The U-Net architecture, built upon the fully convolutional network, has
proven to be effective in biomedical image segmentation. However, U-Net applies
skip connections to merge semantically different low- and high-level
convolutional features, resulting in not only blurred feature maps, but also
over- and under-segmented target regions. To address these limitations, we
propose a simple, yet effective end-to-end depthwise encoder-decoder fully
convolutional network architecture, called Sharp U-Net, for binary and
multi-class biomedical image segmentation. The key rationale of Sharp U-Net is
that instead of applying a plain skip connection, a depthwise convolution of
the encoder feature map with a sharpening kernel filter is employed prior to
merging the encoder and decoder features, thereby producing a sharpened
intermediate feature map of the same size as the encoder map. Using this
sharpening filter layer, we are able to not only fuse semantically less
dissimilar features, but also to smooth out artifacts throughout the network
layers during the early stages of training. Our extensive experiments on six
datasets show that the proposed Sharp U-Net model consistently outperforms or
matches the recent state-of-the-art baselines in both binary and multi-class
segmentation tasks, while adding no extra learnable parameters. Furthermore,
Sharp U-Net outperforms baselines that have more than three times the number of
learnable parameters.

本研究提出了一种名为 Sharp U-Net 的深度卷积神经网络模型，它采用深度卷积和锐化滤波器来解决 U-Net 的模糊和区域过度或不足的问题，在二元和多类医学图像分割任务中，使用该模型获得了超过同领域基线模型的性能表现。