An evaluation of image compression algorithms for colour retinal images

Diabetic retinopathy is the leading cause of blindness in the adult population. Mass-screening efforts, during which high resolution images of the retina are captured, are therefore underway in order to detect the disease in its early stages. In this paper we evaluate the compression performance of several lossless image compression algorithms that could be employed in a retina Picture Archiving and Communications System to lessen the demand on computing resources. The algorithms we analyse are TIFF PackBits, Lossless JPEG, JPEG-LS, and JPEG2000 all of which are incorporated in the current DICOM standard together with the non-standard CALIC algorithm for benchmark comparison. Compression performance is evaluated in terms of compression ratio, compression speed, and decompression speed. Based on a large dataset of more than 800 colour retinal images, divided into groups according to retinal region (nasal, posterior, and temporal) and image size, JPEG-LS is found to be the most suitable compression algorithm, offering good compression ratios combined with high compression and decompression speed. Compression ratios can be further improved through the application of a reversible colour space transformation prior to compression as a second set of experiments show.