Efficient Image-Space Shape Splatting for Monte Carlo Rendering

A typical Monte Carlo rendering method contributes one light path only to a single pixel at a time. Reusing light paths across multiple pixels, however, can amortize the cost and improve the efficiency. The state of the art of path reuse is to employ shift mapping to reduce the cost of path reuse, while its computation cost is still proportional to the number of pixels processed in shift mapping. We propose a general framework for efficiently reusing light paths to multiple pixels arranged in arbitrary two-dimensional shapes. Our shape is defined as a set of multiple pixels, and the framework allows us to reuse light paths among pixels in a shape faster than simply evaluating all pixels via shift mapping. The key idea is to sparsely evaluate the contribution of shifted paths at random pixels within the shape and interpolate the contribution to the other pixels. We apply a debiasing estimator to ensure unbiasedness. Our method can be integrated with many existing rendering methods and brings consistent improvement over its single-pixel counterpart.