Hydrogen column density map of additional gas in the ¹²CO-saturated parts of the Taurus and Perseus clouds, derived from the “γ + τ₃₅₃” (top panel) and “γ + E(B − V)” (bottom panel) analyses of the full region (mask0). The pixels within the grey contours have a lower angular resolution in E(B − V) (mask2). The magenta contours enclose regions with ¹³CO intensities above 2 K km s⁻¹ (Ridge et al. 2006; Narayanan et al. 2008).