The detection performance on raw images of three exemplary categories, where the x-axis indicates the channel index. The x-value ranges from 0 to 11 in (a)–(c), in which a PixelHop of size 2 × 2 × 3 is used. The x-value ranges from 0 to 26 in (d)–(f), in which a PixelHop of size 3 × 3 × 3 is used. Each subfigure shows four performance curves: training AUC (red dashed line), training ACC (red line), validation AUC (green dashed line), and test ACC (blue line).