  Recently, deep learning-based methods have dominated image dehazing domain.
Although very competitive dehazing performance has been achieved with
sophisticated models, effective solutions for extracting useful features are
still under-explored. In addition, non-local network, which has made a
breakthrough in many vision tasks, has not been appropriately applied to image
dehazing. Thus, a multi-receptive-field non-local network (MRFNLN) consisting
of the multi-stream feature attention block (MSFAB) and cross non-local block
(CNLB) is presented in this paper. We start with extracting richer features for
dehazing. Specifically, we design a multi-stream feature extraction (MSFE)
sub-block, which contains three parallel convolutions with different receptive
fields (i.e., $1\times 1$, $3\times 3$, $5\times 5$) for extracting multi-scale
features. Following MSFE, we employ an attention sub-block to make the model
adaptively focus on important channels/regions. The MSFE and attention
sub-blocks constitute our MSFAB. Then, we design a cross non-local block
(CNLB), which can capture long-range dependencies beyond the query. Instead of
the same input source of query branch, the key and value branches are enhanced
by fusing more preceding features. CNLB is computation-friendly by leveraging a
spatial pyramid down-sampling (SPDS) strategy to reduce the computation and
memory consumption without sacrificing the performance. Last but not least, a
novel detail-focused contrastive regularization (DFCR) is presented by
emphasizing the low-level details and ignoring the high-level semantic
information in the representation space. Comprehensive experimental results
demonstrate that the proposed MRFNLN model outperforms recent state-of-the-art
dehazing methods with less than 1.5 Million parameters.
