Marr's primal sketch is a model of human vision that can also be applied to computer vision. It starts by taking a low resolution view of an image, obtained using a Laplacian-of-Gaussian filter, processes that, and then adds successive refinement in areas of interest. Some features may be clearer when viewed at lower resolution, for example broken lines – try screwing up your eyes to see!
Used in Chap. 12: page 183