  Many vision problems require matching images of object instances across
different domains. These include fine-grained sketch-based image retrieval
(FG-SBIR) and Person Re-identification (person ReID). Existing approaches
attempt to learn a joint embedding space where images from different domains
can be directly compared. In most cases, this space is defined by the output of
the final layer of a deep neural network (DNN), which primarily contains
features of a high semantic level. In this paper, we argue that both high and
mid-level features are relevant for cross-domain instance matching (CDIM).
Importantly, mid-level features already exist in earlier layers of the DNN.
They just need to be extracted, represented, and fused properly with the final
layer. Based on this simple but powerful idea, we propose a unified framework
for CDIM. Instantiating our framework for FG-SBIR and ReID, we show that our
simple models can easily beat the state-of-the-art models, which are often
equipped with much more elaborate architectures.
