NUV-i vs. H₂-deficiency relation for the whole HRS galaxy sample. NUV-i colours (in AB system) are corrected for Galactic and internal dust attenuation following Hao et al. (2011). Galaxies are coded according to their H₂-deficiency parameter, where the H₂ − def has been measured using a constant (panel a)) or a luminosity-dependent (panel b)) X_CO conversion factor. Black squares indicate spiral galaxies whose molecular gas content has been determined using aperture corrections, red dots those objects with available CO integrated maps from Kuno et al. (2007). Filled symbols are for galaxies with H₂ − def ≤ 0.3, open symbols for objects with H₂ − def > 0.3. For the black squares, the H₂-deficiency parameter has been determined using the M(H₂) vs. M_star calibration based on all galaxies (lines 3 and 4 in Table 2), for the red symbols the calibration done on the subsample of galaxies with mapped observations from Kuno et al. (2007) (lines 5 and 6 in Table 2).