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

Purpose: To investigate the effects of image digitization and compression on the ability to identify and quantify features in color fundus photographs. Methods: Color fundus photographs were digitized as tagged image file format (TIFF) and high-compression (80:1) and low-compression (30:1) joint photographic experts group (JPEG) images. Rerendered images were subjected to standard grading protocols developed for a clinical trial, and digitized images were subjected to image analysis software for drusen identification and quantitation. Re-created stereoscopic images were compared subjectively with originals. Results: Original, TIFF, and low-compression (30:1) JPEG images were virtually indistinguishable when subjected to close scrutiny with magnification. The overall quality of high-compression (80:1) JPEG images and images digitized at 500 dots per inch was markedly reduced. Protocol grading of original and digitized images was highly concordant within the repeatability of multiple 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 originals for TIFF and low-compression JPEG images. Conclusions: Fundus images can be digitized and stored with significant compression while preserving stereopsis and image quality suitable for quantitative image analysis and semiquantitative grading. Low- compression (30:1) JPEG images may be suitable for archiving and telemedical applications.