Experimental study of distinguishing small retinal heamorrhages from dust artefacts using HLS colour space

Abstract

AbstractPurpose Many ophthalmologists consider it difficult to distinguish small retinal heamorrhages of early diabetic retinopathy from dust artefacts on fundus cameras.Methods Photographs of the fundi of five patients with diabetic retinopathy were taken. Paint Shop Pro v. 8.0 was used to measure HLS colour spaces of both hemorrhagic area and the area around the heamorrhage at two locations of each photograph. We constructed the experimental device, which has an illumination optical system and a photographic optical system separated by a mirror having a hole with 4 mm diameter. The device consists of a canon EOS 50D camera, an EF 50mm f/1.8‐2 camera lens, a Speedlite 270EX flash, an object lens, four double‐convex lenses, two aperture stops and four artificial eyes. The eye ground is a half sphere made of polythene terephthalate painted by four mat colour sprays: red, white brown, ochre and yellow. Five fragments of house dust on the object lens were photographed under each artificial eye. Paint Shop Pro 8.0 was used to measure the HLS colour spaces of dust artefacts and the area around the artefacts.Results The evaluation space of house dust was calculated using the HLS data obtained from the experimental device. Hue was red, −7.1±16.9; white brown, −5.7±7.4; yellow, 3.4±1.6 and ochre 0.3±2.3. Lightness was red, 10.7±3.4; yellow, 9.9±3.0; ochre, 9.5±1.8 and white brown, 8.2±2.1. Saturation was red, 25.5±23.5; white brown, 22.6±12.2; yellow, 15.1±12.3 and ochre, 5.0±2.8.Conclusion The lightness of the HLS colour space helped in distinguishing dust from heamorrhage in all colour spectra. However, hue and saturation could distinguish dust from heamorrhage only under certain conditions.