Anti-aliasing and dithering in the 'Freiburg Visual Acuity Test'.

Anti-aliasing is a technique for improving spatial resolution at the cost of luminance resolution. Dithering is a technique for improving luminance resolution at the cost of spatial resolution. These techniques are applied to the testing of visual function in the 'Freiburg Visual Acuity Test': by employing anti-aliasing, spatial resolution was improved. Thus, even the shape of small Landolt-Cs with oblique gaps is adequate, and visual acuities from 5/80 (0.06) up to 5/1.4 (3.6) can be tested at a distance of 5 m. By employing dithering, subthreshold contrast stimuli can be generated on a conventional display having standard 8-bit video resolution. Rapid acquisition of a semi-objective and reliable acuity estimate makes the 'Freiburg Visual Acuity Test' useful for subject screening in vision research, as well as for routine assessments in the ophthalmic practice.