Example of optimal spectral extraction (source #4). The detector image is shown in the top panel, after background subtraction, with the cross-dispersion profile (w) as a function of wavelength. The corresponding profile along the aperture (integrated signal over the wavelength range vs. w) is shown as a histogram in the bottom panel. The connected squares show the fit of the spatial components in the slit, including source #4 (red profile), the extended background emission, and another slightly extended source in IC 10 matching the location of the H ii region [HL90] 17 (Hodge & Lee 1990), here fitted with 2 point-like sources showed by the green and blue profiles.