Spectrum masking: a) TrES-3 spectrum (light blue line), out-of-transit (OOT) standard deviation (σ_O) of a detrended light curve created using a single spectral pixel (dark blue line), maximum allowed σ_O (light orange horizontal line), OOT standard deviation with a mask (orange line), masked locations (thick black lines at bottom); b) the whole spectroscopic time series, time in the y-axis and wavelength (without wavelength calibration) in the x-axis, inside-transit duration marked between the two horizontal lines; c) broadband light curve with a fourth-order polynomial fitted to the OOT fluxes.