the SF spaxels of all the samples, and the composite and AGN spaxels in the AGN-RPS and AGN-FS. Cells are color-coded according to the value of 12 + log O/H.