Effects of IRIS spatial and spectral resolution and noise on the NUV spectrum near the Mg ii k line. The original spectrum was taken from a single simulation pixel. This pixel was brighter than its surroundings and was chosen so that the Mg ii k intensity was similar to the mean observed value. The S/N is measured at the last wavelength shown (280.042 nm). For clarity, spectra of different S/Ns are offset 0.25 nW m ⁻² Hz ⁻¹ sr ⁻¹ from each other.