  Neural Architecture Search (NAS) for automatically finding the optimal
network architecture has shown some success with competitive performances in
various computer vision tasks. However, NAS in general requires a tremendous
amount of computations. Thus reducing computational cost has emerged as an
important issue. Most of the attempts so far has been based on manual
approaches, and often the architectures developed from such efforts dwell in
the balance of the network optimality and the search cost. Additionally, recent
NAS methods for image restoration generally do not consider dynamic operations
that may transform dimensions of feature maps because of the dimensionality
mismatch in tensor calculations. This can greatly limit NAS in its search for
optimal network structure. To address these issues, we re-frame the optimal
search problem by focusing at component block level. From previous work, it's
been shown that an effective denoising block can be connected in series to
further improve the network performance. By focusing at block level, the search
space of reinforcement learning becomes significantly smaller and evaluation
process can be conducted more rapidly. In addition, we integrate an innovative
dimension matching modules for dealing with spatial and channel-wise mismatch
that may occur in the optimal design search. This allows much flexibility in
optimal network search within the cell block. With these modules, then we
employ reinforcement learning in search of an optimal image denoising network
at a module level. Computational efficiency of our proposed Denoising Prior
Neural Architecture Search (DPNAS) was demonstrated by having it complete an
optimal architecture search for an image restoration task by just one day with
a single GPU.
