7 Sampling and Reconstruction
Although the final output of a renderer like pbrt is a 2D grid of colored pixels, incident radiance is actually a continuous function defined over the film plane. The manner in which the discrete pixel values are computed from this continuous function can noticeably affect the quality of the final image generated by the renderer; if this process is not performed carefully, artifacts will be present. Conversely, if it is performed well, a relatively small amount of additional computation to this end can substantially improve the quality of the rendered images.
This chapter starts by introducing sampling theory—the theory of taking discrete sample values from functions defined over continuous domains and then using those samples to reconstruct new functions that are similar to the original. Building on principles of sampling theory as well as ideas from low-discrepancy point sets, which are a particular type of well-distributed sample points, the Samplers defined in this chapter generate -dimensional sample vectors in various ways. Five Sampler implementations are described in this chapter, spanning a variety of approaches to the sampling problem.
This chapter concludes with the Filter class and the Film class. The Filter is used to determine how multiple samples near each pixel are blended together to compute the final pixel value, and the Film class accumulates image sample contributions into pixels of images.