Best-fitting model for the spiral galaxy NGC 4321 (grey) located in the nearby Virgo cluster, showing the total stellar (blue, the dust attenuation has already been accounted for), nebular (green, also including dust attenuation), and dust (red) emission. The model fluxes in passbands computed using Eq. (10) are indicated with black circles. These fluxes were then fitted to the observations (turquoise cross with the uncertainties indicated with the vertical lines), yielding a final reduced χ² ≃ 0.5.