Special Session: How much quality is enough quality? A case for acceptability in approximate designs

Approximate systems are designed to offer improved efficiency with potentially reduced quality of results. Quality of output in these systems is typically quantified in comparison to a precise result using metrics such as RMSE, MAE, PSNR, or application-specific metrics such as structural similarity of images (SSIM). Furthermore, systems are typically designed to maximize efficiency for a given minimum quality requirement. It is often difficult to determine what this quality requirement should be for an application, let alone a system. Thus, a fixed quality requirement may be overly conservative, and leave optimization opportunities on the table. In this work, we present a different approach to evaluate approximate systems based on the usefulness of results instead of quality. Our method qualitatively determines the acceptability of approximate results within different processing pipelines. To demonstrate the method, we implement three image and signal processing applications featuring scenarios of image classification, image recognition, and frequency estimation. Our results show that designing approximate systems to guarantee acceptability can produce up to 20% more valid results than the conservative quality thresholds commonly adopted in the literature, allowing for higher error rates and, consequently, lower energy cost.