Diagram of U-Net with PPMs: UPPNet. The two RSs on the left create the narrowing path. The downward arrows represent strided residual blocks that decrease the sequence length by a factor of two. The central part has three PPM modules; the bottom one is preceded by a RS. The widening path on the right is a reflection of the narrowing path. Upward arrows represent upsampling by a factor of two. The upsampled features are concatenated with the result from the PPM blocks before being fed into the RS blocks. The depth of this UPPNet is defined as two.