High-Density Image Storage Using Approximate Memory Cells

This paper proposes tailoring image encoding for an approximate storage substrate. We demonstrate that indiscriminately storing encoded images in approximate memory generates unacceptable and uncontrollable quality degradation. The key finding is that errors in the encoded bit streams have non-uniform impact on the decoded image quality. We develop a methodology to determine the relative importance of encoded bits and store them in an approximate storage substrate. The storage cells are optimized to reduce error rate via biasing and are tuned to meet the desired reliability requirement via selective error correction. In a case study with the progressive transform codec (PTC), a precursor to JPEG XR, the proposed approximate image storage system exhibits a 2.7x increase in density of pixels per silicon volume under bounded error rates, and this achievement is additive to the storage savings of PTC compression.