Perceptually optimal optical filters for spatially sampled imagery

Spatial sampling is applied in the majority of electro-optical displays. Too economical sampling densities lead to visible artefacts like dot and line structures, the staircase effect and moire. Low-pass optical filters can reduce the visibility of these artefacts. However, these filters also reduce the sharpness. This paper describes two experiments using circular and elliptical filters, respectively. In these experiments observers were asked to rate the quality of spatially sampled and optically filtered images as a function of the cut-off frequency of the optical filters. Sampling geometry and sampling density of the displayed images were used as parameters. The experimental results show that there is a perceptual optimum for which the visibility of sampling artefacts is reduced, yet the annoyance of blur is still negligible.