FIGURE 13 Three-stage Saak architecture
Multiple Saab structures were used in cascade in PixelHop architecture. The purpose is to learn features from different neighborhood sizes (hop). Like Saab, earlier layers use a higher energy ratio, while later layers use a low energy ratio. Frobenius norms of the difference of the two-covariance matrix were used for faster filter convergence, which rapidly converges to zero. For the CIFAR-10 dataset, four cascaded Saab structures were implemented. The patch and filter sizes were 4x4, 4x4, 2x2, and 2x2 for all the PixelHop units starting from the first to the fourth structure.