The Fourier spectral slope of 31 artworks was compared to the spectral slope of closely matched photographic images. The artworks were found to display a relatively narrow range of spectral slopes relative to the photographs. Two accounts for this range compression were investigated. The first proposes that the band-pass nature of the visual system’s psychophysical ‘window of visibility’ is responsible. Simulation of this effect by application of an appropriate spatial filter to the original photographs could not explain the range compression, unless one assumed a consistent relation between the visual angle subtended by the scene at the artist’s eye, and the scene’s spectral slope (such that scenes with a steep slope subtended larger angles than scenes with a shallow slope). The second account involves more complex ‘artistic’ filtering which smoothes out textural details while preserving edges. Application of two such filters to the photographs was able to reproduce the spectral slope range compression evident in artworks. Both explanations posit a central role for the artist’s visual system in adjusting image spectral slope, which can be modelled using visual filters.