  Beyond the complexity of CNNs that require training on large annotated
datasets, the domain shift between design and operational data has limited the
adoption of CNNs in many real-world applications. For instance, in person
re-identification, videos are captured over a distributed set of cameras with
non-overlapping viewpoints. The shift between the source (e.g. lab setting) and
target (e.g. cameras) domains may lead to a significant decline in recognition
accuracy. Additionally, state-of-the-art CNNs may not be suitable for such
real-time applications given their computational requirements. Although several
techniques have recently been proposed to address domain shift problems through
unsupervised domain adaptation (UDA), or to accelerate/compress CNNs through
knowledge distillation (KD), we seek to simultaneously adapt and compress CNNs
to generalize well across multiple target domains. In this paper, we propose a
progressive KD approach for unsupervised single-target DA (STDA) and
multi-target DA (MTDA) of CNNs. Our method for KD-STDA adapts a CNN to a single
target domain by distilling from a larger teacher CNN, trained on both target
and source domain data in order to maintain its consistency with a common
representation. Our proposed approach is compared against state-of-the-art
methods for compression and STDA of CNNs on the Office31 and ImageClef-DA image
classification datasets. It is also compared against state-of-the-art methods
for MTDA on Digits, Office31, and OfficeHome. In both settings -- KD-STDA and
KD-MTDA -- results indicate that our approach can achieve the highest level of
accuracy across target domains, while requiring a comparable or lower CNN
complexity.
