The perceived orientation of aliased lines

The use of raster display devices for the display of graphics causes problems of aliasing when edges or lines are produced. This can be significant in those psychophysical experiments where the orientational properties of the stimulus are important. We have assessed the perceived orientation of a selection of aliased lines by comparing them with the orientation of pairs of dots. It is found that the perceptual orientation is modelled well by a least-squares metric on the pixels that compose the line. Small deviations from this metric were found, and were also found in a control experiment employing anti-aliased lines. They appear to be due to range effects. Averaged across subjects, orientational acuity was only slightly lower for aliased lines.