Pixel-value distributions of Hα surface brightness for two representative galaxies. Shown are histograms of the HST Hα images for NGC 1300 (upper panels) and NGC 5068 (lower panels), comparing the native data (left), the data convolved to a fixed physical resolution of 10 pc (middle), and the convolved data with additional noise added (right). Histograms are plotted as step lines with shaded areas, and Gaussian fits to the pixel distributions are overlaid as dashed curves. The fit standard deviation – approximately equivalent to the rms noise level of the image – is given in the legend of each panel in units of 10⁻¹⁵ erg s⁻¹ cm⁻² arcsec⁻².