Methods for greyscale representation of HEp-2 colour images

Detection of antibodies via indirect immunofluorescence (IIF) is a common marker in patients with suspected connective tissue diseases. IIF readings are affected by several issues limiting their reproducibility and reliability: hence, the development of a computer-aided diagnosis (CAD) tool supporting IIF diagnostic procedure would be beneficial in many respects. Although some works in the literature use greyscale cooled cameras for IIF image acquisition, recent research as well as commercial CAD solution use colour cameras. Indeed, colour cameras are cheaper than greyscale cameras and have adequate performance for the needs of IIF image acquisition. However, their application asks for studying how to extract useful information from colour images for CAD development. This paper presents an experimental comparison between four different methods converting a colour image into a greyscale one. This analysis has been carried out testing different popular classification paradigms on an annotated IIF image dataset, and also performing pre-clinical tests. Results show that a conversion method based on information derived from RGB primary components outperforms the others relying on different colour models.