  Convolutional Neural Network (CNN) has demonstrated promising performance in
single-label image classification tasks. However, how CNN best copes with
multi-label images still remains an open problem, mainly due to the complex
underlying object layouts and insufficient multi-label training images. In this
work, we propose a flexible deep CNN infrastructure, called
Hypotheses-CNN-Pooling (HCP), where an arbitrary number of object segment
hypotheses are taken as the inputs, then a shared CNN is connected with each
hypothesis, and finally the CNN output results from different hypotheses are
aggregated with max pooling to produce the ultimate multi-label predictions.
Some unique characteristics of this flexible deep CNN infrastructure include:
1) no ground truth bounding box information is required for training; 2) the
whole HCP infrastructure is robust to possibly noisy and/or redundant
hypotheses; 3) no explicit hypothesis label is required; 4) the shared CNN may
be well pre-trained with a large-scale single-label image dataset, e.g.
ImageNet; and 5) it may naturally output multi-label prediction results.
Experimental results on Pascal VOC2007 and VOC2012 multi-label image datasets
well demonstrate the superiority of the proposed HCP infrastructure over other
state-of-the-arts. In particular, the mAP reaches 84.2% by HCP only and 90.3%
after the fusion with our complementary result in [47] based on hand-crafted
features on the VOC2012 dataset, which significantly outperforms the
state-of-the-arts with a large margin of more than 7%.
