With consumer-grade 3D displays becoming widely available, stereoscopic 3D imaging has received increased attention over the last few years. Since a left eye and a right eye image are contained in a stereo pair, stereoscopic imaging requires double the amount of data compared to 2D images. Therefore, efficient data compression techniques are especially critical in these applications. In this paper, we propose a method to determine visibility thresholds (VTs) for 3D displays with active shutter glasses. These VTs are then used in a novel visually lossless compression method for monochrome stereoscopic 3D images.