Left hand panel: the attenuation curve corresponding to the SMC extinction curve (solid magenta line) is shown by an orange dashed line. For comparison, the Calzetti law is also indicated by a dotted green line. It has been shown that the Calzetti law is the result of the attenuation by a medium with an SMC-type dust (Gordon et al. 1997; Inoue 2005). We can recover this result using Eq. (3). Right hand panel: same as in the left hand panel, but for the MEC. The attenuation curve resulting from the MEC is flatter than the Calzetti law, which is generally adopted for quantifying the reddening of galaxies at all epochs.