Image Perforation: Automatically Accelerating Image Pipelines by Intelligently Skipping Samples.

Image pipelines arise frequently in modern computational photography systems and consist of multiple processing stages where each stage produces an intermediate image that serves as input to a future stage. Inspired by recent work on loop perforation [Sidiroglou-Douskos et al. 2011], this article introduces image perforation, a new optimization technique that allows us to automatically explore the space of performance-accuracy tradeoffs within an image pipeline. Image perforation works by transforming loops over the image at each pipeline stage into coarser loops that effectively “skip” certain samples. These missing samples are reconstructed for later stages using a number of different interpolation strategies that are relatively inexpensive to perform compared to the original cost of computing the sample. We describe a genetic algorithm for automatically exploring the resulting combinatoric search space of which loops to perforate, in what manner, by how much, and using which reconstruction method. We also present a prototype language that implements image perforation along with several other domain-specific optimizations and show results for a number of different image pipelines and inputs. For these cases, image perforation achieves speedups of 2 × --10 × with acceptable loss in visual quality and significantly outperforms loop perforation.