  Deformable part models (DPMs) and convolutional neural networks (CNNs) are
two widely used tools for visual recognition. They are typically viewed as
distinct approaches: DPMs are graphical models (Markov random fields), while
CNNs are "black-box" non-linear classifiers. In this paper, we show that a DPM
can be formulated as a CNN, thus providing a novel synthesis of the two ideas.
Our construction involves unrolling the DPM inference algorithm and mapping
each step to an equivalent (and at times novel) CNN layer. From this
perspective, it becomes natural to replace the standard image features used in
DPM with a learned feature extractor. We call the resulting model DeepPyramid
DPM and experimentally validate it on PASCAL VOC. DeepPyramid DPM significantly
outperforms DPMs based on histograms of oriented gradients features (HOG) and
slightly outperforms a comparable version of the recently introduced R-CNN
detection system, while running an order of magnitude faster.
