Grading, image analysis, and stereopsis of digitally compressed fundus images

Purpose: To investigate the effects of image digitization and compression o n the ability to identify and quantify features in color fundus photographs . Methods: Color fundus photographs were digitized as tagged image file forma t (TIFF) and high-compression (80:1) and low-compression (30:1) joint photo graphic experts group (JPEG) images. Rerendered images were subjected to st andard grading protocols developed for a clinical trial, and digitized imag es were subjected to image analysis software for drusen identification and quantitation. Re-created stereoscopic images were compared subjectively wit h originals. Results: Original, TIFF, and low-compression (30:1) JPEG images were virtua lly indistinguishable when subjected to close scrutiny with magnification, The overall quality of high-compression (30:1) JPEG images and images digit ized at 500 dots per inch was markedly reduced. Protocol grading of origina l and digitized images was highly concordant within the repeatability of mu ltiple grading of original images. The area subtended by drusen differed by less than 1.0% for all uncompressed and compressed image pairs quantified. Stereoscopic information was accurately preserved when compared with origi nals for TIFF and low-compression JPEG images. Conclusions: Fundus images can be digitized and stored with significant com pression while preserving stereopsis and image quality suitable for quantit ative image analysis and semiquantitative grading. Low-compression (30:1) J PEG images may be suitable for archiving and telemedical applications.