  Convolutional neural networks (CNNs) have demonstrated superior performance
in super-resolution (SR). However, most CNN-based SR methods neglect the
different importance among feature channels or fail to take full advantage of
the hierarchical features. To address these issues, this paper presents a novel
recursive unit. Firstly, at the beginning of each unit, we adopt a compact
channel attention mechanism to adaptively recalibrate the channel importance of
input features. Then, the multi-level features, rather than only deep-level
features, are extracted and fused. Additionally, we find that it will force our
model to learn more details by using the learnable upsampling method (i.e.,
transposed convolution) only on residual branch (instead of using it both on
residual branch and identity branch) while using the bicubic interpolation on
the other branch. Analytic experiments show that our method achieves
competitive results compared with the state-of-the-art methods and maintains
faster speed as well.
