  Virtual Reality (VR) has the potential of becoming the next ubiquitous
computing platform. Continued progress in the burgeoning field of VR depends
critically on an efficient computing substrate. In particular, DRAM access
energy is known to contribute to a significant portion of system energy.
Today's framebuffer compression system alleviates the DRAM traffic by using a
numerically lossless compression algorithm. Being numerically lossless,
however, is unnecessary to preserve perceptual quality for humans. This paper
proposes a perceptually lossless, but numerically lossy, system to compress
DRAM traffic. Our idea builds on top of long-established psychophysical studies
that show that humans cannot discriminate colors that are close to each other.
The discrimination ability becomes even weaker (i.e., more colors are
perceptually indistinguishable) in our peripheral vision. Leveraging the color
discrimination (in)ability, we propose an algorithm that adjusts pixel colors
to minimize the bit encoding cost without introducing visible artifacts. The
algorithm is coupled with lightweight architectural support that, in real-time,
reduces the DRAM traffic by 66.9\% and outperforms existing framebuffer
compression mechanisms by up to 20.4\%. Psychophysical studies on human
participants show that our system introduce little to no perceptual fidelity
degradation.

Graphics;Human-Computer Interaction