  Deep learning (DL) has advanced the field of dense prediction, while
gradually dissolving the inherent barriers between different tasks. However,
most existing works focus on designing architectures and constructing visual
cues only for the specific task, which ignores the potential uniformity
introduced by the DL paradigm. In this paper, we attempt to construct a novel
\underline{ComP}lementary \underline{tr}ansformer, \textbf{ComPtr}, for diverse
bi-source dense prediction tasks. Specifically, unlike existing methods that
over-specialize in a single task or a subset of tasks, ComPtr starts from the
more general concept of bi-source dense prediction. Based on the basic
dependence on information complementarity, we propose consistency enhancement
and difference awareness components with which ComPtr can evacuate and collect
important visual semantic cues from different image sources for diverse tasks,
respectively. ComPtr treats different inputs equally and builds an efficient
dense interaction model in the form of sequence-to-sequence on top of the
transformer. This task-generic design provides a smooth foundation for
constructing the unified model that can simultaneously deal with various
bi-source information. In extensive experiments across several representative
vision tasks, i.e. remote sensing change detection, RGB-T crowd counting,
RGB-D/T salient object detection, and RGB-D semantic segmentation, the proposed
method consistently obtains favorable performance. The code will be available
at \url{https://github.com/lartpang/ComPtr}.
