  Previous multi-task dense prediction studies developed complex pipelines such
as multi-modal distillations in multiple stages or searching for task
relational contexts for each task. The core insight beyond these methods is to
maximize the mutual effects of each task. Inspired by the recent query-based
Transformers, we propose a simple pipeline named Multi-Query Transformer
(MQTransformer) that is equipped with multiple queries from different tasks to
facilitate the reasoning among multiple tasks and simplify the cross-task
interaction pipeline. Instead of modeling the dense per-pixel context among
different tasks, we seek a task-specific proxy to perform cross-task reasoning
via multiple queries where each query encodes the task-related context. The
MQTransformer is composed of three key components: shared encoder, cross-task
query attention module and shared decoder. We first model each task with a
task-relevant query. Then both the task-specific feature output by the feature
extractor and the task-relevant query are fed into the shared encoder, thus
encoding the task-relevant query from the task-specific feature. Secondly, we
design a cross-task query attention module to reason the dependencies among
multiple task-relevant queries; this enables the module to only focus on the
query-level interaction. Finally, we use a shared decoder to gradually refine
the image features with the reasoned query features from different tasks.
Extensive experiment results on two dense prediction datasets (NYUD-v2 and
PASCAL-Context) show that the proposed method is an effective approach and
achieves state-of-the-art results. Code and models are available at
https://github.com/yangyangxu0/MQTransformer.
